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FOUS11 KWBC 100825
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
325 AM EST Wed Dec 10 2025

Valid 12Z Wed Dec 10 2025 - 12Z Sat Dec 13 2025


...Pacific Northwest through the Northern High Plains...
Days 1-3...

The atmospheric river (AR) plaguing the Pacific Northwest with
copious amounts of rainfall continues today and into Thursday with
anomalous Pacific moisture coupled with >90th climatological
percentile winds within the 700-200mb layer over WA, northern ID,
and much of MT. Snow levels will be on the rise today, reaching
anywhere from 7,000-9,000ft as the 500-200mb jet core drifts north.
This should begin to force most passes to changeover to rain,
while any lingering snow occurs in the more remote areas of the
Cascades and Lewis Range. The only notable area for heavy snowfall
today is along the >9,000ft peaks of the Absaroka, Tetons, Big
Horns, and Wind River ranges of southern MT and western/northern
WY. WPC probabilities show moderate-to-high chanceS (50-70%) for
snowfall totals >8" through Wednesday night.

Focus turns to Thursday as an Alberta Clipper tracking across
eastern MT helps to usher in an Arctic front from southern Canada.
As the Arctic high builds in from the north, low-level easterlies
will upslope into central and western MT at the same time a ribbon
of 700-300mb moisture streams in overhead. 700mb WAA within W-NW
flow will encounter the Arctic air-mass and result in a band of
700mb FGEN over central MT by Thursday night, resulting in a
quasi-stationary zone of heavy snow over the heart of Big Sky
Country. Heavy snow will linger over the heart of MT through Friday
afternoon before drifting east into eastern MT and the western
Dakotas Friday night. As the band advances east, downsloping winds
and a drying within the 800-500mb layer could cause precipitation
to change over to a wintry mix in central MT, potentially
resulting in a glaze of ice atop fresh snow Friday night.

WPC probabilities moderate-to-high chances (50-80%) for snowfall
totals >8" in central MT with even some low-chance probabilities
10-30%) for isolated totals surpassing 18". The Lewis Range above
5,000ft are likely to receive anywhere between 12-24" of snowfall,
with the remote reaches of the Big Snowy and Little Belt Mountains
potentially exceeding 24". The WSSI-P Moderate probabilities in
central MT are >50% in central and south-central MT, with
Interstates 90, 94, and 87 all at risk of seeing hazardous travel
conditions, with some potential for considerable disruptions and
closures as well. This is depicted in the WSSI-P as well,
indicating 10-20% chances for Major Impacts along portions of these
Interstates Friday and into Saturday morning.


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

A shortwave trough responsible for the heavy snow across portions
of the Upper Midwest will strengthen as it tracks through the OH
Valley today. As it does, strong WAA out ahead of the trough will
work in tandem with the left-exit region of a 250-500mb mean
layered left-exit region over the Northeast to produce widespread
precipitation today from the central Appalachians to New England.
An exceptionally cold/dry antecedent air-mass by early December
standards will keep wet-bulb temperatures cold enough to support
snow at the onset across northern PA, the Catskills, Tug Hill,
Adirondacks, Berkshires, and the rest of the New England mountains
through Wednesday afternoon. Farther south, central and eastern
PA, as well as northwest NJ, are likely to see an icy wintry mix
this morning that could result in slick roads, particularly after
following a couple very chilly days where surfaces have been
steadily below freezing. From this "front-end thump" of WAA-driven
and some upslope enhanced snowfall, snowfall totals are likely to
range mostly between 1-4" with the higher totals confined to the
Tug Hill, Adirondacks, Berkshires, Green, and White Mountains where
WPC probabilities show high chances (>70%) for snowfall totals >6"
through Wednesday night.

As low pressure tracks into the St. Lawrence Valley tonight, CAA
within cyclonic flow on the backside of the storm will kick-start
the Lake Effect Snow (LES) machine, as well as supply the central
Appalachians with pronounced upslope snowfall. Precipitation will
fall as snow across the Central Appalachians with lowering snow
levels throughout the day Wednesday and impressive 40-50 kts winds
at 850mb will mix down to cause strong winds within increasing
snowfall rates. This will result in dangerous travel conditions in
the Central Appalachians with whiteout conditions expected above
2,000ft. Snow and winds should gradually taper off Thursday
morning. WPC probabilities show moderate-to-high chances (50-70%)
for snowfall totals >6" with localized low-chance probabilities
(10-30%) for amounts >12". Elsewhere, the LES belts over the
eastern Michigan U.P., northwest section of Michigan`s Mitten,
along the Chautauqua Ride, and down wind of Lake Ontario will see
LES bands that stick around these areas through Thursday, with the
band off of Lake Ontario lingering into Friday as well. Through
Friday morning, the Tug Hill Plateau sports high chances (>70%) for
snowfall totals topping 12", with moderate-to-high chances (40-70%)
for >12" amounts along the Chautauqua Ridge through Friday
morning.


...Northern Plains, Midwest, Lower Ohio Valley, & Central
Appalachians...
Days 2-3...

A potent clipper emerging from eastern MT Thursday morning will
race southeast into the heart of the Midwest by Thursday evening.
Healthy 850mb WAA and FGEN to the north and east of the low track
will cause a narrow band of snow light-to-moderate snow from the
eastern Dakotas and southern MN to the nose of IA, and in some
cases a wintry mix across the northern High Plains. The 850mb
FGEN/WAA pivots over the Lower Ohio Valley Thursday night and
reaches the Central Appalachians by early Friday morning. WPC
probabilities show generally lw-to-moderate chances (20-50%) for
>4" of snow from central MN on south and east across northern IL,
south-central IN, and southern OH. The highest probabilistic
chances for >4" of snowfall resides in the Potomac Highlands and
central Appalachians of eastern WV and western MD. Here, WNWrly
upslope winds within a 290K isentropic regime and higher SLRs will
provide a favorable environment for locally heavy snowfall. WPC
probabilities show most of the Potomac Highland and central
Appalachians in eastern WV and western MD have moderate-to-high
chances (50-70%) for snowfall totals >4", with some guidance
indicating low chances (10-30%) for localized totals surpassing
10".

There are some members of guidance that depict a chance for light
snowfall across the Mid-Atlantic on Friday, particularly the Blue
Ridge of VA/WV and potentially in the northern VA/northern
MD/southern PA. ECMWF and GFS show weak 700mb Q-vector convergence
over the region with just enough 700-300mb layer saturation to
support a chance for light snow. WPC probabilities show low chances
(10-30%) for >1" snowfall totals across southern and central PA,
northern MD, and northwest VA. While referencing >1" snowfall
potential may seem trivial to mention, recent Mid-Atlantic
snowfall events over the past week has seen snowier trends inside
of 60 hours. It is worth monitoring, but overall snowfall and
travel disruption potential at this time would be light. The WSSI-P
does show 10-20% odds for Minor Impacts across portions of northern
VA and northern MD on Friday.


Mullinax




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