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

Valid 12Z Fri May 08 2020 - 12Z Mon May 11 2020


...Appalachians/Northeast...
Days 1-2...

Models continue to show a positive signal for late-season snows
across the region, with significant accumulations possible across
portions of the Northeast. 

A well-defined shortwave moving into the central Plains Friday
morning will continue to move east-southeast into the base of a
longwave trough that is associated with a deep upper low centered
north of the Great Lakes.  As this system continue to move east,
this will support widespread precipitation along an strong
west-east oriented frontal zone extending along the Ohio valley on
Friday.  Thermal profiles will support mostly rain through much of
the Ohio valley on Friday.  However, 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
Pennsylvania, with all snow developing farther north across parts
of Upstate New York into western New England Friday night.  Areas
impacted are expected to include the Poconos, Catskills and
Berkshires, where a few inches of snow are possible.  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.

As the system tracks northeast and deepens off of the New England
coast on Saturday, the overnight models began to show overall
better agreement - indicating a track tucked close enough to the
coast to bring accumulating snows to northern Vermont, New
Hampshire and Maine, but not nearly as heavy as some previous runs
of the ECMWF and GFS had indicated.


...Northern Plains...
Days 1-2...

A mid-level shortwave diving southeast through central Canada is
expected to amplify as it moves into the Dakotas Friday
night-Saturday morning.  Sufficient cold air along with low-to-mid
level frontogenesis and good upper level support are expected to
support snow on the north side of the associated surface low
tracking southeast across the Dakotas into Minnesota early
Saturday, with a few inches of snow likely across portions of
northeastern North Dakota.

The probability of significant icing is less than 10 percent.

Pereira