Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
418 PM EST Tue Feb 02 2021

Valid 00Z Wed Feb 03 2021 - 00Z Sat Feb 06 2021


...Northeast/Eastern Great Lakes...
Day 1...
The strong coastal system currently impacting the Northeast and
northern Mid-Atlantic will continue to gradually move northeast --
with its primary surface low moving from the Gulf of Maine into
the Canadian Maritimes overnight.  Additional snow accumulations
of 4-inches or more can be expected during the evening and
overnight hours across northern Maine and along the U.S.-Canada
border back into northern New York.  Northerly flow across Lake
Ontario is expected to support lake enhanced snows, generating
locally heavy totals across the Finger Lakes region of New York.

...Pacific Northwest and Northern California to the Northern and
Central Rockies...
Day 1...
A mid-to-upper level trough centered along the Northwest coast is
expected to translate east into the Intermountain Region and
Rockies as a low drops along the coast of British Columbia and
into the Pacific Northwest Tuesday night into Wednesday. 
Southwesterly flow ahead of the low is expected to support
moderate to locally heavy snows across the central and southern
Cascades, Klamath Mountains, as well as the northern Sierra. 
Meanwhile, light to moderate snows are forecast to accompany a
low-to-mid level frontal band advancing southeast across the
Intermountain Region and Rockies Tuesday night and Wednesday. 
Some locally heavy snow accumulations are possible across the
northern Rockies and central Rockies.

...Central Rockies...
Day 2...
Locally heavy snows are expected to continue through late
Wednesday across portions of the central Rockies, with an axis of
strong frontogenesis and favorable upper jet forcing bolstering
snowfall rates as it moves across the western to central Colorado
ranges.

...Central Plains to Upper Midwest...
Days 2-3...
As the previously noted trough moves east, surface low pressure
developing over the central High Plains late Wednesday is forecast
to move into the mid Mississippi valley on Thursday.  As energy
begins to be phase aloft and the upper trough begins to assume a
negative tilt, the surface low is expected to rapidly intensify
and lift north into the western Great Lakes Thursday evening. 
While widespread heavy snow accumulations are not expected, strong
low-to-mid level frontogenesis, along with favorable upper
forcing, will likely support at least a brief period of heavy snow
from eastern Nebraska to Wisconsin on Thursday, while strong gusty
winds develop around the rapidly strengthening system.  A wintry
mix at the onset of precipitation may produce some light ice
accumulations, before changing over snow across portions of the
Upper Midwest and western Great Lakes regions.

As the low tracks through the upper Great Lakes on Friday, strong
northerly winds on the backside of the system will support
developing lake effect snows, with heavy accumulations becoming
likely in the Upper Michigan snowbelts, as well as along the
eastern shores of Lake Michigan.

...Pacific Northwest to the Northern and Central Rockies...
Day 3...
A low-amplitude shortwave embedded within fast northwest flow is
expected to bring another round of organized snows across the
northern Cascades Thursday night.  This energy along with a strong
front settling southwest will support periods of snow from the
northern to the central Rockies on Friday.

Pereira