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FOUS11 KWBC 070816
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
316 AM EST Sun Dec 7 2025

Valid 12Z Sun Dec 07 2025 - 12Z Wed Dec 10 2025


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

The Pacific Northwest and Northern Rockies will face a steady
barrage of Pacific moisture over the next few days thanks to a
multi-day strong atmospheric river that is pinned between a strong
subtropical ridge off the coast of CA and a stalled, positively-
tilted upper low in the Gulf of AK. Today, PWATs start out around
the 90th climatological percentile throughout the Northwest, before
a more impressive plume of PWATs above the 99th climatological
percentile stream in on Monday. Even on Tuesday, as the subtropical
ridge expands a little farther north, a fire-hose of Pacific
moisture will continue into the Pacific Northwest that spills into
the Northern Rockies as well. Add in steady synoptically-forced
ascent aloft from a strong 250mb jet stream and persistent upslope
flow into many of these mountains ranges, and the recipe is for
heavy snowfall from the Olympics and Cascades to the western WY
Rockies.

Today, snow levels largely look to start out around 3,000-4,000
ft, but rapidly rise across the Pacific Northwest above 5,000ft.
As the strong AR and its associated WAA aloft approaches on
Monday, these values increase to above 6,000 ft in the northern WA
Cascades and above 7,000 ft from Mt. Rainer and points south.
Farther east, snow levels will rise across the northern Rockies as
well, topping 6,000ft in many cases before falling on D3 as the AR
orients itself farther south as a shortwave trough ejects into the
northern Plains. Starting this morning and lasting through early
Wednesday morning, 72-hr WPC probabilities for more than 12 inches
are high (70-90%) across the WA Cascades above 5,000 ft, as well
as parts of the northern Rockies in ID, western MT, and western WY
above 6,000-7,000 ft. WPC probabilities even show speckled areas
of low-to-moderate chances (20-50%) for localized snowfall totals
>30" in the more remote reaches of these regions through Tuesday
night.


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

This morning, the upper trough responsible for the Midwest storm
on Saturday will generate light-to-moderate snowfall across
Michigan and much of the Northeast (minus the I-95 corridor
megalopolis). Most snowfall totals will range between 1-4",
although some areas within the Tug Hill and Adirondacks may manage
to see localized snowfall totals eclipse 4" on Sunday. The upper-
level disturbance may produce a small area of low pressure off the
Maine coast that produces a fast moving band of snow over Downeast
Maine Sunday night. WPC probabilities do depict low chances
(10-30%) for snowfall totals >4" Monday night.

By Monday night, as high pressure builds in over the Northeast, an
Alberta Clipper makes its way toward the Upper Great Lakes Monday
evening with more light-to-moderate snow expected. Guidance is
coming into better agreement that strong SWrly flow ahead of the
Clipper will produce a band of heavy lake effect snow oriented from
Lake Michigan and far northwest Michigan aimed northward into the
eastern U.P.. WPC probabilities through Tuesday show moderate-to-high
chances (50-80%) for snowfall totals >4" in over the eastern
Michigan U.P. and northwest Michigan. The eastern Michigan U.P.
sports the highest chances for >8" of snowfall (30-50%). As the
Clipper`s warm front moves east, sufficient 290K isentropic ascent
and 850-700mb WAA will give rise to snow over the eastern Great
Lakes and northern New England by Tuesday afternoon. Immediately
downwind of Lakes Erie and Ontario, snowfall totals will generally
range between 1-4". However, the Tug Hill has moderate chances
(40-60%) for snowfall totals >4" through early Wednesday morning.


...Southern Appalachians & Mid-Atlantic...
Days 1-2...

A quick moving 500mb trough will track from the TN Valley Sunday
night to the Southeast Coast by Monday afternoon. 500mb PVA ahead
of the upper trough will be paired with easterly low-level flow
that allows for some upslope enhancement along the southern
Appalachians. Snow will be at its heaviest Monday morning but taper
off by Monday evening. This storm could have a surprise or two up
its sleeve as the 500mb vorticity maximum reaches NC Monday
afternoon, with some guidance showing some 850mb low development
off the coast of NC`s Outer Banks. Should easterly low-level winds
increase, sufficient low-level WAA and moisture advection could
create a band of snow that results in a quick hitting 1-3" snow
event from as far north as the Richmond metro area on south along
I-95 and I-85 towards the Raleigh/Durham area. WPC probabilities
currently show low chances (10-30%) for snowfall totals >4" in
portions of the VA/NC Blue Ridge and Potomac Highlands of WV, but
it is possible those chances increase should the influences of the
500mb trough prove more substantial. This has the potential to
cause slick travel conditions for the Monday evening commute in
southern VA and northern NC.


...Northern Plains & Upper Midwest...
Day 3...

By Tuesday morning, a vigorous 500mb shortwave trough with origins
from the large Gulf of AK longwave trough will race towards the
Northern Plains. Given its origins, this "Alberta Clipper" will be
more intense than most clippers. This is because it will have
exceptional synoptic-scale forcing aloft in the form of a roaring
150kt 250mb jet streak, plus anomalous moisture associated with the
strong AR over the Pacific Northwest. By 18Z Tuesday, the
clipper`s MSLP looks to be sub-990mb, which ranks below the 1st
climatological percentile for this time of year. As the storm works
its way across the Dakotas Tuesday morning, impressive 290K
isentropic lift and corresponding 850-700mb FGEN will not only
help to sustain this potent clipper, but foster a potent band of
snow northeast of the 850mb low track. There is the potential for
an icy wintry mix just along and north of the surface warm front as
a protruding >0C warm nose forces snow to melt into the form of
sleet or freezing rain. But the storm`s fast motion should limit
the impacts to around minor impacts (ice accretions less than a
tenth of an inch most likely).

By Tuesday night, the storm will remain in the mid-980s for
pressure as it races through WI and into MI by Wednesday morning.
WAA out ahead of the storm is likely to cause periods of snow to
envelope the eastern Great Lakes that include areas such as
northwest PA and western NY. From the Northern Plains the the Great
Lakes, not only will snow be problematic for traveling, but gusty
winds are likely to cause blowing and drifting across roads and
cause reduced visibilities. WPC probabilities show a swath of
moderate chance probabilities (40-60%) for snowfall totals >4" from
northeast ND on south and east through the Upper Midwest and the
northern half of Michigan`s Mitten. Note there are also low-to-
moderate chance probabilities (20-50%) for totals >6", which does
show up on several deterministic guidance members.

While the storm`s speedy forward motion should help to reduce the
chances for more prolific snowfall totals, hourly snowfall rates of
>1"/hr combined with gusty winds will allow for Minor Impacts at
the very least. This is supported by the WSSI-P which depicts
moderate-to-high chances (50-70%) for Minor Impacts on Tuesday from
northern ND all the way to northern MI. Residents in the Upper
Midwest and Great Lakes should continue to monitor this storm
closely, as should residents in the Northeast as probabilistic
guidance shows measurable snowfall from this system is possible on
Wednesday.


Mullinax




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