Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
259 PM EDT Fri Oct 17 2025

Valid 00Z Sat Oct 18 2025 - 00Z Tue Oct 21 2025

...Northern Rockies...
Day 1...

A fast moving 500mb shortwave trough at the nose of a 130kt jet
streak will provide sufficient upper-level ascent aloft at the same
time as a cold front passes through the northern Rockies tonight.
The atmospheric column will be saturated enough to support light-
to-moderate mountain snow along the Lewis Range, the Absaroka, and
Big Horns tonight and into Saturday morning. Snow levels in the
Lewis Range will hover as low as 6,000ft while the Absaroka and Big
Horns are as low as 7,000ft. The heavier amounts in the Absaroka
and Big Horns are more likely to be observed above 8,000ft with WPC
probabilities suggest low-to-moderate chances (20-50%) for snowfall
totals >4" through Saturday morning. Most of the Lewis Range will
generally see minor accumulations (coating-3") through Saturday
morning.

...Pacific Northwest and Northern Rockies...
Days 2-3...

A strong northeast Pacific low pressure system will direct its cold
front and attendant atmospheric river at the Pacific Northwest on
Saturday. The rich 850-500mb moisture field will spill over into
western WA Saturday afternoon, then into the ID Panhandle and and
northern Rockies Saturday night and into Sunday. The sternest lift
at mid-to-upper levels of the atmosphere occurs late Saturday
night and into Sunday as sharply decreasing height falls and 500mb
PVA allows to heavier snowfall rates and lowering snow levels.
While this jet stream pattern is supportive of mountain snow, the
cold air in wake of the frontal passage is not exceptionally cold.
For this reason, snow levels in the Cascades and Olympics may reach
as low as 4,000ft but most passes should be just low enough in
elevation to avoid the heavier snowfall totals that are expected
at 5,000ft and up. WPC probabilities show moderate-to-high chances
(50-80%) for snowfall >6" at elevations >5,000ft in the Cascades.
Farther east, the Bitterroots, Lewis Range, Absaroka, and Tetons
are forecast to see minor-to-moderate snowfall that lingers in
parts of western MT through Monday morning. WPC probabilities show
the Lewis Range above 6,000ft and the Absaroka above 8,000ft with
the moderate-to-high chances (40-70%) for snowfall totals >6" by
the time the event concludes Monday afternoon. Localized snowfall
totals over 12" are possible in the tallest peaks of the Lewis
Range and Absaroka.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Mullinax