Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
401 PM EDT Fri May 08 2020

Valid 00Z Sat May 09 2020 - 00Z Tue May 12 2020


...Northeast...
Days 1-2...

Models continue to show a signal for late-season snows across the
region, with significant accumulations possible across interior
portions of New England, centered on northern NH and ME. 

Increasing northerly winds on the backside of a deepening surface
low moving east through the northern Mid Atlantic by Friday
evening are expected to support a changeover to snow across
portions of West Virginia and northeast Pennsylvania, with all
snow developing farther north across higher elevations of Upstate
New York into western New England tonight.  Accumulating snow is
expected across the Poconos, Catskills and Berkshires, where a few
inches of snow are possible. The storm intensifies moving up into
the Gulf of Maine, so so amounts gradually increase in northern NH
to northern Me in the mid level deformation zone inland from the
cyclone track.  Several inches of snow are expected in northern NH
to interior northern ME.
The models have come into much better agreement on the cyclone
track/intensity, so the solutions were given equal weighting.

Meanwhile, strong northwesterly winds behind the departing system
will encourage snow showers along the central and southern
Appalachians into Saturday morning, with accumulating snows likely
as far south as eastern Tennessee and western North Carolina.


...Northern Plains to Upper MS Valley...
Days 1-2...

A mid-level shortwave diving southeast through central Canada is
expected to amplify as it moves into the Dakotas tonight into
Saturday morning.  Sufficient cold air along with low-to-mid level
frontogenesis and a 300 mb divergence maxima are expected to
support accumulating snow on the north side of the associated
surface low tracking southeast across the Dakotas into Minnesota
early Saturday.  2-4 inches of snow is expected in a band in
northeast North Dakota, with isolated higher amounts possible. As
the system moves further southeast into the upper MS Valley, temps
are warm enough that few of the models show an all snow event. 
Amounts are reduced as a result of the precip type uncertainty.
The system will track across the region, with the mostly likely
outcome in the guidance a mix of precip types. The high resolution
NAM and NAM Conus Nest continue to show stronger lift and cooling,
so potential for a band of snow still remains.

The probability of significant icing is less than 10 percent.

Petersen