FOUS11 KWBC 160723
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
323 AM EDT Sun Mar 16 2025

Valid 12Z Sun Mar 16 2025 - 12Z Wed Mar 19 2025


...Great Lakes...
Day 1...

Guidance continues to intensify secondary low pressure developing
across the Ohio Valley early this morning downstream of a potent
shortwave trough emerging from the MS VLY. The resulting
intensification of this surface low is partly due to more
impressive downstream ridging interacting with the shortwave as it
develops a negative tilt over MO/IL/IN. Height falls and the LFQ of
an almost due-north advecting jet streak will help lower surface
pressures, and the the surface low is progged to deepen rapidly as
it lifts across the L.P. of MI and into Ontario province.

Moisture downstream of this surface low will be impressive, with
isentropic ascent lifting north from the Gulf surging PWs to above
the 99th percentile across the Mid-Atlantic, with the increasing
cyclonic flow pushing the accompanying theta-e ridge westward into
Michigan as a modest TROWAL. The overlap of this TROWAL with an
intensifying deformation axis will result in impressive omega,
partially driven by an intersection of fgen into the DGZ, to cause
rapid cooling of the column and resultant heavy snowfall. The
system is progressive off to the northeast, so the duration of
heavy snow is likely to be limited, but both the HREF and WPC
prototype snowband tool indicate a corridor of 1+"/hr snowfall
rates across the western L.P. for the first 6-10 hours of the
forecast. While the intensity has gotten stronger with recent model
runs, the placement has been quite consistent, and despite
antecedent conditions that are not favorable for snow
accumulations, these intense rates should still result in several
inches of snowfall as reflected by WPC probabilities for 2+ inches
that range from 10-30% near Chicago, IL, to above 70% near Traverse
City, MI, with 4-6" possible in the vicinity of the latter.


...The West...
Days 1-3...

The period begins with the Pacific Coast sandwiched between an
anomalous ridge to the east across the Intermountain West, and an
amplifying trough well to the west over the Pacific Ocean. Between
these two features, pinched mid-level flow will surge moisture
eastward into the Pacific Northwest, with IVT progged to approach
750 kg/m/s, funneling along a cold front and focused into OR. As
the upstream trough over the Pacific deepens and pivots eastward,
it will shed periodic lobes of vorticity into the Northwest, with
an accompanying surface low likely moving towards the OR/CA
border at the start of D2 /12Z Monday/. This surface low will
briefly intensify ascent (which will already be impressive through
height falls, PVA, upslope flow, and LFQ jet-level diffluence),
while also pushing the strongest moisture channel southward into
CA. While this suggests the highest PW anomalies will pivot south
as well towards the Sierra, sufficient upper level flow will
maintain elevated moisture well inland through D2, providing the
impetus for continued moderate to heavy snowfall across the terrain as
far east as the NW WY ranges.

For D1, the heaviest snowfall is likely within the plume of highest
IVT along the cold front from the OR Cascades eastward into the
Salmon River/Sawtooth ranges, and south into northern CA and the
Sierra. Here, WPC probabilities are high (>70%) for more than 8
inches of snow, with locally 2-3 feet possible in the Cascades and
near the Shasta/Trinity region, although snow-levels indicate the
heaviest accumulations will remain above 5000 ft before falling in
tandem with weakening snow intensity. During D2, the heaviest snow
becomes primarily focused in the Sierra where a high risk (>70%)
is progged by WPC probabilities for more than 12 inches, leading to
2-day snowfall as much as 2-4 feet in the higher elevations above
4000 ft. This will still result in significantly impacted travel
across the Sierra passes Monday into Tuesday.

Most of the forcing and moisture advect east by D3, so heavy snow
should wane across much of the West as it focuses instead into the
Central Rockies, but additional snowfall of a few inches is
possible (10-30%) in the Wasatch and Northern Rockies.


...Central Rockies to the Central Plains...
Days 2-3...

The next in this impressive series of significant low pressure
systems to impact the Plains will develop late Monday in the
Central Rockies and then strengthen into the Central Plains
Tuesday.

This system will initially develop downstream of a large trough
which will cross out of CA and the Great Basin, reaching the Four
Corners states Tuesday morning. Downstream height falls and PVA
will help drive large scale ascent into the region, which will be
additionally enhanced by a subtropical jet streak strengthening
through the primary trough axis. As this jet streak pivots
poleward, the LFQ will overlap with the mid-level height falls to
help drive surface pressure falls, and lee cyclogenesis the latter
portion of D2 /after 00Z Tuesday/. However, this jet streak will
outrun the primary forcing in response to vorticity shedding
rapidly to the east, with secondary troughing and a more
pronounced, negatively tilted, trough developing over the Central
High Plains later Tuesday. This will result in secondary jet streak development, with even more impressive diffluence overlapping the
more structured height falls/mid-level divergence. It is this
secondary development around 00Z Wednesday that will potentially
become a powerful cyclone with heavy snow across the Central Plains
and into the Upper Midwest by the end of the forecast period.

Although the first low is weaker, it will interact with a cold
front dropping out of the interior Northwest, leading to some
enhanced ascent through fgen and upslope flow across Wyoming on D2.
Moisture streaming into the wave from the E/SE, as well as aloft
from the S/SW will manifest as precipitation across WY, but with
the heaviest snowfall likely occurring in the terrain of the Big
Horns, NW WY ranges, and along the axis of greatest fgen over
N-central WY D2. However, total snowfall is expected to be modest
this period except above 4000 ft in the NW WY ranges and Big Horns,
where WPC probabilities for 6+ inches are above 70%.

Then during D3, snowfall becomes much more expansive and heavy as
the secondary, stronger, low develops and spreads snow from the
Central Rockies into the Central Plains. There is still
considerable placement and intensity uncertainty as reflected by
broad spread in the D3-D4 clusters, but the GFS members appear to
be the deepest and fastest solutions, with the CMC/ECMWF ensembles
supporting slightly less spread and are favored at this time. With
significant spread still in place, WPC probabilities are somewhat
compromised, but still support a high risk (>70%) of 6+ inches from
the Wind Rivers through the Laramie Range and into much of the CO
Rockies where heavy snow rates are likely both through
fgen/upslope flow. Farther east, increasing deformation over the
Central Plains by the end of the period will result in increasing
coverage of heavy snowfall, and while current WPC probabilities for
4+ inches are only around 10% across NE/KS, these will likely
increase and spread northeast into D4.

Additionally, as this secondary low intensifies, the pressure
gradient is progged to become quite intense, regardless of the
model preference, and WSSI-P is already featuring a widespread
30-50% probability of moderate blowing snow impacts, suggesting
the potential for near-blizzard conditions in some areas, but those
details still need to be ironed out as the event approaches.


Weiss



$$

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FOUS11 KWBC 161948
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 PM EDT Sun Mar 16 2025

Valid 00Z Mon Mar 17 2025 - 00Z Thu Mar 20 2025


...The West...
Days 1-2...

The period begins with the Pacific Coast sandwiched between an
anomalous ridge to the east across the Intermountain West, and an
amplifying trough well to the west over the Pacific Ocean. Between
these two features, pinched mid-level flow will continue surge=20
moisture eastward into the Pacific Northwest during the early part
of D1, with IVT falling below 600 kg/m/s through this evening,=20
funneling along a cold front and focused into northern CA and the
northern Great Basin tonight. As the upstream trough over the=20
Pacific deepens and pivots eastward, it will shed periodic lobes of
vorticity into the Northwest, with an accompanying surface low=20
likely moving towards the OR/CA border Monday morning. This=20
surface low will briefly intensify ascent (which will already be=20
impressive through height falls, PVA, upslope flow, and LFQ jet-=20
level diffluence), while also pushing the strongest moisture=20
channel southward into the central Sierra Nevada. While this=20
suggests the highest PW anomalies will pivot south as well towards=20
the Sierra, sufficient upper level flow will maintain elevated=20
moisture well inland through the beginning of D2, providing the=20
impetus for continued moderate to heavy snowfall across the terrain
as far east as the NW WY ranges.

For D1, the heaviest snowfall is likely within the plume of highest
IVT along the cold front from the OR Cascades eastward into the
Salmon River/Sawtooth ranges, and south into central CA and the=20
Sierra. Here, WPC probabilities are high (>70%) for more than 8=20
inches of snow, with locally 1-2 additional feet possible in the=20
Cascades and near the Shasta/Trinity region, although snow-levels=20
indicate the heaviest accumulations will remain above 5000 ft=20
before falling in tandem with weakening snow intensity. During D2,=20
the heaviest snow becomes primarily focused in the Utah ranges and
western WY as the main axis of moisture slides inland with the
sharp upper trough, where probabilities for more than 8" of snow=20
are also high, mainly above 8000 ft.


...Central Rockies/Plains through the Upper Midwest...=20
Days 2-3...

Increasing potential for a strong winter storm to stretch from the
central High Plains to the Upper Midwest between Tuesday and
Wednesday, with blizzard conditions becoming increasingly likely.=20
See the latest Key Messages linked at the bottom of the discussion=20
for more information.

This system will initially develop downstream of a large trough
which will cross out of CA and the Great Basin, reaching the Four
Corners states Tuesday morning. Downstream height falls and PVA
will help drive large scale ascent into the region, which will be
additionally enhanced by a subtropical jet streak strengthening
through the primary trough axis. As this jet streak pivots
poleward, the LFQ will overlap with the mid-level height falls to
help drive surface pressure falls, and lee cyclogenesis on Tuesday.
However, this jet streak will outrun the primary forcing in=20
response to vorticity shedding rapidly to the east, with secondary=20
troughing and a more pronounced, negatively tilted, trough=20
developing over the Central High Plains later Tuesday. This will=20
result in secondary jet streak development, with even more=20
impressive diffluence overlapping the more structured height=20
falls/mid-level divergence. It is this secondary development around
00Z Wednesday that will potentially become a powerful cyclone with
heavy snow across the central Plains and into the Upper Midwest=20
through the end of the forecast period. 00Z NAEFS SAT depicts the=20
low pressure over Kansas Tuesday night below the 0.5th=20
climatological percentile and eventually PWs reaching above the=20
90th percentile across eastern Iowa and Wisconsin on Wednesday=20
where the stronger surge of southerly flow exists, further highlighting
the strength of this system for the time of year.

Although the first low is weaker, it will interact with a cold
front dropping out of the interior Northwest, leading to some
enhanced ascent through fgen and upslope flow across Wyoming on D2.
Moisture streaming into the wave from the E/SE, as well as aloft
from the S/SW will manifest as precipitation across WY, but with
the heaviest snowfall likely occurring in the terrain of the Big
Horns, NW WY ranges, and along the axis of greatest fgen over
N-central WY D2. However, total snowfall is expected to be modest
this period except above 4000 ft in the NW WY ranges and Big Horns,
where WPC probabilities for 6+ inches are above 70%.

Then during D3, snowfall becomes much more expansive and heavy as
the secondary, stronger, low develops and spreads snow from the
Central Rockies into the Central Plains and eventually the Upper
Midwest. There is still some placement and intensity uncertainty,=20
but it has gradually decreased today with subtle slowing of the=20
shortwave in the GFS/GEFS and faster ejection in the ECMWF. WPC=20 probabilities have increased somewhat and still support a high risk

70%) of 6+ inches from the Wind Rivers through the Laramie Range

and into much of the CO Rockies where heavy snow rates are likely=20
both through fgen/upslope flow. Farther east, increasing=20
deformation over the Central Plains and Upper Midwest by the end of
the period will result in increasing coverage of heavy snowfall=20
and rates of 1-2"/hr in the deformation axis northwest of the
strong surface low. Current WPC probabilities for at least 4" are=20
low (10-30%) from eastern Colorado through northern Kansas and=20
central Nebraska, before increasing to around 30-60% from eastern=20
Nebraska through north- central Iowa. Then, a more mature cyclone=20
and combination of WAA/deformation leads to higher probabilities=20
for 6"+ of snow from southeast Minnesota through central/northern=20
Wisconsin and the MI U.P., where the latest WPC chances are 40-60%.
One factor that may impede the higher end potential of snow with=20
this system is that temperatures will be very warm during the days=20
and even hours prior to snowfall development. Highs on Tuesday are=20
forecast to reach the 70s and 80s across the central Plains and=20
Midwest.

Additionally, as this secondary low intensifies, the pressure=20
gradient is progged to become quite intense, regardless of the=20
model preference, and WSSI-P is already featuring a widespread=20
40-70% probability of moderate blowing snow impacts, suggesting=20
the potential for blizzard conditions in some areas. Additionally,
decent overlap in ECMWF EFI snow and wind gust values in the
central Plains are usually a good indicator that impacts=20
associated with blowing snow are possible.


Snell/Weiss




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4G-JYdtnPmNaMvwNDamWE91hSM5-XSIp9aXWD1D2XznQT= v7iri2X1Cw8epp4MumpVVp8xxMW838T7jHXEEFvH6564_k$=20

$$

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FOUS11 KWBC 130703
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 AM EDT Thu Mar 13 2025

Valid 12Z Thu Mar 13 2025 - 12Z Sun Mar 16 2025


...The West...
Days 1-3...

...Extremely active weather pattern will spread heavy snow across
most of the West today through Friday, with a second wave
approaching for the weekend. This lead system will likely become a
significant winter storm in the Northern Plains Saturday. Key
Messages are in effect, and linked below...


The period begins with a short wavelength but extremely amplified
trough aligned on the immediate Pacific coast Thursday morning.
This trough will continue to amplify as it moves across the Great
Basin Thursday evening and then into the Rockies on Friday. During
this evolution, a potent shortwave and accompanying vorticity
maxima will swing through the base of this trough, This feature
will outrun the northern leg of this trough, resulting in a closed
mid-level low pivoting into the Southern Rockies Friday morning and
then into the Southern Plains. This will be an extremely impressive
feature, as NAEFS ensemble tables indicate 500-700mb heights fall
below the minimum within the CFSR database by Friday morning across
the Central and Southern Rockies, with a surrounding large area of
height anomalies below the 1st percentile across most of the
Western U.S.

This mid-level height evolution is a clear signal for a powerful
and widespread system to bring heavy precipitation across an
expansive area. While height falls will drive ascent across a vast
region, this will combine with upper diffluence within the LFQ of a
subtropical jet streak which will wrap around the base of this
trough, producing enhanced deep layer lift, especially into CA and
the Four Corners. Additionally, periods of upslope flow on W/SW 700
mb winds will enhance ascent across much of the terrain, first
across the Sierra and Cascades, and then spreading east across the
Great Basin and into the Rockies Friday. Additionally, W/SW mid-
level flow will isentropically ascend the region, leading to
additionally enhanced lift across a large portion of the region.

In the presence of this pronounced ascent, moisture will steadily
increase as an atmospheric river (AR) pivots onshore downstream of
the primary trough axis. IVT progs from both the GEFS and ECENS
indicate a high probabilities (>90%) for a plume of 250 kg/m/s=20
IVT, although probabilities for 500 kg/m/s IVT are tepid (< 30%).
Still, this pronounced moisture plume will surge PWs to above the
90th climatological percentile from CA through the Southern
Rockies, with more normal PWs farther north. The overlap of the
aforementioned ascent into this moistening column will result in
widespread precipitation, with snow falling in the terrain.

While confidence is high in widespread precipitation, there is
still uncertainty into the snow levels. The steep lapse rates
beneath the core of the deepening upper trough suggest heavy
precipitation rates will drag down snow levels, indicating lower
NBM percentiles are likely more realistic. Using the NBM 25th
percentile as proxy, snow levels could fall to 2000-3000 ft during
periods of heavy snow across much of the West, with heights as low
as 1000-1500 ft across the Cascades. This indicates that travel
across many passes will be greatly impacted, especially where
snowfall rates reach 1-2"/hr, potentially as high as 3"/hr across
the Sierra, Transverse Ranges of CA, and parts of the Great Basin
terrain as reflected by the WPC prototype snowband tool.

Not only will rates be impressive, they will combine with strong
winds to produce substantial impacts, and the WSSI-P is forecasting
a high probability (>90%) for at least moderate impacts for much of
the terrain, especially from CA through the Four Corners. In these
areas, WPC probabilities forecast a high chance (>90%) for at least
8 inches D1 in the Sierra, Transverse/Peninsular Ranges, the
Wasatch, Mogollon Rim, San Juans, Uintas, and Wind River Mountains.
By D2 lingering snowfall may accumulate above 8 inches once again,
but primarily across the CO Rockies. Locally 1-3 feet of event
total snowfall is probable in these ranges.

As this first impulse departs into the Central Plains D2, /00Z-12Z
Saturday/, another wave immediately on its heels will approach the
Pacific Coast and spread renewed height falls onshore as far east=20
as the Central Rockies. This second wave appears to be less intense
as reflected by weaker height and PW anomalies, and is progged to=20
be shifted north of the initial impulse. However, renewed periods=20
of heavy snowfall are likely from the Sierra and northern CA
terrain north and east into the Cascades and then spread east D3
into the Rockies, generally from CO northward as a warm front
pivots through the area. Snow levels with this second wave are
expected to be higher, rising to 4000-5000 ft in CA and 2500-3500
ft elsewhere, but still low enough to be impactful to many passes
as Pacific air is slow to flood eastward.=20

With this second wave, WPC probabilities D2 re-focus in the=20
Sierra, the Shasta/Trinity region of northern CA, and the OR=20
Cascades where they are above 70% for 8+ inches. On D3 these
probabilities shift northeast, with 70%+ probabilities extending
across the WA/OR Cascades, the Olympics, and into the Salmon River
range.


...Central and Northern Plains...=20
Days 2-3...

The southern stream closed low emerging from the Four Corners and
into the Southern Plains Friday morning will become a formidable
winter storm across the Plains Friday into Saturday. As this closed
low emerges into the Plains early Friday, it will continue to
deepen, featuring 500-700mb height anomalies by 00Z Saturday that
are below the minimum percentile within the CFSR climatology=20
between 850-500mb across a large portion of the Plains. This is an=20 exceptionally deep system, and the combination of the intense=20
height falls with the LFQ of a subtropical jet streak rotating=20
through the trough will result in rapid lee-cyclogenesis beginning=20
as early as Friday morning.=20

This surface low will deepen rapidly, approaching March record
pressure levels across the Plains as it tracks from eastern CO
Friday morning to eastern SD Friday evening, and then the U.P. of
MI Saturday aftn. While there is some uncertainty in the exact
placement and track of this low, the overall spread is relatively
small for a D3 system, leading to high confidence in the evolution.
With this low deepening rapidly, significant moisture will be drawn
northward from the Gulf on impressive isentropic ascent, and the
resultant theta-e ridge is progged to lift into a robust TROWAL
which will pivot across WI and into MN/ND/SD Saturday morning. As
this occurs, the combination of increasing ascent, aided by a
pivoting deformation axis W/NW of the low center, and cooling of
the column through both dynamic affects and ageostrophic flow/cold
air drainage from the NNW, will result in a p-type transition from
rain to mixed to snow.=20

There remains uncertainty into how long this transition will take
to occur, but the intense omega into the column Saturday morning
suggests the guidance may be under-doing the speed at which this
occurs, indicating a faster transition from rain to snow, with less
freezing rain/sleet in between. This is more typical of the
conceptual model for this type of system as well, so while mixed
precip is likely at times, the more impactful wintry precipitation
type should be snow, which will likely come down heavy at times. At
the same time, very strong winds, which are progged by model
soundings to exceed 50 kts in the 800-900mb layer, while help to
fracture dendrites leading to low SLRs which will be blow around
considerably. So, while total snowfall may be somewhat modest
except beneath the pivot point of this deformation axis, impacts
will be substantial with near blizzard conditions possible from far
northeast Nebraska through northern Minnesota. In this area, 48-hr
WPC probabilities from 12Z Fri to 12Z Sunday reach as high as
50-70% for 4+ inches, and isolated totals above 6 inches are
possible (10-30%). Additionally, some light freezing rain has a
30-50% chance of accumulating 0.1" or more in a small portion of NW
MN.



Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4JGcCzvCafQcT1jc4Ei5rPfHvAyePsBmOR_cNx3GMRAww= oQNdiaX0-IumDfDLsxIjjgBE0G5slHNYvL7IcLSB4QYBKM$=20

$$

=3D =3D =3D
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FOUS11 KWBC 131945
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 PM EDT Thu Mar 13 2025

Valid 00Z Fri Mar 14 2025 - 00Z Mon Mar 17 2025

...The West...
Days 1-3...

...Extremely active weather pattern will spread heavy snow across
most of the West through Friday, with a second wave approaching=20
for the weekend...

A series of potent upper level shortwave troughs will move across=20
the West through this period, resulting in multiple rounds of heavy
snow across much of the terrain from the Cascades, Sierras, the=20
Front Range, and much of the terrain in between. This very active=20
period with multiple rounds of snow and low snow levels could=20
result in impacts to the various mountain passes across the West,=20
with snow accumulations measured in feet.

The first and most potent of the upper level troughs is moving
across the West right now. A vorticity maximum rounding the base of
the trough along the West Coast now will move into the Southwest
tonight. Ahead of this trough, lee cyclogenesis is ongoing across
the northern and central Plains. The combination of this trough and
surface lows will focus the heaviest associated snow from the
Bighorns of MT/WY south through the Front Range and into the
Sacramento Mountains of NM tonight.

Snow levels will be above 7,000 ft across these easternmost ranges
of the Rockies to start the night, but as the trough and associated
cold air moves in tonight, they will drop to generally between
2,000 and 3,000 ft, allowing snow to begin to accumulate to pass
level by the start of the day Friday. As the Plains low
consolidates into one primary low over western Kansas and Nebraska,
the snow should similarly focus across Wyoming, Colorado, and
eastern Utah Friday morning, where the heaviest snow totals are
expected for the Day 1/Thursday Night & Friday period. WPC 24 hour probabilities through Friday afternoon of 6 inches of snow or more
are as high as 80% in southwest Colorado, but are above 50% across
much of western Colorado, the Uintas of Utah, and the eastern=20
Mogollon Rim of central Arizona. The low shifts into the eastern
Plains by Friday afternoon, ending the snow for the Rockies for
this system.

A second upper level shortwave and the leading edge of a potent
northwesterly jet streak will follow behind the first into the=20
West Coast early Friday morning. The rapid succession of the waves
could mean some of Rockies may have only a brief break in the snow, particularly across the Four Corners region, before precipitation
rates increase once again associated with the approach of the
second wave. This shortwave will be weaker than the first, but=20
will still be potent. The heaviest mountain snow will be across
northern California and southwest Oregon during the day Friday.
With the influx of Pacific moisture, snow levels will rise to
between 3,000 and 4,000 ft in this region, which will still be
plenty low enough to impact the passes, especially when adding
dynamic cooling from any heavy snow on the windward side of the
mountains. 24 hour WPC probabilities for 6 inches or more through=20
Friday are above 50% from the southern Oregon Cascades through the=20
Sierras, with the Klamath Mountains of northern California over
80%.

The most potent upper level energy with this wave will track across
the Southwest Friday night, then rapidly translate eastward to
support the impressive cyclone across the northern Plains and upper
Midwest. This will result in a rapid collapse/weakening of any
organized precipitation across the Southwest during the day
Saturday. A smaller portion of the energy from the original second
wave will retrograde towards the Pacific Northwest and merge with a
third shortwave moving into the coast. This will keep valley rain
and mountain snow ongoing across much of Washington State, Oregon,
and Idaho Friday night into Saturday. The Cascades will be the
focus for the heaviest snow, with 24 hour WPC probabilities for 6
inches or more of snow above 50% for all of the Cascades, and up to
80% for much of the Oregon Cascades.

On Day 3/Saturday Night & Sunday, a fourth trough will approach the
Pacific Northwest in the form of a vertically stacked low. That low
will approach the coast of Washington and Oregon during the day
Sunday. Lingering lift from the previous wave will keep the=20
mountain snow continuing through Saturday night and intensify=20
during the day Sunday, especially across Oregon. It's here that=20
the low will eventually come ashore Sunday night. The greatest lift
and moisture flux will be during the day Sunday into Oregon ahead
of the low, so the heaviest precipitation associated with it will=20
be then.=20

Since the snow is unlikely to stop at all this weekend into the
Cascades, expect the highest elevations to pick up several feet of
snow through the period. The Sawtooths and Bitterroots of Idaho and
Montana as well as the Yellowstone N.P. area will also pick up=20
several feet of new snow through the weekend as the waves that
impact the coast earlier move inland across the Pacific Northwest
through the weekend.

Wegman


...Northern Plains...
Day 2...

...Rapidly deepening low and a transition from rain to a wintry mix
and eventually snow is expected to combine with very strong winds
to lead to possible blizzard conditions across parts of the=20
eastern Dakotas and western Minnesota. See Key Messages linked at=20
the bottom of the discussion for more information...

The southern stream closed low emerging from the Four Corners and
into the Southern Plains Friday morning will become a formidable
winter storm across the Plains Friday into Saturday. As this closed
low emerges into the Plains early Friday, it will continue to
deepen, featuring 500-700mb height anomalies by 00Z Saturday that
are below the minimum percentile within the CFSR climatology=20
between 850-500mb across a large portion of the Plains. This is an=20 exceptionally deep system, and the combination of the intense=20
height falls with the LFQ of a subtropical jet streak rotating=20
through the trough will result in rapid lee-cyclogenesis beginning=20
as early as Friday morning.=20

This surface low will deepen rapidly, approaching March record
pressure levels across the Plains as it tracks from eastern CO
Friday morning to eastern SD Friday evening, and then the U.P. of
MI Saturday aftn. While there is some uncertainty in the exact
placement and track of this low, especially with the potential for
numerous low-level centers to rotate around the broader area of=20
low pressure, the overall spread is relatively small. This leads=20
to high confidence in the storm's evolution and area most likely=20
to experience a brief period of heavy snow. With this low=20
deepening rapidly, significant moisture will be drawn northward=20
from the Gulf on impressive isentropic ascent, and the resultant=20
theta-e ridge is progged to lift into a robust TROWAL which will=20
pivot across WI and into MN/ND/SD Saturday morning. As this occurs,
the combination of increasing ascent, aided by a pivoting=20
deformation axis W/NW of the low center, and cooling of the column=20
through both dynamic affects and ageostrophic flow/cold air=20
drainage from the NNW, will result in a p-type transition from rain
to mixed to snow.

There remains uncertainty into how long this transition will take
to occur, but the intense omega into the column Saturday morning
suggests the guidance may be under-doing the speed at which this
occurs, indicating a faster transition from rain to snow, with less
freezing rain/sleet in between. This is more typical of the
conceptual model for this type of system as well, so while mixed
precip is likely at times, the more impactful wintry precipitation
type should be snow, which will likely come down heavy at times
(1-2"/hr rates). At the same time, very strong winds, which are=20
progged by model soundings to exceed 50 kts in the 800-900mb layer,
will help to fracture dendrites leading to low SLRs which will be=20
blow around considerably. Additionally, even with snow coming down=20
heavily it may struggle to accumulate for the first hour or so=20
given warm antecedent ground conditions and prior rainfall. So,=20
while total snowfall may be somewhat modest except beneath the=20
pivot point of this deformation axis, impacts will be substantial=20
with near blizzard conditions possible from far northeast Nebraska=20
through northern Minnesota. In this area, 24-hr WPC probabilities=20
from 00Z Sat to 00Z Sun reach as high as 50-70% for 4+ inches, and=20
isolated totals above 6 inches are possible (20-40%). Additionally,
some light freezing rain has a 10-30% chance of accumulating 0.1"=20
or more in a small portion of NW MN.

Snell/Weiss


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-C8iDBYFPoy5G9vFU9aA-6dFsvyULo9fMqdic9FGulkTk= 17C2BIIP0UDZ5srNUP5GTTtCZkqcftRY9HxSoF81s2y_vA$=20

$$

=3D =3D =3D
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FOUS11 KWBC 140655
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
255 AM EDT Fri Mar 14 2025

Valid 12Z Fri Mar 14 2025 - 12Z Mon Mar 17 2025

...The West...
Days 1-3...

The active pattern continues across the West with several days of
widespread wintry precipitation impacting much of the area through
the upcoming weekend.

The period begins with a potent closed mid-level low moving across
the Southern High Plains of CO/NM. This feature is quite intense,
reflected by NAEFS 850-500mb height percentiles that are below the
minimum in the CFSR climatology across a large, and expanding,
section of the country centered along the High Plains. As this
feature shifts E/NE this afternoon, it will continue to deepen and
produce near-blizzard conditions across the Northern Plains (more
on that in the section below). Behind this departing system, heavy
snow will continue across the Southern and Central Rockies through
D1 as a combination of mid-level deformation and a trailing cold=20
front overlap to enhance ascent in a region of still elevated 700mb
RH across the Four Corners and into Wyoming. While this snow=20
should wane quickly by 00Z Saturday, and snow levels will generally
be in the 5000-6000 ft range, snow is expected to accumulate=20
several additional inches D1 as reflected by WPC probabilities that
are high (>70%) for 4+ inches across the CO Rockies, the northern
Sangre de Cristos, and as far north as the Big Horn Mountains of
WY.

Any break in precipitation behind this significant, but departing,
system will be short lived as the active pattern sheds another
amplifying shortwave across the Pacific and into CA/OR by 00Z
Saturday /late D1/. This next impulse will be accompanied by an
impressive lobe of vorticity, with the resultant trough development
driving height falls once again from CA through the Four Corners
into D2. Available moisture with this next impulse is progged to=20
be much less than with the first shortwave, reflected by NAEFS PW=20
anomalies that are near normal east of AZ as the maximum IVT=20
downstream of this trough axis is modest (GEFS and ECENS=20
probabilities for 500 kg/m/s less than 10%) and focused generally=20
south into Mexico. Of course, this is pretty typical with ARs that=20
are oriented more W/NW than W/SW, but enough moisture and continued
lowered snow levels of generally 3000-5000 ft will allow for at=20
least modest snowfall accumulations. The heaviest snowfall=20
accumulations D1 into D2 are expected from the Sierra into the=20
Mogollon Rim and into the Four Corners, where WPC probabilities are
high once again for 8+ inches, and locally 1-2 feet is possible in
the Sierra and northern CA terrain near the Shasta/Trinity region.

Interestingly, as the second shortwave digs across the Four Corners
into D2, the upstream flow becomes more favorable for a surge of
moisture and heavy precipitation farther north into the Pacific and
Interior Northwest. A trough over British Columbia/Alberta
interacts with the trough moving across the Four Corners to squeeze
the flow over the Pacific, resulting in fast and zonal flow surging
into WA/OR. Impulses within this flow will help push two distinct
surface lows onshore, the first Saturday morning and the second
early Sunday morning, helping to enhance ascent. Regardless of
those surface lows, deep layer lift becomes impressive and moisture
increases as a strengthening Pacific jet streak pivots onshore and
begins to buckle, lifting meridionally on Sunday downstream of an
even more potent trough approaching the coast.=20

Both ECENS and GEFS probabilities exceed 70% for 500 kg/m/s IVT=20
reaching the coast D3, funneling moisture along a cold front which=20
will elongate into the region. Although the accompanying WAA with
this atmospheric river (AR) will drive snow levels to as high as
6000 ft D3 south of the cold front, considerable moisture and a
sharp gradient in snow levels will likely result in impactful
pass-level snow from the Cascades through the Northern Rockies,
with still impressive snow but generally above pass-levels farther
south from the Great Basin into the Central Rockies, as much of the
West is again covered in elevation-based snowfall. High WPC=20
probabilities (>70%) late D1 through D3 become widespread for 6+
inches each day from the OR Cascades northward into the Olympics
and WA Cascades, and as far east as the Salmon River/Sawtooth area,
north into the Northern Rockies, and even as far as the Tetons.
Event total snowfall is likely to be extreme in the higher terrain
of the OR Cascades where 4-6 feet of snow is possible, with
widespread 1-3 feet in the other higher elevations regions of the
Northwest.


...Northern Plains...
Days 1-2...

Rapidly strengthening low pressure in the lee of the Rockies this
morning will approach or exceed March sea-level pressure records
across the Northern Plains as it tracks northeast through Saturday
aftn. Not only will SLP records be approached, but 850-500mb height
anomalies are progged to fall below the all-time minimums within
the CFSR climatology according to NAEFS, further indicative of the
intensity of this system. The result of this evolution will be a=20
major winter storm impacting the Northern Plains late Friday=20
through Saturday.=20

As the surface low tracks northeast from the Central High Plains,
it will be driven by an overlap of impressive height falls
downstream of the primary closed low and at least modest upper
diffluence in the LFQ of a poleward arcing jet streak east of the
mid-level center. Together, these will drive intense deep layer
ascent aiding in the storm strengthening. At the same time,
confluent low-level flow east of the low will draw impressive=20
moisture northward on 300-305K isentropic ascent. This moisture
will surge am impressive theta-e ridge northward, which will then
rotate cyclonically and lift into a robust TROWAL, pivoting over
eastern NE, SD, ND, and western/central MN Saturday. At the same
time, an impressive deformation axis will overlap with this TROWAL,
supporting an intense axis of maximized ascent to drive heavy=20
precipitation rates.

Initially, the theta-e advection will surge warm air into the
region such that the column will support primarily rain. However,
as the low continues to deepen and move northeast, and mesoscale
ascent intensifies, the combination of dynamic cooling and
ageostrophic flow on NW winds into the low center will rapidly cool
the column. The guidance continues to suggest a period of mixed
precip, including sleet and freezing rain, will occur, but this
again appears to be a conceptual setup where the transition period
is quite rapid. This indicates that while some light icing is
possible, the predominant wintry p-type will be snow, which will
almost certainly become heavy at times (70% probabilities for 1"/hr
according to the HREF). This is supported as well by NAM cross-
sections indicating a region of theta-es lapse rates <0C/km in the
presence of symmetric instability, suggesting the potential for=20
CSI or even CI (thundersnow). Although antecedent conditions are=20
quite warm and some rain will begin this event, these rates should=20
quickly overwhelm this hostility leading to rapid snow=20
accumulation.=20

Finally, impacts during the period of heavy snow are likely to be
impressive due to strong winds that may gust above 50 mph during
the period of heavy snow. While the period of heavy snow rates is
likely to be somewhat temporally modest except beneath the pivot
point of the deformation axis, the overlap of extreme rates of
1-2"/hr and these strong winds will create near blizzard conditions
and extremely dangerous travel. Snowfall will begin late D1 but
accumulations are expected to be modest before 12Z Saturday as
reflected by WPC probabilities of 30-50% for just 2 inches across
far eastern SD. Early D2 snowfall coverage and intensity ramps up,
and WPC probabilities are high (>70%) for 4+ inches near the Coteau
des Prairies and as far north as International Falls, MN. Locally,
8 inches of snow is possible beneath the pivoting deformation,
especially should any thundersnow occur. Additionally, some light
icing across western MN has a 10-30% chance of reaching 0.1+" of
ice accretion.


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5NiP0-ogg52fE6brKTWGycDa8ZLgcXm9WVPtJmLZMYtjB= Mz4CmSB-i13_PYTxzrwGiMEmxiTIy8klKrf4xHL-sy-xic$=20

$$

=3D =3D =3D
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FOUS11 KWBC 141851
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
251 PM EDT Fri Mar 14 2025

Valid 00Z Sat Mar 15 2025 - 00Z Tue Mar 18 2025


...Northern Plains...
Day 1...

Rapidly strengthening low pressure analyzed over the central Plains
this afternoon will approach or exceed March sea-level pressure=20
records across the Northern Plains as it tracks northeast through=20
Saturday aftn. Not only will SLP records be approached, but=20
850-500mb height anomalies are progged to fall below the all-time=20
minimums within the CFSR climatology according to NAEFS, further=20
indicative of the intensity of this system. The result of this=20
evolution will be a major winter storm impacting the Northern=20
Plains late Friday through Saturday with a combination of heavy=20
snow and gusty winds.

As the surface low tracks northeast from the Central High Plains,
it will be driven by an overlap of impressive height falls
downstream of the primary closed low and at least modest upper
diffluence in the LFQ of a poleward arcing jet streak east of the
mid-level center. Together, these will drive intense deep layer
ascent aiding in the storm strengthening. At the same time,
confluent low-level flow east of the low will draw impressive=20
moisture northward on 300-305K isentropic ascent. This moisture
will surge am impressive theta-e ridge northward, which will then
rotate cyclonically and lift into a robust TROWAL, pivoting over
eastern NE, SD, ND, and western/central MN Saturday. At the same
time, an impressive deformation axis will overlap with this TROWAL,
supporting an intense axis of maximized ascent to drive heavy=20
precipitation rates.

Initially, the theta-e advection will surge warm air into the
region such that the column will support primarily rain. However,
as the low continues to deepen and move northeast, and mesoscale
ascent intensifies, the combination of dynamic cooling and
ageostrophic flow on NW winds into the low center will rapidly cool
the column. The guidance continues to suggest a period of mixed
precip, including sleet and freezing rain, will occur, but this
again appears to be a conceptual setup where the transition period
is quite rapid. This indicates that while some light icing is
possible, the predominant wintry p-type will be snow, which will
almost certainly become heavy at times (70% probabilities for 1"/hr
according to the HREF). This is supported as well by NAM cross-
sections indicating a region of theta-es lapse rates <0C/km in the
presence of symmetric instability, suggesting the potential for=20
CSI or even CI (thundersnow). Although antecedent conditions are=20
quite warm and some rain will begin this event, these rates should=20
quickly overwhelm this hostility leading to rapid snow=20
accumulation.=20

Finally, impacts during the period of heavy snow are likely to be
impressive due to strong winds that may gust above 50 mph during
the period of heavy snow. While the period of heavy snow rates is
likely to be somewhat temporally modest except beneath the pivot
point of the deformation axis, the overlap of extreme rates of
1-2"/hr and these strong winds will create near blizzard conditions
and extremely dangerous travel. The changeover to snow will
commence across eastern SD after 06Z Saturday before expanding
north-northeast across western and north-central Minnesota between
12Z-18Z. Recent trends have shifted this band of heavy snowfall
amounts (>4") eastward by about 75 miles or so as guidance is=20
consolidating on a more compact area of low pressure across the=20
Upper Midwest. WPC probabilities for at least 4" are high (>70%)=20
across southwest to north-central Minnesota, with 40-70% chances=20
extending into far eastern South Dakota and far southeast North=20
Dakota. Locally, a narrow swath of at least 8" of snow is possible=20
(20-40%) beneath the pivoting deformation, especially should any=20
thundersnow occur. Additionally, some light icing across north-=20
central MN has a 10-30% chance of reaching 0.1+" of ice accretion.


...The West...
Days 1-3...

The active pattern continues across the West with two separate
systems producing widespread wintry precipitation across much of=20
the area through early next week.

After the significant winter storm departs into the central U.S.,=20
any break in precipitation across the West will be short lived as=20
the active pattern sheds another amplifying shortwave across CA/OR=20
tonight. This next impulse will be accompanied by an impressive=20
lobe of vorticity, with the resultant trough development driving=20
height falls once again from CA through the Four Corners on D1.=20
Available moisture with this next impulse is progged to be much=20
less than with the first shortwave, reflected by NAEFS PW anomalies
that are near normal east of AZ as the maximum IVT downstream of=20
this trough axis is modest (GEFS and ECENS probabilities for 500=20
kg/m/s less than 10%) and focused generally south into Mexico. Of=20
course, this is pretty typical with ARs that are oriented more W/NW
than W/SW, but enough moisture and continued lowered snow levels=20
of generally 3000-5000 ft will allow for at least modest snowfall=20 accumulations.

Interestingly, as this shortwave digs across the Four Corners, the
upstream flow becomes more favorable for a surge of moisture and=20
heavy precipitation farther north into the Pacific and Interior=20
Northwest. A trough over British Columbia/Alberta interacts with=20
the trough moving across the Four Corners to squeeze the flow over=20
the Pacific, resulting in fast and zonal flow surging into WA/OR.=20
Impulses within this flow will help push two distinct surface lows=20
onshore, the first Saturday morning and the second early Sunday=20
morning, helping to enhance ascent. Regardless of those surface=20
lows, deep layer lift becomes impressive and moisture increases as=20
a strengthening Pacific jet streak pivots onshore and begins to=20
buckle, lifting meridionally on Sunday downstream of an even more=20
potent trough approaching the coast.=20

Both 12Z ECMWF and GFS depict 500-700 kg/m/s IVT reaching the=20
coast D2, funneling moisture along a cold front which will=20
elongate into the region. Although the accompanying WAA with this=20 atmospheric river (AR) will drive snow levels to as high as 6000 ft south
of the cold front, considerable moisture and a sharp gradient in=20
snow levels will likely result in impactful pass- level snow from=20
the Cascades through the Northern Rockies and eventually Sierra
Nevada once again on D3, with still impressive snow but generally=20
above pass- levels farther south from the Great Basin into the=20
Central Rockies, as much of the West is again covered in elevation-
based snowfall. For the entire forecast period, high WPC=20
probabilities (>70%) for 8+ inches exist from the Sierra Nevada and OR
Cascades northward into the Olympics and WA Cascades, and as far=20
east as the Salmon River/Sawtooth area, north into the Northern=20
Rockies, and even as far as the Tetons. Event total snowfall is=20
likely to be extreme in the higher terrain of the OR Cascades where
4-6 feet of snow is possible, with widespread 1-3 feet in the=20
other higher elevations regions of the Northwest and Sierra Nevada.


Snell/Weiss




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!8IUy2IMH3gmbJPdc2_VgOZYyqx3DhlOaP9KWRE8dLibJp= kSro1W9Ydg1HuXjtsmvT9M_CoxSWv_e2bud9pzZyUug30I$=20

$$

=3D =3D =3D
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FOUS11 KWBC 150648
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
248 AM EDT Sat Mar 15 2025

Valid 12Z Sat Mar 15 2025 - 12Z Tue Mar 18 2025


...Northern Plains...
Day 1...

The rapidly strengthening low moving across the Northern Plains
which has been advertised the past few days will be well underway
at the start of the period. At 12Z Saturday, the surface low is
progged to be near the Twin Cities, MN, and will be lifting
northeast, reaching Ontario, Canada by 00Z Sunday. N and W of this
low center, a strong and pivoting deformation axis will be helping
to drive intense ascent, causing a changeover from rain to heavy
snow across western MN, resulting in blizzard, and near-blizzard,
conditions through the aftn.

Moisture advection downstream of this strengthening cyclone will
remain impressive through D1, with isentropic ascent surging the
accompanying theta-e ridge into a robust TROWAL which will pivot
cyclonically back into the Dakotas and Minnesota today. The overlap
of this enhanced moisture and the collocated deformation axis will
increase both moisture and ascent to cause a narrow stripe of heavy precipitation, changing rapidly from rain to snow. Dynamic cross-
sections across this region continue to suggest an axis of CSI/CI,
supported by the elevated instability within the TROWAL, to create
snowfall rates that are forecast both by HREF probabilities and the
WPC prototype snowband tool to reach 1-2"/hr. Despite hostile
antecedent conditions due to warm temperatures and rain, these
snowfall rates will rapidly accumulate, and when combined with wind
gusts of 50 mph, will likely result in blizzard and near-blizzard
conditions through the aftn. This is despite accumulations that
will in most areas be modest except within the stripe beneath the
pivoting deformation axis, where WPC probabilities are high (>70%)
for 4+ inches and locally as much as 8 inches is possible.


...The West...
Days 1-3...

The active pattern continues across the West with two separate
systems producing widespread wintry precipitation across much of=20
the area through early next week.

The next impulse within this active pattern will push an impressive
vorticity lobe eastward from OR through the Great Basin to start
Saturday morning, with the resultant trough development driving=20
height falls once again into the Four Corners on D1. PW anomalies=20
that are near normal east of this feature as the maximum IVT=20
downstream of this trough axis is modes and focused generally=20
south into Mexico, but available moisture is still sufficient for a
swath of moderate to heavy precipitation, with snow-levels
generally 3000-5000 ft allowing for moderate snowfall accumulations
above these levels. WPC probabilities D1 are moderate to high
(50-90%) for 4+ inches across the CO Rockies, Sangre de Cristos, White Mountains of AZ, and the Sacramentos.

As this lead shortwave digs across the Four Corners, the upstream=20
flow becomes more favorable for a surge of moisture and heavy=20
precipitation farther north into the Pacific and Interior=20
Northwest. A trough over British Columbia/Alberta interacts with=20
the trough moving across the Four Corners to squeeze the flow over=20
the Pacific, resulting in fast and zonal flow squeezing into=20
WA/OR. Impulses within this flow will help push two distinct=20
surface lows onshore, the first this morning and the second early=20
Sunday morning, helping to enhance ascent. Regardless of those=20
surface lows, deep layer lift becomes impressive and moisture=20
increases as a strengthening Pacific jet streak pivots onshore and=20
begins to buckle, lifting meridionally on Sunday downstream of an=20
even more potent trough approaching the coast.=20

Resultant IVT with this setup becomes moderate to strong once
again, potentially reaching 500-750 kg/m/s as moisture funnels
onshore along a cold front which will elongate into the region.=20
Although the accompanying WAA with this atmospheric river (AR) will
drive snow levels to as high as 6000 ft south of the cold front,=20 considerable moisture and a sharp gradient in snow levels will=20
likely result in impactful pass-level snow from the Cascades=20
through the Northern Rockies and eventually Sierra Nevada once=20
again later D2 into D3. Still impressive snow, but at generally=20
above pass-levels, is forecast farther south from the Great Basin=20
into the Central Rockies, as much of the West is again covered in=20 elevation-based snowfall. For the entire forecast period, high WPC=20 probabilities (>70%) for 8+ inches exist from the Sierra Nevada and
OR Cascades northward into the Olympics and WA Cascades, and as=20
far east as the Salmon River/Sawtooth area, north into the Northern
Rockies, and even as far as the Tetons. Event total snowfall is=20
likely to be extreme in the higher terrain of the OR Cascades where
4-6 feet of snow is possible, with widespread 1-3 feet in the=20
other higher elevations regions of the Northwest and Sierra Nevada.

During the latter half of D3 /Monday evening/ the parent trough
digging across CA and into the Great Basin responsible for the snow
axis shifting south into the Sierra late D2 will pivot eastward
towards the Four Corners/Central Rockies. This will bring a slow
end to precipitation across much of the West (at least briefly) but
may help to produce another significant central U.S. storm by the
middle of next week.


...Central Rockies and High Plains...
Day 3...

A shortwave emerging from the Pacific will amplify as it moves
across CA late Monday and then tracks progressively into the Great
Basin, reaching the Four Corners by the end of the forecast period.
This shortwave will be accompanied by an intensifying sub-tropical
jet streak which will begin to arc poleward downstream of this
amplifying trough. This will have the dual-pronged effect of
transporting moisture into the Central Rockies while also placing
favorable LFQ diffluence atop the region of greatest mid-
level height falls. The resultant deep layer ascent will likely
interact with a cold front dropping southeast into the area, and
the setup appears favorable for developing cyclogenesis in the
central High Plains by Tuesday morning. Where the strongest ascent
overlaps the greatest moisture, especially in areas of expanding
frontogenesis, a swath of heavy snow is likely. WPC probabilities
at this time are modest, just 30-50% for 2+ inches outside of
terrain features across WY, but are higher in the Big Horns and
Black Hills.=20

This system may become the next powerful cyclone across the Plains
through the middle of next week.


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_G4_gqVRI09X9uf3k76Us6Lg-9FRQAPxhvOaXNqa_AGOO= LMDs44fpGtvqtamqFFLFc-ZlFsO6J7kRFr-2GBktzdIvSs$=20

$$

=3D =3D =3D
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FOUS11 KWBC 151842
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
242 PM EDT Sat Mar 15 2025

Valid 00Z Sun Mar 16 2025 - 00Z Wed Mar 19 2025


...Midwest to Great Lakes...
Day 1...

Recent trends have increased the potential for a swath of moderate
snowfall to occur on the backside of a developing secondary low
pressure system racing northward from the Mid- Mississippi Valley
this evening. The mechanism behind this trend is related to a
deepening shortwave crossing the southern Plains this afternoon and
becoming more separated from the exiting upper low over Minnesota.
This leads to increased ridging ahead of this secondary shortwave
(partly amplified by latent heat release from convection across
the South this afternoon) and a repositioning of the 250 mb jet
streak over the Upper Great Lakes to produce more favorable upper
divergence and a broader precipitation shield reaching westward
enough into the cold airmass settling in behind a potent cold front
crossing the region today. While this system will be very
progressive, there is potential for snowfall rates to approach
1"/hr from northern IL and eastern WI through the western L.P. and
eastern U.P. of MI between 06Z to 18Z Sunday. However, even though
this is a D1 forecast and snow begins to develop after 06z tonight
there remains more uncertainty than to be desired. Additionally,
most areas have surface temperatures well above freezing today and
will see precip type start out as rain, leading to possible heavy
snowfall rates driving where most accumulation occurs. WPC
probabilities for at least 4" have increased across the northern
L.P. of MI to around 30-50%, where the 12z HREF depicts the
greatest chances for 1"/hr snowfall rates. Lighter amounts under
3" are anticipated to stretch along a southwest- northeast corridor
from northern IL/southeast WI to the eastern MI U.P.


...The West...
Days 1-3...

The active pattern continues across the West with an atmospheric
river impacting the Oregon Cascades and California ranges through
D2 before the associated upper trough swings across the
Intermountain West and Rockies into D3.

As a shortwave impulse at the base of the upper trough approaches
the Northwest on Sunday the resultant IVT with this setup becomes
moderate to strong, potentially reaching 500-750 kg/m/s at the
start of D1 as moisture funnels onshore along a cold front which
will elongate into the region. Although the accompanying WAA with
this atmospheric river (AR) will drive snow levels to as high as
6000 ft south of the cold front, considerable moisture and a sharp
gradient in snow levels will likely result in impactful pass-level
snow from the Cascades through the Northern Rockies and eventually
Sierra Nevada once again on D2. In fact, NAEFS SAT depicts IVT
values above the 99th climatological percentile on Sunday extending
from the OR/CA coast through the northern Great Basin, further
highlighting the impressive moisture associated with this system.

For the entire forecast period (ending 00Z Weds), high WPC
probabilities (>70%) for 12+ inches exist across the Sierra Nevada
and northern CA ranges, OR Cascades, east to the Salmon
River/Sawtooth area and northern Rockies. Event total snowfall is
likely to be extreme in the higher terrain of the OR Cascades where
4-6 feet of snow is possible, with widespread 1-3 feet in the
other higher elevations regions of the Northwest, Sierra Nevada,
and northern Great Basin.


...Central Rockies and High Plains...
Day 3...

The system impacting the West through early D3 will begin to eject
into the central Plains by the end of the forecast period. This
shortwave will be accompanied by an intensifying sub- tropical jet
streak which will begin to arc poleward downstream of this
amplifying trough. This will have the dual-pronged effect of
transporting moisture into the Central Rockies while also placing
favorable LFQ diffluence atop the region of greatest mid- level
height falls. The resultant deep layer ascent will likely interact
with a cold front dropping southeast into the area, and the setup
appears favorable for developing cyclogenesis in the central High
Plains by Tuesday morning. Where the strongest ascent overlaps the
greatest moisture, especially in areas of expanding frontogenesis,
a swath of heavy snow is likely and at this time is centered over
central WY on Tuesday. WPC probabilities for at least 4" have
increased to 40-80% throughout much of central WY, but remain
higher for at least 6" (70%+) in the Big Horns, Black Hills,
central UT ranges and CO Rockies.


This winter storm may become the next powerful cyclone across the
Plains and Upper Midwest through the middle of next week. See WPC's
Extended Forecast Discussion for more information.


Snell






$$

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FOUS11 KWBC 170755
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
355 AM EDT Mon Mar 17 2025

Valid 12Z Mon Mar 17 2025 - 12Z Thu Mar 20 2025


...The West...
Days 1-3...

Shortwave trough positioned just west of northern CA at 12Z Monday
will deepen into a closed mid-level low as it advects onshore and
drops subtly southeast Monday morning. The core of this low is
progged to track across the northern Great Basin this evening, but
a strong lobe of vorticity immediately in its wake will dig farther
south, amplifying the trough axis into southern CA by the end of
D1. Downstream of this trough, squeezed mid-level flow will produce
moisture confluence, lying directly beneath a strengthening and
meridionally advancing subtropical jet streak. This setup will=20
support impressive moist advection, reflected by PWs surging to=20
above the 90th percentile across CA and the Great Basin according=20
to NAEFS ensemble tables.

Within this moistening column, and beneath the deep layer ascent, a
wave of low pressure will move southeast along a baroclinic=20
gradient/cold front that will be driven eastward by the parent=20
trough evolution. This will maintain the focus of greatest moisture
just south of the front, but will drive some enhanced mid-level=20
isentropic ascent above and behind the boundary. This additional=20
lift, combined with periods of upslope flow into terrain features,=20
will result in widespread precipitation D1 from the Cascades=20
southward through the northern CA terrain and into the Sierra, as=20
well as points well east across the Great Basin and into the=20 Wasatch/Tetons/Wind Rivers.=20

Snow levels will vary considerably across the West during this=20
period due to the passage of the cold front. However, within the
region of greatest moisture/ascent and heaviest resultant snowfall,
snow levels should be generally 4000-6000 ft from the Sierra=20
through the Great Basin and into the Central Rockies. Snow levels=20
crash behind the cold front, allowing for at least moderate=20
snowfall but with more substantial pass level impacts in its wake.=20
WPC probabilities for more than 6 inches of snow are moderate=20
(30-50%) D1 across the Sierra and WA Cascades, but high (>70%)=20
across the Wasatch and into portions of western WY.

Additionally, along this front, impressive 0-2km fgen and increased
low-level RH will move into a corridor of elevated instability (NAM
SBCAPE 100-400 J/kg). This will occur within a region of high SnSq
parameter above 2 from eastern NV Monday evening through UT, WY,
and CO by Tuesday evening. This setup could produce convective=20
snow showers or even snow squalls, which is additionally supported
by simulated reflectivity in the high-res guidance. While any snow
squalls won't produce tremendous snowfall amounts, dangerous travel
is likely through snow-covered roads and rapidly changing
visibility.

This first system moves into the Central Rockies during D2,
becoming a significant winter storm in the Plains, and leaving a
brief respite much of D2 across the West within this otherwise
continued active pattern. This break will be short lived, however,
as yet another strengthening mid-level trough moves across the
Pacific and approaches the Pacific Northwest D3, likely coming=20
onshore Wednesday evening. Although the guidance varies=20
considerably with timing of the associated mid-level waves within=20
this next trough, they all agree that it will be potent, and=20
potentially negatively tilted, as it moves onshore during D3. The=20
downstream affects of this will be increased synoptic lift through=20
mid-level divergence, height falls, and intensifying upper=20
diffluence, all to pivot renewed moisture and forcing back onshore.
The antecedent airmass is cool, so snow levels will are only=20
expected to rise to around 3500 ft within the core of the strongest
WAA, and otherwise be generally 2000-3000 ft, suggesting travel=20
across area passes will again become problematic. This feature will
likely be transient, but have sufficient moisture to produce heavy
snow once again from the Olympics and WA Cascades southward into=20
the Sierra, with some spill over occurring before the end of the=20
period as far east as the Salmon River/Sawtooth/Northern Rockies.

WPC probabilities for 6+ inches of snow on D3 feature a high risk=20

70%) across the Olympics, Cascades, and Shasta/Trinity region of=20

northern CA< with lower probabilities below 50% continuing into the
Sierra and east across parts of the higher elevations of Idaho.


...Central Rockies, Central Plains, Upper Midwest...=20
Days 1-3...

...Another significant winter system likely to bring blizzard=20
conditions to portions of the Plains and Upper Midwest...

This system manifests as two waves of low pressure, a modest lead
wave, followed immediately by the more impressive cyclone. These
will generate from an anomalous trough which will amplify across=20
the Four Corners Tuesday /D2/ leading to impressive height
anomalies that are progged to fall below the 1st climatological
percentile between 700-500mb across the Central Plains by
Wednesday. This deepening and intense amplitude will yield strong
downstream ascent through height falls and mid-level divergence,
and as the subtropical jet streak amplifies it will begin to shift
almost due poleward, placing intense LFQ diffluence atop the region
of greatest height falls.

Together this will produce an environment extremely favorable for a
rapidly deepening cyclone in the lee of the Rockies. However,
before this occurs, a weaker wave is progged to develop near SE WY
Tuesday morning in response to more modest height falls, but in the
presence of increased baroclinicity as a cold front drops southward
from the Northern Rockies/High Plains, aided by the ageostrophic
response (fgen) of the RRQ of a departing jet streak into the Great
Lakes. This first low will eject rapidly east and weaken, but the
strong ascent and plentiful moisture will create heavy snow across
the Central Rockies, especially in WY where low-level upslope
ascent into the best frontogenesis will produce heavy snow rates.
WPC probabilities for more than 4 inches of snow are high (>90%)
across much of NW WY and into the Big Horns, with some elevated
probabilities for 1-2" extending into the lower terrain of eastern
WY as well.

During D2, however, is when the significant low develops. As the
synoptic pattern evolves as described above, lee cyclogenesis will
occur, and this low will be located beneath extremely favorable
synoptic ascent for rapid surface height falls, and nearly all the
ensemble groupings suggest SLP falling to the 980s Wednesday
morning over IA. There is generally good clustering of the ensemble
member low-pressures, but D3 clusters still suggest that the GEFS
is a bit deeper and faster with the progression, although the
spread appears to have decreased in the past 24-hrs. This leads to
high confidence in a rapidly strengthening low pressure, with
moisture steadily increasing as 300K isentropic ascent surges=20
theta-e northward and into the system, eventually lifting into a=20
TROWAL to provide moisture and elevated instability.

As has been the case with the past few of these March systems, the
antecedent airmass is warm, and the moist/warm advection funneling
in the higher PW air will cause the precipitation to begin as rain=20
in many areas, especially outside of terrain and into the Plains.=20
However, this should have minimal affect on snowfall accumulations,
as extreme dynamic cooling combined with ageostrophic flow into=20
low and cold advection as the low moves east will cause a rapid=20
p-type transition from rain to snow, with snow likely becoming=20
quite heavy within the deformation axis NW of the low Wednesday.=20
Snowfall rates that may reach 1-2"/hr (or more? some signals for CI
in a deep and saturated DGZ over IA indicating possible thunder-
snow) will overcome the warm ground quickly. Thus, the limiting=20
factor to snowfall amounts appears to be more the speed of this=20
system as it remains progressive, and CIPS analogs indicate the=20
75th% is only generally 4-8", higher into WI/MI where leading jet-
streak snowfall may add on to amounts before the main system. This=20
is additionally reflected by WPC probabilities for 4+ inches that=20
are below 30% D2, but increase to greater than 70% from western IA=20
northeast into the U.P. of MI D3. These probabilities have trended=20
upward, and locally 6+ inches of snow is likely within this band.

Finally, despite snowfall that may be modest in many areas outside
of the Upper Midwest, the intense winds driven by 850mb northerly=20
flow of 60 kts will produce strong gusts for which DESI indicates=20
has a 90% chance of exceeding 35 mph, and even a 50% chance for 50=20
mph across the Plains. This has led to high (>70%) probabilities=20
for moderate blowing snow impacts from WSSI-P, and despite snow=20
that may start as the heavier/wet variety, will transition to=20
higher SLR and broken aggregates leading to likely blizzard=20
conditions in some areas, especially from central Kansas northeast=20
into southern Minnesota.

By the end of the forecast period, this low will be well into
Ontario, but lingering snow and gusty winds are expected to still
be ongoing across MI, with some lake-enhanced snow across the U.P.,
western L.P. and maybe even into northern Indiana into early D4.


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-8C5lghvvNxUpy34AV8hH1D76lewHLCE8KC2CsIvSnZPq= vURcB7gVVxXBn4nsOvkj4FpvN_SWI3H4sRXWpOEAyZXSs4$=20

$$

=3D =3D =3D
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FOUS11 KWBC 172104
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
504 PM EDT Mon Mar 17 2025

Valid 00Z Tue Mar 18 2025 - 00Z Fri Mar 21 2025


...California, Great Basin, and Pacific Northwest...=20
Days 1 and 3...

Amplified trough along the northern CA coast this afternoon will
dig across the Desert Southwest through Tuesday before swinging
across the Great Plains. Moderate to heavy snow will shift down the
rest of the Sierra Nevada through this evening with probabilities=20
for an additional >6" after 00Z are 50-80% on the southern Sierra
with snow levels dropping from 6000ft to 3000ft. A reinforcing
shortwave shifts over the WA coast this evening providing lift and
enhancement to the onshore flow and moderate snow to the WA/OR
Cascades into Tuesday. Day 1 PWPF for >6" are 30-70% on the
central/southern WA and northern/central OR Cascades.

The cold front shifting inland ahead of this trough will cross from
eastern NV into UT this evening. Increasing frontal forcing, low=20
level moisture, and some instability (12Z HREF mean MUCAPE of 100-200
J/kg) will allow a snow squall potential along the frontal zone.
Expect brief bursts of accumulating snow and rapidly reduced
visibility, causing dangerous overland travel in snow squalls.
Otherwise, terrain enhancements to the flow from the large trough
will allow heavy snow to continue behind the front in eastern NV
and the ranges of UT where Day 1 PWPF for >8" are 40-80% above the
post-frontal snow levels of 3000-4000ft.

The next trough rotates around a Gulf of Alaska low, crossing the
PacNW coast late Wednesday which is then followed by prolonged
onshore flow/continual precip through this weekend. Snow levels
Wednesday night/Thursday fluctuate between 2500ft and 4000ft along
the length of the Cascades and the Klamath Mtns where Day 3 PWPF
for >8" is 40-80%.


...Central Rockies, HIgh Plains...=20
Days 1-2...

...Heavy snow tonight/Tuesday over the north-central High Plains
and WY/CO Rockies...

A wave ahead of the parent trough/low tracks over WY early Tuesday
with strong lee-side cyclogenesis on the south-central Plains (aka
KS) through Tuesday. 1025mb high pressure over the Canadian
Prairies allows a frontal focus for snow over the Bighorn Mtns east
to and north of the Black Hills late tonight, sagging south=20
through Tuesday. This leading swath of snow has increased in=20
intensity and coverage given strong dynamics to overcome marginal=20
thermal conditions (it is currently around 50F in the lower=20
elevations of this swath). Day 1 PWPF for >6" are 50-80% east of=20
the Bighorns into SD and 50-90% for >18" in the Bighorns themselves
with ideal backing flow from east to north encountering upslope on
the Bighorns with ample Pacific and Gulf moisture. The trough to=20
the south will allow heavy snow on the western slopes of the CO=20
Rockies Tuesday where Day 1.5 PWPF for >8" are 50-90%.


...Central Plains through Upper Midwest...
Days 2/3...

...Blizzard conditions for portions of the Central Plains into the
Upper Midwest Tuesday night into Wednesday night...

The trough takes on a negative tilt as it pushes over the south-
central Plains Tuesday night, closing into a mid-level low
Wednesday morning over Iowa before tracking northeast over MI
Wednesday night. Peak intensity of the surface low looks to be
around 985mb along the IA/MO border Wednesday morning which will
generate a powerful wind field.

As has been the case with the past few of these March systems, the
antecedent airmass is warm, and the moist/warm advection funneling
in the higher PW air will cause the precipitation to begin as rain=20
in many areas of the Plains. However, this should have minimal=20
affect on snowfall accumulations, as extreme dynamic cooling=20
combined with ageostrophic flow into low and cold advection as the=20
low moves east will cause a rapid p-type transition from rain to=20
snow, with snow likely becoming quite heavy within the deformation=20
axis NW of the low Wednesday. Snowfall rates of 1-2"/hr, possibly
higher in thundersnow, will overcome the warm ground/low level
thermals quickly. Thus, the limiting factor to snowfall amounts=20
appears to be more the speed of this system as it remains=20
progressive. Confidence continues to increase in a swath of >6"
snow from eastern Neb to Lake Superior with enhancements from the
lake on the Huron Mtns of U.P. where >12" is likely in Day 2, 2.5=20
PWPF.

More modest snow totals of 2-4" are likely from northern KS through
central Neb, though intense winds driven by 850mb northerly flow=20
of 60 kts will produce strong/damaging gusts and blizzard=20
conditions. Blizzard looks to be met well into the Upper Midwest
until the northern forests limit the blowing snow potential which
is highlighted well in the probabilistic WSSI.

Wrap around snow shifts over southern WI/northern IL/MI/IN
Wednesday night into Thursday, though the parent low shifting well
into Quebec by Thursday morning should limit snow potential.


Jackson



...Winter Storm Key Messages are in effect as linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!76sopEbkEJd7dK1iYt_iVkTxW7d-9d5eQfjzBet-YWnbe= kADyvht8GHZALYuKoVdJS3K7qctsKY8604HWIv7ASbfgZw$=20

$$

=3D =3D =3D
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FOUS11 KWBC 180721
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 AM EDT Tue Mar 18 2025

Valid 12Z Tue Mar 18 2025 - 12Z Fri Mar 21 2025


...The West...=20
Days 1-3...

The period begins with an amplifying mid-level trough diving across
the eastern Great Basin and into the Four Corners, pushing a cold
front eastward into the Rockies. This front will have the=20
potential to produce scattered convective snow showers and snow=20
squalls this morning across UT/CO/WY as its forcing driven by 0-2km
fgen moves east into a region of at least modestly unstable air=20
(100-300 J/kg of SBCAPE) and increased low-level RH. While snow=20 accumulations from these squalls will be minimal, brief heavy snow=20
rates and gusty winds could produce dangerous travel through the=20
day.

Behind this front, remnant low to mid level fgen and increased
moisture will drive a swath of heavy snowfall across much of the CO
Rockies and northward into WY and the Black Hills of SD. Large
scale ascent through the height falls downstream of the parent
trough combined with this fgen will allow for some heavy snow
rates, especially into the terrain where upslope flow will
additionally produce lift. WPC probabilities D1 for more than 6
inches are high (>70%) across the Wasatch, CO Rockies, and much of
the terrain of WY where locally more than 12 inches is possible,
especially in the Big Horns. Where the most intense fgen is
progged, primarily along the MT/WY border (a bit north from
previous model cycles), some lower elevation snowfall is likely
which could accumulate 3-6" into the High Plains of southern MT.

As this trough moves into the Plains later D1, brief ridging
blossoms across much of the West bringing an end to precipitation.
However, this respite will be relatively short lived as yet another
deepening trough approaches from the Pacific and moves onshore
Wednesday night. Height falls, PVA, and LFQ diffluence ahead of an
accompanying jet streak will all provide deep layer lift, aided by
upslope ascent as the low-to-mid level flow south of the trough
becomes more zonally oriented. This overlap of zonal/broadly
confluent mid-level flow beneath the upper jet streak will pivot
IVT exceeding 250 kg/m/s onshore, leading to an expanding plume of precipitation beginning Wednesday night /late D2/, and continuing
into D3. Snow levels during this period will be rather low,
starting around 2000-2500 ft, and warm only slowly, reaching
3500-4000 ft by the end of the forecast period. This suggests that
pass-level impacts are likely, and where the most intense ascent
occurs, even the lower valleys could receive some light snow
accumulations.=20

WPC probabilities for heavy snow exceeding 4 inches on D2 reach
above 70% from the northern CA terrain northward through the
Cascades and into the Olympics. On D3, moisture shunts north and
east just a bit, causing a wane in precip over the Sierra, but
expanding WPC probabilities for more than 4 inches from the
Olympics and Cascades east as far as the NW WY ranges and CO
Rockies where they exceed 70% in the higher terrain (especially in
the Cascades, Tetons, and Park Range of CO).


...Central High Plains through the Great Lakes...=20
Days 1-2...

...Significant storm system to bring blizzard conditions to
portions of the Central Plains and Upper Midwest. Key Messages are
in effect for this event...

This system will emerge in response to an amplifying mid-level
trough which will be crossing the Great Basin and approaching the
Four Corners starts to start the period /12Z Tuesday/. This trough
will continue to deepen in response to a sharp shortwave trough and accompanying vorticity lobe swinging through its base, such that=20
by the time it tracks into the Plains Wednesday, 850-700mb heights=20
fall below the minimum within the CFSR climatology according to=20
NAEFS, with 500mb heights dropping below the 2.5 percentile. This=20
is indicative of an exceptionally strong system producing intense=20
synoptic ascent. While height falls and PVA will drive a=20
considerable portion of the deep layer lift, a collocated=20
subtropical jet streak intensifying downstream and gaining rapid=20
latitude (arcing poleward) will place impressive LFQ diffluence=20
atop the region of greatest height falls. This setup will support=20
lee cyclogenesis with rapid intensification, and NAEFS mean MSLP=20
progs suggest that by 12Z Wednesday, this event has a 75-90% chance
of reaching an extreme minimum pressure.

Intense low pressures in March are not exceedingly rare, but this
one will likely result in a wide swath of heavy snow and strong
winds, producing blizzard conditions across the Plains and Upper
Midwest. While there is some uncertainty still among the various
model clusters as to the exact temporal and spatial evolution,
confidence is high that after some heavy snow in the Rockies D1, a
swath of blizzard conditions will develop farther east.=20

This will result in heavy snow developing first across KS/NE late=20
Tuesday night/early Wednesday morning, and then shifting northeast=20
through Wednesday across IA, SD, MN, WI, and finally the U.P. of=20
MI. During this time, the robust moisture funneling northward on=20
300K isentropic ascent will rotate into a strong TROWAL, helping to
support elevated instability and increased moisture. Where the=20
TROWAL is most impressive and lies atop the strongest deformation=20
from eastern NE through northern WI, cross-sections continue to=20
indicate a risk for CI and thundersnow. This will support snowfall=20
rates that have high chance for exceeding 1"/hr and 2"/hr (90% and=20
60% chance, respectively, from the HREF), which is supported as=20
well by the WPC prototype snowband tool. Where CI occurs, rates=20
could reach 3"/hr, and this will be more than sufficient to=20
overcome hostile antecedent conditions.

While some snow may initially melt, snow accumulation will likely
become rapid as SLRs rise due to cooling despite dendritic
fracturing on winds as high as 60 kts below the DGZ. This will
produce blizzard conditions, and the WSSI-P is forecasting a 90%
chance of moderate impacts, and 20% chance of major impacts, even=20
where snow amounts are more modest due to the speed of this system.
As far as snowfall amounts, WPC probabilities have increased, and
while are modest D1, are high (>70%) D2 for more than 6 inches from
far eastern NE through a continuous, but narrow, corridor as far
north as the central U.P. of MI. In this corridor, WPC
probabilities for 12+ inches have increased to as high as 30-50%,
highest from NW IA through the U.P., and WSE plumes indicate a
potential for up to 15" in some areas should this band translate
temporally over some areas a bit longer. Some higher snow totals
are also possible in the Huron Mountains of the U.P. where the
deformation axis and some lake enhanced snowfall combine.

By D3 this entire system shifts well east as the primary low moves
into Ontario and the accompanying cold front surges into the Mid-
Atlantic states. While some wrap-around snowfall will likely
continue through early Thursday, especially where lake enhancement
can occur across the U.P. and northwest L.P. of MI, as well as S/E
of Lake Michigan, additional accumulations are expected to be=20
modest, but have a low chance (10-30%) of exceeding 4 additional
inches in the U.P. and far NW lower Michigan near Traverse City.


...Interior Northeast...
Day 3...

Guidance has trended stronger with a developing low pressure
Thursday evening across the northern Mid-Atlantic states. While
there is still considerable uncertainty at this time range in the
strength of this system, most ensemble systems indicate a rapidly
developing low pressure between 00Z Friday and 12Z Friday lifting
across southern New England.=20

The synoptic setup is favorable for this development. The same
trough responsible for the Plains/Midwest blizzard will continue to
shift east, and while the primary shortwave will lift into Canada,
a secondary southern impulse is progged to deepen over the Central Appalachians. This vorticity lobe will help split the jet stream,
leading to an increasingly coupled pattern as the subtropical jet
streak pivots over the Carolinas and the polar jet stream lifts
towards Greenland. The LFQ of the former and the RRQ of the latter
will overlap the greatest height falls, indicating a strong
likelihood of low development along a surface cold front/baroclinic
gradient. By 12Z Friday, the deterministic global models prog SLP
to be sub 990mb, and this rapid intensification within the synoptic
setup will likely cause a strong deformation axis to develop NW of
the surface low. While the antecedent column is marginal for wintry precipitation, strong ascent in the vicinity of this deformation
will result in rapid dynamic cooling, and rain changing to snow,
possibly heavy, across Upstate NY and interior New England.

Being 6th period, confidence in amounts and placement is still
modest, but a band of heavy snow is becoming more likely, with
significant accumulations possible, especially in higher terrain.
This is reflected by current WPC probabilities that are above 50%
for 2 inches and 10-30% for 4 inches, highest in the Adirondacks
and Catskills.


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!8Yoi7m5O-gBf-TFjhMIUArgMGax2p9dPV5GajNsxk5OeN= fbTd57BRyE5cSgTpi5k87CL0aGohydHKsBTnDFTJSDCsOw$=20

$$

=3D =3D =3D
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FOUS11 KWBC 181921
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 PM EDT Tue Mar 18 2025

Valid 00Z Wed Mar 19 2025 - 00Z Sat Mar 22 2025


...The West...=20
Days 1-3...

Assessment of the latest WV satellite indicates our deep upper
trough located just north of the Four Corners with primary ascent
pattern located in-of far eastern UT, southern WY, and the western
half of CO. Radar trends have materialized as previously forecasted
with scattered bouts of snow showers/squalls located within the
above areas due to the combination of robust mid-level ascent and
the progression of a surface cold front propagating eastward out of
the Great Basin through the Inter-Mountain West with the current
surface analysis indicating the position over western CO and NM.
Elevations above 5500' MSL will be the greatest beneficiaries of
heavier snowfall totals with the latest WPC probabilities for at
least 6 inches located over the interior of CO with >50% probs
located in those higher terrain locales along and west of the
Central Rockies. When coupled with the snow that has already
fallen, totals exceeding 12 inches will be plausible, especially
above 9500' MSL.

As this trough moves into the Plains later D1, brief ridging
blossoms across much of the West bringing an end to precipitation.
However, this respite will be relatively short lived as yet another
deepening trough approaches from the Pacific and moves onshore
Wednesday night. Height falls, PVA, and LFQ diffluence ahead of an
accompanying jet streak will all provide deep layer lift, aided by
upslope ascent as the low-to-mid level flow south of the trough
becomes more zonally oriented. This overlap of zonal/broadly
confluent mid-level flow beneath the upper jet streak will pivot
IVT exceeding 250 kg/m/s onshore, leading to an expanding plume of precipitation beginning Wednesday night /late D2, and continuing=20
into D3. Snow levels during this period will be rather low,=20
starting around 2000-2500 ft, and warm only slowly, reaching=20
3500-4000 ft by the end of the forecast period. This suggests that=20 pass-level impacts are likely, and where the most intense ascent=20
occurs, even the lower valleys could receive some light snow=20 accumulations.=20

WPC probabilities for heavy snow exceeding 4 inches on D2 reach
above 70% from the northern CA terrain northward through the
Cascades and into the Olympics. On D3, moisture shunts north and
east just a bit, causing a wane in precip over the Sierra, but
expanding WPC probabilities for more than 4 inches from the
Olympics and Cascades east as far as the NW WY ranges and CO
Rockies where they exceed 70% in the higher terrain (especially in
the Cascades, Tetons, and Park Range of CO).

Weiss/Kleebauer

...Central High Plains through the Great Lakes...=20
Days 1-2...

...Significant storm system to bring blizzard conditions to
portions of the Central Plains and Upper Midwest. Key Messages are
in effect for this event...

This system will emerge in response to an amplifying mid-level
trough which will be crossing the Great Basin and approaching the
Four Corners starts to start the period /12Z Tuesday/. This trough
will continue to deepen in response to a sharp shortwave trough and accompanying vorticity lobe swinging through its base, such that=20
by the time it tracks into the Plains Wednesday, 850-700mb heights=20
fall below the minimum within the CFSR climatology according to=20
NAEFS, with 500mb heights dropping below the 2.5 percentile. This=20
is indicative of an exceptionally strong system producing intense=20
synoptic ascent. While height falls and PVA will drive a=20
considerable portion of the deep layer lift, a collocated=20
subtropical jet streak intensifying downstream and gaining rapid=20
latitude (arcing poleward) will place impressive LFQ diffluence=20
atop the region of greatest height falls. This setup will support=20
lee cyclogenesis with rapid intensification, and NAEFS mean MSLP=20
progs suggest that by 12Z Wednesday, this event has a 75-90% chance
of reaching an extreme minimum pressure.

Intense low pressures in March are not exceedingly rare, but this
one will likely result in a wide swath of heavy snow and strong
winds, producing blizzard conditions across the Plains and Upper
Midwest. While there is some uncertainty still among the various
model clusters as to the exact temporal and spatial evolution,
confidence is high that after some heavy snow in the Rockies D1, a
swath of blizzard conditions will develop farther east.=20

This will result in heavy snow developing first across KS/NE late=20
Tuesday night/early Wednesday morning, and then shifting northeast=20
through Wednesday across IA, SD, MN, WI, and finally the U.P. of=20
MI. During this time, the robust moisture funneling northward on=20
300K isentropic ascent will rotate into a strong TROWAL, helping to
support elevated instability and increased moisture. Where the=20
TROWAL is most impressive and lies atop the strongest deformation=20
from eastern NE through northern WI, cross-sections continue to=20
indicate a risk for CI and thundersnow. This will support snowfall=20
rates that have high chance for exceeding 1"/hr and 2"/hr (90% and=20
60% chance, respectively, from the HREF), which is supported as=20
well by the WPC prototype snowband tool. Where CI occurs, rates=20
could reach 3"/hr, and this will be more than sufficient to=20
overcome hostile antecedent conditions.

While some snow may initially melt, snow accumulation will likely
become rapid as SLRs rise due to cooling despite dendritic
fracturing on winds as high as 60 kts below the DGZ. This will
produce blizzard conditions, and the WSSI-P is forecasting a 90%
chance of moderate impacts, and 20% chance of major impacts, even=20
where snow amounts are more modest due to the speed of this system.
As far as snowfall amounts, WPC probabilities have increased, and
while are modest D1, are high (>70%) D2 for more than 6 inches from
far eastern NE through a continuous, but narrow, corridor as far
north as the central U.P. of MI. In this corridor, WPC
probabilities for 12+ inches have increased to as high as 30-50%,
highest from NW IA through the U.P., and WSE plumes indicate a
potential for up to 15" in some areas should this band translate
temporally over some areas a bit longer. Some higher snow totals
are also possible in the Huron Mountains of the U.P. where the
deformation axis and some lake enhanced snowfall combine.

By D3 this entire system shifts well east as the primary low moves
into Ontario and the accompanying cold front surges into the Mid-
Atlantic states. While some wrap-around snowfall will likely
continue through early Thursday, especially where lake enhancement
can occur across the U.P. and northwest L.P. of MI, as well as S/E
of Lake Michigan, additional accumulations are expected to be=20
modest, but have a low chance (10-30%) of exceeding 4 additional
inches in the U.P. and far NW lower Michigan near Traverse City.

Mullinax

...Interior Northeast...
Day 3...

Guidance has backed off on the potential across the Interior
Northeast, in-line with the current ML output with subsequent prob
fields degraded compared to previous forecast. The threat for
surface cyclogenesis is still prevelant off the coast of Southern
New England with most of the deterministic running between
990-994mb as of 12z Friday. Despite deepening within the remainder
of the Friday window, the progressive nature of the precip and
marginal thermals currently depicted may limit the greatest threat
for at least 4" to the highest elevations in Northern New England
(Green and White Mountains) with very little chances in the
valleys. Threat for at least 2" is still running between 30-50% for
the Adirondacks and 50-70% for the Green/White Mountains, so the
threat is not muted by any stretch. Considering the potential
hovering near the threshold for impactful snowfall across the
Interior Northeast, will maintain close assessment of any trends as
we move through mid-week.=20

Kleebauer


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5eSpw51GHOXLBKXtAvn3NXL3mW0EEC916Q6UYG90Y9-5V= jumPAxuBz2YnIZZgM8LZg9il9J-lnBSHg6svoMn7FlEv5M$=20

$$

=3D =3D =3D
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FOUS11 KWBC 190719
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 AM EDT Wed Mar 19 2025

Valid 00Z Wed Mar 19 2025 - 00Z Sat Mar 22 2025


...Pacific and Interior Northwest...
Days 1-3...

The seemingly never-ending training of shortwaves and moisture
continues this week across the Northwest CONUS.

The first of these will be the most potent, as a strong shortwave
trough pushes onshore this evening with a subtle negative tilt.
Impressive height falls ahead of this trough will drive ascent,
aided by at least weak LFQ diffluence as a streak pivots through
the base of this trough. Together, this will produce deep layer
lift from the northern Sierra through the Cascades and into the
Interior Northwest, supporting heavy precipitation as IVT surges
northeast on downstream S/SW flow. Snow levels will gradually rise
within the IVT core due to accompanying WAA, before falling again
with the passage of a cold front later D1. Despite this, snow
levels will generally be quite low through the period as the region
remains cold, rising from around 2500 ft to 3500 ft, before
crashing again to 2000-2500 ft behind the cold front. This suggests
that snow will impact many of the Cascades and northern CA Passes,
as well as into the interior NW causing hazardous travel. This
first system is progressive, however, and WPC probabilities peak
around 70% for 6+ inches in the highest peaks of the WA Cascades
and Olympics, with generally 4 inches or less forecast elsewhere.

As this first trough shifts eastward, forcing will weaken across
the Northwest, but flow across the Pacific becomes increasingly
zonal due to squeezing between broad ridging well west off Baja and
a modest trough across the Gulf of Alaska. This zonal flow will
maintain onshore moisture advection to support rounds of
precipitation into the Northwest, with periodic vorticity lobes
swinging eastward (although maintaining latitude generally north of
OR) to enhance ascent. Snow levels D2-3 will fluctuate generally
between 2500ft and 4500ft, with rounds of precipitation leading to
periods of heavy snowfall. WPC probabilities both D2 and D3 are
similar in magnitude and areal extent, reaching 70% or more for 4+
inches from the Olympics, to the WA/OR Cascades, eastward through
the Salmon River/Sawtooth Ranges, and into the Northern Rockies.
2-day snowfall in some of the higher elevations could reach 2-4
feet, with up to 1 foot at the higher passes of the Cascades.


...Central High Plains through the Great Lakes...=20
Days 1-2...

...Significant storm system to bring blizzard conditions to
portions of the Central Plains and Upper Midwest. Key Messages are
being issued for this system...

The low-pressure which has been progged for several days now to
deepen in the Central High Plains is taking shape this morning
noted by pressure falls and increasing convective elements across
CO/KS/NE. The parent PV anomaly is clearly noted in satellite
imagery across far SE CO and into the OK Panhandle, which is
generally S/SW of all available guidance. This suggests that the
E/SE trend that began 24 hours ago is valid, and the event may end
up even farther SE than the 00z suite of models. While the exact
track will be critical to the placement of the most significant
impacts related to this blizzard, a large scale significant event
is still likely from the Central High Plains northeast into the
Great Lakes.

As this low deepens today in response to favorable synoptic and
mesoscale ascent, precipitation will expand downstream. Current WV
imagery shows both the low and mid level moisture streaming into
the developing cyclone, and where isentropic ascent lifts into the
intensifying deformation axis, impressive omega will squeeze out
all available moisture in the form of heavy rain and snow. The
deformation axis on the NW side of this system will likely be quite
intense, and will be overlapped by a cyclonically surging TROWAL to
enhance both ascent and instability. Where this occurs, any rain
will quickly change to snow through dynamic cooling, and then come
down extremely heavily, reaching 2-3"/hr at times where CI
(thundersnow) can occur. This is supported by HREF 1"/hr and 2"/hr probabilities that reach 90% and 70%, respectively, and by the WPC
prototype snowband tool that suggests locally 3"/hr is possible
(20%).=20

These snowfall rates will quickly overwhelm hostile antecedent=20
conditions (some places were near 80 degrees Tuesday and will get=20
heavy snow today!), and WPC probabilities have increased for=20
significant snowfall despite the SE shift. The heaviest=20
accumulations are likely from central NE through NW IA where the=20
environment supports a pivoting deformation band, and WPC
probabilities are high (>70%) for at least 8 inches. Here, locally
12-15 inches is possible (30%) in some locations. Farther=20
downstream, the band will begin to translate more quickly, limiting
the duration of these intense rates, but still heavy snowfall is=20
likely as reflected by WPC probabilities that are high (>70%) for=20
6+ inches from SE Minnesota through the central U.P. of Michigan.=20 Additionally, strong winds of 50 mph or more will accompany this=20
snowfall, so despite SLRs that will generally be below climo, and=20
will start as a heavy/wet snow, as SLRs climb and aggregates=20
fracture, blizzard conditions are expected which will make travel=20
almost impossible in some areas.

Another interesting development that has shown up tonight is for a
secondary deformation axis to potentially develop in the vicinity=20
of the primary PV anomaly behind the surface low, bringing some=20
heavy snow rates of around 1"/hr from SE Iowa to the Chicago metro=20
area. While this is not expected to be as impressive as the axis to
the NW, moderate snowfall accumulations for which WPC=20
probabilities indicate have low chance (10-30%) of exceeding 4=20
inches, which when combined with gusty winds could still produce=20
moderate travel impacts.

This entire system exits quickly on Thursday, with some residual
deformation snow pivoting across lower Michigan, and some northern
flow in its wake leading to lake enhanced snowfall across the U.P.
and southeast of Lake Michigan. Still, additional snowfall should=20
be modest as reflected by WPC probabilities that are just around=20
10% for an additional 2 inches of snow in these areas.



...Interior Northeast...
Days 2-3...

Shortwave energy moving into the Mid-Atlantic will cause a split
jet stream (one rotating across the Carolinas while another pivots
towards Greenland) resulting in a modestly coupled structure to=20
help deepen a surface low south of New England beginning Thursday=20
night. The guidance has trended maybe just a bit weaker with this=20
low the past 24-hrs, but ensemble low points still agree in a=20
deepening system to around 990mb tracking from norther NJ to Cape=20
Cod and then into the Gulf of Maine by Saturday morning.=20
Uncertainty in the intensity and track remains, but spread is=20
relatively minimal for this time range, and deformation developing=20
on the NW side of this low is still likely to result in an axis of=20
rain changing to heavy snow. The GFS remains the deepest solution=20
and is somewhat discounted based on recent upstream performance,=20
but all the guidance indicates that an axis of sloped 850-700mb=20
fgen will drive omega into the deepening DGZ early Friday through=20
Friday night, which will dynamically cool the column to produce an=20
axis of heavy snowfall rates. The antecedent conditions are not=20
ideal for snow accumulations due to warm temperatures and rain, but
higher elevations of the interior Northeast from Upstate NY=20
through Maine could still see impactful accumulating snow.=20
Confidence is low, and trends for this event need to be monitored=20
over the next few model cycles, but WPC probabilities are modest at
just 10-30% for 4+ inches of snow in the higher elevations.


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-KLFzRwvwe_9O_S-S3pOcQrHTcoe2AninTVhdXTk6G8_-= t5JWsp9HrgzSQesCEDSrA4t-02j4-CJfJuCIcAj1l-C19A$=20

$$

=3D =3D =3D
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FOUS11 KWBC 191857
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
257 PM EDT Wed Mar 19 2025

Valid 12Z Wed Mar 19 2025 - 12Z Sat Mar 22 2025


...Pacific and Interior Northwest...=20
Days 1-3...

A series of shortwave troughs will continue impacting the Pacific=20
Northwest and Interior mountains in-of ID/MT/WY over the next 72=20
hrs. Current WV satellite imagery shows a fairly robust upper trough=20
located off the Pacific Northwest coast with a well-defined=20
diffluent structure on the eastern flank of the trough axis. The=20
ridge that has been present downstream is beginning to feel the=20
affects of the upstream disturbance leading to some flattening of=20
the northern ridge extension and a realignment of the ridge further=20
east. This general synoptic progression will lead to increasing mid=20
and upper ascent focused over a large portion of the west coast with=20
the primary impacts focused over Northern CA up through much of=20
OR/WA state. The beneficiary of the heaviest precip core over the=20
course of D1-2 will be situated within the Cascades with snow levels=20 hovering between 3000-4000' MSL prior to the stronger height falls=20
that will occur as the shortwave progresses towards the coast with=20
the mean trough taking on a more negative tilt as it eventually=20
ejects inland later this evening. The cold frontal progression=20
associated with the disturbance will move ashore around the time of=20
the mean trough swinging inland generating a period of falling=20
heights with snow levels dropping closer to 2000-3000' MSL leading=20
to snow accumulations becoming more prevalent in the higher valleys=20
around the Olympic Peninsula and Cascades. Snowfall accumulations of=20
at least 4" remain very high probabilistically (>70%) across the=20
higher elevations of the Cascades and Olympics in WA/OR, as well as=20
the Salmon, Siskiyou and Mount Shasta regions of CA. Mid-level probs=20
between 40-60% for at least 4" are located over the Northern=20
Sierra's with the highest chance in elevations above 7500' MSL.=20

Further inland, the prospects for heavy snow continue later this=20
evening as the shortwave propagates through WA/ID with the greatest=20
forcing aligned over the Cabinet/Lewis/Bitterroot Ranges in the=20
Interior Northwest with the southern extent benefiting the Absaroka=20
Range of northwest WY. Similar probs of >70% for at least 4" of=20
snowfall exist in those terrain focused regions with the impacts=20
falling within the back-half of D1 into much of D2.=20=20


As this first trough shifts eastward, forcing will weaken across the=20 Northwest, but flow across the Pacific becomes increasingly zonal=20
due to squeezing between broad ridging well west off Baja and a=20
modest trough across the Gulf of Alaska. This zonal flow will=20
maintain onshore moisture advection to support rounds of=20
precipitation into the Northwest, with periodic vorticity lobes=20
swinging eastward (although maintaining latitude generally north of=20
OR) to enhance ascent. Snow levels D2-3 will fluctuate generally=20
between 2500ft and 4500ft, with rounds of precipitation leading to=20
periods of heavy snowfall. WPC probabilities both D2 and D3 are=20
similar in magnitude and areal extent, reaching 70% or more for 4+=20
inches from the Olympics, to the WA/OR Cascades, eastward through=20
the Salmon River/Sawtooth Ranges, and into the Northern Rockies.
2-day snowfall in some of the higher elevations could reach 2-4=20
feet, with up to 1 foot at the higher passes of the Cascades.

Weiss/Kleebauer


...Central High Plains through the Great Lakes...=20
Day 1...

...Significant winter storm is producing blizzard across portions
of the Midwest today. Key Messages are being issued for this=20
system...

This powerful winter storm has been as-advertised with wind gusts
topping 50mph that are fostering blizzard conditions, numerous=20
cases of thundersnow, and prolific snowfall rates of 1-2"/hr=20
beneath the TROWAL over northern Kansas and eastern Nebraska. As=20
the 700mb low traverses northern Missouri this afternoon, a ribbon=20
of 700mb FGEN will pivot and extend over northwest Iowa, southeast=20 Minnesota, and as far north and east as northern Wisconsin.=20
Blizzard conditions will be most common from eastern Nebraska to=20
the Mississippi River between MN/WI. An additional 4-8" of snowfall
are forecast in these areas with localized amounts topping 10"=20
possible. Snow accumulations of 1-2" and wind gusts of 50-60 mph=20
are likely in southeast Nebraska and into east-central Kansas. WPC=20
continues to issue Key Messages for the ongoing winter storm and=20
they are available for viewing below.

The storm heads for the Great Lakes tonight with heavy snow from
north-central Wisconsin to the Michigan U.P.. Similar 1-2"/hr
snowfall rates are likely within the heaviest snow bands, along
with wind gusts topping 30 mph. Lake enhanced snowfall is likely
along the eastern half of the Michigan U.P. through Wednesday night
and possibly into early Thursday morning. By 12Z Thursday, the
residual TROWAL on the backside of thew weakening storm system will
keep some light-to-moderate snow in the forecast across western
Michigan and as far south as northern Indiana, but the progressive
nature of the snow bands and warmer soil temperatures should keep
any snowfall totals to minor amounts (coating to 3"). Still, wind
gusts surpassing 30 mph would result in reduced visibilities that
make for hazardous driving conditions Thursday morning. Aside from
periods of light snow traversing the Great Lakes and Ohio Valley,
most of the disruptive snowfall will have concluded by Thursday
morning.

Mullinax


...Interior Northeast...
Days 2-3...

By Thursday afternoon, a lobe of 500mb vorticity tracking towards
the Southeast will foster strong upper-level ascent over the
Northeast coast. At the same time, a frontal boundary approaching
from the west will align itself along a more baroclinically favored
area along the Northeast coast that will give rise to a developing
wave of low pressure Thursday night near Long Island. With the
developing low positioned beneath the diffluent left-exit region=20
of a 250mb jet streak, low pressure will develop quickly and
southerly flow off the Gulf Stream will advect rich Atlantic
moisture around the northern and western flanks of the low. After
initially starting out as rain, a transition to snow will ensue
from the Adirondacks on east through the Berkshires, Green, and
White Mountains on Friday. The storm is a quick mover thanks to the
next upper trough in the active jet stream pattern making its way
towards the Great Lakes. It is worth noting that the EC-AIFS does
show the potential for the storm's deformation axis to linger
longer over central Maine and the White Mountains, which could=20
lead to some locally heavy snow totals in elevated terrain through
Friday afternoon. Any lingering snow in parts of northern Maine=20
should come to an end Friday night. WPC probabilities shows=20
moderate-to- high chances (40-70%) for snowfall totals >2" in the=20
peaks of the Catskills, Adirondacks, Berkshires, Green, and White=20
Mountains. The tallest peaks of the Whites, most notably around Mt.
Washington, could see localized amounts approach 6" through Friday afternoon.=20

Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_tUeCUIUvOwvMaOg6Kt0mVtMIBlbrkQsWTX7P7xqxAUWE= Dw9o0YHoj3fUUfj2w62dI5tqhx1cW-rM0aAkACbdxMyXnU$=20

$$

=3D =3D =3D
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FOUS11 KWBC 191913
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 PM EDT Wed Mar 19 2025

Valid 00Z Thu Mar 20 2025 - 00Z Sun Mar 23 2025


...Pacific and Interior Northwest...=20
Days 1-3...

A series of shortwave troughs will continue impacting the Pacific=20
Northwest and Interior mountains in-of ID/MT/WY over the next 72=20
hrs. Current WV satellite imagery shows a fairly robust upper
trough located off the Pacific Northwest coast with a well-defined
diffluent structure on the eastern flank of the trough axis. The=20
ridge that has been present downstream is beginning to feel the=20
affects of the upstream disturbance leading to some flattening of=20
the northern ridge extension and a realignment of the ridge further east.
This general synoptic progression will lead to increasing mid and=20
upper ascent focused over a large portion of the west coast with
the primary impacts focused over Northern CA up through much of=20
OR/WA state. The beneficiary of the heaviest precip core over the=20
course of D1-2 will be situated within the Cascades with snow levels
hovering between 3000-4000' MSL prior to the stronger height falls
that will occur as the shortwave progresses towards the coast with the
mean trough taking on a more negative tilt as it eventually ejects
inland later this evening. The cold frontal progression associated
with the disturbance will move ashore around the time of the mean=20
trough swinging inland generating a period of falling heights with=20
snow levels dropping closer to 2000-3000' MSL leading to snow=20
accumulations becoming more prevalent in the higher valleys around=20
the Olympic Peninsula and Cascades. Snowfall accumulations of at least
4" remain very high probabilistically (>70%) across the higher=20
elevations of the Cascades and Olympics in WA/OR, as well as the=20
Salmon, Siskiyou and Mount Shasta regions of CA. Mid-level probs=20
between 40-60% for at least 4" are located over the Northern=20
Sierra's with the highest chance in elevations above 7500' MSL.=20

Further inland, the prospects for heavy snow continue later this=20
evening as the shortwave propagates through WA/ID with the greatest=20
forcing aligned over the Cabinet/Lewis/Bitterroot Ranges in the=20
Interior Northwest with the southern extent benefiting the Absaroka=20
Range of northwest WY. Similar probs of >70% for at least 4" of=20
snowfall exist in those terrain focused regions with the impacts=20
falling within the back-half of D1 into much of D2.=20=20

As this first trough shifts eastward, forcing will weaken across
the Northwest, but flow across the Pacific becomes increasingly=20
zonal due to squeezing between broad ridging well west off Baja and
a modest trough across the Gulf of Alaska. This zonal flow will=20
maintain onshore moisture advection to support rounds of=20
precipitation into the Northwest, with periodic vorticity lobes=20
swinging eastward (although maintaining latitude generally north of OR)
to enhance ascent. Snow levels D2-3 will fluctuate generally=20
between 2500ft and 4500ft, with rounds of precipitation leading to=20
periods of heavy snowfall. WPC probabilities both D2 and D3 are=20
similar in magnitude and areal extent, reaching 70% or more for 4+=20
inches from the Olympics, to the WA/OR Cascades, eastward through=20
the Salmon River/Sawtooth Ranges, and into the Northern Rockies.=20
2-day snowfall in some of the higher elevations could reach 2-4=20
feet, with up to 1 foot at the higher passes of the Cascades.

Weiss/Kleebauer


...Central High Plains through the Great Lakes...=20
Day 1...

...Significant winter storm is producing blizzard across portions
of the Midwest today. Key Messages are being issued for this=20
system...

This powerful winter storm has been as-advertised with wind gusts
topping 50mph that are fostering blizzard conditions, numerous=20
cases of thundersnow, and prolific snowfall rates of 1-2"/hr=20
beneath the TROWAL over northern Kansas and eastern Nebraska. As=20
the 700mb low traverses northern Missouri this afternoon, a ribbon=20
of 700mb FGEN will pivot and extend over northwest Iowa, southeast=20 Minnesota, and as far north and east as northern Wisconsin.=20
Blizzard conditions will be most common from eastern Nebraska to=20
the Mississippi River between MN/WI. An additional 4-8" of snowfall
are forecast in these areas with localized amounts topping 10"=20
possible. Snow accumulations of 1-2" and wind gusts of 50-60 mph=20
are likely in southeast Nebraska and into east-central Kansas. WPC=20
continues to issue Key Messages for the ongoing winter storm and=20
they are available for viewing below.

The storm heads for the Great Lakes tonight with heavy snow from
north-central Wisconsin to the Michigan U.P.. Similar 1-2"/hr
snowfall rates are likely within the heaviest snow bands, along
with wind gusts topping 30 mph. Lake enhanced snowfall is likely
along the eastern half of the Michigan U.P. through Wednesday night
and possibly into early Thursday morning. By 12Z Thursday, the
residual TROWAL on the backside of thew weakening storm system will
keep some light-to-moderate snow in the forecast across western
Michigan and as far south as northern Indiana, but the progressive
nature of the snow bands and warmer soil temperatures should keep
any snowfall totals to minor amounts (coating to 3"). Still, wind
gusts surpassing 30 mph would result in reduced visibilities that
make for hazardous driving conditions Thursday morning. Aside from
periods of light snow traversing the Great Lakes and Ohio Valley,
most of the disruptive snowfall will have concluded by Thursday
morning.

Mullinax


...Interior Northeast...
Days 2-3...

By Thursday afternoon, a lobe of 500mb vorticity tracking towards
the Southeast will foster strong upper-level ascent over the
Northeast coast. At the same time, a frontal boundary approaching
from the west will align itself along a more baroclinically favored
area along the Northeast coast that will give rise to a developing
wave of low pressure Thursday night near Long Island. With the
developing low positioned beneath the diffluent left-exit region=20
of a 250mb jet streak, low pressure will develop quickly and
southerly flow off the Gulf Stream will advect rich Atlantic
moisture around the northern and western flanks of the low. After
initially starting out as rain, a transition to snow will ensue
from the Adirondacks on east through the Berkshires, Green, and
White Mountains on Friday. The storm is a quick mover thanks to the
next upper trough in the active jet stream pattern making its way
towards the Great Lakes. It is worth noting that the EC-AIFS does
show the potential for the storm's deformation axis to linger
longer over central Maine and the White Mountains, which could=20
lead to some locally heavy snow totals in elevated terrain through
Friday afternoon. Any lingering snow in parts of northern Maine=20
should come to an end Friday night. WPC probabilities shows=20
moderate-to- high chances (40-70%) for snowfall totals >2" in the=20
peaks of the Catskills, Adirondacks, Berkshires, Green, and White=20
Mountains. The tallest peaks of the Whites, most notably around Mt.
Washington, could see localized amounts approach 6" through Friday afternoon.=20

Mullinax




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_0IBMC2Ropaq74jf96TDz8KiNZS996dksNAe42ALwRotb= CnTe2Q1k3T1o6ZgPKkGBMttNVIQ2rq1E0OJeffRufLhCug$=20

$$

=3D =3D =3D
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FOUS11 KWBC 191917
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
317 PM EDT Wed Mar 19 2025

Valid 00Z Thu Mar 20 2025 - 00Z Sun Mar 23 2025


...Pacific and Interior Northwest...=20
Days 1-3...

A series of shortwave troughs will continue impacting the Pacific=20
Northwest and Interior mountains in-of ID/MT/WY over the next 72=20
hrs. Current WV satellite imagery shows a fairly robust upper
trough located off the Pacific Northwest coast with a well-defined
diffluent structure on the eastern flank of the trough axis. The=20
ridge that has been present downstream is beginning to feel the=20
affects of the upstream disturbance leading to some flattening of=20
the northern ridge extension and a realignment of the ridge further
east. This general synoptic progression will lead to increasing=20
mid and upper ascent focused over a large portion of the west coast
with the primary impacts focused over Northern CA up through much=20
of OR/WA state. The beneficiary of the heaviest precip core over=20
the course of D1-2 will be situated within the Cascades with snow
levels hovering between 3000-4000' MSL prior to the stronger=20
height falls that will occur as the shortwave progresses towards the
coast with the mean trough taking on a more negative tilt as it=20
eventually ejects inland later this evening. The cold frontal=20
progression associated with the disturbance will move ashore around
the time of the mean trough swinging inland generating a period of
falling heights with snow levels dropping closer to 2000-3000' MSL
leading to snow accumulations becoming more prevalent in the=20
higher valleys around the Olympic Peninsula and Cascades. Snowfall accumulations of at least 4" remain very high probabilistically=20

70%) across the higher elevations of the Cascades and Olympics in

WA/OR, as well as the Salmon, Siskiyou and Mount Shasta regions of
CA. Mid- level probs between 40-60% for at least 4" are located=20
over the Northern Sierra's with the highest chance in elevations=20
above 7500' MSL.=20

Further inland, the prospects for heavy snow continue later this=20
evening as the shortwave propagates through WA/ID with the greatest
forcing aligned over the Cabinet/Lewis/Bitterroot Ranges in the
Interior Northwest with the southern extent benefiting the=20
Absaroka Range of northwest WY. Similar probs of >70% for at least
4" of snowfall exist in those terrain focused regions with the=20
impacts falling within the back-half of D1 into much of D2.=20

As this first trough shifts eastward, forcing will weaken across
the Northwest, but flow across the Pacific becomes increasingly=20
zonal due to squeezing between broad ridging well west off Baja and
a modest trough across the Gulf of Alaska. This zonal flow will=20
maintain onshore moisture advection to support rounds of=20
precipitation into the Northwest, with periodic vorticity lobes=20
swinging eastward (although maintaining latitude generally north of OR)
to enhance ascent. Snow levels D2-3 will fluctuate generally=20
between 2500ft and 4500ft, with rounds of precipitation leading to=20
periods of heavy snowfall. WPC probabilities both D2 and D3 are=20
similar in magnitude and areal extent, reaching 70% or more for 4+=20
inches from the Olympics, to the WA/OR Cascades, eastward through=20
the Salmon River/Sawtooth Ranges, and into the Northern Rockies.=20
2-day snowfall in some of the higher elevations could reach 2-4=20
feet, with up to 1 foot at the higher passes of the Cascades.

Weiss/Kleebauer


...Central High Plains through the Great Lakes...=20
Day 1...

...Significant winter storm is producing blizzard across portions
of the Midwest today. Key Messages are being issued for this=20
system...

This powerful winter storm has been as-advertised with wind gusts
topping 50mph that are fostering blizzard conditions, numerous=20
cases of thundersnow, and prolific snowfall rates of 1-2"/hr=20
beneath the TROWAL over northern Kansas and eastern Nebraska. As=20
the 700mb low traverses northern Missouri this afternoon, a ribbon=20
of 700mb FGEN will pivot and extend over northwest Iowa, southeast=20 Minnesota, and as far north and east as northern Wisconsin.=20
Blizzard conditions will be most common from eastern Nebraska to=20
the Mississippi River between MN/WI. An additional 4-8" of snowfall
are forecast in these areas with localized amounts topping 10"=20
possible. Snow accumulations of 1-2" and wind gusts of 50-60 mph=20
are likely in southeast Nebraska and into east-central Kansas. WPC=20
continues to issue Key Messages for the ongoing winter storm and=20
they are available for viewing below.

The storm heads for the Great Lakes tonight with heavy snow from
north-central Wisconsin to the Michigan U.P.. Similar 1-2"/hr
snowfall rates are likely within the heaviest snow bands, along
with wind gusts topping 30 mph. Lake enhanced snowfall is likely
along the eastern half of the Michigan U.P. through Wednesday night
and possibly into early Thursday morning. By 12Z Thursday, the
residual TROWAL on the backside of thew weakening storm system will
keep some light-to-moderate snow in the forecast across western
Michigan and as far south as northern Indiana, but the progressive
nature of the snow bands and warmer soil temperatures should keep
any snowfall totals to minor amounts (coating to 3"). Still, wind
gusts surpassing 30 mph would result in reduced visibilities that
make for hazardous driving conditions Thursday morning. Aside from
periods of light snow traversing the Great Lakes and Ohio Valley,
most of the disruptive snowfall will have concluded by Thursday
morning.

Mullinax


...Interior Northeast...
Days 2-3...

By Thursday afternoon, a lobe of 500mb vorticity tracking towards
the Southeast will foster strong upper-level ascent over the
Northeast coast. At the same time, a frontal boundary approaching
from the west will align itself along a more baroclinically favored
area along the Northeast coast that will give rise to a developing
wave of low pressure Thursday night near Long Island. With the
developing low positioned beneath the diffluent left-exit region=20
of a 250mb jet streak, low pressure will develop quickly and
southerly flow off the Gulf Stream will advect rich Atlantic
moisture around the northern and western flanks of the low. After
initially starting out as rain, a transition to snow will ensue
from the Adirondacks on east through the Berkshires, Green, and
White Mountains on Friday. The storm is a quick mover thanks to the
next upper trough in the active jet stream pattern making its way
towards the Great Lakes. It is worth noting that the EC-AIFS does
show the potential for the storm's deformation axis to linger
longer over central Maine and the White Mountains, which could=20
lead to some locally heavy snow totals in elevated terrain through
Friday afternoon. Any lingering snow in parts of northern Maine=20
should come to an end Friday night. WPC probabilities shows=20
moderate-to- high chances (40-70%) for snowfall totals >2" in the=20
peaks of the Catskills, Adirondacks, Berkshires, Green, and White=20
Mountains. The tallest peaks of the Whites, most notably around Mt.
Washington, could see localized amounts approach 6" through Friday afternoon.=20

Mullinax





...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4RVlA6qYizTHi3nJ8dq8lnm-w6Igfzgqwy_i_-0FaoL8-= gu5wtaNVq7vc29oqv1khbAzlljoFgcq1NpZg6rlft0iijM$=20

$$

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FOUS11 KWBC 200657
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
257 AM EDT Thu Mar 20 2025

Valid 12Z Thu Mar 20 2025 - 12Z Sun Mar 23 2025


...Pacific and Interior Northwest...
Days 1-3...

Progressive pattern out of the North Pacific will maintain an
unsettled period for the Pacific Northwest into the northern
Rockies. Initial front has moved past the Cascades as of early this
morning and will continue eastward across the Divide later today.
Next system will be forced by a modestly strong incoming jet
(130kts) tonight with westerly flow focusing into the Cascades,
followed by height falls from the northwest (southwestern Canada)
late Fri into early Sat. That system will dig much farther west out
ahead of incoming ridging into WA/OR, finally setting up some
drier periods on Saturday.

Low snow levels in the Cascades of around 2000-3000ft this morning
will rise through the day and overnight to around 3500-4500ft
(north to south) coincident with the next surge of moisture. Snow
levels will fall again late Fri into early Sat as the Canadian
height falls push into WA then into northern ID, down to around
1500-3000ft from north to south as the precipitation gradually
ends.

Three-day totals of at least 12 inches of snow are likely (>70%
chance) above 3500-4500ft or so from north to south along the
Cascades with some higher elevations receiving more than 2-3 ft.
Significant snow is also possible at many passes given the lower
snow levels. There is a >60% chance of at least 8 inches of snow
above 2500-3000ft or so. Farther east, significant snow in excess
of 12 inches is likely (>70% chance) across the Blue Mountains, central/northern Idaho, northwestern Montana, and into western
Wyoming. The southern extent of the snow will clip northern Utah
and the CO Rockies as well with light/modest amounts near 6 inches
(UT) and nearing 12 inches into CO, especially above 10,000ft.


...Upper Midwest...
Day 3...

The system exiting the High Plains late Sat will continue to dig
into the northern Plains overnight into early Sun. Low pressure
will coalesce over eastern SD Saturday evening and lift into MN
thereafter, bringing WAA-driven snow to northeastern MN, northern
WI, and the western U.P. of Michigan. Amounts will generally be
light through 12Z Sun, perhaps 1-2.5", and the probability of at
least 4 inches is less than 10%. Additional accumulation is likely
beyond this forecast period.


...Great Lakes/Appalachians/Northeast...
Days 1-2...

Exiting system responsible for blizzard conditions over the
central Plains will move into Canada with snow ending over Michigan
this afternoon. Additional snow accumulations will be light (an
inch or so). To the south, colder air will change rain to snow over
the central/southern Appalachians with upslope-driven
accumulations persisting into early Friday. Several inches of snow
are possible at the higher elevations above 3500ft, but WPC
probabilities for at least 4 inches are low (10-40%) along the
TN/NC border. By day 2, low pressure over Cape Cod early Fri will
lift into Nova Scotia with backside snow over northern New England,
but mostly at higher elevations above 2500ft and amounts will
generally be light (<3 inches). The highest peaks of the White
mountains may see more than 4 inches (probabilities generally
10-50%).


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso

$$

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FOUS11 KWBC 201820
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
220 PM EDT Thu Mar 20 2025

Valid 12Z Thu Mar 20 2025 - 12Z Sun Mar 23 2025


...Pacific/Interior Northwest to Central Rockies...
Days 1-3...

An active Pacific jet stream pattern will keep periods of mountain
snow in the forecast over the next few days. This is largely due to
a persistent troughing pattern over the Gulf of Alaska that
continues to reload this active pattern with storm systems racing
across the North Pacific that eventually reach the northwestern
U.S.. The Washington Cascades and Olympics above 3,500ft will be
the epicenter for the heaviest snowfall where they are more ideally
placed with the best surge of Pacific moisture, favorable upslope
enhancement, and their placement beneath a strong 130kt 250mb jet
streak aloft. The Oregon Cascades will also be on the receiving
end of accumulating snow, but with higher snow levels farther
south, elevations above 4,500ft will be most favored for heavy
snowfall through Friday. Following a brief break in the active
pattern Saturday morning, an approaching warm front from the next
storm system in line over the Gulf of Alaska will cause noticeably
higher snow levels over the Olympics and Washington Cascades
Saturday night and Sunday. Snow accumulations will likely range
between 1-3 feet in these ranges with some of the tallest peaks of
the Olympics and Washington Cascades topping 4 feet of snowfall
through Sunday.

This same plume of Pacific moisture and the aforementioned jet
streak aloft will advance inland across mountain ranges that
include the Blue, Sawtooth, Bitterroots, Lewis Range, Absaroka, and
Tetons tonight, Friday, and into Saturday morning. Elevations above
5,000ft in the Blue, Sawtooth, Bitterroots, and Lewis Range are
favored to receive as much as 1-2 feet of snow through Saturday
morning. Farther south, elevations above 7,000ft are favored in the
Absaroka and Tetons, as well as other neighboring ranges that
include the Big Snowy, Little Belt, Big Horns, and Bear River
ranges. Snowfall totals of 8-12" will be most common in these
mountain ranges, with the Tetons having better odds of seeing some
snowfall totals topping 2 feet. Lastly, some of this Pacific
moisture will bleed far enough south to reach the Colorado
Rockies and southern Wyoming Rockies Friday night and into
Saturday. Elevations above 9,000ft will be most likely to see
snowfall accumulations >6" with the tallest peaks of the Colorado
Rockies receiving over a foot before the snow tapers off Saturday
night.


...Northern Appalachians & Northeast...
Day 1...

This afternoon, a lobe of 500mb vorticity tracking towards the
Southeast will foster increasing upper-level ascent over the
Northeast coast. At the same time, a frontal boundary approaching
from the west will align itself along a more baroclinically favored
area along the Northeast coast that will give rise to a developing
wave of low pressure Thursday night near Long Island. With the
developing low positioned beneath the diffluent left-exit region of
a 250mb jet streak, low pressure will organize quickly and
southerly flow off the Gulf Stream will advect rich Atlantic
moisture around the northern and western flanks of the low. After
initially starting out as rain, a transition to snow will ensue
from the Catskills and Adirondacks on east through the Berkshires,
Green, and White Mountains on Friday. The storm is a quick mover
thanks to the next upper trough within the active jet stream
pattern over the Great Lakes. Any lingering snow in parts of
northern Maine should conclude Friday night. WPC probabilities
depict low-to-moderate chances (20-50%) for snowfall >2" in the
higher elevations of the Green and White Mountains. The tallest
peaks, including Mount Washington, could see some snowfall totals

4" through Friday afternoon.

...Upper Midwest & Great Lakes...
Day 3...

A steepening upper-level trough over the Northern Plains will
provide modest ascent aloft and strengthen low pressure over the
Dakotas. Out ahead of this upper-level trough is increasing
850-700mb WAA that gives rise to low-mid level FGEN over the Upper
Midwest and into the northern Great Lakes Sunday morning. As Sunday
unfolds, a more organized 850mb low is likely to form over
northwest Wisconsin with a much of the atmospheric column well
saturated over northern Minnesota, northern Wisconsin, and the
Michigan U.P.. Based on the track of the 850mb low and the pivoting
deformation axis on the storm's northwest flank, it is northern
Minnesota that presently features the best odds (50-70% moderate
chances) for >4" of snowfall. The Minnesota Arrowhead, with the
added benefit of easterly flow that provides additional lake-
enhancement, has low-to-moderate chances (30-50%) for snowfall
totals >8". Northern Wisconsin and the Michigan U.P. may mix with
rain or stay a wintry mix longer, which combined with generally
lower SLRs may keep snowfall totals a bit more capped compared to
northern Minnesota. However, it will be the CAA on the back side of
the storm and across Lake Superior Sunday night when these areas
see their best chances for measurable snow.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Mullinax




$$

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FOUS11 KWBC 210713
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 AM EDT Fri Mar 21 2025

Valid 12Z Fri Mar 21 2025 - 12Z Mon Mar 24 2025

...Northeast...
Day 1...

Low pressure near Cape Cod this morning will move through the Gulf
of Maine and into Nova Scotia this afternoon, helping to draw in
colder air on the back side of the exiting precipitation shield.
Rain will change to snow from west to east with some light
accumulation over most areas, but the higher terrain of the White
Mountains may see a few inches. There, WPC probabilities of at
least 4 inches of snow are 10-40%. In addition, there is a
possibility of some modest snow amounts over eastern Maine outside
the higher terrain as the low deepens in the Gulf of Maine this
afternoon. Snow will end by midnight over eastern Maine.


...Pacific/Interior Northwest to Central Rockies...
Days 1-3...

Onshore flow continues in the PacNW with a due east jet off the
northeast Pacific aimed into WA/OR. Current jet max along the
Columbia River will continue eastward this morning, but another
will be right on its heels which will promote a moisture plume into
the OR/WA Cascades this afternoon/evening. Snow levels around
3000-5000 ft will still impact the passes today. Snow will lessen
into day 2 (Sat) as height falls dig into the northern Rockies,
which will continue eastward into day 3. By then, upper ridging
will move into the PacNW with a system into the southern AK
Panhandle, allowing snow levels to rise much higher to above 6000ft
Sunday afternoon into early Monday. Three-day totals of at least
12 inches of snow are likely (>70% chance) above 4000ft or so but
primarily on day 1.

West-to-east jet will continue to advance the moisture plume into
the northern Rockies, favoring the Blue, Sawtooth, Bitterroots,
Lewis Range, Absaroka, and Tetons through Saturday morning.
Elevations above 5,000ft in the Blue, Sawtooth, Bitterroots, and
Lewis Range have at least a 70% chance of receiving at least 12
inches of snow through tomorrow morning. Probabilities are a little
lower to the south (Absarokas and Tetons), but many areas will
still see at least 8 inches of snow (>70% chance above 7000ft or
so).

On the south side of the jet and moisture plume, northern UT into
the CO Rockies will likely see at least 8 inches of snow above
9000ft or so (>70% chance), starting later tonight into Saturday
then ending Saturday night.


...Upper Midwest & Great Lakes...
Days 2-3...

Height falls associated with a shortwave exiting Montana Saturday
evening will continue to deepen into MN by Sunday morning in
response to the amplification of the upper pattern upstream. Low
pressure over SD will track eastward into MN with broad WAA ahead
of it over the Upper Midwest. Surface temperatures will be fairly
marginal with some areas starting as rain before mixing with and
changing to snow as the low strengthens on Sunday. As it does,
colder air will wrap around its northwest side over northern MN
moderate snow likely for a time Sunday afternoon. Models have been
wavering on the strength of the upper and sfc features (and thus
the QPF and ultimately the snow), but the eastern Arrowhead (Lake
Shore) may be in a favorable spot for heavier snow due to easterly
flow off Lake Superior. SLRs may start on the lower end below 10:1
then rise as colder air works its way in, but will also combat
afternoon solar insolation where rates are not as heavy. All told,
WPC probabilities for at least 4 inches of snow days 2-3 are at
least 10 percent generally north of I-94, with increasing
probabilities northward and northeastward into the Arrowhead. This
also includes northern WI into the U.P. of Michigan from a
combination of front-end WAA snow and wraparound snow after the low
passes through. Despite likely closing off up to 500mb, the system
will remain progressive but will not clear the area until after
12Z Mon.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso


$$

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FOUS11 KWBC 211823
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
223 PM EDT Fri Mar 21 2025

Valid 00Z Sat Mar 22 2025 - 00Z Tue Mar 25 2025


...Pacific/Interior Northwest to Central Rockies...
Days 1-3...

Onshore flow continues in the PacNW through early next week with
two primary waves of moisture traversing the region with upper
ridging expected to cut off Pacific moisture tap by late D3. For D1
(through 00z Sun), snow levels will drop below 3000 ft across the
Northwest, but also as precipitation quickly dries out and the
focus of upper divergence shifts into the Northern Rockies through
the beginning of D2. Here, snow levels around will start out around
4000-5000 ft but also fall below 3000 ft due to approaching height
falls. By then, upper ridging will move into the PacNW with a
system into the southern AK Panhandle, allowing snow levels to rise
much higher to above 6000ft Sunday afternoon into early Monday as
the next moisture plume clips the Northwest and northern Great
Basin. Totals of at least 12 inches of snow are likely (>70%
chance) above 4000ft or so but primarily on day 1 throughout the
Cascades, Sawtooths, northern ID ranges and western MT ranges, as
well as the Absarokas and Wind River Range of WY. By D2-D3 high
probabilities for at least 6 inches of snow remains confined to the
northern WA Cascades and far northern ID ranges.

On the south side of the jet and moisture plume, northern UT into
the CO Rockies will likely see at least 8 inches of snow above
9000ft or so (>70% chance), starting later tonight into Saturday
then ending Saturday night.


...Upper Midwest & Great Lakes...
Days 2-3...

An upper-level trough exiting the Northern Rockies Saturday
afternoon will track over the Northern Plains and strengthen
Saturday night, providing modest vertical ascent aloft from the
Dakotas to Minnesota. The favorable synoptic-scale source of lift
aloft will provide a favorable environment for a deepening area of
low pressure over South Dakota that will, in turn, generate
increasing 850-700mb WAA in advance of the storm. By Saturday
night, a consolidating 850mb low over the Red River of the North
will wrap modest low-mid level moisture around the northern and
western flanks of the low. As precipitation breaks out from central
North Dakota to as far east as northwest Wisconsin Saturday night,
some precipitation may start out initially as an icy wintry mix.
But as the deformation axis becomes more pronounced, dynamic
cooling aloft will allow for snow to become the primary
precipitation type through Sunday morning. Gusty winds on the
backside of the storm will prompt blowing and rifting snow to ensue
across the Dakota and into northwest Minnesota through Sunday
morning.

The region most likely to witness the heaviest snowfall for this
event is northeast Minnesota or, more specifically, the Minnesota
Arrowhead. The deformation axis is expected to pivot over the
region on Sunday with sufficient vertical velocities throughout
much of the atmospheric column to support heavy snowfall rates

1"/hr, while the Arrowhead, contending with easterlies off of Lake

Superior, provides a lake-enhanced fetch of moisture into the
region Sunday afternoon and into Sunday night. Meanwhile, farther
east, the Michigan U.P., especially the Keweenaw Peninsula on east
to the Hurons and just west of Sault Ste. Marie, the strong WAA
north of the warm front will be sufficient enough to produce a
burst of heavy snow Sunday afternoon and into the evening hours.
This area is a little more unclear on the SLR's and snowfall rates
as there is some evidence of a potential dry slot within the
700-300mb layer working its way in, but there will still be snow to
contend with on the back side of the storm Sunday night. The storm
will work its way over Michigan's U.P. Sunday night with CAA on
the western flank kicking up lake- enhanced snow showers in its
wake across northern Wisconsin and much of the Michigan U.P.. Snow
should finally taper off by Monday afternoon as winds diminish and
lingering lake effect snow showers over the eastern Michigan U.P.
and the tip of Michigan's Mitten wind down.

WPC probabilities show moderate-to-high chances (50-70%) for
snowfall totals >8" along the Minnesota Arrowhead, with similar
probabilities for >6" in northeast Minnesota and in the Michigan
U.P.. Note that there are moderate chances (40-60%) for >4" of
snow as far west as northwest Minnesota and as far south as
northern Wisconsin. Expect hazardous travel conditions in these
areas on Sunday with poor travel conditions lingering over Michigan
U.P.


...Northeast...
Day 3...

As the Upper Midwest and Great Lakes system slides east by D3, a
brief period of moderate snowfall is possible across northern New
England and elevated regions of the Interior Northeast. Mid-level
WAA will be the driving force behind the precipitation pushing
eastward on Monday, with a triple-point surface low developing near
southern New England also providing for potential weak CAD across
parts of ME and NH. WPC probabilities for at least 4 inches of snow
are currently low (10-30%) from the Adirondacks to Green/White Mts
of New England, with slightly higher probabilities in the highest
elevations.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Snell/Mullinax





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FOUS11 KWBC 220720
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
320 AM EDT Sat Mar 22 2025

Valid 12Z Sat Mar 22 2025 - 12Z Tue Mar 25 2025


...Pacific/Interior Northwest to Central Rockies...
Days 1-3...

Shortwave over eastern WA this morning will continue east-
southeastward today across the Rockies. Light snow via onshore flow
will continue over the Cascades while light to modest snows are
expected for northwestern MT/northern ID into WY and northern UT/CO
before ending from NW to SE this afternoon and evening. WPC
probabilities for at least 6 inches of additional snow are >50%
above 5000ft (north) to 8000-10,000ft (south). The next system into
the PacNW D2 will be much milder due to increasing mid-level
ridging with snow levels rising from 4000-5000ft late tonight to
over 8000ft Sunday evening. Any initial snow over the passes will
change over to rain with significant snow at the highest peaks. By
D3, upper ridging will remain in control with light snow for the
high elevations as snow levels settle to between 7000-9000ft.


...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

The upper-level trough exiting the Northern Rockies/western High
Plains this afternoon will push into the Upper Midwest tonight into
early Sunday. Multiple vort maxima will lie beneath the poleward
exit region of the modest jet over MO, providing broad vertical
ascent aloft from the Dakotas to Minnesota. Surface low pressure
over South Dakota will deepen and move into MN, with WAA driving
snow (and some mixed precip/light icing) to its northeast (MN into
WI). On Sunday, sharpening upper pattern will and a slight negative
tilt aloft will help increase snow on the NW side of the low in a
modest but still progressive deformation axis. Wraparound snow amid
dynamic cooling and low-level convergence/enhancement on the west
side of Lake Superior will help to maximize snowfall there, from
near/northeast of Duluth northeastward to Grande Portage. A modest
snowfall is expected elsewhere from central MN across northern WI
and into the U.P. of Michigan near and to the north of the track of
the sfc low pressure (and north of any subsequent secondary low
pressure development out of the Corn Belt).

By late Sunday into early Monday, frontal boundary will continue
to arc eastward, pushing precipitation across the Appalachians into northeastern PA and into NYS, where cold surface temperatures may
support some snow and light icing as WAA invades from the
southwest. Limited cold air will confine most snowfall to areas
north of I-90, but with a sfc low track remaining in Canada, many
areas may change over to rain except for northern NH into
northwestern Maine. Back to the west, colder air across the Great
Lakes will spur some lake-effect snow into the U.P. and western
Lower Michigan as 850 temps briefly drop to -10C or so. The entire
system will wind down late Monday with only some lingering lake-
effect snow by early Tuesday.

WPC probabilities for at least 4 inches of snow through the period
are highest (>70%) over northeastern MN and especially over the
eastern Arrowhead (where probabilities for at least 8 inches of
snow are >50%), northern WI and the entire U.P. of Michigan,
northwestern Lower MI, and into the Tug Hill Plateau.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso

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FOUS11 KWBC 221812
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
212 PM EDT Sat Mar 22 2025

Valid 00Z Sun Mar 23 2025 - 00Z Wed Mar 26 2025


...Pacific/Interior Northwest to Central Rockies...
Days 1-2...

Shortwave crossing MT/WY this evening will continue areas of high
elevation snow showers and favorable upslope conditions through
early Sunday morning in the Northern/Central Rockies until upper
ridging quickly builds into the West, while directing the next
Atmospheric River event into the Pacific Northwest through D2
(Monday). IVT is forecast to peak on Sunday evening and reach above
the 99th climatological percentile per the 00z NAEFS, with the
maximum corridor of 600-700 kg/m*s IVT directed at WA and the
northern Cascades as moisture also bleeds into northern ID/MT. As
expected, snow levels will quickly rise above 6000 ft and pass
level across the Northwest by D2 after starting out around 3000 ft
for the start of the event. High (>70%) WPC probabilities for at
least 8 inches of snow during the entire forecast period exist
across the WA Cascades and far northern ID/northwest MT ranges,
mainly above 5000-6000 ft.

Snell



...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

An upper-level trough exiting the Northern Rockies this afternoon
will track over Northern Plains and strengthen tonight, providing
modest vertical ascent aloft from the Dakotas to Minnesota. The
favorable synoptic-scale source of lift aloft will provide a
supportive environment for a deepening area of low pressure over
South Dakota. Increasing 850-700mb WAA and moisture advection in
advance of the storm's deepening 850mb will give rise to a
consolidated deformation axis late Sunday night over northern
Minnesota. Precipitation may briefly start out as an icy wintry mix
in parts of the Dakotas and northern Minnesota tonight and early
Sunday morning, but as strong vertical velocities manifest
themselves within the deformation zone, snow will become the
primary precipitation type across northern Minnesota. The heaviest
snowfall is likely to ensue along the Minnesota Arrowhead and
across the northern tier of Michigan's U.P.. Snowfall rates topping
1"/hr are most likely to unfold in these areas Sunday and into
Sunday night. Some of the latest guidance has come a bit farther
south on the storm track (closer to the EC-AIFS/UKMET/CMC solutions
but not completely in their camp), which has led to an increase in
snow over northern Wisconsin. CAA on the backside of the storm
system will keep lake-enhanced snowfall ongoing across northern
Wisconsin and the Michigan U.P. on east to the northern most
portion of Michigan's Mitten through Monday before concluding
Monday evening. WPC probabilities show moderate-to-high chances
(50-70%) for snowfall totals >8" in parts of the Minnesota
Arrowhead and the Michigan U.P.. There are also similar moderate-
to-high chances (50-70%) for snowfall >4" in northern Minnesota,
northern Wisconsin, and the northwestern Michigan Peninsula.

By Sunday night, the storm system's warm front will push into the
Northeast with low-level WAA and 290K isentropic ascent aloft. The
air-mass is marginally cold enough to support snow in the northern
Appalachians Sunday night, with the potential for a burst of heavy
snow in the White Mountains and much of interior Maine on Monday.
Guidance has remained split on whether a coastal low forms along
the Maine coastline, but should it form, locally heavy snowfall
totals (>6") could occur. At the moment, WPC probabilities show
low-to-moderate chances (30-50%) for snowfall totals >4" from the
White Mountains to northern Maine Sunday night and into Monday.
Westerlies over Lake Ontario may kick up a lake effect snow band
that becomes located over the Tug Hill on Tuesday. WPC
probabilities show moderate chances (40-60%) for snowfall totals

4" in the Tug Hill on Tuesday.

For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Mullinax




$$

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FOUS11 KWBC 230705
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
305 AM EDT Sun Mar 23 2025

Valid 12Z Sun Mar 23 2025 - 12Z Wed Mar 26 2025


...Pacific/Interior Northwest to Central Rockies...
Days 1-2...

Upper ridging just off the Pac NW coast this morning will continue
to build into the region, pushing snow levels that are around
3500-5000ft at 12Z to well over 6000-8000ft by 00Z over the
Cascades. Farther east over northern ID into MT, snow levels will
still rise today confining much of the accumulating snow to levels
above 5000ft (>6 inch amounts). Into Monday (D2), moisture will
persist into WA and the northern Rockies but with very high snow
levels above 8000ft. Heights will build into Tuesday, essentially
ending any precipitation in the Northwest altogether.

...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

Mid-level shortwave over the Dakotas this morning will move
eastward today into the Upper Midwest as it surface low pressure
center follows suit across central MN into northern WI. By this
evening, the triple point low will start to become the dominant
center (near Green Bay) and move eastward across northern Lower
Michigan and then into southern Ontario as the cold front bows out
through the Northeast early Monday. With an amplifying upper
pattern, this will slow the progression of the system out of the
region, allowing cyclonic flow to persist over the Great Lakes into
the Northeast into Tuesday, favoring lake-effect snow with 850
temperatures < -10C. Though fairly progressive to start, the system
will still yield significant snow for portions of the eastern
Arrowhead and into the U.P. of Michigan via wraparound/convergent
snow in the deformation band on the NW side of the sfc low, WAA-
driven snow ahead of the sfc low (northern WI into the U.P.), or
both over northern/northwester Lower Michigan via the triple point
low. Over the Northeast, south of the eventual track of the surface
low, WAA will drive much of the precipitation on Monday with some
icing at the onset in colder areas turning over to rain and snow
farther north toward the Canadian border where it will take longer
to warm up toward freezing -- and some areas will not as a result
of a new triple point low over the Gulf of Maine, acting to hold
colder air in over northern NH and northwestern ME. Finally, some
lake effect snow will affect the Tug Hill Plateau Tuesday with
lighter upslope snow to the south into the central Appalachians.
Snowfall will finally wind down by early Wednesday (end of this
forecast period).

For the three-day period, WPC probabilities of at least 4 inches
of snow are highest (>50%) over northeastern MN, northern WI, the
U.P. of Michigan, northern/northwestern Lower MI, and in the Tug
Hill Plateau region including some of the Adirondacks. Some areas
of the White Mountains may see in excess of 4 inches of snow as
well. The heaviest snow may fall over far northeastern MN where
local convergence off Lake Superior will add to the snow efficiency
(in addition to higher SLRs in the colder air). There, WPC
probabilities of at least 8 inches of snow are > 70%.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso


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FOUS11 KWBC 231806
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
206 PM EDT Sun Mar 23 2025

Valid 12Z Sun Mar 23 2025 - 12Z Wed Mar 26 2025


...Pacific/Interior Northwest to Northern Rockies...
Day 1...

Ongoing Atmospheric River moving onshore western Washington this
afternoon will continue to spread moisture across the Northwest,
far northern Great Basin and into the northern Rockies through
Monday. Snow levels across the WA Cascades will start out this
evening above 6000 ft and remain between 6000 to 8000 ft throughout
the remainder of the event (above major mountain passes). Snow
levels across the Great Basin and northern Rockies will also
continue to rise above 7000 ft during the D1 period as residual
moisture on the southern edge of the AR reaches into the
western/northern WY ranges. WPC probabilities for at least 6 inches
of snow are medium (30-50%) and are confined to the northern WA
Cascades and highest ranges of MT and WY (above 7000 to 8000 ft).
Precipitation cuts off by D2 as anomalous upper ridging builds
across the western U.S. as the next system approaching the region
cuts off over the northeast Pacific.

Snell


...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

The winter storm has kicked off in the Upper Midwest with the storm strengthening this afternoon as it tracks towards the Upper Great
Lakes tonight. The deformation zone is pivoting beneath the TROWAL
over northern Minnesota. There is also heavy snow unfolding in
northern Wisconsin where strong 850-700mb FGEN and WAA aloft is
paired with dynamic cooling aloft to produce >1"/hr snowfall rates
in some cases. By this evening, the storm will begin its weakening
phase with most snow coming via WAA over the eastern Michigan U.P.
and northern most portion of Michigan's Mitten. Farther west, CAA
on the back side of the low will generate lake-enhanced snowfall
from the Minnesota Arrowhead on east to northern Wisconsin and as
far east as the Keweenaw Peninsula of Michigan's U.P.. Look for
periods of snow lake-effect snow to linger through Monday across
the Michigan U.P. and northern lower Michigan. WPC probabilities
show moderate-to-high chances (50-70%) for additional snowfall
amounts >4" for the areas referenced above, with some localized
areas seeing additional snowfall amounts up to 8", especially in
the Michigan U.P..

Farther east, the storm's warm front will advance east into the
Northeast tonight with low-level WAA and 290K isentropic ascent
aloft. The antecedent air-mass is initially cold enough to support
snow in the as far south as the Poconos and Catskills, but the best
chance for accumulating snowfall will take place over the
Adirondacks, Green, and White Mountains tonight and into Monday
morning. Some minor ice accumulations are possible in parts of the
northern Mid-Atlantic tonight and into early Monday morning. A
wave of low pressure will attempt to develop near Downeast Maine
Monday and could wrap some Atlantic moisture around its northern
and western flank. This would allow for some minor snow
accumulations to unfold from central to eastern Maine through
Monday evening. WPC probabilities do highlight low- to- moderate
chances (20-50%) for some targeted areas of >4" snowfall totals in
parts of the Adirondacks, Green Mountains, White Mountains, and
east-central Maine. As the storm departs Monday night, some lake
effect streamers off Lakes Erie and Ontario should lead to minor
snowfall totals in northwest Pennsylvania, western NY, and northern
New York. The area most likely to see measurable snowfall is the
Tug Hill where the primary band off Lake Ontario and the Tug Hill's
elevation provide a more favorable setup for accumulating
snowfall. WPC probabilities shows low chances (10-30%) for 48-hour
snowfall totals >8" in the Tug Hill, showing there is the potential
for some localized amounts that could be on the heavier side
through Tuesday. Some minor snow accumulations are possible as far
south as the Central Appalachians but totals most totals staying in
the coating-3" range.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Mullinax





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FOUS11 KWBC 240653
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 AM EDT Mon Mar 24 2025

Valid 12Z Mon Mar 24 2025 - 12Z Thu Mar 27 2025


...Pacific/Interior Northwest to Northern Rockies...
Day 1...

Lingering moisture over the Northwest and northern Rockies atop
the upper ridge will slowly dissipate today, with very high snow
levels around 8000ft.


...West Coast...
Day 3...

Next Pacific system will start to bring in some moisture to
western WA/OR and NorCal. Snow levels will still be quite high --
10,000ft on Wednesday -- but dropping to around 5000ft by 12Z
Thursday, which still start to bring snow to some passes.


...Great Lakes/Northeast...
Days 1-2...

Mature winter storm over the Great Lakes this morning will
continue eastward through southern Ontario as a new triple point
low develops near the NY Bight this afternoon. Cold air at the
surface this morning will be slow to erode over the higher
elevations (Catskills, Berkshires/Greens, Worcester Hills, and
parts of Maine) as WAA-driven precip arrives this morning, favoring
some freezing rain amid a snow-to-rain changeover for areas south
of I-90. As the coastal low deepens, it will tend to hold in colder
air over northern New England and much of Maine, with marginal
temperatures toward the coast. This will make for a heavy/wet snow
of a few inches in NH to several inches over interior Maine as the
low pressure moves through the Gulf of Maine this evening. Snow
will end overnight associated with the area of low pressure, but
the large cyclonic circulation over the Great Lakes will sustain
some lake-effect snow today into Tuesday, especially over the
northern U.P. of Michigan, northwestern Lower Michigan, and into
the Tug Hill Plateau. WPC probabilities for at least 4 inches of
snow are >50% over the aforementioned lake-favored areas as well as
over northern NH (White Mountains) into Maine north of I-95 until
Bangor, then along 95 to the Canadian border.


...New England...
Day 3...

Vort max moving through the base of the upper trough over the
Great Lakes on Tuesday will move off the Mid-Atlantic coast and
turn the corner northeastward early Wednesday. Models have wavered
on how close to bring this system to eastern New England, but at
least some light precipitation is likely to affect at least areas
east of I-91. With marginal to somewhat sufficient cold air in
place, some light snow is likely for eastern New England before the
system races northeastward into Atlantic Canada Wednesday evening.
Some of the models were much more vigorous than others, but the
probability of at least 4 inches is still low (10-30%) from
northern NH into Maine.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso


$$

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FOUS11 KWBC 241848
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
248 PM EDT Mon Mar 24 2025

Valid 00Z Tue Mar 25 2025 - 00Z Fri Mar 28 2025



...Great Lakes/Northeast...
Days 1-3...

An active later-season winter pattern will setup across the Great
Lakes and Northeast as troughing amplifies over the east and lobes
of vorticity drop southward out of Canada. This will produce
periodic cool and wintry weather across the region.

The period begins active as a wave of low pressure driven by a
strung out vorticity impulse lifts along the coast of Maine. This
system will move quickly into the Canadian Maritimes by 12Z
Tuesday, but a period of moderate to heavy snow is likely to
continue across Maine before this storm pulls away, and WPC
probabilities indicate a medium chance (30-50%) for an additional
2-4" in far northern Maine.

Behind this wave, cyclonic flow will intensify across the Great
Lakes as the resultant trough amplifies down towards the Mid-
Atlantic states. This will drive increasing CAA over the Great
Lakes, with the core of the coldest 850mb temperatures, falling to
as low as -15 to -18 Celsius, moving over the lakes Tuesday night
into Wednesday morning. This cold core combined with unidirectional
flow across the slowly warming lake waters will result in late-
season lake effect snow (LES), especially in the favored WNW snow
belt regions D1 and D2, with upslope snow into Northern New England
also likely D2. *WPC probabilities for this LES are moderate (50%)
for 4+ inches D1 in the eastern U.P., the far northwest L.P., and
across the Tug Hill Plateau. Probabilities for an additional 4+
inches D2 drop to just 10-30% and focus across the Tug Hill
Plateau.

Finally, an interesting development occurs late D2 into D3 as a
potent shortwave tracks over the Mid-Atlantic states, sharpening
the mid-level trough even more, and then lifts northeast off the
New England Coast. This occurs in tandem with a strengthening jet
streak lifting off into Canada leaving the favorable RRQ east of
New England, into which the amplifying trough will deposit the most
robust height falls. The guidance has trended less amplified with
this evolution, but it still supports a surface low developing and strengthening into Wednesday morning. Depending on the exact track
of this low, some moderate snowfall may spread across New England
once again Wednesday night into Thursday, but at this time a more
suppressed solution is more likely, resulting in WPC probabilities
that are 10-30% for 4+ inches of snow from the Northeast Kingdom of
VT, across the White Mountains, and into much of northern and
central Maine.


...West Coast...
Day 3...

Impressive trough amplifying west of British Columbia will deepen
into a closed low as it pivots towards the Pacific Northwest coast
Thursday. The core of this low is progged to become quite
amplified, falling below the 0.5 percentile with respect to 700mb
heights (1st percentile with respect to 500mb heights). This is
indicative of a very strong low which will move eastward, but then
get pulled north within the amplified flow, reaching just off
Vancouver Island by the end of the forecast period.

This evolution will have a two-pronged effect on the West Coast.
First, confluent downstream flow will overlap with an intensifying
Pacific jet streak rotating around the base of this trough to
advect deeper moisture onshore, with both GEFS and ECENS IVT
probabilities reaching above 60% for a narrow corridor of 500
kg/m/s. This moisture will be acted upon by mid-level divergence
and upper diffluence to wring out this moisture through increasing
lift to result in widespread precipitation moving from central CA
northward through the Cascades and Olympics. Additionally, W/SW
mid-level flow will efficiently upslope into the terrain, leading
to locally more impressive lift and heavy precipitation across the
terrain.

Snow levels will initially be quite high, 7000-8000 ft, but will
drop steadily to as low as 3000 ft by the end of the forecast
period behind a cold front working to the east. With this event, a
lot of the precipitation occurs behind the cold front, but still
most of the heavy snow should remain above pass levels. WPC
probabilities are high (>70%) for 6+ inches from the Northern
Sierra, through the Shasta/Trinity/Siskiyou region, along the spine
of the Cascades, and into the higher Olympics. Locally 12+ inches
of snow is possible in the highest terrain,


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Weiss



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FOUS11 KWBC 250644
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
244 AM EDT Tue Mar 25 2025

Valid 12Z Tue Mar 25 2025 - 12Z Fri Mar 28 2025


...Great Lakes/Northeast...
Days 1-2...

In the wake of the departing system just leaving the Northeast
this morning, broad cyclonic flow centered south of Hudson Bay will
maintain a cold flow of air over the slowly warming Great Lakes,
promoting some lake effect snow for the next couple of days. The
most favored areas will be across portions of the eastern U.P. of
Michigan in any more organized/persistent bands, east of Lake
Ontario along the long fetch of the lake (Tug Hill Plateau), and
into the Green Mountains via upslope enhancement. Two-day totals
will be generally light (1-3") but the aforementioned areas show
the highest probabilities of seeing at least 4 inches of snow
(10-70%, with the highest probabilities of at least 6 inches over
the Tug Hill).


...West Coast...
Days 2-3...

An anomalously deep and impressively wound-up system in the
northeast Pacific late Tue into Wed will start to field moisture
into the West Coast starting Wednesday afternoon. Strong ridging
over the West means snow levels will start very high (>8000ft)
during the middle of day 2 (00Z Thu) but will trend lower into day
3. Then (12Z Thu - 12Z Fri) the upper/sfc low will curl
northeastward to northward to a position just offshore Vancouver
Island, allowing its long occluded front to push inland. This will
take snow levels down to about 5000ft by 12Z Fri over the Cascades
into the far northern NorCal ranges and about 6000-7000ft over the
northern Sierra as a 130kt jet streak moves through. QPF amounts
will be light to modest inland with heavier amounts along the coast
and into the Olympics in WA. Rain will change to snow with low
SLRs and will come in a couple waves -- initially with the front in
the higher PW plume and then with the upper trough. Snow will
accumulate the most at the highest peaks but eventually will get to
some high passes in northern CA. Through 12Z Fri, WPC
probabilities for at least 8 inches of snow are highest (>50%) in
the Olympics, Cascades, and NorCal ranges (Shasta Siskiyous,
Trinity, Klamath, etc.) above 5000ft.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso


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FOUS11 KWBC 252042
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
442 PM EDT Tue Mar 25 2025

Valid 00Z Wed Mar 26 2025 - 00Z Sat Mar 29 2025


...Eastern Great Lakes/Northeast...
Day 1...

An upper low over northern MI this afternoon shifts east over New
England through Wednesday evening. Low level westerly flow will
continue over the eastern Great Lakes through Wednesday morning
before veering northerly into Wednesday evening. PVA ahead of the
upper low center will aid lift on this favored flow across Lakes
Erie and Ontario and help produce lake enhanced snow and upslope
snow on New England mountain ranges. Day 1.5 snow probs for >4"
are generally 30-50% for the Tug Hill, Greens, Whites, and
northwestern Maine.


...Upper Midwest/Great Lakes...
Day 3...

A flattening upper ridge over the northern Great Plains and lee-
side surface cyclogenesis centered over South Dakota Thursday
night allows some warm air advection precip to form
along and north of the ND/MN border early Friday and possibly blossom
toward Lake Superior later Friday. Antecedent cold air and a warm
nose look to bring a (most likely light) wintry mix to northern
ND/MN/WI and the U.P. Day 3 ice probs for >0.1" are 20-50% centered
around Duluth and up the North Shore.


...Cascades into the northern Sierra Nevada...
Days 2-3...

An anomalously deep, cold core low approaches the OR Coast
Wednesday evening before occluding in place off WA through Friday.
Strong ridging over the West now means high snow levels at onset

8000ft) Wednesday afternoon, but will quickly drop to around

4500ft Wednesday night. These lower snow levels are maintained
through Thursday as the upper low approaches the coast, then drops
even further, to around 4000ft Thursday evening as precip rates
increase again with some heavy rates likely. Day 2 snow probs for

8" are 30-60% for the highest Klamath and OR/WA Cascades only.

However, the lower snow levels and increased precip rates make Day
3 snow probs for >8" more expansive with 40-90% probs from the
northern Sierra Nevada, Klamath, and along the spine of the OR
Cascades and WA Cascades.



Jackson



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FOUS11 KWBC 260636
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
236 AM EDT Wed Mar 26 2025

Valid 12Z Wed Mar 26 2025 - 12Z Sat Mar 29 2025


...Northeast...
Day 1...

Compact upper low over southwestern Ontario this morning will move
across northern NY/VT midday and through Maine this evening. This
will spur some more light snow into the Tug Hill Plateau where 1-3"
is likely. Farther east, low probabilities (10-30%) are shown for
more than 4 inches of snow over the Green and White mountains via
upslope enhancement as the feature moves through.



...Upper Midwest/Great Lakes/Northeast...
Days 2-3...

Flattening upper ridging exiting the High Plains Thursday combined
with lee-side surface cyclogenesis centered over South Dakota
Thursday night will favor broad WAA-driven precipitation along and
north of a surface boundary astride the Upper Midwest into the
Great Lakes. With the fast zonal/progressive flow, this will
quickly expand eastward through Canada and into the Northeast with
an influx of moisture from the southwest, reaching into NY Fri
evening then into New England overnight into early Saturday.
Temperatures are marginal for most areas, confining wintry
precipitation to areas closer to the Canadian border. However, that sub-freezing surface layer will be overrun from the S/SW with
warmer air aloft, promoting a rather large area of sleet/freezing
rain from northern MN eastward across the U.P. of Michigan and
northern WI across Ontario and into the Adirondacks. Ptype from the
models (and NBM) show a strong signal for freezing rain
(impressive for late March), but this may be modulated my afternoon
insolation. Nevertheless, WPC probabilities for at least 0.10"
icing are moderate (30-70%) over northeastern MN, the U.P./northern
WI, and the northern part of Lower Michigan. Snow amounts may be
limited, with the highest amounts of a couple inches over northern
MN where WPC probabilities for at least 4 inches are barely 10%.


...Cascades into the northern Sierra Nevada...
Days 2-3...

An anomalously deep, cold core low in the northeast Pacific will
curl up toward Vancouver Island as its wound up occlude front moves
inland tonight. High snow levels (>8000ft) this afternoon will
steadily drop to around 4000-5000ft tomorrow, then to around 4000ft
Friday with the passage of the upper trough. Snow will eventually
get to some of the passes but much of this will fall over the
higher terrain. Two-day probabilities of at least 8 inches of snow
are highest above 5000ft or so along the Cascades southward to the
NorCal ranges and northern Sierra. Moisture will continue inland to
the northern Rockies with a few to several inches of snow for the
Blue Mountains and into SW MT as a frontal boundary in the area
acts as another focus for forcing. There, WPC probabilities for at
least 8 inches of snow are low (10-30%).


Fracasso


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FOUS11 KWBC 262043
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
443 PM EDT Wed Mar 26 2025

Valid 00Z Thu Mar 27 2025 - 00Z Sun Mar 30 2025


...West Coast through Northern Rockies...
Days 1-3...

An anomalously deep, cold-core low off OR near 140W will further
occlude and curl up toward Vancouver Island through Thursday night
with the occluded front crossing the West Coast tonight. High snow
levels (>8000ft) this afternoon will rapidly drop to around
4000-5000ft after midnight, then to around 3500ft Friday with the
passage of the upper trough axis. Accumulating will eventually
reach to some of the passes in the Cascades by Friday, but the
rates will drop around that time as well. So most of the heavy snow
will be in the higher elevations. Day 2 snow probs for >8" are
50-80% for the higher Cascades, Klamath, and northern Sierra
Nevada.

Moisture will continue inland through the northern Rockies Friday
through Saturday with periodic heavy snow above 5000ft snow levels
on Friday and 4000ft on Saturday. A focus for mountain snow remains
from the Blue Mtns of OR through SW MT (and the Bighorns of WY)
where Day 3 snow probs for >8" are 30-60%.


...Upper Midwest/Northern Great Lakes/Northeast...
Days 2-3...

Flattening upper ridging exiting the High Plains Thursday combined
with lee-side surface cyclogenesis centered over South Dakota
Thursday night will favor broad WAA-driven precipitation along and
north of a surface boundary draped over the Upper Midwest into the
Great Lakes. With the fast zonal/progressive flow, this will
quickly expand eastward through southern Canada and the Northeast
with through Friday night. Temperatures are marginal for most
areas, confining snow to areas closer to the Canadian border.
However, a sub-freezing surface layer will be overrun from the
S/SW with warmer air aloft, promoting a long, but narrow swath of sleet/freezing rain from northern MN eastward across the U.P. of
Michigan and northern WI across Ontario, the Adirondacks, and
central New England. Ptype from the models (and NBM) show a strong
signal for freezing rain (impressive for late March), but this may
be initially modulated by Friday afternoon insolation before
focusing over the U.P. of MI Friday evening. Day 2.5 ice
probabilities for >0.25" have risen to 20-40% over much of the U.P.
and the far northern L.P. Day 2.5 snow probs for >4" are 30% up at
the top of the Arrowhead of MN, and 30-70% for Day 3 over the
northern Adirondacks, Greens, and Whites into western Maine.


...Northern Plains...
Day 3...

A shortwave trough axis that crosses the PacNW Friday reaches the
northern Rockies on Saturday promotes Colorado lee-side low
development on Saturday. Broad convergence should allow some
moderate to locally heavy snow bands to form around SD into MN
by Saturday afternoon. The 12Z GFS/EC have come into better
agreement, though the EC remains a bit more progressive. Will need
to monitor the threat for heavy fgen snow banding over portions of
the northern Plains into Upper Midwest Saturday/night.



Jackson


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FOUS11 KWBC 270713
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 AM EDT Thu Mar 27 2025

Valid 12Z Thu Mar 27 2025 - 12Z Sun Mar 30 2025


...West Coast through Northern/Central Rockies...
Days 1-3...

An anomalously deep, cold-core low off OR near 135W will further
occlude and curl up toward Vancouver Island through Thursday night
with the occluded front crossing the West Coast this morning. Snow
levels continue to rapidly drop to around 4000-5000ft today across
the Cascades into the northern CA ranges, then to around 3500ft
Friday with the passage of the upper trough axis. Accumulation
will eventually reach to some of the passes in the Cascades by
Friday, but the rates will drop around that time as well. WPC
probabilities for at least 8" of snow are high (>70%) on Days 1-2
across the high elevations of the Cascades and into the northern CA ranges/northern Sierra.

Moisture will continue inland through the northern Rockies Friday
through Saturday with periodic heavy snow above 5000ft snow levels
on Friday and 4000ft on Saturday. Snow also begins to enter the
central Rockies by Saturday as a trailing shortwave crosses the
region and drops snow levels below 7000-8000 ft. Snowfall
probabilities for at least 8" remain greatest across western MT and
towards the Little Belts and Bighorns of WY, where 50-80% values
are found.


...Upper Midwest/Northern Great Lakes/Northeast...
Days 2-3...

Flattening upper ridging exiting the High Plains Thursday combined
with lee-side surface cyclogenesis centered over South Dakota
Thursday night will favor broad WAA-driven precipitation along and
north of a surface boundary draped over the Upper Midwest into the
Great Lakes. With the fast zonal/progressive flow, this will
quickly expand eastward from southern Canada and the Northeast
through the daytime on Saturday. Temperatures are marginal for
most areas, confining snow to areas closer to the MN- Canadian
border through Friday and northern NY/VT/NH into ME on Saturday.
However, this band of snow could be quite potent as the region
falls within the right entrance region of a 130 kt jet and IVT over
the 90th climatological percentile over the Great Lakes per the
NAEFS on Friday night. The narrow, but intense WAA combined with
favorable synoptic ascent and moisture could lead to snowfall rates
of 1-2"/hr, particularly across parts of New England by the end of
D2.

Meanwhile, a sub- freezing surface layer will be overrun from the
S/SW with warmer air aloft, promoting a long, but narrow swath of sleet/freezing rain from the northern Plains eastward across the
U.P. of Michigan and northern WI through Ontario, the Adirondacks,
and central New England. Ptype from the models (and NBM) show a
strong signal for freezing rain (impressive for late March), but
this may be initially modulated by Friday afternoon insolation
before focusing over the U.P. of MI Friday evening. Day 2 ice
probabilities for >0.25" have risen to 30-60% over much of the U.P.
and the far northern L.P. Day 2-3 ice probabilities for >0.25"
across the Northeast are 20-40% and highest across the northern
Adirondacks as precipitation lingers through the end of Day 3 while
warmer air begins eventually lifting back north. Day 2 snow probs
for >4" have a very sharp gradient along the MN- Canadian border
with 50-70% values at the top of the Arrowhead of MN. For the
Northeast and New England on Days 2-3, probabilities for >6" have
increased to 30-50% for northern VT/NH and into central ME, with
higher values (60-80%) in the Whites of northern VT and neighboring
areas in ME.


...Northern Plains/Upper Midwest/Northern Great Lakes...
Day 3...

Quickly following the northern Great Lakes system on Day 2 a shortwave
trough axis that crosses the PacNW Friday reaches the northern
Rockies on Saturday along with a southern piece of energy crossing
the central Rockies and promotes Colorado lee- side low
development on Saturday. Broad convergence should allow some
moderate to locally heavy snow bands to form around the Black Hills
of SD (maybe far northern NE) eastward into MN by Saturday
afternoon. The 12Z GFS/EC have come into better agreement, though
the EC remains a bit farther north with the axis of heavier snow.
WPC probabilities for at least 4" of snow are 30-50% from northern
WI to the western U.P., with lower probabilities (10-30%) extending
from the Black Hills of SD through central MN. These probabilities
are likely to increase over the next few forecast cycles once
better agreement in the northern extent of QPF comes into focus. With
high pressure remaining locked in over the southern Hudson Bay,
there remains a strong signal for mixed ptype from MN through WI
and into the U.P. and northern L.P. of MI. Day 3 freezing rain
probabilities for >0.25" are currently low (10-30%) from central WI
through the northern L.P. of MI.



Snell


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FOUS11 KWBC 272037
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
437 PM EDT Thu Mar 27 2025

Valid 12Z Thu Mar 27 2025 - 12Z Sun Mar 30 2025


...West Coast through Northern/Central Rockies...
Days 1-3...

A deep, slow-moving low centered off of the Northwest coast will
gradually fill as it lifts to the north over the next couple of
days. However, even as the system lifts out, snow levels across the
Northwest will continue to drop Friday into early Saturday as a
series of shortwave troughs digging south of the low move inland.
This will bring levels down to around 3000-4000ft in the Washington
and Oregon Cascades on Friday, before dropping below 3000ft with
the passage of a well-defined trough Saturday morning. Further to
the south, snow levels starting above 5000ft in the Shasta-
Siskiyou region and the northern Sierra Nevada will drop below
4000ft in many locations before precipitation ends. Although snow
levels will be on the decline, so will the onshore moisture
advection, with guidance showing IVTs dropping off after the start
of the period. The heaviest precipitation is expected to center
across southern Oregon and far northern California, where the best
moisture and forcing is expected to focus later today. By early
Saturday, precipitation is expected to diminish from south to north
as an upper ridge moves inland in the wake of the previously-noted
trough. Probabilities for 72-hr accumulations exceeding 8in are
over 50 percent for parts of the Olympics, Cascades, Klamath
Mountains, and the northern Sierra Nevada.

Meanwhile, moisture spreading inland will begin to interact with a
developing low-to-mid level baroclinic zone and periods of
enhanced forcing associated with the inland moving troughs to
produce light-to-moderate precipitation, including mountain snow
from the northern to the central Rockies. Precipitation coverage is
expected to increase Friday night, with unsettled weather
continuing through the weekend. Snow levels beginning above 5000ft
in the northern Rockies Friday night are forecast to dip below
4000ft in some location by late Saturday. In the central Rockies,
snow levels will drop to 7000-8000ft in the Colorado ranges and
around 5000-6000ft across northern Utah. Probabilities for 72-hr
accumulations exceeding 8in are above 50 percent across portions of
the northern and central Rockies from western Montana to
northwestern and north-central Wyoming and from south-central
Wyoming to north-central Colorado.

...Northern High Plains and Black Hills...
Days 2/3...

A shortwave trough moving into the Southwest on Friday is expected
to lift northeast from the Four Corners across the central Rockies
and into the High Plains Saturday morning. Moisture fed into an
area of strong ascent generated in part by favorable upper jet
forcing will support precipitation north of an associated surface
low that will develop and move east of the Colorado Rockies. Rain
changing to snow is expected from southweastern Montana and
northeastern Wyoming into parts of western to central South Dakota
and Nebraska. The heaviest amounts are forecast to fall across the
Black Hills, where totals exceeding 4in are likely.

...Upper Midwest/Northern Great Lakes/Northeast...
Days 1-3...

A longwave upper trough in the West working in tandem with the
right-entrance region of a 250mb jet streak Friday afternoon will
foster large-scale ascent aloft throughout the Upper Midwest and
Great Lakes. The upper trough and a strong low-level ridge of high
pressure off the Southeast coast supports a strengthening SWrly
low-mid level flow regime that results in exceptional warm-air
advection (WAA) for the regions reference above. The WAA from the
Upper Midwest and Great Lakes to interior New England will clash
with a cold Canadian air-mass anchored by a 1030mb+ high pressure
system over Ontario and Quebec. The result is 925-700mb FGEN that
produces a narrow band of disruptive snow and ice starting Friday
afternoon from northern Minnesota to the Upper Great Lakes,
followed by interior New England's start time of Friday night. The
strong WAA over sub- freezing boundary layer temps is a favorable
setup for freezing rain/sleet that will make for hazardous travel
conditions.

By Saturday morning, a brief break in the action arrives from
northern Minnesota to the Upper Great Lakes, but periods of
mountain snow and valley ice will linger throughout much of the day
in New England. WPC probabilities for this event show moderate
chance probabilities (40-60%) for >0.25" of ice accumulation over
the tip of Michigan's Mitten and the far east section of Michigan's
U.P.. Some instances of scatter power outages and tree damage
cannot be ruled out here. Meanwhile, there is an expansive area of
moderate- to-high chance probabilities (50-70%) for >0.1" of ice
from northeast Michigan, northern Wisconsin, and for the rest of
northern Michigan. Snow will be the primary hazard Friday night and
into Saturday morning over interior New England. WPC probabilities
show moderate-to-high chances (50-70%) for snowfall totals >4"
from northern Vermont (excluding the Champlain Valley) on east
through northern New Hampshire and west-central Maine. The peaks
of the White Mountains could see snowfall totals top 8". WSSI-P
does show some moderate chances (40-60%) for Minor Impacts in these
affected areas of Interior New England.

This active pattern reloads over the Central Plains on Saturday as
the longwave trough in the West ejects a shortwave disturbance
over the Rockies. This feature will spawn a new wave of low
pressure along the 925-850mb front that remains stationary from
Nebraska and southern Minnesota on east through Michigan. There
remains some discrepancies in guidance on the evolution/strength of
this storm system. The ECMWF SATs MSLP guidance shows the low
organizing over eastern Kansas that heads into eastern Iowa by
Sunday morning. Ultimately, the 290K isentropic ascent and strong
WAA mechanisms that supported the first round of wintry weather
will still be present Saturday night and into Sunday from the
Midwest to New England. The ECMWF-AIFS does show the potential for
a deformation zone on the backside of the storm over eastern South
Dakota and into central Minnesota, although thermodynamic profiles
are not sold yet on which areas can dynamically cool enough to stay
all snow. There is higher confidence in yet more freezing
rain/sleet from northern and central Wisconsin on east through
northern Michigan and as far east as northern New England. WPC
probabilities show moderate chances (40-60%) for ice accumulations

0.1" in these areas with low chances (10-30%) for >0.25",

especially in the more elevated terrain. In terms of snowfall, WPC probabilities show low-to-moderate chances (30-50%) for snowfall
totals >4" in far northern Wisconsin and the western Michigan U.P..

Pereira/Mullinax


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FOUS11 KWBC 300721
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 AM EDT Sun Mar 30 2025

Valid 12Z Sun Mar 30 2025 - 12Z Wed Apr 02 2025


...Upper Midwest, Northern Great Lakes, and Northeast...
Day 1...

Ongoing prolonged late-season ice storm continues across portions
of northern WI into the northern MI L.P. and central/eastern U.P.,
as well as New England today. A negatively tilted 250-500mb trough
axis working in tandem with the strongly diffluent right- entrance
region of a 250mb jet streak has organized an area of low pressure
tracking across the Great Lakes today. Sufficiently cold
temperatures remain locked in place to the north of the robust
925-700mb FGEN warm front that is oriented W-E from northern WI to
as far east as New England. This is all thanks to a 1030mb+ high
pressure system over southeastern Canada that is supporting the
ongoing icy setup. As strong SWrly winds overrun the sub-freezing
air-mass, a >0C warm nose protruding into the 850-700mb will cause precipitation to fall in the form of freezing rain and sleet
throughout the Upper Midwest, Upper Great Lakes, the northern
Appalachians, and New England into the end of Day 1. By Monday
morning the low pressure system is forecast to push into southeast
Canada and surge above freezing temperatures throughout the entire
East Coast, with precipitation also gradually ending across the
Great Lakes. While ice will be the more commonly observed winter
weather hazard, there will be light to moderate snow beneath the
deformation zone on the northern and western flanks of the 850mb
low.

Periods of snow will be ongoing across central MN into northern WI
and the MI U.P. this morning, as well as wrapping around the
western side of the low as far south as northwest IA. South of the
snow axis, freezing rain and sleet will be common in northern
Wisconsin, the eastern Michigan U.P., across the tip of Michigan's
Mitten, and into interior New England. The 0C surface line will
gradually lift northward throughout the day east of the low
pressure, but will be stubborn to lift across northern MI and
northern New England. The deformation axis will continue its swath
of snow from southeast Minnesota to central Wisconsin Sunday
afternoon, but it will be progressive and snow falling during the
daytime hours will be tougher to accumulate. Snow within the
deformation axis may continue over northern Michigan Monday morning
before finally exiting to the northeast over Ontario by Monday
afternoon.

WPC probabilities show moderate-to-high chances (60-80%) for >6"
of snowfall for areas along the shore of Lake Superior in the MI
U.P.. In terms of freezing rain, WPC probabilities show moderate
chances (40-60%) for additional ice accumulations >0.25" in
northern Wisconsin, northern Michigan, and in the New England
mountain ranges such as the Greens and especially the Whites.
There is also an area of low chances for an additional >0.5" of
ice accumulation as far eastern MI U.P.. All of these areas can
anticipate hazardous travel conditions with the potential for
additional power outages in those areas sporting better chances
for >0.50" of total ice accumulation.


...The West...
Days 1-3...

An active stretch of wintry weather is expected from the West
Coast to the Front Range of the Rockies through Monday due to
persistent troughing. A pair of shortwaves traversing the Rockies
early this morning is responsible for ongoing mountain snow from
as far north and west as the Absaroka and Bitterroots through the
Wyoming ranges and on south to the Colorado Rockies. As high
pressure builds in over the Canadian Prairies today, easterly
upslope flow and residual moisture aloft will foster additional
mountains snow in the Black Hills and Big Horns. Some lower
elevations snowfall is expected during the day on Sunday as well,
but accumulations will be minor due to the late season sun angle
limiting accumulations. WPC probabilities do depict moderate
chances (40-70%) for snowfall totals >6" in the highest elevations
of the Absaroka, Wind River, and northern Colorado Rockies.

By this afternoon, focus shifts to an exceptional closed upper low
in the northeast Pacific that slowly makes its way east towards
the Pacific Northwest by Monday night. Heavy high elevation
mountain snow (above 6,000ft in the northern CA ranges and above
5,000ft in both the Cascade and Blue Mountains) will be underway,
but as the upper low inches closer to the Northwest U.S., falling
heights and colder temperatures aloft will cause snow levels to
lower into Monday. By 12Z Monday, NAEFS shows just about all
mandatory height levels listed are bottoming out below the 2.5
climatological percentile while IVT values >500 kg/m/s are aimed at
southern California. Then by early Tuesday the parent upper low is
expected to dive southeast across southwest OR and northern CA,
proving a final surge of Pacific moisture within an area of cold
air aloft. From northern California to the interior Northwest, the
region will also be located beneath the divergent left-exit region
of a 200mb jet streak whose wind speeds (>130 kts) are above the
99th climatological percentile. With the IVT located farther south,
the best moisture advection and upslope enhancement will be seen
from California's Siskiyou and Salmon mountains on south and west
along the spine of the Sierra Nevada. On Monday afternoon and into
Monday night, the flood of Pacific moisture aloft will advance
well inland through much of the Intermountain West. Just about
every notable mountain range in the central and northern Rockies is
likely to see measurable snow Monday night into Tuesday.
Meanwhile, cyclonic flow around the upper low will still support
ongoing upslope snowfall in the central and northern California
ranges through Tuesday night.

A very wintry few days are coming to the mountain ranges of the
western U.S.. Through 12Z Wednesday, WPC probabilities show the
northern ranges of California (Siskiyou, Salmon, Shasta) and the
length of the central and northern Sierra Nevada have high chances

70%) for snowfall totals >24". Most of these ranges above

6,000ft are currently forecast to see localized amounts between 3-4
feet through 12Z Wednesday. Heavy snow also reaches into the OR
Cascades with high probabilities for at least 12". Farther inland,
many Intermountain West ranges (Sawtooth, Blue, Uinta, Bear River,
Wind River, Absaroka, Big Horn, and CO/WY central Rockies) are all
likely to see snowfall totals of 6-12" with locally higher amounts
in these ranges as well. Expect hazardous travel conditions for
many road ways that remain open in these mountain ranges.


...Northern Plains and Upper Midwest...
Day 3...

By Tuesday morning, the upper trough responsible for the barrage of
mountain snow in the West will position the 250mb jet streak's
divergent left-exit region over the Great Plains. Modest 500mb PVA
and strengthening WAA at low levels will give rise to lee
cyclogenesis east of the Rockies. Throughout the day Tuesday, a
strengthening LLJ, (NAEFS shows 850mb winds above the 90th
climatological percentile 18Z Tuesday from north Texas to the Red
River of the North), will deliver both increased moisture and
increasing WAA aloft. There also appears to be sufficiently cold
enough air present that precipitation will transition over from
rain to snow from the Black Hills on east across South Dakota and
as far east as central Minnesota Tuesday night.

There are ongoing differences in the position of this developing
deformation axis. All three deterministic guidance members
(EC/GFS/Canadian) along with the EC- AIFS all show this storm
growing in strength and size heading into Day 4, but they do this
in different ways both synoptically and on the mesoscale as well.
The ECMWF EFI does show a growing signal for a potentially
disruptive winter storm from the Dakotas on east across Minnesota
and into the northern Great Lakes, which is in line with where WSO
values of 30-80% exist on Days 3-4. Both snow amounts, along with
snow load and blowing snow are likely to be hazards that the
Northern Plains and Upper Midwest contend with through Wednesday,
with freezing rain most likely on the eastern edge of the WAA
across WI and MI. Current WPC snowfall probabilities (through 12Z
Wednesday) for >4" are 40-80% across the eastern Dakotas and
central MN, with a majority of the snow expected into Day 4.
Residents and those traveling to/from these regions should keep
close eyes on the forecast as additional changes in the types of
impacts, the severity of those impacts, and where/when these
impacts occur are likely to fluctuate for the rest of the weekend.


Snell/Mullinax



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FOUS11 KWBC 280748
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Fri Mar 28 2025

Valid 12Z Fri Mar 28 2025 - 12Z Mon Mar 31 2025


...West Coast through Northern/Central Rockies...
Days 1-3...

A deep, slow-moving low centered off of the Northwest coast will
gradually fill as it lifts to the north over the next day or so.
However, even as the system lifts out, snow levels across the
Northwest will continue to drop into early Saturday as a series of
shortwave troughs digging south of the low move inland. This will
bring levels down to around 3000-4000ft in the Washington and
Oregon Cascades today, before dropping below 3000ft with the
passage of a well-defined trough Saturday morning. Further to the
south, snow levels starting above 5000ft in the Shasta- Siskiyou
region and the northern Sierra Nevada will drop below 4000ft in
many locations before precipitation ends. Although snow levels will
be on the decline, so will the onshore moisture advection, with
guidance showing IVTs dropping off after the start of the period
and a break in precipitation on Day 2. The heaviest precipitation
is expected to center across southern Oregon and far northern
California, where the best moisture and forcing is expected to
focus later today. By early Saturday, precipitation is expected to
diminish from south to north as an upper ridge moves inland in the
wake of the previously-noted trough. Day 1 WPC probabilities for
over 8 inches of snow are 60-80% for parts of the Olympics,
Cascades, Klamath Mountains, and the northern Sierra Nevada. Then,
the next system approaches the West Coast by Day 3 as the closed
upper low off the Pacific Northwest reloads from energy dropping
southward across the eastern Aleutians. This leads to additional
moderate onshore flow amid initial snow levels around 4000-5000ft
(up to 6000ft in the central/southern Sierra). WPC probabilities
for at least 8 inches of additional snow on Day 3 across the Sierra
and northern CA ranges are 40-70%, but are expected to increase as
the bulk of the precipitation moves onshore after 12z/Mon.

Meanwhile, moisture spreading inland across the northern Great
Basin and Rockies will begin to interact with a developing low-to-
mid level baroclinic zone and periods of enhanced forcing
associated with the inland moving troughs to produce light-to-
moderate precipitation, including mountain snow from the northern
to the central Rockies. Precipitation coverage is expected to
increase Friday night, with unsettled weather continuing through
the weekend and ending with a weak area of convergence on Sunday
between western MT and northern CO. Snow levels beginning above
5000ft in the northern Rockies Friday night are forecast to dip
below 4000ft in some location by late Saturday. In the central
Rockies, snow levels will drop to 7000-8000ft in the Colorado
ranges and around 5000-6000ft across northern Utah. WPC Days 1-2
probabilities for at least 8 inches of snow are generally 50-70%
from the Blue Mts of northwest OR through the central ID ranges
into southwest MT, as well as the Absarokas and Wind River Range.
These probs also extend south to the Park Range and Medicine Bow
Mountains of CO/WY.


...Northern Minnesota through the Northern Great Lakes...
Day 1...

A longwave upper trough in the West working in tandem with the
right-entrance region of a 250mb jet streak this afternoon will
foster large-scale ascent aloft throughout the Upper Midwest and
Great Lakes. The upper trough and a strong low-level ridge of high
pressure off the Southeast coast supports a strengthening SWrly
low-mid level flow regime that results in exceptional warm-air
advection (WAA) for the regions reference above. This WAA will
clash with a cold Canadian air-mass anchored by a 1030mb+ high
pressure system over Ontario and Quebec. The result is 925-700mb
FGEN that produces a narrow band of disruptive snow (primarily
north of the U.S.-Canadian border) and ice starting as early as
this morning across far northern MN, but becoming more widespread
across northern MN/WI/MI by this evening. The strong WAA over sub-
freezing boundary layer temps is a favorable setup for freezing
rain/sleet that will make for hazardous travel conditions even
where only light amounts occur. WPC probabilities for at least
0.25" of ice accretion on Day 1 is medium (50-70%) across the
eastern U.P. and northern L.P. of MI, with 20-40% chances extending
westward across the U.P. and into the MN Arrowhead.


...Northeast...
Days 1-3...

This same system is expected to spread a narrow swath of heavy snow
and area of mixed precipitation into the Interior Northeast and New
England by late D1, but with wintry precipitation lingering for
several days. This long-duration event made possible by a trailing
shortwave and developing central U.S. trough which will continue to
reinforce a favorable jet pattern for upper divergence as well as
sufficient mid-upper level moisture content. However, the snowfall
threat peaks early Saturday morning as a jet max passes to the
north of New England and 925-850mb WAA is at it's strongest. 00z
HREF depicts 30-40% chances for 1-2"/hr snowfall rates around
13z/Sat across far northern NY and northern VT/NH. WPC snowfall
probabilities for at least 6 inches of snow on days 1-2 are medium
(40-60%) from northern NH, VT, and into central ME.

South of this heavy snow threat between the northern Adirondacks
and much of central/southern VT and NH, 850-750mb warm nose allows
for a transition area of sleet/freezing rain. After the brief
burst of heavier precip early Sat, forcing weakens and there is
left a weak stream of moisture overrunning a CAD signature due to a
strong 1030mb High situated over the James Bay. This potentially
significant icing threat is expected to linger through Sun morning
until the surface low across the Midwest begins to strengthen and
push warmer air northward across New England by Day 3. However, the
CAD signature in place will continue to support freezing rain
across the typically colder valley locations and areas banked along
the Green/White mountains. WPC probabilities for the entire
forecast period (ending 12z/Mon) are high (70-80%) for at least
0.25" of ice accretion from the NY border with eastern Ontario
through the northern Adirondacks and into central VT/NH.
Probabilities for at least 0.5" also impressive and 40-60% (highest
across western Jefferson county of NY).


...Northern High Plains through the Upper Midwest/Great Lakes...
Days 2-3...

A shortwave trough moving into the Southwest today is expected to
lift northeast from the Four Corners across the central Rockies and
into the High Plains Saturday morning. Moisture fed into an area
of strong ascent generated in part by favorable upper jet forcing
and potent 700mb closed low will support precipitation north of an
associated surface low that will develop and move east of the
Colorado Rockies. Rain changing to snow is expected from
southeastern Montana and northeastern Wyoming into parts of
western to central SD and NE. The highest amounts are forecast to
fall across the Black Hills, but locally heavy totals are also
possible eastward along southern SD and north- central NE. WPC
probabilities for at least 4 inches are 40-70% across the Black
Hills and 10-30% into south-central SD and north- central NE.

As this system develops further Saturday night through Day 3,
increasing WAA and a blossoming precipitation shield is expected to
spread into the Upper Midwest and Great Lakes. Surface low pressure
is expected to track along along the 925-850mb front that remains
stationary from NE and southern MN on east through Michigan. There
still remains some discrepancies in guidance on the evolution/strength
of this storm system, but there is a growing consensus with the
00z guidance on the synoptic scale. The GFS finally has a more
amplified solution (in line with the CMC and ECMWF), which paints
an axis of snow fall extending east-northeast from SD through
central MN into northern WI and the MI U.P.. There is also higher
confidence in yet more freezing rain/sleet from northern and
central WI on east through northern Michigan as high pressure
remains locked in place over James Bay and cold northeast flow
continues to filter into the Upper Midwest/Great Lakes. This is a
very favorable setup for potentially significant freezing rain from
northern WI through northern MI, especially for late-March. WPC
probabilities show moderate chances (30-60%) for ice accumulations

0.25" in these areas with low chances (10-30%) for >0.5" across

parts of northern WI. In terms of snowfall, WPC probabilities show
moderate chances (30-60%) for snowfall totals >6" in far northern
WI and the western MI U.P..

Snell





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FOUS11 KWBC 282111
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
511 PM EDT Fri Mar 28 2025

Valid 00Z Sat Mar 29 2025 - 00Z Tue Apr 01 2025


...Northern/Central Rockies...
Days 1/2...

A shortwave trough ejecting from the remnant/occluded low off WA
crosses the PacNW tonight and the Great Basin through Saturday
night. This maintains moisture spreading across the northern Great
Basin and Rockies will begin to interact with a developing low-to-
mid level baroclinic zone and periods of enhanced forcing
associated with the inland moving troughs to produce light-to-
moderate precipitation, including mountain snow from the northern
to the central Rockies. Precipitation coverage is expected to
increase tonight, with unsettled weather continuing into Sunday
with a weak area of convergence on Sunday between western MT and
northern CO. Snow levels beginning above 5000ft in the northern
Rockies are forecast to dip below 4000ft in some location by late
Saturday. In the central Rockies, snow levels will drop to
7000-8000ft in the Colorado ranges and around 5000-6000ft across
northern Utah. WPC Day 2 probabilities for >8" of snow are
generally 40-70% over southwest MT, the Absarokas and Wind River
Range, and the Park Range and Medicine Bow Mountains of northern CO.


...South Dakota, Minnesota, and Northern Wisconsin/Michigan...
Days 1/2...

...Back to back impactful winter systems through Sunday...

Inverted trough from central High Plains up through lower MI
persists tonight as an upper low approaching the northern Rockies
this afternoon allows lee-side cyclogenesis to focus over western
KS through Saturday morning with a more potent low track from KS to
MI Saturday through Sunday evening.

A very strong baroclinic zone (it's currently low 80s in southwest
MN and mid 20s in the Arrowhead) maintains cold over northern
MN/WI/the U.P. through this weekend while warm air rides over the
boundary to the south. Ongoing wintry mix continues tonight with a
slow southward shift. Day 1 ice probs for >0.1" additional after
00Z is about 20% over far northern WI into the western U.P., but
50-80% over far northeast WI and central/eastern U.P. and northern
L.P. with 70% probs for >0.25" over the northern L.P.

The developing low track over KS on Saturday allows
fgen/deformation banding to develop over over southwest SD into
northwest Neb. Localized banding should overcome the strong March
diurnal insolation, but that should be fairly narrow. Day 1.5 snow
probs for >4" are 30-60% mainly over south-central SD and the Black
Hills.

The impactful wintry weather continues resumes Saturday night over
MN/WI/MI as snow bands intensify in the increasing right entrance
jet dynamics and the comma head forcing from the low tracking over
IA. These snow bands are increasingly likely over north-central MN,
far northern WI and western/central U.P. which would put heavy wet
snow over areas currently getting ice accretion. Day 2 snow probs
for >4" are 30-60% from the Sisseton Hills of northeast SD through
the central U.P. and North Shore of MN with 50-70% probs for >6"
over far northern WI through the Keweenaw Peninsula. The wintry mix
swath is just south of the snow with accumulating sleet and ice
expected to expand south as the cold air wins/advances. Day 2 ice
probs for >0.25" are 30-70% from central MN through northern WI/southern/eastern U.P. and the northern L.P. with a max around
80% in northeast WI.


...Northeast...
Days 1-3...

...Prolonged wintry mix over northern NY/New England through
Sunday...

The inverted trough causing a wintry mix over the northern Great
Lakes today spreads east over northern NY and central New England
this evening with the strong baroclinic zone maintaining fgen
precip/wintry mix through this weekend for portions of New
England. The approaching low crosses New England on Monday.

The heavy snowfall threat peaks late tonight from Lake Champlain
through northern NH into southern Maine as a jet max passes to the
north of New England and 925-850mb WAA is strongest. 12Z HREF
depicts 30-40% chances for 1"/hr snowfall rates from 06Z to 13Z
Saturday across the northern tip of NY and northern VT/NH. Day 1
WPC snowfall probabilities for >6" are 30-60% mainly over the
northern Greens and the Presidential Range of NH.

South of this heavy snow threat between the northern Adirondacks
and much of central/southern VT and NH, 850-750mb warm nose allows
for a transition zone of sleet/freezing rain. After the brief
burst of heavier precip early Sat, forcing weakens and there is
left a weak stream of moisture overrunning a CAD signature due to a
strong 1030mb High situated over the James Bay. This potentially
significant icing threat is expected to linger through Sunday until
the surface low across the Midwest begins to strengthen and push
warmer air northward across New England by Sunday evening.
However, the CAD signature in place will continue to support
freezing rain across the typically colder valley locations and
areas banked along the Green/White mountains. Day 1 WPC
probabilities for >0.25" ice (ending 00Z/Sun) are 40-70% for the
Thousand Islands area, the northern Adirondacks and south-central
VT/NH. This is followed by Day 2 values of 20-50% for an additional
0.25" over the same areas with some expansion through central
VT/NH.


...OR Cascades...Klamath...and northern/central Sierra Nevada...
Day 3...


The next cold core low drifts toward OR, but remains offshore
Sunday through Monday. A rich plume of moisture shifts inland
Sunday with renewed enhancement from an ejecting shortwave trough
Sunday night producing heavy precip over the northern half of CA
Monday. Day 3 snow probs for >8" are 40-90% in the southern OR
Cascades, the Klamath/Trinity Alps, and northern/central Sierra
Nevada with snow levels of 5000-6000ft Sunday dropping to
4000-5000ft by Monday morning.




Jackson



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FOUS11 KWBC 290823
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
423 AM EDT Sat Mar 29 2025

Valid 12Z Sat Mar 29 2025 - 12Z Tue Apr 01 2025


...Central/Northern Plains, Upper Midwest, and Northern Great
Lakes...
Days 1-2...

Long-duration ice storm to impact northern WI through the northern
MI L.P. and much of the central/eastern U.P. through Sunday, while
moderate to heavy snow is likely from SD/Neb through far northern
WI and along the lakeshore of Lake Superior.

A negatively tilted upper trough will cross the Intermountain West
today and usher potent SWrly flow into the north-central U.S.,
while a leading mid-level shortwave ejects into the central Plains
by this afternoon. This leading shortwave is associated with
leeside cyclogenesis along the CO/KS border and an attached sharp
stationary front extending east-northeast through the Midwest and
Great Lakes. As moisture overruns this frontal boundary and
expansive high pressure stretches across Canada, a wintry mix of
snow, sleet, and freezing rain is likely this weekend.

Snowfall is forecast to begin across western Neb into the Black
Hills and south-central SD by this afternoon associated with the
mid-level low crossing overhead leading to sufficient convergence
and bands of snowfall capable of containing 1-2"/hr rates. These
rates will be imperative to achieving heavy accumulations as
boundary layer temperatures start out well above freezing. The 00z
HREF depicts the best chances for these intense snowfall rates are
along the western and central SD/Neb border centered near the Pine
Ridge Reservation. Snowfall rates will likely lower while the
northern precipitation shield expands east-northeast in response to
the progressing surface low and forcing becoming more stretched in
an east-west direction. Moderate snow will extend across SD,
central MN, and towards far northern WI and the MI U.P. by tonight.
There has been some latitudinal uncertainty regarding this swath
of snow, with 00z guidance coming in a touch south. Regardless, WPC probabilities for at least 4" of snow are 30-60% for this region,
with localized pockets up to 80%. Meanwhile, the heaviest snowfall
from this system is most likely from near or just south of Duluth,
MN eastward along the lakeshore of Lake Superior from far northern
WI into the MI U.P. due to snow remaining the dominant ptype
throughout the event. Here, WPC probabilities for at least 6" are
high (60-80%).

South of the heavy snow axis a corridor of impactful sleet and
freezing rain are forecast to stretch from northern WI through much
of northern MI. A prior storm has already led to a corridor of ice
across this region and precipitation may linger continuously today
across northern WI/MI until a resurgence tonight through Sunday.
High pressure (~1030mb) over James Bay will continue to usher in
cold northeasterly flow as the surface low tracks across southern
WI on Sunday. Ice accretion may be limited during daytime hours
given the late-March sun angle, but with the bulk of the wintry mix
occurring Saturday night there is the potential for significant
ice accumulations. WPC probabilities for at least 0.25" of freezing
rain are highest (60-90%) across parts of northern WI and the
northern MI L.P., with chances for >0.5" at 30-60%. Medium
probabilities (30-60%) for at least 0.25" also extend into the
central/eastern MI U.P. as well as into parts of northwestern WI to
the border of MN. In addition to the freezing rain threat, some
areas from northern WI to the MI U.P. could experience over 1" of
sleet.


...Northeast...
Days 1-2...

Prolonged wintry mix expected across the Interior Northeast through
New England this weekend, including the potential for heavy icing
before above freezing temperatures return on Monday.

An initial pulse of heavy precipitation is swinging through
northern NY and New England this morning, including heavy snow up
to 1"/hr until around 14Z across northern VT into central/northern
NH. This snowfall is a result of a jet max passing to the north of
New England and where 925-850mb WAA is strongest, which quickly
wanes later today.

South of this heavy snow threat between the northern Adirondacks
and much of central/southern VT and NH, 850-750mb warm nose allows
for a transition zone of sleet/freezing rain. After the brief
burst of heavier precip this morning, forcing weakens and there is
left a weak stream of moisture overrunning a CAD signature due to
the strong High situated over the James Bay and elevated PWs (above
the 90th climatological percentile per the NAEFS SAT) continuously
advected from the WSW. WAA gains latitude by Sunday as the Great
Lakes low pressure strengthens and tracks northeast into Canada by
Sunday night. Even with this storm track turning the entire northeast eventually over to rain on Monday, a prolonged wintry mix this
weekend could lead to significant freezing rain amounts. Areas most
at risk for heavy icing include northern NY and the Adirondacks,
through the Greens and Whites of VT/NH, where CAD is likely to
remain longest.

WPC probabilities for >0.25" ice are 60-80% for the Thousand
Islands area, the northern Adirondacks and south- central VT/NH.
Probabilities for >0.1" ice extend as far south as the MA
Berkshires and northward along the White Mts through ME into Day 2.


...Northern/Central Rockies...
Days 1-3...

An upper trough sliding eastward across the Intermountain West
today will maintain some Pacific moisture advection into the
northern/central Rockies while also interacting with a developing
low- to- mid level baroclinic zone to produce light-to- moderate
mountain snow this weekend. Precipitation coverage is expected to
peak on Day 1 as the upper trough moves through, with unsettled
weather continuing through Sunday across MT/WY due to the
relatively strong baroclinic zone being reinforced by high
pressure positions over southern Saskatchewan. Snow levels
beginning around 5000ft in the northern Rockies are forecast to dip
below 4000ft in some location by this evening. In the central
Rockies, snow levels will drop to 7000-8000ft in the Colorado
ranges and around 5000-6000ft across northern Utah. WPC Days 1-2
probabilities for >8" of snow are generally 40-70% over southwest
MT, the Absarokas and Wind River Range, and the Park Range and
Medicine Bow Mountains of northern CO.

By the end of Day 3/12z Tuesday, a strong closed upper low returns
to off the Pacific Northwest and extends a 160kt 250mb westerly
jet inland through the central Great Basin. Pacific moisture,
upslope flow, and increasing upper divergence to the north of this
low produces the next round of mountain snow across the
northern/central Rockies. Current WPC Day 3 probabilities for at
least 8" are 30-50% from southwest MT, western WY, into the
northern CO Rockies.


...West Coast through the Intermountain West...
Days 2-3...

The next cold core low drifts toward OR, but remains offshore
Sunday through Monday. A broad plume of Pacific moisture shifts
inland Sunday and lifts northeastward with renewed enhancement
from an ejecting shortwave trough Sunday night producing heavy
precip over the northern half of CA Monday. Days 2-3 snow probs for

8" are 50-90% in the southern OR Cascades, the Klamath/Trinity

Alps, and northern/central Sierra Nevada with snow levels of
5000-6000ft Sunday dropping to 4000-5000ft by Monday morning. Snow
also extends into the central/northern Great Basin Sunday night
through Monday, with snow levels falling below 4000-5000ft on Day 3
across the Idaho ranges and remaining around 5000-6000ft across
UT/NV.


Snell



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FOUS11 KWBC 291908
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
308 PM EDT Sat Mar 29 2025

Valid 00Z Sun Mar 30 2025 - 00Z Wed Apr 02 2025


...Central/Northern Plains, Upper Midwest, and Northern Great
Lakes...
Days 1-2...

A negatively tilted 250-500mb trough axis working in tandem with
the strongly diffluent right-entrance region of a 250mb jet streak
will organize an emerging area of low pressure in the Midwest
tonight and into Sunday. Sufficiently cold temperatures are locked
in place to the north of the robust 925-700mb FGEN warm front that
is oriented W-E from northern MN to as far east as northern NEw
England. This is all thanks to a 1030mb+ high pressure system over
southeastern Canada that is supporting the ongoing icy setup. As
strong SWrly winds overrun the sub-freezing air-mass, a >0C warm
nose protruding into the 850-700mb will cause precipitation to
fall in the form of freezing rain and sleet throughout the Upper
Midwest, Upper Great Lakes, the northern Appalachians, and New
England through Sunday. While ice will be the more commonly
observed winter weather hazard, there will be snow beneath the
deformation zone on the northern and western flanks of the 850mb
low.

Periods of snow will be ongoing in the Sand Hills of Nebraska
and over southern South Dakota this afternoon with snow increasing
in coverage from the Upper Midwest to the Michigan U.P.. South of
the snow axis, freezing rain and sleet will be common in northern
Wisconsin, the eastern Michigan U.P., across the tip of Michigan's
Mitten, and as far east as interior New England. By Sunday morning,
most areas will begin to transition to rain with the exception
being northwest Wisconsin and the western Michigan U.P.. The
deformation axis will continue its swath of snow from southeast
Minnesota to central Wisconsin Sunday afternoon, but it will be
progressive and snow falling during the daytime hours will be
tougher to accumulate. Some lingering freezing rain is possible in
the eastern Michigan U.P.. and northern New England Sunday evening.
Snow within the deformation axis is continue over northern Michigan
Monday morning before finally exiting to the northeast over Ontario
by Monday afternoon.

WPC probabilities show moderate-to-high chances (50-70%) for >4"
of snowfall in parts of northern Nebraska, southern South Dakota,
eastern South Dakota, and central Minnesota. Farther east, similar moderate-to-high chance probabilities are present for >8" of
snowfall in far northern Wisconsin and across the western and
central Michigan U.P.. In terms of freezing rain, WPC probabilities
show moderate chances (40-60%) for ice accumulations >0.5" in
northern Wisconsin, northern Michigan, and in Northeast mountain
ranges such as the Adirondacks, Green, and White Mountains. There
is an expansive area of moderate-to-high chance probabilities for

0.25" of ice accumulation as far west as the MN/WI border and

across the southern tier of Michigan's U.P.. All of these areas can
anticipate hazardous travel conditions with the potential for
power outages in those areas sporting better chances for >0.50" of
ice accumulation.


...The West...
Days 1-3...

An active stretch of wintry weather from the West Coast to the
Front Range of the Rockies through Sunday. A pair of shortwave
troughs traversing the Rockies tonight will be responsible for
mountain snow from as far north and west as the Absaroka and
Bitterroots through the Wyoming ranges and on south to the Colorado
Rockies through early Sunday morning. As high pressure builds in
over the Canadian Prairies on Sunday, easterly upslope flow and
residual moisture aloft will foster additional mountains snow in
the Black Hills and Big Horns. Some lower elevations snowfall is
expected during the day on Sunday as well, but accumulations will
be minor due to the late season sun angle limiting accumulations.
WPC probabilities do depict moderate-to-high chances (50-70%) for
snowfall totals >6" in the highest elevations of the Absaroka,
Wind River, and northern Colorado Rockies.

By Sunday afternoon, focus shifts to an exceptional closed upper
low in the northeast Pacific that slowly makes its way east towards
the Pacific Northwest on Monday. Heavy high elevation mountain snow
(above 6,000ft in the northern CA ranges and above 5,000ft in both
the Cascade and Blue Mountains) will be underway, but as the upper
low inches closer to the Northwest U.S., falling heights and colder temperatures aloft will cause snow levels to lower Sunday night and
into Monday. By 12Z Monday, NAEFS shows just about all mandatory
height levels listed are bottoming out below the 2.5 climatological
percentile while IVT values >500 kg/m/s are aimed at southern
California. From northern California to the interior Northwest, the
region will also be located beneath the divergent left-exit region
of a 200mb jet streak whose wind speeds (>130 kts) are above the
99th climatological percentile. With the IVT located farther south,
the best moisture advection and upslope enhancement will be seen
from California's Siskiyou and Salmon mountains on south and west
along the spine of the Sierra Nevada. By Monday afternoon and into
Monday night, the flood of Pacific moisture aloft will advance well
inland through much of the Intermountain West. Just about every
notable mountains range in the central and northern Rockies is
likely to see measurable snow Monday night into Tuesday. Meanwhile,
cyclonic flow around the upper low will still support ongoing
upslope snowfall in the central and northern California ranges
through Tuesday.

A very wintry few days are coming to the mountain ranges of the
western U.S.. Through 00Z Wednesday, WPC probabilities show the
northern ranges of California (Siskiyou, Salmon, Shasta) and the
length of the central and northern Sierra Nevada have high chances

70%) for snowfall totals >12". Most of these ranges above 6,000ft

are currently forecast to see localized amounts between 2-3 feet
through 00Z Wednesday. Farther inland, many Intermountain West
ranges (Sawtooth, Blue, Uinta, Bear River, Wind River, Absaroka,
Big Horn, and CO/WY central Rockies) are all likely to see snowfall
totals of 6-12" with locally higher amounts in these ranges as
well. Expect hazardous travel conditions for many road ways that
remain open in these mountain ranges.

...Northern Plains and Upper Midwest...
Day 3...

By Tuesday morning, the upper trough responsible for the barrage of
mountain snow in the West will position the 250mb jet streak's
divergent left-exit region over the Great Plains. Modest 500mb PVA
and strengthening WAA at low levels will give rise to lee
cyclogenesis east of the Rockies. Throughout the day Tuesday, a
strengthening LLJ, (NAEFS shows 850mb winds above the 90th
climatological percentile 18Z Tuesday from north Texas to the Red
River of the North), will deliver both increased moisture and
increasing WAA aloft. There also appears to be sufficiently cold
enough air present that precipitation will transition over from
rain to snow from the Black Hills on east across South Dakota and
as far east as central Minnesota by 00Z Wednesday. There are
ongoing differences in the position of this developing deformation
axis. All three deterministic guidance members (EC/GFS/Canadian)
along with the EC-AIFS all show this storm growing in strength and
size heading into Day 4, but they do this in different ways both
synoptically and on the mesoscale as well. The ECMWF EFI does show
a growing signal for a potentially disruptive winter storm from the
Dakotas on east across Minnesota and into the northern Great
Lakes. Both snow amounts, along with snow load and blowing snow are
likely to be hazards that the Northern Plains and Upper Midwest
contend with Tuesday night into Wednesday. Residents and those
traveling to/from these regions should keep close eyes on the
forecast as additional changes in the types of impacts, the
severity of those impacts, and where/when these impacts occur are
likely to fluctuate for the rest of the weekend.


Mullinax






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FOUS11 KWBC 291910
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
310 PM EDT Sat Mar 29 2025

Valid 00Z Sun Mar 30 2025 - 00Z Wed Apr 02 2025


...Central/Northern Plains, Upper Midwest, and Northeast...
Days 1-2...

A negatively tilted 250-500mb trough axis working in tandem with
the strongly diffluent right-entrance region of a 250mb jet streak
will organize an emerging area of low pressure in the Midwest
tonight and into Sunday. Sufficiently cold temperatures are locked
in place to the north of the robust 925-700mb FGEN warm front that
is oriented W-E from northern MN to as far east as northern NEw
England. This is all thanks to a 1030mb+ high pressure system over
southeastern Canada that is supporting the ongoing icy setup. As
strong SWrly winds overrun the sub-freezing air-mass, a >0C warm
nose protruding into the 850-700mb will cause precipitation to
fall in the form of freezing rain and sleet throughout the Upper
Midwest, Upper Great Lakes, the northern Appalachians, and New
England through Sunday. While ice will be the more commonly
observed winter weather hazard, there will be snow beneath the
deformation zone on the northern and western flanks of the 850mb
low.

Periods of snow will be ongoing in the Sand Hills of Nebraska
and over southern South Dakota this afternoon with snow increasing
in coverage from the Upper Midwest to the Michigan U.P.. South of
the snow axis, freezing rain and sleet will be common in northern
Wisconsin, the eastern Michigan U.P., across the tip of Michigan's
Mitten, and as far east as interior New England. By Sunday morning,
most areas will begin to transition to rain with the exception
being northwest Wisconsin and the western Michigan U.P.. The
deformation axis will continue its swath of snow from southeast
Minnesota to central Wisconsin Sunday afternoon, but it will be
progressive and snow falling during the daytime hours will be
tougher to accumulate. Some lingering freezing rain is possible in
the eastern Michigan U.P.. and northern New England Sunday evening.
Snow within the deformation axis is continue over northern Michigan
Monday morning before finally exiting to the northeast over Ontario
by Monday afternoon.

WPC probabilities show moderate-to-high chances (50-70%) for >4"
of snowfall in parts of northern Nebraska, southern South Dakota,
eastern South Dakota, and central Minnesota. Farther east, similar moderate-to-high chance probabilities are present for >8" of
snowfall in far northern Wisconsin and across the western and
central Michigan U.P.. In terms of freezing rain, WPC probabilities
show moderate chances (40-60%) for ice accumulations >0.5" in
northern Wisconsin, northern Michigan, and in Northeast mountain
ranges such as the Adirondacks, Green, and White Mountains. There
is an expansive area of moderate-to-high chance probabilities for

0.25" of ice accumulation as far west as the MN/WI border and

across the southern tier of Michigan's U.P.. All of these areas can
anticipate hazardous travel conditions with the potential for
power outages in those areas sporting better chances for >0.50" of
ice accumulation.


...The West...
Days 1-3...

An active stretch of wintry weather from the West Coast to the
Front Range of the Rockies through Sunday. A pair of shortwave
troughs traversing the Rockies tonight will be responsible for
mountain snow from as far north and west as the Absaroka and
Bitterroots through the Wyoming ranges and on south to the Colorado
Rockies through early Sunday morning. As high pressure builds in
over the Canadian Prairies on Sunday, easterly upslope flow and
residual moisture aloft will foster additional mountains snow in
the Black Hills and Big Horns. Some lower elevations snowfall is
expected during the day on Sunday as well, but accumulations will
be minor due to the late season sun angle limiting accumulations.
WPC probabilities do depict moderate-to-high chances (50-70%) for
snowfall totals >6" in the highest elevations of the Absaroka,
Wind River, and northern Colorado Rockies.

By Sunday afternoon, focus shifts to an exceptional closed upper
low in the northeast Pacific that slowly makes its way east towards
the Pacific Northwest on Monday. Heavy high elevation mountain snow
(above 6,000ft in the northern CA ranges and above 5,000ft in both
the Cascade and Blue Mountains) will be underway, but as the upper
low inches closer to the Northwest U.S., falling heights and colder temperatures aloft will cause snow levels to lower Sunday night and
into Monday. By 12Z Monday, NAEFS shows just about all mandatory
height levels listed are bottoming out below the 2.5 climatological
percentile while IVT values >500 kg/m/s are aimed at southern
California. From northern California to the interior Northwest, the
region will also be located beneath the divergent left-exit region
of a 200mb jet streak whose wind speeds (>130 kts) are above the
99th climatological percentile. With the IVT located farther south,
the best moisture advection and upslope enhancement will be seen
from California's Siskiyou and Salmon mountains on south and west
along the spine of the Sierra Nevada. By Monday afternoon and into
Monday night, the flood of Pacific moisture aloft will advance well
inland through much of the Intermountain West. Just about every
notable mountains range in the central and northern Rockies is
likely to see measurable snow Monday night into Tuesday. Meanwhile,
cyclonic flow around the upper low will still support ongoing
upslope snowfall in the central and northern California ranges
through Tuesday.

A very wintry few days are coming to the mountain ranges of the
western U.S.. Through 00Z Wednesday, WPC probabilities show the
northern ranges of California (Siskiyou, Salmon, Shasta) and the
length of the central and northern Sierra Nevada have high chances

70%) for snowfall totals >12". Most of these ranges above 6,000ft

are currently forecast to see localized amounts between 2-3 feet
through 00Z Wednesday. Farther inland, many Intermountain West
ranges (Sawtooth, Blue, Uinta, Bear River, Wind River, Absaroka,
Big Horn, and CO/WY central Rockies) are all likely to see snowfall
totals of 6-12" with locally higher amounts in these ranges as
well. Expect hazardous travel conditions for many road ways that
remain open in these mountain ranges.


...Northern Plains and Upper Midwest...
Day 3...

By Tuesday morning, the upper trough responsible for the barrage of
mountain snow in the West will position the 250mb jet streak's
divergent left-exit region over the Great Plains. Modest 500mb PVA
and strengthening WAA at low levels will give rise to lee
cyclogenesis east of the Rockies. Throughout the day Tuesday, a
strengthening LLJ, (NAEFS shows 850mb winds above the 90th
climatological percentile 18Z Tuesday from north Texas to the Red
River of the North), will deliver both increased moisture and
increasing WAA aloft. There also appears to be sufficiently cold
enough air present that precipitation will transition over from
rain to snow from the Black Hills on east across South Dakota and
as far east as central Minnesota by 00Z Wednesday. There are
ongoing differences in the position of this developing deformation
axis. All three deterministic guidance members (EC/GFS/Canadian)
along with the EC-AIFS all show this storm growing in strength and
size heading into Day 4, but they do this in different ways both
synoptically and on the mesoscale as well. The ECMWF EFI does show
a growing signal for a potentially disruptive winter storm from the
Dakotas on east across Minnesota and into the northern Great
Lakes. Both snow amounts, along with snow load and blowing snow are
likely to be hazards that the Northern Plains and Upper Midwest
contend with Tuesday night into Wednesday. Residents and those
traveling to/from these regions should keep close eyes on the
forecast as additional changes in the types of impacts, the
severity of those impacts, and where/when these impacts occur are
likely to fluctuate for the rest of the weekend.


Mullinax









$$

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FOUS11 KWBC 301824
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
224 PM EDT Sun Mar 30 2025

Valid 00Z Mon Mar 31 2025 - 00Z Thu Apr 03 2025


...Northern Great Lakes & Northeast...
Day 1...

The winter storm is in its final hours of producing hazardous
impacts across the northern Great Lakes and northern New England.
On the backside of the storm, periods of snow are ongoing from
northern Iowa and southern Minnesota to northwest Wisconsin and
the western Michigan U.P.. Freezing rain is ongoing in parts of
north-central Wisconsin, the eastern Michigan U.P., and from the
White Mountains of New Hampshire on north into Maine. As the storm
heads northeast towards Lake Huron tonight, freezing rain/sleet in
the eastern Michigan U.P. and north-central Wisconsin will
changeover to snow as the deformation zone moves in overhead. The
CAD signature over New England will linger over the White Mountains
and much of Maine (sans the coastal areas) to keep an icy wintry
mix into the early morning hours on Monday. By 12Z Monday, snow
will finally be coming to an end across the northern Great Lakes
while it may take until midday for far northern Maine to finally
see the wintry mix transition to a plain/cold rain.

WPC probabilities show moderate-to-high chances (40-70%) for an
additional >4" of snowfall for areas along the shore of Lake
Superior in the MI U.P, the Huron Mountains of the Michigan U.P.,
and into far northern Wisconsin. In terms of additional freezing
rain, WPC probabilities show low-to-moderate chances (20-50%) for
additional ice accumulations >0.25" in the eastern Michigan U.P.,
the White Mountains, and far western Maine bordering Quebec. Hazardous
travel conditions will linger through Monday morning with the
potential for additional power outages in the areas that could see
an additional 0.25" of ice.


...The West...
Days 1-3...

An active stretch of wintry weather has begun from the West Coast
to the Front Range of the Rockies through Tuesday due to the
prolonged influence of a deep longwave trough over the western
U.S..

This afternoon, focus shifts to an exceptional closed upper low in
the northeast Pacific that slowly makes its way east towards the
Pacific Northwest by Monday night. Heavy high elevation mountain
snow (above 6,000ft in the northern CA ranges and above 5,000ft in
both the Cascade and Blue Mountains) will be underway, but as the
upper low inches closer to the Northwest U.S., falling heights and
colder temperatures aloft will force snow levels to lower into
Monday. By 12Z Monday, NAEFS shows just about all mandatory height
levels listed are bottoming out below the 2.5 climatological
percentile while IVT values >500 kg/m/s are aimed at southern
California. The northern extent of the IVT will sport values >90th climatological percentile through the Sierra Nevada and into the
Great Basin by Monday afternoon. From northern California to the
northern Rockies, the divergent left-exit region of a 200mb jet
streak whose wind speeds (>130 kts) are above the 99th
climatological percentile will be placed directly overhead.

The best moisture advection and upslope enhancement will be seen
from California's Siskiyou and Salmon mountains on south and west
along the spine of the Sierra Nevada. On Monday afternoon and into
Monday night, the flood of Pacific moisture aloft will advance well
inland through much of the Intermountain West. Just about every
notable mountain range in the central and northern Rockies is
likely to see measurable snow Monday night into Tuesday. Meanwhile,
cyclonic flow around the upper low will still support ongoing
upslope snowfall in the central and northern California ranges
through Tuesday night. Then by early Tuesday the parent upper low
is expected to dive southeast across southwest OR and northern
California, proving a final surge of Pacific moisture within an
area of cold air aloft. The bulk of the Pacific moisture advection
will be finished Tuesday night and into Wednesday, but the core of
the longwave trough will be over the Rockies with NAEFS showing
500mb temps that are below the 10th climatological percentile from
the Sierra Nevada to the Front Range of the Colorado Rockies. With
the help of daytime heating, expect numerous snow showers to
envelope most of the western U.S. mountain ranges given the steep
lapse rates.

Through 00Z Thursday, WPC probabilities show the northern ranges
of California (Siskiyou, Salmon, Shasta) and the length of the
central and northern Sierra Nevada have high chances (>70%) for
snowfall totals >24". Most of these ranges above 6,000ft are
currently forecast to see localized amounts between 3-5 feet
through 00Z Thursday. Heavy snow also reaches into the Oregon
Cascades with high probabilities for at least 12". Farther inland,
many Intermountain West ranges (Sawtooth, Blue, Uinta, Bear River,
Wind River, Absaroka, Big Horn, and CO/WY central Rockies) are all
likely to see snowfall totals of 6-12" with locally higher amounts
in these ranges as well. Expect hazardous travel conditions for
many road ways that remain open in these mountain ranges.


...Northern Plains and Upper Midwest...
Day 3...

By Tuesday morning, the upper trough responsible for the barrage of
mountain snow in the West will position the 250mb jet streak's
divergent left-exit region over the Great Plains. Modest 500mb PVA
and strengthening WAA at low levels will give rise to lee
cyclogenesis east of the Rockies. Throughout the day Tuesday a
strengthening LLJ, (NAEFS shows 850mb winds reaching the 97.5
climatological percentile 18Z Tuesday from north Texas to eastern
Kansas), will deliver both increased moisture and increasing WAA
aloft. The upper trough to the west will also direct an IVT of
300-500 kg/m/s into the Upper Midwest, which is topping the 90th
climatological percentile Tuesday afternoon. There appears to be
sufficiently cold enough air present that precipitation will
transition over from rain to snow from the Black Hills on east
across South Dakota and as far east as central Minnesota Tuesday
afternoon that is largely due to strong 300K isentropic ascent and
850-700mb WAA resulting in FGEN at those mandatory height levels.

There are ongoing differences in the position and strength of this
winter storm. The GFS/CMC camps sports a deeper and more northerly
track storm system. The ECMWF and its AI counterpart (EC-AIFS) are
farther south and take a little longer to ramp up the storm system.
The GEFS is on the slower side of the upper trough's progression,
allowing it to be deeper and phase more effectively with nearby
shortwave troughs. The GEPS is more in between the ECENS, with the
latter being a little flatter and taking longer for the trough to
deepen, thus forcing the storm's more southerly track initially.

The ECMWF EFI continues to depict an increasing signal for a
potentially disruptive winter storm from the Dakotas on east across
northern Minnesota. This also aligns fairly well where WSO values

50% exist on Days 3-4. Both snow amounts, along with snow load

and blowing snow, are likely to be hazards that the Northern Plains
and Upper Midwest contend with through Wednesday, with freezing
rain most likely on the eastern edge of the WAA across northern
Wisconsin and northern Michigan. Current WPC snowfall probabilities
(through 00Z Thursday) for >6" are moderate- to-high chance
(50-80%) across the eastern Dakotas and northern Minnesota. There
are also low-to-moderate chance probabilities (20-40%) for snowfall
totals >12" along the Minnesota Arrowhead. Residents and those
traveling to/from these regions should keep close eyes on the
forecast as additional changes in the types of impacts, the
severity of those impacts, and where/when these impacts occur are
likely to fluctuate for another day or so.


Mullinax






$$

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FOUS11 KWBC 302218
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
618 PM EDT Sun Mar 30 2025

Valid 00Z Mon Mar 31 2025 - 00Z Thu Apr 03 2025


...Northern Great Lakes & Northeast...
Day 1...

The winter storm is in its final hours of producing hazardous
impacts across the northern Great Lakes and northern New England.
On the backside of the storm, periods of snow are ongoing from
northern Iowa and southern Minnesota to northwest Wisconsin and=20
the western Michigan U.P.. Freezing rain is ongoing in parts of
north-central Wisconsin, the eastern Michigan U.P., and from the
White Mountains of New Hampshire on north into Maine. As the storm
heads northeast towards Lake Huron tonight, freezing rain/sleet in
the eastern Michigan U.P. and north-central Wisconsin will
changeover to snow as the deformation zone moves in overhead. The
CAD signature over New England will linger over the White Mountains
and much of Maine (sans the coastal areas) to keep an icy wintry
mix into the early morning hours on Monday. By 12Z Monday, snow
will finally be coming to an end across the northern Great Lakes
while it may take until midday for far northern Maine to finally
see the wintry mix transition to a plain/cold rain.

WPC probabilities show moderate-to-high chances (40-70%) for an
additional >4" of snowfall for areas along the shore of Lake=20
Superior in the MI U.P, the Huron Mountains of the Michigan U.P.,
and into far northern Wisconsin. In terms of additional freezing=20
rain, WPC probabilities show low-to-moderate chances (20-50%) for=20
additional ice accumulations >0.25" in the eastern Michigan U.P.,
the White Mountains, and far western Maine bordering Quebec. Hazardous
travel conditions will linger through Monday morning with the=20
potential for additional power outages in the areas that could see
an additional 0.25" of ice.=20


...The West...
Days 1-3...

An active stretch of wintry weather has begun from the West Coast=20
to the Front Range of the Rockies through Tuesday due to the
prolonged influence of a deep longwave trough over the western
U.S..

This afternoon, focus shifts to an exceptional closed upper low in
the northeast Pacific that slowly makes its way east towards the=20
Pacific Northwest by Monday night. Heavy high elevation mountain=20
snow (above 6,000ft in the northern CA ranges and above 5,000ft in=20
both the Cascade and Blue Mountains) will be underway, but as the=20
upper low inches closer to the Northwest U.S., falling heights and=20
colder temperatures aloft will force snow levels to lower into=20
Monday. By 12Z Monday, NAEFS shows just about all mandatory height=20
levels listed are bottoming out below the 2.5 climatological=20
percentile while IVT values >500 kg/m/s are aimed at southern=20
California. The northern extent of the IVT will sport values >90th climatological percentile through the Sierra Nevada and into the
Great Basin by Monday afternoon. From northern California to the
northern Rockies, the divergent left-exit region of a 200mb jet=20
streak whose wind speeds (>130 kts) are above the 99th=20
climatological percentile will be placed directly overhead.=20

The best moisture advection and upslope enhancement will be seen=20
from California's Siskiyou and Salmon mountains on south and west=20
along the spine of the Sierra Nevada. On Monday afternoon and into=20
Monday night, the flood of Pacific moisture aloft will advance well
inland through much of the Intermountain West. Just about every=20
notable mountain range in the central and northern Rockies is=20
likely to see measurable snow Monday night into Tuesday. Meanwhile,
cyclonic flow around the upper low will still support ongoing=20
upslope snowfall in the central and northern California ranges=20
through Tuesday night. Then by early Tuesday the parent upper low=20
is expected to dive southeast across southwest OR and northern=20
California, proving a final surge of Pacific moisture within an=20
area of cold air aloft. The bulk of the Pacific moisture advection=20
will be finished Tuesday night and into Wednesday, but the core of=20
the longwave trough will be over the Rockies with NAEFS showing=20
500mb temps that are below the 10th climatological percentile from=20
the Sierra Nevada to the Front Range of the Colorado Rockies. With=20
the help of daytime heating, expect numerous snow showers to=20
envelope most of the western U.S. mountain ranges given the steep=20
lapse rates.=20

Through 00Z Thursday, WPC probabilities show the northern ranges=20
of California (Siskiyou, Salmon, Shasta) and the length of the=20
central and northern Sierra Nevada have high chances (>70%) for=20
snowfall totals >24". Most of these ranges above 6,000ft are=20
currently forecast to see localized amounts between 3-5 feet=20
through 00Z Thursday. Heavy snow also reaches into the Oregon=20
Cascades with high probabilities for at least 12". Farther inland,=20
many Intermountain West ranges (Sawtooth, Blue, Uinta, Bear River,=20
Wind River, Absaroka, Big Horn, and CO/WY central Rockies) are all=20
likely to see snowfall totals of 6-12" with locally higher amounts=20
in these ranges as well. Expect hazardous travel conditions for=20
many road ways that remain open in these mountain ranges.


...Northern Plains and Upper Midwest...
Day 3...

By Tuesday morning, the upper trough responsible for the barrage of
mountain snow in the West will position the 250mb jet streak's
divergent left-exit region over the Great Plains. Modest 500mb PVA
and strengthening WAA at low levels will give rise to lee
cyclogenesis east of the Rockies. Throughout the day Tuesday a=20
strengthening LLJ, (NAEFS shows 850mb winds reaching the 97.5=20
climatological percentile 18Z Tuesday from north Texas to eastern=20
Kansas), will deliver both increased moisture and increasing WAA=20
aloft. The upper trough to the west will also direct an IVT of
300-500 kg/m/s into the Upper Midwest, which is topping the 90th
climatological percentile Tuesday afternoon. There appears to be=20 sufficiently cold enough air present that precipitation will=20
transition over from rain to snow from the Black Hills on east=20
across South Dakota and as far east as central Minnesota Tuesday=20
afternoon that is largely due to strong 300K isentropic ascent and
850-700mb WAA resulting in FGEN at those mandatory height levels.

There are ongoing differences in the position and strength of this
winter storm. The GFS/CMC camps sports a deeper and more northerly
track storm system. The ECMWF and its AI counterpart (EC-AIFS) are
farther south and take a little longer to ramp up the storm system.
The GEFS is on the slower side of the upper trough's progression,
allowing it to be deeper and phase more effectively with nearby
shortwave troughs. The GEPS is more in between the ECENS, with the
latter being a little flatter and taking longer for the trough to
deepen, thus forcing the storm's more southerly track initially.=20

The ECMWF EFI continues to depict an increasing signal for a=20
potentially disruptive winter storm from the Dakotas on east across
northern Minnesota. This also aligns fairly well where WSO values=20

50% exist on Days 3-4. Both snow amounts, along with snow load=20

and blowing snow, are likely to be hazards that the Northern Plains
and Upper Midwest contend with through Wednesday, with freezing=20
rain most likely on the eastern edge of the WAA across northern=20
Wisconsin and northern Michigan. Current WPC snowfall probabilities
(through 00Z Thursday) for >6" are moderate- to-high chance=20
(50-80%) across the eastern Dakotas and northern Minnesota. There=20
are also low-to-moderate chance probabilities (20-40%) for snowfall
totals >12" along the Minnesota Arrowhead. Residents and those=20
traveling to/from these regions should keep close eyes on the=20
forecast as additional changes in the types of impacts, the=20
severity of those impacts, and where/when these impacts occur are=20
likely to fluctuate for another day or so.

*Key Messages have been issued for this winter storm, and the link
to view them is posted below.


Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5mUr9saW2mUgdKFInrvm9ZuM7Rj6yaW_mk9Qz_H9fTQ7C= _-eS6dNucShydufYM_Qe9nsM57ZHiEwAoUd4L5Mnhwt2wk$=20

$$

=3D =3D =3D
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FOUS11 KWBC 310743
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
343 AM EDT Mon Mar 31 2025

Valid 12Z Mon Mar 31 2025 - 12Z Thu Apr 03 2025


...The West...
Days 1-2...

An active stretch of wintry weather has begun from the West Coast=20
to the Front Range of the Rockies through Tuesday due to the
prolonged influence of a deep longwave trough over the western
U.S. set to move inland over the next few days. Extreme impacts
forecast throughout much of the central Sierra Nevada.

Focus shifts to an exceptional closed upper low in the northeast=20
Pacific today that slowly makes its way east towards the Pacific=20
Northwest by tonight. Heavy high elevation mountain snow (above=20
5000ft in the central Sierra and above 4000ft in both the Cascades
and northern CA ranges) will be underway, but as the upper low=20
inches closer to the Northwest U.S., falling heights and colder=20
temperatures aloft will force snow levels to lower additionally on=20
Day 1 to around 3000ft. The primary IVT axis will be aimed at
southern CA through Day 2, but broad onshore flow and an axis of
greater convergence just to the south of the upper low will provide
ample moisture and upslope flow for the Pacific Mts to experience
very heavy snowfall. The northern extent of the IVT will still sport
values >90th climatological percentile through the Sierra Nevada=20
and into the Great Basin this afternoon. From northern California=20
to the northern Rockies, the divergent left- exit region of a 200mb
jet streak whose wind speeds (>130 kts) are above the 99th=20
climatological percentile will be placed directly overhead.=20

The best moisture advection and upslope enhancement will be seen=20
from California's Siskiyou and Salmon mountains on south and west=20
along the spine of the Sierra Nevada. Through tonight, the flood=20
of Pacific moisture aloft will advance well inland through much of=20
the Intermountain West. Just about every notable mountain range in=20
the central and northern Rockies is likely to see measurable snow
into Tuesday. Meanwhile, cyclonic flow around the upper low will=20
still support ongoing upslope snowfall in the central and northern=20 California ranges through Tuesday night. Then by early Tuesday the=20
parent upper low is expected to dive southeast across southwest OR=20
and northern California, proving a final surge of Pacific moisture=20
within an area of cold air aloft. The bulk of the Pacific moisture=20
advection will be finished Tuesday night and into Wednesday, but=20
the core of the longwave trough will be over the Rockies with NAEFS
showing 500mb temps that are below the 10th climatological=20
percentile from the Sierra Nevada to the Front Range of the=20
Colorado Rockies. With the help of daytime heating, expect numerous
snow showers to envelope most of the western U.S. mountain ranges=20
given the steep lapse rates.=20

Through 12Z Wednesday, WPC probabilities show the northern ranges=20
of California (Siskiyou, Salmon, Shasta) and the length of the=20
central and northern Sierra Nevada have high chances (>70%) for=20
snowfall totals >24". Most of these ranges above 6,000ft are=20
currently forecast to see localized amounts between 3-5 feet=20
through 12Z Wednesday, with WSSI depicting Extreme impacts due to
both snowfall amounts and blowing snow. Travel delays and road
closures are likely at many of the major Sierra passes. Heavy snow
also reaches into the Oregon Cascades with high probabilities for=20
at least 12". Farther inland, many Intermountain West ranges=20
(Sawtooth, Blue, Uinta, Bear River, Wind River, Absaroka, Big Horn,
and CO/WY central Rockies) are all likely to see snowfall totals=20
of 6-12" with locally higher amounts in these ranges as well.=20
Expect hazardous travel conditions for many road ways that remain=20
open in these mountain ranges.


...Northern Plains and Upper Midwest...
Days 2-3...

By Tuesday morning, the upper trough responsible for the barrage of
mountain snow in the West will position the 250mb jet streak's
divergent left-exit region over the Great Plains. Modest 500mb PVA
and strengthening WAA at low levels will give rise to lee
cyclogenesis east of the Rockies. Throughout the day Tuesday a=20
strengthening LLJ, (NAEFS shows 850mb winds reaching the 97.5=20
climatological percentile 18Z Tuesday from north Texas to eastern=20
Kansas), will deliver both increased moisture and increasing WAA=20
aloft. The upper trough to the west will also direct an IVT of
300-500 kg/m/s into the Upper Midwest, which is topping the 90th
climatological percentile Tuesday afternoon. There appears to be=20 sufficiently cold enough air present that precipitation will=20
transition over from rain to snow from the Black Hills on east=20
across South Dakota and as far east as central Minnesota Tuesday=20
afternoon that is largely due to strong 300K isentropic ascent and
850-700mb WAA resulting in FGEN at those mandatory height levels.
Given the early-April sun angle, snowfall will struggle to
accumulate during the day on Tuesday unless rates can reach >1"/hr.
These rates appear most likely after the 21z timeframe once WAA=20
strengthens and could kick start treacherous travel conditions=20
into the overnight period.

There are still some ongoing difference with respect to details,
including how far north the rain/snow line reaches in central MN on
Wednesday, as well as banding potential in the
northern/northwestern precipitation shield within the deformation=20
zone from the Dakotas through northern MN. However, most guidance=20
highlights a similar area of heavy snowfall extending from=20
northeast SD and southeast ND across much of northern MN.

The ECMWF EFI continues to depict an strong signal (values of
0.8-0.9) for a potentially disruptive winter storm from the far=20
eastern Dakotas on east across northern MN. This also aligns fairly
well where WSO values >50% exist on Days 2-3. Both snow amounts,=20
along with snow load and blowing snow, are likely to be hazards=20
that the Northern Plains and Upper Midwest contend with through=20
Wednesday, with freezing rain most likely on the eastern edge of=20
the WAA across northern Wisconsin and northern Michigan. Current=20
WPC snowfall probabilities (through 00Z Thursday) for >8" are=20
moderate- to-high chance (50-70%) across northeast SD, southeast
ND, and northern Minnesota. High probabilities (70-90%) for >8"
exist across the MN Arrowhead. There are also low probabilities=20
(10-30%) for snowfall totals >12" in this region, highest and up to
50% in the MN Arrowhead. Residents and those traveling to/from=20
these regions should keep close eyes on the forecast as additional=20
changes in the types of impacts, the severity of those impacts, and
where/when these impacts occur are likely to fluctuate for another
day or so.

*Key Messages have been issued for this winter storm, and the link
to view them is posted below.


Snell/Mullinax




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4Qu_F5oWxFazWVx-P75TDsvX6JgLRewTq40bPOcPx5pCX= IiXxPsrO6FpwWbUQCi2s7Aa0cf6c80lQI-bUnsxcCFZuKc$=20

$$

=3D =3D =3D
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FOUS11 KWBC 311859
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
259 PM EDT Mon Mar 31 2025

Valid 00Z Tue Apr 01 2025 - 00Z Fri Apr 04 2025


...The West...
Days 1-3...

Elongated Pacific jet coming into NorCal/northern Sierra this=20
afternoon will transition towards a more amplified pattern over the
next day or two as ridging builds into the Gulf of Alaska,=20
favoring downstream troughing into the Western CONUS. Heavy snow is
likely for the northern/central Sierra with major to locally=20
extreme impacts. From the Great Basin eastward, a wide area of=20
snowfall is forecast for the Interior West with modest snows for=20
the northern/central Rockies.=20

The day 1 period features the system that already moved onshore=20
with heavy snow into the Sierra decreasing a bit by tomorrow=20
morning behind the trough axis, but the pattern will support waves=20
of vorticity moving into/through the West Coast as the jet digs=20
farther south. Snow will quickly expand to the central Rockies=20
tonight in the core of the moisture plume that reaches near the=20
90th percentile into the San Juans. Snow levels between 5000-8000ft
to start (this afternoon at 00Z) will continue to fall behind the=20
cold front to around 4000ft or so (Sierra into the Great Basin) but
below 3500ft over the Cascades. By day 2, the trough axis will=20
broaden out as the downstream northern Plains system develops,=20
favoring lighter snowfall for much of the Interior West. The=20
exception may be around SW Montana into the Bighorns near the=20
backside of the developing upper low (again, tied to the northern=20
Plains system). Snow will also expand southward as the jet dips=20
into SoCal and central AZ/NM with some snow to the Mogollon Rim.=20

By day 3, the upper ridge over the Pacific will start to drift to=20
the West Coast, helping to lessen QPF/snowfall for the Cascades to=20
the Sierra. Inland, northern stream height falls are forecast to=20
move southward out of western Canada into the northern Rockies=20
which will favor some modest snowfall over NW MT aided by upslope=20 enhancement. To the south, continued SW flow across the Four=20
Corners will yield some light to modest snow for the San Juans to=20
the northern Sangre de Cristos northward to the Sawatch Range.=20

Total snowfall over the three-day period will likely be highest=20
over the northern/central Sierra and over parts of the northern=20
Rockies in MT. For the Sierra, WPC probabilities for at least 18=20
inches of snow are high (>70%) above 5000-6000ft or so (from north=20
to south) Inland, WPC probabilities for at least 12 inches of snow=20
are above 50% above about 5000-6000ft (MT), 7000ft (Tetons),=20
8000-9000ft (Wasatch), and 10,000ft (CO).=20

Fracasso


...Northern Plains, Upper Midwest, & Northeast...
Days 2-3...

The upper trough responsible for the barrage of mountain snow in=20
the West will position the 250mb jet streak's divergent left-exit=20
region over the Great Plains. Modest 500mb PVA and strengthening=20
WAA at low levels will give rise to lee cyclogenesis east of the=20
Rockies on Tuesday. Throughout the day Tuesday, a strengthening=20
LLJ, (NAEFS shows 850mb winds exceeding the 97.5 climatological=20
percentile 18Z Tuesday from north Texas to eastern Nebraska), will=20
deliver both rich moisture and increased levels of WAA aloft. The=20
upper trough to the west will also direct an IVT of 300-500 kg/m/s=20
into the Upper Midwest, which is approaching the 97.5=20
climatological percentile by late afternoon. This causes strong=20
300K isentropic ascent and 850-700mb WAA resulting in FGEN at those
mandatory height levels. There also appears to be sufficiently=20
cold enough air present, thanks to a nearby dome of Canadian high=20
pressure, for precipitation to transition over from rain to snow=20
from the Black Hills on east across South Dakota and as far east as
central Minnesota Tuesday afternoon. Given the early-April sun=20
angle, snowfall will struggle to accumulate during the day on=20
Tuesday unless rates are >1"/hr. These rates appear most likely to=20
occur Tuesday night once the deformation zone on the northern and=20
western flanks of the 850mb low consolidates, allowing for=20
treacherous travel conditions to rapidly unfold into the overnight=20
and into Wednesday.

Even as we are now inside of 48 hours from the peak of the event,=20
there are still some ongoing difference with respect to some=20
details. The GFS/CMC suite remains on the northern envelope of=20
track solutions, while the ECMWF/EC-AIFS are on the southern flank.
When accounting for ensemble guidance, which takes into account=20
snowfall between Tuesday afternoon and Wednesday night, most=20
guidance favors an area of heavy snowfall extending from northeast=20
South Dakota and southeast North Dakota across much of northern=20
Minnesota. The latest ECMWF EFI has shifted a strong signal (values
of 0.8-0.9) for a potentially disruptive winter storm across much=20
of northern Minnesota, but still sports modest 0.7-0.8 values in=20
eastern North Dakota.

The Northern Plains and Upper Midwest will contend winter hazards=20
such as heavy snow, blowing snow, and snow load on tree branches=20
and power lines starting late Tuesday and continuing through=20
Wednesday. Current WPC snowfall probabilities (through 00Z=20
Thursday) for >8" are moderate-to-high chance (50-70%) across=20
northeast SD, southeast ND, and northern Minnesota. High=20
probabilities (70-90%) for >8" exist across the MN Arrowhead. There
are also low probabilities (10-30%) for snowfall totals >12" in=20
this region as well, with the highest and up to 50% in northeast=20
South Dakota and the MN Arrowhead. In terms of ice, freezing rain=20
is likely on the eastern edge of the WAA across northern Wisconsin,
northern Michigan, and even as far east as far northeast=20
Pennsylvania and western New York. Most ice accumulations will be=20
<0.1", with the lone exception being northern Michigan where there=20
are low-to- moderate chances (20-50%) for ice accumulations >0.1"=20
on Wednesday. Residents and those traveling to/from these regions=20
should continue to monitor the forecast as additional changes in=20
the types of impacts, the severity of those impacts, and where/when
these impacts occur can still fluctuate.

Farther east, the aforementioned Canadian air-mass will be=20
departing off the Atlantic Canadian Maritime Wednesday night, but=20
boundary layer wet-bulb temperatures remain sufficiently cold=20
enough for some wintry precipitation in northern New England=20
Wednesday night and early Thursday morning. The WAA is quite strong
and the air-mass in marginally cold, so ice accumulations will be=20
limited to the northern Appalachian ranges (Adirondack, Green,=20
White) and across northern Maine. WPC probabilities show low-to-=20
moderate chances (10-40%) for ice accumulations >0.1" through=20
Thursday morning. By midday Thursday, rain will be the primary=20
precipitation type throughout most of northern New England (far=20
northern Maine the lone exception).=20

*Key Messages have been issued for this winter storm, and the link
to view them is posted below.


Snell/Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!9f_CYpb8IjjGL2W-OlDkjh8giuHnrKvYZMtTm4BUor8ii= -vM83FiAGr80sKX07Af5HLCSONMCidlzIC_8fSXZT3vuSk$=20

$$

=3D =3D =3D
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FOUS11 KWBC 010804
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Tue Apr 1 2025

Valid 12Z Tue Apr 01 2025 - 12Z Fri Apr 04 2025


...Northern Plains & Upper Midwest...
Days 1-2...

A major winter storm is set to develop today and strengthen=20
through Wednesday across the Northern Plains as a deep upper trough
traverses across the Great Basin and ejects a closed low over the=20
region. This upper level setup places a developing surface cyclone=20
over the central Plains this afternoon into a favorable left-exit=20
region of a potent 150kt 250mb jet diving across the Southwest.=20
Throughout the day today, a strengthening LLJ, (NAEFS shows 850mb=20
winds exceeding the 97.5 climatological percentile 18Z this=20
afternoon from north Texas to eastern Nebraska), will deliver both=20
rich moisture and increased levels of WAA aloft. The upper trough=20
to the west will also direct an IVT of 300-500 kg/m/s into the=20
Upper Midwest, which is approaching the 97.5 climatological=20
percentile by late afternoon. This causes strong 300K isentropic=20
ascent and 850-700mb WAA resulting in FGEN at those mandatory=20
height levels. There also appears to be sufficiently cold enough=20
air present, thanks to a nearby dome of Canadian high pressure, for precipitation to transition over from rain to snow from the Black=20
Hills on east across South Dakota and as far east as central=20
Minnesota by late this afternoon. Given the early-April sun angle,=20
snowfall will struggle to accumulate during the day unless rates=20
are >1"/hr. These rates appear most likely to occur tonight into=20
early Wednesday once the deformation zone on the northern and=20
western flanks of the 850mb low consolidates, allowing for=20
treacherous travel conditions to rapidly unfold. 00z HREF depicts=20
an initial wave of of WAA advection heavy snow (max rates around=20
1"/hr) lifting northward this evening from the Dakotas across=20
central MN into northern WI. Then by about 11z/Weds the surface low
lifts north to become vertically stacked while anomalous IVT=20
advect from the southeastern flank to produce heavy deformation=20
snow bands with rates up to 2"/hr across the eastern Dakotas and=20
northern MN.

Guidance has consolidated on the heaviest snowfall occurring from
the eastern SD-ND border through central/northern MN. The latest=20
ECMWF EFI has shifted a strong signal (values of 0.8-0.95) for a=20
potentially disruptive winter storm across much of northern=20
Minnesota, but still sports modest 0.7-0.8 values in eastern North=20
Dakota and even northeast WI.There also remains modest signal in
hires CAMs and a few global models for QPF enhancement along the
north shores of Lake Superior in the MN Arrowhead due to strong
east-northeast flow and an associated upslope component. The 00z
HREF was particularly aggressive (probably too much so) and will
need to be monitored for an axis of particularly heavy snowfall.

These aforementioned areas will contend winter hazards such as=20
heavy snow, blowing snow, and snow load on tree branches and power=20
lines today through Wednesday night. A few locations, including
Fargo, ND (9.9") and Duluth, MN (12.7") could near 1-day April=20
snowfall records per the 75th percentile NBM. Current WPC snowfall probabilities (through 12Z Thursday) for >8" are moderate- to-high
(50-70%) across northeast SD, southeast ND, and northern=20
Minnesota. High probabilities (70-90%) for >8" exist across the MN=20 Arrowhead, where moderate probabilities (40-70%) for snowfall=20
totals >12" exist as well. For WI and MI, moderate probabilities=20
(40-60%) are found across northeast WI into the south-central MI=20
U.P.. In terms of ice, impactful freezing rain is most likely on=20
the eastern edge of the WAA across northern Wisconsin and into the=20
MI L.P.. Most ice accumulations will be <0.1" due to the rapid=20
warming of the low- mid levels, with the lone exception being=20
northern Michigan Mitten, where there are low-to- moderate chances=20
(30-60%) for ice accumulations >0.1" on Wednesday. Residents and=20
those traveling to/from these regions should continue to monitor=20
the forecast as additional changes in the types of impacts, the=20
severity of those impacts, and where/when these impacts occur can=20
still fluctuate.

*Key Messages have been issued for this winter storm, and the link
to view them is posted below.


...Northeast...
Days 2-3...

Farther east along and north of a lifting warm front, the=20
aforementioned Canadian air- mass will be departing off the=20
Atlantic Canadian Maritime Wednesday night, but boundary layer wet-
bulb temperatures remain sufficiently cold enough for some wintry=20 precipitation in northern New England and parts of the Interior
Northeast Wednesday night and early Thursday morning. The WAA is=20
quite strong and the air- mass in marginally cold, so ice=20
accumulations will be limited to the northern Appalachian ranges=20 (Adirondack, Green, White) and across northern Maine. WPC=20
probabilities show moderate chances (30-60%) for ice accumulations

0.1" through Thursday morning. By midday Thursday, rain will be=20

the primary precipitation type throughout most of northern New=20
England (far northern Maine the lone exception).=20


...California through the Intermountain West...
Day 1...

One additional day of heavy mountain snow is forecast across the
CA ranges and Sierra Nevada through the central Great Basin as an
upper low dives across northern California into the Southwest. This
pattern during the Day 1 period provides broad onshore flow with a
weak focus (and 300 kg/m/s IVT) into the Klamath Mts during the day
today. Snow levels will also remain relatively low and around
3000-4000ft (below major passes) given the upper low crossing=20
directly overhead. Strong westerly flow also provides upslope=20
enhancement across the central Great Basin ranges of NV and UT,=20
where snow levels are expected to remain around 4000 ft. WPC
probabilities for an additional foot of snow are high (70-90%)
across the central Sierra Nevada. Moderate chances for >8" exist in
the northern California Mts, central Nevada ranges, and into the UT
ranges as well.


...Rockies...
Days 1-3...

Multiple systems are forecast over the next few days to impact the
Rockies with moderate snowfall due to a deep upper trough entering
the region and an associated upper low closing off/lingering over
the Southwest through Thursday. For Day 1, strong westerly flow
provides prime upslope potential across the CO Rockies,
particularly for the first half of today. Snow levels start the day
around 5000-6000ft crash to below 4000ft tonight, but also as
Pacific moisture advection decreases and the column gradually dries
out. Meanwhile, as an upper low ejects into the northern Plains a
upper trough inflection leads to some modest convergence across the
MT ranges into the Bighorns.

For Day 2 there appears to be a bit of a lull in activity as the
initial upper low ejects eastward and a trailing upper low digs=20
into the Southwest (cutting off the greatest moisture flux to the=20
south). However, deep troughing (200 mb heights below the 0.5th=20 climatological percentile at the start of Day 2 per the 12z NAEFS)
will allow for steeping lapse rates and scattered snow showers in=20
the high elevations.=20

By Day 3 a shortwave dives south into the northern Rockies and
provides upslope flow in the western MT and northwest WY ranges,
but with moisture relatively meager. Meanwhile, a lobe of vorticity
rounding the base of the deep southwestern U.S. trough ejects into
the central Rockies and spreads light-moderate snowfall potential
into the region, with snow also possible into the CO Front Range on
Thursday. Overall WPC probabilities for Day2-3 are moderate for >6"
both days across most of the Northern and Central Rockies spanning
from northwest MT to the San Juans of CO.

Snell




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5g2a-zWvojf-QV5WRCqARcgVIbBj7rZ-lf3AivSPqDWgv= KeQFjbgAjvgn2TzYNeFIOn3cMWhtWqV6ZFH4Q8zfbrsyUc$=20

$$

=3D =3D =3D
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FOUS11 KWBC 011840
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
240 PM EDT Tue Apr 1 2025

Valid 12Z Tue Apr 01 2025 - 12Z Fri Apr 04 2025


...Northern Plains & Upper Midwest...
Days 1-2...

...Major winter storm to bring heavy snow and gusty winds to
portions of the Dakotas and Minnesota. Key Messages have been
issued for this system and are linked below...

This is no April Fool's joke - a major winter storm will develop
late tonight and then expand and intensify into Minnesota late
Wednesday. The trough responsible for this evolution will be
elongated across the western CONUS at the start of the forecast
period, with an embedded shortwave trough sharpening and digging=20
across the Northern Plains by Wednesday morning. As shortwave
amplifies, it will close off over SD Wednesday, and the continue=20
to deepen, with 850-500mb heights dropping to below the 1st=20
percentile within the NAEFS CFSR climatology. This indicates a=20
strong system, and as the strongest height falls and PVA from the=20
mid-level evolution overlap with the increasingly intense=20
diffluence within the LFQ of a pivoting jet streak, a strong and=20 intensifying surface cyclone will develop and track from eastern=20
Nebraska through the Arrowhead of MN before exiting into Canada=20
Thursday aftn.

There continues to be some latitudinal spread amongst the various
global model systems, leading to a bit lower confidence in the
exact track of the low and subsequent placement of the greatest
impacts. The GEFS/CMCE systems are more aligned with each other
with the surface low track, and are both a bit north of the ECE
ensembles. The key difference appears to be with the dominant
surface, as the ECMWF wants to keep the southern edge of the
elongated low the dominant feature, whereas the GFS and CMC make
the northern low the primary feature. The GFS/CMC also are more
aligned with the now available high-res guidance, so the northern
track seems a bit more supported. Additionally, looking at the D3
clusters (from yesterday), the EC cluster is heavily influenced by
its own ensembles (74%) so it may be a bit under-dispersive as
well. This indicates that a more northern low track is probable
which will allow for warm air to flood farther north, leading to
a mixed precipitation axis from both a warm nose and a subsequent
dry slot, from far northeast SD to potentially across the
Arrowhead.

Northwest of this, however, significant snow accumulations with
heavy snow rates and gusty winds are likely. Despite the now
early-April sun, a potent deformation axis overlapped with an
increasingly impressive TROWAL, especially across northern MN, will
cause heavy snow rates for which the WPC prototype snowband tool
and the HREF probabilities suggest will reach 1-2"/hr. Even these
kinds of rates could overwhelm the warmth due to April sun, leading
to rapid snow accumulations. The heaviest snow amounts are likely
from eastern ND through northern/central MN where the potent
deformation axis will pivot and then translate northeast. Here, WPC probabilities are high for 6+ inches of snow, with locally 8-12
inches possible. The Arrowhead of MN will also be a focus for
locally heavier snowfall as reflected by a 70-90% chance for 8
inches here, but there remains some uncertainty into how
effectively lake enhancement can occur.=20

South of this axis of heavy snow, a swath of mixed precipitation,
including freezing rain, is likely. The heaviest icing is expected
across the Coteau of SD, and parts of lower MI, where WPC
probabilities for 0.1" of ice or more range from 10-50%.


...Northeast...
Day 2...

The same system that will bring the major winter storm to the
Northern Plains/Upper Midwest will bring some wintry weather to the
Northeast as well. As the primary surface low over MN occludes to
the east into the Great Lakes, an attendant warm front will begin
to lift northeast downstream of this secondary low pressure. As
this warm front lifts into the Northeast, it will spread increasing
moisture across Upstate NY and northern New England, especially
after 00Z Thursday. The accompanying lift through WAA will ascend isentropically, especially along the 290K-295K surfaces, which=20
will push PWs to above the 99th climatological percentile according
to NAEFS, while at the same time driving a warm nose above 0C=20
northward. The impressive ascent along this warm front will result=20
in axis of heavy precipitation, but with p-type gradually changing=20
from snow to a mix to rain, even into northern Maine. The fast=20
progression of this event, combined with heavy precipitation rates,
and the transitioning p-type will limit overall amounts, but=20
impacts will still be notable due to snow, sleet, and freezing=20
rain. WPC probabilities for more than 4 inches of snow are modest=20
at just 30-50% in the higher terrain of NH and ME, but more than=20
0.5" of sleet is possible across a larger portion of those areas.=20 Additionally, freezing rain has a 50-70% chance of accreting to=20
more than 0.1" of ice across the Adirondacks, southern Greens, the=20
Northeast Kingdom of VT, and northern NH.


...California...=20
Day 1...

A shortwave trough embedded within the much larger trough
encompassing much of the West will advect onshore central CA at the
start of the period and then continue to traverse southeast into
the Great Basin Wednesday aftn. Confluent flow south of this
feature combined with a slowly departing jet streak will maintain
steady moisture advection onshore, characterized by IVT that will
continue above 250 kg/m/s the first half of D1. This moisture will
be forced efficiently into the Sierra, with upslope flow wringing
out moderate to heavy snow above generally 3000 feet. While the
heaviest accumulations are likely before this forecast period,
additional snowfall will still be significant as snow rates remain
above 1"/hr at times, and many of the area passes will experience=20
impacts to travel. WPC probabilities for more than 6 inches of=20
additional snowfall after 00Z tonight are as high as 70% across the
higher terrain of the Sierra.


...Rockies...
Days 1-3...

Widespread light to moderate snow D1-D2 potentially becomes more
significant across the Southern/Central Rockies late D3.

For D1 and D2 /00Z Wednesday through 00Z Friday/, the entire region
will be covered by large but diffuse troughing extending from the
Pacific Coast through the High Plains. Beneath this large and slow
moving trough, waves of vorticity will rotate through, leading to
periods of enhanced ascent within steep low level lapse rates and
aided by upslope flow. In general, this forcing will be modest
across the region, but an exception is likely across southern
Montana into Wyoming on D1, where a stalled cold front and
accompanying weak wave of low pressure will drive more pronounced
ascent through fgen leading to areas of heavy snow. The heaviest
accumulations D1 are likely above 3500 ft in this region, where WPC probabilities indicate a high risk (>70%) for more than 4 inches of
snow in the Absarokas, Wind Rivers, and into the Black Hills of SD.=20 Elsewhere on D1, light to moderate snowfall across much of the
terrain from the Four Corners and Great Basin Northward has a less
than 30% chance of exceeding 4 inches.

Then through much of D2 forcing again remains modest but widespread
across the Rockies, leading to areas of light to moderate snow in
most of the terrain. A local exception will again exist, this time
across the Northern Rockies and maybe as far south as Yellowstone
NP as a cold front digs out of Canada leading to some increased
fgen and enhanced upslope flow in its wake. This will cause=20
heavier snow rates and at lower snow levels (falling to 2000-3000=20
ft) leading to accumulations that have a high risk (>70% chance) of
exceeding 6 inches around Glacier NP, and 10-30% chance around=20
Yellowstone. Some locally heavier snow is also expected D3 in the=20
vicinity of the Four Corners, especially across UT and CO as a=20
shortwave pivots northeast, and WPC probabilities indicate a=20
moderate risk (30-50%) for more than 6 inches in the southern=20
Wasatch and San Juans.

Then during D3, more impressive and consolidated ascent begins to=20
manifest across the central and southern Rockies, generally from WY
through CO and into NM as the tail shortwave within this larger
trough begins to amplify. There is good agreement that this
shortwave will close off and dig south into the Deserts of AZ,
leading to increasingly impressive mid-level divergence downstream.
At the same time, a subtropical jet streak will intensify and
rotate around the base of this amplifying closed low to place
favorable LFQ ascent into the eastern Rockies, while additionally
the cold front from D2 across the northern Rockies drops south
across WY and CO. The overlap of this baroclinic gradient with the
increasing synoptic ascent could result in an impressive area of
expanding precipitation D3 and even moreso into D4. There is still
uncertainty into the exact evolution of this event, and current WPC probabilities are modest (10-30%) for more than 6 inches of snow,
but during D4 these could increase and expand more impressively.

Weiss




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!6WEDA2CvdT8QFXOcUdZ3aRrtFh7-VP9e1VTjzTv8RU8JK= QUyqkK0UBE7kDNlV3WXkGPz39wKZQS_4UldHFqJigncBrE$=20

$$

=3D =3D =3D
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FOUS11 KWBC 020719
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 AM EDT Wed Apr 2 2025

Valid 12Z Wed Apr 02 2025 - 12Z Sat Apr 05 2025


...Northern Plains & Upper Midwest...
Day 1...

...Major winter storm to bring heavy snow and gusty winds to
portions of the Dakotas and Minnesota today. Key Messages have=20
been issued for this system and are linked below...

The storm system responsible for today's heavy April snow is=20
currently organizing across the central Plains early this morning=20
with an initial impulse of WAA snow showers lifting northward=20
across the Dakotas and Upper Midwest. At the start of the forecast=20
period, broad and deep upper troughing will be situated over the=20 Intermountain West as an ejecting shortwave lifts northward in=20
conjunction with a ridge building over the East Coast. As this=20
shortwave amplifies, it will close off over eastern SD this=20
afternoon and then continue to deepen while sliding northeast=20
across northern MN this evening. For context, the 850-700mb heights
associated with this low pressure system are forecast to drop=20
below the 0.5 percentile and even near the 18Z record minimum=20
within the NAEFS CFSR climatology. This indicates a strong system,=20
and as the strongest height falls and PVA from the mid-level=20
evolution overlap with the increasingly intense diffluence within=20
the LFQ of a pivoting jet streak, a strong and intensifying surface
cyclone will track from eastern Nebraska through the Arrowhead of=20
MN before exiting into Canada Thursday aftn. With this track, the
heaviest snowfall will occur just to the north and northwest of the
low center.

Two main areas most likely to experience heavy snowfall rates=20

1"/hr and accumulating snow despite the early-April sun are along=20

the MN Arrowhead and north shores of Lakes Superior, as well as a=20
corridor from the SD/ND/MN border intersection through northern MN.
The latter region will fall with a potent deformation axis=20
overlapped with an increasingly impressive TROWAL, especially=20
across from west-central through northern MN, causing heavy snow=20
rates for which the WPC prototype snowband tool and the HREF=20
probabilities suggest will reach 1-2"/hr. Even these kinds of rates
could overwhelm the warmth due to April sun, leading to rapid snow accumulations. These impressive snowfall rates may also occur for
several hours (roughly 14Z-21Z per the 00Z HREF) as the upper low=20
crosses overhead and pivots the TROWAL over west-central MN and=20
the eastern Dakotas, which led to an increase in snowfall here
compared to the prior forecast. Here, WPC probabilities are=20
moderate (50-70%) for 6+ inches of snow, with locally 8-10 inches=20
possible. The Arrowhead of MN will also be a focus for locally=20
heavier snowfall as reflected by a 70-90% chance for 8 inches here,
but there remains some uncertainty into how effectively lake=20
enhancement can occur.=20

South of this axis of heavy snow, a swath of mixed precipitation,
including freezing rain, is likely. The heaviest icing is expected
across and parts of lower MI, where WPC probabilities for 0.1" of=20
ice or more range from 10-30%.


...Northeast...
Days 1-2...

The same system that will bring the major winter storm to the
Northern Plains/Upper Midwest will bring some wintry weather to the
Northeast as well. As the primary surface low over MN occludes to
the east into the Great Lakes, an attendant warm front will begin
to lift northeast downstream of this secondary low pressure. As
this warm front lifts into the Northeast, it will spread increasing
moisture across Upstate NY and northern New England, especially
after 00Z Thursday. The accompanying lift through WAA will ascend isentropically, especially along the 290K-295K surfaces, which=20
will push PWs to above the 99th climatological percentile according
to NAEFS, while at the same time driving a warm nose above 0C=20
northward. The impressive ascent along this warm front will result=20
in axis of heavy precipitation, but with p-type gradually changing=20
from snow to a mix to rain, even into northern Maine. The fast=20
progression of this event, combined with heavy precipitation rates,
and the transitioning p-type will limit overall amounts, but=20
impacts will still be notable due to snow, sleet, and freezing=20
rain. WPC probabilities for more than 4 inches of snow are modest=20
at just 30-50% in the higher terrain of NH and ME, but more than=20
0.5" of sleet is possible across a larger portion of those areas.=20 Additionally, freezing rain has a 50-70% chance of accreting to=20
more than 0.1" of ice across the Adirondacks, southern Greens, the=20
Northeast Kingdom of VT, and northern NH into neighboring ME.


...Rockies into the CO Front Range...
Days 1-3...

Widespread light to moderate snow D1-D2 potentially becomes more
significant across the Southern/Central Rockies late D3.

For D1 and D2 /12Z Wednesday through 12Z Friday/, the entire=20
region will be covered by large but diffuse troughing extending=20
from the Pacific Coast through the High Plains. Beneath this large=20
and slow moving trough, waves of vorticity will rotate through,=20
leading to periods of enhanced ascent within steep low level lapse=20
rates and aided by upslope flow. In general, this forcing will be=20
modest across the region, but a local exception will exist across=20
the Northern Rockies and maybe as far south as Yellowstone NP as a=20
cold front digs out of Canada leading to some increased fgen and=20
enhanced upslope flow in its wake by the end of D1 into D2. This=20
will cause heavier snow rates and at lower snow levels (falling to=20
2000-3000 ft) leading to accumulations that have a high risk (>70%=20
chance) of exceeding 6 inches around Glacier and northern Absarokas.
Elsewhere on D1 and D2, moderate to locally heavy snowfall across=20
much of the terrain from the Four Corners and UT ranges into the CO
Rockies has 30-50% chances of exceeding 6 inches, primarily above=20
8000 ft. This is in response to a shortwave rounding the base of=20
the trough in the Southwest pivoting over the Four Corners.

Then during D3, more impressive and consolidated ascent begins to=20
manifest across the central and southern Rockies, generally from WY
through CO and into NM as the tail shortwave within this larger
trough begins to amplify. There is good agreement that this
shortwave will close off and dig south into the Deserts of AZ,
leading to increasingly impressive mid-level divergence downstream.
At the same time, a subtropical jet streak will intensify and
rotate around the base of this amplifying closed low to place
favorable LFQ ascent into the eastern Rockies, while additionally
the cold front from D2 across the northern Rockies drops south
across WY and CO. The overlap of this baroclinic gradient with the
increasing synoptic ascent could result in an impressive area of
expanding precipitation D3 and bleeding into D4, with snow levels
starting around 6000 ft and dropping below 4000 ft and snow into
the High Plains. There is still uncertainty into the exact=20
evolution of this event and how far heavy snow extends into the CO=20
Front Range. Current WPC probabilities on D3 are high (60-90%) for
more than 8 inches of snow in the Sangre de Cristos and eastern San
Juans, with slightly lower into the central and northern CO Mts.


Snell/Weiss




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4OjFZulW8VEM2cyI4-HUPZg-M3eKdDPLgARB_Yx2eWjwf= -iC-wdijc2S98Jkvf9f_9BIBbYu8zg4o9sYeVhxwmGCdec$=20

$$

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FOUS11 KWBC 021904
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
304 PM EDT Wed Apr 2 2025

Valid 00Z Thu Apr 03 2025 - 00Z Sun Apr 06 2025


...Northern Plains & Upper Midwest...
Day 1...

...Major winter storm continues to bring heavy snow and gusty winds
through Thursday afternoon. Key Messages have been issued for this
system and are linked below...

The system which is expected to bring a late season major winter
storm to the Dakotas and Minnesota is organizing this morning as
reflected by an increase in reflectivity across the region in the
vicinity of increasing 925-700mb PVU. This system will deepen today
in response to a mid-level closed low deepening as it moves across
Minnesota and into Ontario by Thursday morning. This low will
become quite intense, reflected by NAEFS 850-700mb height=20
anomalies falling below the 1st percentile in the CFSR database,
with similar 500mb anomalies dropping below 2.5 percentile. This is
reflective of a strong system, with surface low deepening
encouraged by the robust height falls and concurrent/overlapping
upper diffluence as a strengthening jet streak pivots poleward
downstream of the mid-level low. The guidance has come into better
agreement today with the track of this surface low, and it is
expected to track from near Minneapolis this aftn through the
western U.P. of MI by Thursday morning.

This evolution will have a two-pronged impact on the winter weather
impacts. First, this slightly more northern track will help push a
dry slot and a warm nose northward leading to an axis of light
sleet and freezing rain, but accumulations are expected to be
minimal.

More significantly, NW of the surface low, a potent deformation
axis is progged to develop and pivot from eastern ND/SD through
north-central MN. This deformation axis will occur concurrently
with an intensifying TROWAL as theta-e advection on moist
isentropic ascent increases and wraps cyclonically around the
system. The TROWAL will be most impressive from generally 18Z today
through 06Z Thursday across N-Central MN, and cross-sections within
this region suggest a threat for CSI to enhance snowfall rates.
This is additionally supported by both the WPC prototype snowband
tool and HREF snowfall rate probabilities which indicate a moderate
to high risk (50-80%) for 1+"/hr rates, with locally 2"/hr rates
possible. This will overwhelm antecedent warmth and the April sun,
leading to rapid snowfall accumulation beneath this deformation,
and WPC probabilities are moderate (30-50%) for an additional 4+
inches after 00Z, with storm total snowfall of 6-10" in some areas.=20
While there is still some uncertainty into the exact placement of=20
this deformation, and the gradient on the NW and SE side should be=20
pretty significant, this band of heavy snow will be impactful=20
before the entire system exits to the northeast by late Thursday=20 morning/early Thursday aftn.


...Northeast...
Days 1 & 3...

The same system that will be producing heavy snow across the Upper
Midwest D1 will occlude to a secondary low and attendant warm
front farther east. This warm front will lift northeast into
Upstate NY and New England tonight into Thursday, bringing a period
of heavy precipitation through Thursday aftn. The front will lift
rapidly northward, so the duration of precipitation will be
limited, and p-types will vary widely as the warm nose causes a
change from snow, to sleet, to freezing rain, and eventually rain
before ending (likely ending as freezing rain the highest terrain
of NH and northern ME). Despite this, the multitude of=20
precipitation types will create hazardous conditions, especially in
the higher terrain from the Adirondacks through Vermont, New=20
Hampshire, and Maine where WSSI-P probabilities indicate a 10-30%=20
chance for moderate level impacts.

The impressive fgen along this front should result in periods of
heavy precipitation rates as well, regardless of the p-type. This
could result in a few inches of snow and sleet, before changing to
freezing rain. Total accumulations will be generally modest, but
WPC probabilities indicate a high risk (>70%) for at least 4 inches
of snow in the highest terrain of NH and ME, and a 50-70% chance
for at least 0.1" of ice in the Adirondacks and portions of
NH/VT/ME as well, ending by 00Z Friday.

Another round of mixed precipitation is likely as moisture funnels
northward on return flow through the Mississippi Valley and into=20
New England Saturday. At this time any significant wintry=20
precipitation accumulations are expected to be confined to the=20
highest terrain of northern New England, with a mix of snow and=20
freezing rain likely. Total accumulations are expected to be modest
however, as reflected by WPC probabilities for 0.01" of ice that=20
are generally just 10-30%.


...Intermountain West...
Days 1-3...

Expansive mid-level trough will remain entrenched across much of
the West through the weekend, but evolution of embedded shortwaves
will lead to amplification and wavelength shortening by Friday.
Before this occurs, generally modest ascent and modest moisture
will lead to widespread but light snow across much of the terrain
from the Northern Rockies southward through the Four Corners
states. Within this broad ascent, there is likely to be two areas
of more consolidated ascent and heavier snowfall D1: the Northern
Rockies and from the Wasatch to the San Juans. In the Northern
Rockies, a cold front sagging southward will cause some enhanced
fgen and post-frontal upslope on E/NE winds. This will more
efficiently wring out available moisture leading to heavy snow in
the vicinity of Glacier NP where WPC probabilities are high (>70%)
for at least 6 inches of snow. Additionally on D1, a subtle=20
shortwave ejecting from the southern stream will work together with
downstream mid- level divergence and some upslope ascent to=20
increase snowfall from the Wasatch into the San Juans where WPC
probabilities are 70-90% for 4+ inches of snow.

More widespread, generally light, snow occurs across the
Intermountain West terrain on D2, but some focused heavier snowfall
is likely in the vicinity of the MT/WY border, including the
Absarokas, Wind Rivers, and in the vicinity of Yellowstone NP where
the sinking cold front helps to enhance snowfall. WPC probabilities
in this region reach as high as 30-50% for 6+ inches of snow.

Then late D2 into D3, the amplifying trough and concurrent closing
off of an upper low across the Four Corners will yield much more
significant snow across the Southern Rockies and into Colorado.
While there is still uncertainty as to how this system will evolve,
and trends have been for a slightly farther south track, confidence
is increasing that heavy snow will become widespread across
northern NM and into CO. This will be in response to increasing=20
synoptic ascent driven by both downstream divergence and increasing fgen/upslope flow as the cold front continues to sag southward.=20
This will additionally cause isentropic lift to surge moisture=20
northward, and as this pivots back to the west it will yield an=20
expanding area of heavy snowfall, especially in the terrain from=20
the Front Range, to the Palmer Divide, the Raton Mesa, and the
Sangre de Cristos. Additionally, as snow levels crash behind the
front, impactful snow may spread into the High Plains including the
urban I-25 corridor, with at least moderate snow potentially
pivoting into the TX/OK Panhandles late in the forecast period and
into D4. At this time, WPC probabilities begin to rise late D2,
reaching 30-50% for 4+ inches along the Front Range, before
expanding and increasing D3 to 70-90% from the San Juans to the
Raton Mesa and along the Sangre de Cristos. Additionally, with
snowfall expanding and snow levels falling, WPC probabilities
indicate a low risk (10-30%) for at least 4 inches as far east as
the western TX/OK Panhandles and across the northeast NM High
Plains.


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4PDEc2RpYhhn4psPK2OpozF3v2KXxYuoSvnPKyOXX4k56= huCbCnz5xcByi95mbVgQZKdnvM08xY-a-wWVSEz8Aw9IzI$=20

$$

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FOUS11 KWBC 030737
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
337 AM EDT Thu Apr 3 2025

Valid 12Z Thu Apr 03 2025 - 12Z Sun Apr 06 2025


...Northeast...
Days 1 & 3...

An icy wintry mix will continue from the White Mountains and
through much of interior Maine this morning as ongoing WAA and
intense 850mb FGEN sustains an icy setup over northern New England.
The lingering sub-freezing boundary layer will gradually erode as
the warm front advances northward with only northern Maine holding
on to any notable wintry mix through midday. WPC probabilities=20
depict low chances (10-30%) for additional ice accumulations >0.1"
in the White Mountains and western Maine through this morning.

Following a break in the action Thursday night through Saturday
morning, the next round of wintry mix arrives Saturday afternoon=20
as moisture from the Mississippi Valley streams northward into New
England. Similar to the Day 1 setup, low-mid level WAA and 850mb
FGEN are the primary mechanisms of lift that will promote
precipitation. The antecedent air-mass is not nearly as cold as the
Wed-Thurs air-mass. However, the modestly cold air-mass will be=20
tough to erode in the higher terrain, thus making the White=20
Mountains and western Maine the most likely areas to see a mix of=20
snow and freezing rain through Saturday night. WPC probabilities=20
show moderate- to- high chances (50-70%) for >0.1" of ice, with low
chances (10-30%) for ice accumulations >0.25".


...Intermountain West & Southern High Plains...
Days 1-3...

The weather pattern over the western third of the Lower 48 is
primarily driven by a pair of upper level disturbances; one
tracking across Montana today and early Friday, and the other is a
closed upper low over the Southwest. Starting in Montana, a cold=20
front at the leading edge of the 500mb shortwave trough will act as
a trigger for snow showers, some of which could have snow squall-
like impacts with bursts of snow and gusty winds Thursday
afternoon. With high pressure building in from Alberta, easterly=20
upslope flow into the Lewis Range and Absaroka through Thursday
evening. Snow associated with this upper trough is also expected as
far south as the Big Horns and even as far east as western North=20
Dakota Thursday night. By Friday morning, the cold front makes its
way south through the Central Plains and Central Rockies with=20
NErly upslope flow aiding in minor snow accumulations along the
Front Range of the WY/CO Rockies through Friday morning.

Farther south, the closed upper low will make its way toward New
Mexico with 200-500-700mb heights along the AZ/NM and Mexico
borders below the 10th climatological percentile. As the 700mb low
reaches western New Mexico Friday afternoon, winds over southeast=20
CO and northeast NM will turn easterly at the same time the=20
aforementioned cold front to the north plunges south. Southern CO=20
and northern NM will also be co-located beneath the divergent left-
exit region of a 500mb jet streak located over northern Mexico. The
heaviest snowfall looks to ensue Friday afternoon and into Friday=20
night across the Front Range, Palmer Divide, San Juans, and Sangre=20
De Cristo (including Raton Pass). By Saturday morning, snow is=20
forecast for most of the Southern Rockies and even parts of the=20
southern High Plains as the cold front continues to dive south and
the deformation zone on the northern and western periphery of the=20
700mb low moves in overhead. Note that with the time of year, it=20
will have to snow exceptionally hard (>1"/hr) for snow to=20
accumulate outside of the mountain ranges given the higher sun=20
angle and warmer soil temperatures. Still, periods of moderate snow
combined with 30-40 kt 850mb winds will cause poor visibilities=20
through Saturday afternoon before the snow finally tapers off=20
Saturday evenings.

WPC probabilities depict moderate-to-high chances (50-70%) for
snowfall >8" along the >9,000ft peaks of the Sangre De Cristo and
San Juans between Friday afternoon and Saturday afternoon. Along
the I-25 corridor, the most concerning area for heavy snowfall is
along Raton Pass where up to 12" of snow in the forecast. WSSI
depicts Moderate impact potential in the Sangre De Cristo, Raton
Mesa, and San Juans. Note that there are some Moderate Impacts in
the plains of eastern NM and the TX Panhandle with Blowing Snow the
primary impact in these areas.=20


Mullinax


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!98tY52JDmfnm9YgoJzpabNeUnetxTJwssekx90v9jyqvu= GwTLSVsCPSSyblTT1vmYDDXc3ETbXmrnRc5Aqqkexb2J1A$=20


$$

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FOUS11 KWBC 030740
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Thu Apr 3 2025

Valid 12Z Thu Apr 03 2025 - 12Z Sun Apr 06 2025


...Northeast...
Days 1 & 3...

An icy wintry mix will continue from the White Mountains and
through much of interior Maine this morning as ongoing WAA and
intense 850mb FGEN sustains an icy setup over northern New England.
The lingering sub-freezing boundary layer will gradually erode as
the warm front advances northward with only northern Maine holding
on to any notable wintry mix through midday. WPC probabilities
depict low chances (10-30%) for additional ice accumulations >0.1"
in the White Mountains and western Maine through this morning.

Following a break in the action Thursday night through Saturday
morning, the next round of wintry mix arrives Saturday afternoon
as moisture from the Mississippi Valley streams northward into New
England. Similar to the Day 1 setup, low-mid level WAA and 850mb
FGEN are the primary mechanisms of lift that will promote
precipitation. The antecedent air-mass is not nearly as cold as the
Wed-Thurs air-mass. However, the modestly cold air-mass will be
tough to erode in the higher terrain, thus making the White
Mountains and western Maine the most likely areas to see a mix of
snow and freezing rain through Saturday night. WPC probabilities
show moderate- to- high chances (50-70%) for >0.1" of ice, with low
chances (10-30%) for ice accumulations >0.25".


...Intermountain West & Southern High Plains...
Days 1-3...

The weather pattern over the western third of the Lower 48 is
primarily driven by a pair of upper level disturbances; one
tracking across Montana today and early Friday, and the other is a
closed upper low over the Southwest. Starting in Montana, a cold
front at the leading edge of the 500mb shortwave trough will act as
a trigger for snow showers, some of which could have snow squall-
like impacts with bursts of snow and gusty winds Thursday
afternoon. With high pressure building in from Alberta, easterly
upslope flow into the Lewis Range and Absaroka through Thursday
evening. Snow associated with this upper trough is also expected as
far south as the Big Horns and even as far east as western North
Dakota Thursday night. By Friday morning, the cold front makes its
way south through the Central Plains and Central Rockies with
NErly upslope flow aiding in minor snow accumulations along the
Front Range of the WY/CO Rockies through Friday morning.

Farther south, the closed upper low will make its way toward New
Mexico with 200-500-700mb heights along the AZ/NM and Mexico
borders below the 10th climatological percentile. As the 700mb low
reaches western New Mexico Friday afternoon, winds over southeast
CO and northeast NM will turn easterly at the same time the
aforementioned cold front to the north plunges south. Southern CO
and northern NM will also be co-located beneath the divergent left-
exit region of a 500mb jet streak located over northern Mexico. The
heaviest snowfall looks to ensue Friday afternoon and into Friday
night across the Front Range, Palmer Divide, San Juans, and Sangre
De Cristo (including Raton Pass). By Saturday morning, snow is
forecast for most of the Southern Rockies and even parts of the
southern High Plains as the cold front continues to dive south and
the deformation zone on the northern and western periphery of the
700mb low moves in overhead. Note that with the time of year, it
will have to snow exceptionally hard (>1"/hr) for snow to
accumulate outside of the mountain ranges given the higher sun
angle and warmer soil temperatures. Still, periods of moderate snow
combined with 30-40 kt 850mb winds will cause poor visibilities
through Saturday afternoon before the snow finally tapers off
Saturday evenings.

WPC probabilities depict moderate-to-high chances (50-70%) for
snowfall >8" along the >9,000ft peaks of the Sangre De Cristo and
San Juans between Friday afternoon and Saturday afternoon. Along
the I-25 corridor, the most concerning area for heavy snowfall is
along Raton Pass where up to 12" of snow in the forecast. WSSI
depicts Moderate impact potential in the Sangre De Cristo, Raton
Mesa, and San Juans. Note that there are some Moderate Impacts in
the plains of eastern NM and the TX Panhandle with Blowing Snow the
primary impact in these areas.


Mullinax





$$

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FOUS11 KWBC 031909
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
309 PM EDT Thu Apr 3 2025

Valid 00Z Fri Apr 04 2025 - 00Z Mon Apr 07 2025

...Portions of the Rockies and the High Plains...
Days 1,2...

A deep upper level trough over much of the Intermountain West and
associated embedded upper level low over the Southwest will
gradually shift east onto the Plains through Saturday. Shortwave
disturbances moving around both the upper low and a secondary wave
moving along the Canadian border will provide the forcing for
wintry weather over and immediately downwind of those upper level
features.

For Day 1/Tonight through Friday, a potent trough over the Canadian
Prairies will dig southeastward into Montana and the Dakotas. This
will lead to pressure and height falls in the region. Troughing
developing as a response will draw a small portion of the Gulf
moisture plume into the northern Plains, supporting a widespread
generally light snowfall over Montana and the Dakotas. For the
mountains from the Bitterroots of Montana south to the Front Range
of Colorado, localized upslope along the terrain will cause much
heavier snowfall rates and amounts, especially in the Beartooths of
Montana and Bighorns of Wyoming, where new snowfall could approach
a foot through midday Friday. WPC probabilities are over 50% for 4
inches or more of snow for the Front Range of Colorado and the
Beartooths of Montana and Wyoming.

For Day 2/Friday Night and Saturday, the shortwave moving along the
Canadian border will shift east into the Great Lakes, leaving the
area. However, the upper level low/southern extension of the
broader upper trough will begin to tap ever-increasing amounts of
Gulf moisture as the lift ahead of the low moves in closer
proximity to the trough. This will draw more of that moisture
westward into the southern High Plains as the low-level jet
increases in both strength and amounts of Gulf moisture it will be
drawing northward into the nation's mid-section. Upslope will play
an even greater role here, especially as the leeside surface trough
develops over eastern New Mexico. Some of the troughing from the
northern system from Day 1 in the northern Plains will propagate
straight southward along the Front Range and support the heavy
snow. The Sangre de Cristo Mountains of Colorado and New Mexico
will be the range hardest hit with heavy snow, with WPC
probabilities for over 8 inches of snow in the moderate-to-high
(50-70%) range through Saturday evening. The WPC Winter Storm
Severity Index (WSSI) shows areas along the state line near Raton
Mesa with major impacts from the large snowfall expected. The snow
will taper off in the area Saturday night.

...Northern New England...
Day 3...

A strong upper level trough over Hudson Bay Saturday will direct a
strong shortwave along its southeastern periphery towards New
England. Meanwhile, a portion of the moisture associated with the
excessive rainfall over the nation's mid-section will draw
northeastward into the Northeast and New England. Here, that Gulf
moisture will interact with some lingering cold air over the
region, resulting in a variety of precipitation types over the
area. For areas south and west over northern New Hampshire and far
western Maine, a significant icing event is expected as warmer air
above freezing moves in aloft above the cold air in place,
resulting in precipitation changing over from snow to sleet and
freezing rain as the warm air moves in and deepens Saturday night.
There is a moderate-to-high (50-70%) chance of at least a tenth
(0.10") of an inch of ice across much of northern New Hampshire and
far western Maine near the New Hampshire border through Saturday
night, with a low (10-30%) chance of at least a quarter of an inch
of ice.

Further north where the warmer/above freezing air is unable to
reach, a light snowfall is expected, namely for far northern Maine,
where there is a low-to-moderate (30-50%) chance of at least an
inch of snow Saturday night. The moisture plume will shift east
with the cold front Sunday morning, ending the winter precipitation
threat.

Wegman

$$

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FOUS11 KWBC 040735
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EDT Fri Apr 4 2025

Valid 12Z Fri Apr 04 2025 - 12Z Mon Apr 07 2025

...Portions of the Rockies and the High Plains...
Days 1-2...

This morning, a cold front tracking south through the central High
Plains with NErly CAA will cause temperatures to drop and modest
upslope ascent into the Front Range of the Rockies. This air-mass
will be essential for boundary layer wet-bulb temperatures being
cold enough to support snow in the central and southern High
Plains. Farther south, a closed upper low will slowly make its way
east through Arizona and New Mexico on Friday while also injecting
a healthy plume of 300-700mb moisture over the Rockies. This will
support periods of mountain snow from as far west as the Wasatch
and as far south as the Gila Mountains of eastern Arizona. As the
700mb low heads into western New Mexico Friday afternoon, low-mid
levels winds over southeast CO and northeast NM will turn easterly
at the same time as the aforementioned cold front to the north
continues its southerly progression. In addition, the southern and
central Rockies/High Plains will reside beneath the divergent left-
exit region of a 500mb jet streak. Guidance shows a moistening of
the 700-300mb layer Friday afternoon that coincides with what is
likely to be the start of heavy snowfall from the San Juans and
Front Range on south along the Sangre De Cristo and Raton Mesa
Friday afternoon and into Friday night.

By Saturday morning, snow will be falling not only in the Southern
Rockies, but across the southern High Plains thanks to a narrow
area of 700mb WAA to the north of the 700mb low tracking from
southeast NM into western TX. This will prompt the formation of a
deformation zone on the western and northern flanks of the 700mb
low. Note that, with the calendar reading early April and the
increasingly high sun angle, it will have to snow at an
exceptional clip (>1"/hr)for snow to accumulate outside of the
mountain ranges. Still, periods of moderate snow combined with
30-40 kt 850mb winds will cause significantly reduced visibilities
across the southern High Plains of eastern NM and the OK/TX
Panhandles through Saturday afternoon. Snow should finally taper
off by Saturday evening as the 700mb low tracks east over central
OK.

The ECMWF EFI does suggest this is a rather anomalous event in
terms of snowfall for the late March to mid-April time period. The
EFI shows a large swath of 0.8-0.9 values from Raton Pass on south
through much of eastern New Mexico. WPC probabilities show high
chances (>70%) for snowfall totals >12" along the >9,000ft peaks of
the Sangre De Cristo and above 8,000ft in the Raton Mesa. The
latest forecast calls for as much as 12" of snow at the peak of
the Raton Pass along I-25. The WSSI does indicate Major Impact
potential (considerable disruptions; dangerous to impossible
travel) along the Raton Pass Friday night into Saturday morning.
WPC probabilities also show moderate-to-high chances (50-70%) for
snowfall >4" along the I-40 corridor in eastern NM. The WSSI shows
Minor to Moderate Impacts from a combination of Snow Amount and
Blowing Snow across the High Plains of eastern NM and the OK/TX
Panhandles through Saturday with Minor Impacts denoted (winter
weather conditions, hazardous travel possible) in and around the
Amarillo area.


...Northern New England...
Day 2...

Saturday will bring yet another round of wintry weather from the
White Mountains through much of western and northern Maine. While
the air-mass is not as cold as the more recent winter storm that
took place earlier this week, high pressure over Quebec will
provide a weak source of sub-freezing boundary layer temps. As
850-700mb WAA and 300K isentropic ascent amidst brisk SWrly flow
aloft increases, a ribbon of 850-700mb areal-averaged FGEN will
support a band of moderate-to-heavy precipitation that runs
directly over the marginally cold air-mass in northern New England
on Saturday. Precipitation may briefly start out as snow (staying
all snow longest over northern Maine), but the burgeoning nose of

0C temps at low-levels will inevitably switch any snow to a

sleet/freezing rain mixture from the Whites to western Maine
Saturday afternoon. A weak CAD signature will linger longest along
the Maine/Quebec border that will linger through Saturday night. By
Sunday morning, the warm front lifts far enough north to have plain
rain be the primary precipitation type.

WPC probabilities show moderate-to-high chances (50-70%) for ice
accumulations >0.1" from the Whites through western Maine. Some
minor ice accumulations (generally <0.1") are possible in the Green
Mountains and even as far south as the Berkshires. However, if any
locations are to see localized ice accumulations >0.25", it would
be the White Mountains and western Maine where low-to-moderate
probabilities (10-40%) are present. The probabilistic WSSI (WSSI-P)
does indicate moderate-to-high chances (50-70%) for Minor Impacts
as a result of the >0.1" of ice accumulations.

...Northern Great Lakes...
Day 3...

A potent 500mb vort max with origins out of the Arctic Circle will
dive south from south-central Canada towards northern Minnesota
Sunday evening. A 250mb jet streak oriented N-S will place its
divergent left-exit region over the Midwest Sunday night and aid in
the development of low pressure along a strengthening 850mb front.
A narrow band of moderate snow should manifest on the northern
periphery of low pressure as it tracks through Wisconsin and
northern Michigan. In addition to the band of snow, CAA via brisk
northerly winds will trigger lake-enhanced snow showers over
northern Wisconsin and the Michigan U.P. Sunday night and Monday
morning. WPC probabilities highlight low chances (10-30%) for >4"
of snowfall through 12Z Monday in the Michigan U.P. and the tip of
Michigan's Mitten with additional snowfall possible across northern
Michigan through Monday afternoon.


Mullinax




$$

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FOUS11 KWBC 042048
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
448 PM EDT Fri Apr 4 2025

Valid 00Z Sat Apr 05 2025 - 00Z Tue Apr 08 2025

...Southern Rockies and the Southern High Plains...
Days 1-2...

A cold front tracking south through CO this afternoon will push
south through NM tonight as an upper low tracks over the southern
borders of AZ/NM. Moisture ahead of this low combined with the low
level cold behind the front will support heavy mountain snow on the
eastern side of the southern Front Range, Sangre De Cristo and
Raton Mesa through this evening before shifting south through the
Sacramento Mtns Saturday morning. Upslope flow and increasing lift
should enable snow rates of 1-2"/hr to work their way south later
this afternoon through tonight per the 12Z HREF. 1"/hr rates also
shift east over the southern High Plains of NM into the TX
Panhandle. Day 1 snow probabilities for >8" are 50-80% in terrain
from the Raton Mesa through the Sacramento Mtns especially
including the Sangre de Cristos which have 50-70% chances for >12".
Day 1 probs for >4" are 30-60% from the lower reaches of the Raton
Mesa through much of eastern NM and into the Staked Plain of the
western TX Panhandle south of the Pecos where snow persists into
Saturday evening.


...Northern New England...
Days 1/2...

Expect a wintry mix from the White Mountains of NH through western
Maine Saturday/Saturday night. While the airmass is not as cold as
the more recent winter storm that took place earlier this week,
high pressure over Quebec will provide a weak source of sub-
freezing boundary layer temps. As 850-700mb WAA and 300K isentropic
ascent amidst brisk SWrly flow aloft increases, a ribbon of
850-700mb areal-averaged FGEN will support a band of moderate- to-
heavy precipitation that runs directly over the marginally cold
air-mass in northern New England on Saturday. Precipitation may
briefly start out as snow (staying all snow longest over northern
Maine), but the burgeoning nose of >0C temps at low-levels will
inevitably switch any snow to a sleet/freezing rain mixture from
the Whites to western Maine Saturday afternoon. A weak CAD
signature will linger longest along the Maine/Quebec border
through Saturday night. By Sunday morning, the warm front lifts far
enough north to have plain rain be the primary precipitation type.

Day 1.5 WPC probabilities for ice accumulations >0.1" are 30-70% from
the Whites through western Maine with 40% probs for >0.25" in the
Presidential Range of the Whites. Moderate impacts from this icing
are forecast in higher elevations per the WSSI.


...Michigan...
Day 3...

A potent reinforcing shortwave trough swings south of a cold-core
low over Hudson Bay Sunday, reaching the L.P. of Michigan on
Monday. PVA, low level FGEN, and Great Lakes moisture combine to
produce a band of snow Sunday evening over Lake Superior that
shifts south-southeast over the U.P. Sunday night and the L.P.
Monday morning. Trailing cold air advection then produces some
lake- enhanced snow showers behind the front. Day 3 PWPF for >6"
are 10-30% across the northern L.P.


Jackson


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