Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
333 AM EST Sun Dec 06 2020

Valid 12Z Sun Dec 06 2020 - 12Z Wed Dec 09 2020

...New England...
Day 1...

Potent nor'easter will gradually pull into the Canadian Maritimes
through this evening. Continued warm/moist advection north of the
low will spread precipitation across much of Maine, with ascent
provided through a TROWAL, height falls, and a divergence maxima
associated with coupled jet streaks. Heavy snow will persist
across primarily northern Maine after 12Z today, and additional
significant accumulations are likely before snow winds down as
forcing ejects to the east and the column begins to dry. WPC
probabilities are high for an additional 4 inches across northern
Maine with local amounts of up to 8" possible in the highest
terrain, bringing local storm totals in excess of 12" across parts
of Maine.


...Pacific Northwest...
Day 3...

A Pacific jet streak will dive into the PacNW Tuesday accompanied
by a weak shortwave and modest mid-level confluence to drive
increased column moisture to the region. Ascent through weak
height falls and divergence along with a weak wave of low pressure
diving SE will spread moderate snowfall into the terrain of the WA
Cascades and Northern Rockies during D3. However, accumulations
greater than 4 inches are forecast only in the Cascades which has
a longer overlap of ample moisture and forcing. WPC probabilities
for 4 inches are around 30%.


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


Weiss