Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 PM EST Sat Nov 29 2025

Valid 00Z Sun Nov 30 2025 - 00Z Wed Dec 03 2025


...Northern High Plains through the Midwest into the Northeast...
Days 1-2...

...Significant winter storm unfolding across the Midwest today...

A pair of 500mb vorticity maximums are interacting with one another
and helping to carve out a negatively-tilted 250-500mb layer trough
over the Midwest this afternoon. A coupled 250mb jet streak setup
is further strengthening the ongoing storm system at the surface,
while at the same time, strong 850-700mb WAA ahead of the storm is
promoting 290K isentropic glide over the Midwest that is fostering
highly saturated profiles within a mesoscale environment that is
ripe for heavy snow bands. ECMWF ensembles show S-SWrly 850mb winds
in excess of 60 kts over the Middle MS Valley, which are topping
the 99.5 climatological percentile for late Nov and early Dec. This
exceptional LLJ is feeding a slug of 850-500mb moisture northward
that will wrap around the storm system and sufficiently saturate
the DGZ over the Midwest. WPC's Snowband Probability Tracker, which
utilizes HREF members, shows a band of 1-2"/hr snowfall rates from
central IA today that heads east across the MS River and towards
the Great Lakes this evening.

Snow will persist throughout the Great Lakes tonight with snow
arriving over the Northeast and central Appalachians Sunday
morning. LES bands will develop within broad cyclonic flow off
Lakes Superior and Michigan and continue through Sunday evening.
LES bands will stick around a little longer downwind of Lakes Erie
and Ontario but eventually taper off by Monday morning as high
pressure moves in. Locally heavy snowfall is possible in parts of
the Tug Hill on Sunday, as well as the White Mountains above
2,000ft where steady SWrly upslope flow within an atmosphere
remaining sub-freezing.

WPC probabilities depict moderate-to-hgih chances (50-80%) for
additional snowfall totals >6" along and east of the MS River from
eastern IA and southern MN to the Mitten of Michigan. There are
some low chance probabilities (10-30%) for snowfall totals
exceeding 12" in coastal areas of southeast WI, the Chicagoland
metro area, southwest MI, and northern IN where LES bands may
contribute enough snowfall to where over a foot of snow has
accumulated by the time the LES machine concludes. Downwind of Lake
Erie, parts of the Chautauqua Ridge have moderate chances (40-60%)
for snowfall totals >4" through Monday Sunday night. In the
Northeast, the Tug Hill and White Mountains sport moderate-to-high
chances (50-80%) for snowfall accumulations >6" with localized
totals approaching 12" possible by the time this winter storm
concludes. The WSSI continues to summarize this storm well,
highlighting Moderate to locally Major impacts from central IA on
east through the Milwaukee/Chicago metro areas and into northern IN
and southern MI. Expect considerable disruptions to travel in
these areas as travelers are likely to encounter numerous travels
delays by both road and by air today and lingering through tonight.

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


...Central Rockies through the Ohio Valley, Ice in the Ozarks...
Days 2-3...

A positively titled 500mb trough diving south from the Northwest
into the Central Rockies on Sunday will contain both sufficient
synoptic-scale lift and 700-300mb mean layer moisture to support
rounds of mountain snow from central OR and the northern Great
Basin on east across the Wasatch and into the CO Rockies. The
heavier totals in the Great Basin and Wasatch will generally
reside above 8,000ft, while the CO/northern NM Rockies are most
likely to see their heavier snowfall totals above 9,000ft. WPC
probabilities show these listed elevations as having >50% chances
for snowfall >8" with localized totals >12" in the peaks of the CO
Rockies.

As snow continues across the Central Rockies Sunday night, the
aforementioned 500mb trough will begin to eject east into the
Central Plains. A strengthening surge in 700mb WAA and the 500mb
PVA will foster a blossoming area of snowfall from the central
Plains to the Middle MS Valley. Snowfall totals are most likely to
range between a coating-3", although WPC probabilities do show low
chances (10-30%) for snowfall totals >4" over northeast KS,
southeast NE, and northern MO through Monday morning. This narrow
plume of snow races east across the Lower Great Lakes and OH Valley
Monday evening with similar snowfall totals.

Farther south, as low-level WAA and moisture over-run an air-mass
that features sub-freezing temperatures and dry dew points, a setup
for freezing rain unfolds from the ArkLaTex on across much of AR,
northern MS, western TN, and southern MO. The plume of low-level
moisture does not last too long, but 290K isentropic ascent sticks
around long enough for some disruptive ice accumulations in parts
of these areas on Monday. WPC probabilities show low chances
(10-30%) for ice accumulations over a tenth of and inch, but there
are moderate chances (40-60%) for at least a hundredth of an inch.
The WSSI-P does show up to 40% odds for Minor Impacts as a result
of this freezing rain setup on Monday across much of central AR.


...Central Appalachians, Mid-Atlantic, & Northeast...
Day 3-3.5...

...A complex & potentially disruptive winter storm to affect these
regions on Tuesday and into Tuesday night...

Summary: The first accumulating snowfall and disruptive ice event
of the season is likely to occur from the Central Appalachians and
interior Mid-Atlantic to the Northeast. There remain ongoing
changes and disagreements in guidance with snowfall totals, who
sees the heaviest totals, and timing all still lower in confidence.
Those in these regions should monitor the forecast from WPC and
their local WFOs over the next 24-48 hours.

Analysis: As the Central Plains disturbance tracks east Monday
evening, there are three other disturbances that are influencing
this complicated setup. The first is a weak feature over South TX
that is running just out in front of the main upper trough over the
Central Plains. Second: a fast moving 500mb trough over south-
central Canada racing southeastward through the Great Lakes by
Monday night. Third:the departing system over the Northeast on
Monday that races east of Atlantic Canada Monday night. Where
guidance is in agreement is that the primary trough over the
Central Plains works in tandem with the ejecting Deep South
disturbance to direct a plume of 700-300mb moisture at the East
Coast. This moisture source will overrun a residual sub-freezing
air-mass Monday night over the Central Appalachians and Mid-
Atlantic that will support disruptive ice accumulations. However,
the dome of high pressure is departing as the storm approaches. For
areas west and north of I-95 in the Mid-Atlantic, boundary layer
wet-bulb temperatures will support at least a brief period for
accumulating snow. By 18Z Tuesday, a coupling 500mb jet streak
setup will support strong vertical ascent aloft that deepens a
coastal low as it tracks off the coast. To the north of the storm
track, heavy-banded precipitation to the north of a 850-700mb FGEN
band will transpire with snow most likely to occur north of I-95
in the higher terrain.

This is where the agreements in the overall setup end. Guidance
members such as the ECMWF show a less amplified Middle MS Valley
feature and less phasing with the Great Lakes disturbance, with
that Great Lakes feature suppressing the storm tracks with its
ensemble membership over the GEFS. Meanwhile, the GEPS are north
and more amplified compared to the GEFS, making the GEFS the
middle ground in storm position. Notably, the EC-AIFS ensemble
means is stronger with the surface low as it reaches the East
Coast on Tuesday and its QPF footprint is farther up the coast than
the EPS membership is. At the moment, the ECMWF is on the drier
side of guidance, while other like the CMC/NAM are much more
amplified. What today's trends have favored, as of this discussion,
is a slightly faster solution that would allow for precipitation
to arrive sooner on Tuesday morning.

With the cold air-mass retreating on Tuesday, the expectations for
those from northern VA and northern MD on north and east through
southeast PA, the Delaware Valley, and into southern New England
was to favor lower SLRs, which should make for a heavy/wet snow.
That said, the storm track is critical in determining how far north
the rain/snow line gets. As is the case in marginal boundary layer
temperature environments with fast moving coastal lows that are
unable to develop a robust deformation zone, plus baking in
climatology for the time of year, it should be the higher
elevations north and west of I-95 that are most favored for
accumulating snowfall. This setup favors interior New England for
heavy snow, although should the Great Lakes disturbance act to
suppress the storm track, this could shift farther south to the
Catskills and higher terrain of southern New England.

WPC probabilities show moderate-to-high chances (50-70%) for
snowfall totals >4" from east-central PA on north and east through
the Poconos, Catskills, Berkshires, Green, and White Mountains.
Farther south, the Philly/Baltimore/DC metro areas may start out
briefly as snow, but transition to a wintry mix on Tuesday. There
is a possibility for a more icy scenario should cold-air damming
(CAD) stick around longer on Tuesday before transitioning to plain
rain. Speaking of CAD, the Central Appalachians will see sub-
freezing surface temperatures persist long enough to support a
treacherous freezing rain event. WPC probabilities depict
moderate-to-high chances (50-80%) for ice accumulations over a
tenth of an inch from the Blue Ridge of western NC on north through
the WV/VA Appalachians and Shenandoah Valley with low chances
(10-30%) for over a quarter inch of ice. The WSSI-P shows a swath
of >50% chances for Minor Impacts from the Central Appalachians on
north and east through the WV Panhandle, along and west of Parrs'
Ridge in northern MD, through east-central PA, northern NJ,
southern NY, and interior New England. Key messages are ongoing
for this system (Key Message 3 below).


Mullinax



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

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