Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
456 AM EDT Sat Apr 26 2025

Valid 12Z Sat Apr 26 2025 - 12Z Tue Apr 29 2025


...California and Nevada...
Days 1-2...

Upper low crosses the central CA coast this morning before slowly
filling while lifting northeast, reaching south-central NV by
Sunday morning. Lift ahead of the low, aided by left jet exit
dynamics, overlapping sufficient Pacific moisture will allow
expanded precip coverage over CA into this evening with the focus
over NV and the eastern side of the Sierra Nevada overnight through
Sunday.

Snow levels will be 5000-5500ft through Sunday morning. 00Z HREF
mean hourly snow rates are generally 1-1.5"/hr from 12Z to 00Z on
the Sierra Nevada.Day 1 snow probs for >6" are 50-80% for the
Sierra Nevada and highest Transverse Ranges in SoCal. Eastern
slopes of the Sierra Nevada are favored for the heaviest snow with
50-80% probs for >12" over the White Mtns and other ranges along
the NV border up through the eastern side of Tahoe.

As this upper low continues to track northeast, the accompanying
moisture and ascent will bring light to moderate snow to the
higher elevations of NV through Sunday night. Day 2 WPC
snow probs are 50-80% >6" across the Ruby Mountains of NV.


...Northern Rockies...
Days 2/3...

The closed low drifting from the Great Basin Sunday night will
fill and open into a positively-tilted trough Monday as it reaches
WY. Despite the weakening, deep layer ascent will remain
impressive as periodic lobes of vorticity swing northeast
downstream of the trough axis, and work together with mid-level
divergence and upper diffluence in the left exit region of the jet
streak arcing into the Northern Plains. Together, this will cause
pressure falls over CO/WY leading to surface cyclogenesis on the
High Plains.

A cold front digging south through the Northern Rockies Sunday
night into Monday will approach the Plains surface low, leading to
enhanced ascent across parts of MT and WY. This slow moving system
will allow upslope flow with fgen, resulting in heavy snow rates,
with dynamic cooling response to the column occurring even outside
of the higher terrain. Snow levels will be generally around 6000ft.
Day 2 snow probs for >8" are 30-40% in the eastern Sawtooths in ID
and 50-80% over the northern Absarokas in MT. This shifts east for
Day 3 over the eastern Absarokas and Bighorns in WY.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.



Jackson