Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
416 AM EST Thu Feb 06 2020

Valid 12Z Thu Feb 06 2020 - 12Z Sun Feb 09 2020

...Northeast...
Days 1-2...

A shortwave trough currently over the Big Bend of TX is rounding
the positively tilted, full-latitude trough extending from the
Upper Midwest to west TX and will be the main driver for the
eastern CONUS cyclone later today through Friday. An existing
surface trough with subtle pressure centers in the eastern TN
valley has developed under the deep/strong/moist southwesterly jet
ahead of the long-wave trough which results in the widespread
precip across the eastern CONUS. This Big Bend shortwave will
swing the main trough to a neutral tilt by this evening and
negatively tilted overnight and through Friday as it races up the
Eastern Seaboard on a 150 to 180kt jet. As the trough axis crosses
the Southeast tonight the surface pressure center rapidly develops
and slows over the Mid-Atlantic. The deformation axis pivots over
Upstate NY before strengthening and ejecting northeast across the
New England Friday. Heavy snow is expected along this axis with
Day 1.5 probabilities for a foot or more moderate in western NY
south of Lake Ontario increasing to likely for the northern
Adirondacks, Green Mtns, and high probabilities much of far
northern Maine (with likely probabilities for 18 or more inches
over far northwestern Maine on Day 1.5).

Overrunning flow ahead of the low raises the freezing rain risk
with Day 1 ice probabilities moderate in the Alleghenies of
western NY, the Adirondacks, and Green Mtns of VT down into the
Berkshires of western MA as well as 30 percent for the Monadnocks
of NH...and 30 percent for far eastern Maine on Day 1.5.

The departure of the low Friday night up into the Canadian
Maritimes ends the synoptic portion of the event, with precip in
Maine winding down around midnight.


...Northwest across the Northern Great Plains...

Days 1-2...
Confluent flow arcing from the Pacific Northwest and northern
Rockies continues low level frontogenesis with strong moisture
influx through Friday. High snow levels through this zone keep the
heavy snow for Days 1 and 2 to the high terrain of the WA/OR
Cascades/Blue Mtns/Northern Rockies of ID/MT/WY and Wasatch/CO
Rockies with more on Day 1 than Day 2.
48hr probabilities for 18 or more inches are high for all these
areas with the WA Cascades likely to have over 4 feet in the
highest terrain.

Day 3...
The next shortwave will move onshore Friday night, quickly track
across the northern Rockies Saturday and the northern Great
Plains/SD Saturday night. Snow levels drop under the trough to
roughly 2000ft in the Pac NW and northern Rockies and at the
surface for the Great Plains. Day 3 snow probabilities are high
for 8 or more additional for the highest WA/OR Cascades/Blue
Mtns/and northern Rockies of ID/MT/northern WY. Snow probs for 4
or more inches are generally 20 to 30 perfect in a stripe across
eastern MT and along the ND/SD border into southern MN. Good
agreement among global guidance Saturday night warrants moderate
probabilities in this stripe on the SD/MN border.


Jackson