Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
339 PM EDT Thu Sep 28 2023

Valid 00Z Fri Sep 29 2023 - 00Z Mon Oct 02 2023

...Sierra Nevada and highest terrain of the Great Basin
Days 2-3...

A mid-level trough digging across the Pacific will sharpen as it
crosses into the Pacific Northwest Friday night, and then amplify
into a closed low over the Great Basin by Sunday morning. This
deepening trough is progged to feature 700-500mb height anomalies
falling to -3 standard deviations according to the NAEFS ensemble
tables, driving snow levels to as low as 8000 ft in the Sierra
D2-3, and to 9500-10000 ft across the Great Basin and Central
Rockies late in the forecast period. Forcing for ascent through
downstream divergence, height falls, and intensifying diffluence
within the LFQ of a jet streak rotating through the trough will
result in precipitation spreading across the area, which will fall
as moderate snow above these snow levels. WPC probabilities for
more than 4 inches peak high as 30% in the High Sierra (above 9000
ft) day 2.5 before waning the latter stages of D3. This will
likely produce at least minor impacts at the highest passes
including Tioga Pass. Additional very light snowfall accumulations
are possible above 10,000 ft in the Uintas on Sunday.

The probability of any ice accumulation across the CONUS is less
than 10 percent.


Weiss