379
FOUS11 KWBC 100834
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
334 AM EST Fri Jan 10 2025

Valid 12Z Fri Jan 10 2025 - 12Z Mon Jan 13 2025

...Mid-South/Southeast into the Mid-Atlantic...
Day 1-1.5...

...Major winter storm continues to progress eastward through the
Mid-South today with hazardous winter conditions into portions of
the Mid-Atlantic overnight...

A strongly positively-tilted longwave trough, with its axis back
into Mexico, will continue to help develop low pressure along the
Gulf Coast today on the southeast side of a 170kt jet. Gulf
moisture continues to stream northward into the Mid-South atop a
cold surface layer, yielding snow on the north side of the
expansive precipitation shield and a wintry mix of sleet and
freezing rain to the south (and plain rain toward the Gulf Coast).

Mid-level FGEN will drive moderate snow rates (~1"/hr at times)
over Tennessee this morning and early afternoon with a broader
shield of light snow to the north and northeast. Much of the region
from southeastern MO and across most of TN has at least moderate
probabilities (>40%) of seeing at least 4 inches of snow. To the
north, a general 1-3" of snow is forecast as additional northern
stream energy moves through the Midwest.

To the south, milder air aloft will move northward up and over the
cold surface layer, creating a mix of sleet and freezing rain over
northern AL/GA that will continue E/NE through SC into
central/eastern NC as the system evolves later tonight. Where the
surface cold air is most stubborn beneath the >0C air aloft,
several hours of ZR may accrete to near/over 0.25" esp over N GA.
There is a large area from northern AL to central NC where WPC
probabilities of at least 0.10" ice are >30% with an embedded area
of 20-50% probs for at least 0.25" of ice.

By this evening, upper trough will be stretched and elongated and
become dominated by the northern stream approaching the central
Appalachians. Low pressure will reform along the Carolina coast and
light northeastward overnight, spreading snow across interior NC
into VA with lighter snow extending northward into the Northeast.
Low pressure near Cape Fear 09Z Sat will quickly move northeastward
and deepen, with a potential modest band of snow on the northwest
side across southern/southeastern VA and the southern DelMarVa. WPC
Snowband Tool shows several members with ~1"/hr rates early Sat
morning (06-12Z) before the system finally scoots out to sea.
Though the probabilities for at least 4 inches are low (10-40%),
there is potential for some enhanced banding per a couple 00Z Hires
members.

Lastly, across the central Appalachians, orographic upslope will
help wring out several inches of snow over the higher terrain from
the Laurel Highlands southward down to the Smokey Mountains, where
WPC probabilities for at least 4 inches are >50%.



...Northwest to the Upper Midwest/Great Lakes...
Days 1-3...

Fairly sharp mid-level shortwave and sfc front will enter the
PacNW starting Friday morning with mostly higher elevation snow but
lowering snow levels (from ~4500 to ~3000ft) as the front moves
past the Cascades. The shortwave will move southeastward beneath a
weakening upper jet, but the combination of height falls and
upslope enhancement will maximize snow over the mountains, from the
Bitterroots to the Tetons and western MT today then into the
Big/Little Belts into the Bighorns and eventually the Black Hills
Saturday afternoon/evening as the stronger height falls move
through. WPC probabilities for at least 12 inches of snow D1-2 are
>50% above ~5000-6000ft or so (west to east) where two-day totals
could exceed 18-24 inches above 6000-7000ft (40-70% chance).
Farther south, with height falls digging into CO, areas in the
Rockies above ~8000ft have >50% chance of 8 inches of snow.

Additionally, on D2, an Alberta clipper will move into the
northern Plains/Upper Midwest with a swath of generally light snow
via WAA and FGEN on the northern side of an area of low pressure
moving through central ND into southern MN by late Sat/early Sun.
Amounts should generally be on the lighter side of a couple/few
inches, with moderate probabilities (40-70%) of at least 2 inches
of snow from northern ND eastward across northern MN. This low will
intensify during the Day Sunday when it moves over northern
Wisconsin and the U.P. before curling back to the northeast across
the U.P. and into Quebec by early Mon. A reinforcing upper level
low will rotate into northern MN by the end of the period, helping
to slow the progression of the sfc low over the U.P. or over Lake
Superior. This should act to enhanced low-level convergence over
the western U.P where several inches of snow are likely and WPC
probabilities for at least 4 inches of snow on D3 are 30-80%.
Southerly flow ahead of the front will tap some moisture off Lake
Michigan and help enhance totals on the southern side of the
eastern U.P. where WPC probabilities for at least 4 inches are >50%
(in a rather unusual setup).


Fracasso


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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_2.png

$$