Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
339 AM EST Tue Dec 03 2019

Valid 12Z Tue Dec 03 2019 - 12Z Fri Dec 06 2019

Days 1-3...

...New England...
An ongoing winter storm is forecast to continue into Tuesday
across coastal eastern New England across eastern and northern
Maine as the associated sfc low deepens and lifts to the northeast
towards Nova Scotia.  Low-to-mid level frontogenesis and mid level
deformation combine with upper divergence maxima to support
precipitation west of the low.  The heaviest accumulations are
expected to center across central to northeast Maine, where
several inches are possible before the system tracks east into
Nova Scotia Tuesday evening. The models still have forecast track
and intensity differences, with poor initialization in the WRF ARW
vs the satellite and radar (i.e. bands crossing eastern MA not
noted in the forecast).  More weight was given to the 00z
ECMWF/00z WRF ARW2/00z Canadian Regional GEM. Locally heavy totals
are possible as a band of heavy snow in southern NH (recent rates
to 2 inches per hours around Manchester NH) pivots north into
Maine early today. Probabilities indicate a low risk of a foot of
snow on Day 1.  The event ends as the storm departs into southeast
Canada and moves steadily away from New England tonight.

...Great Lakes...
Beginning Tuesday night and continuing through Wednesday, a cold
frontal passage is followed
by cross Lake Ontario and Lake Erie flow.  The cross lake flow
picks up heat and moisture fluxes.  Lee shore convergence combines
with orographic lift to help bolster totals in the Tug Hill
plateau, the hills above the Lake Erie shore, and along the
Allegheny Plateau in western New York and Pennsylvania, where
several inches are possible by early Thursday.
The Canadian regional model joins the ECMWF and GFS in showing QPF
and snow maxima in these areas. The Canadian global was the
outlier with higher QPF and resultant snow than the
ECMWF/GFS/NAM/UKMET in northwest PA/southwest NY, so was given
less weighting. Drier air aloft advecting into the Great Lakes
should end the event Thu.

...Southern California to the Central Rockies...
A closed low centered west of Southern California Tuesday evening
is forecast to move east northeast towards California Wed before
weakening as it moves inland Wed night-Thu into an open wave. This
will bring a period of locally heavy snow to the southern Sierra
and southern coastal ranges on Wednesday.  These snows are
expected to diminish as the system moves quickly to the east
Wednesday evening, with light snow in the ranges of southern UT to
southwest Co.
es across the southern Great Basin and into the central Rockies
Wednesday night.
On Thursday the 700 mb wave departs to the east on the Plains, so
the event should end over southern UT and CO.

For Days 1-3, the probability of 0.25 inches of icing is less than
10 percent.

Petersen