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FOUS11 KWBC 120842
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
342 AM EST Wed Nov 12 2025

Valid 12Z Wed Nov 12 2025 - 12Z Sat Nov 15 2025


...California...
Days 2-3...

A potent, but transient atmospheric river (AR) shifts into far
northern California late Wednesday night and works its way down the
length of the state through Friday. Of particular note with AR is
confidence on the upper trough axis stalling along the northern CA
coast Thursday night instead of shifting inland as previous model
consensus solutions had forecast. Instead, height falls are not as
great over the Sierra Nevada and snow levels are now forecast to
remain above 8000ft for most of the heavy precip and only drop to
around 6000ft Friday morning over the northern Sierra Nevada which
is once rates have dropped off. Heavy snow will still occur over
the High Sierra from Thursday afternoon through Friday morning,
but confidence has risen that the 6" snow contour should generally
stay above 8000ft on the Sierra Nevada which is far less impactful
than prior forecasts with lower snow levels. WPC probabilities for
>12" from 18Z Thursday to 18Z Friday are 50-90% above about 8500ft.

The reason for this warmer solution is the trough that digs down
the coast closes off into a low off SoCal late Friday where it
lingers through Saturday before shifting inland. Warm air advection
east of this low over SoCal keeps snow levels 9000ft or above
through Saturday keeping accumulating snow to pretty much just the
highest peaks of the San Bernardino Mtns.

The higher snow levels also apply to Nevada where the only highest
peaks have any shot at >4" snow through Friday night.


...Pacific Northwest through the Northern Rockies...
Days 2-3...

The northern portion of the full-latitude trough axis off the West
Coast reaching the PacNW coast late Thursday and works its way east
across the northern Rockies through Friday. High snow levels in the
warm air advection ahead of the trough generally drop to around
5000ft Thursday night in the Washington Cascades progressing east
during the day Friday over northern ID/MT ranges. Limited moisture
due to the base of the trough being well down off CA keeps precip
rates low to moderate. Day 2 snow probs for >4"are 40-60% over the
highest Cascades and around North Cascades NP.

Moisture spreading east with the trough axis on Friday brings
moderate snow to central ID north through Glacier NP, as well as
northwest WY where Day 3 snow probs for >4" are 30-70%. Continued
flow over the Cascades with snow levels dipping around 4500ft early
Friday brings moderate snow there with snow probs for >6" 40-80%
over the Washington Cascades.


...Interior Northeast...
Days 1-2...

Troughing continues over the Northeast through Thursday before a
low develops over the Canadian Maritimes. The next shortwave trough
axis is currently over eastern Ontario with southwesterly flow
overspreading Lakes Erie and Ontario to lake enhanced precipitation.
This warm air advection makes for marginal thermal profiles which
requires some elevation increase from lake level for snow
accumulation. The trough axis shifts east over Upstate NY this
afternoon and brings a return to northwesterly flow (and some cold
air advection) over the eastern Great Lakes for tonight. This
should allow some snowfall downstream of Lake Ontario east of the
Finger Lakes into the Catskills. Day 1 snow probabilities for >4"
are 40-70% for the Tug Hill, Adirondacks, Greens, and higher Whites
of NH with a few blips of 20% south of the Mohawk Valley in NY.

This northwesterly flow pattern persists over the Northeast through
Thursday night with some additional cold air advection allowing for
snow levels to drop a bit, particularly under an impulse passage
Thursday evening. Day 2 snow probs for >4" are 20-60% south of the
Mohawk Valley along with the northern Adirondacks, and more of the
Greens and Whites (where probs reach 80%). Only light snow is
forecast on Northeast terrain in the flow wrapping around the
developing low north of Maine on Friday.

The probability of significant icing is less than 10 percent.


Jackson



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