Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
255 PM EST Thu Nov 19 2020

Valid 00Z Fri Nov 20 2020 - 00Z Mon Nov 23 2020


...Pacific Northwest/Northern Rockies...
Day 1...

A weak shortwave embedded in confluent mid-level flow will advect
from the Pacific Northwest into the Northern Rockies on Friday
bringing a modest increase in mid-level RH as moisture spreads
inland from the Pacific. Periods of moderate to heavy snow are
likely in the higher terrain of the N-S oriented ranges which will
aid in some upslope enhancement. Modest snow accumulations are
likely through Friday, with WPC probabilities indicating a high
risk for 4 inches in the WA Cascades where locally 10"+ is
possible. Otherwise, a few inches are likely in the Olympics and
Northern Rockies.

For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Weiss