Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
413 PM EDT Thu Oct 28 2021

Valid 00Z Fri Oct 29 2021 - 00Z Mon Nov 01 2021


...Pacific Northwest to the Northern Rockies...
Days 1-2...
Ongoing heavy precipitation event across Washington is expected to
continue into the evening.  Snow levels have risen to above 8000
ft across much of Washington and the northern Rockies and are
expected to remain high into the evening.  An amplifying upper
trough is forecast to drive a cold front across Washington on
Friday.  This will bring lower snow levels, but also drier air --
ending the threat for heavy precipitation.  The front will also
push southeast of the northwestern Montana Rockies on Friday.  A
period of post-frontal upslope flow will support some locally
heavier amounts in the Lewis Range/Glacier National Park -- where
snow levels are expected to drop down into the valleys Friday
night.  With snow levels dropping below 3000 ft, some light
accumulations are expected farther east out into the High Plains.
Overall, WPC probabilities for heavy snowfall accumulations have
been decreasing.  However for the 48 hour period ending 00Z Oct
31, WPC probabilities remain in the 40-70 percent range for
snowfall accumulations of 4 inches or more across the northern
Lewis Range.

For Days 1-3, the probability of significant icing is less than 10
percent.

Pereira