Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
326 PM EST Fri Jan 25 2019

Valid 00Z Sat Jan 26 2019 - 00Z Tue Jan 29 2019

...Great Lakes...

...Days 1-2...

An active period of lake enhanced and lake effect snow owing to
cyclonic flow will continue across the Great Lakes with episodes
of lake effect snow focused on the day 1 period Friday to early
Sat.  The greatest probabilities for moderate to locally heavy
snowfall will be down off Lake Ontario in the Day 1 period. For
Day 2, the higher snow amounts will be found across the UP of
Michigan.

...Northern Plains to upper MS Valley and adjacent Lake MI...
...End of Day 2 through Day 3...

A strongly forced and dynamic system will drop through the
Canadian Prairies in the Day 2 and Day 3 time frame. Strong 700 mb
moisture advection and convergence will lead to a focused
baroclinic zone, resulting in a swath of moderate to heavy
snowfall from the Dakotas southeastward into the Upper MS River
Valley and lower Great Lakes. As the system wraps up, deepens, and
draws increased moisture, higher QPF is expected across portions
of southeast MN, southern WI, northern IL, and southwest MI where
probabilities are highest for 8-12 inches. In this model cycle,
there was better model agreement in the placement/axis of QPF,
with the WPC forecast based on a blend of the GFS/ECMWF.


...Ranges of central to southern MT/WY/northern CO...
...Days 1 and 3...

A shortwave trough dropping through the northern Rockies will
slide across the Southwest US in the Day 1 period. As it does so,
stronger mid-level forcing in a moist column will promote enough
forcing for ascent for several inches of snow in the favored
upslope areas of MT, WY, CO, and northern UT. Lighter amounts are
expected for Day 2 across MT, but with the passage of another
shortwave trough on Day 3, moderate to locally heavy snows will be
possible across the northern Rockies again.

...Northeast...
...Day 2...

The models forecast a persistent mid-upper level vortex over
Ontario.  Downstream the the circulation, a 700 mb broad 50 kt jet
crosses northern VT/NH across ME, with warm/moisture advection
occurring and a modest 700 mb convergence maxima.  Light snow is
expected as a result, with 2-4 inches of snow possible in northern
ME. Abundant cold air across the region allows for all snow in
interior ME. 

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

Taylor