266
FOUS11 KWBC 281854
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
154 PM EST Fri Nov 28 2025

Valid 00Z Sat Nov 29 2025 - 00Z Tue Dec 02 2025

...Great Lakes & Northeast...
Day 1...

Persistent cyclonic flow will maintain the current long duration
lake effect snow (LES) event into Saturday morning leading to prolific
snowfall totals likely in a few areas.

Elongated but closed mid-level low remains centered over Quebec
driving lowered heights into the Northeastern CONUS. Rounding the
base of this trough, a secondary shortwave and elongated vorticity
lobe is swinging eastward through the western Great Lakes,
eventually making headway into the Northeast tonight, bringing a
brief period of shortwave ridging to the area overnight. This will
be the evolution to finally shut off the LES machine that`s been
present the past 48+ hours.

However, until that transpires, two significantly impactful winter
weather areas continue through this afternoon and early evening.
The first is in the favored WNW snow belts off the Great Lakes:
from the eastern U.P. through the NW L.P. of MI, and then
downstream along the Chautauqua Ridge and the Tug Hill Plateau. 18z
mesoanalysis indicates a broad expanse of 850mb temps between -10
to -15C, driving steepening lapse rates across lake temperatures
that are still generally +6C to +10C according to GLERL. The
cooling column will keep the DGZ relatively shallow, but favorable
ascent crossing the DGZ efficiently has aided in producing a
plethora of multi-band structures with hourly rates upwards of
1"/hr. Hourly max rates will likely reach 2-3"/hr at times in
response to deep inversion depths as high as 700mb, especially in
the singular band structure from a long fetch axis oriented from
Lake Huron down through Georgian Bay then back over Lake Ontario.
The aforementioned persistent singular band is well-defined at this
hour off Lake Ontario through Oswego county extending into
southern Tug Hill and areas downstream. This area will exhibit the
heaviest snowfall accumulations through the period with areas
residing in the band likely to attain well over 12" at this
juncture leading to snowfall totals eclipsing 2ft for the entirety
of the event.

In addition to the LES, a strong cold front pressing east from the
Lakes has allowed for convective snow showers or snow squalls
along this front. Regional radar composite shows a multitude of
convectively based snow showers/squalls across southern NY state
down through western and central PA. The environment remains
favorable as the front advances east with MUCAPE as high as 200
J/kg coincident with modest 0-2km fgen and theta-e lapse rates
falling below 0C/km centered over west-central PA as of 18z. Snow
squall warnings have been issued in response over the past few
hrs, a testament to the environmental favor in place. Any area that
receives these snow squalls will encounter the opportunity for
dangerous travel due to rapidly changing conditions with briefly
heavy snow and gusty winds.

Key Messages remain, but will be the final issuance for the event
(link #1 below).


...Northern High Plains through the Midwest into the Northeast...
Days 1-3...

...Significant winter storm to impact large portions of the
Northern Plains, Midwest, and Great Lakes through this weekend...

The previous forecast discussion remains very relevant for the
incoming significant winter storm development already materializing
over the Plains and Midwest. Latest UA analysis this afternoon
indicates a positively tilted shortwave trough emerging from the
Pacific Northwest, forecast to track southeast into the
Northern/Central Plains as we continue through this afternoon. As
a secondary vorticity impulses rotates into the trough, this will
force downstream amplification of the mid-level pattern, resulting
in a negatively tilted trough and increasing ascent downstream into
the Midwest and Great Lakes. At the same time, jet streaks both
upstream and downstream of this amplifying trough will begin to
couple, producing even more intense deep layer lift, and a surface
low will result - first in the lee of the Rockies and then tracking
gradually northeast into MI by Sunday morning. This low will then
continue to deepen as it shifts across southeast Canada and exits
into the Canadian Maritimes by the end of the forecast period /12Z
Monday/.

The guidance this morning has maintained general continuity with
better agreement on the track and intensity of this system, and
while small temporal and spatial differences among the ensembles
still exist, the spread is minimal compared to previous model runs
leading to a high confidence scenario in both the expected
evolution and snowfall forecast. As the low deepens and moves
northeast, impressive WAA will develop downstream of the developing
cyclone, spreading PWs which will exceed the 90th percentile
northward into MO/IA. The accompanying theta-e ridge will surge in
tandem and isentropically ascent the region, and while guidance is
still not suggesting a strong TROWAL, at least subtle warm air
aloft will help develop modest conditional instability. The
coincident and impressive 290K isentropic ascent will lead to
expanding and intensifying precipitation, with moderate snow likely
across much of the Northern Plains, Upper Midwest, and Great
Lakes, especially Friday night through Sunday morning.

On D1, the heaviest snowfall accumulations are likely in a narrow
band driven by the jet streak aloft and the accompanying
ageostrophic/fgen enhancement between 700-600mb. This has allowed
for a stripe of periodically heavy snow over parts of the Dakotas,
spreading into western IA as of the past few hrs. Despite the band
being relatively narrow, snowfall rates of 0.5"-1"/hr are likely
which could cause 4-6" of snow as reflected by WPC probabilities
for 4+ inches that reach above 70%.

However, the most significant part of this event begins later this
evening across IA, spreading eastward through D2 IL/WI/MI. Here,
the impressive isentropic ascent will be quite moist as reflected
by mixing ratios of 4 g/kg on the 290K surface, leading to a
rapidly saturating column. While in general this upglide will
result in moderate snowfall rates, there appears to be an
increasing risk for heavier snowfall across portions of MO/IA/IL as
the WAA forces an increasing isothermal layer beneath the DGZ
which also begins to deepen. Cross-sections are more robust
featuring a corridor of folding theta-e surfaces within the
elevated RH, suggesting a greater potential for CSI and convective
snowfall rates. There is still some uncertainty into this since
this signal is much more robust tonight than previous model runs,
but locally 1-2"/hr rates appear possible which is supported by the
WPC prototype snowband tool despite a modest overall appearance of
the evolution with respect to conceptual models for heavy snow
bands. Still, multiple bands lifting northward for a long duration
will result in significant snowfall accumulations and major impacts
for the post- Thanksgiving holiday travel.

This will be a significant system with several waves of moderate to
heavy snowfall. On D2, the heaviest accumulations are expected from
far eastern NE through IA, northern IL, and southern WI. WPC
probabilities in this region are 70-100% for more than 6 inches of
snow, and locally as high as 50-70% for more than 12 inches,
highest near the Cedar Rapids over into the Quad Cities of IA.
Later D2 into D3 the heaviest snow shifts eastward and eventually
wanes in intensity, but additional heavy snowfall exceeding 6" is
possible, especially around Lake Michigan and into the L.P. of MI.
Event total snowfall may reach upwards of 15+" in isolated
locations Saturday, potentially setting November and even
encroaching some all-time snowfall records for the 24hr and 48hr
periods.

Moderate snowfall is also expected across the interior northeast
where WPC probabilities D3 are as high as 50-70% for 4+ inches in
the higher terrain of VT, NH, and ME.

Key Messages remain in effect for this system (Link #2 below).


...Central Rockies...
Day 3...

No changes necessary to the anticipated evolution of the next
winter disturbance to impact the Central Rockies. A potent
shortwave will drop out of the Pacific Northwest Sunday morning,
moving progressively southeast, reaching the Four Corners Sunday
night while maintaining a positive tilt. Late D3 this feature will
begin to sharpen, with the resulting downstream jet streak
intensifying into the Central Plains. The overlap of the RRQ of
this jet streak with the greatest height falls ahead of the trough
axis will help spawn low pressure in the Great Basin, and this low
will help to increase ascent across the Central Rockies Sunday
evening. As the overall ascent increases, precipitation will
expand, and periods of moderate to heavy snow are likely, generally
above 5000 ft. This system is expected to remain progressive so
prolonged snowfall is not expected, but WPC probabilities indicate
a moderate risk (50-80% chance) of at least 6 inches of snowfall
across the CO Rockies and northern San Juans, with lighter
accumulations expected as far west as the Wasatch of Utah.


Weiss/Kleebauer


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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png

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



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