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FOUS11 KWBC 280707
QPFHSD

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

Valid 12Z Fri Nov 28 2025 - 12Z Mon Dec 01 2025

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

Cyclonic flow aloft will persist a long duration lake effect snow
(LES) event into Saturday morning, with prolific snowfall totals
likely in a few areas.

The period begins with an elongated but closed mid-level low
centered over Quebec driving lowered heights into the Northeast.
Rounding the base of this trough, a secondary shortwave and
elongated vorticity lobe will swing eastward through the Great
Lakes and into the Northeast tonight, bringing a brief period of
shortwave ridging to the area tonight. This will be the evolution
to finally shut off the LES.

However, until then, two significantly impactful winter weather
areas are expected. 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. 850mb temps falling to as low as -15C (-10C far east
portions) will drive 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 will produce bands of
very heavy snow for which the HREF indicates has a >60% chance of
exceeding 1"/hr, and will likely reach 2-3"/hr at times in response
to deep inversion depths as high as 700mb. Although winds will
fluctuate just enough to prevent stationary single bands (plus the
fetch direction is not along the long-breadth of the lakes in many
areas), narrow corridors of heavy snow are expected, especially
where any upstream connection can occur from Huron/Superior/Georgian
Bay to Lakes Erie and Ontario. The heaviest snow is likely D1 just
southeast of Lakes Erie and Ontario where WPC probabilities for 8+
inches reach 50-90%, and storm total snowfall from this event
could be over 2 feet in a few locations.

In addition to the LES, a strong cold front pressing east from the
Lakes early this morning will reach the Atlantic coast this
evening. The guidance has become increasingly excited in the
potential for convective snow showers or snow squalls along this
front, as reflected by a snow-squall parameter well above 1. The
environment appears favorable for snow squalls from western PA
through northern ME as the front passes east, moving across an
environment with SBCAPE as high as 250 J/kg coincident with modest
0-2km fgen and theta-e lapse rates falling below 0C/km. Moisture
may be the limiting factor away from the Great Lakes, so the best
chance for squalls appears to be well inland of these states, but
any place that does receive a squall this afternoon would likely
experience dangerous travel due to rapidly changing conditions with
briefly heavy snow and gusty winds.

Key Messages remain in effect for this system (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 first widespread significant winter storm of the season begins
in earnest today as a positively tilted shortwave trough emerges
from the Pacific Northwest and tracks southeast into the
Northern/Central Plains. 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 Upper 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 has come into much better agreement with 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 higher confidence in the
evolution. 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 will cause a
stripe of periodically heavy snow from southern ND through western
IA, and although the band should be 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 late D1
across IA and then spreads east through D2 into 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-es 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 70-90% for more than 6 inches of
snow, and locally as high as 50% for more than 12 inches, highest
near 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
15" in isolated locations Saturday.

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...

A potent shortwave will drop out of the Pacific Northwest Sunday
morning and then move 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 (50-70% 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




...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



$$