Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
318 PM EST Mon Nov 02 2020

Valid 00Z Tue Nov 03 2020 - 00Z Fri Nov 06 2020


...Northeast...
Expect another round of heavy snow to develop this afternoon and
continue into the evening, producing additional heavy
accumulations across portions of Upstate New York and northern New
England.  A well-defined, mid-level shortwave/upper level jet max
diving south of James Bay is forecast to dig across the Northeast
Monday evening.  In addition to the strong synoptic scale forcing,
lake-enhanced moisture and upslope flow is expected to support
heavy snowfall rates across the Tug Hill region into the
Adirondacks.  Several HREF members indicate snowfall rates of 1-2
inches per hour persisting for several hours, before veering winds
behind the passing shortwave shift the threat for heavy rates
farther to the south toward the Mohawk Valley for a short period
overnight.  Meanwhile, strong forcing translating farther east
will help support the potential for locally heavy accumulations
developing over the mountains of northern New England during the
evening and overnight hours.  WPC Day 1 probabilities (ending 00Z
Wednesday) for accumulations of 4-inches or more are 50 percent or
greater across the Tug Hill, as well as across large portions of
the Adirondacks and northern Greens.   Snows are expected to move
to the Maine coast, with at least light accumulations likely
overnight as low pressure begins to intensify and move east over
the Gulf of Maine.

...Pacific Northwest...
Onshore flow with a series of embedded shortwaves will mark the
return of wet weather across the Northwest starting Tuesday, with
periods of heavy precipitation likely to continue through the end
of the period.  Snow levels are expected to remain high, confining
significant snow accumulations to the highest peaks of the
northern Cascades through late Wednesday.  However, as an
amplifying shortwave begins to move onshore, snow levels are
expected to lower, expanding the threat for heavy amounts across
portions of the northern Cascades and Olympics on Thursday.

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

Pereira