Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
450 AM EDT Wed Apr 15 2020

Valid 12Z Wed Apr 15 2020 - 12Z Sat Apr 18 2020

...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 throughout the
day today and into parts of the central Rockies by Thursday. In
addition, models still suggest there will be 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 2 into 3...
A sheared shortwave breaking off from the main upper level trough
over the Rockies will help sustain a surface reflection 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.

One consideration for the snow potential will be whether the NCEP
or non-NCEP guidance verifies. Thinking was that the NCEP guidance
may end up being too quick to eject energy from the
Rockies...which has implications in the thermal fields and the
placement of the rain/snow boundary in addition to QPF
differences.  A second consideration will be the precipitation
rates, with snow accumulation most likely for those scenarios
where mesoscale banding sets up and produces dynamic cooling, thus
overcoming what may well initially be warmer boundary layer
temperatures.

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

Hamrick/Bann