Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
334 PM EDT Fri Mar 20 2020

Valid 00Z Sat Mar 21 2020 - 00Z Tue Mar 24 2020


...The West...
Days 1-3...

The persistent closed upper low over the Great Basin will
gradually wind down and shear out to the east through Sunday.
Despite the slow filling of this feature, moist advection on W/SW
700mb flow will maintain sufficient moisture such that ascent
through upper diffluence and upslope flow will produce high
elevation snowfall Saturday. The heaviest snow is expected on in
the Wasatch and Uinta ranges of Utah, as well as much of the
western CO Rockies and San Juans.  Snow amounts taper as the upper
low weakens, with little additional snow Sun. Additional snowfall
may locally be 6-12 inches by Saturday in favored terrain.

On D3, a renewed upper low will drift towards the CA coast
accompanied by the entrance region to a 150kt subtropical jet,
producing strong ascent and moisture into California. As 700mb
flow becomes increasingly orthogonal to the Sierra, heavy snow
will develop and spread northeastward. WPC probabilities on D3 are
high for 8 inches, with localized amounts over 12 inches likely.


...Northeast...
Day 3...

Shortwave moving through the Ohio Valley will lift northeast
towards New England while slowly beginning to tilt negatively. At
the same time, a northern stream impulse rotating down through
Ontario will attempt to interact with this feature, while a jet
streak lifting out to the northeast couples with a subtropical jet
stream arcing across the Tennessee Valley to drive ascent and
pressure falls near the Mid-Atlantic coast. This surface low is
likely to deepen as it heads E/NE to south of New England,
potentially reaching near the Benchmark just beyond this forecast
period. As this low consolidates and deepens along the coast,
intense WAA will spread northward, slowly displacing the wedge of
high pressure in place from Sunday. The column will initially be
cold enough for snow from central PA through New England, the
exception potentially being along the immediate coast. However, as
the low deepens and moves northeast, the WAA will eventually
transition the p-type to rain as far north as southern New
England. The initial WAA may be strong enough to produce snow even
in the I-95 corridor north of Philadelphia, but accumulations from
this event look to be primarily confined to the interior, elevated
parts of PA, NY, and New England. WPC probabilities are high for 4
inches from the Poconos, through the Catskills, Adirondacks, and
Berkshires, with lower probabilities elsewhere. There remains
uncertainty into the intensity of track of this low, but
significant snowfall is becoming more likely just inland from the
urban I-95 corridor Sunday night through Tuesday.


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

Weiss