Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
344 AM EST Fri Nov 18 2022

Valid 12Z Fri Nov 18 2022 - 12Z Mon Nov 21 2022

***Paralyzing lake effect snowfall (LES) downwind of Lakes Erie
and Ontario with heavy LES east of the other lakes***

...Eastern Great Lakes...
Days 1-3...

A long duration, intense lake effect snow event will continue a
very active phase today as shortwave energy rounds the base of a
northern stream trough from a deep and cold low over Hudson Bay.
Broad single band LES will continue off Lakes Erie and Ontario
will remain fairly steady state through this evening before slowly
tilting north on slowly backing flow ahead of the main trough axis
which is progged to cross the Great Lakes Sat/Sat night. Strong
CAA will continue to bring the saturated layer through the DGZ
over water than is in the low 50s per buoys in Erie/Ontario.
Extreme lake-induced instability nearing 2500 J/kg, with inversion
heights of 10-15 kft will continue to support lightning within the
most intense snow bands. Near steady-state shear aligned with the
length of Lakes Erie and Ontario will keep snow bands in a very
similar location to present through today, making for crippling
snowfall for mainly southern sections of the Buffalo metro as well
as down the remainder of the NY shore of Erie and east of Ontario
including Watertown. 00Z HREF indicates than 2-3"/hr snow rates
will persist over the same areas today before lifting north
tonight. Day 1 snow probs for an additional 18+" are 50 to 80%
with locally much more in these two snow belts.

Flow looks to back enough by Saturday morning to direct the bands
off Erie/Ontario into Canada. An approaching cold front Saturday
evening should veer flow and send the bands back into NY Saturday
evening until the cold frontal passage Saturday night after which
northwesterly flow and multi-bands setup for Sunday. A surface
ridge shifts east over the Eastern Great Lakes Sunday evening,
which finally brings an end to this prolonged event. Snow probs
Saturday night/Sunday for 6 or more additional inches are high
from eastern Cleveland to southern Buffalo as well as the Tug
Hill. 3-day snowfall will likely eclipse 3 feet in the prime bands
today. Expect local storm totals exceeding 50".

...Western Great Lakes...
Days 1-2...

Heavy snow in a multi-band/mesolow setup off Lakes Superior and
Michigan will persist through this morning before backing flow
ahead of the upper trough axis that crosses early Saturday
disrupts the bands through this evening and providing a bit of a
lull tonight. While Day 1 snow probabilities for 6 or more inches
are rather low outside of the mesolow area north of Traverse City,
the localized nature of the bands/mesolows should allow many
planes in MI to receive at least 6" additional today. The cold
front associated with the upper trough crosses Lake Superior late
tonight and Lake Michigan Saturday which will bring another round
of LES with the DGZ quite low behind the potent cold front. Day 2
snow probs are moderately high for 6 or more inches over the
western and eastern U.P., along much of the western L.P. The upper
trough axis shifts east from the eastern Great Lakes Sunday, so
most of the LES off Superior/Michigan should wane through the day
Sunday.


Key Messages for Lake Effect Snow in the Great Lakes:

--Periods of heavy lake effect snow will persist through Sunday
downwind of each of the Great Lakes. The most intense snowfall is
expected through this evening.

--East of Lakes Erie and Ontario, snowfall will at times be
accompanied by lightning, gusty winds, and rates of 3+ in/hr. This
will produce near zero visibility, nearly impossible travel,
damage to infrastructure, and paralyze the hardest-hit communities.

--Across parts of the Upper Peninsula and western Lower Peninsula
of Michigan, snowfall rates will reach 1-2 in/hr and combine with
gusty winds to produce near zero visibility and dangerous travel.

--Total snow amounts of 1-2 feet are expected in many locations,
with 2-3 feet likely east of Lakes Erie and Ontario. Historic
snowfall exceeding 4 feet is possible south of Buffalo, NY.

--Very cold air will accompany this event with temperatures 20
degrees below normal forecast by the weekend.



Jackson