Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 PM EST Sun Feb 16 2020

Valid 00Z Mon Feb 17 2020 - 00Z Thu Feb 20 2020


Days 1-3...

...Pacific Northwest to the Northern and Central Rockies/central
High Plains...
As a 700 mb shortwave trough digs southeast across WA/OR  and then
across ID and WY, confluent flow and modest vertical velocity
maxima bring a period of light to moderate snows across the ranges
of the Pacific Northwest and northern to central Rockies.  On
Monday night into Tue, the axis of confluent flow and modest lift
remains in central MT and also in central CO.  The models indicate
light snow amounts, with little potential for heavy accumulations.
On Day 3, a positively titled upper trough drifts south to  the
central Plains, with the confluent 700 mb flow and pooled moisture
axis drifting south across WY to SD and NE. Modest lift leads to
more light snow amounts. Likewise, a weak, low amplitude wave
crosses central to eastern CO, with light accumulating snow in the
Sangre DeCristo mountains.

...Upper MS Valley/Great Lakes and Northeast...
Shortwave energy moving east across the northern Plains into  the
upper MS Valley supports a deepening surface low lifting northeast
from the lower Missouri valley into the western Great Lakes region
on Monday.  Models show favorable upper jet forcing along with
low-to-mid frontogenesis producing a stripe of light to moderate
snows from northern Iowa and southern Minnesota and
southern/eastern Wisconsin to northern Michigan/eastern UP of MI
Monday evening. 3 to 6 inches should occur over these areas.

Models show the low tracking northeast of the Upper Great Lakes
into eastern Ontario and western Quebec with widespread warm
advection precipitation moving across the Northeast on Tuesday. 
While areas from northern Pennsylvania to southern New England are
expected to begin as snow but quickly change to rain, areas to the
north, including the Adirondacks and northern New England are
forecast to remain primarily snow.  The heaviest potential is for
several inches across mountains from the Adirondacks of NY, Green
Mountains of VT, and White Mountains of NH. The wave should depart
for Canada Tue night, so the snow events concludes.

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

Petersen