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

Valid 00Z Mon Jan 13 2025 - 00Z Thu Jan 16 2025

...Northern Rockies/Western High Plains...
Day 1...

Lingering upslope flow and the passage of a weak 500mb vort max
Monday morning will keep periods of mountain snow in the forecast
in parts from the Little Belt and Big Snowy in central Montana,as
well as the Absaroka, Big Horns, and Black Hills through midday
Monday. Snowfall will taper Monday afternoon once the 500mb vort
max passes to the south. WPC probabilities in the aforementioned
mountain ranges (particularly in the less populated, higher
elevation areas) sport high chances (>70%) for additional snowfall
>4" through 06Z Tuesday.

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

An occluding area of low pressure is responsible for a swath of
snow over the Upper Great Lakes this afternoon. Periods of snow
will continue and fall heavily at times over the Minnesota
Arrowhead this afternoon thanks to additional lake-enhancement from
onshore winds of Lake Superior. As the low moves over Lake
Superior tonight, CAA on the backside of the storm will
reinvigorate LES bands from far northern Wisconsin to the western
half of the Michigan U.P.. The system will make its way slowly east
over Lake Superior on Monday with the TROWAL on the backside of the
storm helping to sustain ongoing LES bands over the Michigan U.P.
Monday night and into Tuesday morning. Most of the northern coast
of the Michigan U.P. sports high chances (>70%) for snowfall
totals >8" through Tuesday night, but the highest totals are
likely to occur in the Huron Mountains and along the Keweenaw
Peninsula where WPC probabilities show moderate-to-high chances
(50-70%) for snowfall totals >12".

Farther east, the cold front tracking across the Great Lakes gives
rise to CAA withing WSW flow over Lakes Michigan, Erie and
Ontario. Expect multi-banded segments emerge off of Lake Michigan
tonight and linger through Tuesday with the heaviest totals over
northwest portions of Michigan's Mitten. WPC probabilities do show
moderate-to-high chances (50-70%) from snowfall totals >8" along
the northern most tier of Michigan's Lake Michigan coast through
Tuesday evening. Farther east, dominant LES single-banded segments
will develop off Lakes Erie and Ontario beginning Monday and
persist into the middle of the week. WPC probabilities show high
chances (>70%) for snowfall amounts >18" in the Tug Hill with some
localized spots potentially approaching 30". Farther south, the
Chautauqua Ridge and areas from northwest PA to western NY
communities just south of Buffalo could see as much as 12-18" of
snowfall through Tuesday evening. Note snow is likely to continue
into Tuesday night, although the passage of a 500mb shortwave
trough may shift the LES single-bands farther south into central NY
and along the PA/NY east of Lake Erie. The WSSI already depicts
Major Impact potential for areas south of Buffalo (including a
subsection of I-90) and in the Tug Hill for Monday night and into
Tuesday.

...Northern Mid-Atlantic...
Days 2-3...

While actual snowfall amounts are expected to be minor, both Monday
and Tuesday have the chance to see snow squalls traverse the region
each afternoon and evening. Monday's snow squall potential comes
via a cold front that will push through the Southern Tier of New
York and all of Pennsylvania. Lapse rates will steepen but the
strength of the front and depth of the lapse rates should make for
hit-or-miss squall potential. By Tuesday, a positively tilted 500mb
trough will provide a better source of synoptic-scale lift aloft,
along with strong 700mb CAA. Latest guidance shows western PA and
along the NY/PA border posing the better chances for squalls
Tuesday afternoon, but these snow squalls may be able to traverse
the Keystone State Tuesday evening given the exceptional PVA aloft.
While any totals would generally be on the lighter side, the
sudden bursts of heavy snow could mean dramatic reductions in
visibility and quick accumulations on roadways.


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


Mullinax