458
FXUS63 KLOT 282127 CCA
AFDLOT

Area Forecast Discussion...CORRECTED
National Weather Service Chicago/Romeoville, IL
327 PM CST Fri Nov 28 2025

.KEY MESSAGES...

- Winter Storm Warning in effect for all of our Illinois and
  Indiana counties for late tonight into Saturday night.

- Impactful snow will spread across the area late tonight through
  Saturday night. There is a >90% chance for 6"+ amounts and
  higher end travel impacts along and north of Pontiac to Kankakee
  to Valparaiso line. The highest snowfall rates and worst
  conditions are expected Saturday afternoon into early evening.

- Increasing chance (60%) of light accumulating snow late Monday
  afternoon and night.

- Well below normal temperatures will persist through next week.

&&

.DISCUSSION...
Issued at 255 PM CST Fri Nov 28 2025

Through Monday:

All eyes are on the expected widespread early season heavy snow
event across the region beginning late tonight and continuing
into at least Sunday morning.

The parent trough responsible for the incoming system is
currently analyzed near the Grand Tetons. The trough will
continue on an ESE/SE trajectory through tonight as it phases
with a remnant subtropical wave now over the far southern
Rockies. The resultant amplification of the trough will swing
across the far western Great Lakes while exhibiting a slight
negative tilt by Saturday evening. The kinematic and
thermodynamic set-up continue to become more impressive as the
event nears. Loose coupling of a departing upper jet streak over
the western Great Lakes and a strengthening 130 knot jet streak
entering MO and southern IL late Saturday afternoon will
provide plenty of upper-level support. Meanwhile, decent height
falls and expansive mid-level diffluence will spread across the
region. Stepping downward, guidance has shown a substantial
trend toward a sharpening 700 hPa frontogenesis axis while also
exhibiting increasing mid-level isentropic ascent below 7C/km
600-400 hPa lapse rates. Lastly, robust low-level moisture
transport of 50 knot southerly winds will provide a continuous
feed of moisture into the system. Needless to say, the continued
favored low track from the IA/MO/IL triple point to over
Chicago would not climatologically support a large snow-maker in
late November. But with the cold post-Thanksgiving airmass in
place and abundant forcing noted above, we are trending toward a
decent snow event for much of the forecast area.

There remain a few varying fail modes for widespread heavy snow
across the area. First, initial deep saturation on the western
extent of a rather dry airmass centered over the Tennessee
Valley will likely result in top-down saturation under only the
strongest ribbons of low/mid-level isentropic ascent and
frontogenesis. So as snow begins to spread eastward late tonight
and into Saturday morning, narrow bands of moderate to heavy
snow may be interspersed within a broader area of light snow.

Second, the steep lapse rates aloft will support borderline
upright convection above the impressive 700 hPa f-gen band, with
a decent amount of CSI present wherever upright convection does
not develop near and north of the band. In this case, a narrow
band of very heavy snow would settle over west-central Illinois
through the morning and early afternoon before lifting ENE over
much of the CWA later in the afternoon and early evening. This
would possibly cut down on snow totals through the morning and
limit the higher snow rates of 1"/hr or higher to a <6hr window
mid-afternoon into early evening over northern Illinois.

Finally, the more northern track of the surface low and
negative tilt of the trough suggest that a rapidly advancing dry
slot will cut off much of the better snow production, even
transitioning to drizzle, for much of the southeast half of the
CWA by early Saturday evening. Like the second point above, this
would limit the window for the higher snowfall rates to only
around 6 hours or so.

Regardless of all that said above, the combination of deep
moisture and very strong forcing will result in a period of
heavy snow with very hazardous travel conditions Saturday
afternoon into early evening. Additionally, the northern low
track now means that stronger SE winds with gusts over 25 mph
will become prevalent and create some blowing and drifting snow
concerns in open areas during the afternoon and early evening.
Snow totals areawide still look to fall in the 6 to 10 inch
range with a likely embedded band of more than 10 inches
somewhere over the area. The entire area remains in a Winter
Storm Warning late tonight through much of Saturday night.


Sunday and Sunday Night:

A 1035-1040 hPa high building into the Great Plains impinging
on the low over Lake Huron and Georgian Bay on Sunday will
induce strong gradient winds and a modest 3-6mb/3hr pressure
rise over much of the area. Some shallow blowing and drifting
snow will likely persist for open areas conditional on a drier
character of the expected snow pack. Will include patchy
blowing snow in the forecast for now, with the greatest concerns
on N/S-oriented roadways in open areas west of the Fox River
Valley. Additionally, ongoing strong CAA with shallow stratus
under a steadily lowering subsidence will support some lingering
light snow showers or flurries well into the day Sunday. The
lower inversion will also limit lake effect snow intensity near
the lake in northwest Indiana, but additional minor
accumulations are probable for northeast Porter County.

The inversion should lower enough to erode remaining stratus
Sunday night as the surface ridge edges toward the area. As long
as stratus does not persist well into the night, diminishing
winds with a fresh snow pack will promote a rather chilly Sunday
night with lows potentially at or below zero across interior
northern Illinois.

Kluber



Monday Night through Friday:

The primary forecast focus beyond this weekend`s winter storm
is the increasing potential for another round of accumulating
snowfall during the Monday afternoon-Monday night. The multi-
model consensus this morning continues to advertise a secondary
shortwave dropping south through the Great Basin Sunday night
and eventually ejecting across the Central Plains on Monday as a
positively-tilted trough. This orientation would result in a
fairly progressive system overall, but intensifying mid-level
frontogenesis is forecast to result in an expanding region of
generally light snow across parts of our forecast area. A
significant north-south spread exists persists in the guidance
and ensemble output today, but in general, the favored location
for fgen-enhanced snowfall appears to be setting up somewhere
across the southeastern two-thirds of the forecast area.

Main concern during this period is that snow would be falling
into a cold airmass with surface temperatures in the upper teens
to mid 20s which would easily result in slick/hazardous travel
even with modest snowfall amounts. The other aspect that has our
attention is some degree of near-upright/convective instability
in recent model guidance above the main frontogenetic
circulations which could end up locally-enhancing precip rates.
At this time, liquid amounts are generally a quarter inch or
less which would support perhaps 2-4 inches of snowfall given
generally modest ascent through the DGZ and and cold surface
temperatures. Too much uncertainty at this point to pinpoint the
main threat area, but something we`ll be keeping a close eye on
over the coming days.

Increased cloud cover may end up tempering overnight lows/wind
chills a bit more than the currently-advertised NBM grids, but
cold conditions will nonetheless prevail next week. A
reinforcing shot of cold air is generally forecast to arrive
midweek as a roughly 1040 mb arctic high slides southward across
the central CONUS, perhaps with an additional round of snow or
at least flurries as the boundary layer saturates into the base
of a very deep dendritic growth zone.

Carlaw

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1126 AM CST Fri Nov 28 2025

- Snow overspreads the region late tonight/early Saturday
  morning.

- Cigs/vsbys will steadily deteriorate through the morning.
  Periodic dips to LIFR/VLIFR anticipated, particularly midday
  Saturday onward.

- Snowfall rates generally around one half inch per hour, but
  expected to peak near 1 inch/hour Saturday afternoon. Bulk of
  snow accumulations expected from about 1 pm to 8 pm.

Northwesterly winds will turn southerly this evening and
eventually southeasterly tonight. Generally VFR conditions are
expected today, with some patches of high-MVFR strato-cu
developing.

Snow will overspread the terminals late tonight into early
Saturday morning. Some uncertainty regarding the exact start
time of light snow remains, but snow will gradually fill in and
become steady through the morning hours with widespread IFR
vsbys expected. Snowfall intensity is expected to peak Saturday
afternoon, and this is the period most likely to result in
LIFR/VLIFR conditions--at least on a temporary basis. The bulk
of snowfall accumulations are expected during the roughly
12pm-8pm timeframe, with snowfall rates intermittently nearing 1
inch per hour during this period.

Southeasterly winds will also gradually increase through the
day, with gusts increasing towards 25 kts during the afternoon.

Finally, just beyond the end of the current TAF periods: a mid-
level dryslot is expected to quickly work its way northward
Saturday evening. Temperatures will also begin to slowly warm,
and this combination may result in snow mixing with or even
changing to drizzle Saturday evening. This appears to be a lower
potential at RFD, and locally greater potential at GYY and MDW.

Carlaw

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Storm Warning from 3 AM Saturday to 6 AM CST Sunday for
     ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-
     ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ103-ILZ104-
     ILZ105-ILZ106-ILZ107-ILZ108.

     Winter Storm Warning from 3 AM Saturday to midnight CST
     Saturday night for ILZ033-ILZ039.

IN...Winter Storm Warning from 3 AM Saturday to 6 AM CST Sunday for
     INZ001-INZ002.

     Winter Storm Warning from 3 AM CST /4 AM EST/ Saturday to
     midnight CST /1 AM EST/ Saturday night for INZ010-INZ011-
     INZ019.

LM...Small Craft Advisory from 9 AM Saturday to 10 PM CST Sunday
     for the IL nearshore waters.

     Small Craft Advisory until 3 PM CST this afternoon for Calumet
     Harbor IL to Burns Harbor IN.

     Small Craft Advisory from 9 AM Saturday to 7 AM CST Monday for
     the IN nearshore waters.

     Small Craft Advisory until 7 PM CST this evening for Burns
     Harbor to Michigan City IN.

&&

$$

Visit us at weather.gov/chicago