Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
231 PM EST Tue Feb 20 2024

Valid 00Z Wed Feb 21 2024 - 00Z Sat Feb 24 2024

...The West...
Days 1-2...

The upper low responsible for the deluge of rain and heavy
mountain snow over California dating back to this past weekend
will work in tandem with another lobe of 500mb vorticity rotating
on the southern flank of the upper low to direct additional
850-500mb Pacific moisture into the western third of the CONUS
through mid-week. Over the next few days, snowfall will be at its
heaviest over the Sierra Nevada, the northern Wasatch, and the
Uinta Range today and tonight as the highest concentration of
Pacific moisture coincides with these mountain ranges' placement
beneath the divergent left-exit region over a roaring 170kt 250mb
jet streak over southern California. The orientation of the
southwesterly 850-300mb mean layer flow pattern will also support
enhanced upslope flow into these ranges, in particular along the
Sierra Nevada and Uinta. From the central and southern Sierra
Nevada, on south to the peaks of the Transverse Ranges, and east
into the central Great Basin and Utah ranges, elevations above
7,000ft will be in better position to witness heavy snow. As the
aforementioned lobe of 500mb vorticity approaches southern
California tonight, the 250mb jet streak and surge in Pacific
moisture will advance farther inland. The heaviest round of snow
is likely to unfold in Utah early Wednesday morning, while the
Rockies of northern Colorado and southern Wyoming also contend
with heavier rounds of snow throughout the day on Wednesday. Snow
will come to an end over the Sierra Nevada by Wednesday afternoon,
then taper off over the Intermountain West by Wednesday night.

WPC PWPF show moderate chances (>40-60%) for >8" of additional
snowfall over the central and southern Sierra Nevada >6,000ft
through Wednesday morning, while moderate-to-high probabilities
(50-80%) for >8" of snowfall exist in parts of the Wasatch and
Uinta above 8,000ft. Farther inland, the Park Range of northern
Colorado and Ferris Mountains of southern Wyoming also have
moderate-to-high chances (50-80%) of measuring >8" of snowfall
late Tuesday night and into Wednesday. The WSSI shows Moderate to
Major Impacts with Snow Amount being the primary driver in
expected impacts. The Probabilistic WSSI (WSSI-P) also shows low
chances (10-30%) for Moderate Impacts due to Snow Rate in the
southern Sierra Nevada. Meanwhile, in the >7,000ft peaks of the
Transverse Ranges, the WSSI shows some localized Major Impacts
possible. In areas seeing at least Moderate Impacts, disruptions
to daily life are expected that include (but are not limited to)
hazardous travel, delays and road closures, and disruptions to
infrastructure that could include potential tree damage and power
outages. Farther inland, the WSSI shows some spotty areas of Major
Impacts in the Great Basin at elevations >7,000ft and along the
Wasatch and Uinta Ranges >8,000ft. Moderate Impacts are depicted
along the Park Range in northern Colorado and the Ferris Mountains
of southern Wyoming.


The probability of receiving at least 0.1" of ice is less than 10
percent Day 1-3.


Mullinax