Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
302 PM EST Fri Mar 06 2020

Valid 00Z Sat Mar 07 2020 - 00Z Tue Mar 10 2020


Days 1-3...

...Northeast...
A closed low/upper trough moving across the mid Atlantic and
Northeast will interact with the southern stream energy lifting
along the Mid Atlantic coast and support a rapidly deepening
surface cyclone tracking northeast off of the mid-Atlantic and
Northeast coasts tonight into early Saturday. While the system is
expected to track far enough east to preclude moderate-heavy snows
along the bulk of the Eastern Seaboard, the 12Z guidance still
hints at the potential for mesoscale banding across across
southeastern Massachusetts tonight into Saturday morning. Models
have trended lower with the QPF compared to previous cycles --
including the 12Z ECMWF and more recent NBM runs. This idea is
supported by relatively weak 700-500 mb theta-e lapse rates, never
dropping below +4 C/KM. Moreover, boundary layer temperatures are
expected to be marginal at the onset, thus the lower threat of
heavy precipitation would mitigate the probability of dynamical
cooling through the layer, thus likely precluding significant
(watch/warning criteria) snow accumulations.

...Western U.S....
Cold front associated with an offshore upper trough will advance
south and east as energy moving through the base of the trough
pivots toward the coast tonight into Saturday.  This will bring
some light to moderate snows south from the Cascades into the
Sierra Saturday in Sunday.  Meanwhile, post-frontal upslope flow
behind a front settling south from Canada, enhanced by a low level
wave dropping southeast across Montana, will support moderate to
heavy snows along the northwestern Montana ranges during the
weekend.

For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Hurley/Pereira