FOUS11 KWBC 050755
QPFHSD
Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
255 AM EST Wed Nov 5 2025
Valid 12Z Wed Nov 05 2025 - 12Z Sat Nov 08 2025
...Pacific Northwest through the Central Rockies...
Days 1-3...
An active pattern across the Pacific will continue through the week
as a closed low lifts slowly into British Columbia, leaving
persistently confluent W/SW flow across the Pacific and channeled
into the West Coast. This fosters an extend period of impressive
moisture advection and IVT surging onshore, and probabilities for a
strong atmospheric river (AR) moving onto the coast exceed 80%
from both the GEFS and ECENS ensemble systems on D1. The intensity
of this moist advection is additionally reflected by NAEFS IVT
percentiles that exceed the 99.5 percentile across CA Wednesday
afternoon.
This suggests an impressive precipitation plume will push from
CA/OR northeast Wednesday aftn through Thursday aftn, with
precipitation spillover reaching as far as the Northern and Central
Rockies. However, most of this precipitation will fall as rain as
the accompanying WAA surges snow levels to 7000-8000 ft, keeping
any snow well above pass levels through Thursday. A secondary surge
of precipitation associated with another disturbance embedded
within the confluent onshore flow will lower snow levels at least
slightly, to around 5000 ft, with additional heavy precipitation.
At this time, impactful snow will likely occur at some of the
higher passes, especially Washington Pass in the WA Cascades before
Friday morning, before a final impulse shifts east causing precip
to wind down across the Cascades but continue, in lighter fashion,
across the Northern and Central Rockies.
WPC probabilities D1 are moderate (50-70%) for >6" inches of snow
in the northern WA Cascades, before expanding and shifting east
into Salmon River/Sawtooth ranges, the Tetons, and Northern
Rockies, while at the same time continuing across the northern WA
Cascades. On D2 and bleeding into D3, the heaviest snow is
expected across the WA Cascades where WPC probabilities reach above
70% for 8+ inches above 5000 ft, with moderate probabilities
(30-50%) for 6+ inches continuing across portions of the Northern
Rockies and higher elevations of ID and NW WY. Cumulatively through
Friday night, 3-day snowfall probabilities show some moderate
chances (40-60%) for snowfall totals to eclipse 12" in the tallest
reaches of the northern WA Cascades, the Sawtooth, and Tetons.
...Northern New England and the Adirondacks...
Day 1...
A rapidly intensifying clipper-type low pressure will move
progressively E/SE from Ontario, across New England, and then out
to sea south of the Canadian Maritimes by Thursday afternoon. This
low will spread significant moisture eastward on robust low-level
FGEN leading to a pronounced TROWAL pivoting across Northern New
England. The accompanying WAA will help spread significant
moisture into the area, but the WAA will also drive snow levels up to
4000-5000 ft, suggesting that except for the highest peaks of
northwest Maine, the pre-low precipitation will be all in the form
of rain Wednesday afternoon. However, as the low tracks towards the
New England coast, rapid CAA in its wake, aided by impressive
isallobaric flow into the deepening system and topographically-
enhanced upslope flow, will cool the column dramatically,
reflected by snow levels falling to 500-1000 ft by 12Z Thursday.
This results in a period of moderate to heavy snowfall in the
higher terrain, with light snow gradually spreading into the lower
elevations of VT/NH/ME and Upstate NY before the DGZ dries and
precipitation dissipates Thursday afternoon.
The heaviest snowfall is likely to unfold above 2000ft in the
Adirondacks and Whites, although some moderate accumulations are
also likely in the highest Greens. This is reflected by WPC
probabilities which indicate a moderate risk (50-70% chance) for
more than 4 inches of snow, with locally as much 8 inches in the
highest Presidential Range peaks. Light accumulations of a dusting
or more are likely elsewhere from Lake Ontario through central
Maine, except across the Champlain Valley, resulting in the first
notable snow of the year in some of the lower elevations of
northern New England.
The probability of significant ice across the CONUS is less than
10 percent.
Mullinax/Weiss
$$
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