Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
337 PM EST Wed Nov 25 2020

Valid 00Z Thu Nov 26 2020 - 00Z Sun Nov 29 2020

Days 1 to 3...

...Western U.S...

An upper-level trough moving through the Intermountain West
tonight and on Thanksgiving Day will bring lower snow levels and
sufficient energy/forcing in conjunction with a modest mid-level
Pacific moisture tap for some additional accumulating snow for the
higher terrain, and especially the northern Rockies with several
inches of new snow expected for the Sawtooth, Bitterroots, Tetons,
and the Wind River range. Farther south as energy begins to dig
southeastward across the interior, a few inches will be locally
possible across the Wasatch as well. On Friday and Saturday, the
latest model guidance agrees in developing an upper low which will
swing east over the Four Corners region and this will yield
locally a few inches of snow over the higher terrain of the
central and southern Rockies, and especially the San Juans of
southwest CO.

...Northern New England...

Energy associated with a relative compact, and robust mid-level
trough and associated closed low will quickly move across the
lower Great Lakes region and into the Northeast overnight and
through Thanksgiving Day. Strong warm-air advection ahead of the
advancing surface low will bring mainly rain along its path, but
as the system encounters persistent, yet shallow subfreezing
temperatures across northern New England, some light freezing rain
(with locally up to near a 0.10" of ice accretion) will be
expected before a changeover to rain occurs from south to north on
Thanksgiving Day. The heaviest ice accumulations will generally be
across areas of west-central to southwest ME where the combination
of cold air and somewhat heavier precipitation will be noted. All
of the precipitation should begin to taper off and come to an end
by tomorrow night.

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

Orrison