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

Valid 12Z Thu Mar 19 2020 - 12Z Sun Mar 22 2020


Four Corners to CO Rockies...Central Plains ...Western Great
Lakes...
Days 1-3...

A potent closed upper low positioned over Arizona moves northeast
today across Co. There will remain considerable moist advection as
Pacific moisture is transported northeastward across CO. The
heaviest and most widespread snowfall is likely on Thu as a well
defined upper divergence maxima/700 mb convergence maxima crosses
northern CO into southeast WY and Ne. 
WPC probabilities for 12 inches are moderate to high in the
central to northern CO Rockies.
By day 2, a respite will occur with only light snow expected.

Considerable uncertainty persists across Nebraska, where initial
temperatures are too warm for snow.  The cold front drifts south
today, with cold advection changing rain to snow in the frontal
band.  A few solutions remains which indicate a mesoscale wave
riding up along the frontal boundary, producing a secondary max of
snow across the NE panhandle north of the CO border to northeast
NE. There is not much overlap among the ECMWF, UKMET, Canadian,
and high res windows on the location for banding potential.  The
surface low is expected to lift to the northeast from CO early
today to KS before dissipating, leading to a decreasing threat of
snow by late Thu night.

A coupled jet region forms with the northern stream wave crossing
the upper MS Valley into the upper Great Lakes. 
The low will interact with a low-level cold front to produce a
swath of enhanced low/mid level frontogenesis to enhance ascent
across the upper peninsula of Michigan. While the column will
initially be too warm to support snowfall, as the low moves
northeast and the front drops southward, cooling will cause precip
type to transition from rain to snow.  Light sleet/freezing rain
is possible in the transition over the central to eastern Up of
MI. 

The enhanced frontogenesis around the low should produce a band of
moderate to at times heavy snow, with several inches of snow
expected off Lake Superior into the western UP of MI.  Lake
enhanced snow continues into early Fri before drying aloft cuts
back on snowfall coverage/intensity.

A stripe of modest freezing rain is likely Thursday across eastern
SD/adjacent southwest MN. This is in response to the drying of the
Dendritic Growth Zone while low-levels remain saturated, producing
an environment favorable for light freezing rain or freezing
drizzle. Accretions are expected to be light, but WPC
probabilities indicate a low risk for 0.1 inches. 

...Mountains of Interior New England...
Light freezing rain accumulations are also possible in the higher
elevations of VT/NH/interior ME on Fri as low level cold air just
below freezing is in place while precip breaks out within the
strong low level warm advection pattern.  The continued warming
into Fri during the day allows temps to rise above freezing,
limiting the event potential.  

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