Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
418 PM EST Tue Feb 25 2020

Valid 00Z Wed Feb 26 2020 - 00Z Sat Feb 29 2020


Day 1...

...Mid Mississippi Valley to the Great Lakes...
The daytime models runs continued their southeastward shift, with
a slight downward trend in snowfall amounts associated with a open
wave upper trough forecast to pivot east across the mid
Mississippi valley Wednesday morning.  Expect light to moderate
snows to develop within the associated deformation axis and move
northeast from the Mid Mississippi valley early Wednesday into the
southern Great Lakes region during the day on Wednesday, with the
heaviest amounts centering across northeastern Indiana to
southeastern Lower Michigan and northwestern Ohio.  WPC PWPF shows
high probabilities for accumulations of 4-inches or more across
this area, but shows a diminishing threat for heavier amounts.   


Days 2 and 3...
...Northeast...
As the aforementioned shortwave begins to assume a negative tilt
and lift from the Ohio valley to the Northeast, surface low
pressure over the Mid Atlantic will begin to rapidly strengthen
and lift to the north into the Lower Great Lakes Region Wednesday
evening.  Strong low level warm advection along with favorable
upper jet forcing will support widespread precipitation across the
Northeast late Wednesday into Thursday.  Ahead of this low, expect
mostly rain across New York with significant snow confined largely
to the northern Adirondacks.  A secondary wave forecast to develop
near Long Island and southern New England before moving north
along the northern New England coast on Thursday is expected to
raise the threat for heavy amounts across northern New Hampshire
into central and northern Maine.  Heaviest snows across Upstate NY
will likely be lake effect driven and are expected to occur as the
primary low lifts north of Lake Ontario on Thursday.  Strong
westerly flow and cold air advection on the backside of the low
will set the stage for a prolonged, significant lake effect event
with heavy accumulations, on the order of 1-2 feet likely east of
Lake Ontario into the Tug Hill region beginning Thursday and
continuing into Friday.

For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Pereira