Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
417 PM EDT Tue Apr 20 2021

Valid 00Z Wed Apr 21 2021 - 00Z Sat Apr 24 2021

...Ohio Valley/Great Lakes/Northeast...
Days 1-3...
An amplified shortwave will continue to drive the leading edge of
an unseasonably cold airmass from the Midwest into the eastern
U.S., while supporting late-season accumulating snows from the
Ohio Valley northeastward into the interior Northeast.  Heavy
accumulations are possible across portions of Upstate New York and
northern New England.

The upper level shortwave associated with the significant snowfall
that occurred across portions of the central Rockies and Plains
overnight and earlier today is forecast to lift from the Ohio
Valley into the Lower Lakes region overnight.  Anomalously cold
air along with low-to-mid level frontogenesis west of a deepening
surface low will support a stripe of light to moderate snows from
the Ohio Valley into the Lower Lakes overnight, with the WPC PWPF
showing that at least an inch or two of accumulating snow is
likely from central Indiana to the shores of lakes Erie and
Ontario.  As the shortwave continues to lift north, with a closed
low developing along the U.S./Canada border, snow will shift east
across the interior Northeast on Wednesday.  The low is expected
to continue to deepen as it moves tracks into Atlantic Canada on
Thursday, with windy conditions and snow showers expected across
the Northeast on the backside of the departing system.  Three day
snowfall totals of 6-inches or more are likely across portion of
western New York, the Finger Lakes and Tug Hill -- where lake
effect following the synoptic snows are expected to bolster
totals.  Overall, the heaviest snowfall totals are expected to
occur across the Adirondacks and the New York North Country, as
well as far northern Vermont to Maine, where accumulations of
8-inches or more are likely.

For Days 1-3, the probability of significant icing (0.25-inch or
more) is less than 10 percent.

Pereira