FOUS11 KWBC 072007
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
407 PM EDT Mon Apr 7 2025

Valid 00Z Tue Apr 08 2025 - 00Z Fri Apr 11 2025

...Interior Northeast...
Days 1,2...

A compact low tracking from Lake Huron this afternoon east along
the Canadian border and across Maine through Tuesday afternoon will
cause an area of mostly light snow to fall along its track, as most
locations near the track stay below freezing, favoring mostly snow
as the precipitation type. The initial front is largely over the
Ontario Peninsula (the area bounded between Lakes Huron, Erie, and
Ontario) at the time of this writing. Temperatures with this band
are largely above freezing, so any snow embedded within it is not
sticking, especially to roads. Going into tonight, however, without
solar insulation, it's likely on the higher elevations of the
Chautauqua Ridge, and eventually Adirondacks and points further
east, snow will begin sticking and have some impacts.

The greatest impact from this low for most areas is likely to be
the potential for flash freezing. As sub-freezing air moves in with
the snow, road/ground temperatures could rapidly drop, resulting in
a thin glaze of ice on some colder surfaces. This of course may
have travel impacts. With the snow itself, in some of the stronger
convective cells, visibility in any snow may drop enough to cause
travel impacts as the winds with the snow and cold front become
gusty. Fortunately, the snow is not expected to become very strong,
as a stronger low along the moisture plume off the Eastern Seaboard
saps a lot of energy from this polar low as they track parallel to
one another.

As far as snow amounts are concerned, impacts from this low will
start tonight, increase through the day Tuesday, then peak Tuesday
evening as the snow rates wane as the parent low moves off to the
east. A few inches of accumulation are possible in the valleys from
the Champlain Valley east to coastal Maine. Meanwhile, locally
much greater impacts from much higher accumulations are expected
from the Tug Hill Plateau of central New York to the west, to the
Adirondacks, the northern Greens and Whites of VT and NH,
respectively, and much of western Maine. Local accumulations on the
highest elevations could approach a foot of new snow by the time
the snow is all said and done.

WPC Probabilities are moderate-to-high (50-70%) across far northern
New Hampshire and much of western Maine for 6 inches or more of
snow. Since the heaviest snow will be falling during the day
further west across northern New York and Vermont, those
percentages are much lower (10-30%) in those mountains. Minor
impacts are expected in these areas, though where snow falls
heavier in any convective snow showers, locally greater impacts are
probable.

...Great Lakes...
Days 1-3...

Extensive lake-effect snow is expected behind the aforementioned
low that is moving through the Great Lakes currently. 850 mb temps
will be falling to the west (cold side) of the low to between -12C
and -18C across all of the Great Lakes tonight. Despite this being
the climatologically unfavored time of year for lake-effect (due to
usual warm air in place over the cold lakes), the air will be cold
enough in this case for all of the lakes to support multiple bands
and cellular lake-effect convection from the U.P. of Michigan,
where lake-effect snow is ongoing presently, to western Michigan
off its namesake lake, and later tonight off the lower lakes
through the Chautauqua Ridge and Tug Hill Plateau. As usual with
lake-effect, the typical impacts such as rapidly reduced
visibilities, snow-covered roads, and blowing snow are likely in
the aforementioned impacted areas. The heaviest lake-effect and
greatest snowfall amounts are expected on the Tug Hill where
amounts approaching 10 inches are possible through Tuesday.

A developing low along a slow-moving warm front extending from the
Arrowhead of Minnesota through southern lower Michigan and
eventually into portions of northern New York may cause additional
areas of snow Wednesday Night into Thursday morning. As is typical
during April, temperatures will be hovering right around freezing,
so precipitation type between snow and rain will be a major
determining factor as to accumulations in any one area. A general
1-3 inches of snow are possible in these areas from the low and
front.


...Northern Rockies and Cascades...
Days 1,2...

A pair of shortwave troughs rotating east along the base of a
longwave trough over the northeast Pacific will direct plumes of
Pacific moisture into the Pacific Northwest through Wednesday. Snow
is expected to remain at higher elevations, especially over the
Olympics and Cascades. Higher elevations such as Mt. Rainier may
see multiple feet of snow through the period due to very persistent
and heavy upslope snow. Accumulations will be extremely elevation
dependent, as many valley locations see mostly rain or snow light
enough to not be able to stick to warm surfaces. Measurable snow
will impact many of the mountain ranges of the Pacific Northwest,
including the Blue, Sawtooth, Bitterroots, Absaroka, Teton, and
Lewis Ranges. Strong ridging building in behind the troughs by
Wednesday and Wednesday night will end any remaining high elevation
snow.


Wegman

$$

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FOUS11 KWBC 080726
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
326 AM EDT Tue Apr 8 2025

Valid 12Z Tue Apr 08 2025 - 12Z Fri Apr 11 2025

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

Low pressure tracking through the St. Lawrence River Valley will
direct its strong cold front east across the I-95 corridor this
morning. There could still be some remnant potent snow showers
early this morning, but additional snow showers may develop
throughout the interior Northeast and northern Mid-Atlantic due to
lingering low-level moisture and steepening low-level lapse rates.
Little accumulation from these snow showers is expected.

Farther north across far northern New York and northern New
England, snow on the northern flank of the storm and lake-effect
bands on the backside of the storm will result in accumulating snow
today and into Tuesday night. Gusty winds on the backside of the
storm will make for reduced visibilities, while the heaviest rates
are located across much of northern Maine, the White Mountains of
northern New Hampshire, and the Green Mountains of northern
Vermont. Snow will taper off by early Wednesday morning as the
storm system tracks towards Nova Scotia. WPC probabilities show moderate-to-high chances (50-70%) for snowfall >8" in the Green and
White Mountains, as well as west-central Maine. Some localized
snowfall amounts approaching 12" are possible in west-central
Maine. Over northern New York, moderate chance probabilities
(40-60%) for >4" of snowfall are present in the Tug Hill and along the northern-most portions of the Adirondacks. The WSSI continues to
depict Minor Impacts across northern New England, suggesting some
hazardous travel conditions are possible anticipated through
Tuesday night.

By Thursday night, an amplifying upper trough over the Ohio Valley
will develop low pressure over the Carolinas. It will direct a
plume of moisture northward into the Northeast that could be
sufficiently cold enough to support mountains snow in parts of the
Interior Northeast. There remains a fair amount of uncertainty
regarding the QPF and if the boundary layer is also sufficiently
cold enough to support snow. At the moment, WPC probabilities due
show low chances (10-30%) for snowfall >2" in parts of the highest
elevations of the Adirondacks, Green, and White Mountains.


...Great Lakes...
Days 2-3...

A complex forecast for much of the Great Lakes from Wednesday into
early Thursday. As a 500mb shortwave trough approaches from the
west on Wednesday, it will generate modest upper-level divergence
at the same time as 850mb FGEN ensues over the Lower Great Lakes.
The GFS/CMC is stronger with the 850mb FGEN and southwesterly WAA
compared to the ECMWF. This means there is a more solidified area
of precipitation and better dynamic cooling in the GFS/CMC suite
along the northern flank of a developing wave of low pressure,
while the ECMWF is flatter and less supportive for snow. Even if it
does snow in the GFS/CMC solutions, marginal boundary layer and
surface temperatures will make it tough for snow to accumulate
efficiently. WPC probabilities are <10% for snowfall totals >2" for
the time being, but this setup will be closely monitored in future
forecast cycles.


...Northern Rockies, Cascades, and Olympics...
Days 1-3...

A series of shortwave troughs rotating east at the base of a
longwave trough over the northeast Pacific will impose upper-level
divergence and direct plumes of Pacific moisture at the
Northwestern U.S. mountain ranges through Thursday. Snow across the
Olympics and Cascades will continue today as an IVT topping 400
kg/m/s directs its best injection of the Pacific moisture at these
ranges this morning and into the afternoon hours. Meanwhile,
Pacific moisture will also spill over into the Northern Rockies
that results in measurable in mountains such as the Blue, Sawtooth, Bitterroots, Absaroka, Teton, and Lewis Range. Snow should taper
off throughout the northwestern U.S. Wednesday afternoon, but look
for another round of high-elevation (generally above 5,000ft) snow
in the Olympics and Cascades Thursday night as another Pacific
disturbance tracks north towards British Columbia.

With a lack of a sufficiently cold/dry air-mass in place, look for
most snowfall accumulations >4" to be confined to the higher/more
remote peaks of the northwestern U.S. mountain ranges. Snowfall
accumulations >6" are most likely at elevations >4,000ft in the
Olympics and Cascades. Notable passes that could see measurable
snowfall include Snoqualmie (3-6") and Stevens (4-8") where
hazardous travel are possible. The snowfall in the Northern Rockies
will be light-to-moderate with 1-4" of snowfall most common. Some
peaks of the Lewis Range and Absaroka may eclipse 6" by the time
snow concludes on Wednesday.


WPC probabilities for ice accumulations above 0.1" throughout the
CONUS are less than 10%.


Mullinax




$$

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FOUS11 KWBC 081822
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
222 PM EDT Tue Apr 8 2025

Valid 00Z Wed Apr 09 2025 - 00Z Sat Apr 12 2025


...Northern New England & Maine...
Day 1...

Low pressure tracking through the St. Lawrence River Valley will
direct its strong cold front east across the remainder of New
England this afternoon as a compact occluded low slides eastward
across Maine this evening. This will prompt a healthy precipitation
shield across northern New England and Maine until early
Wednesday, when the system weakens and accelerates east over Nova
Scotia.

The heaviest snowfall rates (1-2"/hr) are expected through about
06Z Wednesday as a combination of favorable upslope northwesterly
flow across northern New England and an inverted low-to- mid level
trough develops across central Maine. Additional snowfall amounts
of 3-6" are expected across the northern Greens of VT and Whites of
NH/ME as well as a stripe through central ME towards the Interior
Downeast. WPC probs for an additional >4" are 30-60% for these
areas.


...Great Lakes & Interior Northeast...
Days 2-3...

A complex forecast for much of the Great Lakes from Wednesday into
early Thursday, which could lead to a swath of light to locally
moderate snowfall. As a 500mb shortwave trough approaches from the
west on Wednesday, it will generate modest upper-level divergence
at the same time as 850mb FGEN ensues over the Lower Great Lakes.
There remains some subtle differences with the evolution of this
trough and the interaction of several shortwaves, which could
strengthen or weaken the 850mb FGEN. Even if it does snow as with
the stronger solutions, marginal boundary layer and surface
temperatures will make it tough for snow to accumulate efficiently.
WPC probabilities are nonexistent for >4", but have increased for

2" across the southern MI L.P. to 10-30%. Additionally, persistent

light precipitation on the northern periphery of the diving
shortwaves could produce 1-4" snowfall amounts along the North
Shores of Lake Superior.

By Thursday night, an amplifying upper trough over the Ohio Valley
will develop low pressure over the Carolinas. It will direct a
plume of moisture northward into the Northeast that could be
sufficiently cold enough to support mountain snow in parts of the
Interior Northeast. There remains a fair amount of uncertainty
regarding the QPF and if the boundary layer is also sufficiently
cold enough to support snow. At the moment, WPC probabilities due
show low chances (10-40%) for snowfall >2" in parts of the highest
elevations of the Adirondacks, Green, and White Mountains.


...Northern Rockies, Cascades, and Olympics...
Days 1 & 3...

A series of shortwave troughs rotating east at the base of a
longwave trough over the northeast Pacific will impose upper-level
divergence and direct plumes of Pacific moisture at the
Northwestern U.S. mountain ranges through Friday with a brief break
Wednesday night. Snow across the Olympics and Cascades will
continue tonight as IVT weakens and snow levels fall below 4,000ft.
Meanwhile, Pacific moisture will also spill over into the Northern
Rockies that results in measurable in mountains such as the Blue,
Sawtooth, Bitterroots, Absaroka, Teton, and Lewis Range. Snow
should taper off throughout the northwestern U.S. Wednesday
afternoon, but look for another round of high- elevation (generally
above 5,000ft) snow in the Olympics and Cascades Thursday night as
another Pacific disturbance tracks north towards British Columbia.

With a lack of a sufficiently cold/dry air-mass in place, look for
most snowfall accumulations >6" to be confined to the higher/more
remote peaks of the northwestern U.S. mountain ranges. Snowfall
accumulations >6" are most likely at elevations >4,000ft in the
Olympics and Cascades. Notable passes that could see measurable
total snowfall include Snoqualmie and Stevens, where hazardous
travel are possible. The snowfall in the Northern Rockies will be light-to-moderate with 1-4" of snowfall most common. Some peaks of
the Lewis Range and Absaroka may eclipse 6" by the time snow
concludes on Wednesday.


WPC probabilities for ice accumulations above 0.1" throughout the
CONUS are less than 10%.


Snell/Mullinax







$$

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FOUS11 KWBC 090740
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Wed Apr 9 2025

Valid 12Z Wed Apr 09 2025 - 12Z Sat Apr 12 2025


...Great Lakes & Interior Northeast...
Days 1-2...

A fast approaching upper-level trough producing modest PVA aloft
at the same time as the diffluent left-exit region of a 120kt jet
streak moves in over the Great Lakes Wednesday afternoon and
through Wednesday night. As a wave of low pressure tracks east
along a strenghtening low-level warm front, a swath of
precipitation along the warm front and on the northern flank of the
storm will be capable of producing periods of snow. The setup
continues to feature very marginal boundary layer temperatures,
making it essential for dynamic cooling and the transition to snow
after sunset Wednesday evening to help snow accumulate. The wide
ranging solutions in guidance include little to no snow or as much
as several inches from southern Wisconsin on east to southern
Michigan and both northern Indiana and Ohio (showcasing the
complexities of the setup detailed above). WPC probabilities show
low chances (10-30%) for snowfall totals >2" across southern
Michigan, while most areas in the Lower Great Lakes see a coating
to 2" throughout the Lower Great Lakes.

A similar setup for light snow occurs over the Northeast mountains
Wednesday night into Thursday. Mountain ranges such as the
Catskills, Adirondacks, and Berkshires could see between a coating
to 2" of snowfall through Thursday night. A break in the snow
arrives Friday morning before another round of mountain snow
arrives late Friday into Saturday.


...Northern & Central Appalachians...
Day 3...

As the upper-level trough over the Ohio Valley deepens Thursday
night, excellent upper-level divergence via PVA ahead of an
embedded shortave disturbance will spawn a strengthening area of
low pressure in the Mid-Atlantic. Out ahead of the upper trough is
an IVT >400 kg/m/s that will deliver copious amounts of moisture
into the northern Mid-Atlantic and Northeast Friday and into
Saturday. While there is some residual sub-freezing air in the
Northeast, there is only enough to support snow in the more
elevated terrain of the central and northern Appalachians.
Elevations above 2,000ft are most favored for snowfall, but some
areas as low as 1,000ft in elevations could see rain transition to
snow Friday night. This is a sensitive setup given the time of year
with lack of sub-freezing temps and dynamic cooling being
necessary to support heavier snowfall rates. WPC probabilities show
10-20% chances for snowfall >2" in the tallest peaks of the
Catskills, Adirondacks, Green, and White Mountains through Saturday
morning.


WPC probabilities for ice accumulations above 0.1" throughout the
CONUS are less than 10%.


Mullinax










$$

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FOUS11 KWBC 130710
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
310 AM EDT Sun Apr 13 2025

Valid 12Z Sun Apr 13 2025 - 12Z Wed Apr 16 2025


...Maine...
Day 1...

Upper trough will finally start to push east of 70W today with the
last wave lifting toward the Gulf of Maine. Rain along the coast
and snow inland will slowly ease out of the area overnight tonight
into early Monday, with some modest QPF amounts that have trended
up in just the past 24 hrs (with a slower exit of the system
altogether). Temperatures remain marginal for most areas, but snow
should still accumulate over northwestern Maine and in the higher
elevations even during the daytime when precip rates may be
highest. Still, SLRs will be not much better than about 7-9:1,
making for a west and heavy snowfall. WPC probabilities for at
least 4 inches of snow after 12Z today are at least 40% over much
of northern Maine, with low probabilities (10-30%) of at least 8
inches in some of the highest elevations.


...Northern to Central Rockies...
Day 1...

A strong/compact upper low will move out of western MT this
morning, with some with some trailing snow along a surface trough
axis back toward the middle of the state that will end late this
afternoon. To the south, a weaker shortwave will move from UT to
CO, helping to wring out some snow for the high Rockies and lighter
snow below 7500ft as colder air comes in. WPC probabilities for at
least 4 inches of snow after 12Z today are moderate (40-70%)
across some of the central MT mountains (e.g., the Little Belts)
and over the northern CO Rockies (above 10,000ft).


...Western Great Lakes...
Days 1-2...

The mid-level low exiting MT today will strengthen more over the
northern Plains as a 120kt jet streak develops over Iowa. An area
of surface low pressure at the tip of this jet will deepen over
northern WI and help foster an expanding area of precipitation
throughout the region. Temperatures will be mild initially (upper
50s into central MN/WI), but once the low tracks into Lake
Superior, north to northwest winds will rapidly bring in colder air
to northern areas of MN and eventually into the U.P. of Michigan
Monday night into early Tuesday. Rain will change to snow and
become more widespread with accumulation likely over most of the MN
Arrowhead and northern WI into the U.P. and northern Lower
Michigan. By Tuesday, with the surface low well into Ontario,
northerly winds will advect in 850mb temperatures of around below
-6C which may be enough to spur some lake enhancement (Lake
Superior temperatures around 4-5C). The snow will end from west to
east on Tuesday. WPC probabilities for at least 4 inches of snow
through 00Z Wed are moderate (30-60%) in northeastern MN. For
areas downwind of Lake Superior (far northern WI through the U.P.
of Michigan), higher amounts are likely Monday night through
Tuesday, with WPC probabilities depicting 20-60% chances for at
least 8 inches of snow in the favored areas just inland from the
lake shore and with any elevation (e.g., Porcupine and Huron
Mountains). For northern Lower MI, WPC probabilities for at least
4 inches of snow are low (10-30%).


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

Low pressure will continue through Canada with its cold front
rushing across the Northeast on Tuesday. Behind it, colder air will
filter in with lingering precipitation downwind of the eastern
Great Lakes with some upslope in the central Appalachians as well.
Temperatures will be marginal for some lower elevations and also
near the lake waters, but light accumulation is likely over much of
western and northern NY (Chautauqua Ridge, Tug Hill Plateau,
Adirondacks). There, WPC probabilities for at least 4 inches of
snow are 10-60%, highest in the Adirondacks.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso








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FOUS11 KWBC 131835
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
235 PM EDT Sun Apr 13 2025

Valid 00Z Mon Apr 14 2025 - 00Z Thu Apr 17 2025


...Colorado Rockies...
Day 1...

Shortwave will move from UT to CO tonight and help wring out some
snow for the high Rockies and lighter snow below 7500ft as colder
air comes into CO by Monday. WPC probabilities for at least 6
inches of snow after 00Z tonight are moderate (40-70%) across a
narrow region of the northern CO Rockies along the Front Range
(above 10,000ft) just west of Boulder.


...Western Great Lakes...
Days 1-2...

The mid-level low exiting MT today will strengthen more over the
northern Plains as a 120kt jet streak develops over Iowa. An area
of surface low pressure at the tip of this jet will deepen over
northern WI and help foster an expanding area of precipitation
throughout the region. Temperatures will be mild initially (upper
50s into central MN/WI), but once the low tracks into Lake
Superior, north to northwest winds will rapidly bring in colder air
to northern areas of MN and eventually into the U.P. of Michigan
Monday night into early Tuesday. Rain will change to snow and
become more widespread with accumulation likely over most of the MN
Arrowhead and northern WI into the U.P. and northern Lower
Michigan. By Tuesday, with the surface low well into Ontario,
northerly winds will advect in 850mb temperatures of around below
negative 6C which may be enough to spur some lake enhancement
(Lake Superior temperatures around 4-5C). The snow will end from
west to east on Tuesday. WPC probabilities for at least 6 inches
of snow through 00Z Wed are moderate (30-50%) in northeastern MN.
For areas downwind of Lake Superior (far northern WI through the
U.P. of Michigan), higher amounts are likely Monday night through
Tuesday, with WPC probabilities depicting 20-60% chances for at
least 8 inches of snow in the favored areas just inland from the
lake shore and with any elevation (e.g., Porcupine and Huron
Mountains). For northern Lower MI, WPC probabilities for at least 4
inches of snow are low (10-30%).


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

Low pressure will continue through Canada with its cold front
rushing across the Northeast on Tuesday. Behind it, colder air will
filter in with lingering precipitation downwind of the eastern
Great Lakes with some upslope in the central Appalachians as well.
Temperatures will be marginal for some lower elevations and also
near the lake waters, but light to moderate accumulation is likely
over much of western and northern NY (Chautauqua Ridge, Tug Hill
Plateau, Adirondacks). WPC probabilities for at least 4 inches of
snow are 10-30% in far western WY, with highest chances (50-80%) in
the Adirondacks and Tug Hill Plateau.


...Northwest Montana...
Day 3...

Active and wintry weather returns to northwest MT by the end of D3
and is expected to expand further into much of the Intermountain
West/Rockies on D4. Deepening upper troughing is forecast to
develop over the West anchored by a meandering upper low
approaching southern CA on Wednesday. Meanwhile, a sharp shortwave
diving southward from British Columbia into northern WA/ID by
Wednesday evening will help start the event. Behind a cold front
racing southward across northwest MT, ample lift underneath a
strengthening mid-level low combined with upslope flow along the
Lewis Range could support locally heavy snowfall on Wednesday.
Here, WPC probabilities through 00Z Thursday are currently 30-50%
for at least 4 inches of snowfall, but should increase once the
entire event enters the forecast period.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell




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FOUS11 KWBC 140746
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
346 AM EDT Mon Apr 14 2025

Valid 12Z Mon Apr 14 2025 - 12Z Thu Apr 17 2025


...Western Great Lakes...
Days 1-2...

Vigorous mid-level upper low over the MN Arrowhead this morning
will continue moving eastward across Lake Superior today along with
its attendant surface low pressure. Temperatures in the upper 30s
to low/mid-40s this morning will fall as winds increase from the
north and northwest around the area of low pressure, changing rain
to snow from northern/northeastern MN into northern WI and the U.P.
of Michigan this afternoon and into the evening. After 00Z
tonight, additional mid-level energy will swing around the backside
of the departing upper low, favoring a surge in snowfall into the
northwestern U.P. that may be boosted by some lake-induced steeper
lapse rates (lake temps 4-5C with 850mb temps below -6C). Some
heavier rates of >1"/hr are possible overnight tonight (30-60%
probs from the HREF) which could lead to modest snow totals there
along with gusty winds. Snow will continue across the U.P. into
northern Lower Michigan early Tuesday with additional accumulation.
On Tuesday, snow will end from west to east during the afternoon
into the evening as heights rise from the west. WPC probabilities
for at least 4 inches of snow are highest (>70%) over the U.P. and
moderate (30-60%) over the northern L.P. of MI. In addition,
probabilities for at least 8 inches of snow are >50% over some of
the favored lake areas around the Porcupine and Huron Mountains.


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

Canadian low pressure will continue through Quebec as its cold
front brings in colder air to the region. Once the front clears the
coast, another area of low pressure may develop along the
occlusion near northern Maine late Tue/early Wed before finally
moving away on Wednesday mid-day. Rain will change to snow from
west to east as the column cools post-FROPA, setting up some lake- enhanced/effect snow for areas east of Lakes Erie/Ontario and
upslope snow for the central Appalachians and into the Adirondacks
and Green/White Mountains. WPC probabilities for at least 4 inches
of snow are 20-50% in far western WY south of BUF, 50-90% in the
Adirondacks and Tug Hill Plateau, and 40-80% in the northern Green
and White Mountains into far northwestern Maine. Low (10-20%)
probabilities for at least 4 inches of snow are present over the
central Appalachians and northern Maine.


...Northwest Montana...
Day 3...

Strong height falls plunging southward out of southwestern Canada
late Wed will drive a cold front through Montana, setting up a
period of wintry weather. Northeasterly flow post-FROPA will
provide plenty of upslope enhancement into northwestern MT amid
ample lift in the column and lowering snow levels. Moderate to
perhaps heavy snow is likely along the Lewis and Flathead Ranges on
Wednesday with lighter snow extending southward and southeastward
into northwestern WY (continuing into Day 4). WPC probabilities for
at least 6 inches of snow are high (>70%) over the Lewis Range and
low (10-40%) into the Little Belts, Crazy Mountains, and into the
Absarokas.


...Central Sierra...
Day 3...

Meandering upper low west of California will finally move into
SoCal late Wednesday night/early Thursday morning, with some
downstream generally light precipitation into the Sierra. Snow
levels will be quite high (>8000ft) and there are low probabilities
(10-40%) of at least 4 inches of snow through 12Z Thu in the high
central Sierra above 10,000ft.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso



$$

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FOUS11 KWBC 091827
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
227 PM EDT Wed Apr 9 2025

Valid 00Z Thu Apr 10 2025 - 00Z Sun Apr 13 2025


...Great Lakes & Interior Northeast...
Days 1-2...

As a wave of low pressure tracks east along a strengthening low-
level warm front into this evening, a swath of precipitation along
the warm front and on the northern flank of the storm will be
capable of producing periods of snow. The setup continues to
feature very marginal boundary layer temperatures, making it
essential for dynamic cooling and the transition to snow after
sunset this evening to help snow accumulate. Solutions have
trended towards little to no accumulating snow from southern
Wisconsin on east to southern Michigan and both northern Indiana
and Ohio. WPC probabilities show low chances (10-15%) for snowfall
totals >2" across southern Michigan, while most areas in the Lower
Great Lakes see a coating to 2".

A similar setup for light snow occurs over the Northeast mountains
tonight into Thursday. Mountain ranges such as the Catskills,
Adirondacks, and Berkshires could see between a coating to 3" of
snowfall through Thursday night, with WPC probabilities of 20-40%
for >2". A break in the snow arrives Friday morning before another
round of mountain snow potentially arrives late Friday into
Saturday.


...Northern & Central Appalachians...
Day 3...

As the upper-level trough over the Ohio Valley deepens Thursday
night, excellent upper-level divergence via PVA ahead of an
embedded shortwave disturbance will spawn a strengthening area of
low pressure in the Mid-Atlantic. Out ahead of the upper trough is
an IVT >400 kg/m/s that will deliver copious amounts of moisture
into the northern Mid-Atlantic and Northeast Friday and into
Saturday. While there is some residual sub-freezing air in the
Northeast, there is only enough to support snow in the more
elevated terrain of the central and northern Appalachians.
Elevations above 2,000ft are most favored for snowfall, but some
areas as low as 1,000ft in elevations could see rain transition to
snow Friday night. This is a sensitive setup given the time of year
with lack of sub-freezing temps and dynamic cooling being
necessary to support heavier snowfall rates. The GFS remains the
most amplified and westernmost solution, which eventually floods
the Northeast with above freezing temperatures even into the
highest terrain of the Northeast by Saturday. WPC preferred a
multi-model blend and the CMC/ECMWF/ECAIFS solution which keeps
colder air in place for the elevated terrain of the northern
Appalachians, as well as less QPF into northern New England due to
a more suppressed low track. In this scenario there is also a
potential for light freezing rain accretion across the southern
Green Mts, where WPC probabilities for >0.1" of freezing rain are
10-20%. For snowfall, WPC probabilities show 40-70% chances for >2"
in the higher terrain of the Catskills, Adirondacks, southern
Green, and White Mountains through Saturday evening. There also the
potential for accumulating snowfall throughout the central
Appalachians, but this area has more uncertainty and relies on a
combination of upslope flow and the position of the closed 500mb
low.


...Cascades to Northern Rockies...
Day 3..

Approaching negatively tilted upper trough approaching the Pacific
Northwest Friday night into Saturday won't have a typical strong
plume of moisture, but as the low begins to close off across
western MT by the end of the period decent upper divergence will
support light to moderate snow across parts of the Cascades and
Northern Rockies. Snow levels will be low across the Cascades
(<2,000ft) by the day on Saturday, but with precipitation mostly
scattered and tied to the terrain. Snowfall totals are expected to
remain around 2-4", with higher amounts above 7,000ft. For the
Northern Rockies, snow levels will vary from 5,000-6000ft in
northern ID and northwest MT to above 8,000ft to start for the
remainder of the Rockies before crashing by the end of the forecast
period across MT. WPC probabilities for at least 6" of snow are low
(10-30%) from the Salmon River Range through the southwest MT
ranges.



Snell/Mullinax





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FOUS11 KWBC 100809
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Thu Apr 10 2025

Valid 12Z Thu Apr 10 2025 - 12Z Sun Apr 13 2025


...Great Lakes & Interior Northeast...
Days 1...

Light snow is expected this morning across portions of north
central PA into southwest NY. Marginal temperatures support mostly
rain by mid morning, but before then areas could see a coating to
inch of accumulation. As the system moves slowly east do expect
more coverage of light snow by tonight as temperatures cool over
eastern NY into New England. Guidance has trended a bit cooler,
and so anticipate the ptype to become mainly snow or a rain snow
mix overnight, with the exception of coastal areas which will most
likely stay rain. Most areas will pick up a coating to inch of
snow, although probabilities of exceeding 2" have increased over
the Berkshires, southern Green Mountains, Catskills and southern
Adirondacks, with a 40-60% of amounts locally exceeding 2".


...New York into New England... Day 2 and 3...

A large scale trough and developing closed low will bring another
round of precipitation to the Mid-Atlantic and Northeast Friday
into Saturday. More uncertainty with the details of this system,
with notable spread in the 00z guidance. The general trend has
been a further south and east track of the developing low, likely
making this a colder system. However temperatures will still be
marginal, and any axis of notable accumulating snowfall will
probably be rather narrow on the northern periphery of the
precipitation axis. The 00z GFS is the most aggressive solution,
bringing ample precipitation into the colder airmass resulting in
a more significant snowfall solution from eastern NY into northern
New England. On the other end of the model spectrum some solutions
have trended far enough south and east to result in a suppressed
enough solution that little to no precipitation falls in the form
of snow. The most likely scenario is in between this more
suppressed solution and snowier GFS solution.

The expectation is that precipitation lifting north into the
colder air will be snow by later Friday night into Saturday
morning. While some mix with snow is possible in lower elevations,
the best chance of accumulating snow will be in areas of
terrain...with the Catskills, Berkshires, Green Mountains and the
Worcester Hills into the White Mountains the most favored areas.
The probabilities of 2" have increased over these areas, generally
in the 50-80% range, with 4" probabilities over 40% on a localized
basis. A solution in between the 00z GFS and ECMWF (closer to the
ECMWF) best aligns with this axis of higher probabilities...with
the 00z AIFS also well aligned with the current WPC forecast. The
00z ECMWF being a bit further south brings more accumulating
snowfall into the Poconos of northeast PA into portions of
northwest NJ. While this is a lower probability outcome it can not
be ruled out, thus some chance amounts over these areas see some
upward adjustment in future forecasts.


...Cascades to Northern Rockies...
Day 1-3..

Periods of light to moderate snow area expected over the Cascades
today through saturday, with snow levels lowering with time. Some
accumulating snowfall is likely as low as around 2,000 feet, with
total snowfall over 6" expected in the more favored terrain areas.

A strong mid level shortwave moving across the Northwest will
bring a snow threat to the Northern Rockies by Saturday into
Saturday night. Southerly flow ahead of this shortwave will result
in a warm system initially, with most snow falling above 6,000
feet. However behind the shortwave temperatures will rapidly drop,
resulting in lowering snow levels and bringing the threat of some
accumulating snowfall to more of central MT. More uncertainty with
this lower elevation snowfall as model differences in the low
track and strength will impact the amount of precipitation on the
cold side of the system. So the greater confidence for
accumulating snowfall remains over the higher terrain over 6,000
feet, with probabilities of exceeding 6" through 12z Sun as high as
50-80% over the Little Belt Mountains and the Lewis and Swan
Ranges of northwest MT.

Chenard

$$

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FOUS11 KWBC 101824
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
224 PM EDT Thu Apr 10 2025

Valid 00Z Fri Apr 11 2025 - 00Z Mon Apr 14 2025


...Northern Mid-Atlantic to New England...
Days 1-2...

Two rounds of mostly elevation-dependent spring snow are forecast
to impact areas from northeast PA and far northern NJ through
Upstate NY and into New England through Saturday. The first wave of precipitation is already moving into the Northeast this afternoon
ahead of a weak surface wave and leading upper shortwave trough.
Current surface 0 degree C wet-bulb temp is confined to the
Adirondacks and northern New England, which depicts the marginal
boundary layer thermals. These marginal temperatures will remain,
although dynamically cooling beneath heavier precipitation and
850mb temps ranging from +1C to -2C, through the weekend and lead
to a typical distribution of accumulating mid- April snowfall.
Amounts through Friday morning are expected to add up to around 1-4
inches across the Catskills, Adirondacks, and southern New England
Mts, with a dusting or conversational flakes possible down to the
I-95 corridor of CT/RI/MA.

The next round of precipitation is expected to enter the region
Friday night into Saturday as the large scale eastern U.S. trough
consolidates into a closed low and strengthens over the Mid-
Atlantic and gradually slides east. More uncertainty with the
details of this system remain, but have consolidated on the
southernmost cluster of solutions from prior forecasts. This leads
to potentially moderate snow reaching as far south as the Poconos,
northern NJ, and the Litchfield Hills of western CT as 850mb temps
drop below 0C near and just northwest of strengthening 700mb FGEN.
However, temperatures will still be marginal, and any axis of
notable accumulating snowfall will probably be rather narrow on the
northern periphery of the precipitation axis. Additionally,
approachable QPF amounts might not reach as far north and
therefore lowering the potential for heavy snow from the
Adirondacks through the northern Greens and Whites. Snowfall
amounts on Day 2 (00z Sat to 00z Sun) are generally expected once
again to range between 1-4 inches, with low chances (<10%) for >4
inches outside of the tallest peaks of the Catskills.


...Cascades to Northern Rockies...
Day 1-3..

Periods of light to moderate snow area expected over the Cascades
tonight through Saturday, with snow levels lowering over time.
Some accumulating snowfall is likely as low as around 2,000 feet,
with total snowfall over 4-6" expected in the more favored terrain
areas.

After a quick-moving cold front moves across the northern Cascades
tonight with a brief burst of snowfall above 3,000-4,000ft, a
strong mid level shortwave moving across the Northwest will spread
the snow threat into the Northern Rockies by Saturday. Southerly
flow ahead of this shortwave will result in a warm system
initially, with most snow falling above 6,000 feet. However behind
the shortwave temperatures will rapidly drop, resulting in lowering
snow levels and bringing the threat of some accumulating snowfall
to more of central MT. More uncertainty with this lower elevation
snowfall as model differences in the low track and strength will
impact the amount of precipitation on the cold side of the system,
with most trends leaning towards lower QPF amounts. So the greater
confidence for accumulating snowfall remains over the higher
terrain over 6,000 feet, with probabilities of exceeding 6" through
00z Sun as high as 40-60% over the Little Belt Mountains, northern
Absarokas, as well as the Lewis and Swan Ranges of northwest MT.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell




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FOUS11 KWBC 110646
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
246 AM EDT Fri Apr 11 2025

Valid 12Z Fri Apr 11 2025 - 12Z Mon Apr 14 2025


...Northern Mid-Atlantic to New England...
Days 1-2...

Ongoing light snow this morning will taper off just after 12Z, but
will then turn to the next area of wintry weather later tonight
into Saturday. Upper trough axis will slowly approach the East
Coast with front-side/downstream upper low development over the
Mid-Atlantic. This will favor another surge of moisture northward
into marginally cold air over the Northeast/northern Mid-Atlantic
as mostly snow to the north away from the coast (roughly south of
I-90/I-84) but perhaps a small area of sleet as well. Ptypes will
be dependent on rates where temperatures are marginal, with some
areas alternating between rain/snow. In addition, accumulation may
be limited to grassy areas given mild ground/road temperatures and
also may be limited within a few hours of solar noon as we approach
mid-April. However, some more vigorous WAA over higher terrain
could yield several inches of snow on Saturday for places like the
Catskills, Berkshires, and southern Green/White mountains where WPC probabilities for at least 4 inches of snow are generally 20-50%.
The northern extent of the snow is still a bit in question as the
system tries to consolidate toward the Gulf of Maine Sunday before
moving out of the area.


...Cascades to Northern Rockies...
Day 1-3..

Broad SW flow this morning will continue light snow for the
Cascades today while the trough axis slowly approaches out of the
northeastern Pacific. By Saturday, a stronger mid-level shortwave
will come into WA and strengthen across ID/MT, promoting light to
modest WAA-driven snow over NW MT into northern WY as the upper jet
slips southeastward into the Plains. Temperatures will fall behind
the front and lower snow levels to below 4000ft as precipitation
lightens and then ends from west to east on Sunday/Sunday night.
The system will be fairly progressive but it could snow moderately

1"/hr) for a time Saturday evening. WPC probabilities for at

least 8 inches of snow for the period are highest around Glacier NP
and across the Little Belt Mountains (>50%).


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso



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FOUS11 KWBC 111845
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
245 PM EDT Fri Apr 11 2025

Valid 00Z Sat Apr 12 2025 - 00Z Tue Apr 15 2025


...Northern Mid-Atlantic to New England...
Day 1...

Complex April snowstorm to begin overnight and impact areas from
northeast PA through New England with mainly high elevation heavy
snow, but with the potential for even lower elevations to see light accumulations. Upper trough axis approaching the East Coast this
afternoon will close off near southern MD and lift northeastward
through Saturday. This will favor a surge of moisture northward
into marginally cold air over the Northeast/northern Mid- Atlantic
as mostly rain quickly changes to snow away from the coast, but
perhaps a small area of sleet as well. Ptypes will be dependent on
rates where temperatures are marginal (generally below 1,000ft),
with some areas alternating between rain/snow. These rates are
highlighted well in the latest 12z HREF, beginning around 06Z
tonight along and near I-84 before lifting northward through the
Interior Northeast and New England while weakening by about 15Z
Sat. In addition, accumulation may be limited to grassy areas given
mild ground/road temperatures and also struggle within a few hours
of solar noon on Saturday as we approach mid- April. However, some
more vigorous WAA over higher terrain and pronounced TROWAL will
prompt areas of 1"/hr rates, with some pivoting of the deformation
band on the northwestern periphery. It is this evolution that could
yield several inches of snow (maybe as much as 6") by Saturday
morning for places like the Poconos, Catskills, Berkshires, and
southern Green/White mountains.

Here, WPC probabilities for at least 4 inches of snow are
generally 20-50%, but do increase to 60-80% for areas above
2,000ft. Lower elevations could see a slushy 1-3" from northeast
PA and northern NJ through CT, northern RI, and MA. The northern
extent of the snow is expected to ride along the Whites into
western ME, with low chances (<10%) for amounts to exceed 4 inches.
The ECMWF EFI is intriguing and has values of 0.7-0.9 for the
impacted area with a maximum SOT of 2, which would signify an
"unusual" event compared to mid-Aprils dating back to 2004 (the
ECMWF reforecast period).


...Cascades to Northern Rockies...
Days 1-2...

A strong mid-level shortwave will move into WA and strengthen
across ID/MT Saturday morning, promoting light to modest WAA-
driven snow over NW MT into northern WY as the upper jet slips
southeastward into the Plains. Temperatures will fall behind the
front and lower snow levels to below 4000ft as precipitation
lightens and then ends from west to east on Sunday/Sunday night.
The system will be fairly progressive but it could snow moderately

1"/hr) for a time Saturday evening. WPC probabilities for at

least 8 inches of snow for the period are highest around Glacier NP
and across the Little Belt Mountains (>30%). As a related cold
front pushes southward with the progressing closed low moving
eastward across the northern Plains, the northern CO Rockies have
low chances for heavy snow Sunday night.


...Northern Minnesota...
Day 3...

As the aforementioned closed low moves eastward into the Upper
Midwest by Sunday night it is forecast to strengthen and
dynamically cool the column, leading to potentially local heavy
snowfall bands. Currently, WPC Day 3 snowfall probabilities for at
least 4 inches are 20-40% across far northern MN.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell






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FOUS11 KWBC 120644
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
244 AM EDT Sat Apr 12 2025

Valid 12Z Sat Apr 12 2025 - 12Z Tue Apr 15 2025


...Northern Mid-Atlantic to New England...
Day 1...

Storm system just off the DelMarVa this morning will continue to
lift northeastward to a position just east of Cape Cod by early
Sunday morning. With an amplified jet, moisture already across much
of the northern Mid-Atlantic into the Northeast will turn to snow
as temperatures cool just enough on northeasterly surface flow.
Snow will pick up in intensity toward daybreak, and by the start of
this period (12Z Sat), moderate snow is likely (rates >1"/hr) over
parts of the Catskills, Berkshires, and Green and White Mountains
through mid-day. By this afternoon, drier air toward the mid-levels
will help decrease any snow or rain/snow mix across much of the
area except for northern New England where temperatures will rise
to around freezing where snow continues to fall. Precipitation will
mostly end by early Sunday but continue over northern Maine into
the afternoon. WPC probabilities for at least 4 inches of snow are
highest (>50%) over the higher elevations above 1000-1500ft or so
with 1-3" over lower elevations and a rain/snow mix with little
accumulation in the lowest elevations (valleys and near the water
south of I-90).


...Northern to Central Rockies...
Days 1-2...

A strong mid-level shortwave over WA this morning will strengthen
across ID/MT today, promoting light to modest WAA-driven snow over
NW MT/northern ID into northern WY as the upper jet slips
southeastward into the Plains. Temperatures will fall behind the
front and lower snow levels to below 4000ft as precipitation
lightens and then ends from west to east on Sunday/Sunday night. By
then, the cold front will slow across the central Rockies, helping
to wring out some snow over CO. The system will be fairly
progressive overall but it could snow moderately (>1"/hr) for a
time this evening over NW MT and NW WY. WPC probabilities for at
least 6 inches of snow for the period are highest around Glacier
NP, across the Little Belt Mountains, and near Yellowstone NP
(30-60% probs). Over the CO Rockies, amounts will be lighter
overall, but some areas could still see several inches of snow
(above 10,000ft). There, WPC probabilities for at least 6 inches of
snow are 40-60%.


...Western Great Lakes...
Day 3...

The mid-level low exiting MT Sunday will strengthen more over the
northern Plains as a 120kt jet streak develops over Iowa. An area
of surface low pressure will deepen and help foster an expanding
area of precipitation over the northern Plains into the Upper
Midwest. Temperatures will be marginal to mild initially, but once
the low tracks into Lake Superior, north to northwest winds will
bring in colder air to northern areas of MN and eventually into the
U.P. of Michigan Monday night into early Tuesday. Snow will become
more widespread with accumulation likely over most of the MN
Arrowhead and northern WI into the U.P. of Michigan. There, WPC
probabilities for at least 4 inches of snow through 12Z Tue are
moderate (40-70%).


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso


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FOUS11 KWBC 121848
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
248 PM EDT Sat Apr 12 2025

Valid 00Z Sun Apr 13 2025 - 00Z Wed Apr 16 2025


...Maine...
Day 1...

System that brought locally heavy snow to portions of the Northeast
and New England today is weakening, but the associated upper trough
off the East Coast will become reinvigorated tonight and throughout
the day on Sunday as additional shortwaves swing over the Mid-
Atlantic. This will allow for a few waves of precipitation to surge
northward into northern New England and Maine, which is where a
marginally cold airmass remains for mid-April standards. Within
bands of heavier precipitation and areas above 2,000 ft elevation,
ptype should remain mostly snow or a mix of rain/snow. Snowfall
amounts through Sunday night are generally expected to remain
around 1-3", but with locally higher amounts around Mount Katahdin
(40-70% probabilities for >4") into east-central/northeast Maine
(10-40% probabilities for >4").


...Northern to Central Rockies...
Days 1-2...

A strong mid-level shortwave over the northern Great Basin this
afternoon will strengthen across western MT this evening.
Associated frontal boundary will sweep eastward into the Plains,
with temperatures forecast to fall behind the front and lower snow
levels below 4000ft as precipitation lightens and then ends from
west to east on Sunday/Sunday night. By then, the cold front will
slow across the central Rockies, helping to wring out some snow
over CO. The system will be fairly progressive overall but it could
snow moderately (>1"/hr) for a time tonight over NW MT. WPC
probabilities for at least 6 inches of snow for the period are
highest around Glacier NP, across the Little Belt Mountains, and
near Yellowstone NP (30-60% probs). Over the CO Rockies, amounts
will be lighter overall, but some areas could still see several
inches of snow (above 10,000ft). There, WPC probabilities for at
least 6 inches of snow are 40-60% on Day 2.


...Western Great Lakes...
Days 2-3...

The mid-level low exiting MT Sunday will strengthen more over the
northern Plains as a 120kt jet streak develops over Iowa. An area
of surface low pressure will deepen and help foster an expanding
area of precipitation over the northern Plains into the Upper
Midwest. Temperatures will be marginal to mild initially, but once
the low tracks into Lake Superior, north to northwest winds will
rapidly bring in colder air to northern areas of MN and eventually
into the U.P. of Michigan Monday night into early Tuesday. Snow
will become more widespread with accumulation likely over most of
the MN Arrowhead and northern WI into the U.P. of Michigan. WPC
probabilities for at least 4 inches of snow through 00Z Wed are low
(10-30%) in northwest MN and moderate (40-70%) in the MN. For areas
downwind of Lake Superior from far northern WI through the U.P. of
Michigan, higher amounts are likely Monday night through Tuesday,
with WPC probabilities depicting 10-40% chances for at least 8
inches of snow.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell/Fracasso





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FOUS11 KWBC 141830
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
230 PM EDT Mon Apr 14 2025

Valid 00Z Tue Apr 15 2025 - 00Z Fri Apr 18 2025


...Great Lakes & Interior Northeast...
Days 1-3...

The combination of a deep upper trough moving across the Great
Lakes and Northeast as well as an associated surface low sliding
from southeast Canada on Tuesday towards the Gulf of St. Lawrence
will usher in strong CAA and lake-effect snow. An upper shortwave
diving over the Midwest this evening will kick start the
changeover from rain to snow across the MI U.P. and eventually the
northern MI L.P. by early Tuesday. This snowfall may be boosted by
some lake- induced steeper lapse rates (lake temps 4-5C with 850mb
temps below -6C). Some heavier rates of >1"/hr are possible
overnight tonight in the western U.P. (30-60% probs from the HREF),
which could lead to modest snow totals there along with gusty
winds. On Tuesday, snow will end from west to east during the
afternoon into the evening as heights rise from the west. WPC
probabilities for at least 4 inches of snow are highest (>70%) over
the U.P. and low (10-30%) over the northern L.P. of MI. In
addition, probabilities for at least 8 inches of snow are 40-50%%
over some of the favored lake areas around the Porcupine and Huron
Mountains.

As the Canadian low pressure continues through Quebec its strong
cold front will sweep colder air throughout the eastern Great Lakes
and Northeast on Tuesday. Once the front clears the coast, another
area of low pressure may develop along the occlusion near northern
Maine late Tue/early Wed before finally moving away on Wednesday
mid- day, bringing the potential for accumulating snowfall for far
northern Maine. Rain will change to snow from west to east as the
column cools post- FROPA, setting up some lake- enhanced/effect
snow for areas east of Lakes Erie/Ontario and upslope snow for the
central Appalachians and into the Adirondacks and Green/White
Mountains. Lapse rates will be steep and around 7-9C/km across
much of the Northeast, but warm boundary layer temperatures should
keep snowfall confined to higher elevations and areas downwind of
the Great Lakes. WPC probabilities for at least 4 inches of snow in
Days 2-3 are 20-50% in far western WY south of BUF, 50-90% in the
Adirondacks and Tug Hill Plateau, and 40-80% in the northern Green
and White Mountains into far northwestern Maine. Low (10-20%)
probabilities for at least 4 inches of snow are present over the
central Appalachians and far northern Maine.


...Northern Rockies...
Days 2-3...

Strong height falls plunging southward out of southwestern Canada
late Wed will drive a cold front through Montana and Wyoming,
setting up a period of wintry weather through Thursday.
Northeasterly flow post- FROPA will provide plenty of upslope
enhancement into northwestern MT on Day 2 amid ample lift in the
column and lowering snow levels. Moderate to perhaps heavy snow is
likely along the Lewis and Flathead Ranges while also extending
southward and southeastward into WY on Day 3. Snow levels are
expected to drop to below 3,000 ft by Thursday across MT, but
remain slightly higher across WY. There is the potential for a
corridor of snowfall to reach into portions of the MT High Plains
on Weds night associated with modest mid-level fgen, but
uncertainty remains high with these details. WPC probabilities for
at least 6 inches of snow are high (>70%) over much of the MT and
northern WY mountains, including areas extending from the Lewis
Range to the Absarokas and Big Horns (mostly above 6,000 ft).


...Central Sierra...
Day 3...

Meandering upper low west of California will finally move into
SoCal late Wednesday night/early Thursday morning, with some
downstream generally light precipitation into the Sierra. Snow
levels will be quite high (>8000ft) and there are low probabilities
(30-60%) of at least 4 inches of snow through 00Z Friday in the
high central Sierra above 10,000ft.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell/Fracasso






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FOUS11 KWBC 150657
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
257 AM EDT Tue Apr 15 2025

Valid 12Z Tue Apr 15 2025 - 12Z Fri Apr 18 2025


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

Upper low along the Ontario/Quebec border this morning will
continue eastward into the Gulf of St. Lawrence by tomorrow
morning, with a surface cold front moving offshore the Northeast
today. That will bring in colder air to the region and a changeover
from rain to snow. 850mb temperatures will drop to -6 to -8C over
the interior with surface temperatures in the upper 20s to low 30s,
supporting snowfall over the higher elevations and even some snow
into many lower elevations from western/central NY to the North
Country west of the Hudson Valley. The strong CAA will help promote
lake-effect snow to areas south of Buffalo and into the Tug Hill
Plateau as lake temperatures are near 3-6C. Snow will have a harder
time accumulating this afternoon due to the initial warmth, but
overnight most accumulation will occur across NYS. Into Wednesday,
westerly flow will promote upslope enhanced snow into the
Adirondacks and northern Green/White Mountains as well as
northwestern Maine, where some favored ski areas (esp VT) may see
over a foot of snow. Snowfall will end Wednesday evening through
early Thursday from west to east as heights begin to build back
through the Great Lakes into the Northeast. WPC probabilities for
at least 4 inches of snow are >50% over areas south of Buffalo,
over the Tug Hill/Adirondacks, and into northern VT/NH.
Probabilities for at least 8 inches are highest over northern VT

50%).

...Northern/Central Rockies...
Days 2-3...

Strong height falls plunging southward out of southwestern Canada
late Wed will drive a cold front through Montana and Wyoming,
setting up a period of wintry weather through Thursday (north) and
Friday (south). Northeasterly flow post-FROPA will provide plenty
of upslope enhancement into northwestern MT Wednesday amid ample
lift in the column and lowering snow levels. Moderate to perhaps
heavy snow is likely along the Lewis and Flathead Ranges (HREF
probs for >1"/hr rates are around 30-60%) which will see the
highest snowfall totals. Snow will expand southward late Wed into
Thu through WY as snow levels crash from over 8000ft to below
3500ft (reaching the valley floors). Lighter snow will extend
eastward into the western High Plains beneath a split upper jet and
also west of the Divide with less upslope/moisture. By later Thu
into early Friday, the cold front will move into northern CO with
snow expanding into the central Rockies as well as across UT which
will feel some affect from the incoming SoCal upper low. WPC
probabilities for at least 8 inches of snow during this period are
high (>70%) over much of the MT and especially northern WY
mountains, including areas extending from the Lewis Range to the
Absarokas and Bighorns (mostly above 6000-7000 ft). Much of the
Wind River Range has probabilities >70% for at least 8 inches of
snow and many of these ranges have at least moderate (40-70%)
chances of a foot of snow or more. Lower probabilities exist over
UT/CO for at least 6 inches of snow through 12Z Fri but more snow
is to come there into Saturday.


...Central Sierra...
Days 2-3...

A slow-moving upper low west of California today will finally move
into SoCal on Thursday, with some downstream generally light
precipitation into the Sierra Wed/Thu. Snow levels will be quite
high (>8000ft) Wed and only fall slightly on Thu (7500-8000ft) with
slightly more QPF by later on day 3 (Thurs evening/overnight). WPC probabilities for at least 8 inches of snow through 12Z Friday are
low (10-30%) in the high central Sierra above 10,000ft.



The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso


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FOUS11 KWBC 151927
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 PM EDT Tue Apr 15 2025

Valid 00Z Wed Apr 16 2025 - 00Z Sat Apr 19 2025


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

Upper low across Ontario will slowly pivot east-northeastward
through the course of the D1 time frame leading to height falls
across much of the interior Northeast. At the surface, a cold front
is analyzed from the VT/NH border down through the Mid Atlantic
with an accompanying CAA regime occurring in wake of the front.
Coldest air that will help contribute to a switch from liquid to
frozen dominant precip is still situated back across the Central
Great Lakes, but the forecast is generally on track for the CAA
pattern to lead to a changeover from rain to snow within the next
3-6 hours. 850mb temperatures will drop to -6 to -8C over the
interior with surface temperatures in the upper 20s to low 30s
overnight, supporting snowfall over the higher elevations and even
some snow into many lower elevations from western/central NY to the
North Country west of the Hudson Valley. The strong CAA will help
promote lake-effect snow to areas south of Buffalo and into the Tug
Hill Plateau as lake temperatures are near 3-6C. Snow will have a
harder time accumulating this afternoon due to the initial warmth,
but overnight most accumulation will occur across NYS. Into
Wednesday, westerly flow will promote upslope enhanced snow into
the Adirondacks and northern Green/White Mountains as well as
northwestern Maine, where some favored ski areas (esp VT) may see
over a foot of snow. Snowfall will end Wednesday evening through
early Thursday from west to east as heights begin to build back
through the Great Lakes into the Northeast. WPC probabilities for
at least 4 inches of snow are >50% over the higher elevations
within the Chautauqua Ridge, over the Tug Hill/Adirondacks, and
into northern VT/NH. Probabilities for at least 8 inches are
highest over northern VT (>50%) encompassing Jay Peak.


...Northern/Central Rockies...
Days 2-3...

There has been little change in the forecast synoptic pattern that
will yield some impressive snowfall totals in-of the Northern and
Central Rockies into the Inter-Mountain west. Strong height falls
plunging southward out of southwestern Canada Wednesday morning
will drive a cold front through Montana and Wyoming, setting up a
period of wintry weather through Thursday (north) and Friday
(south). Northeasterly flow post-FROPA will provide plenty of
upslope enhancement into northwestern MT Wednesday amid ample lift
in the column and lowering snow levels. Moderate to perhaps heavy
snow is likely along the Lewis and Flathead Ranges (HREF probs for

1"/hr rates are around 50-80%) which will see the highest snowfall

totals. Snow will expand southward late Wed into Thu through WY as
snow levels crash from over 8000ft to below 3500ft (reaching the
valley floors). Lighter snow will extend eastward into the western
High Plains beneath a split upper jet and also west of the Divide
with less upslope/moisture. By later Thu into early Friday, the
cold front will move into northern CO with snow expanding into the
central Rockies as well as across UT which will feel some affect
from the incoming SoCal upper low.

WPC probabilities for at least 8 total inches of snow during the
D2-3 period are high (>70%) over much of the higher terrain of
western MT and especially northern WY mountains, including areas
extending from the Lewis Range to the Absarokas and Bighorns
(mostly above 6000-7000 ft). Much of the Wind River Range has
probabilities >70% for at least 8 inches of snow and many of these
ranges have at least moderate (40-70%) chances of a foot of snow or
more. Significant totals >6" are increasingly likely across the
Central Rockies within CO with the highest probabilities (>70%)
located within the Laramie Mtns for D3 bleeding into what would be
D4. A secondary maxima is forecast within the southern UT
mountains, especially over the Tushar Mtns. where the combination
of favored upper ascent due to the ULL to the southwest will
interact with a digging shortwave out of the Northern Rockies
creating a stronger height anomaly across the Great Basin leading
to heavy snow prospects over the final 24 hrs of the forecast
cycle. The favored trend has led to probabilities for >8" to
increase to 50-70% across the above area with >70% over elevations
greater than 8500ft.


...Central Sierra...
Days 2-3...

There has been no change to the previous forecast as our upper low
currently analyzed off the SoCal coast will continue meandering
eastward over the course of the forecast cycle creating a
marginally favorable environment for moderate snow totals over the
Central Sierra's. As the upper low encroaches, light to
occasionally moderate precip will initiate over the terrain given
the prevailing southwesterlies providing upslope ascent. Snow
levels remain quite high (>8000ft) Wed and only fall slightly on
Thu (7500-8000ft) with slightly more QPF by later on day 3 (Thurs evening/overnight). WPC probabilities for at least 8 inches of snow
through 00z Saturday Friday are low (10-30%) in the high central
Sierra above 10,000ft lending credence to only minor impacts
overall, in agreement with the latest WSSI.



The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso/Kleebauer





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FOUS11 KWBC 160836
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
436 AM EDT Wed Apr 16 2025

Valid 12Z Wed Apr 16 2025 - 12Z Sat Apr 19 2025


...Interior Northeast...
Days 1...

A departing upper low will bring continued snow showers to the
interior northeast today and this evening, winding down by later
tonight. One more reinforcing piece of shortwave energy diving
into New England should support an uptick in snow shower activity
this afternoon, and while snow may fall even into lower elevations,
most of the accumulation will stay in the favored terrain
generally above 1500 feet. These higher terrain areas of VT and NH
could pick up an additional 2-6" of snow today into this evening.

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

There has been little change in the forecast synoptic pattern that
will yield some impressive snowfall totals across the Northern and
Central Rockies into the Inter-Mountain west. A longwave trough and
embedded closed low will dive south southeast across the region,
with colder air filtering in behind a cold frontal passage.
Northeasterly upslope flow behind the front, combined with ample
large scale lift associated with the trough/closed low, will drive
a heavy snowfall threat across the region. Snowfall will initially
focus across the Lewis and Flathead ranges of northwest MT today
and will likely be heavy at times, with rates exceeding 1"/hr. WPC probabilities highlight a high chance (>70%) of exceeding 8" of
snow in the favored east facing terrain generally above 4500 feet.

By Wednesday night the snow risk shifts into southern MT, with the
heaviest accumulations expected above 4000 feet. Above this
elevation there is a high chance (>70%) of exceeding a foot of
snow, and localized totals could approach two feet in the highest
terrain areas. The forecast remains less confident over the lower
elevations of southeast MT. Thermal profiles will be marginal, but
the overnight timing and moderate to heavy rates, should be enough
to change rain to an accumulating snow. Just how much accumulation
remains to be seen, but amounts did trend up this cycle, with 4"
exceedance probabilities increasing into the 30-50% range for
Billings and surrounding lower elevation areas. The greatest bust
potential for this forecast is probably over the lower elevations
of southern MT and we could see amounts continue to trend up. The
potential for stronger banding during the overnight hours does
suggest there is at least some potential for snowfall to
overperform across these areas, so will need to to continue to
monitor.

By Thursday the heavy snow is overspreading WY with the greatest
accumulations again focusing across the favored
higher terrain...such as the Absaroka Range, Bighorn Mountains,
Wind River Range, Laramie Mountains, Medicine Bow Mountains and the
Sierra Madre. All of these areas have at least a 50% chance of
exceeding 12 inches of snow with this system. With the colder air
filtering in snow is also likely across the lower elevations, with
forecast snow amounts increasing this cycle across much of central
to southeast WY. The probability of exceeding 4" of snow has
increased into the 50-80% range over much of these lower elevation
areas across this part of the state.

By Thursday night into Friday the snow shifts southward into CO.
With marginal boundary layer temperatures the better accumulations
will likely be confined to elevations above 6000 feet, where
probabilities of exceeding 8" are over 70%. A bit more
uncertainty as you drop into the Front Range and foothills of the
Rockies. We do expect some accumulation to get into these
relatively lower elevations, but marginal boundary layer
temperatures will probably cut into snow ratios. Another negative
factor for higher accumulations in these areas is the fact that the
peak of the event is during daytime hours Fri...thus given the
high sun angle and borderline temperatures...it will likely take
heavier rates to get any efficient accumulation. Nonetheless, WPC
probabilities show a 50-80% chance of exceeding 2" and a 20-50%
chance of exceeding 4" over these areas.


...Central Sierra and Central UT...
Days 1-3...

Elsewhere, high (>70%) probabilities of exceeding 6" of snow
exists across the higher elevations (generally above 8000 feet) of
central UT. This snow will be associated with a southward dropping
cold front Thursday into early Friday, and should be accompanied
by pretty high snowfall rates.

Snow showers are likely today above 8000 feet across the Sierra of
central CA, with a 50-70% chance of seeing some areas exceed 4".

Chenard


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FOUS11 KWBC 161903
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 PM EDT Wed Apr 16 2025

Valid 00Z Thu Apr 17 2025 - 00Z Sun Apr 20 2025


...Interior Northeast...
Days 1...

Upper low across Quebec will continue moving northeast with the
trailing energy pushing through northern NYS through Northern New
England. Negative vorticity advection in-of NYS will allow for a
quick degrading of the precip field with only some very light snow shower/flurry activity after 00z. This will lead to little, if any
additional snowfall over the area as we move into the evening.
Remnant snowfall will be ongoing across the northern Green and
White Mtns with the primary areas of focus present within the Jay
Peak and Stowe areas of VT along with the Presidential's in NH.
Additional accums of 1-4" are plausible after 00z in those higher
elevations leading to totals between 4-8" in the Presidential Range
and 6-12" across the Jay Peak/Stowe ski areas of northern VT.
Lighter snow totals will be present in the valleys, but will
maintain little impact. Snow threat will wane between 06-12z in
those affected locations.

Kleebauer


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

The forecast remains on track with regards to the expected heavy
snow threat across the Northern and Central Rockies into portions
of the Inter-Mountain West thanks to an anomalously evolving height
pattern across the Western CONUS. At the surface, a strong cold
front is analyzed over south-central MT with a forward propagation
running due south along the lee of the Northern Rockies. Recent
RTMA analysis shows 24-hr temp changes >20F from the Canadian
border to not far behind the frontal position. Attendant
height falls within the digging shortwave pattern out of Canada
have assisted in a transition from liquid to fully frozen
hydrometeors in wake of the front with a rooted scattered to
widespread snow setup across the Lewis Range to the higher plains
adjacent. Locally heavy snowfall will continue to impact the
Northern Rockies through the course of the day with the precip
threat scaling back somewhat by early Thursday morning, but still
maintaining some light QPF from remnant light to moderate snow
within the Lewis Range. 12z HREF signals for >1"/hr rates are
high (>70%) within those higher elevations in-of the Northern
Rockies, particularly in the Lewis Range, but also some lower end
probs for similar rates adjacent to the mountains on the eastern
flank. Snowfall totals between 6-12" with locally higher will be
common above 8000ft with 2-6" more likely in the lower valleys and
foothills adjacent.

By this evening, the heavy snow risk shifts into southern MT, with
the heaviest accumulations expected above 4000 feet. Above this
elevation there is a high chance (>70%) of exceeding a foot of
snow, and localized totals could approach two feet in the highest
terrain areas of the northern Absaroka and Big Horns. The forecast
confidence has increased a bit more over the lower elevations of
southeast MT within this forecast cycle. Thermal profiles will be
marginal, but the overnight timing and moderate to heavy rates,
should be enough to change rain to an accumulating snow. Recent
probabilities for at least 4" exceedance have increased towards the
40-60% range for Billings and surrounding lower elevation areas,
and the hi-res deterministic outputs have now leaned closer to the
4-6" output for the event entirety. The highest probabilities for

4" will still be aligned with the higher terrain on the upslope

side of the northerly flow pattern, however there is still some
potential for lower elevation areas within adjacent valleys of
Southern MT to bust high pending on the magnitude and depth of the
CAA regime and forecasted 700mb frontogen intersecting creating a
better ascent pattern within the DGZ. This has been entertained
within some of the hi-res suite, so it's something to continue
monitoring for short term trends.

By Thursday the heavy snow is overspreading WY with the greatest
accumulations again focusing across the favored
higher terrain...such as the Absaroka Range, Bighorn Mountains,
Wind River Range, Laramie Mountains, Medicine Bow Mountains and the
Sierra Madre. All of these areas have at least a 50% chance of
exceeding 12 inches of snow with this system. One of the bigger
changes in the forecast is a greater magnitude of snowfall within
the Wind River Range where probabilities for >18" over the 72 hr
period are upwards of 50-80%, a solid increase compared to the
previous forecast. Totals of 1-2ft with locally higher totals are
expected in those ranges across the state. With the colder air
filtering in, snow is also likely across the lower elevations with
forecast snow amounts remaining steady this forecast cycle across
much of central to southeast WY. The probability of exceeding 4" of
snow has remains elevated into the 50-80% range over much of these
lower elevation areas across this part of the state.

By Thursday night into Friday the snow shifts southward into CO.
With marginal boundary layer temperatures the better accumulations
will likely be confined to elevations above 6000 feet, where
probabilities of exceeding 8" remain over 70%. The setup remains
borderline across the lower elevations within the Front Range,
including the Denver metro as antecedent warmth prior to the
incoming cold along with the primary precip output occurring in the
middle of the day may curb the threat somewhat, limiting totals <4"
for the metro and points east. Nonetheless, WPC probabilities
maintain a signature of a 50-80% chance of exceeding 2" and a
20-50% chance of exceeding 4" over these areas adjacent to the
Rockies. Heavy snow threat will shift south later Friday into
Saturday with a fairly robust snowfall footprint within the Sangre
de Cristos and San Juan Mountains across Southern CO. Probabilities

70% for at least 8" of snowfall are forecast for the event within

those zones with the San Juans most likely to see totals >12"
during the 36 hr period from Friday evening into Saturday night.


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

Elsewhere, high (>70%) probabilities of exceeding 6" of snow
exists across the higher elevations (generally above 8000 feet) of
central and northern UT. This snow will be associated with a
southward dropping cold front Thursday into early Friday, and
should be accompanied by pretty high snowfall rates. Trends for
upwards of foot snow have improved a bit this forecast within the
Monte Cristo and Uinta Mtns. Threats for over 6" also exist across
the Tushar and Escalante Mtns. in south- central UT with slightly
lower probs compared to areas further north (50-70%).

Chenard/Kleebauer



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FOUS11 KWBC 170704
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
304 AM EDT Thu Apr 17 2025

Valid 12Z Thu Apr 17 2025 - 12Z Sun Apr 20 2025


...Northern/Central Rockies & Adjacent Central High Plains...
Days 1-3...

Ongoing moderate to heavy snow across parts of the northern
Rockies this morning will slide and expand southward over the next
few days. This leads to a decent footprint of heavy spring snowfall
for the Rockies and into adjacent sections of the central High
Plains. The latest WSSI highlights moderate to locally major
impacts associated mainly with snow amount and snow load across
much of the higher elevations, with minor impacts expanding into parts
of eastern WY and the CO Foothills. The driving force behind this
event is a positively- tilted trough and embedded mid- level lows
churning at its base as it swings from the Great Basin on Day 1 to
the southern Rockies on Day 3, while also tilting more neutral to
negative with time. This trough will aid in producing ample upper
diffluence near and north of a 120kt jet streak extending from the
subtropical Pacific. Meanwhile, an associated cold front will also
surge southward over the next few days, with much colder air in its
wake and favorable upslope into the northern and eastern facing
slopes. Snow levels south of this front will begin above 8,000 ft,
but quickly crash below 5,000 ft and equate to accumulating
snowfall into the High Plains of WY, SD, NE, and CO.

For Day 1 (ending 12Z Fri), much of the focus for heaviest snow
will be centered over WY as the best upslope component and 700mb
convergence exists. This includes the potential for 1-2"/hr rates
as depicted by the 00Z HREF. Ranges such as the Absarokas,
Bighorns, Wind River, Rattlesnake and Black Hills, as well as the
Laramie and Shirley Mts are expected to see over a foot of snow

70% probabilities), with some of the higher north- northeast

facing peaks seeing 1-2+ feet. Additionally, lower elevations that
aren't shadowed can also expect anywhere from 3 to 6 inches of
snow.

By Day 2 (ending 12Z Sat) the cold front and precipitation shield
quickly pushes south into CO while gradually waning in WY. The
greatest forcing and mid-level convergence focuses on the CO
Rockies, including the Palmer Divide and as far east as the Urban
Corridor, where more uncertainty exists regarding how much
accumulation occurs given the mid-April sun angle on Friday. As the
base of the trough approaches the Four Corners and eventually the central/southern High Plains by the end of the period, lingering
snowfall exists over southern CO/northern NM and specifically for
the San Juans and Sangre de Cristo Mts. Total snowfall amounts
throughout the entire event are expected to exceed 1 foot (>70%)
across the CO Rockies above 10,000ft, with over 8 inches possible
(30-60%) along the Palmer Divide. Probabilities of 50-80% for
snowfall totals above 4 inches extend into the High Plains just
east of the Denver metro.


...Utah & Arizona...
Days 1-2...

Elsewhere, high (>70%) probabilities of exceeding 6" of snow
exists across the higher elevations (generally above 8000 feet) of
UT and some of the higher terrain of AZ. This snow will be
associated with a southward dropping cold front today into early
Friday, and could be accompanied by pretty high snowfall rates
given the potent upper low crossing directly overhead and
increasing lapse rates over 7-8C/km. Over a foot of snow is
possible (50-70%) across the highest peaks of the UT ranges, with
probabilities for over 8 inches around 30-50% for the Kaibab
Plateau, as well as the White, Carrizo, and Chuska Mts of AZ and
northwest NM.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell





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FOUS11 KWBC 171823
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
223 PM EDT Thu Apr 17 2025

Valid 00Z Fri Apr 18 2025 - 00Z Mon Apr 21 2025


...Central and Southern Rockies, Adjacent High Plains...
Days 1-3...

Significant mid-April winter storm expands and intensifies this
evening, bringing heavy snow to a large portion of the Central and
Southern Rockies. Uncertainty continues into how much of the High
Plains will be impacted.

The period begins /00Z tonight/ with a positively tilted but
amplifying trough with its core centered over Utah. This feature
will deepen as it digs south tonight into Friday morning,
potentially closing off over the Four Corners Friday evening, with
the resultant trough amplifying into full latitude as it digs from
the Northern Plains into the Desert Southwest. The northern portion
of this trough will likely split off to the east by Saturday
afternoon while the southern /closed/ portion stalls over the Four
Corners. This evolution will result in widespread and impressive
synoptic ascent across much of the Intermountain West, leading to
periods of heavy precipitation, likely falling as snow, across much
of the region.

As this trough digs south, areas of locally enhanced ascent will
develop to force impressive snowfall rates and amounts. East of the
closing mid-level low, robust mid-level deformation will develop
across WY and CO, which will be aided by at least periphery LFQ
diffluence as a jet streak pivots around the base of this trough
and lifts meridionally into the Central Plains. At the same time, a
strong cold front will race southward, from northern CO 00Z Friday
to the Texas Panhandle 00Z Saturday, while banking westward against
the Front Range and Sangre de Cristos. SW flow between 700-300mb
will help enhance moisture from the Pacific and cause additional
isentropic ascent, further enhancing the coverage of heavy snow
from WY through NM/AZ.

The heaviest snow is expected in the higher terrain of CO and WY as
snow levels crash rapidly behind the cold front. Initially, snow
levels will be as high as 8000-9000 ft ahead of the front, but will
crash to below 3000 ft immediately in its wake. In addition to the
lowering snow levels, this front will cause post-frontal NE flow to
enhance upslope ascent into the terrain, as well as lead to
increasing low to mid level frontogenesis, especially in the
850-600mb layer. For the upslope flow, cross-sections indicate a
developing robust barrier jet east of the Front Range and Sangre de
Cristos, with omega overlapping some folding of theta-e surfaces in
response to this jet forcing. This suggests enhanced snowfall rates
and local maxima of snowfall amounts in upslope regions.
Additionally, the impressive fgen will help drive strong ascent
despite a lack of a TROWAL, as the cold conveyor becomes the
dominant mechanism for heavy snow. Both the WPC prototype snowband
tool and the WPC HREF probabilities suggest this will result in at
least 1"/hr snowfall rates in these regions, despite SLRs that will
likely be less than climo, with a heavier than typical snowfall
leading to substantial travel and even some infrastructure impacts
as reflected by the WSSI-P.

The more challenging aspect of this forecast is what will happen in
the I-25 urban corridor and eastward into the High Plains/lower
elevations. While it is likely that heavy snow will accumulate
across both the Palmer Divide and Raton Mesa, there is considerable
uncertainty farther east as reflected by a large spread in the
10th-90th percentile (6-8 inches) according to DESI. With
impressive ascent likely even into the High Plains, it seems
plausible that at least periods of heavy snow will impact the urban
corridor and out into the High Plains (especially the Pine Ridge
area of western Nebraska), but farther south into CO and NM the
displaced jet streak may limit the eastward advance of heavy snow.
NBM v5.0 probabilities in the lower elevations are much lower than
then NBM v4.2 probabilities, but are matched well with the
calibrated probabilities, so this suggests that the risk for heavy
snow farther east is lower than the NBM would suggest, but still a
plowable snow is probably across much of eastern WY and CO.

The heaviest snowfall is likely 00Z Friday through 12Z Saturday
before forcing begins to become more diffuse and pushes off to the
southeast. Periods of moderate to heavy snow may linger across the
Sangre de Cristos through 12Z Sunday, however with weakening
forcing, this may end as a period of rain and snow mixed, even at
some of the higher elevations, before coming to an end during D3.

On D1, WPC probabilities are high (>70%) for more than 6 inches
across much of the higher terrain of WY and CO, including the Wind
Rivers, Laramie Range, Front Range, Park Range, and San Juans.
Locally more than 12 inches of snow is possible in the higher
elevations, especially across the Wind Rivers and Laramies. By D2
as things shift south, WPC probabilities above 70% for 6+ inches
pivot into the southern Front Range and along the Sangre de
Cristos, while continuing across the San Juans as well. 2-day
snowfall in some of these areas will also likely exceed 12 inches,
with locally as much as 2 feet in the San Juans. By D3, much of the
precip winds down, but an additional 2-4" is possible (30-50%)
across the Sangre de Cristos of New Mexico.

Although slightly more removed from the worst of the winter
weather, the upper trough pivoting across the Four Corners will
also result in periods of heavy snow in the Wasatch, along the
Mogollon Rim, and into the White Mountains late D1 into D2, and
here WPC probabilities reach as high as 50% for 6+ inches of snow.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Weiss



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FOUS11 KWBC 180631
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
231 AM EDT Fri Apr 18 2025

Valid 12Z Fri Apr 18 2025 - 12Z Mon Apr 21 2025


...Central/Southern Rockies & Adjacent High Plains...
Days 1-2...

Significant mid-April winter storm continues to slide southward
throughout southern WY, the CO Rockies and northern NM Mts. Heavy
snow is forecast for much of the higher elevations and the
immediately adjacent foothills.

The period begins this morning with a positively tilted longwave
trough stretching from south-central Canada with its core centered
over Utah. This feature will deepen as it digs south today,
potentially closing off over the Four Corners into early Saturday.
The northern portion of this trough will likely split off to the
east by Saturday afternoon while the southern /closed/ portion
stalls over the Four Corners. This evolution will result in
widespread and impressive synoptic ascent across much of the
Intermountain West, leading to periods of heavy precipitation,
likely falling as snow, across much of the region until exiting
late-Saturday.

As this trough digs south and strengthens, areas of locally
enhanced ascent will develop to force impressive snowfall rates and
amounts. East of the closing mid-level low, robust mid-level
deformation will continue early D1 across southern WY and expand
across much of CO, which will be aided by at least periphery LFQ
diffluence as a jet streak pivots around the base of this trough
and lifts meridionally into the Central Plains. At the same time, a
strong cold front will race southward, reaching the northern TX
Panhandle this morning, while banking westward against the Front
Range and Sangre de Cristos. SW flow between 700-300mb will help
enhance moisture from the Pacific and cause additional isentropic
ascent, further enhancing the coverage of heavy snow from southern
WY through NM/AZ.

The heaviest additional snowfall is expected in the higher terrain
of CO northern NM as snow levels crash rapidly behind the cold
front. Initially, snow levels will be as high as 8000-9000 ft ahead
of the front, but will fall to below 3000 ft immediately in its
wake. In addition to the lowering snow levels, this front will
cause post- frontal NE flow to enhance upslope ascent into the
terrain, as well as lead to increasing low to mid level
frontogenesis, especially in the 850-600mb layer. For the upslope
flow, cross- sections indicate a developing robust barrier jet east
of the Front Range and Sangre de Cristos, with omega overlapping
some folding of theta-e surfaces in response to this jet forcing.
This suggests enhanced snowfall rates and local maxima of snowfall
amounts in upslope regions. Additionally, the impressive fgen will
help drive strong ascent despite a lack of a TROWAL, as the cold
conveyor becomes the dominant mechanism for heavy snow. Both the
WPC prototype snowband tool and the WPC HREF probabilities suggest
this will result in at least 1"/hr snowfall rates in these regions,
despite SLRs that will likely be less than climo, with a heavier
than typical snowfall leading to substantial travel and even some infrastructure impacts as reflected by the WSSI-P.

The more challenging aspect of this forecast remains what will
happen in the I-25 urban corridor and eastward into the High
Plains/lower elevations. While it is likely that heavy snow will
accumulate across both the Palmer Divide and Raton Mesa, there is
considerable uncertainty a bit farther east as reflected by a
large difference in the 25th-75th percentile (3-4 inches)
according to the 01Z NBM. With impressive ascent likely even into
the High Plains, it seems plausible that at least periods of heavy
snow will impact the urban corridor, but farther south into CO and
NM the displaced jet streak may limit the eastward advance of heavy
snow. NBM v5.0 probabilities in the lower elevations are much
lower than then NBM v4.2 probabilities, but are matched well with
the calibrated probabilities, so this suggests that the risk for
heavy snow farther east is lower than the NBM would suggest, but
still a plowable snow is probably across much of southeast WY and
the CO foothills.

The heaviest snowfall is likely 12Z Friday through 18Z Saturday
before forcing begins to become more diffuse and pushes off to the
southeast. Periods of moderate to heavy snow may linger across the
Sangre de Cristos through 06Z Sunday near and just north of the
upper low, however with weakening forcing, this may end as a
period of rain and snow mixed, even at some of the higher
elevations, before coming to a complete end by the start of D3.

For days 1-2, WPC probabilities are high (>70%) for more than 8
inches across much of the CO Rockies, including the Front Range,
Park Range, Sawatch and San Juans, as well as the Sangre de
Cristos into NM. More than 12 inches and locally as high as 2 ft of
snow is possible above 9,000-10,000 ft in the southern Sawatch and
northern Sangre de Cristos in CO. Outside of the Palmer Divide and
Raton Mesa region, WPC probabilities for greater than 4 inches
reach 30-50% (higher west and lower east) along the I-25 corridor
through the Denver metro.

Although slightly more removed from the worst of the winter
weather, the upper trough pivoting across the Four Corners will
also result in periods of heavy snow in the Wasatch, along the
Mogollon Rim, and into the White Mountains D1, and here WPC
probabilities reach as high as 50% for 6+ inches of snow.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell/Weiss






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FOUS11 KWBC 181805
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
205 PM EDT Fri Apr 18 2025

Valid 00Z Sat Apr 19 2025 - 00Z Tue Apr 22 2025


...Central/Southern Rockies & Adjacent High Plains...
Days 1-2...

Significant mid-April winter storm continues through Saturday
evening, bringing heavy snow primarily to the higher terrain of CO
and NM before ending from west to east.

As of this morning, the amplified but positively tilted trough is
clearly evident on GOES-E WV and IR imagery, centered across Utah.
This trough will continue to amplify, and as the northern portion
of this trough ejects to the east, the southern portion will close
off across the Four Corners. This amplification will result in
pronounced downstream synoptic lift, as mid-level divergence
intensifies and at least peripherally overlaps with the LFQ of a
poleward arcing jet streak into the Central Plains. At the same
time, the cold front being driven south by the amplified trough
will dig into Texas and reach the Rio Grande Valley by the end of
D1, leaving impressive 850-600mb fgen in its wake tilted north into
NM and CO. This even more enhanced ascent will overlap with upslope
flow on post-frontal E/NE winds, to drive intense snow rates across
the Front Range, Sangre de Cristos, and San Juans through D1 and
into early D2 (lingering farther south into D2).

This deep layer ascent (and additional mesoscale through
fgen/upslope) will occur within a moistening column as 700-300mb
flow remains out of the SW downstream of the primary trough axis.
Although PWs progged by NAEFS will be around normal values, this
will be sufficient to be wrung out as heavy snow, with rates
possibly (50-60% chance) exceeding 1"/hr, especially in the Sangres
and San Juans. Snow levels will be falling during this time as
well, reaching as low as 3000 ft, producing significant impacts
even at pass levels across much of the region.

The more challenging aspect of this forecast remains what will
happen in the I-25 urban corridor and eastward into the High
Plains/lower elevations. While it is likely that heavy snow will
accumulate across both the Palmer Divide and Raton Mesa, the NBM
probabilities have dropped off a bit into the lower elevations
including the urban corridor. With impressive ascent likely even
into the High Plains, it still seems plausible that at least
periods of heavy snow will impact the lower elevations, and WSSI
features at least minor impacts, but still a plowable snow is
probable across much of the CO foothills and into northeast NM.

For the remainder of this event, the heaviest snow is likely across
the Sangre de Cristos and the San Juans, where WPC probabilities D1
are high (>70%) for more than 12 inches of snow, and locally 18-24"
is possible through D2 despite rapidly warning coverage and
intensity of snow after 06Z Sunday. Some moderate snowfall of 4-6
inches is also expected across portions of the Mogollon Rim, White
Mountains of AZ, and other higher elevations of northern AZ through
D1.



The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Weiss



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FOUS11 KWBC 181811
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
211 PM EDT Fri Apr 18 2025

Valid 00Z Sat Apr 19 2025 - 00Z Tue Apr 22 2025


...Central/Southern Rockies & Adjacent High Plains...
Days 1-2...

Significant mid-April winter storm continues through Saturday
evening, bringing heavy snow primarily to the higher terrain of CO
and NM before ending from west to east.

As of this morning, the amplified but positively tilted trough is
clearly evident on GOES-E WV and IR imagery, centered across Utah.
This trough will continue to amplify, and as the northern portion
of this trough ejects to the east, the southern portion will close
off across the Four Corners. This amplification will result in
pronounced downstream synoptic lift, as mid-level divergence
intensifies and at least peripherally overlaps with the LFQ of a
poleward arcing jet streak into the Central Plains. At the same
time, the cold front being driven south by the amplified trough
will dig into Texas and reach the Rio Grande Valley by the end of
D1, leaving impressive 850-600mb fgen in its wake tilted north into
NM and CO. This even more enhanced ascent will overlap with upslope
flow on post-frontal E/NE winds, to drive intense snow rates across
the Front Range, Sangre de Cristos, and San Juans through D1 and
into early D2 (lingering farther south into D2).

This deep layer ascent (and additional mesoscale through
fgen/upslope) will occur within a moistening column as 700-300mb
flow remains out of the SW downstream of the primary trough axis.
Although PWs progged by NAEFS will be around normal values, this
will be sufficient to be wrung out as heavy snow, with rates
possibly (50-60% chance) exceeding 1"/hr, especially in the Sangres
and San Juans. Snow levels will be falling during this time as
well, reaching as low as 3000 ft, producing significant impacts
even at pass levels across much of the region.

The more challenging aspect of this forecast remains what will
happen in the I-25 urban corridor and eastward into the High
Plains/lower elevations. While it is likely that heavy snow will
accumulate across both the Palmer Divide and Raton Mesa, the NBM
probabilities have dropped off a bit into the lower elevations
including the urban corridor. With impressive ascent likely even
into the High Plains, it still seems plausible that at least
periods of heavy snow will impact the lower elevations, and WSSI
features at least minor impacts, but still a plowable snow is
probable across much of the CO foothills and into northeast NM.

For the remainder of this event, the heaviest snow is likely across
the Sangre de Cristos and the San Juans, where WPC probabilities D1
are high (>70%) for more than 12 inches of snow, and locally 18-24"
is possible through D2 despite rapidly waning coverage and
intensity of snow after 06Z Sunday. Some moderate snowfall of 4-6
inches is also expected across portions of the Mogollon Rim, White
Mountains of AZ, and other higher elevations of northern AZ through
D1.



The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Weiss






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FOUS11 KWBC 190610
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
210 AM EDT Sat Apr 19 2025

Valid 12Z Sat Apr 19 2025 - 12Z Tue Apr 22 2025


...Southern Rockies...
Day 1...

Significant mid-April winter storm continues for one additional day
across the Rockies of southern CO and northern NM.

As of early this morning, the amplified but positively tilted
trough is clearly evident on GOES-E WV and IR imagery, centered
across northern Arizona. This trough will continue to amplify, and
as the northern portion of this trough ejects to the east, the
southern portion will close off across the Four Corners. This
amplification will result in pronounced downstream synoptic lift,
as mid-level divergence intensifies and at least peripherally
overlaps with the LFQ of a poleward arcing jet streak into the
Central Plains. At the same time, the cold front being driven south
by the amplified trough will dig into Texas and reach the Rio
Grande Valley by this afternoon, leaving impressive 850-600mb fgen
in its wake tilted north into NM and CO. This even more enhanced
ascent will overlap with upslope flow on post-frontal E/NE winds,
to drive intense snow rates across the Sangre de Cristos and San
Juans through the first half of D1.

This deep layer ascent (and additional mesoscale dynamics through
fgen/upslope) will occur within a moistening column as 700-300mb
flow remains out of the SW downstream of the primary trough axis.
Although PWs progged by NAEFS will be around normal values, this
will be sufficient to be wrung out as heavy snow, with rates
possibly (30-60% chance) exceeding 1"/hr, especially in the
Sangres and San Juans. Snow levels will begin to slowly rise today
as the cold airmass once in place begins to modify, rising from
around 5,000 ft to 7,000 ft.

For the tail end of this event, the heaviest snow is likely across
the Sangre de Cristos and the San Juans, where WPC probabilities
D1 are high (>70%) for more than 8 inches of snow, and locally over
1 foot is possible despite rapidly waning coverage and intensity
of snow after 00Z Sunday.


...Washington Cascades & Northern Rockies...
Days 2-3...

Shortwave entering the Northwest Sunday evening and crossing over
the northern Rockies on Monday will be accompanied by favorable
upper jet dynamics, with the LFQ situated over the region.
Associated height falls will also be coincident with lowering snow
levels, starting out around 3,500 ft in the WA Cascades before
crashing to 2,500 ft briefly. For the northern Rockies, snow levels
around 6,000 ft will fall to around 4,000 ft in northwest MT and
5,000 ft near Yellowstone. The heaviest snowfall is expected across
the northern WA Cascades and parts of western MT into Yellowstone
Country, where 6-12 inches are possible in the higher peaks. WPC
probabilities are high (>70%) through D3 for at least 6 inches of
snow across parts of the WA Cascades and the western/south-central
MT ranges above 7,000 ft.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell







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FOUS11 KWBC 191810
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
210 PM EDT Sat Apr 19 2025

Valid 00Z Sun Apr 20 2025 - 00Z Wed Apr 23 2025


...Southern Rockies...
Day 1...

The significant winter storm that has been plaguing the Central and
Southern Rockies since Thursday will wane quickly tonight, with
lingering moderate to heavy snow persisting primarily across the
Sangre de Cristos through Sunday morning. The weakening and waning
of this system is due to the opening of the parent closed mid-level
low as it moves across NM tonight, leaving the strongest ascent
through overlapping height falls, divergence, and jet level
diffluence displaced to the east across the Southern Plains and
into a much warmer column. By 12Z Sunday, all remaining
precipitation across NM and into the Southern Plains is expected to
be rain. Until that happens, WPC probabilities indicate a low risk,
10-30% chance, for an additional 4 inches of snow across the
southern Sangre de Cristos, generally above 6000 ft.


...Washington Cascades & Northern Rockies...
Days 1-2...

A shortwave embedded within broad troughing across the western
CONUS will eject south along the coast of British Columbia and dive
across WA/OR Sunday evening. This feature will amplify modestly as
it crosses the Northern Rockies Monday morning, stringing out into
the Northern Plains on Tuesday. This progression will drive a
surface cold front southeast across the region Monday, with
synoptic ascent through overlapping height falls and weak jet
diffluence atop the baroclinic zone leading to weak surface low
development as well. Together, this will spread moderate
precipitation across the region, with intensity and coverage
peaking D2. Snow levels during this time will fall steadily from
around 4500-5000 ft to 2500-3000 ft, leading to at least some pass-
level snow accumulations, although the general modest forcing and
transient nature of the feature will keep snowfall moderate. WPC
probabilities D1 for more than 4 inches of snow are moderate
(30-50%) across the higher WA Cascades, and low (10-30%) for the
Northern Rockies near Glacier NP as well as parts of the Absarokas.
During D2, elevated probabilities above 50% for an additional 4+
inches continue in the WA Cascades, but expand and become higher
(70-90%) across the Absarokas and into the Wind River Range.


...Western Great Lakes..
Days 2-3...

A strengthening low pressure system moving out of the Southern
Plains Sunday afternoon will lift progressively northeast, reaching
the Upper Peninsula of Michigan by Monday afternoon. As this
occurs, precipitation will expand downstream in response to
increasing moist advection along the 295-300K surface north from
the Gulf Coast. While the column will generally be too warm for
wintry precipitation, increasing ascent through a developing axis
of deformation NW of the surface low will lead to local dynamic
cooling effects, which will be most pronounced in the higher
elevations of the U.P. and Arrowhead of MN. Here, there remains
quite a bit of spread among the various deterministic models, but
northerly flow combined with the enhanced mesoscale lift across the
higher elevations will result in precipitation changing to snow,
with briefly heavy snow rates of 1"/hr possible. While total
accumulations will still likely be limited,as reflected by WPC
probabilities that peak around 30% for just 2" of snow in the
Keweenaw Peninsula and the Huron Mountains, at least minor snow
impacts are probable Monday in these areas due to briefly heavy
snow rates.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Weiss


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FOUS11 KWBC 200705
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
305 AM EDT Sun Apr 20 2025

Valid 12Z Sun Apr 20 2025 - 12Z Wed Apr 23 2025


...Washington Cascades & Northern Rockies...
Days 1-2...

A shortwave embedded within broad troughing across the western
CONUS will eject south along the coast of British Columbia and dive
across WA/OR this evening into early Monday. This feature will
amplify modestly as it crosses the Northern Rockies Monday morning,
stringing out into the Northern Plains on Tuesday. This
progression will drive a surface cold front southeast across the
region Monday, with synoptic ascent through overlapping height
falls and weak jet diffluence atop the baroclinic zone leading to
weak surface low development as well. Together, this will spread
moderate precipitation across the region, with intensity and
coverage peaking the end of D1 into D2. Snow levels during this
time will fall steadily from around 4500-5000 ft to 2500-3000 ft,
leading to at least some pass- level snow accumulations, although
the general modest forcing and transient nature of the feature will
keep snowfall moderate. WPC probabilities D1-D2 for more than 6
inches of snow are moderate (40-70%) across the higher WA Cascades
and for the Northern Rockies near Glacier NP as well as parts of
the Absarokas and Wind River Range.


...Western Great Lakes..
Days 1-2...

A strengthening low pressure system moving out of the Southern
Plains this afternoon will lift progressively northeast, reaching
the Upper Peninsula of Michigan by Monday afternoon. As this
occurs, precipitation will expand downstream in response to
increasing moist advection along the 295-300K surface north from
the Gulf Coast. While the column will generally be too warm for
wintry precipitation, increasing ascent through a developing axis
of deformation NW of the surface low will lead to local dynamic
cooling effects, which will be most pronounced in the higher
elevations of northern WI, the western MI U.P. and Arrowhead of
MN. Here, there remains quite a bit of spread among the various
deterministic and CAMs with respect to snowfall intensity and
location, but northerly flow combined with the enhanced mesoscale
lift across the higher elevations will result in precipitation
changing to snow. Snow could come down heavy for a brief period at
onset, with rates of 1"/hr possible beginning around 06Z-12Z
Monday. While heavy accumulations may be limited, as reflected by
WPC probabilities that peak around 30% for at least 4 inches of
snow in the Keweenaw Peninsula, Porcupine/Huron Mountains, and
along the Gogebic Range into northern WI, at least minor snow
impacts are probable Monday in these areas due to briefly heavy
snow rates.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell/Weiss





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FOUS11 KWBC 201810
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
210 PM EDT Sun Apr 20 2025

Valid 00Z Mon Apr 21 2025 - 00Z Thu Apr 24 2025


...Northern Rockies...
Day 1...

A shortwave will be moving onshore the WA/OR coast at the start of
the forecast period /00Z tonight/ and then move progressively
eastward with modest amplification through Monday. The accompanying
trough axis is progged to lift northeast into Saskatchewan and the
Dakotas just after 00Z Tuesday, and the subtle negative tilt
indicated in model progs suggest downstream ascent will be
maximized across the Northern Rockies as this evolution occurs.
The progression of this shortwave combined with at least weak upper
diffluence will help drive pressure falls, and a wave of low
pressure is expected to track east through the region, dragging a
cold front in its wake. While this low will be weak and contribute
minimally to ascent, the trailing cold front will help both to
lower snow levels (from 6000-7000 ft early to 3000-5000 ft late)
and provide the impetus for upslope enhancement on the post-frontal
flow. The overall modest ascent and transient nature of this system
will limit snow totals, but WPC probabilities indicate a moderate
risk (50-70%) for 6+ inches for portions of the Northern Rockies in
the vicinity of Glacier NP, as well as the Absarokas and Wind
Rivers.


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

The guidance has continued to trend stronger with a low pressure
system moving across the Upper Midwest this evening and into the
Western Great Lakes Monday morning. Additionally, the trend has
been for a slightly farther east track in response to the 500mb low
closing off a bit later over Iowa before lifting into the eastern
U.P. of Michigan, collocated with the LFQ of a poleward arcing jet
streak, which will strengthen modestly as it pivots around the
closed low.

As this entire feature shifts northeast, increasing moisture on
295K-300K isentropic ascent will wrap into the system, leading to
an expansion of precipitation, some of which will become heavy in
response to strong fgen along the leading warm front. This will
remain in the form of rain, but to the NW as the upper low deepens,
an axis of deformation is still progged to rotate southward across
western Lake Superior, and the accompanying ascent should
dynamically cool the column to change rain to periods of heavy
snow. While accumulating snow will be confined to periods when the
snowfall rates are the heaviest (and both HREF and WPC snowband
tool probabilities indicate a 10-30% chance of 1+"/hr snowfall
rates), the potential for significant accumulations has increased,
especially in the higher terrain of the MN Arrowhead, Keweenaw
Peninsula, Huron Mountains, and Porcupine Mountains. Here, WPC
probabilities are as high as 50-70% for 2+ inches, and as high as
10-30% for 4+ inches. As this will be a heavy and wet snow, the
potential for moderate impacts and disruptive driving due to snow
load and snow rates have also increased.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Weiss


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FOUS11 KWBC 210639
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
239 AM EDT Mon Apr 21 2025

Valid 12Z Mon Apr 21 2025 - 12Z Thu Apr 24 2025


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

By the start of the forecast period (12Z Mon), a deep low pressure
system tracking across central WI and accompanying deformation
zone in northern WI/western MI U.P. is expected to dynamically cool
the column enough for potentially heavy snowfall rates. This
transition from a cold rain to wet snow should be well underway by
12Z this morning (as early as 08Z per several CAMs) and lead to at
least a few hours with snowfall rates up to 1"/hr from the MN
Arrowhead through the western Lake Shores of Superior into inland
portions of northern WI through early this afternoon. However,
given current wet- bulb temperatures in the mid-to-upper 30s along
with moderate rainfall, snowfall accumulations will likely be
limited. Still, at least a few inches of snow are possible and
could lead to some travel impacts where higher rates are realized
and visibility is lowered. WPC probabilities for at least 2 inches
are moderate (30-60%) from far northern WI through the western MI
U.P., including the Keweenaw Peninsula, Porcupine Mts and Bayfield
Peninsula.


...Northern Rockies...
Day 1...

A shortwave crossing the northern Rockies today is already
producing a broken precipitation shield across the region early
this morning, which includes mountain snow showers. This system
will slide eastward with modest amplification through tonight. The
accompanying trough axis is then progged to lift northeast into
Saskatchewan and the Dakotas just after 00Z Tuesday, with a subtle
negative tilt indicated in model progs suggesting downstream ascent
will be maximized across the northern Rockies as this evolution
occurs. The progression of this shortwave combined with at least
weak upper diffluence will help drive pressure falls, and a wave of
low pressure is expected to track east through the region,
dragging a cold front in its wake. While this low will be weak and
contribute minimally to ascent, the trailing cold front will help
both to lower snow levels below 5,000 ft and provide the impetus
for upslope enhancement on the post- frontal flow. The overall
modest ascent and transient nature of this system will limit snow
totals, but WPC probabilities indicate a moderate risk (50-70%) for
6+ inches throughout portions of the northern Rockies in the
vicinity of Glacier NP as well as the northern Absarokas.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.



Snell




$$

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FOUS11 KWBC 211911
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
311 PM EDT Mon Apr 21 2025

Valid 00Z Tue Apr 22 2025 - 00Z Fri Apr 25 2025


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

Weak and broad troughing over the northwestern CONUS will yield
generally light snow to the high terrain of northwestern MT this
evening before tapering off. Drier conditions will prevail over
much of the region Tuesday ahead of a shortwave moving through
Oregon Wednesday. This feature will move into the northern Rockies
thereafter, spreading snow across southwestern MT and northwestern
WY starting Wednesday morning. Amounts will be light, focused on
the Absarokas, Wind River, and Bighorns where WPC probabilities for
at least 8 inches of snow through the period (especially days 2-3)
are moderate (40-70%) at the highest elevations.

The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso

$$

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FOUS11 KWBC 220653
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 AM EDT Tue Apr 22 2025

Valid 12Z Tue Apr 22 2025 - 12Z Fri Apr 25 2025


...Northern Rockies...
Days 2-3...

A drier stretch is expected to prevail today outside of a few high
elevation snow showers near Yellowstone before the next shortwave
slides over the northern Rockies Wednesday night into Thursday.
This feature will spread snow across southwestern MT and
northwestern WY ahead of a much deeper upper trough approaching the
West Coast by the end of D3. Broad west-southwesterly flow will
aid in overspreading Pacific moisture into the region, while also
rising snow levels to around 6,000-8,000 ft during this time frame.
Amounts will be generally light, focused on the Absarokas, Wind
River, and Bighorns, where WPC probabilities for at least 8 inches
of snow through 12Z Friday are low (20-40%) at the highest
elevations.

The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell




$$

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FOUS11 KWBC 221914
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Tue Apr 22 2025

Valid 00Z Wed Apr 23 2025 - 00Z Sat Apr 26 2025


...Northern Rockies...
Days 1-2...

Shortwave moving into/through Oregon this evening/overnight will
spread a new round of generally light snow across southwestern MT
and northwestern WY as it deepens over the northern Great Basin.
Upper jet will be positioned over the northern Plains, aiding in
ascent over the region where temperatures are mostly mild,
confining snowfall to areas above 7000ft or so. This feature will
weaken as it pushes through Idaho and into western Montana Thursday
night with snow tapering off by Friday morning. WPC probabilities
for at least 8 inches of snow are moderate (40-70%) over the
Absarokas and Wind River ranges and generally less than 50% over
the Bighorns.


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

A deep upper trough in the northeastern Pacific will dig
and deepen into a closed low just west of NorCal by Friday, sending
in some moisture to the region. Snow levels will start high,
confining generally light snow to areas above 7000ft where WPC
probabilities are low (10-40%) through 00Z Sat. More snow is
expected thereafter.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.

Fracasso


$$

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FOUS11 KWBC 230654
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
254 AM EDT Wed Apr 23 2025

Valid 12Z Wed Apr 23 2025 - 12Z Sat Apr 26 2025


...Northern Rockies...
Days 1-2...

Shortwave moving through OR this morning will spread a new round
of generally light snow across southwestern MT and northwestern WY
as it deepens over the northern Great Basin tonight. Upper jet
will be positioned over the northern Plains, aiding in ascent over
the region where temperatures are mostly mild, confining snowfall
to areas above 7000ft or so. This feature will weaken as it pushes
through ID and into western MT Thursday night with snow tapering
off by Friday morning. WPC probabilities for at least 8 inches of
snow are moderate (40-70%) over the Absarokas and Wind River ranges
and generally less than 40% over the Bighorns.


...Oregon & California...
Day 3...

A potent upper trough in the northeastern Pacific will dig and
deepen into a closed low just west of NorCal by Friday, sending in
some moisture to the region. This upper low is then forecast to begin
moving inland over central CA Friday night, with some lingering
uncertainty regarding exact timing. Snow levels will start high and
around 7000ft, but fall to around 5000ft by 12Z Saturday just as
the precipitation shield becomes more expansive in response to the strengthening upper jet over SoCal. WPC probabilities on day 3 for
at least 6 inches are low (10-40%) across the southern OR Cascades
into the NorCal ranges and central Sierra Nevada. More snow is
expected into the day 4 timeframe.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell





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FOUS11 KWBC 231915
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
315 PM EDT Wed Apr 23 2025

Valid 00Z Thu Apr 24 2025 - 00Z Sun Apr 27 2025


...Northern Rockies...
Days 1-2...

A shortwave moving through the northern Great Basin tonight will
spread generally light snow across central ID, southwestern MT, and northwestern WY Thursday as it deepens a bit then lifts
northeastward into southwestern Montana tomorrow afternoon. Right
entrance region of a retreating upper jet will promote broad ascent
over the region where temperatures are mostly mild, confining
snowfall to areas above 7000ft or so. Snow will taper off by Friday
morning as the feature weakens over western Montana. WPC
probabilities for at least 8 inches of snow over the next 36 hours
are moderate (40-70%) over the Absarokas and Wind River ranges and
generally less than 50% over the Bighorns.


...Oregon & California...
Days 2.5-3...

A potent upper trough in the northeastern Pacific Thursday will
dig and deepen into a closed low just west of NorCal by Friday,
sending in some moisture to the region as early as Thursday
evening. This upper low is then forecast to move inland over
central CA Saturday morning, with a trend to the south since
yesterday. Snow levels will start high (over 7000ft), but fall to
below 6000ft by early Saturday as the precipitation shield expands
in response to the strengthening upper jet over SoCal. WPC
probabilities for at least 6 inches of snow are low (~10%) for the
Oregon Cascades due to the decrease in QPF, low (10-40%) over the
northern CA ranges, and moderate (40-70%) over the northern/central
Sierra Nevada (generally above 7000ft). Snow is expected to
continue into the day 4 timeframe.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso



$$

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FOUS11 KWBC 240714
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
314 AM EDT Thu Apr 24 2025

Valid 12Z Thu Apr 24 2025 - 12Z Sun Apr 27 2025


...Northern Rockies...
Day 1...

A shortwave trough over the Great Basin (axis currently over the
NV/ID border) will shift ENE over the Yellowstone region this
evening. Some moist flow ahead of the trough will lift over a
stationary front over southern WY and continue to bring light to
locally moderate mountain snow until the trough crosses this
evening to higher portions of the Absarokas, Wind River, and
Bighorns, where Day 1 probabilities for an additional >4" snow
after 12Z are 10-30%. Snow levels in this mild airmass are
generally 7000ft or higher in northern WY.


...Sierra Nevada...
Days 2/3...

A negatively-tilted upper trough reaches the central CA coast
tonight as an upper low develops offshore and tracks to the central
CA coast through Friday night. This low then drifts to southern NV
through Saturday night. Moisture inflow and topographical lift over
the central Sierra become sufficient for higher elevation snow by
later Friday afternoon with a prolonged light to locally moderate
snowfall then into Sunday. Snow levels begin around 6500ft, but
drop to as low as 5000ft under the upper low. Day 2.5 WPC
probabilities for >6" are 30-50% for the Sierra Nevada generally
above 7000ft in 24hrs (00Z Sat to 00Z Sun).


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Jackson


$$

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FOUS11 KWBC 241934
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
334 PM EDT Thu Apr 24 2025

Valid 00Z Fri Apr 25 2025 - 00Z Mon Apr 28 2025


...Sierra Nevada...
Days 1-3...

Digging trough west of 130W this evening will slip into the CA
coast overnight with light snow breaking out tomorrow over the high
Sierra as initial height falls cross the mountains. Upper low will
eventually come ashore on Saturday with downstream light to
occasionally moderate snow for the Sierra as snow levels lower to
around 5000-6000ft with the approach of the cold core. By Sunday,
the upper low will cross through the Great Basin, with snow ending
from west to east. WPC probabilities for at least 8 inches of snow
over the next three days are >50% above 6500ft or so.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.

Fracasso

$$

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FOUS11 KWBC 250713
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 AM EDT Fri Apr 25 2025

Valid 12Z Fri Apr 25 2025 - 12Z Mon Apr 28 2025


...Sierra Nevada...
Days 1-2...

Positively-tilted trough approaching the central/northern CA coasts
will provide some onshore flow and High Sierra snow today as
initial height falls cross the mountains with snow levels 7000ft or
higher. Slight southward trend continues in upper low track that
reaches the central CA coast Saturday with downstream light to
occasionally moderate snow for the Sierra through Saturday evening
as snow levels lower to around 5000ft. By Sunday, the upper low
will cross through the Great Basin, with Sierra snow ending from
west to east. Day 2 WPC probabilities for >6" are 20-30% in the
5500-6500ft range and 30-60% above 6500ft or so.


...Great Basin and Northern Rockies...
Day 3...

The upper low that crosses the Central CA Coast Saturday pivots
northeast from southern NV to central WY Sunday through Sunday
night. Left exit jet dynamics aid lift ahead of the low where
sufficient moisture is present for valley rain and mountain snow
with snow levels around 6500ft. Day 3 snow is most likely over the
NV ranges, northern Wasatch, with Sunday night snow bands
developing over the Absarokas where there's potential for brief
bursts of heavy snow.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Jackson


$$

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FOUS11 KWBC 251712
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
112 PM EDT Fri Apr 25 2025

Valid 00Z Sat Apr 26 2025 - 00Z Tue Apr 29 2025


...Sierra Nevada and Great Basin...
Days 1-3...

An impressive closed mid-level low (NAEFS 500mb height anomalies
falling below the 1st percentile) will move onshore southern CA
Saturday aftn before slowly filling while lifting northeast through
the Great Basin on Sunday. Downstream of these robust height
anomalies, significant synoptic lift will occur downstream through
height falls, mid-level divergence, and overlapping upper
diffluence as the LFQ of a strengthening subtropical jet streak
digs through the trough axis and ejects meridionally. The overlap
of this ascent into a region moistened by 700mb S/SW flow and an
accompanying ribbon of IVT above the 90th percentile (from NAEFS)
will result in widespread precipitation Saturday morning through
Sunday afternoon.

Snow levels during this time will be quite low in
response to the anomalous upper low, falling to around 4500 ft,
which is nearing the 10th percentile. This suggests that snow will
accumulate across much of the CA and Great Basin terrain above this
level through Sunday, but at least light accumulations or mixing
with snow is possible much lower due to steep lapse rates and
dynamic cooling. The heaviest accumulations, however, should remain
across the Sierra, where D1 and D2 probabilities for 6+ inches
exceed 70%, and 30%, respectively, and locally more than 12 inches
is possible before precipitation wanes late D2.

As this upper low continues to track northeast, the accompanying
moisture and ascent will move across the Great Basin, bringing some
light to moderate snow to the higher elevations of NV through
Monday morning. WPC probabilities D3 reach as high as 50% for 6+
inches across the Ruby Mountains.


...Northern Rockies...
Day 3...

The closed low ejecting from the Great Basin will fill and open
into a positively tilted trough Monday as it shifts east into the
Rockies. Despite this evolution, deep layer ascent will remain
impressive as periodic lobes of vorticity swing northeast
downstream of the trough axis, and work together with mid-level
divergence and upper diffluence in the LFQ of a jet streak arcing
into the Northern Plains. Together, this will cause pressure falls
over CO/WY leading to surface cyclogenesis, and this low will then
track northeast into the Dakotas and Minnesota by the end of D3.
While there is good model agreement in the general synoptic setup
and evolution, low-clusters from the various ensembles still
feature considerable spread in both timing and placement,
additionally reflected by modest differences in the primary 500mb
EOF on the D3 WPC clusters.

The primary driver of these variances appears to be the speed at
which this trough opens and ejects, with 2/3 of the ECENS
suggesting a lower ejection, while 50% of the GFS members make up
the faster end of the envelope, and by the end of D3 there are
height differences among the cluster means of more than 80m across
the Central High Plains. At this time, a solution somewhere between
the camps as a consensus is probably best.

While the exact placement of the low and its associated synoptic
forcings will be critical, a cold front digging south through the
Northern Rockies Sunday night into Monday will likely interact with
an inverted surface trough, leading to enhanced ascent across parts
of MT and WY D3. This is likely to occur regardless of the low
evolution, but a slower system may produce more enhanced ascent and
stronger accompanying deformation than a faster ejecting system.
Either way, impressively combined upslope with fgen should result
in heavy snow rates, with dynamic cooling response to the column
occurring even outside of the higher terrain. Snow levels will be
generally low anyway, (near the NBM 10th percentile after
coordination with the local WFOs), suggesting that while the
heaviest accumulation will remain above 5500 ft, significant
accumulations are possible to 4500 ft, and lighter accumulations
even lower than that. This is reflected by WPC probabilities that
are high (>70%) D3 across the Big Horns, Absarokas, and other
terrain around Yellowstone NP, but also much more widespread
moderate probabilities for 2" expanding across much of the ID/MT/WY
juncture.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Weiss


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FOUS11 KWBC 260856
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
456 AM EDT Sat Apr 26 2025

Valid 12Z Sat Apr 26 2025 - 12Z Tue Apr 29 2025


...California and Nevada...
Days 1-2...

Upper low crosses the central CA coast this morning before slowly
filling while lifting northeast, reaching south-central NV by
Sunday morning. Lift ahead of the low, aided by left jet exit
dynamics, overlapping sufficient Pacific moisture will allow
expanded precip coverage over CA into this evening with the focus
over NV and the eastern side of the Sierra Nevada overnight through
Sunday.

Snow levels will be 5000-5500ft through Sunday morning. 00Z HREF
mean hourly snow rates are generally 1-1.5"/hr from 12Z to 00Z on
the Sierra Nevada.Day 1 snow probs for >6" are 50-80% for the
Sierra Nevada and highest Transverse Ranges in SoCal. Eastern
slopes of the Sierra Nevada are favored for the heaviest snow with
50-80% probs for >12" over the White Mtns and other ranges along
the NV border up through the eastern side of Tahoe.

As this upper low continues to track northeast, the accompanying
moisture and ascent will bring light to moderate snow to the
higher elevations of NV through Sunday night. Day 2 WPC
snow probs are 50-80% >6" across the Ruby Mountains of NV.


...Northern Rockies...
Days 2/3...

The closed low drifting from the Great Basin Sunday night will
fill and open into a positively-tilted trough Monday as it reaches
WY. Despite the weakening, deep layer ascent will remain
impressive as periodic lobes of vorticity swing northeast
downstream of the trough axis, and work together with mid-level
divergence and upper diffluence in the left exit region of the jet
streak arcing into the Northern Plains. Together, this will cause
pressure falls over CO/WY leading to surface cyclogenesis on the
High Plains.

A cold front digging south through the Northern Rockies Sunday
night into Monday will approach the Plains surface low, leading to
enhanced ascent across parts of MT and WY. This slow moving system
will allow upslope flow with fgen, resulting in heavy snow rates,
with dynamic cooling response to the column occurring even outside
of the higher terrain. Snow levels will be generally around 6000ft.
Day 2 snow probs for >8" are 30-40% in the eastern Sawtooths in ID
and 50-80% over the northern Absarokas in MT. This shifts east for
Day 3 over the eastern Absarokas and Bighorns in WY.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.



Jackson



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FOUS11 KWBC 261813
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
213 PM EDT Sat Apr 26 2025

Valid 00Z Sun Apr 27 2025 - 00Z Wed Apr 30 2025


...California and Nevada...
Day 1...

An intense closed mid-level low (500-700mb heights below the 1st
percentile according to NAEFS) will move onshore southern
California just before the start of the forecast period, with
gradual filling/weakening occurring thereafter as it lifts
northeast. As this low moves from CA through the Great Basin, it
will drive deep layer ascent through height falls and downstream
500mb divergence, which will overlap at least modestly with a
strengthening jet streak wrapping around the downstream side of the
trough. Together, this will result in periods of moderate to heavy precipitation, which will fall as snow in the higher elevations.
While most of the snow accumulations will be above 5500 ft across
the Sierra and into the Ruby Mountains, where WPC probabilities
for 6+ inches reach 70-90%, the anomalously cold pool aloft and
steep lapse rates may allow for at least light accumulations down
below the NBM 10th percentile snow level, or as low as 4000 ft
before the system ejects to the northeast and ends on D2.


...Northern Rockies...
Days 2-3...

The closed low emerging from the Great Basin will pivot into WY/UT
and then begin to fill/open into a trough as it shifts east slowly
into Tuesday. DUring this evolution, the primary trough axis will
become positively tilted and split as northern stream energy ejects
into the Great Lakes while a southern stream shortwave stalls over
the Desert Southwest. This development will result in prolonged
deep layer ascent beneath the slowly advancing trough, with
additional, but weakening, ascent through the LFQ of a downstream
jet streak helping to produce surface cyclogenesis from CO into MN
during D2. As this low tracks northeast, a cold front will dig out
of Canada, leading to enhanced post-frontal ascent into the terrain
and increased fgen in the vicinity of the front. This will work in
tandem with some increased fgen and deformation which develops on
the NW side of the surface low to enhance ascent and increase the
intensity of precipitation from western ND through eastern ID.

The guidance has trended a bit slower and warmer with the
evolution, leading to snow levels and an atmospheric column that
are warmer, at least at precipitation onset around 00Z-06Z Monday.
Thereafter, however, the combination of the cold front and the
increasing ascent through the mesoscale forcing (fgen and
deformation) will help dynamically cool the column and lower snow
levels such that heavy snow rates will accumulate efficiently in
both higher terrain and some of the elevated valleys. There is
still uncertainty into how much snow can accumulate in the lower
levels, especially below around 4500 ft (NBM 10th percentile snow
level). However, it is likely that a lower-than-climo SLR will
result in heavy wet snow that should be impactful to many areas as
snowfall rates potentially reach 1-2"/hr at times, and this is
reflected by WSSI featuring moderate to locally major impacts,
focused in the Absarokas, Big Horns, and in the vicinity of
Yellowstone NP. These areas are also where the highest WPC
probabilities for 6+ inches exist, reaching above 90%, with locally
1-2 feet possible in the Absarokas.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.



Weiss


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FOUS11 KWBC 270836
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
436 AM EDT Sun Apr 27 2025

Valid 12Z Sun Apr 27 2025 - 12Z Wed Apr 30 2025


...Great Basin and Northern Rockies...
Days 1-2...

Upper low over central NV will slowly track to northern UT through
today where it will stall and fill through tonight. Mountain snow
continues over the higher NV ranges with snow levels of
6000-7000ft. The Ruby Mtns stand out in NV for impacts with Day 1
snow probs for >8" 50-90%.

A reinforcing trough ejects over the northern High Plains tonight
into Monday which allows a slowly pivoting swath of moderate to
locally heavy precip this afternoon through Monday morning from
central ID through southern MT. Snow levels in this swath start
high, above 8000ft through this evening, but decrease overnight to
5000 to 6000ft over the northern Absarokas. The resulting
positively-tilted trough axis shifts south Monday bringing some
moderate snow to terrain in WY. Day 1.5 snow probs for >8" are
70-90% in the Red Lodge area of the northern Absarokas in southern
MT (where storm totals over 2ft are locally likely) and 50-80% in
the Madison/Gallatin ranges, Absarokas east of Yellowstone, and the
Bighorns.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.



Jackson



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FOUS11 KWBC 271831
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
231 PM EDT Sun Apr 27 2025

Valid 00Z Mon Apr 28 2025 - 00Z Thurs May 1 2025


...Great Basin and Northern Rockies...
Days 1-2...

An upper low traversing the Great Basin today will be responsible
for periods of higher elevation snow through the northern Nevada
ranges this afternoon and evening. Snow levels will be as low as
6,000ft in some cases, but the heavier amounts are likely to resume
above 7,000ft. As the upper low weakens and moves east tonight,
mountains snow will ensue within the more remote reaches of the
Wasatch and Uinta of Utah, while minor amounts are possible as far
east as the peaks of the Colorado Rockies through Monday morning.
Additional snowfall accumulations of 2-6" are forecast in the

6,000ft ridge lines of northern Nevada through early Monday

morning.

The ranges most likely to see the heaviest snowfall will be in the
Absaroka, the Tetons, and the Big Horns. These ranges will reside
favorably beneath the the best PVA at 250-500mb and a pivoting axis
of >90th climatological percentile 500-700mb moisture content
aloft. 850-700mb winds will back of out of the NE-E as the upper
low slides south of these ranges and a surface cold front passes
through tonight. While the cold front does provide a brief
infection of CAA aloft, the cold air source is not sufficient
enough to produce much more than minor snowfall accumulations
below 7,000ft. The heaviest amounts will be confined to elevations
at/above 8,000ft in the ranges listed above, with some locally
heavier amounts as low as 7,000ft in the Big Horns. Snow tapers off
by Monday afternoon and evening as the upper low races east
towards the Northern Plains Monday evening. WPC probabilities
highlight high chances (>70%) for snowfall totals >12" in the
Absaroka above 7,000ft with some totals in the Absaroka-Beartooth
Wilderness seeing totals above 24 inches in some cases above
9,000ft. WPC probabilities show moderate-to-high chances (50-70%)
for snowfall totals >12" in the Big Horns above 7,000ft, while
similar chances for >6" of snow exist in the Tetons above 8,000ft.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Mullinax






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FOUS11 KWBC 280833
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
433 AM EDT Mon Apr 28 2025

Valid 12Z Mon Apr 28 2025 - 12Z Thu May 01 2025


...North-Central Rockies...
Day 1...

Positively-tilted trough axis from the western Dakotas to Nevada
will sag south today as a leading shortwave tracks to the Upper
Midwest while a filling low drifts south over Utah. The surface low
associated with the leading wave is over SD with comma head/cold
conveyor belt flow resulting in a swath of moderate to locally
heavy precip across southern/eastern MT. Snowfall rates above the
6500ft snow levels in southern MT around 7000ft will rapidly rise
through this morning, particularly in the Red Lodge portion of the
northern Absarokas where rates will soon exceed 2"/hr per the 00Z
HREF. This precip swath will shift south over WY today where snow
levels will also be around 7000ft and rates in the higher terrain
will generally be 1-2"/hr. Day 1 snow probs for >8" additional
snow after 12Z are 40-70% in the Absarokas and 60-90% in the
Bighorns.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Jackson



$$

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FOUS11 KWBC 281834
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
234 PM EDT Mon Apr 28 2025

Valid 00Z Tue Apr 29 2025 - 00Z Fri May 02 2025


...Northern & Central Rockies...
Days 2-3...

After light-to-moderate snow quickly ends across WY by the start
of day 1 following the departure of a postively-tilted trough
sliding eastward into the Upper Midwest, a separate upper shortwave
and associated cold front is forecast to swing over the northern
Rockies on Wednesday. This will lead to an area of broken
precipitation with an upslope emphasis on the highest peaks and
northward facing slopes as the system slides south into the CO
Rockies on Thursday. Snow levels will fall below 8,000ft in western
MT and northwest WY shortly behind the cold front and as low as
6,000ft. However, these relatively lower snow levels also coincide
with a drier column and only lighter precipitation. For the
central Rockies, snow levels are expected to remain around
8,000-9,000ft through the end of day 3. WPC probabilities for at
least 6 inches of snow during the days 2-3 time frame are moderate
(40-70%) across the high elevations of southwest MT, WY, and CO.
This primarily includes the Absarokas, Bighorns, Wind River Range,
and Medicine Bow Mts above 9,000-10,000ft.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell






$$

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FOUS11 KWBC 290834
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
434 AM EDT Tue Apr 29 2025

Valid 12Z Tue Apr 29 2025 - 12Z Fri May 02 2025


...Montana, Wyoming, and Colorado...
Days 1-3...

The next system of note in the West is an upper shortwave and
associated cold front that shifts south over the northern Rockies
from MT this afternoon through Wednesday. Snow levels of
6000-7000ft are expected in western MT and closer to 8000ft in
northwest WY tonight. The parent trough shifts east over the
northern Plains Wednesday night as the cold front slowly shifts
south over CO into Thursday. However, snow levels remain around
8,000-9,000ft through Thursday.

Day 1 snow probs for >6" are 30-50% in ranges around Glacier NP.
Day 1.5 snow probs for >6" are 30-70% over the Absarokas, Tetons,
and Bighorns. Day 2.5 snow probs for >6" are 40-80% for the Front
Range in CO.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Jackson



$$

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FOUS11 KWBC 291801
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
201 PM EDT Tue Apr 29 2025

Valid 00Z Wed Apr 30 2025 - 00Z Sat May 03 2025


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

Positively-tilted trough over southwestern Canada/northern Divide
this evening will carry a cold front through the region with colder
air in its wake and lowering snow levels. Precipitation will
translate from northwest to southeast Days 1-2 from southwestern MT
through Wyoming then into the CO Rockies. By Wednesday evening,
the trough will moving into the High Plains as heights rebound into
Day 3, ending any snowfall over the region. Snow levels will start
around 8000ft near/ahead of the cold front then drop to
6500-7000ft during the morning hours behind the front, only to rise
again over 7000ft during the day. This will confine the most snow
to the mountain ranges like the Absarokas, Tetons/Wind River,
Bighorns, and CO Rockies. WPC probabilities for at least 8 inches
of snow for this period are at least 50% above 10,000ft or so.

The probability of at least 4 inches of snow on Day 3 is less than
10%.

The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso


$$

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FOUS11 KWBC 300838
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
438 AM EDT Wed Apr 30 2025

Valid 12Z Wed Apr 30 2025 - 12Z Sat May 03 2025


...Rockies...
Days 1-2...

Positively-tilted trough over the northern Rockies this morning
with a vort lobe over the Bitterroots will drift south through
Thursday. Focus for precip is along a surface boundary ahead of the
upper trough axis with light to moderate rates over WY today and CO
tonight Thursday. Snow levels will be elevated - around 8000ft
in WY and 9000ft in CO. Day 1 snow probs for >6" are around 30% in
the southern Absarokas/Wind River and 40-60% over the Bighorns. Day
1.5 snow probs for >6" are 40-70% through the Front Range and the
Mosquito Range.


The probability of any freezing rain across CONUS is less than
10%.


Jackson



$$

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FOUS11 KWBC 301814
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
214 PM EDT Wed Apr 30 2025

Valid 00Z Thu May 01 2025 - 00Z Sun May 04 2025


...Central/Southern Rockies...
Days 1-2...

Cold front associated with a shortwave over the Northern Plains to
the central Rockies will continue southeastward through Colorado
and into New Mexico Thursday. QPF has decreased in the past 24
hours but some light snow over the high mountains will fall,
generally above 8000-9000ft, where WPC probabilities for at least 4
inches of snow are >50% above 10,000ft or so. Snow will end from
north to south over the San Juans and Sangre de Cristos Thursday
evening.

...Sierra Nevada...
Days 1&3...

Combination of a small upper low off the central/southern CA coast
tonight into Thursday with a trough axis across the Great Basin
will bring some light snow to the high Sierra tonight/Thursday.
Amounts may only be an inch or two with low probabilities of at
least 4 inches (<40%) as snow levels remain above 9000ft.

After a break on Day 2, a deeper trough with origins in the
northeastern Pacific will bring in a more robust moisture plume to
the West Coast on Day 3 (Saturday) that will continue into the
medium range. Through 00Z Sun, snow levels will be high (>9000ft)
with the initial surge in (modest) moisture, yielding low
probabilities for at least 4 inches of snow (<30%) in the central
Sierra as well as across the highest peaks of the Oregon Cascades.


The probability of significant freezing rain across the CONUS is
less than 10%.

Fracasso


$$

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FOUS11 KWBC 010703
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 AM EDT Thu May 1 2025

Valid 12Z Thu May 01 2025 - 12Z Sun May 04 2025


...Sierra Nevada...
Day 3...

A potent closed low will dig along the CA coast Saturday into
Sunday, with rapid amplification of this feature expected by Sunday
morning. This is reflected by NAEFS height anomalies falling to
below the 1st percentile with respect to 700-500mb heights over
southern CA by 12Z Sunday. Although the accompanying jet streak
will intensify as well as it pivots around the upstream side of
this trough and through the base, the overall evolution will keep
the most intense ascent displaced south/east of the Sierra, but
sufficient lift and increasing moisture will still result in
periods of snowfall D3. Snow levels during this time will begin
around 8000-9000 ft, so only the higher Sierra Passes will begin as
snow, but as the upper low digs across CA, snow levels are progged
to fall to as low as 7000 ft, bringing at least some accumulations
to Donner Pass as well. Overall, significant snowfall accumulation
will be confined to above pass level, where WPC probabilities for
more than 6 inches of snow are as high as 50%, but light snow down
to most Sierra Pass levels is also likely before precip winds down
by Sunday morning.


The probability of significant freezing rain across the CONUS is
less than 10%.

Weiss



$$

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FOUS11 KWBC 011822
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
222 PM EDT Thu May 1 2025

Valid 00Z Fri May 02 2025 - 00Z Mon May 05 2025


...Sierra Nevada...
Day 3...

A potent closed low will dig along the CA coast Saturday into
Sunday, with rapid amplification of this feature expected by Sunday
morning. This is reflected by NAEFS height anomalies falling to
below the 1st percentile with respect to 700-500mb heights over
southern CA between 12Z Sunday and 00Z Monday. Although the
accompanying jet streak will intensify as well as it pivots around
the upstream side of this trough and through the base, the overall
evolution will keep the most intense ascent displaced south/east of
the Sierra, but sufficient lift and increasing moisture will still
result in periods of snowfall D3. Snow levels during this time
will begin around 8000-9000 ft, so only the higher Sierra Passes
will begin as snow, but as the upper low digs across CA, snow
levels are progged to fall to as low as 7000 ft, bringing at least
some accumulations to Donner Pass as well. Overall, significant
snowfall accumulation will be confined to above pass level, where
WPC probabilities for more than 6 inches of snow are as high as
60%, but light snow down to most Sierra Pass levels is also likely
before precip winds down by Sunday midday.


The probability of significant freezing rain across the CONUS is
less than 10%.

Weiss/Snell






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FOUS11 KWBC 020709
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
309 AM EDT Fri May 2 2025

Valid 12Z Fri May 02 2025 - 12Z Mon May 05 2025


...Sierra Nevada...
Days 2-3...

An anomalous closed mid-level low (700-500mb heights reaching -3
sigma by Sunday aftn) will dive along the CA coast before turning
into the Four Corners states Sunday night. Impressive height falls
and downstream divergence will combine with a sharpening jet streak
to produce deep layer ascent across CA and into the Great Basin
late Saturday through late Sunday. This will result in expanding
coverage of precipitation, with snow likely in the higher terrain
of the Sierra. Initially, snow levels will be quite high, generally
8000-9000 ft, but as the closed low pivots south of the region,
colder air will funnel in and drop snow levels to 7000-7500 ft.
This will keep most of the heavy snow accumulations above the area
Passes, but at least light accumulations are possible even as low
as Donner Pass before precip wanes late Sunday. WPC probabilities
across the Sierra peak around 50% for 6+ inches of snow D2 into D3,
with the highest amounts expected in the higher terrain of the
southern Sierra where locally 8-10 inches is possible.


...Central Rockies...
Day 3...

A complex mid-level synoptic evolution will occur late in the
forecast period across the Intermountain West as the extremely
amplified flow across the CONUS exhibits minimal change into early
next week. Dual closed lows, one over the Ohio Valley and another
across the Four Corners will meander with little movement, as flow
stalls over the country. The important low for winter purposes will
be the one drifting across the Four Corners, which will shed
multiple lobes of vorticity around it as nearly a carousel of
shortwaves rotates southward from Canada and towards Baja and
around the primary closed low. The interaction of these shortwaves
with the primary low and secondary developing subtropical jet
streak will result in expanding precipitation, with snow likely in
the higher terrain of the San Juans before the close of D3 /12Z
Tuesday/. More significant precipitation, including more widespread
heavy snow across the Rockies, is possible beyond this forecast
period as a cold front drops through the region as well, but at
this time, for D3, WPC probabilities indicate a 70-90% chance of 6+
inches, focused in the higher elevations of the San Juans.



The probability of significant freezing rain across the CONUS is
less than 10%.

Weiss


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FOUS11 KWBC 021848
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
248 PM EDT Fri May 2 2025

Valid 00Z Sat May 03 2025 - 00Z Tue May 06 2025


...Sierra Nevada...
Days 1-3...

An anomalous closed mid-level low (700-500mb heights reaching -3
sigma by Sunday aftn) will dive along the CA coast before turning
into the Four Corners states Sunday night. Impressive height falls
and downstream divergence will combine with a sharpening jet streak
to produce deep layer ascent across CA and into the Great Basin
late Saturday through late Sunday. This will result in expanding
coverage of precipitation, with snow likely in the higher terrain
of the Sierra. Initially, snow levels will be quite high, generally
8000-9000 ft, but as the closed low pivots south of the region,
colder air will funnel in and drop snow levels to 7000-7500 ft.
This will keep most of the heavy snow accumulations above the area
Passes, but at least light accumulations are possible even as low
as Donner Pass before precip wanes late Sunday. WPC probabilities
across the Sierra peak around 50% for 6+ inches of snow D2, with
the highest amounts expected in the higher terrain of the southern
Sierra where locally 8-10 inches is possible.


...Central Rockies...
Days 2-3...

A complex mid-level synoptic evolution will occur late in the
forecast period across the Intermountain West as the extremely
amplified flow across the CONUS exhibits minimal change into early
next week. Dual closed lows, one over the Ohio Valley and another
across the Four Corners will meander with little movement, as flow
stalls over the country. The important low for winter purposes will
be the one drifting across the Four Corners, which will shed
multiple lobes of vorticity around it by the end of D2 as nearly a
carousel of shortwaves rotates southward from Canada and towards
Baja and around the primary closed low. The interaction of these
shortwaves with the primary low and secondary developing
subtropical jet streak will result in expanding precipitation, with
snow likely in the higher terrain of the northern/central Rockies
as well as the UT ranges by the close of D3 /00Z Tuesday/. Snow
levels are expected to remain rather high (9000-10000ft) outside of
the northern Rockies by Monday evening, where levels drop to
around 8000ft. More significant precipitation, including more
widespread heavy snow across the Rockies, is possible beyond this
forecast period as a cold front drops through the region. At this
time, primarily for D3, WPC probabilities indicate a 70-90% chance
of 6+ inches, focused in the higher elevations of the San Juans
above 11000ft with low probabilities (10-30%) for 12+ inches.



The probability of significant freezing rain across the CONUS is
less than 10%.

Weiss/Snell





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FOUS11 KWBC 030645
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
245 AM EDT Sat May 3 2025

Valid 12Z Sat May 03 2025 - 12Z Tue May 06 2025


...Sierra Nevada...
Days 1-3...

Light to at times moderate precipitation will persist across the
Sierra and Great Basin through Sunday as an anomalous closed low
drifts across CA and into the Four Corners region. Although this
feature will be impressive, the best ascent through height falls
and the overlapping of a subtropical jet streak rotating through
the base will occur east into a warmer column. This suggests that
the only significant accumulating snow will be across the Sierra,
generally above 7000 ft, with the heaviest accumulations in the
high southern Sierra. In this area, WPC probabilities indicate a
low to medium chance (30%) for 6+ inches both D1 and D2.


...Northern and Central Rockies...
Days 2-3...

The closed low drifting across the Desert Southwest Sunday will
lift slowly northeast into the Four Corners and then pause nearly
in place through the remainder of the forecast period. This slow
evolution is due to a highly amplified pattern across the CONUS
with dual closed lows bookending an impressive omega block across
the center of the Nation. With little impetus for features to move,
this will result in an extending period of unsettled weather
across the Rockies as height falls in the vicinity of the closed
low, modest diffluence within the LFQ of a modest but favorably
oriented upper jet streak, and a southeast advancing cold front
interact to provide broad and long-lasting lift to the region.

As this pattern evolves across the West, moisture will steadily
increase as a surge of theta-e lifts out of the Gulf and ascends
isentropically along the 305-310K surfaces as far north as CO and
UT as it wraps cyclonically around the low and into the Great
Basin. This will be most impressive late Monday into Tuesday thanks
to pinched and nearly unidirectional southerly flow through the
column helping to advance moisture return. Forcing impinging into
the moistening column will lead to rapid expansion of
precipitation, with much of the Intermountain West experiencing
rain and high-elevation snow beginning 00Z Monday, with periods of
heavy precipitation rates likely.

Snow levels during precipitation expansion will be quite high,
generally 9000-11000 ft across much of the Rockies. The exception
will be in the vicinity of a cold front dragging into ID/MT late
D2 into D3, behind which snow levels will crash to 4000-5500 ft.
These lowest snow levels are progged by the NBM to remain generally
north of Wyoming, but farther south into the Central and Southern
Rockies, snow levels will also fall beneath the core of the upper
low, reaching to 7000-8000 ft. These lowering snow levels will help
expand the wintry precipitation areas, with periods of heavy snow
becoming more widespread late D3, especially from ID through WY
where fgen along the front will drive more pronounced mesoscale
lift. It is across these areas, generally from Glacier NP southward
through the Absarokas, towards Yellowstone NP, and into the Wind
River range where snowfall will be heavy, as reflected by WPC
probabilities that reach as high as 50% for 6+ inches on D3.
Additionally, heavy snow accumulations exceeding 6" are likely D2
(70-90%) and possible D3 (30-50%)in the higher terrain of the San
Juans where storm-total snowfall of 10-15" is possible.

The probability of significant freezing rain across the CONUS is
less than 10%.

Weiss


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FOUS11 KWBC 031828
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
228 PM EDT Sat May 3 2025

Valid 00Z Sun May 04 2025 - 00Z Wed May 07 2025


...Sierra Nevada...
Days 1-2...

Digging upper trough just off the CA coast this evening will
deepen and close off as it moves into/through SoCal overnight and
early Sunday. The best dynamics will quickly move into the Interior
West, but light upslope-driven snow will continue over the
central/southern High Sierra with snow levels generally near/over
8000ft. Main upper low will move through AZ into the Four Corners
though trailing streams of vorticity from the north will keep light
snow going over the Sierra until late Monday. WPC probabilities
for at least 8 inches of snow are generally 20-60% for the High
Sierra (above 10,000ft).


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

Combination of the incoming upper low through the Southwest and a
slowly-moving trough axis in the northern stream pushing its way
across Montana will promote a period of unsettled weather for much
of the Interior West/Rockies through the period, including higher
elevation snow. The upper low is forecast to only move from
central AZ Monday morning to around the Four Corners region by
Tuesday morning then onto the western High Plains by the end of the
period as the upper jet carves out breaks down over the region.
This will favor an influx of moisture from the southeast
(TX/western Gulf) in combination with rotating vort maxes around
the main upper low atop a slowly-moving cold front at the surface
to the north (in addition to the one to the south ahead of the main
upper low). Snow levels will be high in the central/southern
Rockies, generally above the Front Range around 8000-10,000ft
(lowest beneath the cold core upper low) but lower farther north
behind the cold front to around 5000-7000ft across MT into WY. Snow
will be light to moderate and should maximize into the San Juans
via southerly flow but then into the CO Rockies and Sangre de
Cristos as the upper low moves eastward and the flow turns to more southeasterly to easterly and northeasterly later in the evolution
of the system. Snow to the north will be driven by the surface
front and low-level convergence, but with more limited moisture and
lighter snowfall amounts.

For the three-day period, WPC probabilities for at least 8 inches
of snow are above 50% across the terrain of southern UT into CO
above 10,000ft or so and are at least 40% for at least 18 inches of
snow above 12,000 ft. To the north, probabilities are a bit lower
for at least 8 inches of snow through the period (20-50%), mostly
over the Wind River Range, Uintas, and across SW MT.


The probability of significant freezing rain across the CONUS is
less than 10%.


Fracasso


$$

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FOUS11 KWBC 040722
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
322 AM EDT Sun May 4 2025

Valid 12Z Sun May 04 2025 - 12Z Wed May 07 2025



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

Stagnant but impressively amplified upper pattern characterized by
dual closed lows across the CONUS will result in increasing
precipitation beneath the slow moving vortex across the western
CONUS beginning today. The core of this low will emerge from the
Desert Southwest today before drifting slowly across the Four
Corners through Tuesday. On D3 /Tuesday into Wednesday/ a northern
stream impulse pushing a cold front southward will phase with the
larger gyre across the Four Corners bringing more widespread height
falls to the region, while also amplifying moist advection out of
the Gulf. This will lead to more impressive precipitation focused
across CO and northern NM, with snowfall occurring in the higher
terrain of the Front Range and Sangre de Cristos above generally
9000 ft. It is likely that the heaviest snowfall of the period
will occur D3 in this area as upslope flow combined with modest
fgen in the vicinity of the cold front and the large scale, but
broad, synoptic lift combine. This will result in heavy snow, for
which WPC probabilities suggest have a 70-90% chance of exceeding 8
inches in the Front Range and Sangre de Cristos, with 2-day
snowfall of 1-2 feet possible above 9000 ft. With periodic heavy
snow rates dragging down some colder air, especially in areas of
pronounced upslope, some light accumulations are possible in the
highest terrain of the Palmer Divide as well, impacting I-25.

Otherwise, during D1 and D2, heavy snow is likely across the San
Juans, generally above 10,000 ft, with more moderate snowfall
expected in the Sangre de Cristos (for the latter, this is separate
from the heavier snow D3). WPC probabilities across these areas are
high (>70%) for 6+ inches D1, and moderate (30-50%) D2.

Additionally, lighter snow accumulations are progged from the
Northern Rockies through the Absarokas and into the terrain around
Yellowstone NP, including the Wind River Range from D1 into D2
where WPC probabilities suggest there is a 30-50% chance for at
least 4 inches, and locally more than 8 inches is possible.

The probability of significant freezing rain across the CONUS is
less than 10%.


Weiss



$$

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FOUS11 KWBC 041851
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
251 PM EDT Sun May 4 2025

Valid 00Z Mon May 05 2025 - 00Z Thu May 08 2025


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

The very blocky upper pattern (typical for May during our
atmospheric spindown into summer) is manifesting itself as two
closed lows over the CONUS, the western one of which will be
responsible for a wintry thump of snow over the Rockies. As of
Sunday evening, the upper low will move from the CA deserts/CO
River Valley northeastward through AZ on Monday then into northern
NM Tuesday before finally moving into the Plains Wednesday. The
southern track of the upper system will keep the largest negative
anomalies (height and temperatures) over northern Mexico and
astride the southern US border, meaning snow levels will be on the
higher side over the Rockies (9000ft +/- 500ft). Later, colder air
will eventually advect in from the northeast (modestly) which
should decrease snow levels a bit to around 8000ft (and a bit lower
at times). Significant snow is expected for the mountains in CO
and northern NM with moderate to major impacts near/above the
treeline.

The storm system will progress in phases, with the initial WAA-
driven snow first on southerly flow D1 to be followed by jet/PVA-
driven snow as the upper low approaches northern NM D2 as the flow
turns to more easterly, maximizing upslope potential on the east
side of the Rockies. Finally by D3, as the system unwinds/extends,
and modest snow to start will gradually wind down but not fully end
until just after the end of this D3. Areas in favor of the most
snow include San Juans D1, Sangre de Cristos northward to the
higher elevations of the Front Range D2-3. There, snowfall rates of
1-3"/hr are possible (>50% probs for 2"/hr in the HREF) D2. WPC
probabilities for at least 8 inches of snow over the next three
days are highest (>50%) above 10,000ft with >50% probs for at least
18 inches above 12,000ft. As some colder air filters in early
Wednesday, some snow may fall into the higher elevations of the
I-25 corridor (Palmer Divide and Raton Mesa along the CO/NM
border).

Farther north, an incoming cold front will aid in producing some
mountain snow for the Uintas, Wind River Range, Absarokas and
Bighorns, and southwestern Montana where snow levels will be a bit
lower (6000-8000ft). There, WPC probabilities for at least 8 inches
of snow Days 1-2 are moderate to high (50-80%).

The probability of significant freezing rain across the CONUS is
less than 10%.


Fracasso



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FOUS11 KWBC 050653
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 AM EDT Mon May 5 2025

Valid 12Z Mon May 05 2025 - 12Z Thu May 08 2025


...Intermountain West...
Days 1-2...

The interaction of an anomalous and slow moving closed mid-level
low with a surface cold front wavering across the Central Rockies
will result in widespread heavy precipitation through Wednesday
before everything kicks out to the east during D3. The primary
mechanisms for ascent will be the intense closed low (500-700mb
height anomalies below the 1st percentile according to NAEFS) and a
cold front that will stall generally from the Dakotas across
Colorado and into the Great Basin. Intensifying and veering low to
mid level flow will encourage the impressive draw northward of
moisture, leading to robust isentropic ascent at 305K from the Gulf
into the Rockies on the downwind side of this feature. With
moisture confluence becoming impressive, ascent through height
falls and convergence along the front, aided by both strong upslope
flow (especially into the Sangre de Cristos and Front Range) and
elevated frontogenesis will wring out this moisture as expansive
and heavy precipitation from Montana through New Mexico.

Additionally, impressive easterly flow leading to the pronounced
upslope flow will correspond with some reduction (and isolated
folding) of the theta-e surfaces leading to some elevated
instability. This enhanced forcing combined with a lowering trend
in snow levels (NBM 10th% down to 7500 ft) could allow for more
impactful snow into lower elevations of the foothills, especially
across the Palmer Divide and Raton Mesa, including the I-25
corridor in that vicinity. After coordination with WFO BOU, opted
to raise SLRs a bit in this region for the potential, with some
impacts becoming more probable even east of the Front Range and
Sangres.

WPC probabilities across this area are high (>70%) for 6+ inches
both D1 and D2 in the San Juans, Sangre de Cristos, and Front
Range, with 1-2 feet of snow likely up around 9,000 ft, and locally
as much as 3+ feet above 10,000 ft. While accumulations in the
foothills and lower elevations down to 7,000 ft will be much less,
heavy snow rates with low-SLR could cause impacts even into the
I-25 corridor, especially Tuesday evening/night.

Farther north, snow levels will crash behind the cold front as it
sags southward, so while across WY and southern MT they too will
begin around 9,000 ft, by D2 snow levels are expected to fall to as
low as 6,000 ft, especially in MT and in the vicinity of
Yellowstone NP. Across this area, WPC probabilities are high
(70-90%) for 6+ inches D1 across the Absarokas and surrounding
elevations of southern MT, with probabilities reaching 50% across
the Wind Rivers, Big Horns, and in the vicinity of Yellowstone NP.

The probability of significant freezing rain across the CONUS is
less than 10%.


Weiss


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FOUS11 KWBC 051841
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
241 PM EDT Mon May 5 2025

Valid 00Z Tue May 06 2025 - 00Z Fri May 09 2025


...Intermountain West...
Days 1-2...

A deep upper low over AZ will slowly wobble eastward over the next
two days as an influx of Gulf moisture wraps in from the
southeast. This will set up a major winter storm for the high
elevations of the central/southern Rockies with snowfall rates of
1-3"/hr at times and total accumulations well over 1-2ft at the
highest peaks. The environment will be mild overall given the late
season timing and focus of colder air well south (central AZ/NM),
meaning that much of the I-25 corridor will remain snow-free
(except for the typical higher elevations along the corridor in the
Palmer Divide and Raton Mesa). The system will become elongated
and stretch eastward tomorrow which will signal the end of modest
snow, but lighter snow will persist into the evening/overnight and
largely end by Thursday morning.

The system will come in two phases for many areas, with the lead-
in WAA-driven lighter snow early D1 (tonight) and the dynamically-
driven heavier snow tomorrow by the afternoon through the evening
as the upper low approaches the central CO/NM border from the WSW.
Models indicate a robust system with strong isentropic ascent at
the 305K level from the Gulf and strong/anomalous/record easterly
flow at 700mb by midday tomorrow (per the CFSR period). As can be
typical with strong systems, dynamical cooling may bring down snow
levels from ~8000-8500ft to 7500ft or so, reaching farther down the
Front Range toward the high elevations of the I-25 corridor before
then rising as the upper low pulls away.

Favored areas for the heaviest snowfall are over the San Juans
this evening/overnight on southerly to southeasterly flow, then
transitioning to the east/upslope side of the CO Rockies and into
the Sangre de Cristos. Total snow may be 2-3ft (perhaps more) at
the highest elevations including Pike's Peak and along the spine of
the Sangre de Cristos. Impacts will be moderate to major per the
WSSI. WPC probabilities for at least 8 inches of snow over the next
two days are >50% above 8500ft or so and >50% above 10,500ft or
so. Depending on the time of day and amount of dynamical cooling,
there are low probabilities (10-40%) of at least 2 inches of snow
as low as 6500ft or so.

Farther north, snow levels will continue to fall behind a cold
front currently through WY with precipitation trailing to its
northwest through Montana, tied to northern stream
troughing/vorticity diving south-southwestward tonight/early
tomorrow. This rain/snow will continue to progress southward, with
snow levels around 6000-8000ft from north to south, favoring snow
over portions of southern MT, the Absarokas, and into the Bighorns
and Wind River Range. There, WPC probabilities of at least 8 inches
of snow are at least 30% (highest in the Absarokas).

The probability of at least 4 inches of snow on day 3 are less
than 10%.

The probability of significant freezing rain across the CONUS is
less than 10%.


Fracasso


$$

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FOUS11 KWBC 060728
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EDT Tue May 6 2025

Valid 12Z Tue May 06 2025 - 12Z Fri May 09 2025


...Central and Southern Rockies...
Days 1-2...

Pinwheeling upper lows within a larger gyre centered over the Four
Corners will continue to produce significant winter weather in the
higher elevations of the Rockies through Wednesday morning.

The first, and less impressive, area of snow is expected to drift
south across WY today as a cold front driven southward by a
vorticity center drops through the area. Height falls and
convergence along the front will produce ascent, with post-frontal
upslope aiding ascent. PWs this far north will be somewhat less
impressive than points farther south, but an impressive stream of
moisture emerging from the Gulf will lead to PW anomalies above the
90th percentile into WY on D1. With snow levels fall from as high
as 9000 ft near Cheyenne to around 5000 ft around Yellowstone,
significant accumulations are likely in the favored upslope
terrain, especially above 7000 ft, before precip wanes after 00Z
Wednesday. Additional snow after 12Z Tuesday (beginning of D1) will
be modest, but WPC probabilities suggest a low-risk (10-30%) for an
additional 2-4 inches of snow.

Farther south, a more significant snowfall is expected from the
Front Range through the Sangre de Cristos, potentially including
portions of the I-25 urban corridor. The larger upper low swinging
across NM will pivot slowly eastward leading to height falls to
drive synoptic lift, while moisture surging northward from the Gulf
pivots NW as a theta-e ridge into the region. Low-level flow will
become increasingly from the east, leading to additional ascent
through upslope flow and isentropic ascent as weak high pressure
builds down the terrain. This will induce impressive lift from the
Sangres northward into the Front Range, which could produce
snowfall rates of 1-3"/hr at times as reflected by the WPC
prototype snowband tool. These rates will be confined to the
highest terrain, generally above 8500 ft, but folding theta-e
surfaces within the terrain and in the presence of the
strengthening barrier jet and accompanying ascent will likely lead
to dynamic cooling to allow snow accumulations falling to as low as
7000 ft, below the NBM 10th percentile. While the heaviest snow
accumulations will remain above 9,000 ft, light but impactful snow
is possible into the Foothills including the Palmer Divide and
Raton Mesa, with hazardous travel possible along portions of I-25.

As far as accumulations, this does appear to be a significant event
and the latest EFI suggests a higher than 95% probability of an
extreme event with SoT exceeding 2 in the Sangre de Cristos. In
this area, heavy snow accumulating to above 8 inches is likely

70%) from the Front Ranges through the southern Sangre de

Cristos, and including portions of the San Juans and eastern CO
Rockies. 1-2 feet of snow is likely above 9,000 feet, with 3 feet
or more expected in the highest peaks such as Pike's Peak. Farther
east, light snow of a few inches remains possible, especially
across the Palmer Divide and Raton Mesa, impacting the portion of
I-25 that traverses those crests. Most of this snow occurs D1, as
by D2 only lingering probabilities for 4+ inches continue across
the San Juans.


The probability of significant freezing rain across the CONUS is
less than 10%.


Weiss


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FOUS11 KWBC 061831
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
231 PM EDT Tue May 6 2025

Valid 00Z Wed May 07 2025 - 00Z Sat May 10 2025


...Central and Southern Rockies...
Days 1-2...

Upper low over northeastern NM this evening will continue eastward
and pull away from the Rockies, allowing any moderate/heavy snow
to taper to light snow into Wednesday. For this evening, the strong
moisture plume from the western Gulf will support snowfall rates
of 1-2"/hr over parts of the CO Rockies into the Sangre de Cristos
before lessening in intensity and becoming lighter Wednesday
morning. For Wednesday itself, troughing will remain over the
central Rockies and a trailing smaller/compact upper low over the
CA/AZ border will act to prolong the rebound in heights, allowing
some light snow to persist over the San Juans tomorrow afternoon.
By tomorrow night into Thursday, heights will rise as will snow
levels, confining only light snow to the highest mountain peaks
above 11,000ft or so.

WPC probabilities for at least 8 inches of snow after 00Z tonight
are >50% above 10,000ft or so. Some snow is possible down to around
7000ft this evening.

The probability of at least 4 inches of snow on day 3 is less than
10 percent.

The probability of significant freezing rain across the CONUS is
less than 10%.


Fracasso


$$

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FOUS11 KWBC 070646
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
246 AM EDT Wed May 7 2025

Valid 12Z Wed May 07 2025 - 12Z Sat May 10 2025


...Central and Southern Rockies...
Day 1...

Closed low over the Central Rockies will finally begin to fill and
lift off to the east today, while a secondary closed mid-level
impulse rotates cyclonically around it, moving over the Four
Corners tonight while dissipating. This evolution will result in
the primary forcing beginning to weaken over CO and NM due to
weaker lapse rates aloft, a lack of height falls, and decreasing
upslope flow. While this will force the most significant
precipitation to wind down quickly after 12Z this morning, the
secondary feature moving into the region will maintain at least
modest ascent and steepened lapse rates into tonight. This will
shift the focus of the heaviest snowfall from the Front Range and
Sangre de Cristos Tuesday night/Wednesday morning, to the San
Juans. Snow levels will remain elevated, around 8000-9000 ft,
keeping the heaviest snow confined to the highest terrain, and WPC probabilities suggest a moderate risk (50%) for at least an
additional 6 inches of snow across the San Juans.


The probability of significant freezing rain across the CONUS is
less than 10%.


Weiss



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FOUS11 KWBC 071814
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
214 PM EDT Wed May 7 2025

Valid 00Z Thu May 08 2025 - 00Z Sun May 11 2025


...Colorado...
Day 1...

Lingering vorticity on the western side of the departing upper low
will still trigger some light snow over the San Juans this evening
before tapering off tonight/early Thursday. WPC probabilities for
at least an additional 4 inches of snow after 00Z are low (10-40%)
above 11,000ft.

For days 2-3, the probability of at least 4 inches of snow is less
than 10%.

The probability of significant freezing rain across the CONUS is
less than 10%.

Note - this is the last regularly scheduled discussion (QPFHSD)
for the 2024-2025 winter season. Unless a significant winter
weather threat emerges, this discussion will next be updated on or
about September 25, 2025.


Fracasso



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FOUS11 KWBC 250728
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EDT Thu Sep 25 2025

Valid 12Z Thu Sep 25 2025 - 12Z Sun Sep 28 2025

Note: Beginning today, WPC has officially resumed staffing the
Winter Weather Desk for the upcoming 2025-26 cold season.

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.

Mullinax

$$

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FOUS11 KWBC 280728
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EDT Sun Sep 28 2025

Valid 12Z Sun Sep 28 2025 - 12Z Wed Oct 01 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Mullinax



$$

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FOUS11 KWBC 281806
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
206 PM EDT Sun Sep 28 2025

Valid 00Z Mon Sep 29 2025 - 00Z Thu Oct 02 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Snell




$$

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FOUS11 KWBC 290728
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EDT Mon Sep 29 2025

Valid 12Z Mon Sep 29 2025 - 12Z Thu Oct 02 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Mullinax







$$

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FOUS11 KWBC 291732
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
132 PM EDT Mon Sep 29 2025

Valid 00Z Tue Sep 30 2025 - 00Z Fri Oct 03 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Weiss


$$

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FOUS11 KWBC 300748
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Tue Sep 30 2025

Valid 12Z Tue Sep 30 2025 - 12Z Fri Oct 03 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Mullinax




$$

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FOUS11 KWBC 251735
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
135 PM EDT Thu Sep 25 2025

Valid 00Z Fri Sep 26 2025 - 00Z Mon Sep 29 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Weiss


$$

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FOUS11 KWBC 260722
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
322 AM EDT Fri Sep 26 2025

Valid 12Z Fri Sep 26 2025 - 12Z Mon Sep 29 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Mullinax





$$

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FOUS11 KWBC 261821
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
221 PM EDT Fri Sep 26 2025

Valid 00Z Sat Sep 27 2025 - 00Z Tue Sep 30 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Snell



$$

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FOUS11 KWBC 270728
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EDT Sat Sep 27 2025

Valid 12Z Sat Sep 27 2025 - 12Z Tue Sep 30 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Mullinax






$$

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FOUS11 KWBC 271910
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
310 PM EDT Sat Sep 27 2025

Valid 00Z Sun Sep 28 2025 - 00Z Wed Oct 01 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.


Snell





$$

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FOUS11 KWBC 301820
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
220 PM EDT Tue Sep 30 2025

Valid 00Z Wed Oct 01 2025 - 00Z Sat Oct 04 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.

Fracasso

$$

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FOUS11 KWBC 010720
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
320 AM EDT Wed Oct 1 2025

Valid 12Z Wed Oct 01 2025 - 12Z Sat Oct 04 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.

Mullinax


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FOUS11 KWBC 011801
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
201 PM EDT Wed Oct 1 2025

Valid 00Z Thu Oct 02 2025 - 00Z Sun Oct 05 2025

The probability of significant snow and ice accumulations across
the CONUS is less than 10 percent.

Fracasso


$$

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FOUS11 KWBC 020626
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
226 AM EDT Thu Oct 2 2025

Valid 12Z Thu Oct 02 2025 - 12Z Sun Oct 05 2025

...Northern Rockies...
Day 3...

An upper low over the Great Basin on Friday opens into a trough and
shifts east over the Rockies late Saturday. Lee-side cyclogenesis
over western South Dakota occurs during this time enhancing flow
from Gulf-sourced moisture over the Plains through the northern
Rockies. Snow levels through Saturday are around 9000ft over the
Absarokas, Wind Rivers, and Bighorns, above which probs for >6"
snow from 12Z Saturday to 12Z Sunday are 40-80%.


The probability of significant icing is less than 10 percent.


Jackson


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FOUS11 KWBC 021827
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
227 PM EDT Thu Oct 2 2025

Valid 00Z Fri Oct 03 2025 - 00Z Mon Oct 06 2025

...Northern Rockies...
Day 3...

Dual shortwaves embedded within amplifying troughing across the
western CONUS will result in the first significant snowfall across
the higher terrain of the Northern Rockies beginning Saturday
night.

A closed low exiting the Great Basin will begin to fill as it
pivots northeast and shear out in the westerlies, reaching the
Northern Plains by 12Z Sunday. Immediately in its wake, a secondary
impulse, albeit of weaker intensity, will drop into the Northern
Rockies, driving additional height falls into portions of MT and
WY. This secondary impulse will be accompanied by a cold front
digging southward at the surface, leading to cooling temperatures
and additional ascent through forced upslope. Although the greatest
moisture (PWs above the 90th percentile according to NAEFS) will
shift steadily northeast away from the region, as a surface low
strengthens over the Northern Plains, at least some theta-e ridging
will pivot westward back into WY at the same time mid-level SW flow
re-ignites over the region downstream of the secondary impulse.
This will provide sufficient moisture to regenerate precipitation,
with much of this turning to snow from the Northern Rockies to the
Absarokas, and into the ranges of NW WY including the Tetons, Big
Horns, and around Yellowstone NP. As snow levels fall to as low as
7000 ft late in the period, WPC probabilities for more than 6
inches of snow climb to above 70% across this region, with locally
as much as 12 inches possible (10-30%) in the highest terrain of
the Big Horns and Absarokas.

The probability of significant icing is less than 10 percent.

Weiss





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FOUS11 KWBC 030808
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Fri Oct 3 2025

Valid 12Z Fri Oct 03 2025 - 12Z Mon Oct 06 2025

...Northern Rockies...
Days 2-3...

A pair of shortwaves moving across the Intermountain West will
interact with well above normal amounts of atmospheric moisture in
the area to cause the area's first winter storm of the season at
the higher elevations from Glacier NP in northern Montana south and
east through the ranges of northern and western Wyoming through
Sunday. The first shortwave begins the period Saturday morning over
Utah, and then tracks northeast towards the northern Plains by
Sunday morning. As the stronger of the two shortwaves getting first
dibs at the excess moisture across the area, expect heavier and
longer duration snow across the ranges of far southern Montana and
northwestern Wyoming, including Yellowstone and Grand Teton NPs.
Snowfall amounts of 6-12 inches are expected at the highest
elevations where the snow is most persistent.

As that first shortwave tracks into the Plains Sunday morning, the
second shortwave rounding the back of the longwave trough will dive southeastward out of Alberta through much of Montana from Saturday
night through much of the day on Sunday. This shortwave will result
in a period of heavy snow across much of Glacier NP late Saturday
night through Sunday morning. This secondary forcing will keep the
snow that began with the first shortwave Saturday ongoing through
Sunday. The snow will end from north to south Sunday and Sunday
night. WPC probabilities for more than 6 inches of snow remain over
50% for the Beartooth and Absaroka Ranges.

The probability of significant icing is less than 10 percent.

Wegman



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FOUS11 KWBC 031808
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
208 PM EDT Fri Oct 3 2025

Valid 00Z Sat Oct 04 2025 - 00Z Tue Oct 07 2025

...Northern Rockies...
Days 2-3...

Dynamic longwave pattern will transpire across the western CONUS
as we move into the weekend with a deep closed upper-low over the
Great Basin pivoting northeast into the northern Rockies before
opening up into a relatively strong negatively-tilted shortwave
trough before exiting. Strong height-falls occurring over the Basin
through the northern Rockies will allow for freezing levels to
plummet over the course of Friday night into Saturday, continuing
further into early Sunday morning. Combination of falling heights
and strong upper-level ascent across the region mixing with
elevated PWATs will generate a transition from rain to snow across
portions of the Tetons over into the Absaroka/Beartooth Ranges of
MT/WY, followed by the Big Horn mountains a bit downstream. Snow
levels will tumble to around 7000ft MSL by Sunday morning across
the terrain with a reasonable precip distribution contributing to
periods of moderate to locally heavy snow within the terrain and
adjacent foothills.

As that negatively-tilted shortwave tracks into the Plains Sunday
morning, a second shortwave rounding the back of the longwave
trough will dive southeastward out of Alberta through much of
MT from Saturday night through much of the day on Sunday. This
shortwave will result in a period of heavy snow across much of
Glacier NP late Saturday night through Sunday morning. This
secondary forcing will keep the snow that began with the first
shortwave Saturday ongoing through Sunday. The snow will end from
north to south Sunday and Sunday night. WPC probabilities for more
than 6 inches of snow remain between 50-90% for the Beartooth,
Absaroka, and Big Horn Ranges.

The probability of significant icing is less than 10 percent.

Wegman/Kleebauer






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FOUS11 KWBC 040724
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
324 AM EDT Sat Oct 4 2025

Valid 12Z Sat Oct 04 2025 - 12Z Tue Oct 07 2025

...Northern Rockies...
Days 1-2...

The weather pattern across the northern Rockies remains very
similar to previous runs of the guidance. The dynamic upper level
pattern will feature a deep upper level low over Utah ejecting
northeastward into the northern Plains by early Sunday morning.
Anomalous moisture to 2.5 sigma above normal will support waves of
showers and a few thunderstorms tracking northeastward as a
developing leeside low becomes the dominant surface feature through
the weekend. The leeside low will take advantage of a shortwave
trough also pushing northeastward. This will allow the surface low
to intensify as it makes its way to the Plains. Combined with
upslope enhancement, these ingredients all coming together will
lead to a prolonged period of heavy snow. The Beartooth, Absaroka,
and Big Horn Ranges will all come in with over 50% probabilites
for 6 inches or more of snow or more through Sunday. Behind this
first, stronger shortwave, a second shortwave will dive south out
of Alberta and into the Northern Rockies on Sunday. The presence of
this second shortwave will support maintaining heavy snow into
northern MT, especially Glacier NP. This digging second shortwave
will allow the larger longwave trough to remain in place, even
expanding and growing south and west. Similarly important to the
presence of these 2 shortwaves moving through the flow and taking
advantage of the abundant low level moisture, a large polar surface
high will effectively end the wintry threat from north to south.
This is because the polar high will also be quite dry, so it will
move the moisture feeding the snow on towards the north and east.
With that polar low in place, expect temperatures to tumble well
down into the 30s. Thus, as is very common in the wintertime, the
limited time between the advancing cold/dry air and the retreating
atmospheric moisture will favor certain areas, such as the
Beartooth Range, while keeping many others on the Plains bone dry.
With the advancing cold air, snow levels will fall to as low as
5,000 ft, but the dryness should hold any heavy snow occurring to
Sunday morning, before the snow ends from north to south.

WPC probabilities for 6 inches or more of snow remain between 50
and 90% for the Beartooth and Absarokas, while probabilities are a
bit lower, between 60 and 80% for the Wind River and Bighorn
ranges.

The probability of significant icing is less than 10 percent.

Wegman



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FOUS11 KWBC 041812
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
212 PM EDT Sat Oct 4 2025

Valid 00Z Sun Oct 05 2025 - 00Z Wed Oct 08 2025

...Northern Rockies...
Days 1-2...

Upper level progression remains steadfast from previous forecasts
with the closed upper reflection now analyzed as a vigorous open
wave taking on a negative tilt as it migrates northeast out of the
Great Basin into the adjacent northern Rockies. Consensus on heavy
snow beginning across the higher terrain of southwest MT into
northwest WY later this afternoon remains with some of the ridges
likely to have switched over in the past few hrs. as heights
continue to fall precipitously with the upper level progression. At
the surface, a strong surface reflection is analyzed over the UT/CO
border with an expected progression to the north-northeast over the
next 24 hrs. The combination of a favorable upper level
progression and strengthening axis of deformation over southern MT
and northern WY will lead to a significant heavy snow event, the
first of the season across the Absaroka/Beartooth/Wind River ranges
with the Big Horns getting into the heavy snow threat a little
later this evening as the height falls shift east. Heavy snow is
likely over these ranges overnight into early tomorrow morning
leading to rates between 1-2"/hr at times generating a swath of 6+"
totals a likelihood by the time we reach sunrise tomorrow.

Behind this first, stronger shortwave, a second shortwave will
dive south out of Alberta and into the Northern Rockies on Sunday.
The presence of this second shortwave will support maintaining
heavy snow into northern MT, especially Glacier NP. This digging
second shortwave will allow the larger longwave trough to remain in
place, even expanding and growing south and west. Similarly
important to the presence of these 2 shortwaves moving through the
flow and taking advantage of the abundant low level moisture, a
large polar surface high will effectively end the wintry threat
from north to south. This is because the polar high will also be
quite dry, so it will move the moisture feeding the snow on towards
the north and east. With that polar low in place, expect
temperatures to tumble well down into the 30s. Thus, as is very
common in the wintertime, the limited time between the advancing
cold/dry air and the retreating atmospheric moisture will favor
certain areas, such as the Beartooth Range, while keeping many
others on the Plains bone dry. With the advancing cold air, snow
levels will fall to as low as 5,000 ft, but the dryness should hold
any heavy snow occurring to Sunday morning, before the snow ends
from north to south.

WPC probabilities for 6 inches or more of snow remain elevated between
50 and 90% for the Beartooth, Absarokas, and Big Horn ranges while probabilities are a bit lower, between 60 and 80% for the Wind
River range.

The probability of significant icing is less than 10 percent.

Wegman/Kleebauer






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FOUS11 KWBC 050704
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
304 AM EDT Sun Oct 5 2025

Valid 12Z Sun Oct 05 2025 - 12Z Wed Oct 08 2025

...Northern Rockies...
Day 1...

A positively-tilted upper level trough stretching from the northern
Plains to Central California is directing much smaller shortwave
troughs around its periphery. As each shortwave moves across the
area, they've been producing an area of rain and higher elevation
snow as a surface low develops in response to the movement of the
individual shortwaves. The first shortwave is moving over the
Dakotas and taking a well-developed surface low along with it. The
surface lows have been taking advantage of an anomalous plume of
moisture from the northern Rockies to the northern Plains. This
abundance of moisture has helped support areas of snow at the
highest elevations. As the low pulls away, there may be a brief
break in the steadiest precipitation into the mountains. Meanwhile,
a second trough, not as strong but still potent, is diving south
across Idaho and will slow and turn eastward across southern
Wyoming by Monday morning. Behind this shortwave a strong polar
high will dive southward, bringing with it a much colder and drier
air mass. The combination of subsidence with the high, and the dry
air will very quickly end the snow from north to south. Into the
Beartooths and Absarokas, enough moisture may hang on to keep much
lighter snow ongoing into Tuesday morning in a few isolated areas.
By Tuesday morning, the entire longwave trough will have moved
eastward, allowing strong ridging to build into the West Coast.
This feature too will act to limit the heaviest precipitation in
all areas as subsidence works to end the snow.

With the overall forecast largely unchanged, we will see the back
edge of the precipitation move southeastward out of Canada and into
Montana by Monday afternoon. While localized upslope is a
possibility, the drier air with the advancing area of surface high
pressure will quickly win out, allowing some areas to get some
sunshine this afternoon.

WPC probabilities for over 8 inches of snow are between 60 and 80
percent for the Bighorns and Wind River Ranges through Monday
morning.

The probability of significant icing is less than 10 percent.


Wegman



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FOUS11 KWBC 051821
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
221 PM EDT Sun Oct 5 2025

Valid 00Z Mon Oct 06 2025 - 00Z Thu Oct 09 2025

...Northern Rockies...
Day 1...

Broad positively tilted upper trough across the Northern Rockies
will maintain prevalence over the next 12-24 hrs with a strong
surface ridge pressing down out of Alberta in tandem with a
shortwave progressing around the trough base, currently analyzed
over the southern portion of the ID/MT border. Forecast has been
largely unchanged with the current radar/sat composite indicating a
prevailing upslope regime across the Absaroka and northern Big
Horns with an expectation for precip to ignite over the course of
the afternoon and evening as we move into the Wind River range.
This is thanks to the progression of the shortwave migrating out of
ID leading to the final chapter in the first heavy snow event of
the season for the northern Rockies. Additional accumulations of
4-8", local to 12" are anticipated across the higher terrain

8000ft MSL) with a respectable 3-6" for areas between

5500-7000ft MSL. Light snow accumulations will be forecast below
5000ft MSL, but impacts will be negligible in the grand scheme.

WPC probabilities for the remainder of the event (00-12z Monday)
still hover between 50-70% for an additional 4+" over the Wind
River Range, but a surge of drier air with the incoming surface
ridge and vacating shortwave will lead to a quick decay of snow
chances from north to south as we move through the rest of the D1.
By tomorrow morning, snow will taper off to just scattered light
snow with only smaller additional accums expected. The threat for
winter weather will be over prior to 18z.

The probability of significant icing is less than 10 percent.


Kleebauer





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FOUS11 KWBC 060600
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
200 AM EDT Mon Oct 6 2025

Valid 12Z Mon Oct 06 2025 - 12Z Thu Oct 09 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Wegman

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FOUS11 KWBC 061713
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
113 PM EDT Mon Oct 6 2025

Valid 00Z Tue Oct 07 2025 - 00Z Fri Oct 10 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Wegman/Kleebauer




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FOUS11 KWBC 070630
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
230 AM EDT Tue Oct 7 2025

Valid 12Z Tue Oct 07 2025 - 12Z Fri Oct 10 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Wegman


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FOUS11 KWBC 080600
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
200 AM EDT Wed Oct 8 2025

Valid 12Z Wed Oct 08 2025 - 12Z Sat Oct 11 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Wegman

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FOUS11 KWBC 071849
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Tue Oct 7 2025

Valid 00Z Wed Oct 08 2025 - 00Z Sat Oct 11 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Mullinax



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FOUS11 KWBC 081914
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Wed Oct 8 2025

Valid 00Z Thu Oct 09 2025 - 00Z Sun Oct 12 2025

The probability of significant snow and ice across the CONUS is
less than 10 percent.

Mullinax




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FOUS11 KWBC 090719
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 AM EDT Thu Oct 9 2025

Valid 12Z Thu Oct 09 2025 - 12Z Sun Oct 12 2025

...Northern Rockies...
Day 3...

By the end of the short range forecast period (Sunday morning) a
sharp, negatively-tilted upper trough is forecast to impact the
northern Rockies with moderate to heavy precipitation and lowering
snow levels. The upper trough configuration is expected to develop
as a closed-low currently off the coast of the Pacific Northwest
opens up and interacts with a diving shortwave out of British
Columbia. Additionally, this pattern is favorable for increasing
upper jet dynamics and is supported by model guidance depicting a
120-140kt southwesterly jet streak extending from the central
Great Basin to the central/northern Rockies. This places the
northern Rockies in the left-exit region of the upper jet and most
favorable for upper divergence and widespread moderate
precipitation. As the upper trough moves over the region Sat night
(500 mb heights estimated to be just below the 10th climatological
percentile per the 12z NAEFS) snow levels are expected to also fall
below 6,500ft across much of the northern Rockies by early Sunday
and below 5,000ft across the Pacific Northwest, where lighter
precipitation will be located.

The most impactful snowfall through this timeframe is expected to
be located across southwest Montana as moderate precipitation
overlaps with the lowering snow levels. Latest WPC probabilities
for at least 6 inches of snowfall are 20-40% across the high
terrain of southwest Montana above 8,000ft, which is still above
many of the major mountain passes. Additionally, WSSI-P values for
moderate impacts reach 30-40% in these areas primarily due to snow
load concerns.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell



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FOUS11 KWBC 091923
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
323 PM EDT Thu Oct 9 2025

Valid 00Z Fri Oct 10 2025 - 00Z Mon Oct 13 2025

...Northern Rockies...
Day 3...

A strong upper-level trough traversing the Pacific Northwest on
Saturday will provide ample upper-level ascent over the Northern
Rockies Saturday night and into Sunday. The EPS shows a classic
"kissing jets" setup Saturday night with the diffluent left-exit
region of a strong 120-140 kt 250mb jet over Utah and the diffluent right-entrance region of a >100kt 250mb jet over south-central
Canada both located over western Montana. ECMWF PWAT percentiles
are likely to remain above the 90th climatological percentile
through early Sunday morning with ample moisture aloft to saturate
the DGZ over the Absaroka, Lewis Range, and Tetons. There remains
plenty of uncertainty with varying solutions on the depth/phasing
of two 500mb disturbances over the Northwest. The GFS is the most
amplified of the bunch but is is more amplified compared to the
GEFS mean, while the ECMWF/UKMET/EC-AIFS are in the middle ground
compared to the more overly amplified GFS and weaker/sheared CMC
solution.

With a lack of sub-freezing air ahead of the trough, even with a
encroaching colder, western Canadian high pressure system on
Sunday, this setup tends to favor the higher elevations of the
Northern Rockies. While a more amplified solution like the GFS
cannot be ruled out yet, the antecedent air-mass both ahead of the
storm and trailing behind the system are not overly impressive for
mid-October. As high pressure builds in from the north, colder
temperatures and easterly upslope flow will keep snow lingering
along the Lewis Range into Sunday night. Snowfall rates could
approach 1"/hr in the Lewis Range and around Glacier Nat'l Park
Sunday morning, which could also foster hazardous travel conditions
in nearby passes.

WPC probabilities depict moderate chances (40-60%) for snowfall >8"
in the peaks of the Lewis Range above 7,000ft (including Glacier
Nat'l Park) on south along the Absaroka/Tetons above 8,000ft
through Sunday afternoon. Lighter snowfall accumulations as low as
6,000ft in the Lewis Range/northwest Montana and 7,000ft in the
Absaroka/Tetons are expected. WPC's Probabilistic Winter Storm
Severity Index (WSSI-P) show similar moderate chances for Minor
Impacts for the event in these mountain ranges. Other mountain
ranges are likely to receive light snow totals (2-4") as far west
as the Bitterroots and as far south as the Teton and Wind River
Ranges in western Wyoming.

The probability of significant freezing rain across CONUS is less
than 10 percent.

Mullinax



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FOUS11 KWBC 100748
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Fri Oct 10 2025

Valid 12Z Fri Oct 10 2025 - 12Z Mon Oct 13 2025

...Northern Rockies & WA Cascades...
Days 2-3...

A strong upper-level trough traversing the Pacific Northwest on
Saturday will provide ample upper-level ascent over the Northern
Rockies Saturday night and into Sunday. The EPS shows a classic
"kissing jets" setup Saturday night with the diffluent left-exit
region of a strong 120-140 kt 250mb jet over Utah and the diffluent right-entrance region of a >100kt 250mb jet over south-central
Canada both located over western Montana. 18z ECMWF depicts PWAT
percentiles are likely to remain above the 90th climatological
percentile through early Sunday morning with ample moisture aloft
to saturate the DGZ over the Absaroka, Lewis Range, and Tetons.
There remains some uncertainty with varying solutions on the
depth/phasing of two 500mb disturbances over the Northwest. The GFS
is the most amplified of the bunch and is more amplified compared
to the GEFS mean, while the ECMWF/UKMET/EC-AIFS are in the middle
ground compared to the more overly amplified GFS and weaker/sheared
CMC solution.

With a lack of sub-freezing air ahead of the trough, even with a
encroaching colder, western Canadian high pressure system on
Sunday, this setup tends to favor the higher elevations of the
Northern Rockies. While a more amplified solution like the GFS
cannot be ruled out yet, the antecedent air-mass both ahead of the
storm and trailing behind the system are not overly impressive for
mid-October. As high pressure builds in from the north, colder
temperatures and easterly upslope flow will keep snow lingering
along the Lewis Range into Sunday night. Snowfall rates could
approach 1"/hr in the Lewis Range and around Glacier Nat'l Park
Sunday morning, which could also foster hazardous travel conditions
in nearby passes.

Additionally, a separate upper low is forecast to drop south into
the Pacific Northwest on Sunday within the same longwave western
U.S. trough. This will allow for snow levels to remain rather low
for this time of year (around and slightly below 4,000 ft) across
the WA Cascades along with favorable upper ascent, which may lead
to some light accumulating snow for the major mountain passes.

WPC probabilities through early Monday depict moderate chances
(40-70%) for snowfall >8" in the peaks of the Lewis Range above
6,000ft (including Glacier Nat'l Park) on south along the
Absaroka/Tetons above 8,000ft through Sunday afternoon. Lighter
snowfall accumulations as low as 5,000ft in the Lewis
Range/northwest Montana and 7,000ft in the Absaroka/Tetons are
expected. WPC's Probabilistic Winter Storm Severity Index (WSSI-P)
show similar chances for Minor Impacts for the event in these
mountain ranges. Other mountain ranges are likely to receive light
snow totals (2-4") as far west as the Bitterroots and as far south
as the Teton and Wind River Ranges in western Wyoming.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell/Mullinax




$$

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FOUS11 KWBC 101926
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
326 PM EDT Fri Oct 10 2025

Valid 00Z Sat Oct 11 2025 - 00Z Tue Oct 14 2025

...Northern Rockies & WA Cascades...
Days 2-3...

A strong upper-level trough traversing the Pacific Northwest on
Saturday will provide ample upper-level ascent over the Northern
Rockies Saturday night and into Sunday. The synoptic-scale snapshot
of this setup features a classic "kissing jets" setup aloft
Saturday night with the diffluent left-exit region of a strong
120-140 kt 250mb jet over Utah and the diffluent right-entrance
region of a >100kt 250mb jet over south-central Canada, both
located over western Montana. Guidance across the board indicate
PWAT percentiles are likely to remain above the 90th climatological
percentile through early Sunday morning with ample moisture aloft
to saturate the DGZ over the Absaroka, Lewis Range, and Tetons.
There remains some uncertainty with varying solutions on the
depth/phasing of two 500mb disturbances over the Northwest. The GFS
remains the most amplified of the bunch, while the ECMWF/UKMET/EC-
AIFS are in the middle ground compared to the more overly amplified
GFS and weaker/sheared CMC solution.

With a lack of sub-freezing air ahead of the trough, even with a
encroaching colder, western Canadian high pressure system on
Sunday, this setup tends to favor the higher elevations of the
Northern Rockies. The antecedent air-mass both ahead of the storm
and trailing behind the system are not exceptionally cold for mid-
October. As high pressure builds in from the north, colder
temperatures and easterly upslope flow will keep snow lingering
along the Lewis Range into early Monday morning. Snowfall rates
could approach 1"/hr in the Lewis Range and around Glacier Nat'l
Park Sunday morning, which could also foster hazardous travel
conditions in nearby passes.

Farther west, a separate upper low is forecast to drop south into
the Pacific Northwest on Sunday within the same longwave western
U.S. trough. Snow levels to remain rather low for this time of year
(around and slightly below 4,000 ft) across the WA Cascades along
with favorable upper ascent, which may lead to some light
accumulating snow for the major mountain passes. Most snowfall
accumulations topping 4" are likely to be confined to elevations
above 5,000ft.

WPC probabilities through early Monday depict moderate chances
(40-70%) for snowfall >8" in the peaks of the Lewis Range above
6,000ft (including Glacier Nat'l Park) on south along the
Absaroka/Tetons above 8,000ft through Sunday afternoon. Lighter
snowfall accumulations as low as 5,000ft in the Lewis
Range/northwest Montana and 7,000ft in the Absaroka/Tetons are
expected. WPC's Winter Storm Severity Index (WSSI) shows Minor
Impacts from the Bitterroots and Idaho Panhandle on east through
much of Montana's mountain ranges and on south through northwest
Wyoming. Some localized Moderate impacts in the higher elevations,
largely impacting passes within these ranges, are possible.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Mullinax/Snell







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