Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
359 AM EST Tue Dec 3 2024

Valid 12Z Tue Dec 03 2024 - 12Z Fri Dec 06 2024

...Michigan...
Days 1-3...

LES from NNWly flow continues through mid-morning over the eastern
U.P. and down the western shore of the L.P. Localized additional
amounts of 4" are possible between 12Z and 18Z in far SW MI given
the orientation of the flow into that area as well as the current
radar coverage for the strong banding shifting down Lake Michigan.

Surface ridging ahead of the next wave spreads over MI today
shifting flow to the SW and bringing a reprieve to snow this
afternoon to the state. However, the SWly flow quickly saturates
and warm air advection snow begins over the U.P. this evening as
the moisture plume from the next low shifts in. Lake Michigan
enhancement to this snow will really kick in overnight with
heavy/repeating snow north from Grand Traverse Bay and over the
southern shore of the eastern U.P. which continues into Wednesday
morning. Day 1.5 probabilities for >12" snow are around 60% north
of Petoskey and across the Mackinac Straits.

A strong cold front from the low tracking north of the Great Lakes
sweeps across MI Wednesday afternoon with a quick return to LES
banding. Potent cold air advection over the Lakes brings heavy
bands to NW flow prone snow belts into Thursday. Particularly
strong winds can be expected given the pressure gradient between
the 990mb low and the 1037mb high over the Dakotas, so impacts will
be enhanced by the wind. Day 2 PWPF for >6" is 50-80% over the U.P.
north shore and the NW sector of the L.P. with potential prolonged
banding southeast from Grand Traverse Bay with a Superior and Lake
Michigan fetch contributing given the NW flow turning NNWly. LES
slowly decays and the wind gradiently quickly drops off on
Thursday.


Eastern Great Lakes and Northeast...
Day 1...

NWly flow will continue to produce heavy LES over the Chautauqua
Ridge from fetch over Lake Huron and then over Lake Erie through
much of today before it diminishes/pivots east as flow shifts SWly
behind a ridge axis that moves through. An additional 3-6" can be
expected today over the Chautauqua Ridge area. This afternoon the
SWly flow will bring snow, possibly banded, to around Buffalo and
the easten shore of Lake Ontario that persists into the overnight;
Day 1 PWPF for >4" are 20-40%.


Days 2/3...

SWly flow ahead of a developing clipper-type low tracking north of
the Great Lakes saturates over the interior Northeast, increasing
coverage and intensity of snow on Wednesday that continues to
expand and shift north over New England through the overnight. The
Mohawk Valley/southern Adirondacks are favored for heavier snow
Wednesday afternoon where the combination of topographic lift and
antecedant cold air overlap. Higher terrain of the Greens and
Whites get snow in this time, but the greater coverage is expected
over central Maine, generally inland from Bangor Wednesday night.
Day 2 PWPF for >6" is 50-80% over the Mohawk Valley as well as in
central Maine. The WAA based precip spreads across the rest of
Maine Thursday morning with a rain/snow line developing interior
from the Maine coast with a quick transition to heavy snow
on the cold side.

The strong cold front crossing Michigan on Wednesday crosses the
eastern Great Lakes late Wednesday night with a quick onset back to
heavy snow again on NWly flow off eastern Erie starting before
sunrise Thursday with aided fetch from Lake Huron. A decent banding
situation arrises from Lake Ontario over the Tug Hill down the
Mohawk Valley, possibly overlapping well with the snow from
Wednesday.Day 2.5 PWPF for >8" is unfortunately 60-90% from Erie Co
PA to the South Towns of Buffalo. These bands may extend decently
far inland given the rather strong winds from the 990mb low moving
into southern Quebec and the 1035mb high over South Dakota Thursday
morning.

The low quickly exits to the Canadian Maritimes Thursday with
guidance wanting to end most of the heavier banding Thursday night.
Guidance is usually too quick to cut off LES banding, but at least
in this case the surface high tracking over the Ohio Valley on
Friday should cause disruption to the bands. Day 3 PWPF for >8" is
90% over Erie Co PA and around 30% over northern Maine where the
surface low tracks and for upslope flow over the northern Greens
and Adirondacks.


The probability of significant ice across the CONUS is less than
10 percent.


Jackson