NWS Chicago Decision Support Briefing - Forecast

313
FXUS63 KLOT 220001
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
601 PM CST Wed Jan 21 2026

.KEY MESSAGES...

- A strong Arctic front will bring a 1-3 hour period of gusty
snow showers (greatest coverage north of I-80). Winds gusting
to 40+ mph may lead to patchy blowing and drifting snow
through tonight where snow falls.

- A second Arctic front will usher in an extended period of
dangerous cold Thursday night through early next week.

- An Extreme Cold Watch remains in effect for late Thursday
night into Friday morning for areas near and north of
Interstate 55, where wind chills may drop below -30F.

- Fluffy accumulating snow paired with cold temperatures may
cause hazardous travel conditions late Saturday into Sunday.

&&

.DISCUSSION...
Issued at 320 PM CST Wed Jan 21 2026

The primary weather concerns through the period include:

- Strong gusty snow showers this evening. Confidence high

- Dangerous cold Thursday night through Saturday. Confidence high

- Increasing potential for accumulating snow and associated
hazardous travel late Saturday into Sunday. Confidence in
specifics is low.

No changes have been made to the going Extreme Cold Watch, which
is in effect for late Thursday night into Friday morning for a
good portion of northern IL along and northwest of I-55.

In the near term, we continue to monitor the threat and timing of
a period of strong gusty winds, along with accumulating snow
showers/squalls this evening. Water vapor imagery depicts the
next approaching impulse currently shifting east-southeastward
into far southwestern MN/far northwestern IA. This feature is
driving an accompanying surface trough and strong cold front
eastward into western and central IA early this afternoon. As this
feature tracks eastward into our area towards and after 6 PM
this evening, a period of locally intense snow showers are
expected as low-level lapse rates steepen in advance of the
approaching cold front. This will particularly be the case
near/north of I-80/I-88 to near the WI state line, where a quick
1/2 to 1" of snow could fall prior to 10 PM.

Also of concern this evening is the expectation for a couple hour
"pop" of strong west-northwesterly winds (perhaps briefly gusting
40 to 50 mph, strongest south of I-80) as strong surface pressure
rises (~5 mb/3hr) onset just behind the cold frontal passage.
The main window for these strong winds will be in the 8 to 11 pm
timeframe. While the strongest winds may lag the more intense
snow showers this evening, the magnitude of these winds will
result in blowing and drifting snow in areas that get
accumulating snow early this evening across far northern IL.
Accordingly, expect some adverse impacts to travel across
northern IL due to reduced visibilities (briefly under a 1 mile)
and snow covered roads, most notably near the WI state line. We
can`t rule out short-fused hazard products (advisory or even
snow squall warnings), if needed.

Winds will ease gradually after midnight through daybreak
Thursday, though westerly winds will remain breezy. Forecast
highs on Thursday will be colder, with temperatures remaining in
the 20s. Later in the day, the next (and more significant)
Arctic front will drop southward across the area. This front
will again be paired with some gusty winds, and possible snow
showers, albeit with less coverage than that expected this
evening. Blustery northwesterly winds (gusting up to 30-35 mph)
in the wake of this front will usher in our dangerously cold
airmass Thursday night, with plummeting air temperatures
expected to fall several degrees below zero prior to daybreak
Friday morning. When combined with the blustery northwest winds,
wind chills early Friday morning will be as low as 25F below to
35F below zero (coldest in the current watch area near/northwest
of I-55).

The center of the 1045 mb Arctic high will build into the Upper
Mississippi Valley late Friday. This will result in gradually
abating winds late Friday into Friday night, which in turn will
support "some" minor improvement in the wind chills late Friday
into Saturday morning. Our current Extreme Cold Watch only covers
the most extreme cold through Friday morning. While some very
minor improvement to the wind chill is forecast Friday afternoon
as the winds begin to ease, dangerous cold will persist into
Saturday as actual air temperatures remain at, or below, zero.
Accordingly, following the Friday morning end time of the Extreme
Cold Watch, a Cold Weather Advisory is likely to be needed
through Saturday morning.

The next item of interest is the threat for accumulating snow
sometime late Saturday into Sunday. A significant winter storm is
expected to impact a large chunk of the central, southern, and
eastern CONUS this weekend, and we will largely reside along and
near the northern periphery of this storm. In spite of this,
there continues to be signs that the expansive precipitation
shield to our south may expand northward across our area
sometime Saturday into Sunday. While model and ensemble guidance
does continue to trend in this direction, it is important to
note that considerable uncertainty continues with the specifics
of this system. This is especially the case considering that
some complex interactions are likely to occur with a few
separate waves transitioning through the larger aggregate trough
in the west. Nevertheless, if snow does end up making into our
area, very cold temperatures will support high ratio (20+ to 1)
fluffy snow which would make for widespread hazardous travel
across the area through the second half of the weekend. Stay
tuned!

KJB

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 601 PM CST Wed Jan 21 2026

A quick-moving disturbance will bring periods of SHSN across
the terminals this evening. An initial band of SN aloft is
struggling to fully saturate to the surface, but should result
in a brief period of MVFR to perhaps very briefly IFR visibility
at onset prior to 01Z. A second axis of SHSN with more robust
coverage and intensity is expected roughly in the 01-02Z window,
followed by a final strong band of SNSH with a cold front in
the 03-04Z window. Conditions are expected to vary considerably,
with visibility ranging briefly down to 1/2SM or less in the
strongest showers to P6SM between the showers. The showers also
have the potential to produce gusts of 30 to 40 knots,
particularly toward the end of the 01-04Z window, resulting in
SNSQ conditions at some locations.

The cold front is expected to cross the Chicago terminals
around 04Z. WNW/NW winds will gust around 30 knots behind the
front and through much of the overnight hours, but especially
for the first couple hours behind the front. During this time,
SHSN coverage and intensity will diminish, ending by daybreak
Thursday.

Expect W winds to gust around 20 knots Thursday morning and
over 25 knots during the afternoon before an arctic front veers
winds NW with gusts around 30 knots early in the evening. A
narrow band of light SN or scattered SHSN with generally MVFR
visibility may precede the front for a couple hours. Shallow
MVFR stratocumulus with flurries will likely proceed the front,
but limited saturation of the cloud layer is enough to maintain
a dry post-frontal TAF at this time.

Kluber

&&

.MARINE...
Issued at 320 PM CST Wed Jan 21 2026

A Gale Warning remains in effect for all of our nearshore zones
tonight. Another formidable arctic cold front is slated to push
through the region this evening, causing west- southwesterly
winds to turn westerly/west-northwesterly and gust to at least
35 kts behind the front. Some potential for 40 kt gales exists
as well, though confidence in this is only low- medium at this
time. Gusts will gradually subside with time Thursday morning as
the front and associated low pressure center progress eastward.

Some consideration may need to be given to a Heavy Freezing
Spray Warning for our nearshore zones adjacent to Porter County,
IN. However, at this time, it appears that the more significant
heavy freezing spray risk will remain over the open waters of
Lake Michigan.

Ogorek/Castro

&&

.HYDROLOGY...
Issued at 258 PM CST Mon Jan 19 2026

Area hydrographs and ice spotter reports confirm that ice
continues to develop and spread across areal rivers. Localized ice
jams are already present along the Rock, Des Plaines, and Fox
Rivers. Continued cold temperatures tonight and Tuesday will
cause ice to continue expanding and thickening.

After a brief warm-up in temperatures to above 20 degrees on
Tuesday-Wednesday, another push of bitterly cold temperatures
will arrive Thursday night. As a result, the threat for ice
jams including localized flooding will increase further toward
the end of the week and through the weekend.

- NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Extreme Cold Watch from late Thursday night through Friday
morning for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-
ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

Wind Advisory until midnight CST tonight for ILZ019-ILZ021-
ILZ023-ILZ032-ILZ033-ILZ039.

IN...Wind Advisory until midnight CST /1 AM EST/ tonight for INZ010-
INZ011-INZ019.

LM...Small Craft Advisory until 7 PM CST this evening for the IL
and IN nearshore waters.

Gale Warning until 6 AM CST Thursday for the IL and IN
nearshore waters.

Heavy Freezing Spray Warning from midnight tonight to 10 AM
CST Thursday for Gary to Burns Harbor IN-Burns Harbor to
Michigan City IN.

&&

$$

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