Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
337 PM EST Wed Jan 30 2019

Valid 00Z Thu Jan 31 2019 - 00Z Sun Feb 03 2019


...Great Lakes...
Days 1/2...

The deep low just north of the Great Lakes today lifts northeast
into Canada through Thursday with westerly flow under an unstable
layer into Friday across the northern Lakes. A shortwave trough
crosses southern Lake Michigan and Lake Erie Thursday night with
light synoptic snow and southerly flow. Day 1 WPC probabilities
are high for over four inches in the UP of MI and east of both
Lakes Erie and Ontario. Lake Erie is becoming quite ice covered,
but the ongoing heavy bands south of Buffalo indicate there is
still enough fetch for LES. The heaviest snow should be in the Tug
Hill Plateau east of Lake Ontario where there are moderate Day 1
probabilities for 18 inches.

The westerly flow over Lake Ontario persists until midday Friday
with moderate probabilities for an additional 6 inches in the Tug
Hill. Moderate probabilities for two inches skirt the south shore
of Lake Erie on Day 2 from the Alberta Clipper passing to the
south.


...Midwest to Mid-Atlantic...
Day 2...

An Alberta Clipper rounds the ejecting deep low from the Great
Lakes Thursday night through Friday with a track from roughly WI
to NJ. Continental air over the upper Midwest will limit snow to
around 2 inches on southerly flow ahead of the mid-level impulse.
However, Gulf-sourced moisture reaches the central OH Valley with
increased precip east from there to the central Appalachians. Low
probabilities for four inches begin over OH with moderately high
probabilities for four inches in the upslope areas of western
PA/MD/WV where prefrontal south flow then trailing upslope flow
combines for an extended light to moderate snow period.

Downsloping flow east of the crest of the Central Appalachians
will reduce precip to the Chesapeake Bay/Delaware Water Gap.
However, the mid-level trough axis is strong enough pushes over
the mountains in the afternoon, allowing bands to redevelop over
the Delmarva and southern NJ. The strength of these bands remains
to be seen with the 1 inch line extended to southern NJ for now.
This could have a potential impact to the Friday evening commute
in the northern Mid-Atlantic metro areas.


...The West...
Days 1-3...

A closed low till push down the southern CA coast Thursday with
precip extending inland and some higher elevation snows for the
southern Sierra Nevada and transverse ranges around the LA basin.
Moderate Day 1 WPC probabilities for two inches are over these
areas.

A deep trough with surface low approaches northern CA Friday,
pushing inland through Saturday. Considerable Pacific moisture
shifts inland across the west. Heavy snows are expected across the
Sierra with potential for two feet on Day 3 with moderate to high
probabilities for six inches across higher elevations of
NV/UT/OR/ID/MT and the Washington Cascades.


The probability for significant icing is less than 10 percent
nationwide days 1-3.

Jackson