Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
430 PM EST Sat Nov 16 2019

Valid 00Z Sun Nov 17 2019 - 00Z Wed Nov 20 2019


Day 1...

The probability of significant icing (0.25-inch) and/or snow
(4-inches) is less than 10 percent.

Days 2-3...

...Northeast...
Surface low pressure will track north off of the Southeast and
Mid-Atlantic coasts through the remainder of the weekend before
spreading moisture across the Northeast as it approaches
southeastern New England on Monday.  Models have been trending
slower with this system, allowing drier air to remain in place
longer and delaying the onset of precipitation and wintry
conditions - especially across northern New England on Monday. 
However by Monday afternoon and evening, there is still a good
signal for a wintry-mix to develop, resulting in icy conditions
across portions of Upstate New York and northern New England. 
Warm air aloft, with subfreezing boundary layer temperatures will
support precipitation changing to sleet and freezing rain across
some areas.  As the low tracks along the Gulf of Maine toward Nova
Scotia, precipitation is expected to continue across northern New
England into the overnight hours before tapering off Tuesday
morning.  Heaviest ice accumulations are expected to center along
the Green Mountains of Vermont and across northern Maine, where
WPC probabilities indicate a Moderate Risk (40 percent or greater)
for storm total ice accumulations of a 0.25-inch or more.  Some
areas of northern Maine, may change to or remain mostly snow
through Monday night - supporting some higher probabilities for
snow accumulations of 4-inches or more across far northern Maine.

...Northern Rockies...
Models show a progressive shortwave trough moving east across the
Pacific Northwest into the northern Rockies on Tuesday.  A brief
period of upper jet forcing coinciding with low-to-mid level
frontogenesis and upslope flow is expected to support a period of
heavier snowfall, resulting in some locally heavy amounts along
the Lewis Range in northwestern Montana on Tuesday.

Pereira