Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
332 AM EST Wed Nov 17 2021

Valid 12Z Wed Nov 17 2021 - 12Z Sat Nov 20 2021

...Pacific Northwest to the northern Rockies...
Days 2 and 3...
A Pacific system in the mid-latitudes will approach the Oregon
coast by early Friday, with broad ascent via the northern stream
jet across British Columbia on Thursday. Snow levels will rise in
modest warm air advection with generally light snow on day 2 over
the Olympics and Washington Cascades. By day 3, mid-level
shortwave and the surface low will weaken as its associated
moisture continue inland into the Idaho panhandle, Bitterroots,
and the Teton Range as snow levels rise to about 5000 feet. 

...New England...
Day 1...
Warm front over the Mid-Atlantic this morning will lift through
the Northeast today into tomorrow morning, with
snow/sleet/freezing rain and rain progressing in tandem with the
warm advection. Areas in deeper cold air (northern Maine) will see
a period of accumulating snow before a changeover to sleet and
freezing rain then rain. Portions of the northern White Mountains
through the Allagash will see a period of ice accumulation up to
around a tenth of an inch overnight tonight as milder air moves
in.

...Great Lakes...
Days 2 and 3...
Modest cyclone moving through Ontario day 2 will usher colder air
(around -10C at 850mb) across the relatively warmer lake waters.
With sufficient but modest low-level moisture, multi-band snows
are favored off Lake Superior into the U.P. and northern Lower
Michigan Thursday, and eventually downwind of Lakes Erie and
Ontario on WNW winds. Favored areas include some northeast Ohio
snow belts through Erie County, PA into the western Southern Tier
of New York. Several inches of snow will be possible in each of
these areas.

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

Fracasso