FOUS11 KWBC 020859
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
359 AM EST Mon Dec 2 2024

Valid 12Z Mon Dec 02 2024 - 12Z Thu Dec 05 2024

..Great Lakes... Day 1...

*** Heavy Lake-Effect Snow continues through tonight in Michigan, 
 through Tuesday for eastern Great Lakes ***

Reinforcing shortwave trough axis is over central MN early this
morning and will continue to round the longwave trough axis over
the interior Northeast by crossing the Midwest today and track near
the VA/NC line tonight before moving offshore.

Michigan Lake Effect...
Flow over Lakes Superior and Michigan will remain veer more NNWly
today behind the shortwave trough axis and maintain heavy snow over
the eastern U.P. and along the western shore of the L.P. into far
northern IN. Day 1 PWPF for >6" is 40-70% around Grand Traverse Bay
and far SW MI to the IN border.

Eastern Lake Effect...
Flow over the eastern Great Lakes continues to veer NWly with the
trough passage this morning. This means that while the single band
that had been pushing into the eastern shore of Lake Erie on Wly 
flow will be disrupted, the NWly flow will continue to produce
heavy LES over the Chautauqua Ridge from fetch over Lake Huron and
then over Lake Erie. Day 1 PWPF is 60-90% over that portion of
extreme western NY with probabilities dropping off toward Erie PA.
Banding off Lake Ontario is expected to continue for the Syracuse 
area today with an additional 6" possible.

Day 2...
High pressure currently centered near NW ND will shift down the 
Mid- Mississippi Valley Tuesday with a more amplified ridge 
extending north over the Great Lakes. Behind this ridge axis, flow 
over Lakes Michigan and Superior quickly shifts to the SW which 
ends the LES bands from overnight. However, as this new fetch 
saturates, warm air advection induced snow develops across the U.P.
tonight, particularly as a surface low ahead of the next wave 
approaches Lake Superior from the NW late tonight and pivots east 
Wednesday. The air remains cold enough for SWly flow driven lake 
enhanced snow into the far eastern U.P. Day 2 PWPF for >6" is 
limited to the Keweenaw Peninsula and near the Mackinac Strait. 

The ridge axis does not shift over the eastern Great Lakes until
Tuesday night, so LES will continue and essentially shift back
toward a single-band appearance on SWly flow, though the warm air
advection makes for a wetter snow than recent days. Day 2 PWPF is
40-60% around the Chautauqua Ridge with low probs for >4" for the
south towns of Buffalo.

The ongoing lake-effect snow is the subject of the Key Message linked below.

Day 3...
The low over Ontario further develops and sends a strong cold front
over the Great Lakes Wednesday into Thursday. 850mb temps quickly
drop into the DGZ behind the front, so LES resumes with a vengeance
on NWly flow through the day over Michigan and that night/Thursday
morning for the eastern Great Lakes. Day 3 PWPF >6" is 30-70% for
NWly snow belts across the northern U.P. and the northern L.P.
Marginal thermals for snow and warm air advection limit eastern 
Great Lakes snow Wednesday, but quickly shifts snowy overnight. Day
3 PWPF for >6" is around 20% off Lake Erie and prolonged moderate
snow over the Tug Hill makes for 40-60% probs there.

LES looks to continue over the eastern Great Lakes on the NWly flow
into Friday.

...New England... Day 3...

The upper low tracks across northern Lake Huron Wednesday night
with strong warm air advection and increasing precip into an
initially cold airmass over New England allowing moderate to
locally heavy snow over the terrain of the Greens/Whites/and much
of Maine. Day 3 PWPF for >6" 30-60% for these areas. The low
crosses Maine on Thursday when there is a greater snow threat for
interior New England.

...Southern Appalachians... Day 1...

A clipper-type trough currently over central MN shifts to eastern
TN by this evening. Upslope flow enhances precip which is cold
enough for snow and SLRs around 17:1 to produce 30-60% probs for
>4" snow tonight for mainly the western slopes of the Great Smokey Mtns.

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

Jackson

...Winter Storm Key Messages are in effect. Please see current 
 Key Messages below...

https://www.wpc.ncep.noaa.gov/key_messages/La...

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