Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
505 AM EDT Mon Apr 13 2020

Valid 12Z Mon Apr 13 2020 - 12Z Thu Apr 16 2020


...Upper MS Valley to the Upper Great Lakes...
Day 1...
A deep surface low will continue to become better organized as it
tracks northward across the western Great Lakes region today and
eventually into Canada.  Any on-going snow in the deformation zone
should be tapering off during the day, although some lingering
light snow may well continue down-wind of Lake Superior well after
the low departs given the cold air advection southward behind the
system and a long trajectory over the waters. 

...CO Rockies to High Plains...
Days 1-2 ...
Confluent low level flow and moisture pooling up along the high
Plains, foothills, and front range combine with sporadic upper
divergence maxima in the west-east jet maxima cross CO to produce
periods of generally light snow today...with a couple of inches
possible before snow tapers off in response to dry air aloft
moving across the state.

...Southwest to the Southern High Plains...
Days 1-2 ...
Mid level energy and upper divergence maxima in the difluent flow
aloft will continue to stream across the Southwest U.S., with
enhanced moisture and lift at 700 mb supporting a stripe of
organized precipitation, including high elevation snows, across
northern Arizona and New Mexico during the day today.  The models
still show a narrow band of heavy amounts possible from portions
of the AZ Mogollon Rim across the mountains of central NM with
including on either side of Albuquerque, and along the NM Sangre
de Cristo Mountains.  Areas of snow will move out over the
adjacent High Plains region later this afternoon or evening...with
accumulating snows over northeastern New Mexico and into the Texas
and Oklahoma panhandles and southwestern Kansas through Tuesday
morning.  The threat ends as the wave progresses steadily east
into warmer air in the more eastern Plains.  Light ascent keeps
amounts modest western TX/OK.

Northern to Central Rockies Day 3...
The models show a 700 mb wave developing north of the
International Border region and dropping south across parts of
Montana on Tuesday evening...and eventually reaching as far south
as Wyoming on Wednesday. Embedded areas of 700 mb lift within the
associated moisture plume progress across ID/western MT and then
down into Wyoming should result in several inches of snow within
these area, with amounts enhanced where flow turns upslope in the
ranges of western to central Montana, Bitterroots of Idaho, and
Absarokas of southern Montana and adjacent portions of northwest
Wyoming.

Eastern West Virginia to the Border of Virginia and Western
Maryland Late Day 2...
Multiple models/ensembles, including the ECMWF/UKMET/Canadian
global/GFS, show a region of confluent 700 mb flow crossing
steadily northeast across WV and western MD/western VA Tue night. 
It is cold enough in the mountains of eastern WV that a period of
snow is expected, with several inches likely if these models are
correct.  The wave continues downstream into lower elevations of
western WV to central MD but the models show initial temps too
warm for snow, limiting duration of snow and thus snow amounts. 
The departure of the wave to the east coast Wed afternoon should
cause the event to end.

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

Bann