Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
524 PM EDT Tue Apr 14 2020

Valid 00Z Wed Apr 15 2020 - 00Z Sat Apr 18 2020

...Central Appalachians...

Days 1...
A shortwave crossing the Great Lakes region will rapidly track
eastward in conjunction with a jet streak situated over the Ohio
Valley, and this will induce a wave of low pressure along the
front that is situated along the southeast U.S. coast.  The low
will be close enough to advect moisture inland across portions of
western Virginia, western Maryland, and eastern West Virginia. 
There will be enough cold air advection for rain to change to wet
snow, and probably all snow for locations above 3000 feet where
accumulations could reach 4 inches.  Several hours of enhanced
lift within the dendritic growth zone late this evening will
likely result in a period of moderate snow.  There was enough
deterministic model agreement to merit a general model blend for
thermal profiles.


...Northern to Central Rockies and western High Plains...

Days 1-3...
A reinforcing trough drops southward across the northern Rockies
on Wednesday, and amplifies by the time it reaches the northern
Great Basin Thursday.  Broad cyclonic flow across the western U.S.
with moisture from both the Pacific and Gulf of Mexico being
lifted by the terrain will create a favorable environment for
moderate to heavy snow across the northern Rockies through
Wednesday.  Day 1 snow probabilities for 8 or more inches is high
across western Montana and northwest Wyoming.  The heaviest snow
then becomes established over the higher terrain of south-central
Wyoming and central Colorado going into Thursday as the best lift
and dynamics will be centered over this region.  In addition, an
enhanced period of moist upslope flow across portions of western
Nebraska and western Kansas will likely lead to several inches of
snow for these areas, especially southwest Nebraska.


...Missouri to northern Ohio Valley...

Day 3...
A sheared shortwave breaking off from the main upper level trough
over the Rockies will help sustain a surface wave along a
quasi-stationary front.  Although the majority of the QPF
associated with this will be rain, temperatures will likely be
just cold enough to support a corridor of slushy accumulations up
to 2 inches from northern Missouri to northern Ohio.  This will
also be dependent on precipitation rates, with snow accumulation
most likely for those scenarios where mesoscale banding sets up
and produces dynamic cooling, thus overcoming initially warmer
boundary layer temperatures.


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

Hamrick