Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
326 PM EDT Wed Oct 28 2020

Valid 00Z Thu Oct 29 2020 - 00Z Sun Nov 01 2020


...Texas Panhandle...
Day 1...
Strong upper low which has been meandering across the Desert
Southwest will gradually shift eastward tonight into Thursday. As
this feature moves towards the Texas Panhandle overnight, intense
synoptic and mesoscale forcing will occur in the vicinity. Deep
layer ascent through the LFQ of a downstream jet streak combined
with mid-level divergence and height falls will be robust.
Additionally, a strong TROWAL is likely to wrap around the
mid-level low, focused across the Panhandle of TX, coincident with
a deformation axis and modest fgen. The atmospheric column will be
marginal in the low levels for snow, however, intense ascent aloft
should dynamically cool the column, and persistent moisture
wrapping through the TROWAL and within the WCB is likely to fall
as heavy snow across parts of the region. Snowfall rates could
reach 2"/hr as evidenced by the HREF mean hourly snowfall
probabilities, and a narrow corridor of heavy snow is likely
through Thursday morning. There is still some uncertainty as to
where the heaviest snow band will setup, as well as the temporal
duration of that band. However, confidence is increasing in a band
of more than 4" of snow, and WPC probabilities are moderate for
this amount in the TX Panhandle. Isolated amounts of 6-8" are
possible.


...Northeast...
Day 2...

As it begins to interact with the northern stream, the previously
noted upper low is forecast to transition to an open wave and
accelerate eastward from the southern Plains early Thursday to the
Mid-Atlantic coast by Friday morning.  Moisture lifting to the
north, interacting with cold high pressure over Canada and an
associated low-to-mid level fgen zone, is expected to support a
stripe rain changing to snow across portions of northern
Pennsylvania, Upstate New York and southern to central New England
Thursday night into Friday morning.  The general trend of the
models has been toward a more suppressed solution, with a more
rapid drying of the DGZ coincident with CAA during the p-type
transition to snow. This suggests a lesser potential for valley
snow accumulations, and the risk for impactful snowfall seems to
be more confined to the terrain/elevated regions. There is still
high confidence in some accumulating snow in the Catskills,
Berkshires, southern Greens and southern Whites, where WPC
probabilities for 4 inches are moderate. Elsewhere, some light
accumulations are possible at lower elevations and along the coast
of Maine.


The probability for significant ice (0.25" or greater) is less
than 10 percent all 3 days.


Weiss