Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
430 PM EST Mon Nov 21 2022

Valid 00Z Tue Nov 22 2022 - 00Z Fri Nov 25 2022

...Northwest/Northern Rockies...
Days 1-2...

Warm advection precipitation ahead of an approaching shortwave
trough is expected to spread into western Washington and Oregon
tomorrow morning.  Snow levels are forecast to climb above 5000 ft
tomorrow morning, before lowering below 4000 ft as the associated
cold front pushes through the region tomorrow night.  For the Day
1 period, WPC PWPF shows that any moderate probabilities (greater
than 40 percent) for snowfall accumulations of 6 inches or more
are confined to the higher elevations of the northern Cascades. 
East of the crest, shallow low level cold air is expected to
remain, raising the threat for freezing rain.  WPC PWPF shows
moderate probabilities for measurable ice across a large portion
of the Washington Columbia Basin on Day 1. 

Tomorrow night into Wednesday, the shortwave trough is forecast to
amplify and move east from the Pacific Northwest to the northern
Rockies.  While continuing across portions of the northern
Cascades, snows are forecast to develop farther east across parts
of the northern Rockies late tomorrow into Wednesday morning. 
Expect precipitation to diminish from west to east as an
amplifying ridge moves across the region on Wednesday.  For Day 2,
moderate probabilities for snow accumulations of 6 inches or more
are confined to the high peaks of the northern Cascades and the
northern Idaho ranges.   

Pereira