NWS Chicago Decision Support Briefing - Forecast

547
FXUS63 KLOT 221732
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1132 AM CST Thu Jan 22 2026

.KEY MESSAGES...

- Another Arctic frontal passage later today will usher in an
extended period of dangerous cold temperatures late tonight
into the upcoming weekend.

- An Extreme Cold Warning is now in effect late tonight through
Friday morning for areas near and north of I-55 where wind
chills are expected to drop between -30 to -40F. A Cold
Weather Advisory in effect for remaining areas where wind
chills may drop between -20 to -30F.

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

&&

.UPDATE...
Issued at 1115 AM CST Thu Jan 22 2026

No big changes to the forecast this morning, but extended the
Cold Weather Advisory for our SE CWA through 15z Saturday and
tacked on a Cold Weather Advisory to the end of the Extreme
Cold Warning and also ran that advisory through 15z Saturday.

Small patch of some stratocu over NW IL has had a few flurries
with it, so certainly plausible that there would be a few
flurries at times this afternoon, mainly near the WI border.
This stratocu deck has some horizontal convective rolls in the
strong cold air advection tonight will remain prone to
occasional flurries as clouds are in cold enough layer for ice
nuclei to be present. Very common for flakes to leak from
stratocumulus in bitter cold air masses like the one that comes
in tonight.

We`re taking a close look at incoming model data and will have
an update on snow chances this weekend this afternoon.

- Izzi

&&

.DISCUSSION...
Issued at 330 AM CST Thu Jan 22 2026

Through Friday Night:

Focus through the end of the workweek remains the potential for
dangerous cold returning late tonight as surface high pressure
expands across the region in the wake of another Arctic front.

Snow showers have shifted east of the area early this morning
with mostly clear skies and cold air advection allowing
temperatures to steadily drop into the teens. Winds will remain
breezy through the remainder of the daytime hours with gusts in
the 25 to 35 mph range making for a cold and blustery Thursday.
Sporadic gusts up to 40 mph can`t be ruled out during the
afternoon and early evening.

The second of two Arctic fronts is currently moving into
Minnesota and will usher in our next round of bitterly cold
temperatures and dangerous wind chills as it moves across the
area later today. There are patches of stratus across portions
of IA, WI, and MN ahead of and behind the front that are
producing flurries and even a few snow showers given the cold
airmass in place. As these clouds shift southeast over the area
can`t rule out isolated snow showers and flurries here locally
during the late morning through the early evening timeframe.
Still not expecting notable accumulations from this, perhaps at
most a very localized light dusting and brief reductions in
visibility when paired with the gusty winds.

While winds are expected to ease slightly this evening they
will remain breezy through the night into early Friday morning.
This paired with steadily dropping temperatures will lead to
wind chills dropping into the -20 to -40F degree range across
the area, coldest across interior northern Illinois. Have
upgraded the Extreme Cold Watch to a Warning with this update
and issued a Cold Weather Advisory for remaining portions of
east central Illinois and northwest Indiana. Given how sensitive
wind chill values are to wind speed and air temperature once it
gets this cold, some uncertainty on the degree of cold exists
due to continued model spread on how cold the air temperatures
end up. Have maintained a blended approach for now since it
properly captures the message that dangerous cold will occur
late tonight through Friday morning. In fact, wind chills may
remain near and below 20F through Saturday morning for areas
north of I-55 where a follow-up Cold Weather Advisory will
likely be needed once the warning expires.

Lake effect snow showers likely develop across portions of
northwest Indiana into Friday as the colder airmass paired with
north northwesterly fetch sets up across Lake Michigan. Given a
signal for weak convergence developing amidst expansive surface
high pressure, have increased snow shower chances accordingly
for northeast Porter County where accumulating snow will be
possible. The band may shift west into Lake County late Friday
night through confidence in this distance is on the lower side.

Petr


Saturday through Wednesday:

The primary concern and challenge is the potential for
accumulating snow Saturday through Sunday night along with the
chance for lake enhancement across far northeast IL.

High pressure will be slowly weakening as it moves across the
Great Lakes region Saturday into Saturday night. With the warmer
waters of Lake Michigan, the models try to develop a lake effect
snow band Friday night as convergence develops that may persist
into Saturday morning. Low confidence for how much may actually
develop as well as low confidence for it reaching land but
blended slight chance pops for northeast IL Saturday morning
seem reasonable for now for this potential.

The local area will then be on the northern edge of a winter
storm affecting much of the eastern half of the country this
weekend. Over the past 24-48 hours the models and their
ensembles have made a decisive shift north with the precip
shield, which will be all snow here. While confidence is slowly
increasing, there still remains uncertainty for specifics. The
ECMWF and its ensembles remain in very good agreement with snow
spreading across the area during the day Saturday and then
continuing into Sunday for a long duration snow event. The GFS
is further south with its ensembles about 50/50 for snow for the
local area. Canadian is roughly in between the ECMWF/GFS. How
much precip that can make it this far north is still in
question given the large swath of heavy qpf expected further
south. An upper level trough will also be digging across the
Plains Sunday and shifting east Sunday night. The speed of this
trough could play a large role in how far north the snow is able
to spread. If the snow does spread across the entire area, there
would then be the potential for lake enhanced snow across far
northeast IL, possibly shifting east into northwest IN Sunday
night as it ends.

With all of the above in mind, the blended pops have increased
into the likely range for Saturday night/early Sunday morning,
mainly southeast of I-55 and this seems reasonable at this time.
Too early for any amounts but snow ratios will be high and
likely dependent on forcing. Made no changes to the blended
ratios of 20 to 1 which also match WPC. But should a ECMWF
solution pan out, with more qpf and better forcing, then higher
snow ratios may materialize.

The pattern will continue to favor cold/very cold temps through
the middle of next week with a re-enforcing blast of cold air
on Monday with wind chills in the 10 below to 20 below zero
range Monday morning. Highs may try to get into the 20s Tuesday
with another possible blast of cold air midweek. cms

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1132 AM CST Thu Jan 22 2026

Aviation forecast concerns for the 18Z TAFs:

- Strong west-northwest winds with gusts around 30 kts into
tonight.

- Chance of flurries/snow showers mainly this evening.

A surface trough will move east across the terminals early this
afternoon, producing a subtle wind shift to the west-northwest
with gusts approaching 30 kts. A few flurries may squeeze out of
a VFR stratocu deck along/ahead of the front, though these are
expected to be inconsequential and rather spotty per upstream
observations.

A stronger arctic cold front will push east across the terminals
this evening, accompanied by a mid-level disturbance. This will
further shift winds to the northwest, with a period of 30-35 kt
gusts behind the front into the overnight hours. A slightly
deeper layer of low-level moisture along/ahead of this front may
support scattered flurries/snow showers, some of which could
produce brief MVFR visibilities and perhaps a dusting of snow
accumulation. More shallow high-end MVFR/low-end VFR strato cu
may produce additional inconsequential flurries overnight.

Northwest winds will gradually ease late tonight into Friday,
with decreasing coverage of low-level cloud cover as a very cold
arctic high pressure system builds into the area.

Ratzer

&&

.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 Warning from 3 AM to noon CST Friday for ILZ003-
ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-
ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ103-ILZ104-ILZ105-
ILZ106-ILZ107-ILZ108.

Cold Weather Advisory from noon Friday to 9 AM CST Saturday
for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-
ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ103-
ILZ105-ILZ106-ILZ107-ILZ108.

Cold Weather Advisory from 3 AM Friday to 9 AM CST Saturday
for ILZ033-ILZ039.

Cold Weather Advisory from noon to 1 PM CST Friday for ILZ104.

IN...Cold Weather Advisory from 3 AM CST /4 AM EST/ Friday to 9 AM
CST /10 AM EST/ Saturday for INZ001-INZ002-INZ010-INZ011-
INZ019.

LM...Gale Warning until 3 AM CST Friday for the IL and IN nearshore
waters.

Small Craft Advisory from 3 AM to 3 PM CST Friday for Winthrop
Harbor IL to Gary IN.

Heavy Freezing Spray Warning from 9 PM this evening to 3 PM
CST Friday for Gary to Burns Harbor IN-Burns Harbor to
Michigan City IN.

Small Craft Advisory from 3 AM Friday to 3 AM CST Saturday for
Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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