FOUS11 KWBC 301923
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
223 PM EST Sat Nov 30 2024

Valid 00Z Sun Dec 01 2024 - 00Z Wed Dec 04 2024

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

*** Heavy Lake-Effect Snow event into early Tuesday ***

Broad cyclonic flow from the upper levels to the surface will=20
continue across eastern Canada and across the Great Lakes through=20
Tuesday when the trough will finally start to move out of the=20
Northeast. With Great Lake SSTs well above average for this time of
year (+8C to +14C per GLERL) and 850mb temps around -10C, the=20
sfc-850 delta-T will remain ~20C which supports strong/intense=20
uplift/instability. The sometimes extreme instability will support=20
cellular convection embedded within well-formed lake-effect bands=20
and may include thundersnow.

The cyclonic flow and continued moisture influx will also favor=20
broad atmospheric lift irrespective of the lakes. This favorable=20
atmosphere will maximize each lake's ability to continue producing=20
heavy lake-effect snow. The general northwesterly flow will also=20
allow for the upper lakes to feed the lake-effect off the lower=20
lakes. This will be a large contributor to the prodigious snow=20
totals forecast southeast of the lower lakes. Lake Superior and=20
Georgian Bay (part of Lake Huron) will feed into Lake Ontario's=20
lake band, while the bulk of Lake Huron will feed into Lake Erie's=20
lake-effect bands. Lake Erie will be increasingly dependent on Lake
Huron's support as the winds shift more northwesterly and become=20
more perpendicular to the long axis of the lake. Upslope into the=20
terrain of far northwest Pennsylvania and far western NY for Lake=20
Erie's bands and into the Tug Hill east of Lake Ontario will=20
locally further enhance the lift and ability of the bands to=20
produce incredibly heavy snowfall -- at times exceeding several=20
inches per hour.

Storm total snowfall could approach 6 feet east of Lake Ontario=20
and 3-4 feet southeast of Lake Erie. Off of the upper lakes, the=20
broader geography of the larger lakes makes single band formation=20
much more difficult, so multiple smaller bands of moderate to=20
occasionally heavy snow are likely to impact portions of the U.P.=20
and the northwestern lower peninsula. Snowfall amounts over a foot=20
are expected in the eastern U.P. and far western U.P. as well as=20
east of Traverse City. WPC probabilities of at least an additional=20
18 inches of snow are high (>70%) near Watertown-Fort Drum through=20
Sunday afternoon. Over southwestern NY, WPC probabilities for at=20
least an additional foot of snow are high (>70%) just south of=20
Buffalo along I-90.

The latest Winter Storm Severity Index values show extreme impacts
through Monday in the Watertown, NY area east of Lake Ontario and=20
along the I-90 corridor from the Buffalo southtowns through=20
Ashtabula, OH, including through Erie, PA southeast of Lake Erie.=20
Travel will remain extremely dangerous to near impossible with=20
numerous road closures.=20

By Tuesday, the upper trough will finally start to shift eastward=20
with its axis moving east of 70W by the afternoon, helping to=20
slowly diminish the lake effect snowfall. Upstream, another weak=20
disturbance will move out of southern Canada into the northern=20
Plains/Upper Midwest with light snow spreading across northern MN.=20
Amounts look fairly light at this time, and WPC probabilities for=20
at least 4 inches of snow are around 10% through 00Z Wednesday=20
right along the Canadian border.

The ongoing lake-effect snow is a subject of the Key Message=20
linked below.



...Southern IN/northern KY to West Virginia...=20
Day 1...

Broad upper troughing over the eastern CONUS will carry a weak=20
disturbance out of the MS Valley this evening and across TN tonight
as it slowly weakens. Attendant surface front and weak area of low
pressure will promote a light west-to-east axis of snowfall along=20
the I-64 corridor east of MO tonight. Recent guidance has trended=20
just a tick south and lighter with QPF (thus snowfall), and WPC=20
probabilities for at least 2 inches are low (10-40%) mostly over=20
southern IN and somewhat across northern KY. Farther east, upslope=20
into the central Appalachians will be the main driver for heavier=20
amounts and WPC probabilities for at least 4 inches of snow are=20
>70% above 1500ft or so.=20


The probability of significant ice across the CONUS is less than=20
10 percent.=20


Fracasso/Wegman


...Winter Storm Key Messages are in effect. Please see current=20
 Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=
stKeyMessage_1.png__;!!DZ3fjg!9oslp7Gz5btZZ6TW0FkEUMLCGx5PGPlDZm90ljG7WgmXO=
twhkXQCAaerv_Fbq5QHI3thZNmfl9dYUI00cYDgbZbManA$=20

$$

=3D =3D =3D
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