Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
117 PM EST Sat Mar 8 2025

Valid 00Z Sun Mar 09 2025 - 00Z Wed Mar 12 2025


...Pacific Northwest through the Northern Rockies...
Days 1-2...

A deepening trough off the Pacific Coast will amplify into a closed
low positioned west of CA by Monday, while a vorticity streamer cut
off from this feature sheds eastward into the Pacific Northwest.
Downstream of this energy, intensifying SW flow between this trough
and a expanding ridge centered over the Four Corners will drive
modest IVT exceeding 250 kg/m/s into the Pacific Northwest. The
intensifying ascent through WAA, height falls, and diffluence from
the departing RRQ of an upper jet streak into this moistening
column will result in expanding precipitation, first in the
Olympics late D1 and then spreading eastward through the Cascades
and into the Northern Rockies by late D2 before ending quickly. The
transitive nature of the ascent combined with modest available
moisture will limit total precipitation, but heavy snow
accumulations are still likely above 4000-5000 ft. WPC
probabilities D1 are above 70% for 6+ inches, but only across the
Olympics and far northern WA Cascades. Heavy snow expands and
spreads east during D2, reflected by a high risk (>70%) for 6+
inches in the WA Cascades, with a moderate risk (30-50%) across the
Lewis Range in the Northern Rockies.


The probability of significant icing is less than 10 percent.


Weiss