557
FOUS11 KWBC 092030
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
330 PM EST Tue Dec 9 2025

Valid 00Z Wed Dec 10 2025 - 00Z Sat Dec 13 2025


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

Atmospheric River (AR) event to continue through the rest of the
week with heavy rain/snow for the Pacific Northwest into/through
the northern Rockies and western High Plains.

The strong AR will continue this evening/overnight over the
Cascades and push high snow levels into the region from the
southwest, initially from 4000-5000ft over northern WA but rising
to over 7000- 9000ft by early Wednesday as the jet lifts northward
across British Columbia. Any snow at the higher passes will change
to rain even into the higher terrain of NW MT tomorrow with the
strong IVT push (exceeding the 99.5th percentile) as snow levels
rise to 7000ft. Farther southeast, mid-level shortwave will help
yield snow to the higher terrain of WY as well through Wednesday.
For Day 1, WPC probabilities for at least 8 inches of snow are >50%
above 5000- 6000ft over northern areas and above 8000-9000ft over
WY into northern CO.

Into Day 2, upper jet will wobble a bit across southern BC but
keep the Northwest in mild conditions with snow levels 7000-9000ft
to start. Through the day Thursday, ridging over the Northeastern
Pacific may allow snow levels to slip a bit, especially by Thursday
evening as the intense moisture plume subsides a bit. WPC
probabilities for at least 8 inches of snow are >50% above about
6000ft. Much colder air will dive southward east of the Divide
across Montana setting up a significant snowfall by Friday.

By Day 3, ridging will establish itself on a NNW axis from NorCal
into the Northeast Pacific, allowing the moisture plume to lift
northward through BC and also dig southward along/east of the
Divide across much of Montana. At the same time, the strong cold
front will have brought in much colder air to most of the state
east of the Divide, coincident with cold Canadian high pressure
from the north. With a continued moisture surge (albeit less than
earlier in the period but still a quite respectable >90th
percentile PW and IVT), snow will expand and strengthen over
central/eastern MT as snow ratios rise as well. Strong low/mid-
level FGEN may support a heavier axis of snow from central to
southeastern MT but there remains disagreement on the placement as
the upper jet meanders over northeastern MT. For just Day 3 through
00Z Sat, WPC probabilities for at least 6 inches of snow are
highest in areas above 6000ft in the northern Rockies. Over central
to eastern/southeastern MT, WPC probabilities for at least 6
inches of snow are >50% from just east of Great Falls southeastward
through Billings to near the WY border. Snow will continue past
this period as well.


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

An amplified shortwave and accompanying vorticity lobe will
quickly dive from the Upper Midwest to across the southern Great
Lakes and into the Northeast through Thursday morning. The
impressive height falls ahead of this wave will overlap efficiently
with the LFQ of a stout Pacific jet streak, producing intense deep
layer lift which will help deepen the resulting surface low. This
surface low / Alberta Clipper will scoot across lower Michigan by
Wednesday morning and northern Maine/Quebec by Thursday morning.
Above normal moisture in conjunction with the impressive dynamics
will lead to a swath of moderate to heavy snowfall along the
surface low track. WPC probabilities for snowfall >4" remains
moderate to high (45-75%) across the heart of WI and central Lower
Michigan, with low probabilities (10-30%) of snowfall >6". South of
the axis of snowfall, a stripe of freezing rain is possible across
portions of southeast MN, northeast IA, southern WI, northern IL,
southern MI, northeast IN and northwest OH, though any ice
accretions will be less than a tenth of an inch.

As this clipper system moves from the Upper Midwest and Great
Lakes and into the Northeast, the downstream strong WAA will
overrun a very cold antecedent airmass. This will create a
broadening plume of wintry precipitation, falling primarily as snow
from Upstate NY through northern New England, with some mixing,
including periods of freezing rain, expected farther south into the
northern Mid- Atlantic and southern New England. Total
accumulations of wintry precipitation should be less than areas
upstream, but WPC probabilities Day 1 into Day 2 for 4+ inches of
snow reach 60-95% for portions of western PA and across the
southern Adirondacks, Greens, Whites, and terrain of northern ME.
Meanwhile, WPC probabilities for freezing rain >0.01" are low to
moderate (30-60%) for the higher terrain of northeast PA and
northwest NJ.

Finally, behind this system a brief period of favorable NW flow
will create lake effect snow (LES) and upslope snow across the
eastern Great Lakes through Day 3. While some of this snow will
fall on top of the synoptic snow noted above (and is included in
the snowfall probabilities), an additional 4+ inches of snow has
moderate to high probabilities (50-95%) downwind of Lake Erie and
especially Lake Ontario. The Tug Hill Plateau, in particular, has
rather high chances (>70%) for snowfall totals surpassing 8" with
even low-to-moderate chances (30-60%) for snowfall topping 12
inches.


...Midwest and Lower Ohio Valley to the Central Appalachians...
Day 3...

A vigorous Clipper system (mid level vort lobe) across the Midwest
Friday morning will pivot through the Lower OH Valley and into the
WV Mountains Friday afternoon and early evening. Overall the model
QPFs (at least the blended means) have come up at 12Z, though
latitudinal differences remain (not surprising given a day 3
forecast). WPC deterministic QPF incorporated a PMM of the latest
GFS/ECMWF/NAM/RRFS, which yields a rather elongated footprint of
0.25-0.35" liquid QPF from north-central IL east-southeast through
central IN, southern OH, far northern KY, and essentially the
middle 2/3rds of WV.

Highest QPFs (0.50+ liquid) again were noted across the most
elevated windward slopes in WV, where the westerly upslope is most
favorable. This is also where the latest WPC probabilities of at
least 4" in 24hrs are highest -- currently between 50-70+ percent.
Elsewhere across north-central IL into central portions of IND,
spotty 4"/24hr probabilities between 30-60% were noted.


Fracasso/Miller/Hurley

$$