Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
357 PM EDT Thu Mar 19 2020

Valid 00Z Fri Mar 20 2020 - 00Z Mon Mar 23 2020


...Four Corners...
Days 1-2...

A deep closed upper low over the central Great Basin will fill
slowly, nearly in place, before shearing out to the east on
Saturday. Despite the slow filling of this feature, moist
advection on W/SW 700mb flow with a tropical Pacific connection
will maintain sufficient column moisture such that ascent through
height falls and periodic PVA combined with upper diffluence will
produce high elevation snowfall into Saturday. The heaviest snow
is expected on D1 when WPC probabilities for 8 inches are moderate
in the Wasatch and Uinta ranges of Utah, as well as much of the CO
Rockies. Probabilities for heavy snowfall drop considerably on D2,
with only light accumulations persisting as the forcing weakens
and moves away. Total snowfall may locally exceed 12-15" by
Saturday.


...Western Great Lakes...
Days 1...

Consolidated area of low pressure moving out of the lee of the
Rockies in CO will eject rapidly to the northeast and into
southeast Canada on Friday. This system will move quickly in
response to a weakening mid-level low which will open and lift
northeast. Despite the weakening of both the surface and mid-level
lows, synoptic ascent will be robust through height falls, PVA,
and diffluence through coupled jet streaks. In the lower levels,
frontogenesis will remain strong as a low-level baroclinic zone
along a cold front interacts with the surface wave lifting
northeast. This band of enhanced fgen will strengthen ascent to
produce a a stripe of moderate to heavy snow from northern IA
through the U.P. of MI. The heaviest snow from this event is
likely in the U.P. where LES is likely to contribute to
accumulations as northerly fetch behind the surface low produces a
period of LES in the favored regions for northerly bands off Lake
Superior. WPC probabilities for 6 inches are high only in the
U.P., and isolated amounts to 10 inches are possible.


The probability of greater than 0.25 inches of freezing rain is
less than 10 percent.

Weiss