Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
425 AM EDT Thu May 07 2020

Valid 12Z Thu May 07 2020 - 12Z Sun May 10 2020


...Southern and Central Appalachians to the Northeast...
Days 2-3 (12Z Friday - 12Z Saturday)...

A significant late-season winter storm is expected to produce
accumulating snows from the southern and central Appalachians into
the Northeast, with heavy amounts possible across portions of
northern New England.

Models continue to show a late-season winter storm developing
Friday into Saturday as a potent shortwave emanating from the
western U.S. interacts with a deep upper low centered over the
Great Lakes.  A well-defined shortwave currently moving east of
the northern Rockies into the High Plains is expected to dive
southeast into the longwave trough south of the low and begin to
move along the Ohio valley by Friday morning.  This will support a
developing low moving east along a strong low-to-mid level,
west-east oriented baroclinic zone.  While the column is expected
to be marginal initially for frozen precipitation, strong forcing
may dynamically cool the column supporting accumulating snow
across the upper Ohio valley into central Pennsylvania by Friday
afternoon.  With the loss of daytime heating, expect accumulating
snows to become more widespread as the system moves farther east
into northeastern Pennsylvania and Upstate New York, with
significant accumulations possible across the Poconos and
Catskills Friday evening into the overnight.  Meanwhile as cold
air spills southeast in the wake of the advancing low, a
changeover to snow is expected across the higher elevations of the
central and southern Appalachians, with accumulating snows
possible as far south as western North Carolina and eastern
Tennessee.  Accumulating snows will continue to shift east
overnight into New England, with impacted areas expected to
include the Berkshires, southern Greens and Worcester Hills early
Saturday morning.  Saturday morning, as the shortwave begins to
assume a negative tilt, lifting north ahead of the upper low,
surface low pressure is expected to further strengthen and track
north along the northern New England coast.  This will set the
stage for potentially heavy snowfall accumulations across portions
of interior northern New England.  While the overnight guidance as
a whole still showed a fair amount of spread, the GFS moved into
good agreement with the ECMWF - showing heavy accumulations across
far northern New Hampshire and northern Maine - where storm total
amounts of 8-inches or more likely across the higher terrain.

The probability of significant icing is than 10 percent.

Pereira