FOUS11 KWBC 120743
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
243 AM EST Sun Jan 12 2025

Valid 12Z Sun Jan 12 2025 - 12Z Wed Jan 15 2025

...Northern Rockies/Western High Plains...
Days 1-2...

The southwest side of a positively-tilted upper-level trough will
carry waves of vorticity across the northern Rockies today with
additional snowfall over the higher peaks of central Montana into
Wyoming as well as across northern NM. Another wave will sink
southward through eastern Montana tomorrow with a bit more light
snow for the Black Hills. WPC probabilities for at least 6 inches
of snow are >50% in the Little Belt and Big Snowy Mountains as well
as the Big Horns.


...Great Lakes...
Days 1-3...

Area of low pressure over MN this morning will lift northeastward
across northern WI into the U.P. of Michigan and Lake Superior this
afternoon as it takes on a negative tilt in response to an
approaching upper low moving southward out of central Canada. This
will favor much of the U.P. and the northeastern Arrowhead of MN
for modest snow today beneath the TROWAL as the system occludes.
WPC probabilities for at least 4 inches of snow are high (>70%)
over the northeastern Arrowhead (~Grand Marais to Grand Portage),
over the Keweenaw Peninsula into the Porcupine Mountains, and also
around the Hiawatha National Forest via southerly flow ahead of the
front.

By D2, the deep upper low will cross into northern MN with a core
of 850mb temps < -20C. Sfc trough will still linger across Lake
Superior as the main area of low pressure only slowly drifts
eastward, allowing height falls to push into the U.P. to continue
the snow through Monday. Downstream, the cold front will continue
eastward and help foster in a westerly to WSW flow over the eastern
Great Lakes, allowing lake effect snow to increase into NW Lower
Michigan first, then downwind of Lakes Erie and Ontario. Core of
the upper low will continues its path southeastward across the
Great Lakes Mon into Tue eventually pushing off the Northeast coast
by the end of the period. However, NW flow will remain which will
continue the lake effect snow over all the Great Lakes, but
especially off Lakes Erie/Ontario D3.

For the D2-3 period, WPC probabilities for at least 8 inches of
snow are highest off Lake Erie from Erie, PA to the Buffalo
southtowns across the Chautauqua Ridge. Localized totals may be in
the 12-18 inch range. East of Lake Ontario, the Tug Hill will help
maximize snow totals there, especially south of Watertown in the
higher elevations (Redfield) where WPC probabilities for at least
12 inches of snow are >70%.


For the Day 1-3 period, the probability of significant icing of at
least 0.10" is less than 10 percent across the CONUS.


Fracasso



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