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FOUS11 KWBC 031948
QPFHSD

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

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

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

An active pattern begins tonight across the Northwest and
eventually spilling into the Intermountain west, as a series of
three distinct impulses moving eastward across the region.

The first of these will lift onshore near OR early tonight, with a
weakening surface wave also pushing northeast beneath it. This will
channel modest moisture onshore, and as the system progressively
pushes east, a stripe of light to moderate precipitation will occur
from the WA/OR coast through the Northern Rockies. In general
snowfall will accumulate above 4000-5000 ft, but total
accumulations are expected to be modest as reflected by WPC
probabilities for 4+ inches that are above 70% only in the highest
terrain near Mt. Rainier as well as across the Lewis Range in the
Northern Rockies.

A stationary front wavering across the area will serve initially
as the demarcation between higher snow levels to the south and
lower to the north, but this boundary will begin to push north as a
warm front D2. This evolution will be driven by an impressively
amplifying trough over the eastern Pacific downstream of a closed
low which will lift into northern British Columbia Thursday.
Strongly confluent and southerly flow ahead of this feature will
surge impressive IVT into the Pacific Northwest, reflective of a
strong atmospheric river which will peak in intensity on D2. This
impressive IVT (>90% chance of exceeding 750 kg/m/s) will reignite
precipitation across the area while concurrently driving snow
levels to 7000-8000 ft. This should preclude considerable impacts
from snow at any of the passes, but heavy snow is likely in the
highest terrain from Mt. Shasta northward along the Cascades where
WPC probabilities for 6+ inches are above 70%.

Finally during D3, precipitation associated with this AR will spill
eastward, reaching the Northern and Central Rockies as far as
Wyoming, while a tertiary impulse moves into the Pacific Northwest
once again with renewed heavy precipitation. Snow levels will fall
gradually behind the impulse on D2, but remain somewhat elevated at
around 5000-6000 ft D3. WPC probabilities for more than 4 inches of
snow accumulation extend from the WA Cascades through the
Sawtooth/Salmon River ranges of ID and into the region around
Yellowstone NP where they peak at 70-90%.


...Northern New England and the Adirondacks...
Day 1...

A low pressure system moving well east of New England will interact
with a shortwave racing southeast out of Ontario to draw moisture
back into New England tonight. While the duration of available
moisture will be limited due to rapid drying behind the cold front
accompanying the aforementioned shortwave, upslope flow during a
period of CAA will result in periods of moderate to heavy snow,
especially in the Presidential Range of NH, with additional light
accumulations across the Adirondacks. WPC probabilities for 4+
inches of snow are as high as 10% in the Adirondacks, but above 80%
near Mt. Washington where locally 8-10 inches of snow is likely.

Day 3...

A clipper type low pressure will race southeast out of Ontario
beginning late Thursday, crossing northern New England while
amplifying through Friday morning. The system will be progressive
and exit the Maine coast by 12Z Thursday, but moisture will persist
behind the low as an impressive TROWAL pivots cyclonically around
the rapidly deepening system. Initially, precipitation will be all
rain as snow levels are elevated and WAA prevents any cooling.
However, as the low departs, rapid cooling is likely both through
isallobaric flow into the strengthening system, but also aided by
impressive CAA in its wake. This will result in a crash of snow
levels from around 3000 ft early D3 to as low as 500-1000 ft by 12Z
Thursday before precipitation wanes Thursday aftn. The lowering
snow levels combined with impressive ascent through the TROWAL and
in response to increasing upslope on veering N/NW winds will help
snowfall accumulate in the terrain of Northern New England on
Thursday. The heaviest snow is expected near Mt. Washington and
across the interior mountains of northern Maine where WPC
probabilities are 30-50% for 4+ inches of snow.



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


Weiss


$$