Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
326 AM EST Tue Nov 16 2021

Valid 12Z Tue Nov 16 2021 - 12Z Fri Nov 19 2021


...Pacific Northwest to the Northern Rockies...
Days 1 and 3...
Trailing shortwave behind the cold front pushing through Montana
will support lingering snow for the Washington Cascades and near
the Montana/Idaho border through the evening and overnight hours
before diminishing by Wednesday morning. After a dry period on day
2, another shortwave out of the Gulf of Alaska will merge with an
incoming Pacific system to bring additional snow to parts of the
Pacific Northwest. Focus will be on the southern Washington
Cascades into the Oregon Cascades with snow levels rising to
3000-5000 ft during Thursday into early Friday. WPC probabilities
for at least 4 inches of snow are around 10-30 percent near
4000-5000 ft day 3.

...Maine...
Day 2...
Warm front lifting through New England will bring in warm
advection precipitation (snow or sleet to freezing rain) to Maine
late Wednesday into early Thursday before turning to rain as
temperatures warm above freezing. WPC probabilities for at least
0.1" ice are about 10-40 percent in the Allagash toward the White
Mountains.


...Great Lakes...
Day 3...
A cyclone moving eastward through southern Canada day 2 will lift
northeastward toward Hudson Bay day 3 and modestly deepen as it
helps to drag down colder air over the western Great Lakes. 850mb
temperatures are forecast to fall to near -10C by Thursday evening
with sufficient low- and mid-level moisture to support a few
multi-band snows off Lake Superior into the U.P. of Michigan where
several inches of snow is possible. Lighter amounts are favored
downwind of the rest of the Great Lakes. WPC probabilities for at
least 4 inches of snow are only near 20 percent but may trend
higher.


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

Fracasso