FOUS11 KWBC 302021
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 PM EST Sun Nov 30 2025

Valid 00Z Mon Dec 01 2025 - 00Z Thu Dec 04 2025

...Great Lakes to the Interior Northeast... Day 1...

The storm system responsible for the heavy and disruptive snowfall
that blanketed the Midwest and Great Lakes is tracking into Ontario
this afternoon. Cyclonic flow and CAA within WNW-NW winds will
reinvigorate the LES machine across the Upper Great Lakes, snow
belts of western MI and northern IN, and typical snow belts to the
east of Lakes Erie and Ontario. Snow bands will be capable of
producing anywhere between 1-2"/hr snowfall rates due to the
favorably unstable low-level profiles and a pivoting 850-700mb
trough over head this evening. WPC probabilities show moderate
chance probabilities (40-60%) for additional snowfall totals >4"
over far northwest PA and across the Tug Hill. An additional 1-4"
of snow is forecast in the Green and White Mountains before
tapering off by early Monday morning.

...Central Rockies/Central Plains/Mid-South/OH Valley... Days 1-2...

A 500mb positiviely-tilted trough is tracking through UT today and
will head for the CO/NM Rockies by early Monday morning. The
combination of height falls with a strengthening jet streak will
produce large scale ascent across the Central Rockies and Four
Corners today and into tonight. Heavy snowfall will be primarily
confined to the >10,000ft peaks of the CO/NM Rockies, although some minor-to-moderate accumulations between 7,000-10,000ft are
possible.

As the upper trough tracks east towards the Central Plains tonight,
healthy 500mb PVA coupled with a strengthening 250mb jet streak
will foster healthy synoptic-scale divergence aloft. Guidance also
shows a strengthening 850-700mb WAA regime and corresponding 290K
isentropic ascent over the Central Plains that is likely to result
in a band of moderate-to-heavy snow tracking from northern KS early
Monday morning and across the heart of the Midwest by Monday
afternoon. Temperatures are cold enough aloft to support fluffy
SLRs (>15:1 in most cases) and it is progressive. WPC probabilities
show most accumulations will range between 1-4", given WPC
probabilities for >4" are low (10-30% at most in northeast
KS/northwest MO). However, there are some guidance members that
depict some localized totals >4" by the time the band of snow exits
to the east Monday evening. The same mechanism producing snow in
the Central Plains heads for the OH Valley and western PA. Snowfall accumulations will generally range between 1-4" through Tuesday morning.

Farther south, as low-level WAA and Gulf moisture spreads over and
air-mass that features sub-freezing temperatures and dry
dewpoints, freezing rain is expected to unfold from the
ArkLaTex eastward across central and southern AR and into western
TN. the plume of low-level moisture does not last long, but 290K
isentropic ascent sticks around long enough for some disruptive
ice accumulations in these areas on Monday. WPC probabilities show
low chances (10-30%) for ice accumulations than one-tenth of an
inch, but there are moderate chances (40-60%) for ice
accumulations over one-hundreth in central AR. The WSSI shows a
large swath of Minor Impacts across central AR and as far north as
the MO/AR border, but some localized Moderate Impacts in central AR
are possible.

...Central Appalachians & Northeast... Days 2-3...

...Widespread hazardous snow and ice to blanket portions of the
Mid-Atlantic and Northeast Monday night and through Tuesday...

By Monday evening, the 500mb trough producing periods of snow over
the OH Valley will track across the Middle MS Valley Monday night
with a secondary disturbance tracking south of it towards the
Southeast. As a third disturbance approaches from the Great Lakes,
a strengthening 250mb jet streak over the Northeast will work with
a second 250mb jet streak over the South to creating a classic
"coupling jet streak" setup off the Mid-Atlantic coast. This will
be the basis for a strengthening winter storm that tracks initially
through the Southeast Monday night and up the East Coast by Tuesday
afternoon.

The primary ingredients are generally agreed upon on all guidance,
although how they come together and where the storm tracks is
still coming into focus. High pressure over the Northeast will
initially provide a sufficiently cold air-mass to support wintry
precipitation at the onset from the Central Appalachians on north
and east, but it will be exiting off Atlantic Canada on Tuesday. As
925-700mb WAA advances north Monday night and into Tuesday, any
initial snow over the Central Appalachians will changeover to a
sleet/freezing rain mix, then all freezing rain. Cold air damming
(CAD) will linger long enough in the higher terrain to support
disruptive ice accumulations that result in slick travel conditions
Monday night and into Tuesday morning. WPC probabilities show >50%
chances for ice accumulations over a tenth of an inch from the
Blue Ridge of western NC on north through the mountains of western
VA and eastern WV. There are some low-chance probabilities (10-30%)
for over a quarter inch of ice from VA's Skyline Drive on south and west
to the WV/VA border. The latest WSSI does depict Minor to Moderate
Impacts in these regions with a focus on treacherous travel
conditions.

Farther north over the Mid-Atlantic, precipitation is likely to
start out as snow over northern VA/MD, southern PA, and on north
towards the NYC metro Tuesday morning. Guidance then begins to
disagree on the handling of the transition and northward expansion
of the snow-wintry mix area. Low-level SErly flow is strong enough
to where most areas along I-95 should flip over to plain rain on
Thursday morning, but farther inland over the Piedmont of VA,
northern MD, and Lower Susquehanna Valley, low-lvel cold may stick
around long enough for a wintry mix to hang around longer. This is
likely to be the region's first accumulating snowfall, so there are
likely to detrimental impacts to travel even if snowfall and ice
accumulations are minor (1-3" of snow for these areas, up to a
tenth of an inch of ice in western MD and northwest VA). However,
from the Lehigh Valley and Poconos on north and east through
northwest NJ, the Catskills, and into interior southern New
England, snow is likely to remain the primary precip type.

The storm by Tuesday afternoon will begin to develop a closed lower
over the Delaware Valley that deepens south of Long Island by
Tuesday evening. To the north and east of the 850mb low, a
consolidated 850-700mb FGEN area will develop and result in a band
of heavy snow somewhere from northeast PA and southern NY (north of
NYC) through southern New England. Snowfall rates within this band
are likely to at least top 1"/hr. There still remains some
uncertainty on where this band sets up, but probabilistic guidance
is showing increase odds on a snowfall swath of >6" from the
Poconos and Catskills on north and east. The higher terrain across
New England (Berkshires, Worcester Hills, Green, Whites, Downeast
Maine) are the most favored for locally heavy snowfall as WPC
probabilities shows low-to-moderate chances (30-50%) for over 12"
in some spots. The latest WSSI does depict Moderate Impacts due to
snow from western MA and northern CT to southern NH and southern
ME with locally Major Impacts possible.

In summary, this is going to be the first accumulating snow of the
season for many areas from southern PA to areas just west of I-95,
potentially including the Boston metro area should more southern
guidance come to fruition. Expect travel delays on Tuesday and into
Tuesday night in affected areas. High pressure and dry conditions
return to the Northeast by early Wednesday morning.

Key Messages remain in effect for this system and are linked below
(Key Message #3)

Mullinax

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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_3.png

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