Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
244 PM EST Tue Nov 03 2020

Valid 00Z Wed Nov 04 2020 - 00Z Sat Nov 07 2020


...Pacific Northwest to the Northern Rockies...
Progressive onshore flow with embedded mid-level energy and deep
moisture will continue to support periods of heavy precipitation
along the orographically favored regions of the Northwest through
midweek.  However, snow levels are expected to remain high through
Wednesday -- confining the threat for heavy snowfall accumulations
to the highest peaks of the northern Cascades.  Then on Thursday
as an amplifying shortwave begins to move onshore, snow levels
will begin to lower across the Northwest -- expanding the
potential for heavy snow accumulations across the northern
Cascades. 

Overall consensus of the models shows an upper trough continuing
to amplify over the northwestern U.S., with an upper low closing
off over Oregon/Northern California on Friday.  This will bring
the threat for high elevation heavy accumulations farther south
into the southern Cascades.  Meanwhile, strong low-to-mid level
frontogenesis extending from western Montana to eastern Oregon,
along with falling snow levels, will help set the stage for
locally heavy snows beginning to develop from the northeastern
Oregon mountains to the ranges of the northwestern Montana. 

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

Pereira