FOUS11 KWBC 171936
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
236 PM EST Mon Feb 17 2025

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


...Great Lakes...=20
Days 1-2...

Impressive winter storm exiting into the Canadian Maritimes today
will leave cyclonic flow in its wake and across the Great Lakes.
This will promote continued CAA through D1, with 850mb temps
plummeting to as low as -25C (Lake Superior) and -20C over Lake
Ontario. This will support bands of lake effect snow (LES)
especially D1 during the most intense CAA before the mid-level flow
pattern relaxes downstream of a deepening trough centered over the
Northern Plains/Upper Midwest later Wednesday. The generally W/NW
flow will support heavy LES bands, likely in the form of single
bands within unidirectional shear, and strong ascent focused into
the low-level but deep DGZ will support heavy rates that could
reach 2-3"/hr at times D1, heaviest east of Lake Ontario where an
upstream moisture connection to Lake Huron will exist. These bands
should be prolonged and intense D1, leading to WPC probabilities
that are high (>70%) for more than 6 inches east of Lake Ontario
and the far eastern U.P. Although LES will wane during D2,=20
additional snowfall exceeding 4 inches is possible (30%) in these
same areas. Downstream of Lake Ontario, total snowfall of 1-2
feet is possible before LES winds down.


...Pacific Northwest through the Central Rockies...
Days 1-3...

Two rounds of moisture spreading inland through enhanced IVT will
spread wintry precipitation across much of the coastal and interior
West.

The period begins with a longwave positively tilted trough
extending from the interior Northwest through the Northern Plains.
This trough will deepen with time, diving into the Great Basin
Tuesday morning and then pivoting into the Four Corners by the end
of D1 as shortwave energy traverses through it. At the same time,=20
a stationary front will be aligned from inland WA state southeast=20
into the CO Rockies, as onshore flow from the Pacific spreads=20
inland and lifts isentropically producing some modest enhancement=20
of lift. Shortwave ridging expanding along the Pacific Coast late=20
D1 will cut off Pacific moisture by Wednesday morning, but a axis=20
of moderate to heavy snow is likely before this occurs, primarily=20
along the stationary front and into downstream terrain. WPC=20
probabilities are high (70-90%) for more than 6 inches in the=20
terrain above generally 3000 ft from the Sawtooth into the Tetons=20
and as far southeast as the Park Range of CO.

After a brief respite, a more pronounced system will approach the
Pacific Coast as a potent shortwave closes off over the Pacific
Ocean and sheds eastward. This feature is progged to come onshore
near the WA/OR border Wednesday evening, and there is good model
consensus in this evolution despite modest differences in
amplitude. The core of this trough coming onshore WA/OR will
manifest as impressive height falls as far south as central CA, and
as the downstream ridge erodes, this entire feature will elongated
and pivot into the Great Basin/Central Rockies by the end of the
forecast period. Modest jet level ascent through the development of
a jet streak rotating around the base of this trough will enhance
lift, but in general forcing is expected to be broad and driven
primarily by height falls through D2-D3. Despite that, some
enhanced IVT progged to exceed the 90th percentile within the CFSR
climatology will spread inland within WAA downstream of the trough
axis, leading to rising snow levels but enhanced wintry=20
precipitation prospects. During this time, WPC probabilities for
more than 6 inches climb above 30% in the Cascades D2, but with
snow levels climbing above pass levels, with additional moderate
chances (30-50%) for 6+ inches on D3 in the same general areas.


...Central Plains through the Mid-Atlantic States...
Days 1-3...

A significant winter storm begins tonight across the Central Plains
and then spreads almost due east to the Mid-Atlantic on Wednesday.
There is still considerable uncertainly as to how this evolves off
the coast Wednesday night, but at least moderate snow and
significant icing is likely for many areas.

The system begins to take shape tonight as a shortwave ejects from
the Four Corners and traverses to the east, reaching the Central=20
Plains Tuesday evening. This will occur just north of a surface
cold front that will surge south into Texas, and the interaction of
this impulse with the elevated baroclinic zone will help induce
some backing of the low-level winds, leading to enhanced moist
isentropic ascent emerging from the Gulf, especially along the
285-290K surfaces where mixing ratios will rise to 3-4 g/kg. At=20
the same time, a jet streak angled into the Northeast will leave
its favorable RRQ for ascent atop the region, resulting in an=20
overlap of synoptic and mesoscale ascent. With moisture continuing=20
to surge into the region, this will result in an expanding axis of=20
heavy snow, especially from eastern KS and OK into northern AR,
southern MO, and western TN/KY. Here, the overlap of ascent and
moisture will combine with a deepening DGZ (SREF probs for 100mb of
depth exceeding 70% Tuesday evening and Tuesday night, resulting in
an axis of heavy snowfall. Additionally, a secondary jet streak
intensifying downstream of the sharpening trough will produce an
environment supporting modestly coupled jet streaks, and the
resultant ageostrophic response to the already impressive fgen will
likely (>80% chance) drive snowfall rates to 1-2"/hr as shown by
both HREF probabilities and the WPC prototype snowband tool.

This system will become increasingly progressive to the east, but
an 18-24 hour period of moderate to heavy snow with fluffy SLRs in
the cold environment will support rapid and significant snowfall
accumulations, especially Tuesday night from the Central Plains
into the western Tennessee Valley. Here, WPC probabilities for
more than 8 inches reach as high as 70%, with locally 12+ inches
possible in the vicinity of the most intense banding. South of this
heavy snow, an axis of mixed sleet and freezing rain is likely,
with locally more than 0.1" of ice possible (30%), highest across
southern AR.

This shortwave begins to race eastward towards the Mid-Atlantic
Wednesday as it gets squeezed into more zonal flow downstream of a
more impressive northern stream trough (500mb heights falling below
the 2.5 percentile anomaly according to NAEFS) digging out of the=20
Northern Plains. This is where the the forecast begins to get more
challenging. This northern stream trough will dive southeast
towards the Ohio Valley while continuing to deepen into a potent
closed low, resulting in downstream (south/east) jet development
which will intensify beyond 150 kts. The overlap of the impressive
height falls and LFQ of this jet streak will drive pronounced
ascent into the Mid-Atlantic states, concurrent with continued
moist isentropic lift from the Gulf into the area. This suggests
that after a modest "break" in intensity of precipitation in the
vicinity of the central Appalachians, renewed heavy precip will
develop, especially as secondary surface low pressure develops
offshore.

There has been a steady trend in guidance to keep this
precipitation suppressed south across the Carolinas and Virginia,
with the most uncertainty now involving the speed and placement at
which the secondary low develops and moves northeast up the coast.
With the southern stream less amplified and faster, phasing of
energy is progged to occur much later which should spare the
northern Mid-Atlantic and Northeast much if any snow. However,
heavy snow and mixed precipitation is still likely from eastern
TN/KY into NC and VA, with a swath of the heaviest snow most
likely across eastern VA. There is still a lot of uncertainty,
however, and clusters indicate the primary EOF is dependent on the
amplitude of this trough, with the GEFS members appearing to be a
bit under-dispersive with a flatter wave, while the EC/CMC are a
bit deeper in general. However, these deeper waves are also
generally slower, again suggesting the threat for a phased major
winter event are quite low.=20

However, with the low eventually deepening rapidly offshore, a=20
potent deformation axis collocated with the greatest moisture will=20
result in heavy snow accumulations, for which WPC probabilities=20
indicate a high risk (70-90%) for 6+ inches centered along the=20 Norfolk/Virginia Tidewater region. Surrounding this maximum, WPC=20 probabilities for 4 or more inches are 10-30% from eastern KY=20
through WV and east towards coastal Delaware and far northern NC.=20
Southeast of the snow, a mix of sleet and freezing rain is=20
expected, and freezing rain potential has increased beneath the=20
warm nose lifting northward. WPC probabilities for 0.1" peak above=20
70% D2 into D3 in parts of eastern and southeastern NC, with=20
locally 0.25-0.35 inches of ice possible.=20


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_2.png__;!!DZ3fjg!61uyEcFGG2mhbmpbK41-RYzUYY-t9gpiwDFhlNCjM0ALO= YlI-0m1WzVHjnsIDgZT2eEPce6SKoqCNmbYxpTHo16Awgo$=20

$$

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FOUS11 KWBC 180811
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
311 AM EST Tue Feb 18 2025

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


...Great Lakes...=20
Days 1-3...

Cyclonic flow over southern Canada and the Great Lakes on the=20
western side of the elongated upper trough axis will favor a=20
continuation of the lake effect snow for the next couple of days.=20
With 850 temperatures in the -20sC and NW to WNW flow, multi-bands=20
will form off the Upper Lakes with a strong single band off Lake=20
Ontario with an impressive multi-lake moisture feed. THe pattern=20
will be slow to unfold, but by early Wednesday a closed low will=20
begin to form over the Corn Belt which will help disrupt the=20
pattern enough to diminish the lake effect snow, but then those=20
height falls will bring in a general/light snow to the region on=20
Thursday. WPC probabilities for at least 8 inches of snow over the=20
next two days are near 50% over the eastern U.P. of Michigan. Over=20
central NY between ROC-FZY-SYR, the strong single band will=20
continue to dump snow at 1-3"/hr rates with significant=20
accumulation in a narrow swath -- perhaps more than 12-18 inches=20

60% probs). By day 3, snowfall will be light with most areas=20

seeing less than 4 inches of snow.


...Pacific Northwest through the Central Rockies...
Days 1-3...

Height falls over the Great Basin this morning will continue=20
southeastward today, giving some additional snow to the CO Rockies.
To the north, additional height falls out of Canada will drop=20
through central MT with some light snow to the central ID ranges,=20 southwestern MY, and the western WY ranges where WPC probabilities=20
for at least 6 inches of snow are low (<40%) to the north but high=20

70%) over western WY and the high peaks of the northern CO=20

Rockies.=20

By day 2, a Pacific system will start to move into the Northwest,=20
spanning the latitudes from NorCal up to the Canadian border. IVT=20
will be modestly high (~90th percentile) into NorCal/southern=20
OR/northern NV toward Idaho, supporting light to moderate snows for
the terrain with snow levels near 3000ft to the north and 5000ft=20
to the south that will rise a bit as the core of the moisture plume
pushes through. The system will move steadily along and clear the=20
coast with QPF starting early Thursday, pushing into northern=20
UT/southern ID and into the Rockies. However, moisture will wane=20
and snow will become lighter overall into D3 with the snow confined
mainly to the Unitas and higher CO Rockies by then. For the 3-day=20
period, WPC probabilities for at least 8 inches of snow are highest

70%) over the higher terrain above 6000ft closer to the coast,=20

7000-8000ft over the Great Basin, and 9000ft over CO/WY.=20


...Central Plains through the Mid-Atlantic States...
Days 1-2...

A significant winter storm is underway over the Central Plains=20
which will spread eastward through the Mid-South into the southern=20 Mid-Atlantic with potentially major impacts including heavy snow=20
and significant ice.=20

Snow is already underway across KS into MO this morning, driven by
lead shortwaves ahead of the Rockies trough. Through this morning,
as the stronger height falls approach the region, snow will expand
over the central and southern Plains eastward beneath the RRQ of=20
the upper jet and atop the Arctic air mass driven in by the strong=20
cold front overnight. With sufficient moisture influx from the=20
Gulf, snow rates will increase over southern KS into southern MS=20
later this morning into the afternoon with >1"/hr rates at times=20
per the WPC snowband tool and HREF probs. Snow will advance=20
eastward into the Mid-South later this evening and overnight but=20
likely diminish somewhat in intensity. To the south, the shallow=20
Arctic air mass will continue southward but southerly flow aloft=20
will maintain >0C temperatures, favoring a mix of sleet and=20
freezing rain over parts of OK into AR, northern LA, and western=20
MS. For the D1 period, WPC probabilities of at least 4 inches of=20
snow are high (>70%) from southeastern KS and northeastern OK=20
eastward to western KY. Within this region, probabilities of at=20
least 8 inches of snow are >60% near Joplin to Springfield, MO.=20
Icing to the south should generally be light but there is a low=20
change (10-30%) of at least 0.10" accretion near the Oachita=20
Mountains in AR.=20

By Wednesday morning, the next phase of the system will take shape
over the northern Gulf as the entrance region of the upper jet=20
touches the LA/MS coast, helping to favor cyclogenesis. The=20
northern part of the system will still spread snow across the Mid-
South eastward to the central Appalachians where some orographic=20
lift will help wring out several inches of snow into eastern=20
KY/southern WV/southwestern VA. The larger QPF-maker will be the=20
forming Gulf low that is forecast to track ENE to NE across north=20
FL before turning northeastward along the Gulf Stream just off the=20
SC/NC coasts. With the cold air mass in place through the East,=20
this sets up a southern slider snow event with an axis of heavy=20
snow along the VA/NC border into the Tidewater and southern=20
DelMarVa. The incoming northern stream upper low will lag behind=20
just enough to not phase until farther downstream, but enough=20
ingredients will be coming into place in the formative stages of=20
this system to yield a modest to heavy snowfall for parts of the=20
southern Mid-Atlantic, with a cutoff near a line along I-66/I-95=20
into southern NJ. WPC probabilities for at least 6 inches of snow=20
are highest over southeastern VA and northeastern NC, squarely=20
through the Norfolk area.

Like places farther west, the >0C air aloft will rise up and over=20
the cold surface temperatures over eastern NC, setting up a=20
freezing rain event that may be significant along and east of I-95
between the VA border and into northeastern SC. There, WPC=20
probabilities for at least 0.10" icing are >50% with some areas=20
receiving more than 0.25" accretion.=20


...Southeastern Mass...
Day 3...

The exiting system from the Southeast/southern Mid-Atlantic will=20
track northeastward, and may clip southeastern MA/Cape Cod D3 on=20
its way into Atlantic Canada. The question revolves around the=20
speed of the incoming northern stream upper low and how much it can
capture the exiting system. Given the uncertainty leading into the
event in the Southeast/Mid-Atlantic, there are still a wide range=20
of solutions from zero to moderate snow over part of the region.=20
For now, there are low (10-40%) probabilities of at least 4 inches=20
of snow over Cape Cod and the Islands.=20


Fracasso


...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_2.png__;!!DZ3fjg!92kKkwbOehKBV2BtOiSCq2THIYORCAmTDDpxygk-jF7Q0= 5Y6P3T0r05kbzgsuHmq3WS3DKk8WDp5dXVNWHc5cX6IEaA$=20

$$

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FOUS11 KWBC 181953
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 PM EST Tue Feb 18 2025

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


...Central Plains through the Mid-Atlantic States...
Days 1-2...

A significant winter storm is underway over the Central Plains=20
which will spread eastward through the Mid-South into the southern=20 Mid-Atlantic with potentially major impacts including heavy snow=20
and significant ice. See the latest Key Messages linked at the end
of the discussion.=20

Current radar/sat composite is pretty revealing this afternoon with
the development of a significant swath of precip developing in-of
the Central Plains into the adjacent Lower to Mid-Mississippi
Valley. Shortwave trough ejecting out of the Central Rockies will
continue downstream with general mid-level ascent pattern maximized
within the corridor extending from southeast KS to points east
within Southern MO/Northern AR with a heavy snow footprint
forecast to align within the above corridor. WPC prob snowbands at
the 12z update was still pretty aggressive for a several hr time
frame of 1-2"/hr rates embedded within the primary precip shield=20
moving across the Ozarks until about the three-river confluence at=20
the MO/TN/AR border. Heavy snows over the span of several hours=20
will produce total accumulations generally >8" across that same=20
expanse from KS through northern AR and southern MO through=20
Wednesday morning. High probs (50-80%) for >4" exists just for the=20
00-12z Wednesday period across southern MO, northern AR, and far=20 southwestern KY with lower probs (25-50%) extending further east=20
through the Ohio Valley for the remainder of the period.=20

Further south into Central AR down through northern LA, dominant=20
ptype will continue to trend more favorable for IP/ZR as a shallow=20
warm layer is progged due to the meridional push of Gulf air=20
advecting over top the shallow cold air mass being pushed south on
the southern flank of the Arctic high drilling south over the=20
course of today and tomorrow. Thankfully the ascent pattern is=20
strongest further north, so ice accums are not anticipated to be=20
severe, but still relatively impactful with probs of ice >0.1"=20
holding between 10-30% across the AR/LA border over the course of=20
the forecast period. Ice probs decrease downstream for D2, but=20
still maintain some low probs for between 0.01-0.1" ice accums=20
across northern MS/AL/GA for mainly the 06-14z time frame on=20
Wednesday before precip moves out of the area the second half of=20
the D2 period.=20

By early Wednesday morning, increased jet dynamics over the
Southeast and Mid-Atlantic will aid in generating a surface low
along the Central Gulf coast, propagating east-northeast over the=20
course of Wednesday with a surface low located off the NC coast by
early Thursday morning. The primary disturbance to the west will
still motion across the Ohio Valley into the mountains of the
central and southern Mid-Atlantic leading to moderate snow
accumulations on D2 across eastern KY/southern WV/southwestern VA
leading to probs around 30-50% for at least 4" of snowfall in those
locales during the 12z Wednesday to 12z Thursday period falling
in-between both D1 and D2. Further east into the coastal southern
Mid-Atlantic, our aforementioned surface cyclone over the Gulf into
the Western Atlantic will lead to the greatest QPF footprint for
the D2 period with heavy synoptic based precipitation over places
like the Tidewater of VA down into northeastern NC, mainly in the
form of snow. Moderate precip focus will align within the NC=20
Piedmont across into southeastern NC with a mixed ptype regime
likely to cause some formidable ice accums in the form of sleet
(IP) and freezing rain (ZR). The area across the VA Tidewater will
be the epicenter for the most significant snowfall forecast with
totals between 6-12" expected for areas like Norfolk up through the
U13 corridor between VA Beach/Chincoteague, well-documented with
the latest >4" probs a solid 80+% within that entire zone and >8"
probs up into the 40-60% range. Modest probs for >4" also extend
south into northeastern NC with a decent area of 40-70% probs
existing from Elizabeth City and points northwest.=20

Freezing rain prospects exist across a good portion of eastern NC
and the northern Piedmont of SC with the heaviest totals likely to
fall over areas along and east of I-95. WPC probabilities between
50-80% are forecast for >0.1" ice accretion across portions of
eastern NC with low probs (10-30%) for the northern most portion of
the SC Piedmont. 10-30% probs also exist for as much as 0.25" of
ice accretion over eastern NC as well, although the deterrent for
the threat is the heaviest precip falling within marginally cold
enough air at the surface (30-32F) with periods of heavier precip
falling during the day time which historically curbs ice accretion
rates, especially at these latitudes.=20

Kleebauer


...Great Lakes...=20
Days 1-3...

Cyclonic flow over southern Canada and the Great Lakes on the=20
western side of the elongated upper trough axis will favor a=20
continuation of the lake effect snow for the next couple of days.=20
With 850 temperatures in the -20sC and NW to WNW flow, multi-bands=20
will form off the Upper Lakes with a strong single band off Lake=20
Ontario with an impressive multi-lake moisture feed. The pattern=20
will be slow to unwind, but by early Wednesday a closed low will=20
begin to form over the Corn Belt which will help disrupt the=20
pattern enough to diminish the heavy lake effect snow, but then=20
those height falls will bring in a general/light snow to the region
on Thursday and Friday. WPC probabilities for at least 8 inches of
snow only exist on Day 1 (Wednesday) parts of the Michigan U.P.=20
and off southern Lake Ontario. For central NY between ROC- FZY-=20
SYR, the strong single band will steal the show and continue to=20
dump snow at 1-3"/hr rates with significant accumulation in a=20
narrow swath -- perhaps more than 12 inches of additional snow=20
(10-20% probs). By days 2 and 3, snowfall will be light with most=20
areas seeing less than 4 inches of snow. The greatest potential for
additional snowfall over 4 inches (20-50%) is forecast off Lake=20
Michigan into western L.P. and far northern Indiana on Thursday,
positioned along the eastern and northern periphery of the upper
low.


...Pacific Northwest through the Central Rockies...
Days 1-3...

Initially for tonight, additional height falls out of Canada will=20
drop through central MT with some light snow to the central ID=20
ranges, southwestern MT, and the western WY ranges where WPC=20
probabilities for an additional 6 inches of snow are low (<40%) to
the north but high (>70%) over southern WY and the high peaks of=20
the northern CO Rockies.=20

By early Wednesday, a potent but progressive Pacific system will=20
start to move into the Northwest, spanning the latitudes from=20
NorCal up to the Canadian border. IVT will be modestly high (~90th=20 percentile) into NorCal/southern OR/northern NV toward Idaho,=20
supporting light to moderate snows for the terrain with snow levels
near 3000ft to the north and 5000ft to the south that will rise a=20
bit as the core of the moisture plume pushes through. The system=20
will move steadily along and clear the coast with QPF starting=20
early Thursday, pushing into northern UT/southern ID and into the=20
Rockies. However, moisture will wane and snow will become lighter=20
overall into the end of D2 with the snow confined mainly to the=20
Unitas and higher CO Rockies by then. For the 3-day period, WPC=20 probabilities for at least 8 inches of snow are highest (>70%) over
the higher terrain above 6000ft closer to the coast, 7000-8000ft=20
over the Great Basin, and 9000ft over CO/WY. The next system begins
to enter the Northwest by the end of D3 with lighter snow entering
the northern Cascades.


...Southeastern Mass...
Day 2-3...

The exiting system from the Southeast/southern Mid-Atlantic will=20
track northeastward, and may clip southeastern MA/Cape Cod on
Thursday on its way into Atlantic Canada. The question revolves=20
around the speed of the incoming northern stream upper low and how=20
much it can capture the exiting system and pump up the downstream
ridge. Recent 12z guidance has nudged northward, which is common in
the short range with developing low pressure systems off the coast
as CAMs incorporate latent heat release and stronger WAA in
relation to convection in the warm sector of the system. However,
the best chances for snowfall over 4 inches remains over Nantucket
(70-80%) as well as both Martha's Vineyard and Cape Cod (40-60%),
with low probs (10-20%) clipping far eastern Long Island, southern
CT and the remainder of southeast MA.


Fracasso/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_2.png__;!!DZ3fjg!5mPmuoW5LsnP4ytmASZ9XcFvE4QBoZOAMQWVvp_1zHOla= XspwSo7cpI_J7s1J04ovX_4L1NURYZIDHud1WBb0slpltc$=20

$$

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FOUS11 KWBC 190701
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
201 AM EST Wed Feb 19 2025

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


...Southern Mid-Atlantic States...=20
Day 1...

A significant winter storm will continue to spread eastward into=20
the southern Mid-Atlantic with potentially major impacts including=20
heavy snow and significant ice. See the latest Key Messages linked=20
at the end of the discussion.=20

Surface low along the Central Gulf coast will cross North Florida=20
early this afternoon and parallel the Southeast Coast tonight. The=20
northern stream shortwave responsible for the heavy snow in the=20
Plains will continue eastward into the southern Mid-Atlantic,=20
helping to spread generally light snow to the southern=20
Appalachians, aided by some orographic enhancement. WPC=20
probabilities for at least 4 inches are generally <30%.

As the Gulf low transitions to a western Atlantic/coastal low,=20
precipitation will progress to the VA/NC coast with snow to the=20
north (solidly cold column over VA) and freezing rain and sleet to=20
the south where warmer air aloft will overrun the cold surface=20
temperatures near and just below freezing over eastern NC and into=20
portions of eastern SC as well. Snowfall to the north will likely=20
maximize later this afternoon and evening as the surface low starts
to deepen over the Gulf Stream, with locally heavier rates >1"/hr=20
over southeastern VA, leading to moderate/heavy amounts. WPC=20
probabilities for at least 6 inches of snow are >50% there. There=20
is a much larger footprint of >2" probabilities of at least 40%,=20
extending from southwestern VA eastward, as far north as=20
Fredericksburg, VA to Rehoboth Beach, DE, and as far south as the=20 Raleigh-Durham metro.=20

Into NC, several hours of freezing rain are likely starting this=20
afternoon and continuing into the evening. Accretion will depend on
rainfall rates (which limit accretion), wind, and time of day, but
most of the guidance still indicates the potential for a couple=20
tenths of an inch of ice, roughly along and east of I-95 in eastern
NC. WPC probabilities for at least 0.10" ice are >40% with some=20
areas likely seeing >0.25" ice. Precipitation will wind down=20
overnight and end by Thursday morning.


...Great Lakes/Northeast...=20
Days 1-2...

Lake effect snow will diminish this morning as height falls over=20
the Corn Belt move into the region, favoring widespread light snow=20
over the Great Lakes and Midwest tonight into Thursday. WPC=20
probabilities for at least 4 inches of snow are low (<40%) except=20
for some lingering lake bands and/or lake enhanced snows.


...Pacific Northwest through the Central Rockies...
Days 1-3...

A potent but progressive Pacific system will start to move into=20
the Northwest this morning, spanning the latitudes from NorCal up=20
to the Canadian border. IVT will be modestly high (~90th=20
percentile) into NorCal/southern OR/northern NV toward Idaho,=20
supporting light to moderate snows for the terrain with snow levels
near 3000ft to the north and 5000ft to the south that will rise a=20
bit as the core of the moisture plume pushes through. The system=20
will move steadily along which will end QPF from west to east=20
starting as early as tonight over the Cascades and on Thursday over
the Great Basin. Moisture will wane with decreasing synoptic=20
support into Thursday, with snow confined mainly to the Unitas and=20
higher CO Rockies by then. For the 2-day period, WPC probabilities=20
for at least 8 inches of snow are highest (>70%) over the higher=20
terrain above 6000ft closer to the coast, 7000-8000ft over the=20
Great Basin, and 9000ft over CO/WY. A new system will to enter the=20
Northwest by D3 with lighter snow into the northern Cascades.


...Southeastern Mass...
Day 2...

The exiting system from the Southeast/southern Mid-Atlantic will=20
track northeastward and may clip southeastern MA/Cape Cod on=20
Thursday on its way into Atlantic Canada. The question revolves=20
around the speed of the incoming northern stream upper low and how=20
much it can capture the exiting system and pump up the downstream=20
ridge. 00Z guidance still shows at least some snow into the region,
but vary on how much. The best chances for snowfall over 4 inches=20
remains over Nantucket (~70%) as well as both Martha's Vineyard and
Cape Cod (40-60%), with low probs (10-20%) from Block Island to=20
New Bedford to Plymouth.


Fracasso


...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_2.png__;!!DZ3fjg!9sVcZe4TlHpniV6jCGyvBRat6RhwKKhfV5vDeJcEpZbHI= 3DIxoXOdFgeWi1xsDCLbhLvxvOujjMZE38LNF3kw8MjcUs$=20

$$

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FOUS11 KWBC 192113
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
413 PM EST Wed Feb 19 2025

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


...Mid-Atlantic and Carolinas...=20
Day 1...

Major winter storm continues into tonight for southern Mid-
Atlantic with heavy snow and notable icing. See the latest Key=20
Messages linked at the bottom.=20

Developing surface low ahead of southern stream wave is off SC/GA=20
border this afternoon. This coastal low strengthens as it shifts=20
northeast off Cape Hatteras through tonight. Heavy snow bands will
persist over southeast VA into northeast NC through this evening
where Day 1 snow probs for an additional >4" after 00Z are 40-70%.
Snow bands shift offshore after midnight. A wintry mix of mainly=20
freezing rain will persist over southern and eastern NC through=20
this evening. Day 1 ice probs for an additional >0.1" after 00Z are
40-70% over portions of the MHX and ILM CWAs.

The northern stream upper low is currently over Iowa and will=20
track to Ohio through tonight before pushing over the northern Mid-
Atlantic Thursday. Generally light snow is expected from this=20
upper low over the Ohio Valley tonight and over the central/=20
southern Appalachians into the DC metro area Thursday morning. Day
1 snow probs for >2" are 40-70% over the WV Highlands and the Great
Smokies.


...Great Lakes/Massachusetts Cape and Islands...=20
Days 1-2...

Lake effect snow reinvigorates over Lake Michigan tonight into
Thursday on the back side of the aforementioned upper low. NNWly
flow brings single band LES to far southwest MI into northern IN
through Thursday where Day 1 snow probs for >4" are 40-60%. NWly
flow late Thursday brings lake enhanced snow downwind of Erie
despite the lake being nearly frozen over. However, fetch from Lake
Huron will aid snowfall. Day 1.5 snow probs for >4" are around 20%
near Erie, PA.

The system developing off the Mid-Atlantic coast Thursday tracks up
off Nova Scotia Thursday night. This will bring the precip shield
with bay/ocean enhanced snow to southeastern MA/Cape Cod and
Islands Thursday afternoon/evening. Day 1.5 snow probs for >4" are
40-70% for the Cape and Islands.


...Pacific Northwest through the Central Rockies...
Days 1-3...

A potent but progressive Pacific system over the PacNW coast early
this afternoon will dig south as it moves inland with the base of
the trough reaching CO by late Thursday. Snow levels drop to 3000ft
over the WA Cascades through this evening before precip cuts off
with Day 1 snow probs for >4" 40-80% at and above pass level.=20

Snow levels over the northern Rockies are around 4000ft and closer
to 6000ft over CO through Thursday as this trough approaches.
Moderate elevation snow can be expected with Day 1 snow probs for

6" 40-80% around the Bitterroots on the ID/MT border,

northeastern NV ranges, the Wasatch, Uinta and Tetons. Snow=20
continues over the CO Rockies through Thursday night with Day 2
snow probs for >6" 30-60% across central and northern CO ranges.=20

The next wave pushes into the Queen Charlotte Sound Friday evening
with another atmospheric river pushing across WA Friday afternoon,
expanding south through OR Sunday. Snow levels at onset are around
4500ft in the WA Cascades Friday, increasing to 5000ft Friday=20
night and 6000ft over WA (and 8000ft over OR) on Saturday. Day 3=20
snow probs for >6" are 30-40% over the only higher WA Cascades with=20
the very high snow levels over OR precluding snow probs for the
isolated higher Cascade peeks at this time.


Jackson



...Winter Storm Key Messages are in effect and linked...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!7p_seGd11bEmj7cMHpvlL3_O0eakYUdrJUNQ2hZcx0xUM= E5s86ssTwHh9rDSkn4s-uaYBrvouwtuxQoVeOll3LvOpCI$=20

$$

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FOUS11 KWBC 200622
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
122 AM EST Thu Feb 20 2025

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


...Central Appalachians to New England...
Day 1...

A major winter storm which brought significant snow to the
Tidewater area of Virginia and surrounding portions of VA/NC will
continue to eject to the E/NE today while deepening. Snow will end
quickly this morning over VA, but as the low deepens and tracks
well southeast of the 40N/70W benchmark, snow will overspread
portions of coastal southern New England, especially Cape Cod and
the Islands. The system is progressive, but moisture spreading
north ahead of it will maintain periods of snow in far southeastern
MA, with some additional ocean enhanced snowfall likely across the
Cape Thursday night. Total additional snowfall is expected to be
modest, but may exceed 4" especially across the Outer Cape and
Nantucket as reflected by WPC probabilities of 30-50%.

Behind this potent surface low, an anomalous upper low will race
from the Ohio Valley to off the Mid-Atlantic coast by this evening,
bringing an arc of 500mb heights below the 2.5th climatological
percentile according to NAEFS. Steep lapse rates beneath this upper
low combined with moistening of the low-to-mid levels of the
column will result in a pivoting axis of moderate snowfall, which
may accumulate significantly in the higher terrain of WV where WPC probabilities for 4+ inches are locally 50-70%. Farther east,=20
moderate snow rates may bring some light accumulations from near=20
Greensboro, NC northeast through Hartford, CT. Although=20
accumulations will be less than 1 inch in most places, this snow=20
falling atop very cold ground could cause hazardous travel.


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

Lake effect snow (LES) will develop in the wake of the potent upper
low moving through the Ohio Valley and into the Mid-Atlantic today.
NW flow and accompanying CAA will produce a favorable environment
across the lakes, most notably SE of Lake Michigan early D1, and
then shifting to downstream (SE) of Lakes Erie and Ontario tonight
into Friday morning. The flow is not ideal along the long fetch of
the lakes except Lake Michigan, and duration is likely to be
relatively short, but WPC probabilities for 4+ inches of snow reach
as high as 30-50% across far SW MI near the lakeshore of Lake
Michigan, as well as along the Chautauqua Ridge east of Lake Erie.



...Central Rockies...=20
Day 1...

A weakening shortwave moving out of the Great Basin will dig E/SE
into the Central Rockies Thursday, combining with a weak jet streak
aloft to produce widespread deep layer ascent to support wintry
precipitation from Idaho through Colorado. A surface low beneath
the shortwave will traverse across Utah and Colorado, providing
additional ascent, and although moisture is near normal according
to NAEFS PW anomalies, this will result in a swath of moderate to
heavy snow, especially in the higher terrain of the Wasatch,
Uintas, and CO Rockies, primarily above 4000 ft. The waning=20
amplitude of this upper trough will allow precip to wane towards=20
the end of D1, but WPC probabilities for 6+ inches of snow are high

70%) along the Wasatch, higher terrain of the Uintas, and into

portions of the CO Rockies.


...Pacific Northwest...
Days 2-3...

A deepening trough well off the Pacific Coast will begin to advect
moisture onshore the Pacific Northwest beginning Friday night. This
moisture plume will be characterized by IVT within an atmospheric
river (AR) which has a high probabilities (>70%) of exceeding 500
kg/m/s according to both the GEFS and ECENS. Additionally, this
AR will have significant duration as probabilities for 500 IVT
exceeding 50% persist for around 48 hours from Friday night through
just beyond the end of this forecast period. The overlap of this
robust IVT and accompanying WAA with intensifying jet level
diffluence and mid-level divergence will result in expanding
precipitation, likely occurring in two distinct waves: one Friday
night into Saturday morning, and another Saturday night through
Sunday.=20

Within the first wave, snow levels will rise gradually to 4000-6000
ft along and west of the Cascades, but cold air remaining
entrenched to the east will keep snow levels below 3000 ft across
portions of interior OR and WA. With the second surge, however,
stronger WAA will lift snow levels to 6000-8000 ft, generally
keeping significant snow accumulations above pass levels. On D2,
WPC probabilities for 4+ inches that are above 50% are confined to
the highest terrain of the WA Cascades, although Washington Pass
may receive a few inches of snowfall D2. During D3, WPC
probabilities for 4+ inches increase in the WA Cascades, but again
at only the higher elevations, while additionally spreading east
into the Northern Rockies.



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_2.png__;!!DZ3fjg!-YC_Rzo2-WTs32sNk5n8Uk_LEXPHuF_vLsQR2QfQ2V1f-= wQVDZjlj7ng55ZUCqc-mv48rLqVnSf_OoIqT3TfpyjPdvk$=20

$$

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FOUS11 KWBC 202027
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 PM EST Thu Feb 20 2025

Valid 00Z Fri Feb 21 2025 - 00Z Mon Feb 24 2025


...Colorado Rockies and Central High Plains...=20
Day 1...

Shortwave trough axis over Utah this afternoon will shift east over
CO tonight and into western KS Friday morning. Weak jet streak=20
aloft and PVA from the trough will produce widespread deep layer=20
ascent to support snow over CO tonight with banding extending east
over the Palmer Divide, through eastern CO and into western KS late
tonight into Friday. Day 1 snow probs for >6" after 00Z are 40-80%
in the I-70 corridor of north-central CO Terrain and around 30% on
the I-25 corridor over the Palmer Divide near Castle Rock.
Probabilities for >2" spread east along I-70 to Limon, but given
the banding potential from upper forcing, there is potential for
over an inch into KS.=20


...Pacific Northwest to the Northern Rockies...=20
Days 2-3...

Mid-level low pressure pushes across the Queen Charlotte Sound
Friday evening with moisture advection and relatively short-lived=20
moderate precip to the south over the Pacific Northwest Friday=20
night. A broader trough approaches the Pacific Northwest this
weekend with heavier precip then expected Saturday afternoon
through Sunday.=20
For Friday night expect snow levels to gradually rise to 5000 ft=20
along the west side of the WA Cascades with cold air entrenched on
the east side keeping snow levels around 2000ft. Day 2 snow probs=20
for >6" are 50-80% for only the higher WA Cascades and far northern
ID terrain.


The broader moisture surge Saturday afternoon brings widespread
6000-8000 ft snow levels, keeping significant snow accumulations=20
above Cascades pass levels, with 6000ft snow levels inland over the
northern Rockies. Day 3 snow probs for >6" are 40-80% on the higher
WA Cascades, western Sawtooths, ranges around Glacier NP, and the
Tetons. Moderate precip will continue over terrain into Sunday
night.


Jackson




...Cold Key Messages are in effect for much of the southern U.S. as
linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!5ROePMOUawYh1Xj1cMQMIqeJ98h-81saYOQHqDbWQYjou= dqHOFkqgbcrz3CTnxnk4zLaxO9YIIgnhhn6VjNcX7Ke1R8$=20

$$

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FOUS11 KWBC 210623
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
123 AM EST Fri Feb 21 2025

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


...Pacific Northwest to the Northern Rockies...=20
Days 1-3...

An increasingly active pattern across the Pacific and into the
Northwest CONUS will drive two rounds of wintry precipitation
across the region through the weekend.

The first of these will approach this evening as a modest shortwave
impulse sheds from a larger closed low over the Pacific and moves
onshore by 00Z/Saturday. This will push a weakening cold front
onshore from an occluded low filling across British Columbia.
Modestly pinched mid-level flow will help surge moisture into the
region ahead of this front, characterized by PWs above the 90th
climatological percentile across WA according to NAEFS. The
accompanying ascent through WAA and then convergence along the
front itself will help expand precipitation across the region, but
with snow levels rising to 5000 ft west of the Cascades, and rising much
more slowly to the east. This will keep snow accumulations=20
generally above pass level (Washington Pass the exception), with=20
light icing possible across eastern WA state/the Columbia Basin.=20
Duration and intensity of precipitation D1 into D2 is likely to be
limited, so WPC probabilities for more than 4 inches of snow above
50% are confined to just the highest peaks of the WA Cascades.

After a brief break in precipitation Saturday, a more substantial
plume of moisture pivots onshore beginning Saturday evening/night,
driven by an atmospheric river (AR) which has high probabilities

90%) in both the ECENS and GEFS for IVT to exceed 500 kg/m/s.

This plume will be advected eastward thanks to increasingly
confluent flow just west of the coast and downstream of a
sharpening closed low, aided by a strengthening upper level jet
streak. By 00Z Sunday, IVT according to NAEFS will exceed the 99.5
percentile within the CFSR database, and this will continue to
spread across WA, northern ID, and into MT/WY by the end of the=20
forecast period. This impressive moisture combined with strong=20
synoptic ascent will result in an expansion of heavy precipitation,
but with snow levels concurrently rising to 6000-8000 ft. This=20
indicates that despite precipitation being very heavy at times,=20
most of the snow will be confined to the highest elevations and=20
well above pass levels. This is reflected by WPC probabilities D2=20
that are 70% or more for 6+ inches in the higher WA Cascades, which=20
then expand eastward, reaching 70% or more for 6+ inches across=20
portions of the Sawtooth, Northern Rockies, and Grand Tetons D3.


Weiss


...Extreme Cold Key Messages are in effect. Please see current Key
Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!7iftjcGbJrqAmFrnSmucZ6olkRGypWtc5hu11AASOZYzz= wxmh1cjHTXHb8PVQNqvJwsdcBMgkPHm7e6lKPV_xWjo1HQ$=20

$$

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FOUS11 KWBC 220711
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
211 AM EST Sat Feb 22 2025

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



...Pacific Northwest through the Northern Rockies...
Days 1-3...

A closed mid-level low tracking slowly south of the Aleutians will
shed lobes of vorticity eastward and onshore the Pacific Coast,
spreading precipitation from the Pacific Northwest through the
Northern Rockies into early next week.

Generally W to SW flow will persist across the Pacific during this
time, with enhanced confluence south of the Aleutian Low enhancing
moisture advection and IVT as an atmospheric river (AR). Both ECENS
and GEFS probabilities indicate that IVT will almost certainly

90%) exceed 500 kg/m/s, with potentially 3 consecutive days of

IVT exceeding 250 kg/m/s surging onshore beginning this evening.
Within this moisture plume, PWs are progged by NAEFS to exceed the
99.5 percentile of the CFSR database, especially late D1 through
the end of D2 from the WA/OR coasts to as far inland as the Central
Rockies. Shortwaves/vorticity spokes rotating within this flow will
cause periodic enhancement to ascent leading to heavier and more
widespread precipitation. Although the timing of these features is
not fully agreed upon by the guidance, consensus suggests bouts of
heavier precipitation are likely beginning late D1 and again late
D2. While this will result in heavy snow in higher terrain features
across the region through the period, snow levels will climb
steadily within the AR/accompanying WAA. Snow levels begin the
period around 4000-6000 ft, then climb to as high as 7000-9000 ft,
especially during D2. This will keep most significant snow
accumulations above area pass levels.

Although waves of heavy snow are likely in the higher terrain each
day, the heaviest accumulations are forecast on D2 when WPC
probabilities support a high risk (>70%) for more than 6 inches of
snow across the higher WA Cascades, the Northern Rockies near
Glacier NP, the Sawtooth, and near the Grand Tetons/Yellowstone NP.
During D3, the highest probabilities shift back into the WA/OR
Cascades with slightly lower snow levels supporting high
probabilities (>70%) for more than 6 inches, and 3-day snowfall in
the Cascades could be measured in several feet above 5000 ft
elevation. Additionally, some light icing is expected in the
Columbia Basin and parts of eastern OR where WPC probabilities D2
reach 10-30% for up to 0.1" of ice.

Weiss




$$

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FOUS11 KWBC 220710
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
210 AM EST Sat Feb 22 2025

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



...Pacific Northwest through Northern Rockies...
Days 1-3...

A closed mid-level low tracking slowly south of the Aleutians will
shed lobes of vorticity eastward and onshore the Pacific Coast,
spreading precipitation from the Pacific Northwest through the
Northern Rockies into early next week.

Generally W to SW flow will persist across the Pacific during this
time, with enhanced confluence south of the Aleutian Low enhancing
moisture advection and IVT as an atmospheric river (AR). Both ECENS
and GEFS probabilities indicate that IVT will almost certainly

90%) exceed 500 kg/m/s, with potentially 3 consecutive days of

IVT exceeding 250 kg/m/s surging onshore beginning this evening.
Within this moisture plume, PWs are progged by NAEFS to exceed the
99.5 percentile of the CFSR database, especially late D1 through
the end of D2 from the WA/OR coasts to as far inland as the Central
Rockies. Shortwaves/vorticity spokes rotating within this flow will
cause periodic enhancement to ascent leading to heavier and more
widespread precipitation. Although the timing of these features is
not fully agreed upon by the guidance, consensus suggests bouts of
heavier precipitation are likely beginning late D1 and again late
D2. While this will result in heavy snow in higher terrain features
across the region through the period, snow levels will climb
steadily within the AR/accompanying WAA. Snow levels begin the
period around 4000-6000 ft, then climb to as high as 7000-9000 ft,
especially during D2. This will keep most significant snow
accumulations above area pass levels.

Although waves of heavy snow are likely in the higher terrain each
day, the heaviest accumulations are forecast on D2 when WPC
probabilities support a high risk (>70%) for more than 6 inches of
snow across the higher WA Cascades, the Northern Rockies near
Glacier NP, the Sawtooth, and near the Grand Tetons/Yellowstone NP.
During D3, the highest probabilities shift back into the WA/OR
Cascades with slightly lower snow levels supporting high
probabilities (>70%) for more than 6 inches, and 3-day snowfall in
the Cascades could be measured in several feet above 5000 ft
elevation. Additionally, some light icing is expected in the
Columbia Basin and parts of eastern OR where WPC probabilities D2
reach 10-30% for up t0 0.1" of ice.

Weiss

$$

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FOUS11 KWBC 212029
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 PM EST Fri Feb 21 2025

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


...South-Central Texas...
Day 1...

Low level NEly flow from high pressure centered over Arkansas will
persist over the eastern half of Texas through Saturday morning.
Dry/cold air advection in this flow will continue to be overrun by southerly/Gulf-moisture laden air with an expansion of precip from
South to Central Texas tonight. There is question to how far sub-
freezing temps make it tonight, but as of now there is sufficient
confidence in freezing rain accumulating over central Texas, around
and a bit east of the San Antonio metro area (where WFO EWX has an
advisory). There is potential for some elevated ice glaze farther
south into the CRP CWA, but that fine line is not that clear as of
this time. Day 1 ice probabilities for >0.01" are 40-60% in and
east of San Antonio with 10% probs extending from the Austin metro
to Laredo.


...Pacific Northwest through Northern Rockies...
Days 1-3...

Pacific moisture advects over the PacNW to the northern Rockies
through Monday with a few upper trough passages expected. Higher
elevation snow is expected through the next three days with the
heaviest precip Saturday afternoon through Sunday when there are
rather high snow levels.

An upper low moves over the Queen Charlotte Sound through this
evening. 0.75" PW air flows across WA through Saturday morning with
snow levels west of the Cascades crest generally rising from 4500ft
to 5500ft while persisting around 3000ft east of the crest over the
northern Columbia Basin due to entrenched cold air. Day 1 snow
probs for >6" are 40-70% in the north WA Cascades and the Selkirks
in far north Idaho.

The next wave in this zonal flow arrives to Vancouver Island
Saturday midday with a plume of 1 to 1.25" PW air streaming over
WA/OR Saturday afternoon through Sunday. Snow levels rapidly rise
to 8000ft in this plume for Saturday night, though snow levels drop
to around 6000ft in the north WA Cascades Sunday afternoon under
the next shortwave trough axis. This moisture also spreads across
the northern Rockies where snow levels will be 5000-6000ft. Day 2
snow probs for >6" are 40-70% in the north WA Cascades, western
Sawtooths, Bitterroots, and ranges around Glacier NP. THe pattern
for the Day 3 snow probs for >6" are similar to Day 2 just with
lower probs for the Sawtooths and Bitterroots with an expansion
over the southern Absarokas and Tetons (40-70% there). Three day
snow totals over 3ft are possible in the highest WA Cascades with
more like 1-2ft in the higher Sawtooths, Tetons, and Lewis Range at
Glacier NP.

This is nearly all above mountain road passes and is generally a
beneficial precip event for watersheds in the NW.


Jackson



$$

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FOUS11 KWBC 221908
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
208 PM EST Sat Feb 22 2025

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

...Pacific Northwest through the Northern Rockies...
Days 1-3...

The overall synoptic evolution forecast remains pretty consistent
among guidance as of the 12z NWP suite. A closed mid- level low
tracking slowly south of the Aleutians will continue shedding
lobes of vorticity eastward and onshore the Pacific Coast,
spreading precipitation from the Pacific Northwest through the
Northern Rockies into early next week.

Generally W to SW flow will persist across the Pacific during this
time, with enhanced confluence south of the Aleutian Low enhancing
moisture advection and IVT as an atmospheric river (AR). Both ECENS
and GEFS probabilities indicate that IVT will almost certainly

90%) exceed 500 kg/m/s, with 3 consecutive days of IVT exceeding

250 kg/m/s surging onshore beginning this evening. Within this
moisture plume, PWs are progged by NAEFS to exceed the 99.5
percentile of the CFSR database, especially late D1 through the end
of D2 from the WA/OR coasts to as far inland as the Central
Rockies. Shortwaves/vorticity spokes rotating within this flow will
cause periodic enhancement to ascent leading to heavier and more
widespread precipitation. Although the timing of these features is
not fully agreed upon by the guidance, consensus suggests bouts of
heavier precipitation are likely beginning late D1 and again late
D2. While this will result in heavy snow in higher terrain features
across the region through the period, snow levels will climb
steadily within the AR/accompanying WAA. Snow levels begin the
period around 4000-6000 ft, then climb to as high as 7000-9000 ft,
especially during D2. This will keep most significant snow
accumulations above area pass levels.

As me move into D3, a tertiary shortwave trough will pivot
underneath the prominent gyre to the north generating a more
significant height fall pattern as we step into Tuesday morning.
Snow levels that rose considerably in the periods prior will see
them decrease rapidly as the advancing shortwave trough allows for
colder temps to seep down into the previous 4000-6000 ft range
culminating in more widespread heavy snowfall across the Northern
Cascades and higher elevations of the Olympics in WA. Steady
progression of colder air mixing further into the column will
protrude areas east of the coastal ranges with areas inland
towards northern ID and northwestern MT seeing an uptick in
snowfall for the 12-00z time frame Tuesday into Wednesday. Heaviest
snow will still be confined to the Cascades, but some areas east
of the mountain chain will see >4" of snowfall, namely over the
Bitterroot Range extending northeast towards the Cabinet Mtns., and
southeast into the Absaroka Range.

The heavy snow footprint continues to be most prominent in that D2
to D3 time frame with the highest probs (>70%) for >4" located over
the ranges above. Additional high probs over 70% will exist in the
highest elevations of the Olympics by D3 due to the incoming
disturbance. Totals >8" are split between the remainder of D1 with
a break between D1 and part of D2, but will pick up significantly
in both magnitude (50-80%) and spatial coverage of the higher probs
across the PAC Northwest by the end of D2 into D3 within the
vicinity of the Cascades, Olympics, and Bitterroot Ranges. This
will culminate in the highest elevations encountering several (4+)
feet of snow over the next 72 hrs. with 1-3 feet forecast for areas
between 4000-7000 ft MSL. Additionally, some light icing is
expected in the Columbia Basin, as well as parts of eastern OR
where WPC probabilities D1 into early D2 reach 10-30% for up to
0.1" of ice.

Weiss/Kleebauer

...Tug Hill through Northern Green & White Mountains...
Day 1-2...

Shortwave trough analyzed over the northern Great Lakes will
continue pushing downstream into neighboring Quebec with the
southern fringes of the energy bisecting Upstate NY through
Northern New England by this evening. Sufficient low-level
buoyancy generated by modest delta-T's over Lake Ontario will
create a moderately strong singular band that will align downwind
of the lake with the fetch aimed into the Central and Southern Tug
Hill Plateau. Combined moisture fetch and local upslope component
will allow for a targeted area of heavy snow to those areas within
the band placement. High probs of 70-90% for >4" exist within the
window of 00-18z Sunday with a very small area of 40-70% probs for

6" intersecting the Tug Hill area between Watertown to Pulaski and

points inland. This is the primary zone for heavy snow within the
Northeastern U.S, but some upslope snows within the Northern Green
and White Mountains of VT/NH also point to some modest
probabilities of >4", especially as you enter the Greens from Mount
Mansfield and points north.

Kleebauer

$$

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FOUS11 KWBC 230738
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
238 AM EST Sun Feb 23 2025

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

...Pacific Northwest through the Northern Rockies...
Days 1-3...

Long duration atmospheric river (AR) begins before the forecast
period, and continues through Tuesday. This AR is driven by
confluent mid-level flow overlapped by multiple impressive Pacific
jet streaks, resulting in pronounced onshore flow of moisture. The
accompanying IVT has a high probability (>80% from ECENS and GEFS)
of exceeding 500 kg/m/s through Monday, with a slow wane
thereafter. Within this plume of moisture, forcing for ascent will
be periodically enhanced by shortwave troughs rotating through the
flow as impulses shed from a strong closed mid-level low out over
the Pacific Ocean. Each of these impulses will produce enhanced
ascent to expand and intensify the accompanying precipitation,
leading to rounds of heavy snow from the Cascades through the
Northern Rockies. However, the WAA within the AR will lift snow
levels to as high as 8000 ft, before latitudinal variations develop
on either side of a stalled front.

For D1, a closed 500mb low pushing onshore British Columbia will
pulse a lobe of vorticity into WA state, accompanied favorably by
coupled jet streaks. This will combine with a cold front pushing
eastward to enhance ascent and drive rounds of heavy precipitation
from northern CA through the Northern Rockies, with upslope flow
into terrain features resulting in the heaviest accumulations of
precipitation. Snow levels during this time will rise to generally
6000-8000 ft, keeping snow confined above pass levels. However,
where it does snow, accumulations will be significant as reflected
by WPC probabilities that indicate a high risk (>70%) for 8+ inches
in the Sawtooth, Northern Rockies near Glacier NP, and the Tetons
of WY.

This first front will then become elongated west-east as the
mid-level pattern becomes flattened in response to a sharper trough
approaching from the West. This will allow some colder air to drain
southward but remain confined generally to WA, northern ID, and MT,
with a sharp gradient in snow levels existing along this boundary
(3000 ft north, 6000 ft south). This will be relatively short lived
however, as the stronger trough axis drives a potent closed low and accompanying surface low towards the WA/OR coast late Monday. This
will once again result in enhanced ascent through WAA, PVA, and
upper diffluence, with a second surge in precipitation expanding
east across the area. Snow levels climb again to as high as 6000 ft
in many areas late Monday into early Tuesday, before the associated
cold front drives eastward by the end of the period. While this
will cause snow levels to fall quickly, it will also result in
rapid drying of the column, bringing an end to the heavy
precipitation.

D2 snowfall is likely to be heaviest along the spine of the
Cascades and into the Olympics of WA, where WPC probabilities are
high (>90%) for 8 inches, and locally 1-3 feet is possible in the
highest elevations. During D3 the heaviest precipitation spreads
inland as far as the Northern Rockies and into the vicinity of
Yellowstone NP, but the heaviest accumulations are likely again
across the WA Cascades where WPC probabilities are above 50% for an
additional 8+ inches of snow.


Weiss


$$

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FOUS11 KWBC 231916
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
216 PM EST Sun Feb 23 2025

Valid 00Z Mon Feb 24 2025 - 00Z Thu Feb 27 2025

...Pacific Northwest through the Northern Rockies...
Days 1-3...

Current assessment of the mid-level WV satellite across the Eastern
Pacific denotes a textbook multi-wave structure within a long axis
stretch of progressive shortwave troughs migrating underneath a
prominent trough axis nestled over the Gulf of Alaska. The current
AR across the Pacific Northwest is driven by the confluent mid-
level flow overlapped by multiple impressive Pacific jet streaks
accompanying each shortwave trough, resulting in a pronounced
onshore flow of moisture centered over the OR/WA coasts, extending
inland. The accompanying IVT has a high probability (>80% from
ECENS and GEFS) of exceeding 500 kg/m/s through tomorrow (Monday),
with a slow wane thereafter. Within this plume of moisture,
forcing for ascent will be periodically enhanced by the
aforementioned shortwave troughs pivoting through the flow as these
impulses shed from a strong closed mid-level low out over the
Pacific Ocean. Each of these impulses will produce enhanced ascent
to expand and intensify the accompanying precipitation, leading to
rounds of heavy snow from the Cascades through the Northern
Rockies. However, the WAA within the AR will lift snow levels to as
high as 8000 ft, before latitudinal variations develop on either
side of a stalled front.

For D1, a closed 500mb low pushing onshore British Columbia will
pulse a lobe of vorticity into WA state, accompanied favorably by
coupled jet streaks. This will combine with a cold front pushing
eastward to enhance ascent and drive rounds of heavy precipitation
from northern CA through the Northern Rockies, with upslope flow
into terrain features resulting in the heaviest accumulations of
precipitation. Snow levels during this time will rise to generally
6000-8000 ft, keeping snow confined above pass levels. However,
where it does snow, accumulations will be significant as reflected
by WPC probabilities that indicate a high risk (50-80%) for 8+
inches in the Sawtooth, Northern Rockies near Glacier NP, and the
Tetons of WY.

This first front will then become elongated west-east as the
mid-level pattern becomes flattened in response to a sharper trough
approaching from the West. This will allow some colder air to drain
southward but remain confined generally to WA, northern ID, and MT,
with a sharp gradient in snow levels existing along this boundary
(3000 ft north, 6000 ft south). This will be relatively short lived
however, as the stronger trough axis drives a potent closed low and accompanying surface low towards the WA/OR coast late Monday. This
will once again result in enhanced ascent through WAA, PVA, and
upper diffluence, with a second surge in precipitation expanding
east across the area. Snow levels climb again to as high as 6000 ft
in many areas late Monday into early Tuesday, before the associated
cold front drives eastward by the end of the period. While this
will cause snow levels to fall quickly, it will also result in
rapid drying of the column, bringing an end to the heavy
precipitation.

D2 snowfall is likely to be heaviest along the spine of the
Cascades and into the Olympics of WA, where WPC probabilities are
high (>70%) for 8 inches, and locally 1-3 feet is possible in the
highest elevations. A secondary maxima will align within the
highest elevations of Northern ID near the MT/ID border as the
moisture advection and progressive cold front propagate inland
during the back half of D2 leading to moderate probs of 40-70% for
potential of 8+ inches. During the front half of the D3 time
frame, the heaviest precipitation will continue to spread inland
as far as the Northern Rockies and into the vicinity of Yellowstone
NP, but the heaviest accumulations are likely again across the WA
Cascades where WPC probabilities are above 50% for an additional 8+
inches of snow. Drier air advecting into the Northwestern U.S
during the latter half of Tuesday will spell the end to the
extended AR impacts that have been in place the past several days.


Weiss/Kleebauer


$$

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FOUS11 KWBC 240647
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
147 AM EST Mon Feb 24 2025

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

...Pacific Northwest through the Northern Rockies...
Days 1-2...

Ongoing atmospheric river (AR) will intensify and continue through
today and into Tuesday before eroding as the driving trough pivots
inland. Until that occurs, persistent advection of moisture on IVT
exceeding 500 kg/m/s is expected into WA/OR and then spilling as
far east as portions of the Northern Rockies. This AR will be
driven by confluent flow downstream of an impressive closed low
(NAEFS 500-700mb height anomalies below -1 sigma) which will be
overlapped by a strengthening upper jet streak. Weak impulses
shedding eastward from this closed low as it moves into British
Columbia will help to periodically enhance ascent, with additional
lift likely in the vicinity of a surface low moving near the Strait
of Juan de Fuca Tuesday morning. Impressively confluent flow will
keep moisture advection nearly perpendicular to the Cascades and
other N-S ranges, leading to strong upslope ascent as well.

The guidance is well aligned overall with the synoptic and
mesoscale features, leading to high confidence in the evolution of
this event. However, the consensus has trended colder Monday in
areas north of a draped front from west-east near the WA/OR border.
This will keep snow levels more suppressed, generally remaining
around 3000-3500 ft in WA, ID, MT D1 before a slow rise occur late
D1 due to the enhanced WAA as a warm front lifts north ahead of
the surface low. Thereafter, snow levels crash again quickly during
D2 as the accompanying cold front pivots east. Despite the lowering
snow levels D2, this will occur in tandem with a drying column,
which indicates most of the heavy snow should accumulate only at
the higher elevations thanks to rapid wane of precipitation
coverage and intensity by the second half of D2.

WPC probabilities for heavy snow accumulating to more than 6 inches
are high (>90%) in the Olympics and along the crest of the Cascades
D1, with locally 2-3 feet possible at the highest elevations.
Additionally, impactful pass-level snow is likely especially at
some of the higher passes like Washington Pass. During D2, heavy
snow continues across the Cascades but also expands eastward
towards the Northern Rockies. WPC probabilities D2 are high (>70%)
for 6+ inches across the higher elevations of these ranges, before precipitation winds down into D3.


Weiss



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FOUS11 KWBC 241937
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
237 PM EST Mon Feb 24 2025

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

...Pacific Northwest through the Northern Rockies...
Days 1-2...

Our current AR over the Pacific Northwest is ongoing with the
sat/radar composite outline a textbook warm frontal band of
precipitation across coastal OR/WA. The cold front accompanying
the surface low off the coast is already being analyzed off the
northwestern CA and southwest OR coasts with light precip already
situated along and ahead of the axis of frontal convergence. Deep
moisture anomalies continue to be the driver of heavier
precipitation potential with IVT's hovering between 400-600 kg/m/s
during the strongest precip period occurring now through at least
early Tuesday morning. IVT anomaly is squarely within 3-5
deviations above normal according to the latest NAEFS output, a
typical marker for marginal AR intensity. This should provide
sufficient deep layer moisture for heavier snowfall potential over
the higher elevations of the Olympics and Cascades this afternoon,
even as warmer air filters inland and snow levels rise into the
evening.

The guidance is still well aligned overall with the synoptic and
mesoscale features, leading to high confidence in the evolution of
this ongoing event. Consensus overnight did trend colder today in
areas north of a draped front from west-east near the WA/OR border,
but the propagation of the warm front will lead to snow levels
rising incrementally through the afternoon and early evening hours
across WA/ID/OR/MT. Thereafter, snow levels will plateau during the
overnight time frame, then crash again quickly during front half
of D2 as the aforementioned cold front off the Pacific coast pivots
east accompanying falling heights aloft. Despite the lowering snow
levels D2, this will occur in tandem with a drying column, which
indicates most of the heavy snow should accumulate only at the
higher elevations thanks to rapid wane of precipitation coverage
and intensity by the second half of D2.

WPC probabilities for heavy snow accumulating to more than 6 inches
remain high (>90%) in the Olympics and along the crest of the
Cascades the remainder of D1, with locally 2-3 feet possible at
the highest elevations (Above 7000ft MSL). Additionally, impactful
pass- level snow is likely especially at some of the higher passes
like Washington Pass. During D2, heavy snow continues across the
Cascades but also expands eastward towards the Northern Rockies.
WPC probabilities D2 are high (>70%) for 6+ inches across the
higher elevations of these ranges, before precipitation winds down
into D3.

Weiss/Kleebauer


$$

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FOUS11 KWBC 250630
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
130 AM EST Tue Feb 25 2025

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

...Pacific Northwest through the Northern Rockies...
Day 1...

Strong surface low pressure will be moving eastward near the Strait
of Juan de Fuca, pivoting onshore beneath a strong but filling
upper level shortwave trough. This upper feature will weaken
rapidly as it gets replaced by upper level ridging, resulting in
the surface low eroding as it moves across WA state. E/SE of this
stacked system, the ongoing atmospheric river (AR) will persist
another 12 hours as reflected by GEFS/ECENS IVT probabilities,
surging moisture into the Pacific Northwest and Northern Rockies
D1. The lingering precipitation D1 is expected to be lighter than
the heavy amounts that have fallen already, but still should
result in heavy snow in the WA Cascades and Northern Rockies,
including the Bitterroots and Lewis Range, especially above
3000-3500 ft. In these areas, WPC probabilities for 6+ inches of
snow are high (>90%), and pass level impacts will continue until
snow wanes at the end of D1.


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

A modest wave of low pressure will move northeast from the Great
Lakes across New England Thursday into Friday, with an accompanying
cold front trailing in its wake. The low will likely track across
central New England, with the accompanying WAA causing
precipitation to expand in the form of snow across northern New
England. Although the system will be fast moving, brief heavy snow
is likely in the higher terrain of the White Mountains of NH where
WPC probabilities reach 30-50% for 4+ inches of accumulations.
Later D3, as the cold front passes to the east, post-frontal
upslope flow will develop into the Adirondacks and northern Greens,
with modest lake enhancement occurring into the Tug Hill Plateau.
In these areas, WPC probabilities for 4+ inches reach 30-50% as
well, but generally later in the D3 period than what will occur
across the NH terrain.


Weiss

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FOUS11 KWBC 251905
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
205 PM EST Tue Feb 25 2025

Valid 00Z Wed Feb 26 2025 - 00Z Sat Mar 01 2025

...Pacific Northwest through the Northern Rockies...
Day 1...

Potent surface low moving ashore far northwest WA along with a
weakening upper low opening into an upper shortwave over the
Northern Rockies tonight will continue to produce areas of heavy
snow through early Wednesday. The atmospheric river once associated
with this system will end by this evening as IVT values drop to
below 250 kg/m*s once upper ridging builds along the West Coast.
However, lingering precipitation is expected across the northern
WA Cascades and northern ID/western MT ranges overnight, including
the Bitterroots and Lewis Range, especially above 3000-3500 ft. In
these areas, WPC probabilities for an additional 6+ inches of snow
are high (>70%), and pass level impacts will continue until snow
wanes during the middle of D1.


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

A modest wave of low pressure will move northeast from the Great
Lakes across New England Thursday into Friday, with an accompanying
cold front trailing in its wake. The low will likely track across
central New England, with the accompanying WAA causing
precipitation to expand in the form of snow across northern New
England. Although the system will be fast moving, brief heavy snow
is likely in the higher terrain of the White Mountains of NH where
WPC probabilities reach 30-50% for 4+ inches of accumulations.
There is a chance for some light ice accumulations (<0.1") associated
with the WAA across the Catskills, Adirondacks, and Berkshires on
Thursday, but with the surface low crossing to the west there
won't be much time for ice to accrete after the mid-level warm
nose changes ptype to rain. By D3, as a secondary cold front passes
to the east, post- frontal upslope flow will develop into the
Adirondacks and northern Greens, with modest lake enhancement
occurring into the Tug Hill Plateau. In these areas, WPC
probabilities for 4+ inches reach 50-70%, but with higher values
(70-90%) across the Tug Hill.


...Upper Great Lakes...
Day 3...

By Thursday night into Friday morning, a clipper system diving
southeast across south-central Canada will begin to spread a swath
of WAA driven snow into far northern MN. This system will progress
eastward quickly with snowfall spreading across the majority of
the Upper Great Lakes on Friday, including northern WI, the MI
U.P. and northern L.P. There remains some north-south uncertainty
with GFS/GEFS depicting a more southerly solution and heavy (4+
inches) amounts extending across the MN Arrowhead through northern
MI, while the ECMWF/ECENS depicts the heaviest snow confined to
the eastern U.P. The GFS is likely on the southern end of the
guidance due to a slightly more amped downstream 500 mb pattern
ahead of the clipper system. Current day shift forecast fell in
between, while leaning towards the northern ECENS solution. WPC
probabilities are largely 20-40% across the region for 4+ inches of
snow on D3, with 40-60% chances across the eastern U.P. of MI.


Snell/Weiss




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FOUS11 KWBC 260711
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
211 AM EST Wed Feb 26 2025

Valid 12Z Wed Feb 26 2025 - 12Z Sat Mar 01 2025



...Upper Great Lakes through the Northeast...
Days 2-3...

A series of shortwave troughs moving through the flow this week
will result in an amplified longwave trough deepening across the
eastern CONUS. This will create period of active wintry weather
from the Upper Great Lakes through northern New England.

The first of these shortwaves will pivot southeast from the Upper
Midwest Wednesday night, reaching the Great Lakes before 12Z
Thursday and then pushing into New England on Friday. This will
sharpen the associated longwave trough across the east, driving a
cold front across the region, which will be draped from a wave of
low pressure likely developing downstream of the lead shortwave. As
this low moves E/NE from Michigan to New England, accompanying WAA
will help spread precipitation northeastward as PWs surge to +1 to
+2 sigma according to NAEFS ensemble tables. The surface low
tracking across northern New England will allow precipitation to
start as snow in many places from Upstate New York into New
England, but changeover to a mix and then rain across all but the
higher terrain of the Adirondacks, Whites, and northern Maine.

Then as the subsequent cold front pushes through on Thursday,
upslope flow in a still moist column will drive periods of moderate
snowfall across the Adirondacks, Greens, and Tug Hill Plateau, the
latter aided by lake Ontario moisture enhancement. This will
result in locally heavy snow exceeding 4 inches as reflected by WPC probabilities D2 that are moderate to high (30-70%) across these
mountain ranges, with locally 6+ inches possible in the higher
terrain and across the Tug Hill Plateau.

A subsequent shortwave will race southeast immediately on the heels
of this first system, pushing an Alberta Clipper type low from
northern MN early Friday to New England Saturday. This system will
be compact and progressive, but a strengthening shortwave and
favorable positioning of an upper level jet streak will produce
significant ascent to spread moderate to heavy precipitation across
the region. Although this system will Alas be progressive, a
region of overlapping frontogenesis and deformation north of the
surface low will result in an axis of heavier precipitation, and
since the column will be quite cold behind Thursday's cold front,
this will produce a swath of heavy snow from the Arrowhead of MN,
across the U.P. of MI, eastward into northern New England. WPC
probabilities D3 are high (>70%) for 4+ inches from the eastern
U.P. through the far northern portion of the L.P., with 30-70%
chances for 4+ inches encompassing that region as far west as the
tip of the Arrowhead to as far east as the western Adirondacks.

Weiss


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FOUS11 KWBC 261840
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
140 PM EST Wed Feb 26 2025

Valid 00Z Thu Feb 27 2025 - 00Z Sun Mar 02 2025


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

The first in a series of progressive shortwaves to impact the
Northeast with wintry weather over the next few days will pivot
southeast from the Upper Midwest tonight, reaching the Great Lakes
before 12Z Thursday and then pushing east of New England on Friday.
This will sharpen the associated longwave trough across the east,
driving a cold front across the region, which will be draped from a
wave of low pressure likely developing downstream of the lead
shortwave. As this low moves E/NE from Michigan to New England,
accompanying WAA will help spread precipitation northeastward as
PWs surge to +1 to +2 sigma according to NAEFS ensemble tables. The
surface low tracking across northern New England will allow
precipitation to start as snow in many places from the PA-NY line
into New England, but changeover to a mix and then rain across all
but the higher terrain of the Adirondacks, Whites, and northern
Maine. WPC probabilities for 4+ inches of snow through Thursday
evening are medium (50-70%) along the White Mts of NH and ME, with
lower probs (10-20%) stretching eastward to just northwest of
Portland. Chances for ice accretion over 0.1" are low outside of
the Catskills, but a glaze of freezing rain is possible across the
favorable elevated sections of New England.

Then as the subsequent cold front pushes through on Thursday,
upslope flow in a still moist column will drive periods of moderate
snowfall across the Adirondacks, Greens, and Tug Hill Plateau into
early Friday, the latter aided by lake Ontario moisture
enhancement. This will result in locally heavy snow exceeding 4
inches as reflected by WPC probabilities D2 that are moderate to
high (30-70%) across these mountain ranges, with locally 6+ inches
possible in the higher terrain and across the Tug Hill Plateau.


...Upper Great Lakes through the Northeast...
Days 2-3...

A subsequent shortwave will race southeast immediately on the
heels of this first system, pushing an Alberta Clipper type low
from northern MN early Friday to New England Saturday. This system
will be compact and progressive, but a strengthening shortwave and
favorable positioning of an upper level jet streak will produce
significant ascent to spread moderate to heavy precipitation across
the region. Although this system will Alas be progressive, a
region of overlapping frontogenesis and deformation north of the
surface low will result in an axis of heavier precipitation, and
since the column will be quite cold behind Thursday's cold front,
this will produce a swath of heavy snow from the Arrowhead of MN,
across the U.P. of MI, eastward into northern New York State. WPC
probabilities D3 are high (>70%) for 4+ inches in these regions,
with lower probs (10-30%) situated across northern New England on
D3 outside of the elevated Green and White Mts. The greatest
potential for at least 8 inches of snow (40-60%) exists along a
WNW-ESE swath from the MN Arrowhead to the eastern U.P. (including
the Keweenaw Peninsula).

Snell/Weiss




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FOUS11 KWBC 270803
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 AM EST Thu Feb 27 2025

Valid 12Z Thu Feb 27 2025 - 12Z Sun Mar 02 2025


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

The first in a pair of winter storms tracks through the Northeast
today. NAEFS shows a sub 1004mb low tracking through the eastern
Great Lakes that is below the 10th percentile. This low is also
directing a narrow >500 kg/m/s IVT towards New England that is
above the 90th climatological percentile. As anomalous moisture is
directed towards the northern Appalachians, a sufficiently cold
air-mass located over New England will support periods of snow,
particularly in the northern Appalachian ranges. With low-level WAA
and 290k isentropic glide aloft, periods of snow will be ongoing
from the Adirondack on east through the Green and White Mountains
this morning. As low pressure tracks into the Champlain Valley
around midday, snow will track into the northern two-thirds of
Maine with a wintry mix just north of the Maine coastline. The
storm will race northeast into the St. Lawrence Valley of southern
Quebec by Thursday evening with a dry slot moving in aloft that
effectively shuts off most accumulating snowfall beyond 00Z Friday.
WPC probabilities show low-to-moderate chances (30-50%) for
snowfall >6" in the peaks of the Green and White Mountains. Most
snowfall totals >500ft in elevation that are not in the Green and
White Mountains are most likely to see anywhere from 1-4" of
snowfall through Thursday afternoon. The WSSI does show a swath of
Minor Impacts from southern VT and central NH on east through the
southern half of Maine. Residents in these areas could contend with
hazardous driving conditions, particularly in areas with complex
terrain.


...Upper Great Lakes through the Northeast...
Days 2-3...

An unusually strong clipper system diving southeast from southern
Canada will head for the Upper Great Lakes on Friday. The storm
will reside beneath the diffluent left-exit region of a 90-100 knot
500mb jet streak, while also sporting an unusually strong NWrly IVT
that surpasses 300 kg/m/s on the western flank of the Clipper. The
low-level circulation at 850mb is also rather potent with heights
that are below the 0.5 climatological percentile by 18Z Friday
according to NAEFS. This equates to what would be a "front-end
thump" of heavy snow late Thursday night across the Minnesota
Arrowhead, then across the Michigan U.P. and far northern Michigan
Friday morning where the best 850mb FGEN ensues. Just north of the
850mb FGEN is where snowfall rates of 1-2"/hr are possible for
several hours. A dry slot and warming boundary layer should limit
snowfall over the Michigan U.P. and northern Michigan Friday
afternoon. As the storm heads east though, additional snow is
likely on the back side of the storm as low-level CAA over Lake
Superior increases Friday evening. Snow should taper off by
Saturday morning in the Upper Great Lakes. WPC probabilities show moderate-to-high chances (50-70%) for snowfall totals >6" in the
MN Arrowhead with similar chances for >8" in the Keweenaw
Peninsula, the, Huron Mountains, and eastern Michigan U.P..
Localized amounts approaching a foot are possible closer to Sault
Ste. Marie, MI.

The storm continues its march east into southern Ontario Friday
evening with the same method of producing periods of heavy snow as
far east as the Tug Hill and Adirondacks of northern New York.
Unlike the Upper Great Lakes, however, the storm track is farther
north through the St. Lawrence Valley. WPC's Snowband Probability
Tracker, utilizing the 00Z HREF guidance, shows the potential for
1"/hr rates from the Tug Hill to as far east as the Green and White
Mountains Friday night. The dryslot and warming low level-
temperatures arrive Saturday morning with only northern Maine
likely to still see periods of moderate-to-heavy snow through rest
of the day Saturday. Snow should taper off throughout the Interior
Northeast by Saturday night. WPC probabilities show moderate-to-
high chances (50-70%) for snowfall >6" in the Tug Hill and
Adirondacks neighboring the Tug Hill through Saturday morning.


Mullinax


$$

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FOUS11 KWBC 271845
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
145 PM EST Thu Feb 27 2025

Valid 00Z Fri Feb 28 2025 - 00Z Mon Mar 03 2025


...Upper Great Lakes through the Northeast...
Days 1-2...

An unusually strong clipper system (MSLP below the first
climatological percentile per the ECMWF) diving southeast from
southern Canada will head for the Upper Great Lakes on Friday. The
storm will reside beneath the diffluent left- exit region of a
90-100 knot 500mb jet streak, while also sporting an unusually
strong NWrly IVT that surpasses 300 kg/m/s on the western flank of
the surface low. The low- level circulation at 850mb is also rather
potent with heights that are below the 0.5 climatological
percentile by 18Z Friday according to NAEFS. This equates to what
would be a "front- end thump" of heavy snow late Thursday night
across the Minnesota Arrowhead, then across the Michigan U.P. and
far northern Michigan Friday morning where the best 850mb FGEN
ensues. Just north of the 850mb FGEN is where snowfall rates of
1-2"/hr are possible for several hours and supported by the latest
12z HREF, which has trended slightly north over the last few
forecast cycles. A dry slot and warming boundary layer should
limit snowfall over the Michigan U.P. and northern Michigan Friday
afternoon, leading to a relatively narrow swath of heavy snow. As
the storm heads east though, additional snow is likely on the back
side of the storm as low- level CAA over Lake Superior increases
Friday evening. Snow should taper off by Saturday morning in the
Upper Great Lakes. WPC probabilities show moderate-to-high chances
(50-70%) for snowfall totals >6" in the MN Arrowhead with similar
chances for >8" in the Keweenaw Peninsula, Huron Mountains, and
eastern Michigan U.P.. Localized amounts approaching a foot are
possible closer to Sault Ste. Marie, MI and locations just south
and east.

The storm continues its march east into southern Ontario Friday
evening with the same method of producing periods of heavy snow as
far east as the Tug Hill and Adirondacks of northern New York.
Unlike the Upper Great Lakes, however, the storm track is farther
north through the St. Lawrence Valley. WPC's Snowband Probability
Tracker, utilizing the 12Z HREF guidance, shows the potential for
1"/hr rates from the Tug Hill to as far east as the Green and White
Mountains Friday night. The dryslot and warming low level-
temperatures arrive Saturday morning with only northern Maine
likely to still see periods of moderate-to-heavy snow through rest
of the day Saturday. Snow should taper off throughout the Interior
Northeast by Saturday night, with some lake-effect showers
lingering into Sunday. WPC probabilities show moderate- to- high
chances (50-70%) for snowfall >6" in the Tug Hill and Adirondacks
neighboring the Tug Hill through Saturday morning. These chances
drop across the remainder of New England, with 30-50% probabilities
of 6+ inches found only across northern ME.

Additionally, some lingering upslope/lake-effect snow is likely
tonight across the Interior Northeast following the passage of a
strong cold front, extending from as far south as the central
Appalachians. WPC probabilities for at least 4 inches of snow are
low (10-30%) across the central Apps, western Upstate New York, the Adirondacks, Green Mts and White Mts of New England.


...California...
Day 3...

An upper trough traversing the eastern Pacific Saturday is forecast
to close-off by Sunday and follow a weakness in a western U.S.
ridge behind a weaker upper low swinging across the Four Corners.
This will allow for a period of light to moderate precipitation to
spread onshore the West Coast on Sunday. IVT values are expected to
remain weak (below 250 kg/m/s), so overall amounts shouldn't add
up to much. Nonetheless, with snow levels around 4000-5000 feet,
WPC probabilities for at least 6 inches of snow through Sunday
night are medium (30-50%) across the Sierra Nevada and Shasta
Siskiyous of northern California, highest probs mainly above 8000
feet.


Snell/Mullinax





$$

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FOUS11 KWBC 280808
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
308 AM EST Fri Feb 28 2025

Valid 12Z Fri Feb 28 2025 - 12Z Mon Mar 03 2025


...Upper Great Lakes through the Northeast...
Days 1-2...

An unusually strong clipper system (MSLP below the first
climatological percentile per the ECMWF) diving southeast from
southern Canada will head for the Upper Great Lakes this morning.
The storm will reside beneath the diffluent left-exit region of a
90-100 knot 500mb jet streak, while also sporting an unusually
strong NWrly IVT that surpasses 300 kg/m/s on the western flank of
the surface low. The low-level circulation at 850mb is also rather
potent with heights that are below the 0.5 climatological
percentile by 18Z Friday according to NAEFS. This equates to what
is effectively a "front-end thump" of heavy snow that began
overnight in the Minnesota Arrowhead and is now heading for the
Michigan U.P. and far northern Michigan today where the best 850mb
FGEN occurs. The 00Z HREF suggests snowfall rates of 1-2"/hr are
possible for several hours this morning. A dry slot and warming
boundary layer should limit snowfall over the Michigan U.P. and
northern Michigan Friday afternoon, resulting in a narrow swath of
heavy snow. As the storm heads east though, additional snow is
likely on the back side of the storm as low-level cold-air
advection (CAA) over Lake Superior increases Friday evening. Snow
should taper off by Saturday morning in the Upper Great Lakes. WPC probabilities show moderate-to-high chances (50-70%) for snowfall
totals >6" in the MN Arrowhead with similar chances for >8" in the
Keweenaw Peninsula, Huron Mountains, and eastern Michigan U.P..
Localized amounts approaching a foot are possible closer to Sault
Ste. Marie, MI and neighboring communities to the south along the
coast.

The storm continues its march east into southern Ontario Friday
evening with the same method of producing periods of heavy snow as
far east as the Tug Hill and Adirondacks of northern New York.
WPC's Snowband Probability Tracker, utilizing the 12Z HREF
guidance, shows the potential for 1"/hr rates from the Tug Hill to
as far east as the Green and White Mountains Friday night. Unlike
the Upper Great Lakes, however, the storm track is farther north
through the St. Lawrence Valley. This burst of heavy snow will
eventually give way to diminishing snowfall rates late Friday night
and into Saturday morning in these areas. By Saturday morning,
only northern Maine likely to still see periods of moderate-to-
heavy snow through rest of the day Saturday. However, as the
Arctic front approaches midday Saturday, steepening lapse rates
and strong upper-level ascent aloft is a recipe for snow squalls.
Plummeting temperatures could result in quick accumulations on some
surfaces, but the biggest concern is for dramatic reductions in
visibilities within impacted areas of northern New York and as far
east as northern New England Saturday afternoon. Travelers on
roadways should be sure to have a reliable way to receive snow
squall warnings should they be issued on Saturday. Snow should
gradually taper off throughout the Interior Northeast by Saturday
evening, with some lake-effect showers lingering into Sunday. WPC
probabilities show moderate-to-high chances (50-70%) for snowfall

6" in the Tug Hill and Adirondacks neighboring the Tug Hill

through Saturday morning. Similar probabilities for >4" of snowfall
are depicted across northern Maine, as well as the Green and White
Mountains through Sunday morning. Localized amounts topping 8" are
possible in the tallest peaks of the Green and White Mountains.


...California & Great Basin...
Day 3...

A closed upper-low approaching California on Sunday will direct an
IVT that is topping out not much higher than 250 kg/m/s at the
Sierra Nevada and Southern California ranges. 850mb and 700mb winds
topping the 90th climatological percentile (per NAEFS) may aid in
some modest upslope flow, but this IVT is not particularly strong,
which should limit most heavy amounts to the highest/more remote
elevations. Snow levels will be as low as 4,000ft from the Sierra
Nevada on east into the Great Basin, but the heavier amounts will
generally be confined to elevations above 6,000ft. Snow will fall
heaviest over the Sierra Nevada and as far north as the
Shasta/Siskiyou Sunday afternoon and into Sunday night. As the
upper low approaches Sunday night, Pacific moisture will spill over
into the Great Basin with moderate-to-heavy snowfall along the
ridge lines of central Nevada Sunday night and into Monday. WPC
probabilities depict moderate-to-high chance probabilities (50-70%)
for snowfall >8" at elevations above 7,000ft in the Sierra Nevada
through Monday morning. Similar moderate-to-high chance
probabilities for >4" of snowfall exist along the ridges of
central Nevada through Monday morning.


Mullinax



$$

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FOUS11 KWBC 281912
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
212 PM EST Fri Feb 28 2025

Valid 00Z Sat Mar 01 2025 - 00Z Tue Mar 04 2025


...Great Lakes through the Northeast...
Day 1...

An unusually strong clipper system (MSLP below the 0.5
climatological percentile per the NAEFS) swinging across the Upper
Great Lakes this afternoon will track eastward just to the north of
New England on Saturday. Modest WAA ahead of the storm will allow
for a period of moderate snowfall across northern New England, Tug
Hill, and northern Adirondacks tonight before mid-level dry air
and warming of the column quickly ends any widespread snowfall by
Saturday afternoon. Then, on the backside of the system, beginning
first throughout the Upper Great Lakes this evening, CAA increases
and drives up chances for renewed lake-effect snow and eventually
favorable upslope conditions from the central Appalachians to
northern New England. Additionally, as the CAA peaks along the East
Coast on Saturday and low-level lapse rates increase with diurnal
heating during the afternoon hours, snow showers and localized snow
squalls are possible from the eastern Ohio Valley through New
England. WPC probabilities show high chances (70-90%) for snowfall
totals >4" across the Tug Hill Plateau and northern Adirondacks of
New York, as well as the Green and White Mountains, plus parts of
far northern Maine. Lake-effect snow downwind of Lake Superior have
also prompted medium probabilities (40-60%) of an additional >4"
of snow throughout parts of the Michigan U.P.


...California & Great Basin...
Days 2-3...

A closed upper-low approaching California on Sunday will direct an
IVT that is topping out not much higher than 250 kg/m/s at the
Sierra Nevada and Southern California ranges. 850mb and 700mb winds
topping the 90th climatological percentile (per NAEFS) may aid in
some modest upslope flow, but this IVT is not particularly strong,
which should limit most heavy amounts to the highest/more remote
elevations. Snow levels will be as low as 4,000ft from the Sierra
Nevada on east into the Great Basin, but the heavier amounts will
generally be confined to elevations above 6,000ft. Snow will fall
heaviest over the Sierra Nevada and as far north as the
Shasta/Siskiyou Sunday afternoon and into Sunday night. As the
upper low approaches Sunday night, Pacific moisture will spill over
into the Great Basin with moderate-to-heavy snowfall along the
ridge lines of central Nevada Sunday night and into Monday.
Moisture and a potent upper low will then eventually reach the
central Rockies late Monday. WPC probabilities depict moderate-
to- high chances (50-80%) for snowfall >8" at elevations above
7,000ft in the Sierra Nevada through Monday morning. Similar
moderate-to- high chance probabilities for >4" of snowfall exist
along the ridges of central Nevada and Utah ranges through Monday
evening.


Snell/Mullinax






$$

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FOUS11 KWBC 010805
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
305 AM EST Sat Mar 1 2025

Valid 12Z Sat Mar 01 2025 - 12Z Tue Mar 04 2025


...Great Lakes through the Northeast...
Day 1...

The winter storm responsible for periods of heavy snow in parts of
northern Michigan marches east into southern Ontario today. Periods
of snow will stick around from the White Mountains to northern
Maine this morning. Following a break in the snow this morning, the
passage of a strong Arctic front paired with a deep upper trough
approaching from the west will provide a source of lift aloft.
Combine increasing surface-based heating that steepens low-level
lapse rates, and the stage is set for scattered snow showers and
snow squalls from the Great Lakes and Upper Ohio Valley on east
through the Interior Northeast throughout much of the day Saturday.
Plummeting temperatures could aid in rapid snowfall accumulations
in wake of the cold frontal passage, but there is also a concern
for bursts of heavy snow and gusty winds that cause dramatic
reductions in visibility for those on roadways and for aviation.
Travelers on roadways should be sure to have a reliable way to
receive snow squall warnings should they be issued. Snow should
taper off not long after sunset Saturday evening, although some
residual lake-effect snow showers may stick around into parts of
Saturday night. WPC probabilities through 06Z Sunday show moderate-
to-high chances (50-70%) for >4" of additional snowfall in the Tug
Hill, the White Mountains, and far northern Maine.


...California & Great Basin...
Days 2-3...

A closed upper-low tracking into California on Sunday will direct
an IVT topping out around 250 kg/m/s at the Sierra Nevada and
Southern California ranges. While SWrly low-level winds may provide
some marginal upslope flow enhancement, this IVT is not
particularly strong, thus limiting most heavy amounts to the
highest/more remote elevations. Snow levels are expected to be as
low as 4,000ft from the Sierra Nevada on east into the Great Basin,
but the heavier amounts will generally be confined to elevations
above 6,000ft. Snow will fall heaviest over the Sierra Nevada and
as far north as the Shasta/Siskiyou Sunday afternoon and into
Sunday night. As the upper low approaches Sunday night, Pacific
moisture will spill over into the Great Basin with moderate-to-
heavy snowfall along the 6,000-7,000ft ridge lines of central
Nevada Sunday night and into Monday. Moisture and a potent upper
low will then eventually reach the central Rockies late Monday. WPC probabilities depict moderate-to-high chances (50-80%) for
snowfall >8" at elevations above 7,000ft in the Sierra Nevada
through Monday morning. Similar moderate-to-high chance
probabilities for >6" of snowfall exist along the ridges of
central Nevada through Monday evening.

...Northern & Central Rockies to the Central Plains...
Day 3...

The upper low responsible for the mountain snow in the mountain
ranges of California and the Great Basin will make its way into the
Central Rockies on Monday. Falling heights and residual Pacific
moisture will support moderate to locally heavy snowfall in the
Wasatch, Uinta, southern Wyoming Rockies, and northern Colorado
Rockies. WPC probabilities show moderate-to-high chances (50-80%)
for snowfall >6" at elevations above 9,000ft. Farther north,
temperatures will gradually cool as a cold front ushering in
Canadian high pressure moves south. Lingering Pacific moisture,
combined with weak easterly upslope flow will allow for light-to-
moderate snowfall in the Northern Rockies between Monday afternoon
and Tuesday morning.

There remains a fair amount of spread regarding the snow potential
in the Central and Northern Plains. The synoptic-scale jet stream
setup is generally agreed upon; a strong jet streak over northern
Mexico will place its divergent left-exit region over the central
Plains Monday night. Along with strong PVA ahead of the 500mb low
in the Rockies will result in cyclogenesis in lee of the Colorado
Rockies that will organize and strengthen a surface low rather
quickly by Tuesday. Where guidance differs are on the storm track,
the rate at which the storm deepens, and the extent to which the
colder air to the north is in place soon enough to result in a
swath of heavy snow in the Northern Plains. The GEFS members are
generally are a little faster, farther north, and deeper with the
storm by 12Z Tuesday compared to the ECENS which is slower and
farther south. The one thing these ensembles have in common is
focusing on the Palmer Divide and over the Raton Pass with strong
enough NErly upslope flow, along with strong dynamic cooling aloft
to support heavier snowfall. Even in this case, however, any faster
storm motion could mean less snowfall, and the opposite for
heavier snow should the storm slow down. Through 18Z Tuesday, WPC
probabilities show moderate chances (40-60%) for snowfall >4" along
the Palmer Divide, but lesser chances (10-20%) along Raton Pass.

With a lack of sufficiently cold air east of the Rockies, snowfall
potential will be more directly tied to the deformation axis
placement and dynamic cooling aloft from the Denver metro on north
and east. Residents in the Central and Northern Plains will want
to monitor the forecast closely over the weekend as this is a
complex storm system whose final storm track is not resolved yet.


Mullinax




$$

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FOUS11 KWBC 011935
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
235 PM EST Sat Mar 1 2025

Valid 00Z Sun Mar 02 2025 - 00Z Wed Mar 05 2025


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

Strong surface low pressure system exiting northern New England
this evening will continue to usher potent CAA behind an arctic
cold front clearing the East Coast tonight. Outside of lingering
wrap-around snow across northern Maine, heavy accumulating
snowfall through Sunday will be confined to localized lake-effect
bands. With 20-35 kt 850 mb winds out of the northwest, the best
chances for additional moderate snowfall is across the eastern MI
U.P. and areas southeast of Lake Ontario. Here, WPC probabilities
are low (10-30%) for an additional 4"+ of snow.


...California & Great Basin...
Days 1-2...

A closed upper-low tracking into California on Sunday will direct IVT
topping out around 250 kg/m/s at the Sierra Nevada and Southern
California ranges. While SWrly low-level winds may provide some
marginal upslope flow enhancement, this IVT is not particularly
strong, thus limiting most heavy amounts to the highest/more remote
elevations. Snow levels are expected to be as low as 4,000ft from
the Sierra Nevada on east into the Great Basin, but the heavier
amounts will generally be confined to elevations above 6,000ft.
Snow will fall heaviest over the Sierra Nevada and as far north as
the Shasta/Siskiyou Sunday afternoon and into Sunday night. As the
upper low approaches Sunday night, Pacific moisture will spill over
into the Great Basin with moderate-to- heavy snowfall along the
6,000-7,000ft ridge lines of central Nevada Sunday night and into
Monday. Moisture and a potent upper low will then eventually reach
the Central Rockies late Monday. WPC probabilities depict
moderate- to-high chances (50-80%) for snowfall >8" at elevations
above 7,000ft in the Sierra Nevada through Monday morning. High
chances (70-90%) for >6" of snowfall exist along the ridges of
central Nevada through Monday evening.


...Northern & Central Rockies to the Central Plains...
Day 3...

The upper low responsible for the mountain snow in the highly
elevated ranges of California and the Great Basin will make its
way into the Central Rockies on Monday and eventually the Central
Plains on Tuesday. Falling heights and residual Pacific moisture
will support moderate to locally heavy snowfall in the Wasatch,
Uinta, southern Wyoming Rockies, and northern Colorado Rockies. WPC probabilities show moderate-to-high chances (50-80%) for snowfall

8" at elevations above 9,000ft. Farther north, temperatures will

gradually cool as a cold front ushering in Canadian high pressure
moves south. Lingering Pacific moisture, combined with weak
easterly upslope flow will allow for light-to- moderate snowfall in
the Northern Rockies between Monday afternoon and Tuesday morning.

There remains a fair amount of spread regarding the snow potential
in the Central and Northern Plains. The synoptic-scale jet stream
setup is generally agreed upon; a strong jet streak over northern
Mexico will place its divergent left-exit region over the central
Plains Monday night. Along with strong PVA ahead of the 500mb low
in the Rockies will result in rapid cyclogenesis in lee of the
Colorado Rockies that will organize and strengthen a surface low by
Tuesday. Where guidance differs are on the storm track, the rate
at which the storm deepens, and the extent to which the colder air
to the north is in place soon enough to result in a swath of heavy
snow in the Northern Plains. Today's guidance is starting to come
into better agreement with a dynamically colder band of
precipitation breaking out across the central High Plains Tuesday
morning, but with above average spread remaining on exact
placement. The GEFS members remain generally little faster and
therefor deeper/north with the storm by 00Z Wednesday compared to
the ECENS which is slower and farther south. This leads to some
differences regarding the location and magnitude of a potential
swath of snow on D3 extending from eastern Colorado through the
central Plains into eastern North Dakota. The one thing these
ensembles have in common is focusing on the Palmer Divide and
southeast WY with strong enough NErly upslope flow, along with
stronger dynamic cooling aloft to support heavier snowfall.
Interestingly, NAEFS mean IVT reaches >97.5th climatological
percentile even though flow is out of the north. However, any
faster storm motion could mean less snowfall, and the opposite for
heavier snow should the storm slow down. Through 00Z Wednesday, WPC probabilities show moderate chances (40-60%) for snowfall >6"
along the Palmer Divide and parts of southeast Wyoming, with lesser
chances for >4" (10-30%) over parts of western Nebraska and south-
central South Dakota.

With a lack of sufficiently cold air east of the Rockies, snowfall
potential will be more directly tied to the deformation axis
placement and dynamic cooling aloft from the Denver metro on north
and east. Given the potentially record-strong low pressure over the
Midwest by Tuesday night, greater impacts could be related to
strong winds. Residents in the Central and Northern Plains will
want to monitor the forecast closely over the weekend as this is a
complex storm system.


Snell/Mullinax







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FOUS11 KWBC 020854
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
354 AM EST Sun Mar 2 2025

Valid 12Z Sun Mar 02 2025 - 12Z Wed Mar 05 2025


...California & Great Basin to the Central Rockies...
Days 1-3...

A closed upper-low tracking into California today will direct IVT=20
of ~300 kg/m/s at the southern Sierra Nevada and Southern=20
California ranges. While SWrly low-level winds may provide some=20
marginal upslope flow enhancement, this IVT is not particularly=20
strong, thus limiting most heavy amounts to the highest/more remote
elevations. Snow levels are expected to be as low as 4,000ft from=20
the Sierra Nevada on east into the Great Basin, but the heavier=20
amounts will generally be confined to elevations above 6,000ft.=20
Snow will fall heaviest over the Sierra Nevada and as far north as=20
the Shasta/Siskiyou through Sunday evening. As the upper low=20
approaches Sunday afternoon, Pacific moisture will spill over into
the Great Basin with moderate-to-heavy snowfall along the=20
6,000-7,000ft ridge lines of central Nevada Sunday afternoon and=20
into Monday. WPC probabilities depict moderate-to-high chances=20
(50-80%) for snowfall >8" at elevations above 7,000ft in the Sierra
Nevada through Monday morning. High chances (70-90%) for >6" of=20
snowfall exist along the ridges of central Nevada through Monday=20
evening.

The closed upper low will make its way into the Central Rockies on
Monday and eventually the Central Plains by Monday night. Falling=20
heights, strong jet-streak dynamics aloft, and residual Pacific=20
moisture will support moderate to locally heavy snowfall in the=20
Wasatch, Uinta, southern Wyoming Rockies, and northern Colorado=20
Rockies. WPC probabilities show moderate-to-high chances (50-80%)=20
for snowfall >8" at elevations above 9,000ft. Farther north,=20
temperatures will gradually cool as a cold front ushering in=20
Canadian high pressure moves south. Lingering Pacific moisture,=20
combined with weak easterly upslope flow will allow for light-to-=20
moderate snowfall in the Northern Rockies between Monday afternoon=20
and Tuesday morning. Most snowfall totals will range between 1-4"
with localized totals topping 4" in the peaks of the Big Snowy,
Little Belt, Lewis Range, Absaroka, and Big Horns.=20


...Central Plains to Upper Midwest...
Days 2-3...

...Powerful winter storm to inflict a plethora of dangerous weather
hazards from the Great Plains to the eastern U.S, including
blizzard conditions in the Central Plains...

The synoptic-scale evolution and primary features are generally=20
agreed upon by all guidance; a strong jet streak over northern=20
Mexico will place its highly divergent left-exit region over the=20
central Plains Monday night. Paired with strong PVA ahead of the=20
500mb low in the Rockies aloft will organize and strengthen a=20
surface low in lee of the Colorado Rockies as early as Monday=20
afternoon. Guidance seems to be in decent agreement on the position
of the upper low through 06Z Tuesday (ECENS slightly farther south
than the GEFS) and these ensembles will remain in these camps will=20
through 12Z Wednesday as the storm moves into the Midwest.=20
Interestingly, NAEFS/ECWMF SATs depict mean IVT surpassing the=20

97.5th climatological percentile over eastern CO early Tuesday=20

morning. This is a byproduct of the exceptional 500-700mb moisture=20
aloft that is associated with the deformation axis producing a=20
burst of heavy snow. This will focus the heaviest snow along the=20
Palmer Divide and southeast Front Range of southeast WY via strong=20
enough NErly upslope flow, along with stronger dynamic cooling=20
aloft to support heavier snowfall in the most elevated terrain
through Tuesday morning. These areas are also at risk for strong
wind gusts. The ECMWF EFI shows >0.8 values along the Palmer=20
Divide for snow and wind gusts, suggesting the potential for=20
significant impacts via those to weather hazards. Through 00Z=20
Wednesday, WPC probabilities show moderate-to-high chances=20
(40-70%) for snowfall >6" along the Palmer Divide and the Front=20
Range of southeast WY.

The snowfall potential east of the Rockies, however, will be=20
primarily tied to the deformation axis placement and dynamic=20
cooling aloft east of the Denver metro and points north and east.=20
This dynamic storm system is not working with an antecedent air-=20
mass that is overly cold/dry. That said, the changeover to snow=20
from eastern Colorado, southeast Wyoming, and into much of NE/KS=20
will coincide with considerable wind gusts that range between 50-70
mph in some cases. Snowfall amounts will vary in these areas and=20
are likely to be difficult to measure given the powerful winds. The
expectation is any snowfall (1-4" worth) combined with >50mph wind
gusts will likely result in blizzard conditions for motorists and=20
aviation. The WSSI-P shows a wide swath of 50-70% probabilities for
Moderate Impacts related to Blowing Snow alone from the Palmer=20
Divide and southeast WY on east through northwest KS, and through=20 west-central NE. This is likely to result in whiteout conditions,=20
power outages, and closures in affected areas on Tuesday.=20

By Tuesday evening, the storm continues to strengthen as it heads
for the Midwest. Intense vertical velocities beneath the TROWAL
will support dynamic cooling that forces precipitation to fall in
the form of snow Tuesday night from eastern Nebraska and northeast
Kansas on north through western Iowa and into the Upper=20
Mississippi Valley. Periods of heavy snow and whiteout conditions=20
are likely in these areas with heavy snow even stretching into the
Michigan U.P.. From Minnesota on east to northern Wisconsin and=20
the Michigan U.P., these areas are more at risk for heavy snow=20
thanks to a more aptly-timed cold frontal passage cooling the
boundary layer more effectively while also being co-located beneath
the TROWAL. Though 00Z Thursday, WPC probabilities depict=20
moderate-to-high chances (40-70%) for snowfall >6" from southeast=20
MN to northern Wisconsin and the central Michigan U.P.. The ECMWF=20
EFI depicts >0.8 values for heavy snow and wind gusts in these=20
areas. Expect significant travel disruptions are anticipated due to
the combination of heavy snow and high winds through Wednesday
afternoon.

WPC has initiated Key Messages for this powerful storm system. The
link to view the Key Messages are 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!7cLHK2TMAm9ydtPin_-tnjoyqnnYVKAgIaRRx0dKCtpJm= tWub5O5OF70D-fTWDvP1OdUoXWYWfhYXPsZMaqfJCaTMCk$=20


$$

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FOUS11 KWBC 022047
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
347 PM EST Sun Mar 2 2025

Valid 00Z Mon Mar 03 2025 - 00Z Thu Mar 06 2025

...California & Great Basin to the Central Rockies...
Days 1-3...

A progressive but highly amplified upper level pattern will set up
across the country through the middle of the workweek. This highly
energetic pattern will support widespread wintry weather across=20
the Rockies. Starting tonight, a deep upper level trough will be=20
over California and the Great Basin, with instability induced by=20
the cold air aloft supporting widespread snow across many of the=20
local mountain ranges from the west coast to the Uinta Mountains of
Utah. The snow will spread east to the Front Range of Colorado by=20
Monday as the upper level trough pushes east and lee cyclogenesis=20
begins in eastern Colorado. Meanwhile, an upper level front will=20
follow behind the trough across the Pacific Northwest through=20
Tuesday morning. The front will provide the forcing for snow to=20
continue from Washington State east through Montana, while a=20
surface polar high over the Canadian Prairies provides cold air=20
from the north, keeping snow levels low (under 4,000 ft. in some=20
areas) from the Sierras north and east through Montana. Integrated=20
Vertical Transport (IVT) values through Tuesday will generally peak
between 200 and 300 kg/ms. These are modest values, implying that=20
at first, lack of available moisture will limit accumulations,=20
especially where orographic uplift is not present to wring out=20
additional snowfall. WPC Probabilities remain high (70-90%) for at=20
least 4 inches of snow through Monday afternoon across the ridges=20
of central and northeastern Nevada.

As the upper level low pushes east through Tuesday and the
developing Plains cyclone takes over as the primary forcing
mechanism for heavy snow, the probabilities of heavy snow will=20
also shift east into Idaho, Wyoming and Montana, as well as into
the Front and Park Ranges of Colorado. A shortwave embedded within
the upper level trough will locally increase upper level=20
divergence in the favorable left exit region of a 150 kt jet that=20
extends into west Texas. The low level jet will be strengthening=20
from east Texas into Arkansas, drawing Gulf moisture northward.=20
However, in these early stages of the low's development, moisture=20
into the northern half of the storm will still be limited. Thus,=20
the heaviest forecast snow totals will be limited to the Front and=20
Park Ranges and adjacent mountains where orographic uplift will=20
provide a larger fraction of the overall lift causing the heavy=20
snow. There is a moderate (50-70%) chance of at least 6 inches of=20
snow through Tuesday afternoon at 8,000 ft. and higher in the=20
latest WSSI-P. Further north and west across Wyoming and Montana,=20
where the upper level front will be the dominant forcing mechanism=20
and further away from the Gulf, snowfall totals will be lighter.=20
There is a low (10-30%) chance of 4 inches or more of snow in these
areas in the WPC probabilities.

A second deep trough in the upper level flow will move into the
West Coast on Wednesday, with yet another round of heavy snow
possible from the Sierras into northern Nevada through the day on
Wednesday. A surface low may develop to the lee of the Sierras
across southern Nevada as a result of the forcing and leeside flow
over the Sierras. The timing of how fast the cold air can fill in
behind (north and west) of the low, as well as the extent of the
precipitation shield will be critical as to potential snowfall
accumulations. There remains considerable uncertainty about those
factors, which will become more clear with future updates in the
guidance.

...Central Plains to Upper Midwest...
Days 2-3...

...Powerful winter storm to cause widespread heavy snow and blowing
snow with localized blizzard conditions across the central Plains
from Monday night into Tuesday and then into the upper Midwest
Tuesday night through Wednesday...

The upper level trough that ejects from the Rockies into the Plains
Monday night will have an embedded low that moves across Colorado
and into Kansas. This will be the focus for where the surface low
will form and rapidly intensify during the day on Tuesday. The
trough will become negatively tilted Tuesday, resulting in a
steadier intensification of the surface low as it tracks northeast
from Kansas to northern Michigan by Wednesday evening. North and
west of this track, from northeastern Colorado to western Iowa,
southern Minnesota, Wisconsin, and northern Michigan, a period of
heavy snow is likely as the comma-head of the storm moves over the
region. Meanwhile, the surface low will deepen well into the 980s
hPa range. With a polar high providing cold air and adding to the
baroclinic instability with the remarkably strong LLJ pumping Gulf
moisture northward ahead of the storm, very strong winds will
accompany the heavy snow, causing widespread blowing snow and=20
possible blizzard conditions.

The latest WPC Winter Storm Severity Index (WSSI) shows a large
area of Moderate impacts (disruptions to daily life, with extra
caution needed while driving) through Wednesday morning from the
northeast corner of New Mexico north across almost all of the=20
eastern Colorado Plains, the western two-thirds of Nebraska, and
south-central South Dakota. This is being driven almost entirely by
the blowing snow component of the WSSI. Due to both the intensity
of the storm and its fast movement, there will be a rapid
transition of precipitation-type from rain to snow on the west/cold=20
side of the storm. Also due to the strong winds and resultant
blowing snow, there is considerable uncertainty as to snowfall
amounts from the Plains to the U.P. of Michigan, as blowing and
drifting will cause large variability in accumulations from place
to place. Thus, for most areas, expect the impacts from blowing
snow to outweigh the impacts from snow amounts alone. Further, the
high winds will likely break apart any larger snowflakes, resulting
in lower SLRs and lower accumulations, but increasing the number of
partial flakes in the air and contribute to lower visibilities.

There is likely to be an area of lower accumulations in and around
eastern Nebraska as the low refocuses and develops. This will occur
when the upper level trough supporting the low first turns
negatively tilted Tuesday afternoon, and the southern jet streak
rounding the base of the trough extends far enough northward ahead
of the trough to maximize the upper level divergence by Tuesday
evening between that jet streak and a second west-east oriented
jet streak extending from the Arrowhead of Minnesota east across
the Canadian Provinces of Ontario and Quebec.

Wegman

...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!9ymDF-SiR9avKm5oo18FacgpBrzO1VrsXnyLWbfEnxXSE= uS_wwBDEPVdPZHI2oXGji43XcNKqdSsY2eVrLdABwXYd-w$=20

$$

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FOUS11 KWBC 030833
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
333 AM EST Mon Mar 3 2025

Valid 12Z Mon Mar 03 2025 - 12Z Thu Mar 06 2025

...Great Basin to the Central Rockies...
Days 1-2...

A potent 500mb closed upper-low barreling through the=20
Intermountain West will generate exceptional divergence aloft while
modest 700-300mb moisture wraps around the northern and western=20
flanks of the closed low. The result is high elevation snow from=20
central Nevada on east through the Wasatch, the Uinta, as far south
as the Mogollon Rim, and east to the southern Wyoming and Colorado
Rockies. WPC probabilities show high chance probabilities (>70%)=20
for snowfall >6" in the Nevada ranges above 6,000ft, the Utah=20
ranges above 8,000ft, and northern Arizona ranges above 7,000ft.=20

By 00Z Tuesday, the 500mb low tracking across southern Colorado
will work in tandem with the divergent left-exit region of a
250mb jet streak to support lee cyclogenesis over the central High
Plains. As the closed low aloft strengthens at 700mb and 850mb, a
strong 50+ knot LLJ will direct a stream of low-level moisture
northward through the Southern Plains that wraps around the
700mb low. The northerly flow with embedded moisture aloft is
strong enough to the point that by 12Z Tuesday, there is a=20
northerly >200 kg/m/s IVT over eastern Colorado. This anomalous=20
moisture source, combined with the robust synoptic-scale=20
enhancement will support heavy snow in the Front Range of the=20
Colorado and southern Wyoming Rockies, and as far south as the=20
Palmer Divide. The Palmer Divide in particular is particularly at=20
risk for blizzard conditions Monday night into Tuesday morning as=20
700mb winds of 50-70 knots result in whipping wind gusts. WPC=20
probabilities show high chance probabilities (>70%) for snowfall=20

8" in the northern Colorado Rockies above 9,000ft. Along the

Palmer Divide, WPC probabilities show moderate-to-high chances
(50-70%) for snowfall >6" through Monday evening. Snow should=20
taper off around midday Tuesday along the Front Range of the=20
Rockies.


...Central Plains to Upper Midwest...
Days 1-3...

...Powerful winter storm to cause widespread heavy snow and blowing
snow with localized blizzard conditions across the central Plains
from Monday night into Tuesday and then into the Upper Midwest=20
Tuesday night through Wednesday...

By 06Z Tuesday, a closed and potent 500mb low will track into
western Kansas with a rich plume of low-level moisture advected
northward by a >50kt LLJ over the Southern Plains. Moisture will=20
wrap around the deepening cyclone, resulting in strong 850-700mb=20
WAA that causes a narrow axis of moderate snow embedded within a=20
wind field that could produce >70mph wind gusts late Monday night=20
and into Tuesday morning. The upper-low takes a subtle dip south=20
and east along the KS/OK border midday Tuesday before tracking=20
northeast towards the Midwest Tuesday evening. The 700mb will will=20
track over the Kansas City metro by 00Z Wednesday and the pivoting=20
axis of best 850-700mb FGEN will pivot from eastern Nebraska and=20
northeast Kansas on northeast through Iowa and into the Upper=20
Mississippi Valley. The enhanced mesoscale forcing will be co-=20
located beneath a "kissing jets" setup; where the developing storm=20
system lies beneath the divergent left-exit region of a jet streak=20
over Texas, and beneath a strengthening jet streak over the upper=20
Great Lakes. Plus, 850mb and 700mb heights at this time over
eastern Kansas are below the observed heights for this time of year
in the CFSR climatology. With robust ascent aloft and strong=20
mesoscale forcing within the deepening TROWAL, the deformation axis
of heavy snow will be capable of producing up to 1"/hr snowfall=20
rates and whipping wind gusts of 50mph. While the band will be=20
progressive as it moves through eastern Kansas and eastern=20
Nebraska, that 3-6 hour wind of heavy snow can still cause=20
significant reductions in visibilities for motorists and aviation=20
Tuesday evening.

The storm then tracks through eastern Iowa Tuesday night with its=20
expansive deformation axis producing snow from the Kansas/Missouri=20
border on north through central Iowa and as far north as the=20
Michigan U.P.. Strong wind gusts topping 40 mph are possible in=20
these areas Tuesday night and into Wednesday. The heaviest snowfall
by Wednesday morning will be found across southeast Minnesota,=20
northern Wisconsin, and the Michigan U.P.. The Michigan U.P., in=20
particular, is most favored for heavy snow due to the help of=20
lake-enhanced snowfall and colder boundary layer temperatures.=20
Snowfall will be more difficult to accumulate during the day=20
Wednesday on the fringes of where it is snowing rather than beneath
the heaviest rates, but the blustery wind gusts still can cause=20
near whiteout conditions in some cases. In addition, the high=20
moisture content and lower SLRs from central and northern Wisconsin
to the Michigan U.P. suggests the combination of a heavy/wet snow=20
on trees and power lines could lead to some cases of power outages=20
and downed tree branches.=20

WPC probabilities shows moderate chances (40-60%) for snowfall >4"
from western and northern Nebraska to southern South Dakota. There
is then another swath of moderate-to-high chance probabilities
(40-70%) for >4" of snowfall from eastern Nebraska to northern
Iowa. Southern Minnesota on north and east through northern
Wisconsin and the Michigan U.P. sport 50-70% odds of snowfall
totals >6". There are some low chance probabilities (10-30%) for
localized snowfall totals >12" in parts of far northern Wisconsin
and along the Michigan U.P.. Overall, blowing snow will be the
most detrimental impact from the central High Plains to central=20
Iowa and southern Minnesota, while snow amount, snow load, and=20
blowing snow all make for a treacherous day of travel in portions=20
of the Upper Mississippi Valley Tuesday night and through=20
Wednesday.

...California, Great Basin, & Intermountain West...=20
Day 3...

Guidance is in agreement on an approaching upper-level trough off
the California coast that will interact with the subtropical jet in
the East Pacific. This interaction will produce a strengthening IVT
that tops out around 400 kg/m/s IVT at 12Z Wednesday and directs
its moisture well into the Southwest U.S.. By 00Z Thursday, the=20
IVT and its broad >200 kg/m/s footprint extends into the Wasatch=20
and Central Rockies. As the upper trough takes on a more negative=20
tilts along the California coast Wednesday afternoon and eventually
over the Great Basin Wednesday night, heavy snow will gradually=20
descend along the spine of the Sierra Nevada and into central=20
Nevada as well. WPC probabilities show high chances (>70%) for >12"
of snowfall at elevations above 9,000ft in the southern Sierra=20
Nevada with similar high-chance probabilities for >8" of snowfall=20
in the central Sierra Nevada. WPC probabilities also show some=20 moderate-to-high chance probabilities (50-80%) form snowfall totals

4" in central Nevada on east to the Wasatch and Uinta through 12Z

Thursday. Periods of snow are forecast to continue across the=20
Intermountain West into Thursday.


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!_S99kqepjj8tQGohwbg5c9-HCBK00NaCVbY8RPp8iRNkO= V_HifVsumpI6KzDNmhmO7JYjaOq6q9KXmxEr8BSuvMmZaI$=20

$$

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FOUS11 KWBC 032041
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
341 PM EST Mon Mar 3 2025

Valid 00Z Tue Mar 04 2025 - 00Z Fri Mar 07 2025

...Central Rockies and High Plains to the Upper Midwest...=20
Days 1-3...

...A powerful storm will move into the central U.S. tonight=20
Tuesday, producing multiple hazards through Wednesday, including=20
periods of heavy snow from the central High Plains to the northern=20
Great Lakes, as well as blizzard conditions across parts of the=20
central Plains and strong winds throughout the Plains...=20

A deep upper low is forecast to continue its track across the
western U.S., rolling out from the central Rockies into the High
Plains tonight. Snow will continue to spread across the central
Rockies, with several more inches likely across the western to
central Colorado ranges before diminishing on Tuesday.=20

Meanwhile, rain changing to wind-driven snow is expected to=20
develop on the backside of the surface cyclone deepening over=20
eastern Colorado this evening. Increasing low level moisture=20
advection into an area of strong ascent afforded in part by low-=20
to-mid level frontogenesis, upper jet forcing, and orographic=20
ascent will support the development of heavy snow along the=20
northwestern to western extent of the low -- impacting areas from=20
the Colorado Palmer Divide northeastward through portions of=20
western Nebraska and into parts of western and central South Dakota
tonight into Tuesday. While marginal temperatures may keep=20
accumulations in check at the onset, heavy rates (1-2+ in/hr) after
the changeover to snow is expected to produce areas of locally=20
heavier amounts, with WPC guidance showing higher probabilities (=20
greater than 50 percent) for accumulations of 4 inches or more=20
across portions of the region. Low-to-mid level frontogenesis will=20
help extend a stripe of rain changing to snow further to the=20
northeast through eastern South Dakota into central Minnesota, but=20
guidance indicates snowfall accumulations across those areas will=20
remain light through 00Z Wednesday.

By late Tuesday, guidance shows a deep, nearly vertically-stacked
low moving moving into the lower Missouri and mid Mississippi
valleys. Models show a powerful low level jet drawing moisture into
an area of strong ascent generated by a coupled upper jet and low-
to-mid level forcing. Dynamic cooling will support rain changing=20
to snow, with some guidance indicating heavy snowfall rates of 1-2=20
in/hr quickly developing within the associated comma head as it=20
extends from portions of eastern Kansas and western Missouri to=20
southern Minnesota and Wisconsin late Tuesday into Wednesday. The=20
models have trended wetter and colder in some areas, especially=20
across parts of the lower Missouri valley, resulting in an uptick=20
in probabilities for heavier accumulations.

Influenced by an amplifying northern stream trough to its
northwest, the storm is forecast to turn to the northeast, with
heavy snow continuing to develop on its northwest side as it moves
from the mid Mississippi Valley Tuesday night to the northern Great
Lakes by late Wednesday. Strong forcing and moisture advection=20
pivoting across southeastern Minnesota into central Wisconsin is=20
expected to contribute to some of the higher storm totals, with WPC
guidance showing high probabilities for accumulations greater than
6 inches across the region. Otherwise, WPC guidance indicates the=20
heaviest amounts are most likely to fall across parts of northern=20
Wisconsin and Upper Michigan, where the initial swath of=20
synoptically driven snow, followed by lake effect showers will=20
likely contribute to totals exceeding a foot in some locations.=20

Even for areas where heavy snow does not occur, powerful winds will
become a concern throughout much of the Plains into the Midwest,
gusting to over 70 mph in some locations. Snow combined with wind
will result in reduced visibility, with blizzard conditions likely
to develop in some areas, especially across portions of the=20
central Plains into the lower Missouri Valley on Tuesday.
=20
...California, Great Basin, Southwest, and central Rockies...=20
Days 2-3...

A mid-to-upper level shortwave pivoting east ahead of a low=20
dropping south from the Gulf of Alaska is expected to tap deeper=20
Pacific moisture as it approaches the West Coast, drawing it=20
across central into southern California beginning Wednesday=20
afternoon, before directing it further south and east into the=20
Southwest and Great Basin. Heavy snow will initially focus across=20
the central to southern Sierra Nevada (above 9000 ft), where=20
favorable upper dynamics in addition to orographics will=20
contribute to higher rates. Then by late Wednesday and continuing=20
into Thursday, the threat for heavy mountain snow will spread=20
across the Great Basin, northern Arizona, and into the central=20
Rockies. In addition to the Sierra Nevada, the greatest threat for=20
snow amounts of 6 inches or more will include the Nevada, Utah, and west-central Wyoming ranges.=20

Pereira


...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!4XMbcBhpH_2iDxhy-MFbqZz3YgQGbvJ799_98q-RueYF_= 4PEuZgiAA9ztTYWZTAYBH4Fa4D_qFimoA_t2djfJtZDunA$=20

$$

=3D =3D =3D
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FOUS11 KWBC 040840
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EST Tue Mar 4 2025

Valid 12Z Tue Mar 04 2025 - 12Z Fri Mar 07 2025

...Central Rockies and High Plains to the Upper Midwest...=20
Days 1-2...

...A powerful storm moving into the central U.S. will produce=20
multiple hazards through Wednesday, including periods of heavy snow
from the central Plains to the northern Great Lakes, as well as=20
blizzard conditions across parts of the central Plains and strong=20
winds throughout the much of the nation's heartland...=20

A powerful winter storm takes center stage today with periods of
snow and whipping wind gusts producing blizzard conditions in parts
of the central High Plains this morning. A clue to identifying how
powerful a storm is; reviewing the NAEFS/ECMWF situational=20
awareness tools and seeing each variable (temperatures, winds,=20
moisture, pressure, vapor transport) all either in the "max" or=20
"min" categories. By 12Z Tuesday, the storm's 700mb and 850mb=20
heights over western Kansas will be near the lowest in the observed
CFSR climatology, while mean specific humidity at the 500-700mb=20
layers are also above the 90th percentile. Periods of snow will=20
envelope portions of eastern CO (including as far west as the Front
Range and Palmer Divide), western and central Nebraska, and=20
western Kansas where wind gusts may exceed 70mph in some cases.=20
This will result in blizzard conditions that make travel by road=20
and air very difficult due to whiteout conditions. WPC=20
probabilities show low chances (10-30%) for snowfall >4" in=20
northwest Kansas and southwest Nebraska, but they jump up to=20 moderate-to-high chances (50-70%) over north-central Nebraska. Snow
should taper off by Tuesday afternoon but lingering strong wind=20
gusts are likely to linger through Tuesday evening.

As the storm marches west towards eastern Kansas Tuesday=20
afternoon, the mean 250-500mb trough axis will take on a negative
tilt that provides excellent diffluent flow aloft over the Midwest.
Plus, a classic "kissing jets" setup; denoted by the divergent
left-exit region of a jet streak over Texas and the divergent
right-entrance region of a jet streak positioned over the upper
Great Lakes. As strong 850-700mb warm air advection (WAA) pivots=20
north and west around the storm and anomalous moisture content
rotates around the 700mb low, a TROWAL will support intensifying
precipitation rates and lead to a narrow band of heavy snow that
originates over eastern Nebraska and northeast Kansas Tuesday=20
evening. The newest 00Z HREF guidance suggests the potential for=20

1"/hr snowfall rates within this band that could stretch as far=20

south as the Kansas/Missouri border. There are some hi-res
soundings do do show some elevated instability aloft that may lead
to thundersnow within this band. Farther north, the same slug of=20
moisture over northern Iowa, southern Minnesota, western and=20
norther Wisconsin, and the Michigan U.P. will also transition to=20
snow Tuesday night with >1"/hr rates possible there as well.=20
Combined with the strong wind gusts in excess of 40 mph, especially
along the Missouri River Valley on east into central Iowa,=20
blizzard conditions are possible in these areas Tuesday night. WPC probabilities shows western Iowa and directly along the Missouri
River on south to far northeast Kansas as having moderate chances
(40-60%) for snowfall >4". However, should the band pivot long
enough over the region, localized amounts of 6-8" are possible.=20

The heaviest snowfall is likely to occur from northern Iowa and
southeast Minnesota to northern Wisconsin and the Michigan U.P..
This is where the 850mb FGEN will be sticking around the longest,
while also being ideally placed beneath that 250mb jet streak's=20
divergent right-entrance region. Some lake-enhancement and upslope=20
component into the more elevated terrain of northern Wisconsin and=20
the Michigan U.P. will help to sustain periods of heavy snow into=20
Wednesday evening. The storm will be a quick mover and snow across=20
the Upper Midwest will be out of the picture by Thursday morning.=20
WPC probabilities now depict high chances (>70%) for snowfall total

12" from the Hurons of Michigan's U.P. on west to the Michigan=20

U.P.northern Wisconsin border. The Huron Mountains actually have=20
moderate chances (40-60%) for snowfall totals surpassing 24" for=20
the event. Farther southwest, WPC probabilities show moderate-to-=20
high chances (50-70%) for snowfall >8" from far northern Iowa to=20
the Mississippi river dividing southeast Minnesota and western=20
Wisconsin. With the combination of heavy snow and blustery winds,=20
there is the concern for heavy/wet snow weighing down tree branches
and power lines that could result in tree damage and power outages
from southeast Minnesota to the Michigan U.P..

=20
...California, Great Basin, Southwest, and central Rockies...=20
Days 2-3...

An approaching upper rough off the California coast will interact
with the subtropical jet in the East Pacific. This interaction will
produce a strengthening IVT that exceeds 400 kg/m/s and stretches=20
as far inland as the Lower Colorado River Basin. ECMWF SATs show
the >400 kg/m/s over portions of the Desert Southwest topping the=20
99th climatological percentile by 00Z Thursday. This IVT will
introduce rich subtropical moisture into northern Arizona, much of
Utah, and into the central Rockies. At the same time, the
approaching upper trough will induce strong vertical ascent over
the Intermountain West. By 12Z Thursday, a closed 700mb low over
southern Idaho will become elongated to the east and develop
another 700mb low in lee of the Rockies by Thursday afternoon. The
track of the 700mb low places much of Wyoming in a favorable spot
for heavy snow, especially from the Tetons to the Wind River,
Medicine Bow, and Laramie Ranges. This developing storm in the
central High Plains will generate strong WAA at low-levels that
cause 850-700mb FGEN from eastern Wyoming to as far east as the=20
Missouri River early Friday morning. Details on snow amounts east
of the Rockies are not as clear, but additional snowfall is growing
in confidence north of I-80 across the Sand Hills of Nebraska with
lighter amounts closer over the western Corn Belt.

When it comes to areas with the best odds of seeing >18" of
snowfall, the southern Sierra Nevada and peaks of the Wasatch are
the better bets. WPC probabilities show moderate-to-high chances
(50-70%) for >18" of snowfall at elevations above 9,000ft in the=20
southern Sierra Nevada, while the central and Sierra Nevada are=20
more likely to see 6-12" above 6,000ft. Farther east, mountain=20
ranges such as the Uinta, Bear River, Teton, Wind River, Medicine=20
Bow, and Laramie have moderate-to-high chances (40-70%) for=20
snowfall >12". Even the lower elevations of Wyoming, as low as
4,000ft in eastern Wyoming have high chances (>70%) for >4" of
snowfall through 12Z Friday.

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!9ICMgntx5YBtPe5VJ6b1b2yF5S71x8O1mj3IP1esLAkZW= clygV_lL6ckKBLcruADYdf05y6POSOYAXjaTKVnJsHWlMw$=20

$$

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FOUS11 KWBC 041921
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
221 PM EST Tue Mar 4 2025

Valid 00Z Wed Mar 05 2025 - 00Z Sat Mar 08 2025

...Central Plains through the Great Lakes and into the Northeast...
Days 1-3...

...Powerful storm to bring blizzard conditions to portions of the
Central Plains and Upper Midwest...

A rapidly strengthening surface low pressure is clearly evident on
the WV imagery this morning across the Central Plains, and it is
this feature which will bring a powerful blizzard to portions of
the country through mid-week. This surface low will traverse
northeast and begin to occlude tonight as the anomalous upper low=20
(850-700mb height anomalies falling to nearly -5 sigma and below
the minimum in the CFSR climatology according to NAEFS) stacks
vertically and crawls northeast, reaching the Great Lakes by=20
Wednesday aftn. Later Wednesday, this upper low will begin to fill
and open into a negatively tilted trough, ejecting into Ontario
Thursday morning, pushing the attendant cold front and accompanying post-frontal trough eastward through the Mid-Atlantic and
Northeast.

The intensity of this upper low will help sharpen a jet streak
which will rotate through the base of the trough and then lift
meridionally from near the Gulf states, placing the favorably
diffluent LFQ atop the best height falls to result in maintaining
strength of the surface low. This impressive synoptic ascent will
also help to draw significant moisture northward from the Gulf, as
an arc of PWs above the 97.5 percentile surges northward into the
Upper Midwest. This moisture will push north within enhance
isentropic ascent, and this is progged to lift into an impressive
TROWAL, especially from IA through the Great Lakes on D1 /Tuesday
night into Wednesday/. This TROWAL is likely to overlap with a
strengthen deformation axis collocated with strong frontogenesis=20
and a deepening DGZ (SREF 100mb depth probabilities 30-50%)=20
suggesting a stripe of heavy snow is likely from NW MO through the=20
western Great Lakes. This is additionally supported by the WPC=20
prototype snowband tool indicating nearly a 100% chance of 1-2"/hr=20
snowfall rates within this band.

Significant moisture, plentiful ascent, and a deep low pressure all
indicate that an impressive swath of precipitation will spread from
the Central Plains through the western Great Lakes D1, with the
primary challenge being where the snow/rain line will setup.
Guidance suggests the precip will begin as rain along and southeast
of a line from near Marquette, MI, to Minneapolis, MN, through all
of Iowa and into eastern KS. However, as the low continues to
deepen and pulls east, the resultant CAA combined with the
ageostrophic flow into the low will transition rain to snow
quickly, with the heavy snow then collapsing east through
Wednesday. The heaviest snow accumulations will occur within this
collapsing band of snow, and although amounts aren't expected to be
extreme, impressive winds of more than 50mph will create major
impacts due to blizzard conditions from snow that has a high chance

70%) of exceeding 6 inches from far NW Iowa through the Twin

Cities of MN and into the western U.P of MI. Locally 12+ inches of
snow is likely in the U.P.

As the low fills and moves more rapidly to the northeast and into
Canada D2, the attendant cold front and post-frontal trough will
race eastward producing a period of strong CAA on NW flow in its
wake. This will likely result in periods of moderate to at times
heavy snow, especially in the favored upslope regions in the
Central Appalachians and Adirondacks. WPC probabilities for more
than 4 inches of snow as moderate (30-50%) in the Central
Appalachians, and 30-50% for 2+ inches along the Chautauqua Ridge
and into the Tug Hill Plateau/Adirondacks.

This system has prompted the issuance of Key Messages which are
linked below.

Then during D3 /Thursday night and Friday/ another potent surface
low will emerge from the Central Rockies and race eastward as it
becomes embedded within more confluent downstream flow towards the
Ohio Valley. Ridging immediately downstream of this feature will
somewhat limit moisture return from the Gulf, and the accompanying
mid-level wave is progged to weaken rapidly into the flatter flow
east. Despite that, a swath of heavy snow north of the low track is
expected as some strung out 700-600mb fgen aligns west to east to
enhance ascent from Nebraska through Iowa and potentially as far
east as lower Michigan. There is considerable uncertainty and
spread with both the timing and intensity of this second low,
leading to lower confidence in the footprint of snow and resultant
impacts. However, at this time, WPC probabilities for more than 4
inches of snow peak around 50% in northern Nebraska.

=20
...California, Great Basin, Southwest, and central Rockies...=20
Days 1-3...

A progressive upper level trough will move into the West Coast
Wednesday afternoon, then reorganize over the Rockies through
Friday. As it reorganizes, its forward motion will slow
considerably, allowing cold air to pool over the West as Pacific
moisture advects into the region, resulting in areas of heavy snow.
Multiple embedded shortwaves will rotate around the trough, which
will support more widespread snow over several Western states. On
Wednesday, a pair of jet streaks will further enhance the lift over
California, with the southern Sierras in both the left exit region
of one and the right entrance region of another. Ahead of the=20
upper level trough, a surface cold front will move south and east=20
off the Pacific and into the West Coast. The front will have a=20
limited tropical connection, increasing the moisture flux into
southern California. IVT values will peak around 400 kg/ms. That=20=20
Pacific moisture will rising into the 99th percentile compared to=20 climatology as it moves into southern California on Wednesday. As
this moisture pushes inland, the southern Sierras will get the
first opportunity to uplift that moisture in the form of heavy
snow. WPC probabilities are the highest in this region, with a
moderate (40-60%) chance of 18 or more inches of snow.

As the trough moves inland, the moisture moving northeastward ahead
of it will cause widespread mountain snow and valley rain and snow
across much of the Intermountain West through Thursday. A surface=20
low will develop over northeastern Nevada and move across Utah and
southern Wyoming through Thursday in response to the forcing from
the upper level trough and embedded shortwaves. The trough will
become more consolidated as an upper level low tries to form within
it on Thursday. This will increase the divergence in the left exit
region of the jet which will have moved into the Four Corners
region on Thursday. That jet streak will have embedded winds over
130 kt, so it will have plenty of energy for that surface low to
work with. The highest probabilities through Thursday night east of
the Sierras will be across the Uintas of northeast Utah and the
Wind River Range of central Wyoming, where there's a high (70-90%)
chance of 8 inches or more of snow. Lower (20-50%) chances of 8
inches of snow extending in a broad swath of the West from Nevada
northeast through Colorado and Wyoming, including some lower
elevations. Colder air associated with the trough will get time to
settle as the upper level trough/low stalls and reorganizes.

A surface low will develop over the Colorado Plains Thursday
evening. This low will take over as the primary forcing for the
heaviest snow as the snow shifts east across Nebraska along with
the low. By Friday morning, all organized heavy precipitation will
have moves east and out of the region. A secondary small low may
cause a brief burst of heavy snow over northern Arizona during the
day Friday for the higher elevations along the Mogollon Rim.


Weiss/Wegman


...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!9y3rk78-ESVyfVyZSn0RnaS3hhf461rndehwc1MyvDbjI= hQmIT_XkiLOZ4gRAoHYvdbmJ2AjgEl-pdNk001fatWLN4c$=20

$$

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FOUS11 KWBC 050906
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 AM EST Wed Mar 5 2025

Valid 12Z Wed Mar 05 2025 - 12Z Sat Mar 08 2025

...Upper Midwest through the Great Lakes and into the Northeast...
Days 1-3...

...Powerful storm to bring blizzard conditions to portions of the
Upper Midwest...

The powerful winter storm continues to produce heavy snow and
blizzard conditions in some cases from northwestern Missouri
through the Upper Mississippi Valley this morning. This deformation
axis of snow, placed beneath the TROWAL and the right-entrance
region of a robust 250mb jet streak over southern Canada, will
support a band of snow generating 1-2"/hr snowfall rates. The
storm will track over the Wisconsin/Illinois border through late
morning with the swath of snow moving across most of Wisconsin and
the Michigan U.P.. Persistent NErly flow over Lake Superior will
keep periods of snow in the forecast across the Michigan U.P.
through Wednesday evening, but snow should finally taper off by
Thursday morning. Note that some periods of snow are expected on
the backside of the storm on Thursday downwind of the usual snow
belts of Lakes Erie and Ontario, as well as down the spine of the
Appalachians. Light snow totals will linger into Friday as well,
especially in the Tug Hill, Adirondacks, and the Whites. Most=20
snowfall amounts in these areas are likely to range between 1-4"=20
with some localized amounts approaching 6" in the Tug Hill.=20

WPC probabilities show moderate-to-high chances (50-70%) for
additional snowfall totals >12" in the Huron and Porcupine
Mountains along the Michigan U.P. Meanwhile, there are high chance probabilities (>70%) for additional snowfall totals >4" from
northern Iowa to southeastern Minnesota and western Wisconsin. Some
additional localized amounts of 4-6" are possible in west-central=20
Iowa on the back side of the storm through this morning. Expect
hazardous travel conditions in these affected areas, especially in
areas under blizzard warnings where visibilities may be near zero.

=20
...California, Great Basin, Southwest, and central Rockies...=20
Days 1-3...

An approaching upper trough off the California coast will interact
with the subtropical jet in the East Pacific. This interaction will
produce a strengthening IVT that exceeds 400 kg/m/s and stretches
as far inland as the Lower Colorado River Basin. ECMWF SATs show=20

400 kg/m/s over portions of the Desert Southwest that are topping

the 99th climatological percentile by 00Z Thursday. This IVT will
introduce rich subtropical moisture into the Great Basin and
Central Rockies. At the same time, the approaching upper trough
will induce strong vertical ascent over the Intermountain West. By
12Z Thursday, a closed 700mb low over southern Idaho will become
elongated to the east, developing another 700mb low in lee of the
Wyoming Front Range by Thursday afternoon. the track of the 700mb
low places much of Nevada, southern Idaho, and Wyoming in a
favorable position for heavy snow, especially from the Absaroka,
Tetons, and Wind River ranges to the Medicine Bow, Big Horn, and
Laramie Mountains. As the 700mb low stalls over the Tetons and Bear
River Range, a secondary shortwave trough revolving beneath the
longwave trough over the West will sustain a >200 kg/m/s IVT
directed at the southern Rockies. In addition to the upper-level
ascent out ahead of the upper trough, falling heights and lowering
snow levels will support periods of mountains snow along the
Mogollon Rim, the San Juans, the Sangre de Cristo, and the Front
Range of the Colorado Rockies. The snow in the Front Range and
Sangre de Cristo is a byproduct of upslope flow with low pressure
developing over the southern Plains and high pressure over the
northern Plains.

WPC probabilities show high chances (>70%) for snowfall exceeding
12" in the Sierra Nevada above 6,000ft, the >7,000ft ridge lines in
the Nevada, the Wasatch, Uinta, Tetons, Wind River, Laramie, and
San Juan ranges. Some portions of the Sierra Nevada, Wasatch, and
Uinta sport moderate-to-high chances (50-80%) for snowfall >24"
through Friday. Mountains of southern Idaho, the Absaroka, and the
Big Horns also have high chances (>70%) for snowfall >8" through
Friday. Much of the Mogollon Rim above 6,000ft are forecast to see
any where from 6-12" of snowfall. Some of the valleys in Wyoming=20
can also expect as much as 6-12" of snowfall through Friday=20
morning. The WSSI range from Moderate to Major Impacts with the=20
Major Impacts confined to the highest elevations of the mountain=20
ranges listed.


...Central Plains...
Days 2-3...

By Thursday, as the upper trough in the West aids in the
development of low pressure in lee of the Rockies, strong 700mb WAA
will foster 700mb FGEN over southeast Wyoming and Nebraska. A band
of heavy snow will stretch across these areas, including the Black
Hills and Sand Hills Thursday afternoon. Snow in these areas will
continue Thursday night and should taper off by Friday morning.=20
Some measurable snow may make it as far south as northeast Colorado
and possibly into the Midwest Thursday night into Friday, but=20
guidance suggests milder boundary layer temperatures may make it=20
tougher for much more than minor snowfall totals. WPC probabilities
show moderate-to-high chances (50-70%) for snowfall >6" in the
eastern Wyoming High Plains, the Black Hills, and northwest
Nebraska. Low chances (10-30%) for >4" of snowfall extend as far
east as east-central Nebraska.=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!_FIk615MMQwmdbhpmum_q_7cfCr5UpQMXSTW_emsmb3KI= 2JYJHc_zFFLDg9S0EeZ5n43YxgAZm49EcPxvumrAI6duMk$=20

$$

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FOUS11 KWBC 051904
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
204 PM EST Wed Mar 5 2025

Valid 00Z Thu Mar 06 2025 - 00Z Sun Mar 09 2025

...Great Lakes and Central Appalachians...
Day 1...

Powerful low pressure will continue to produce blizzard conditions
across portions of the Upper Midwest and Great Lakes tonight, but
this system will gradually weaken through D1. The weakening of this
system will be in response to the opening of the upper closed this
evening, becoming negatively tilted as it shifts northeast into
Ontario. At the same time a secondary shortwave trough embedded
within the longwave cyclonic flow across the east will pivot into
the Mid-Atlantic states, and the interaction of these features will
push the primary surface low into Canada will driving a post-
frontal trough across the Appalachians. The overall weakening of
ascent and reduction in moisture will cause precipitation coverage
to fade and become more showery/snow-showery in nature, with the
primarily exception occurring across the U.P. of MI early D1, and
then across the Central Appalachians where pronounced upslope flow
will enhance snowfall Thursday afternoon. WPC probabilities for 4+
inches across these areas are generally 30-50%.


...California, Great Basin, Southwest, and Central Rockies...
Days 1-3...

A closed mid-level low dropping along the Pacific Coast Thursday
will amplify into a full-latitude trough centered across the Great
Basin Thursday night. This will manifest as height anomalies that
are progged via NAEFS to reach as low as -3 sigma with respect to
500-700mb heights late D1, with these anomalies persisting as the
trough slowly moves east with time into the weekend. As the core of
this mid-level low moves across the Four Corners, a downstream
subtropical jet streak will amplify, reaching 150+ kts as it
surges into the Southern Plains. This will place favorable LFQ
diffluence over the Four Corners and into the Central Rockies,
enhancing deep layer lift over the region.

Beneath this upper low, two distinct surface cyclones will also
move across the West. The first will be directly beneath the upper
low moving across the Great Basin and into the Central Rockies D1,
which will tap into increasing PW to expand precipitation across a
large portion of the area. The accompanying air mass if full of
Pacific air, so snow levels will be generally modest, around
4000-6000 ft, but will fall behind the low and accompanying cold
front to 2000-3000 ft. However, this also occurs with decreasing
precipitation coverage and intensity. While coverage of snow is
likely to be widespread D1, the heaviest is expected across
northern UT and into WY where the accompanying warm front will
result in enhanced fgen to drive stronger mesoscale ascent and more
prolonged snowfall rates of 1+"/hr. In this area, WPC probabilities
are high (>70%) for more than 12 inches on D1 across the terrain of
eastern NV, into the Wasatch, Uintas, and Wind Rivers, with
widespread high probabilities (>70%) for 4 inches across much of
NV, eastern ID, and WY. Additionally on D1, WPC probabilities are
high for 6+ inches of snow across the Sierra, and the Transverse
and Peninsular Ranges of CA. By D2, heavy snowfall persists across
the higher terrain of UT and WY while expanding into the CO
Rockies, where WPC probabilities for 6+ inches of additional snow
reach 70-90%.

SW of this secondary low, the pivoting upper low moving across the
Four Corners will drive another area of pronounced ascent leading
to periods of moderate to heavy snow across the Desert Southwest
and extending into the TX/OK Panhandles. The column across this
region is modestly cold enough to support snow, with snow levels
around 5000-6000 ft, but steep lapse rates aloft beneath the cold
core low will help cause strong omega to dynamically cool the
column. This suggests a mixture of rain and snow, possibly becoming
all snow near the surface at times of heavier precipitation rates.
At this time, WPC probabilities D1 are moderate (50-70%) for 6+
inches of snow across the Mogollon Rim, and moderate to high D3
(50-90%) in the Sangre de Cristos. Light snow may expand as far
east as the Panhandle of TX D3 as well.


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


Secondary lee cyclogenesis will occur east of the Rockies (beneath the aforementioned overlap of jet diffluence and height falls) D2,
leading to a rapidly deepening surface low pressure that will race
eastward in response to confluent/fast flow across the middle of
the country. The parent upper low will weaken with time as it
becomes embedded within this downstream confluent 500mb pattern,
causing the associated vorticity lobe to string out to the east.
Despite this weakening evolution, robust WAA and isentropic ascent,
especially along the 290-295K surfaces, will draw moisture
northward leading to enhanced precipitation shield. The guidance is
in good agreement that a swath of heavy snow, driven primarily by
the overlap of the LFQ of an upper jet streak and low-level
increasing frontogenesis, will drive a translating band of heavy
snow from eastern WY through Iowa D2 into D3. The most intense
fgen will drive ascent into a deepening DGZ (SREF probabilities for
50mb of DGZ depth above 70%) which will support a stripe of heavy
snowfall rates nearing 1"/hr. Although there remains some
latitudinal uncertainty into where this will track, current WPC
probabilities are high (>70%) for 4+ inches D2 from the Pine Ridge
eastward through much of northern NE, with low probabilities
(10-30%) extending into IA D3.


Weiss


$$

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FOUS11 KWBC 060901
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
401 AM EST Thu Mar 6 2025

Valid 12Z Thu Mar 06 2025 - 12Z Sun Mar 09 2025

...Great Lakes and Maine...
Days 1-2...

Primary surface low near the northern Ontario/Quebec border will
continue to drift northeast through today. The negatively tilted
upper trough south of this low will shift up the Mid-Atlantic coast
today with rapid surface cyclogenesis tonight over the Gulf of
Maine. LES on northeasterly flow develops tonight over the eastern
U.P. and over Upstate NY (particularly near Syracuse) where Day
1.5 snow probs for >4" are 40-60%. Wrap around snow lifts over
eastern/northern Maine late tonight/Friday morning with Day 1.5
snow probs for >4" are 40-60% over northern Maine.


...Southwest, Central Rockies across the Central Plains into the
Midwest, then Southern Rockies, and Southern Plains...
Days 1-2...

...Heavy snow bands today into Friday from Wyoming across northern
Nebraska into northern Iowa...

Mid-level low along the far northern CA coast will shift south to
southern CA through tonight before further developing over the Four
Corners Friday night and shifting east to the TX Panhandle Saturday.
Meanwhile, the leading base of the trough currently over SoCal
will eject northeast over the southern Rockies by this afternoon,
across the central Plains tonight before weakening as it approaches
Chicago Friday.

Strengthening SWly jet ahead of the leading trough will allow for
quick ejection and rapid lee-side cyclogenesis over eastern CO/KS
this afternoon through tonight. Rapid banding of precip north of
this low will spread north over much of WY this morning, then shift
east over northern Neb tonight, persisting, but in a weakened state
over IA Friday. Snow totals have increased through this swath with
Day 1 snow probs for >8" over 80% in central WY terrain and 40-70%
over northern Neb. Ample Pacific moisture ahead of this wave will
keep snow levels over the Great Basin and Four Corners 4000-7000 ft
today, but will fall under the upper trough to 3000-4000ft. Day 1
WPC probabilities are high (>70%) for >8" across the terrain of
eastern NV, the Wasatch, Uintas, Wind Rivers, western CO ranges and
the highest terrain along the Mogollon Rim. Day 1 snow probs are
also high for >6" in the SoCal peninsular ranges.

SW of this secondary low, the pivoting upper low moving across the
Four Corners will drive another area of pronounced ascent leading
to periods of moderate to heavy snow across the Desert Southwest
and extending east through the TX/OK Panhandles. The column across
this region is modestly cold enough to support snow, with snow
levels around 5000-7000 ft, but steep lapse rates aloft beneath
the low will help cause strong lift to dynamically cool the
column. This suggests a mixture of rain and snow, becoming all snow
near the surface at times of heavier precipitation rates and in
terrain. Day 2.5 WPC for >6" are 40-80% over the southern Sangre
De Cristos with >4" probs 20-60% east of terrain such as the Raton
Mesa.


Jackson



$$

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FOUS11 KWBC 061859
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
159 PM EST Thu Mar 6 2025

Valid 00Z Fri Mar 07 2025 - 00Z Mon Mar 10 2025

...Great Lakes and Maine...
Day 1...

Negatively tilted longwave trough extending between two pronounced
shortwaves will pivot northeast across New England and the
Mid-Atlantic tonight. This trough is the remnant of the closed low
which produced a powerful blizzard over the Upper Midwest, and the
southern impulse will likely cause secondary cyclogenesis with
rapid strengthening off of New England and into the Gulf of Maine
tonight. As this low lifts into the Canadian Maritimes, it will
spread heavy snow across Maine, with upstream resultant NW flow
from the Great Lakes into New England driving a combination of lake
effect snow (LES) and upslope snow into the Adirondacks and
Greens/Whites. The heaviest snow is likely across portions of
northeast Maine where WPC probabilities reach 50-70% for 4+ inches
and 30% for 6+ inches. Moderate to heavy snow is also likely across
the eastern U.P., southeast of lake Ontario, and into the
Greens/Whites where WPC probabilities for 4+ inches are as high as
50%.


...Central Rockies through the Upper Midwest...
Days 1-2...

Lee cyclogenesis east of the Rockies will develop this evening
downstream of a positively tilted but amplified upper level trough
swinging through the Great Basin and towards the Central Rockies.
An intensifying and meridionally shifting jet streak downstream of
the primary trough axis will place favorable LFQ diffluence across
the High Plains, additionally supporting the rapid development of
this cyclone. As the low strengthens, it will move almost due east
in response to confluent and increasingly zonal flow across the
central/eastern parts of the CONUS.

As this low pivots east from Colorado to Illinois by Friday night,
it will drive a swath of heavy precipitation to its north, caused
by an overlap of synoptic ascent through the left-exit of the jet
streak aloft, and expanding 850-600mb frontogenesis. At the same
time, moist isentropic ascent, especially in the 290-295K layer
will surge northward creating PWs that will rise to above the 90th
percentile within the CFSR climatology, upon which the ample ascent
will drive a stripe of heavy snow. The warm/moist advection
lifting northward and being acted upon by intense fgen will result
in translating bands of heavy snow. Neutral static-stability
reflected by theta-e lapse rates nearing 0C/km within the axis of
strongest ascent could cause snowfall rates to reach 1+"/hr at
times, which is additionally supported by the WPC prototype
snowband tool, especially from eastern WY through NE. Where these
bands linger, heavy snowfall exceeding 6 inches is likely (>70%)
according to WPC probabilities across eastern WY and NE, with
moderate probabilities (30%) for 4+ inches extending as far east as
central IA.


...Four Corners States...
Days 1-2...

The forecast period begins with an amplified longwave trough
positioned across the Great Basin and extending into the Northern
Rockies. This trough will gradually pivot eastward through D1 and
into D2 as two distinct shortwaves drop from the interior Northwest
through the trough axis and then eject eastward into the Southern
Rockies, eventually merging into a closed low over New Mexico on
Saturday. Impressive height anomalies falling to below the 10th
percentile according to NAEFS ensemble tables over the Southwest
will combine with an increasingly meridionally shaped downstream
jet streak to provide ample ascent across the Four Corners into
Saturday.

At the same time, a surface low will move along the CA coast
beneath this trough evolution and then shift onshore into AZ and
then NM, producing additional ascent to support widespread
precipitation. Snow levels throughout the region will generally
hover in the 4000-5000 ft range, but downstream of the low and
within the most robust warm advection, they may at times rise to as
high as 7000 ft, especially in the Sangre de Cristos D1 into D2
before crashing later Saturday. WPC probabilities D1 for more than
6 inches of snow are high (>70%) in the Ruby Mountains of NV, along
the Wasatch, into the Uintas, CO Rockies, San Juans, and along the
Mogollon Rim. During D2, the highest probabilities become confined
to the Sangre de Cristos and along the Raton Mesa where locally as
much as 12 inches of snow is possible.


Weiss



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FOUS11 KWBC 070855
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
355 AM EST Fri Mar 7 2025

Valid 12Z Fri Mar 07 2025 - 12Z Mon Mar 10 2025

...New York/New England...
Days 1-3...

Negatively tilted longwave trough over New England will lift north
over the Canadian Maritimes today as the surface low continues to
develop on its transit of the Gulf of St. Lawrence. Heavy snow on
the back side of this surface low under the upper trough will
continue over eastern/northern Maine this morning where Day 1 PWPF
for >6" is 50-80%.

WNW flow off Lake Ontario will continue to allow lake effect snow
(LES) over Upstate NY today with upslope snow over the Adirondacks,
northern Greens, and Whites. Day 1 PWPF for >4" are 20-40% over the
southern Tug Hill down through Syracuse and Utica as well as over
the Presidential Range in NH (which are repeated for Day 2 on
continued upslope flow).

A northern Alberta Clipper tracks over Ontario on Sunday, reaching
northern NY/New England Sunday night. Day 3 PWPF for >4" is around
20% for the northwest facing Adirondacks.


...Central Plains through the Midwest to the North-Central
Appalachians...
Day 1...

The leading shortwave trough from Low pressure over the West is now
over northeast CO and will eject east through the Midwest today on
a strengthening WSWly jet. Robust, but narrow banding continues
across northern Neb/IA early this morning, and shifts east over
Chicago this afternoon. However, the wave is being sheared and the
surface low is filling, so the banding intensity should continue to
wane as it tracks east. Sufficient overlap of synoptic ascent
through the left-exit of the jet streak aloft, 850-600mb
frontogenesis, and ample Gulf-sourced moisture will continue to
drive the snow bands that should see rates drop to moderate by
mid-morning. PWPF for additional snow >2" after 12Z are 30-60% from
northeast Neb across north-central IA and along the IL/WI border.
Snow tonight reaches western PA and the central Appalachians where
there are 20-40% PWPF for >2".


...Four Corners States through Oklahoma/Texas Panhandles...
Days 1-2...

A closed low over over the southern CA border is at the base of the
still positively-tilted trough over the West. This low tracks over
southern AZ today and NM tonight before moving over the TX
Panhandle on Saturday. Further reinforcing troughs will slow the
progress east and prolong the snow fall over AZ terrain today and
the southern Rockies onto the southern High Plains tonight into
Saturday. Snow levels hover in the 4000-5000 ft range over the
Southwest, but start around 6000ft this evening over the I-25
corridor near the CO/NM border/Raton Mesa. Day 1 PWPF for >8" are
50-90% along the Mogollon Rim/White Mtns, and over the southern San Juans/Sangre de Cristos including the Raton Mesa.

Decent dynamics make for snow levels around 3500ft in the TX
Panhandle in banding on the north side of the sfc low. Snow
probabilities have risen here with Day 1.5 PWPF for >4" 40-70%
over the TX/OK Panhandles and over 80% in northeast NM.


...Western Washington...
Days 2-3...

A hearty plume of Pacific moisture tracks into western WA ahead of
the next low dropping south from the Gulf of Alaska Saturday
through Sunday night. Snow levels are generally around 4000ft
through Sunday in the WA Cascades before dropping to 2000ft Sunday
night under the trough axis. Day 2.5 PWPF for >6" is limited to the
highest Olympics/northern WA Cascades, but the Day 3 drops down to
pass level with greater coverage of >40% probabilities.


Jackson



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FOUS11 KWBC 071855
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
155 PM EST Fri Mar 7 2025

Valid 00Z Sat Mar 08 2025 - 00Z Tue Mar 11 2025

...New England...
Day 1...

Sharp cyclonic flow will persist across New England Friday night
and Saturday as an upper low spins across eastern Canada. Within
this flow, a shortwave is progged to drop southeast across New
England Friday night, pushing a surface trough eastward which will
additionally enhance the low-level NW flow. The result of this
evolution will be increased upslope ascent into the Greens and
Whites, leading to rounds of moderate snowfall through D1. The
coverage of snowfall is likely to be modest and confined to the
highest elevations, but WPC probabilities indicate a 50-70% chance
for 4+ inches of snow in northern VT and near the Presidential
Range of NH before precip winds down before D2.


...Four Corners States through Oklahoma/Texas Panhandles...
Day 1...

Strong closed mid-level low characterized by 500mb heights falling
below the 2.5 percentile of the CFSR database will move eastward
slowly across AZ/NM tonight, before slowly beginning to fill over
the TX/OK Panhandles Saturday. Downstream of this closed low, an
upper jet streak will amplify across the Southern Plains, reaching
150 kts while emerging meridionally from near Baja. Together, these
features will produce strong deep layer ascent into the Southern
Rockies. At the same time, moisture being advected into the column
will be impressive as both low-level moisture through S/SE flow
into the system, and upper level moisture on SW isentropic ascent
combine across the region, angling elevated PWs into the southern
High Plains.

The overlap of this deep layer lift and increasing moisture will
result in an axis of moderate to heavy precipitation across NM and
into the OK/TX Panhandles, with low-level easterly flow on Saturday contributing enhanced upslope ascent into the Sangre de Cristos and
along the Raton Mesa. In general, snow levels will be 5000-6000 ft,
but will crash through D1 to as low as 4000 ft before precip wanes
by early D2, but before this occurs heavy snow is likely across the
White Mountains of AZ and especially into the Sangre de Cristos and
along the Raton Mesa where WPC probabilities are high (>70%) for
12+ inches of snow.

Farther east into the Panhandles of TX/OK, the column is marginally
conducive for wintry precipitation. However, strong ascent through
both synoptic and mesoscale forcing could cause periods of dynamic
cooling sufficient to bring snow to the surface. This is most
likely across the TX Panhandle as reflected by HREF 1"/hr snow rate probabilities. The most likely timing for this heavy snow is during
the afternoon hours which will also limit accumulations, but where
dynamic cooling is strong enough and snow can persist, some locally
moderate snowfall accumulations of 2-4" are possible (30-50%
chance).


...Pacific and Interior Northwest...
Days 2-3...

A deepening trough over the Pacific will interact with a building
ridge across the Desert Southwest to funnel strengthening S/SW flow
into the Pacific Northwest beginning Sunday. This will begin to
advect higher moisture onshore as IVT pushes above 250 kg/m/s
according to GEFS and ECENS probabilities. Into this moistening
column, despite the primary trough cutting off and remaining over
the Pacific, a weak shortwave and accompanying vorticity lobe will
swing onshore Sunday evening, and work together with the RRQ of a
jet streak over Canada to induce lift. This will result in
increasing wintry precipitation over the WA Cascades and Olympics,
pivoting into the Northern Rockies by the end of the forecast
period. Snow levels will generally be around 4000 ft during the
heaviest precipitation, but will crash to as low as 1500 ft just
before precip ends Monday aftn. This combined with the transient
nature of forcing suggests most of the impactful snow will remain
above pass levels, but WPC probabilities during D3 rise to as high
as 70-90% for 4+ inches in the WA Cascades, Olympics, and near
Glacier NP.



Weiss



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FOUS11 KWBC 080840
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EST Sat Mar 8 2025

Valid 12Z Sat Mar 08 2025 - 12Z Tue Mar 11 2025


...Southern Rockies through Oklahoma/Texas Panhandles into western
Oklahoma...
Day 1...

Closed low over AZ/NM border will slowly fill as it shifts east to
northwest TX today and along the Red River tonight. A strong SWly
jet streak persists over west TX today, aiding ascent as the
associated surface trough shifts east. This deep layer lift and
increasing moisture will result in expanding precip over N Texas
and OK through this afternoon with an axis of moderate to heavy
precipitation across the TX Panhandle through central OK. Height
falls under the upper low and dynamic cooling in the banding should
allow snow to fall/accumulate over the TX Panhandle into western
OK this afternoon. 00Z HREF mean snow rates are generally not that
high, up to 0.75"/hr, though diurnal effects are probably causing
some of the limitation. Generally speaking, if snow bands become
strong/heavy enough they can overcome diurnal effects and
accumulate. Day 1 PWPF for >4" is 40-60% across the central TX
Panhandle, particularly along the I-40 corridor. Some probabilities
for >2" extend east into OK, but really it comes down to the
banding. The NAMnest likely remains too heavy/snowy, but the recent
HRRRs have trended a bit colder/snowier and a blend of these two
models is probably a decent approach.


...Washington to northwest Montana...
Days 2-3...

A deepening trough from low pressure over the Gulf of Alaska will
interact with a building ridge across the Desert Southwest to
funnel strengthening S/SW flow into western WA tonight, expanding
east to the northern Rockies through Monday. A weak shortwave and
accompanying vorticity lobe will swing onshore Sunday evening, and
along with the right entrance of a jet streak over Canada, enhance
lift. This will result in increasing wintry precipitation over the
WA Cascades and Olympics, pivoting into the Northern Rockies Sunday
night. Snow levels on the WA Cascades will generally be around
4000 ft during the heaviest precipitation, but will crash to as low
as 1500 ft just before precip ends Monday morning. This combined
with the transient nature of forcing suggests most of the impactful
snow will remain above pass levels, but Day 2 WPC probabilities
for >6" are 70-90% in the WA Cascades, with Day 2.5 probs 30-60%
for the Lewis Range in Glacier NP.


The probability of significant icing is less than 10 percent.


Jackson


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FOUS11 KWBC 081817
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
117 PM EST Sat Mar 8 2025

Valid 00Z Sun Mar 09 2025 - 00Z Wed Mar 12 2025


...Pacific Northwest through the Northern Rockies...
Days 1-2...

A deepening trough off the Pacific Coast will amplify into a closed
low positioned west of CA by Monday, while a vorticity streamer cut
off from this feature sheds eastward into the Pacific Northwest.
Downstream of this energy, intensifying SW flow between this trough
and a expanding ridge centered over the Four Corners will drive
modest IVT exceeding 250 kg/m/s into the Pacific Northwest. The
intensifying ascent through WAA, height falls, and diffluence from
the departing RRQ of an upper jet streak into this moistening
column will result in expanding precipitation, first in the
Olympics late D1 and then spreading eastward through the Cascades
and into the Northern Rockies by late D2 before ending quickly. The
transitive nature of the ascent combined with modest available
moisture will limit total precipitation, but heavy snow
accumulations are still likely above 4000-5000 ft. WPC
probabilities D1 are above 70% for 6+ inches, but only across the
Olympics and far northern WA Cascades. Heavy snow expands and
spreads east during D2, reflected by a high risk (>70%) for 6+
inches in the WA Cascades, with a moderate risk (30-50%) across the
Lewis Range in the Northern Rockies.


The probability of significant icing is less than 10 percent.


Weiss



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FOUS11 KWBC 090846
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
446 AM EDT Sun Mar 9 2025

Valid 12Z Sun Mar 09 2025 - 12Z Wed Mar 12 2025


...Upstate New York and Northern New England...
Day 1...

A clipper currently crossing into Ontario will track across
northern New England late tonight. Some Great Lake moisture will be
present in the otherwise continental airmass. Upslope flow onto the
Adirondacks and northern Greens/Whites will lead to snow tonight
with potential for 0.5"/hr snow rates per the 00Z HREF. Given a
weaker clipper will cross this morning, snow from both has Day 1
PWPF for >6" of 30-70% in the highest terrain.


...Washington State to Northwest Montana...
Day 1...

Northern stream shortwave trough crosses WA this evening and
northern MT late tonight. The transitive nature of the trough
combined with modest available moisture will limit total
precipitation, but heavy snow accumulations are still likely above
4000-5000 ft. Day 1 WPC snow probabilities are above 70% for 6+
inches in the higher northern WA Cascades, generally above pass
level, and 30-60% in the higher ridges around Glacier NP. Precip
from this trough quickly cuts off Monday morning across the
Northwest.


...Northwest and California...
Day 3...

A much stronger trough amplifies as it digs off the West Coast
Tuesday night. Enhanced moisture and height falls from the
approaching trough allow moderate precip to cross the PacNW coast
Tuesday night. Snow levels at onset will be near 3500ft in WA,
4500ft in OR, and 5000ft in CA, dropping thereafter through
Wednesday ahead of the trough axis. Particularly heavy snow is
expected in California in noted by Key Messages found on the wpc
website. Further information can also be found in the medium range
discussion (PMDEPD) and from local WFO products.



The probability of significant icing is less than 10 percent.


Jackson



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FOUS11 KWBC 091929
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 PM EDT Sun Mar 9 2025

Valid 00Z Mon Mar 10 2025 - 00Z Thu Mar 13 2025


...Upstate New York and Northern New England...=20
Day 1...

A fast moving clipper-type low will race southeast across Ontario
tonight and move offshore New England Monday morning. Forcing
associated with this clipper will be enhanced downstream due to
height falls/weak PVA ahead of the accompanying shortwave and
modest upper diffluence in the LFQ of a jet streak pivoting across
Canada. Overall, ascent is transient and modest, and available
moisture is just slightly above climo according to NAEFS, so
precipitation is not expected to be heavy. However, where ascent
maximizes, especially into the higher terrain of the upslope
regions of the Adirondacks, Greens, and Whites, snowfall rates of
0.5" to 1" per hour are likely at times. This will result in local
snowfall exceeding 4" as reflected by WPC probabilities that are as
high as 30-50% in these areas.


...Washington State to Northwest Montana...=20
Day 1...

Fast moving shortwave trough of modest amplitude will shed from an
amplifying longwave trough over the Pacific and race across the
Northwest tonight through Monday. Height falls associated with this
impulse will drive synoptic lift, while a subtle period of WAA on
backing mid-level flow to more S/SW enhances moisture on IVT which
is progged by NAEFS to briefly pulse above the 97th climatological
percentile. Jet-level support is modest, but sufficient deep layer
lift into the moistening column will result in periods of moderate
to heavy snow, especially in the Cascades and Northern Rockies
where low to mid level westerly flow drives additional upslope
enhancement. Snow levels above 4000-5000 ft will confine heavy
accumulations to only the highest passes and higher elevations, but
in these regions WPC probabilities for 6+ inches are as high as
70-90%.


...Pacific Coast...=20
Day 3...

A much stronger trough than the one from D1 above amplifies off the
Pacific Coast beginning Tuesday, driving an expansive area of
height anomalies between 700-500mb that fall to below the 2.5
climatological percentile according to NAEFS by 00Z/Thursday. While
these height falls are progged to remain just west of the coast by
the end of the forecast period, the resultant downstream shift to
S/SW flow onshore CA and the Pacific Coast will surge IVT onshore
as an atmospheric river (AR). Recent IVT probabilities from both
the GEFS and ECENS have increased, and although the GEFS remains
more amplified (40% IVT exceeding 500 kg/m/s), the ECENS has a few
members that feature IVT exceeding 750 kg/m/s. Regardless of the
maximum IVT, it is likely that heavy precipitation will spread
onshore, with elevated instability due to deep lapse rates
exceeding moist adiabatic levels as the trough advects east. This
suggests that despite general short duration of the highest IVT,
precipitation coverage and intensity will be significant.

Within the WAA which demarcates the onset of the AR, snow levels
will climb to around 3000 ft over WA state, and as high as
5000-6000 ft in CA according to the NBM deterministic forecasts.=20
As the accompanying surface low and attendant upper trough swing=20
towards the coast late (and more into D4), snow levels will drop=20
rapidly, becoming more impactful to many western passes. At this=20
time, through D3, the heaviest snow accumulations are expected=20
across the northern Sierra and Shasta/Trinity region of CA where=20
WPC probabilities feature a high risk (>70%) for 8+ inches and=20
locally 1-2 feet is possible. Farther north into the Cascades of WA
and OR, as well as the Olympics, lighter snows have a moderate=20
chance (30-50%) of exceeding 6 inches, but with snow levels around=20
3000 ft more area passes will experience impactful snow.

This system will likely become significant across much of the West
into the medium range, and Key Messages, linked below, have been
issued for this event.


The probability of significant icing is less than 10 percent.=20


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!8KPdSJ-mo2IcmjWkJDJ1tS4OyVRV-4twy5qGpfX5gRsKo= J3Quf8iulZTABuqctFNYZq_m-fd1yLonMB_MnXkktl-SYU$=20

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FOUS11 KWBC 100848
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
448 AM EDT Mon Mar 10 2025

Valid 12Z Mon Mar 10 2025 - 12Z Thu Mar 13 2025


...The Bitterroots...=20
Day 1...

A plume of Pacific moisture continues to push northeast from
northern OR through western MT this morning as a quick-moving=20
northern stream shortwave trough of modest amplitude shifts east
over the northern Rockies. Moderate snow rates can be expected
above the roughly 4000ft snow levels in this plume that will be
focused on the Bitterroots along the ID/MT border this morning. Day
1 PWPF for >6" additional snow after 12Z is 30-60% along the
Bitterroots and toward the western slopes around Glacier NP.


...Pacific Coast...=20
Days 2/3...

...Impactful heavy snow for California terrain Wednesday and
Thursday. See Key Messages linked below...

A powerful and deep trough digs off the West Coast Tuesday night
before shifting onshore Wednesday night through Thursday. The=20
orientation of this trough, with its base digging south from the=20
Central CA to Southern CA coasts Thursday brings a fairly short
lived surge of Pacific moisture that when combined with upslope
flow and height falls from the approaching trough brings a potent
heavy snow event for the length of California. This heavy snow
begins in the Klamath and CA Cascades late Tuesday night and the
length of the Cascades Wednesday into Thursday and SoCal ranges
Thursday. Snow levels of 4000 to 5000ft can be expected during the
heaviest snow for all California terrain. Day 3 PWPF for >18" is
60-90% for the highest Klamath/CA Cascades and 70-100% for the
length of the Sierra Nevada.

Lighter precip rates are expected over WA/OR which will be well
north of the base of the trough. Snow levels on Wednesday are close
to 3000ft in WA and 4000ft in OR. Day 3 PWPF for >6" are 50-70% in
the WA/OR Cascades as well as the Sawtooths of ID.

Snow and wind will spread across the Intermountain West and Rockies
Thursday into Friday before rapid development occurs over the
Plains as noted in the Key Messages and the medium range discussion
(PMDEPD).


The probability of significant icing is less than 10 percent.=20


Jackson




...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!6bl38HPUTWxgEiSI7mRxEPXjaMbgnGedZ19lAV5k_3qEs= zA4oslTxCmo2WQjkaOMBTCzeJpSt97EfgY50x2UcFFsD4E$=20

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FOUS11 KWBC 101902
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
302 PM EDT Mon Mar 10 2025

Valid 00Z Tue Mar 11 2025 - 00Z Fri Mar 14 2025


...The West...
Days 2-3...

...Impactful heavy snow from the California mountain ranges=20
Wednesday to the Intermoutnain West late week. Please see current=20
Key Messages below...

An upper-level trough in the northeast Pacific will direct an
atmospheric river at California starting Tuesday night and
continuing through Wednesday. Mountain snow begins Tuesday night from
the Cascade Range on south to the Siskiyou/Shasta and northern=20
Sierra Nevada. By 18Z Wednesday, ECMWF SATs shows a SWrly >400=20
kg/m/s IVT that surpasses the 97.5 climatological percentile over=20
central California. This enhanced moisture transport combined with=20
a cold frontal passage and falling heights aloft will result if=20
plummeting snow levels Wednesday night along the Sierra Nevada=20
with heavy snow as low as 5,000ft in elevation. Hourly snowfall=20
rates between 2-3"/hr are expected in these ranges, with the=20
combination of heavy/wet snow also posing a potential risk for=20
scattered areas of power outages and tree damage. Snow will also=20
unfold into the Southern California ranges north and east of Los=20
Angeles and San Diego Wednesday night and into Thursday morning.=20
Minor snow accumulations are possible as low as 4,000ft in the San=20
Rafael, San Gabriel, and San Bernadino Mountains through the day on
Thursday. WPC probabilities between 00Z Wed - 00Z Fri show high=20
chances (>70%) for snowfall totals >24" along the entire length of=20
the Sierra Nevada above 6,000ft. Some areas above 8,000ft could see
as much as 4-5 feet of snowfall by the time a break in the snow=20
arrives Thursday night. The WSSI is depicting Major to Extreme=20
Impacts in the Sierra Nevada that is driven due to the Snow Amount=20 algorithm, as well as some inclusion of the Snow Load and Blowing=20
Snow elements as well. Note that the Cascades above 4,000ft and=20
Olympics above 3,000ft have high chances (>70%) for snowfall=20
accumulations >6" through Thursday afternoon.

East of the Pacific Mountain ranges, the expansive swath of
Pacific moisture will expand well inland Wednesday night and into
the second half of the week. The heaviest snowfall is likely to
occur on Thursday as the cold front sweeps across the Intermountain
West and the diffluent left-exit region of a 250mb jet streak
positions itself overhead. Snow is likely to continue a little
longer into Tuesday night and Friday, so for more on those=20
potential snowfall details, please refer to our medium range=20
discussion. WPC probabilities through 00Z Friday depict high=20
chances (>70%) for snowfall >8" in parts of the Blue, Sawtooth,=20
central and southern Nevada terrain, portions of the Wasatch, and=20
the tallest peaks of the Mogollon Rim.=20

Mullinax

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-IQTm_3w1FygAcymNlQ8IwRhPbTWgNwRlD0GP28prHj5D= LW3yx0e3hNGkWQs-DmBFznU6h7fL2c4WS__FPaaMfFDaVA$=20

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FOUS11 KWBC 110849
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
449 AM EDT Tue Mar 11 2025

Valid 12Z Tue Mar 11 2025 - 12Z Fri Mar 14 2025


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

...Impactful heavy snow for most California mountain ranges=20
Wednesday into Thursday, then mostly the southern Intermountain=20
West and Rockies late week. Please see current Key Messages linked=20
below...

A strong northern stream trough currently rounding a cold-core low
over the Gulf of Alaska will further strengthen as it dives south
off the West Coast through Wednesday. The base of the trough
continues to dig south from the Central to Southern California
Coasts Thursday before ejecting east over the Four Corners Thursday
night and re-developing into a deep low over the south-central=20
Plains Friday.=20

Mountain snow begins tonight as moisture streams in ahead of the
trough axis along the length of the Cascade Range through the=20 Siskiyou/Shasta and northern Sierra Nevada. Day 1 snow
probabilities for >6" are 30-70% in the WA Cascades which will
expand and increase for Day 2 as snow rates increase to moderate=20
and snow levels drop below many Cascades passes.

This moisture surge shifts inland over CA Wednesday through=20
Wednesday night with the now heavy precipitation axis shifting=20
south with the base of the trough with snow levels generally 5000=20
to 6000ft at the onset of heavy snow. Height falls from the=20
approaching trough axis allow snow levels to drop Wednesday=20
afternoon through night along the Sierra Nevada with heavy snow as=20
low as 4,500ft in elevation before rates decrease (as low levels=20
further drop). The cooling column and ample moisture should result=20
in extreme hourly snowfall rates of 2-4"/hr in these ranges. The=20
combination of heavy/wet snow and increasing winds also posing a=20
potential risk for scattered areas of power outages and tree=20
damage. Day 2 snow probabilities for >18" are 50-99% in the=20
Shasta/Siskiyou and along the length of the higher Sierra Nevada.=20
1 to 4ft can generally be expected above about 6000ft.

Heavy snow will also reach the Transverse Ranges in Southern=20
California Wednesday night through Thursday morning with snow
levels dropping from around 6000 to 4000ft. Day 2.5 WPC snow
probabilities are 50-90% for the higher San Gabriel and San
Bernardino Ranges. 00Z Wed

East of the Pacific Mountain ranges, the expansive swath of
Pacific moisture will expand well inland Wednesday night through
Thursday night. The heaviest inland snowfall is likely to occur on
Thursday as the powerful cold front sweeps across Nevada, Utah, and
northern Arizona before shifting across Colorado and New Mexico=20
Thursday night. Day 3 snow probabilities for >8" are 40-80% over
the central and southern NV ranges, much of Utah terrain, the=20
Kaibab Plateau north of the Grand Canyon, along the Mogollon Rim to
the White Mtns of AZ, and the San Juans of southwest CO. This low
rapidly re-develops Friday over the south-central Plains.=20

The next wave quickly shifts toward the OR/CA border Thursday night
on a powerful NWly jet. Further info on the redeveloping low over
the Plains and the next wave into the West Coast can be found in
the WPC medium range discussion (PMDEPD), and from local WFOs.


The probability of significant icing is less than 10 percent.

Jackson


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

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!772UHlvrtnBNkfIjPO3UqHE03jBZmrTEFUbYxmudJYhU5= Ahm4ZbiK5vPtQFAeXiMkcbZ_h6sPJfqxyXAgWLn2bfA3Ro$=20

$$

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FOUS11 KWBC 111907
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
307 PM EDT Tue Mar 11 2025

Valid 12Z Tue Mar 11 2025 - 12Z Fri Mar 14 2025


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

...Impactful heavy snow for most California mountain ranges=20
Wednesday into Thursday, then mostly the southern Intermountain=20
West and Rockies late week. Please see current Key Messages linked=20
below...

An upper-level trough in the northeast Pacific will dive south
towards the West Coast and direct an atmospheric river at
California starting Tuesday night and continuing into the second
half of the week. The enhanced moisture transport combined with a
cold frontal passage and falling heights aloft will result in
plummeting snow levels along the Cascade Range on south to the
Shasta/Siskiyou tonight, then along the Sierra Nevada through
Wednesday and into Wednesday night. By 00Z Thursday, a >400 kg/m/s
SWrly IVT (topping out near the 99th climatological percentile via
ECMWF SATs) will be aimed at central California at the same time
the cold front pushes through "The Golden State". This when
snowfall rates will be at their heaviest; Wednesday afternoon into
Wednesday night, along the Sierra Nevada. Snowfall rates of 2-3"/hr
will be common from 6,000ft and up along the Sierra Nevada at the
snow's peak intensity. Farther south, the Transverse Ranges as well
as the peaks of the Peninsula Ranges are likely to see heavy snow
above 5,000ft through Thursday morning. Some upslope flow will=20
linger into the Sierra Nevada Thursday morning, before a brief=20
lull in the action arrives Thursday afternoon. By Friday morning,=20
yet another Pacific storm system arrives, but with notably higher=20
snow levels compared to the Wed-Thurs storm system.=20

Overall, this is an exceptionally snowy pattern for the
Salmon/Siskiyou/Shasta of northern California and along the entire=20
length of the Sierra Nevada. Snowfall will be measured in feet with
as much as 4-5 feet forecast in the peaks of the Sierra Nevada.=20
For elevations above 5,000ft in northern California, above 6,000ft=20
in the central/southern Sierra Nevada, and above 6,000ft in the San
Gabriel and San Bernadino of southern California, snowfall amounts
are likely to range between 1-3 feet of snow. WPC's WSSI shows=20
Major to Extreme Impacts in most of these ranges with Snow Amount=20
the primary impact denoted in the algorithm, but some impacts as a
result of Snow Load and Blowing Snow are expected as well.=20
Dangerous to impossible travel are anticipated with the potential=20
for some instances of power outages and tree damage as well.

The highly anomalous IVT responsible for the barrage of heavy snow
in the California mountain ranges will advect moisture well inland
across much of the Intermountain West as well. Heavy mountain snow
is expected in the more remote areas of the Blue, Sawtooth, and
Absaroka of the northern Rockies. The same recipe that produced
heavy snow in the Sierra Nevada (moisture advection, strong cold
FROPA, upslope flow) will coincide with the added help of strong
diffluent flow downstream of the upper trough to generate heavy=20
snow from the Tetons on south through the Bear River, Wasatch,=20
Uinta, central Nevada ridges, the Mogollon Rim, and Colorado=20
Rockies. WPC probabilities show high chances (>70%) for snowfall=20
totals >8" in all of these mountain ranges, but it is the Wasatch,=20
Uinta, and Mogollon Rim most notably that could see snowfall totals
between 1-2 feet through Friday.


The probability of significant icing is less than 10 percent.


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!_ou8Slwrrxr1jRi9f6xFz5MYD7l8CGNKyR4gSO6EGFnFf= 43foJjm1O1Kl4uKTrtYSAIIjs25nhEgk_9-FQ-4SgLKV00$=20

$$

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FOUS11 KWBC 120907
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
507 AM EDT Wed Mar 12 2025

Valid 12Z Wed Mar 12 2025 - 12Z Sat Mar 15 2025


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

...Impactful heavy snow for most California mountain ranges=20
this afternoon into Thursday, mostly the southern Intermountain=20
West terrain and Rockies late week, then blizzard potential on the
northern Plains Saturday. Please see the latest Key Messages=20
linked at the bottom...

Potent upper-level trough continues to dig as it tracks south with
the parent low drifting south from the Gulf of Alaska. The base of
the trough approaches northern CA this afternoon, then digs south
to the northern Baja through Thursday. Enhanced moisture transport
has raised snow levels to around 3500ft in WA, 4500ft in OR,=20
5000ft in northern CA and 6000ft on the Sierra Nevada. However, the
cold frontal passage and falling heights aloft will result in snow
levels generally around 3500ft along the Cascade Range on south to
the Shasta/Siskiyou this evening and 2500ft late tonight as snow=20
rates decrease after the upper trough passage.=20

The Sierra Nevada will be the focus of the moisture plume which
features >400 kg/m/s SWrly IVT (near the 99th climatological=20
percentile via ECMWF SATs) just ahead of the cold frontal passage
this evening. This when snowfall rates will be at their heaviest...=20
2-3"/hr will be common per 00Z HREF for several hours between 20Z=20
and 10Z Thursday down the length of the Sierra Nevada above about=20
6,000ft which is where Day 1 PWPF for >18" snow is categorical. Some
upslope flow will linger into the Sierra Nevada Thursday morning,=20
before a brief lull in the action arrives Thursday afternoon.=20

By Friday morning, the next Pacific storm system arrives, producing
more moderate snow rates for the Cascades and Sierra Nevada.
However, snow levels now progged to remain low through this time,=20
around 1500ft in western WA, and 2500 to 3000ft OR through the
Sierra Nevada. Day 3 PWPF for >8" is 40-80% for the OR Cascades and Shasta/Siskiyou, peaking around 60% for the WA Cascades and Sierra
Nevada.

Farther south, the Transverse Ranges as well as the higher peaks=20
of the Peninsular Ranges will see heavy snow late tonight through=20
Thursday morning as the snow levels drop from 5500ft to 4000ft. Day
2 PWPF for >8" are 40-80% in the higher terrain.


Overall, this is an ideal pattern for somewhat brief, but heavy
snow for the Shasta/Siskiyou and along the entire length of the=20
Sierra Nevada. Snowfall will be measured in feet with as much as=20
4-5 feet forecast in the peaks of the Sierra Nevada and 3 feet at
the higher pass levels such as on I-80. The WSSI retains shows=20
Major to Extreme Impacts in most of these ranges with Snow Amount=20
the primary impact, but some impacts as a result of Snow Load and=20
Blowing Snow are expected as well. Dangerous to impossible travel=20
are anticipated with the potential for some instances of power=20
outages and tree damage as well.

The highly anomalous IVT responsible for the barrage of heavy snow
in the California mountain ranges will advect moisture well inland
across much of the Intermountain West as well. Heavy mountain snow
is expected in the Blue, Sawtooth, and Absaroka of the northern=20
Rockies. The high moisture plume will coincide with the added help
of strong diffluent flow downstream of the upper trough to=20
generate heavy snow from the Tetons on south through the Wasatch,=20
Uinta, central Nevada ridges, the Kaibab Plateau and Mogollon Rim,
and western Colorado Rockies. Day 1.5 and 2 WPC probabilities show
high chances (>70%) for snowfall totals >8" in all of these=20
mountain ranges, but it is the Wasatch, Uinta, and Mogollon Rim=20
most notably that could see snowfall totals between 1-2 feet=20
through Friday.


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

The trough takes on a negative-tilt Thursday night over NM and
closes in to a mid-level low over KS Friday morning. This low
further deepens/strengthens as it tracks northeast over MN into
Saturday. The southern stream wave crossing the southern Plains=20
today limits Gulf moisture from streaming up the Plains until=20
Thursday night, limiting the the moisture available moreso than if
the wave weren't crossing today. While enough Pacific- sourced=20
will be present to allow some wrap around banding on the low over=20
the High Plains Friday that banding should be fairly sparse until=20
Friday night when the activity should be over central Neb/SD. This
is notable as the area is in drought and will be experiencing
strong winds ahead of the system - in some areas of the High Plains
there may be just a dry wind shift. Once those bands do develop as
they head for the eastern Dakotas and MN, heavy snow banding is
possible. Powerful winds with the system will immediately result in
blowing snow and a potential blizzard. Marginal thermals at the
onset should result in a rain to wintry mix to snow progression
with some ice accretion potential most likely over the Red River of
the North Basin along the ND/MN border.


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!_nmiYIOHPo2OAAoL3oAPwm67D4v9iY77Xadgu2ho1RewG= E3T8xDMOs4bcqJeiY3YhlrHad8jMBEpnm-i_diVoCQcsIE$=20

$$

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FOUS11 KWBC 121919
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 PM EDT Wed Mar 12 2025

Valid 00Z Thu Mar 13 2025 - 00Z Sun Mar 16 2025


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

...Storm system to produce impactful heavy snow for most=20
California mountain ranges through Thursday, the southern=20
Intermountain West terrain and Rockies late week, then emerge over=20
the Central U.S. on Saturday with blizzard potential over parts of=20
the northern Plains. Please see the latest Key Messages linked at=20
the bottom...

Potent upper-level trough continues to dig as it tracks south with
the parent low drifting south from the Gulf of Alaska. The base of
the trough and associated cold front approaches northern CA this=20
afternoon, then digs south to the northern Baja while also pushing
inland through Thursday. Enhanced moisture transport has raised=20
snow levels to around 4000ft in WA, 4500ft in OR, 5000ft in=20
northern CA and 6500ft on the Sierra Nevada. However, the cold=20
frontal passage and falling heights aloft will result in snow=20
levels generally around 3500ft along the Cascade Range on south to=20
the Shasta/Siskiyou this evening and 2500ft late tonight as snow=20
rates decrease after the upper trough passage.=20

The Sierra Nevada will be the focus of the moisture plume which
features >400 kg/m/s SWrly IVT (near the 99th climatological=20
percentile via NAEFS SATs) just ahead of the cold frontal passage=20
this evening. This is when snowfall rates will be at their=20
heaviest per the 12z HREF and around 2-3"/hr for several hours=20
between 00Z and 10Z Thursday down the length of the Sierra Nevada=20
above about 6,000ft, which is where Day 1 PWPF for >24" snow is=20
above 80%. Some upslope flow will linger into the Sierra Nevada=20
Thursday morning, before a brief lull in the action arrives=20
Thursday afternoon.=20

By Friday morning, the next quick-hitting Pacific storm system=20
arrives, producing more moderate snow rates for the Cascades and=20
Sierra Nevada. However, snow levels are progged to remain low=20
throughout this time period, around 1500ft in western WA, and 2500
to 3000ft OR through the Sierra Nevada. Eventually, the next=20
progressive shortwave digging across the northern Pacific produces
upstream ridging across the West Coast by Friday night and raises=20
snow levels up to 4000ft across northern CA on Saturday. This sets=20
the stage for the next Atmospheric River event progged to impact=20
northern CA and southern OR primarily on Day 4. For the Day 2-3=20
time frame, PWPF for >8" is 60-90% for the OR Cascades and=20
Shasta/Siskiyou.

Farther south, the Transverse Ranges as well as the higher peaks=20
of the Peninsular Ranges will see heavy snow late tonight through=20
Thursday morning as the snow levels drop from 5500ft to 4000ft. Day
1 PWPF for >8" are 60-90% in the higher terrain.

Overall, this is an ideal pattern for somewhat brief, but heavy
snow for the Shasta/Siskiyou and along the entire length of the=20
Sierra Nevada. Snowfall will be measured in feet with as much as=20
4-5 feet forecast in the peaks of the Sierra Nevada and 3 feet at
the higher pass levels such as on I-80. The WSSI retains Major to=20
Extreme Impacts in most of these ranges with Snow Amount the=20
primary impact, but some impacts as a result of Snow Load and=20
Blowing Snow are expected as well. Dangerous to impossible travel=20
are anticipated with the potential for some instances of power=20
outages and tree damage as well.

The highly anomalous IVT responsible for the barrage of heavy snow
in the California mountain ranges will advect moisture well inland
across much of the Intermountain West as well. Heavy mountain snow
is expected in the Blue, Sawtooth, and Absaroka of the northern=20
Rockies. The high moisture plume will coincide with the added help
of strong diffluent flow downstream of the upper trough to=20
generate heavy snow from the Tetons on south through the Wasatch,=20
Uinta, central Nevada ridges, the Kaibab Plateau and Mogollon Rim,
and western Colorado Rockies. Days 1-2 WPC probabilities show high
chances (>70%) for snowfall totals >8" in all of these mountain=20
ranges, but it is the Wasatch, Uinta, and Mogollon Rim most notably
that could see snowfall totals between 1-2 feet through Friday.


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

The trough takes on a negative-tilt Thursday night over NM and
closes in to a mid-level low over KS Friday morning. This low
further deepens/strengthens as it tracks northeast over MN into
Saturday. MSLP of this low is expected to drop into the 970s (mb)
and drop below the 1st climatological percentile per the GEFS and
ECENS. This extremely low pressure will be the driving force behind
the widespread strong winds poised to be the primary weather=20
hazard across the northern Plains.

The southern stream wave crossing the southern Plains today limits
Gulf moisture from streaming up the Plains until Thursday night,=20
cutting off the moisture available moreso than if the wave weren't
crossing today. While enough Pacific- sourced will be present to=20
allow some wrap around banding on the low over the High Plains=20
Friday that banding should be fairly sparse until Friday night when
the activity should be over central Neb/SD. This is notable as the
area is in drought and will be experiencing strong winds ahead of=20
the system - in some areas of the High Plains there may be just a=20
dry wind shift. Once those bands do develop as they head for the=20
eastern Dakotas and MN, heavy snow banding is possible. Powerful=20
winds with the system will immediately result in blowing snow and a
potential brief blizzard. Marginal thermals at the onset should=20
result in a rain to wintry mix to snow progression with some ice=20
accretion potential most likely over the Red River of the North=20
Basin along the ND/MN border. This transition occurring during the
overnight period could limit snowfall totals as well. Latest WPC=20 probabilities for at least 4" of snow are medium (40-60%) from the=20
eastern Dakotas through far western and north- central Minnesota.=20
WSSI-P values for moderate impacts are mainly associated with=20
Blowing Snow and are within the 50-70% range for this region.


Snell/Jackson




...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!5aU9N937f7uNKvw_kUgp6fyzcmNgN7juUKpq3BExQTmus= oI0UywSgFcPSTjy2-LCHxL1MAZ39zTZVOKY7M_axVBY5Jo$=20

$$

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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

$$

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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

$$

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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

$$

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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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