Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
336 PM EDT Mon Mar 25 2019

Valid 00Z Tue Mar 26 2019 - 00Z Fri Mar 29 2019


...Pacific Northwest/Northern California to the Northern Rockies...

A deep upper low centered near 43N/140W is forecast to drift
slowly east toward the Pacific Northwest over the next few days. 
Mountain snows are expected for portions of the Cascades and
northern Sierra as a leading shortwave and its associated frontal
band move inland this evening.  However, widespread heavy amounts
are not expected through the Day 1 period (ending 00Z Wednesday). 
The threat for heavy snow is forecast to increase across the
northern Sierra by late Wednesday.  A well-defined shortwave
moving south of the low is expected to move into California along
with a second front and deeper plume of moisture -- supporting
heavier precipitation across northern California.  WPC
probabilities for Day 2 (ending 00Z Thursday) show a moderate risk
for accumulations of a foot or more along the western slopes of
the northern Sierra above 6000 ft.  With the onshore winds waning,
the threat for heavy snow is expected to diminish along the Sierra
on Day 3.  However, with shortwave energy lifting northeast,
increasing divergent flow aloft, along with low to mid level
frontogenesis are expected to raise the threat for heavy snows
across portions of the northern Rockies.  WPC Day 3 probabilities
(ending 00Z Friday) indicate a Moderate Risk for accumulations of
a foot or more for portions of the southwest Montana ranges.

Pereira