Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 PM EST Thu Jan 30 2020

Valid 00Z Fri Jan 31 2020 - 00Z Mon Feb 03 2020


Days 1-3...

...Pacific Northwest to the Northern Rockies...
An approaching warm front and a long fetch of deep moisture is
expected to bring heavy precipitation back into western Washington
Thursday night.  However, with snow levels rising dramatically,
any threat for heavy snow will be largely confined to areas above
7000-ft in the northern Cascades.

Snow levels are forecast to remain high across the Northwest into
the weekend ahead of an approaching cold cold, before plummeting
as the front moves inland by late Saturday.  By late Saturday,
with snow levels dropping to around 4000-ft, the threat for heavy
snow accumulations along the northern Cascades is expected to
become more widespread. 

As the front continues to push south and east of the region,
models show precipitation diminishing across the Northwest on
Saturday night night into Sunday.  However, onshore flow along
with embedded upstream energy will continue to support snow
showers across western Washington.  As snow levels continue to
fall, this could produce some light accumulations across the
western Washington Lowlands. 

The front is expected to push through the northern Rockies late
Saturday into early Sunday.  As snow levels drop, Strong
low-to-mid level inflow along with upper level forcing is expected
to help support heavy snows along the mountains of northwestern
Montana.


...Northeast...
Low pressure developing along the North Carolina Coast on Saturday
is forecast to track offshore toward the Canadian Maritimes. Low
end probabilities for snow accumulations of 4-inches or more
across Downeast Maine late Saturday-early Sunday are a reflection
of a few ensemble guidance members which track the system farther
west.  However, the general consensus of the 12Z deterministic
guidance keeps the system well offshore -- showing little threat
for significant snow accumulations along the Northeast coast.

The probability of significant icing (0.25-inch or greater) is
less than 10 percent.

Pereira