Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
334 AM EDT Tue Mar 24 2020

Valid 12Z Tue Mar 24 2020 - 12Z Fri Mar 27 2020


Days 1-3...

...Day 2 Upper MS Valley to the Northern Great Lakes...
A mid level shortwave triggers low pressure development on a front
traversing the Upper MS Valley to the upper Great Lakes. The
timing places the low departing the Upper MS Valley Wed evening
and crossing northern MI by Thu morning, then across into southern
Ontario.
Low-mid level frontogenesis/ favorable upper jet forcing are
expected to support a stripe of generally light amounts north of
the front across South Dakota Wednesday morning and then across
northern Wisconsin and the U.P. of Michigan late Wednesday into
early Thursday. The stronger cyclone in the NAM leads to  higher
amounts than the weaker cyclone in the GFS.  Greater weighting was
given to the intermediate ECMWF and UKMET forecasts.  The
departure of the low on Thu morning should bring the event to an
end.

...Western U.S....
Models a broad positively-tilted upper trough settling southeast
across the western U.S. this period.  This is expected to produce
some high elevation, locally heavy amounts across portions of the
California Sierra Nevada Mountains and Mountains of northern Utah
today. 
An axis of foot of snow is expected in the northern to central CA
Sierra Nevada on day 1/Tue. Snow occurs in response 
to a low-to-mid level frontal zone settling south across the
Sierra and Great Basin, accompanied by a 300 mb jet of 110-130 kt
and upper divergence maxima. 

The 00z GFS shows a wave on the 700 mb front that enhances low
level convergence and lift coming across eastern NV into UT on
Wed-Wed night.
Several additional inches of snow are expected int he higher
elevations of east central NV and northern UT, where 2 day totals
of 12-18 inches are possible.

The front slowly sags south across NV and UT, so the frontal
convergence and ascent in the mountains should also persist and
gradually move south with the front.  Several more inches of snow
are possible in the UT Wasatch/Uintas and mountains near the
southern UT/NV border. The upper jet maxima forecast to exit UT
into CO allows snow showers to develop in the mountains of
northwest CO to southern WY.

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

Petersen