FOUS11 KWBC 011917
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
217 PM EST Sun Dec 1 2024

Valid 00Z Mon Dec 02 2024 - 00Z Thu Dec 05 2024

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

*** Heavy Lake-Effect Snow continues through Tuesday ***

Amplified longwave trough spinning across the eastern CONUS and
centered near James Bay will slowly shift eastward Monday, with a=20
final shortwave digging through the trough and across the Mid-=20
Atlantic on Tuesday. This evolution will maintain lake effect snow=20
(LES) across the region, but with bands gradually but inexorably
shifting more to the S/SW rather than the W/NW which has plagued
the Lakes the past few days. While this will continue CAA across
the still very-warm lakes leading to bands of intense LES, the
shifting direction will bring a reprieve to some of the hardest hit
areas, while also resulting in generally less intense snow rates
with less than ideal fetch direction.=20

The exception to this will likely be along the Chautauqua Ridge SE
of Lake Erie which has been crushed with snow the past few days,
and late D1 into D2 will experience a resurgence as a nearly ideal
upstream moisture connection to Lake Huron occurs. The other region
that will see more intense LES, especially early D2 /Monday night
into Tuesday/ will be south of Lake Michigan as the northerly fetch
drives a robust and single band of LES into northern IN. These two
areas will likely receive the heaviest additional snow, reflected
by WPC probabilities exceeding 70% for 6+ inches both D1 (east of=20
Lake Erie) and into D2 in far SW MI and northern IN (and continue
east of Lake Erie). Locally 1-2 additional feet are possible.

Downstream of the other lakes, including the U.P., western L.P.,
and down into the Finger Lakes region of NY, ***WPC probs...***
before shortwave ridging builds in across the region bringing an
end, at least briefly, to most LES as WAA develops. Some light LES
is likely early D3 during the wind shift, especially near Buffalo,
NY and Watertown, NY, but only modest additional LES accumulations
are expected.

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


...Upper Midwest/Upper Great Lakes...
Day 3...

A potent shortwave digging out of northern Saskatchewan will race
southeast within the amplified trough plaguing much of the eastern
CONUS. As this shortwave dives towards the Northern Plains, it will
begin to amplify, pushing 500-700mb heights to as low as -2 sigma
according to NAEFS, while concurrently enhancing downstream
divergence as it interacts with modest shortwave ridging to the
east. During this evolution, an impressive upper jet streak /up to
160kts/ will dig southward as well, with the favorable LFQ driving
enhanced deep layer lift to produce cyclogenesis near Lake Superior
Wednesday morning. This low will then deepen as it tracks
progressively to the east, with the accompanying WAA driving a
swath of precipitation from the Upper Midwest through the eastern
Great Lakes.

The warm and moist advection downstream of this low will surge PWs
to nearly +1 sigma, and the column will be sufficiently cold that
most of the precip will occur as snow. There remains some
uncertainty amongst the various global models as to how far south
the heavy snow will spread, but with impressive WAA (winds up to
50 kts at 800mb) deepening the isothermal layer beneath the DGZ,
and favorable fgen driving ascent, periods of moderate to heavy=20
snow are becoming more likely from northern MN through Upstate NY=20
on Wednesday. WPC probabilities for 4+ inches are generally around
30% from the Arrowhead of MN through far western Upstate NY, with
locally higher probabilities reaching 70% across the eastern U.P.
and in some of the favored lake-enhanced areas near Traverse City,
MI and downwind of Lake Ontario.


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

Weiss



...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!42ECxC3hxrtu1vSOUXxFlIbpSRTo41SMiHNvkisY7ZTqK=
4SRNSLIsqcNqRiw5k-2oRPkJDABqunsWjDb9mjEcx10HN8$=20

$$

=3D =3D =3D
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