Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
226 PM EST Sat Feb 17 2024

Valid 00Z Sun Feb 18 2024 - 00Z Wed Feb 21 2024

...Great Lakes...
Day 1...

Trough axis across Hudson Bay will allow another shortwave to
rotate around its base tonight and Sunday before lifting out
through Maine Sunday night. This will invigorate another round of
lake effect snow as a surface cold front pushes through the region
from NW to SE. WNW flow over the Upper Lakes will favor mostly the
eastern U.P. but also into NW Lower MI, where WPC probabilities
for at least 4 inches of snow are >50% (U.P.) but only around 10%
in Lower MI. SW flow across Lakes Erie/Ontario will favor single
bands into BUF and ART areas where probabilities for at least 4
inches are >50% (BUF) and >80% around ART. There, in the Thousand
Islands region, probabilities of at least 12 inches are 10-50%.
All lake snows will end by Monday morning as heights rise and high
pressure moves in.


...West...
Days 1-3...

Lead weakening system will continue to move through the
PacNW/NorCal/northern Great Basin tonight into Sunday with the
strongest moisture flux into the northern Sierra and
Shasta/Siskiyous. Snow levels will fluctuate around 5000ft or so,
with WPC probabilities for at least 8 inches of snow highest
(>50%) in the Sierra crest and Shasta/Siskiyous above about
7000ft.

The next upper low moves eastward along 40N tomorrow into early
Monday, advancing moisture off the Pacific into much of northern
to central California as a 165kt jet moves into SoCal.
Modest/strong PW/IVT anomalies (90-95th percentiles) will focus
into the northern/central Sierra, where significant snow is likely
above ~6000ft. Sharpening of the upper trough would allow for a
longer residence time of moisture flux into the region, and
several feet of snow are likely into the crest and some of the
higher passes where travel may become difficult to impossible.
Probabilities for at least 12 inches of snow are >50% above about
7000ft in the Sierra and into the Shasta/Siskiyous.

By Tuesday, D3, moisture will continue to stream into California
and the interior NW/northern Great Basin, but with much less
intensity. Nevertheless, additional snowfall over 8 inches is
likely (>70%) in the Sierra above 7000ft as snow levels only
slowly fall as the upper trough gets closer to the coast. Broad SW
flow into the Great Basin will spread light to locally moderate
snow to the Tetons southward to the Wasatch with more to come into
D4.

Resident cold air over the Columbia Basin/Gorge does allow for
some risk for light freezing rain in the surrounding Cascades and
perhaps the northern Oregon Coast Ranges tonight where
probabilities for >0.1" ice remain 10-20%.


Fracasso