Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
414 AM EDT Wed Mar 25 2020

Valid 12Z Wed Mar 25 2020 - 12Z Sat Mar 28 2020


Day 1-3...

...Western U.S....
A positively-tilted upper trough will continue to settle southeast
across the . through Thursday.  An associated low-to-mid level
front is expected to provide the focus for periods of organized
heavier snow from the Sierra Nevada of CA to the ranges of
northern UT today. 
WPC PWPF continues to indicate high probabilities for
accumulations of 8 inches or more across the higher terrain near
the NV/UT border and northern UT.

On Thu and Thu night, this front is expected to drift slowly
southeast across the ranges of southern CA, southeast NV, UT and
northern CO.
Pockets of enhanced moisture and ascent occur within the frontal
band, resulting in additional areas of moderate snow expected.
Impacted areas on Day 2 (ending 00Z Friday) are forecast to
include the east-central Nevada to far west-central Utah ranges -
where WPC PWPF is showing moderate probabilities for accumulations
of 8-inches or more across the higher terrain.

On Day 3, accumulations of several inches are possible in the
ranges of western to northern CO as the front moves across these
areas.  The events winds down as the front departs for the Plains.
 A Low risk for 8 inches is shown given the system is expected to
move out on to the Plains.

...Front Range, Foothills, and High Plains of WY and CO...
Day 3...
The models indicate a 700 mb wave moves from UT across CO,
becoming a closed low as the low emerges on to the high Plains. 
The surface low drifts slowly into southeast CO.  This sets up
northeast CO and southeast WY for return moisture advection and
ascent as the ECMWF shows a 300 mb jet max over eastern NM and
southeast CO, placing favorable difluent flow across northeast CO
to southeast WY. The synoptic lift combines with lift from
orographics to produce the likelihood of snows in the front range
of northern Co into southeast WY, with locally heavy snows in
favored upslope areas.  As the low drifts east on to the high
plains, temperatures cool, so rain may change to snow.  The
limited duration of cold temperatures limits snowfall potential. 


...Northern Plains to the Upper Great Lakes...
Mid level energy emanating from the western U.S. will support the
development of a weak wave that will move east along the frontal
boundary across the Northern Plains to the upper Great Lakes, with
moisture getting lifted in the mid level frontogenesis band north
of the front.  This along with favorable upper jet forcing will
support a stripe of light to moderate precipitation across South
Dakota early Wednesday before shifting east across southern
Minnesota to northern Wisconsin and the U.P. of Michigan later in
the day into the night.  Marginal temperatures during the day
should keep accumulations in check. NAM and SREF Guidance does
show the potential for banded precipitation, producing locally
heavier precipitation rates which could raise accumulations in the
frontal band. The snow ends as the wave crosses into Ontario Wed.

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

Petersen