Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
320 PM EST Sun Mar 05 2023

Valid 00Z Mon Mar 06 2023 - 00Z Thu Mar 09 2023

...West/Rockies...
Days 1-3...

Upper ridging nosing into Alaska from the northeast Pacific and a
strong upper high near Baffin Island will help maintain blocking
over the high latitudes that favors troughing over the western
portion of Canada and into the Pacific Northwest for the next few
days. A punctuated stream of vorticity along a cyclonically-curved
jet (150kts) racing across NorCal and the central Rockies will
maintain broad scale lift across the region with enhancement as
each shortwave moves through. The most favored areas will be over
southwestern Oregon and over the NorCal ranges into the northern
Sierra on the southern side of the vorticity stream. This extends
across the Great Basin to the central Rockies following in tandem
with the easterly-translating jet. East of the Sierra, snowfall
will be focused on D1 with light to modest accumulations for the
Wasatch and light snow elsewhere. With 700mb temperatures below
normal (-1 to -2 sigma), snow levels will generally be below
2000ft except a bit higher over the CO Rockies. Impactful snow is
likely at many of the mountain passes with at least moderate
accumulations in the coastal ranges and light snow likely even in
the lowlands of California with cold air and generally light
onshore flow over the Pacific Northwest leading to localized
moderate snowfall. On D1, WPC probabilities for at least 8 inches
of snow are >50% over the northern Sierra with many terrain areas
receiving near/over 6" from the Cascades to the Wasatch. D2-3 will
focus over northern CA/Sierra as another (but weaker) jet streak
moves through. The greatest probabilities of at least 6 inches of
snow D2 and 3 will lie across the northern Sierra, Klamath,
Coastal, and Shasta-Siskiyou.

...Upper Midwest/Northern Great Lakes...
Days 1-2...

Shortwave moving quickly into the Corn Belt tonight and Great
Lakes on Monday will aid in bringing some WAA-driven snow to
northern WI and the U.P. into northern L.P of Michigan as a
surface low arcs through the Midwest. Nose of the elongated jet
will help with broader lift on the LFQ side while sufficient
moisture wrings out in a cold enough air mass (where more snow is
expected). FGEN should enhance an area over northeastern WI in the
U.P. where over 6 inches are quite possible. WPC probabilities for
at least 4 inches of snow are >50% in these areas. Lighter snow
will extend ESE-ward in PA/NY with lower amounts expected.

Northern Plains...
Days 2-3...

Embedded shortwaves ejecting east-northeastward out of the Rockies
will move into the northern Plains D2-3 into a colder air mass
over the Dakotas. East to southeast to southerly flow in the lower
levels (sfc-700mb) will help bring in and maintain sufficient
moisture to bring periods of light snow to the region, with
localized enhancement over the Black Hills D2. This will move
northeastward through North Dakota D3 with a broad area of light
snow. Two-day probabilities of at least 4 inches of snow are >50%
from around the Black Hills in SD northeastward into south central
ND.

For days 1-3, the probability of significant icing greater than
0.25" is less than 10 percent.


Fracasso