FOUS11 KWBC 131930
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
230 PM EST Mon Jan 13 2025

Valid 00Z Tue Jan 14 2025 - 00Z Fri Jan 17 2025

...Northern Rockies/Plains...
Day 1...

Deep northwesterly flow, with embedded energy aloft, will support
periods of snow and a stripe of mostly light accumulations from
the northern Rockies southeastward into the mid Missouri Valley.
Additional accumulations after 00Z are expected to be no more than
an inch or two for most locations. However, WPC probabilities
indicate that orographic enhancement may support some totals of at
least 4 inches in the north-central Wyoming and south-central
Montana mountains and in the Black Hills.


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

An occluded surface low will move east of the Great Lakes through
the St. Lawrence Valley, leaving deep cyclonic flow in its wake.
Lake effect snows will continue to develop and intensify, with
locally heavy amounts beginning to accumulate in the typical
snowbelts this evening. Lake effect snows will continue into
Wednesday before an approaching shortwave diving southeast through
central Canada introduces some warm advection/synoptic-driven
snows into the region by late in the day.

Some of the heaviest lake effect snows are expected to fall east
of Lake Ontario where a single band is expected to drift slowly
south across the region over the next day. WPC probabilities
indicate that accumulations greater than a foot are likely from
this evening into late Tuesday across the region. Other areas
impacted will likely include the northwestern Pennsylvania and far
western New York counties, where localized two-day totals over a
foot can be expected. Lesser accumulations are expected elsewhere,
including the northern Michigan snowbelts.


...Pennsylvania...
Day 1...

Steep lapse rates in addition to an amplified shortwave moving
through the base of the broader scale trough may support snow
showers and potential squalls east of Lake Erie on Tuesday. The NAM
and GFS continue to show Snow Squall Parameter values greater than
2, especially across western to central Pennsylvania tomorrow
afternoon/evening. Accumulations will generally be light, but a
brief period of intense, wind-driven snow may create hazardous
driving conditions.


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


Pereira




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