Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
224 AM EDT Thu May 05 2022

Valid 12Z Thu May 05 2022 - 12Z Sun May 08 2022


...Pacific Northwest...
Days 1-3...

Multiple short waves will move through the Pacific Northwest over
the next several days as the upper jet slowly transitions toward
increased troughing over the Western CONUS. The strongest moisture
surge will be Day 1 in advance of a modest cold front, but snow
levels will be quite high -- above 5000ft over the WA Cascades and
7000ft over the OR Cascades. Next system approaches the coast on
Day 2 as the 130kt jet max reaches the coast, promoting broad lift
over the region. Snow levels will rise before the cold front then
lower below 5000ft by the end of Day 2, with additional
accumulation of over a foot at the highest peaks. Farther east,
several inches of snow are expected over the central Idaho ranges
into western Montana where snow levels will be between
6000-7000ft.

On Day 3, troughing will broaden and deepen out of the
northeastern Pacific as another shortwave heads toward the OR/WA
coast. Temperatures will trend colder and moisture will be modest
but enhanced by upslope flow. Snow levels will lower below 4000ft
and perhaps down to near or below 2000ft by the end of Day 3 as
700mb temperatures crash to below -10C through much of the Pac NW
(-2 sigma departure). This will extend into central Idaho and
western Montana as well by Sunday. WPC probabilities for at least
4 inches of snow are moderate (>40%) by Day 3 to elevations around
3000ft.

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

Fracasso