Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
222 PM EST Sun Feb 13 2022

Valid 00Z Mon Feb 14 2022 - 00Z Thu Feb 17 2022


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

A wave of low pressure moving northeast off the New England coast
will skirt just east of the Benchmark tonight before lifting
towards Nova Scotia on Monday. An inverted trough extending NW
from this feature will interact with robust RRQ diffluence to
produce some enhanced snowfall across southeast MA and along the
immediate coast of Maine. Overall snowfall should be modest, but
WPC probabilities for 4+ inches above 50% are confined to Cape Cod
and the farthest eastern coast of Maine.


...Pacific Northwest through the Central Rockies...
Days 1-3...

An impressive closed mid-level low will dig out of the Gulf of
Alaska and shift onshore WA state D1, and then continue to shift
southward into the Great Basin D2 and move eastward towards the
Four Corners on D3. As this shortwave evolves into an amplified
longwave trough across the West, the trailing pole jet streak
upwind of the primary trough axis will begin to couple with an
intensifying sub-tropical jet streak arcing across the Pacific
into the Great Basin. The overlap of these features will lead to
several waves of low pressure developing along the southeast
moving cold front, with a more impressive wave of low pressure
likely developing D3 across the Central Rockies. There is likely
to be an expansive area of precipitation downstream of the primary
trough axis, as robust synoptic lift taps into near normal PWs
across the region. Snow levels will initially be 5000-6000 ft,
although a rapid decrease to 2000-3000 ft is likely from NW to SE
behind the cold front. However, much of the precipitation is
likely to occur within the WAA ahead of the front, so on D1, even
as WPC probabilities for 6+ inches are moderate across the
Cascades, with locally more than 10 inches likely, the Cascade
Passes should receive only minimal accumulations on D1. By D2 the
best overlap of ascent and moisture will produce heavy snowfall
across the Northern Rockies, Absarokas, Sawtooth, and ranges of NW
WY where WPC probabilities for 6+ inches are as high as 40%.

By D3 /Tuesday night and Wednesday/ the most intense deep layer
ascent will focus over the Central Rockies, where upslope flow
behind the surface front may drive some orographic enhancement as
well. There remains some uncertainty into the placement of the
strongest forcing and whether it will maximize atop the low-level
baroclinic gradient to enhance overall lift, but WPC probabilities
for more than 6 inches are as high as 20% in the Front Range and
San Juans. Lighter snows are likely to be quite broad in coverage
on D3, with WPC probabilities for more than 2 inches over 30%
continuing in the Northern Rockies and extending as far south as
the Mogollon Rim and White Mountains of AZ and east into the High
Plains of CO, including the I-25 corridor.

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


Weiss