Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
308 PM EDT Sat Oct 18 2025

Valid 00Z Sun Oct 19 2025 - 00Z Wed Oct 22 2025

...Pacific Northwest and Northern Rockies...
Days 1-2...

A large, yet weakening, northeast Pacific storm system will direct
its cold front and attendant atmospheric river at the Pacific
Northwest tonight and Sunday morning. ECMWF PWATs are above the
90th percentile tonight and the IVT tops out around 800 kg/m/s.
This same moisture source looks to spill over into eastern WA,
northern ID, western MT, and northwest WY late tonight and into
Sunday. The strongest lift at mid-upper levels occurs overnight and
into Sunday morning as sharply decreasing heights and 500mb PVA
allows for heavier snowfall rates (1-2"/hr in some cases) and
falling snow levels. The cold front is expected to come ashore
around 06Z tonight, which will coincide with a gradual decrease in
QPF at the same time as snow levels steadily decrease to around
5,000ft. Some of the higher passes (such as Washington Pass/SR-20,
elevation 5,477ft) will be at risk of receiving hazardous snowfall
accumulations tonight and through Sunday morning. Farther east,
snow levels will range generally between 6,000-8,000ft (closer to
6,000ft farther north, closer to 8,000ft in the Tetons and Wind
River Range) but some areas as low as 5,000ft in the ID Panhandle
and Lewis Range could see minor-to- moderate snowfall totals. Snow
will linger into Sunday night for the Northern Rockies's ranges
before tapering off Monday morning.

WPC probabilities for >8" of snowfall are moderate-to-high (50-80%)
in the northern WA Cascades and moderate (40-70%) in Bitterroots
and Lewis Range above 6,000ft. Anywhere between 6-12" of snowfall
is possible around Glacier Nat'l Park through Monday morning. The
WSSI does show generally Moderate Impacts around the Glacier Nat'l
Park, with some of the higher peaks potentially dealing with Major
Impacts. Expect icy and hazardous travel conditions in the higher
peaks of the Cascades and Northern Rockies.

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

Mullinax