Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
352 AM EST Sun Nov 26 2023

Valid 12Z Sun Nov 26 2023 - 12Z Wed Nov 29 2023

...Great Lakes and Northern New England...
Days 1-3...

A multi-day significant lake effect snow (LES) event begins today
and persist through mid-week. A shortwave pivoting across the
Great Lakes today will amplify in response to a vorticity maxima
rotating through the base, resulting in amplified and persistent
cyclonic flow developing over the eastern third of the CONUS. This
will drive a cold front eastward, with potent CAA developing in
its wake. 850mb temps are progged to reach -10C to -15C, more than
cold enough to produce strong lake-induced instability atop lake
surface temperatures that are generally +5C to +12C. This will
result in SBCAPE approaching 1000 J/kg, and steepening lapse rates
through an inversion depth approaching 15 kft. The lead shortwave
will pivot east into New England tonight, with a secondary
reinforcing piece of energy moving overhead Monday night into
Tuesday. This secondary feature will also add more significant
synoptic moisture to the environment, and it appears late Monday
through Tuesday evening will feature the most intense LES,
although some wavering in wind direction may modulate snowfall
accumulations at times. A brief reduction in LES intensity and
coverage may develop late in the forecast period as shortwave
ridging lifts towards the Great Lakes, but additional LES is
likely beyond this forecast period as the environment becomes
favorable once again.

On D1, the heaviest LES is likely across the U.P. and western
portions of the L.P. of MI, especially in the Porcupine and Huron
Mountains, as well as near Grand Traverse Bay. WPC probabilities
are high (60-80%) for more than 4 inches, with slightly lower
probabilities extending along the length of Lake Michigan towards
Grand Rapids due to shorter fetch. Local total more than twice
that amount are likely in a few areas. More significant LES is
progged to develop over the eastern Great Lakes late Monday
through Tuesday when the DGZ crashes concurrently with an increase
in depth, while forcing remains quite robust over the lakes.
Additionally, flow on Monday will likely provide upstream
connection providing additional moisture downstream of Lakes Erie
and Ontario where snowfall could be quite heavy. LES is expected
to be widespread across much of the favored W/NW snow belts during
D2, but will be most intense across the Chautauqua Ridge and Tug
Hill Plateau where WPC probabilities for more than 6 inches are
70-90%, and locally 12-18 inches is possible where the most
intense bands can persist. During D3 the best banding may shift
southward off Lakes Ontario and Erie, and begin to wind down east
of the other lakes in response to subtle height rises. WPC
probabilities on D3 for more than 6 inches are again high east of
Lake Ontario, and moderate east of Lake Erie. The long duration of
this event, despite some wavering in band placement and evolution,
could result in locally more than 2 feet of snow in some places,
especially in the Tug Hill. Additionally, although the LES will
generally feature above climo SLRs resulting in fluffy and
efficient accumulations, the SLRs with this event could be
somewhat lower than other LES events due to the very warm waters
and only modestly cold surface temperatures, generally 15-20:1, so
some snow load impacts are possible, which is reflected by minor
probabilities in the WSSI-P.

The lead shortwave will also help drive surface cyclogenesis near
New England Sunday night and this low will deepen as it moves
rapidly northeast across Maine. The guidance has shifted a bit
farther NW tonight resulting in a warmer, but also wetter,
solution. While most of the precipitation across New England
should be rain, or a brief period of snow becoming rain, the
elevated terrain of the White Mountains and far northern Maine
will likely receive heavy snow as this low passes the region. WPC
probabilities for more than 6 inches are 10-30% D1.5 to D2,
highest in the White Mountains.


Weiss