Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
255 PM EST Mon Feb 19 2024

Valid 00Z Tue Feb 20 2024 - 00Z Fri Feb 23 2024

...California and The West...
Days 1-3...

The deep upper low responsible for the deluge of rain and heavy
mountain snow over California will work in tandem with another
lobe of 500mb vorticity rotating on the southern flank of the
upper low to pump 850-500mb Pacific moisture into the western
third of the CONUS. Over the next few days, snowfall will be its
heaviest over the Sierra Nevada, the northern Wasatch, and the
Uinta Range today and into Tuesday 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. The northern Sierra Nevada and other northern
California ranges (such as the Trinity/Shasta and Salmon) are
likely to see heavy snowfall at elevations above 5,500ft. From the
central and southern Sierra Nevada on south to the peaks of the
Transverse Ranges and on east into the central Great Basin and
Utah ranges, elevations above 7,000ft will be in better position
to witness heavy snow. Timing-wise, the California ranges heavy
snowfall will be well underway, but only just begin this afternoon
from the Great Basin on east to the central Utah and southwest
Wyoming. As the aforementioned lobe of 500mb vorticity approaches
southern California late Tuesday, the 250mb jet streak and surge
in Pacific moisture will advance farther inland. The heaviest
round of snow is likely to unfold in Utah Wednesday morning, while
the northern Colorado Rockies also begin to see 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 48-hr PWPF show high chances (>70%) for >18" of snowfall over
the northern Sierra Nevada and the northern California mountain
peaks >6,000ft, while similarly high probabilities for >12" of
snowfall exist in parts of the northern Wasatch and Uinta above
8,000ft. Farther inland, the Park Range of northern Colorado and
Ferris Mountains of southern Wyoming have moderate-to-high chances
(50-80%) of measuring >8" of snowfall late Tuesday night and into
Wednesday. The WSSI is showing Major to even Extreme Impacts in
the northern California ranges and along the Sierra Nevada with
Snow Amount and Snow Load being the primary drivers in expected
impacts. The Probabilistic WSSI (WSSI-P) also shows high chances
(>70%) for Major 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 Major Impacts, considerable disruptions to daily
life are expected, including but not limited to dangerous, and
even near impossible travel, numerous 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.


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


Mullinax