949
FXUS63 KLOT 241728
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1128 AM CST Mon Nov 24 2025

.KEY MESSAGES...

- Increasing low-level cloud cover this morning, with locally
  dense fog possible.

- Light rain or drizzle expected tonight into early Tuesday,
  along with the possibility for another period of locally
  dense fog.

- Very windy (gusts up to 45 mph or stronger) and much colder on
  Wednesday with light snow showers and flurries possible for some,
  and then continued blustery and cold on Thanksgiving Day.

- There is a growing signal for accumulating snow and associated
  travel impacts in the region late Friday night through
  Saturday.

&&

.DISCUSSION...
Issued at 316 AM CST Mon Nov 24 2025

Through Tuesday:

We continue to monitor the northward expansion of an area of
very low stratus and fog early this morning. As of this writing,
the northern extent of this low stratus and fog was roughly
oriented from southeastern IA, back east-southeastward into
central IL, just to the south and southwest of the LOT CWA. The
expectation is for this stratus and fog to continue expanding
northward through the early to mid morning hours today,
particularly across the western half or so of IL. As it does, we
cannot rule out the need for a northward expansion of the dense
fog advisory into portions of our area. However, with it
remaining somewhat unclear as to how extensive the dense fog
threat will be in northern IL this morning, we have opted to
hold off in doing so for the present time. The areas most at
risk for a period of dense fog this morning look to be areas
generally west of I-57 and west of I-355 in northern IL. We will
continue to monitor observational trends in the coming hours.

The low stratus and fog is likely to have staying power today,
particularly across northwestern IL (generally northwest of the
I-55 corridor and west of most of the Chicago metro area). With
this in mind, I have maintained the idea of cooler high
temperatures today in this general area. Yesterday, this same
area of cloud cover was persistent through the day across
portions of MO, and temperatures there never warmed out of the
middle and upper 40s. I thus anticipate similar temperatures
this afternoon under the most persistent and thicker low-level
stratus, which again looks to be most probable across
northwestern IL (generally northwest of I-55). Conversely, areas
along and east of I-55 (including parts of the Chicagoland
area) look to have shallower cloud depths, which may allow them
to diurnally dissipate for a period this afternoon. This will
thus make for a tricky temperature forecast this afternoon, as
temperatures outside the thicker low-level cloud cover are
likely to end up several degrees warmer (low to mid 50s).

Regardless of which areas are able to shed the low-level
stratus this afternoon, it will expand back across the entire
area later this evening and overnight. This is expected as
deeper moisture begins to shift into the area with the
approaching mid-level impulse. While a period of light rain
continues to be in the cards for tonight into early Tuesday
morning as this impulse passes across central IL, it appears the
activity will remain more showery with northward extent across
northern IL. For this reason, rainfall amounts are expected to
remain quite light (only up to a tenth of an inch or so). The
precipitation may even end up transitioning to a period of fog,
very low clouds and drizzle into Tuesday morning. We will thus
have to keep an eye on the potential for more dense fog in or
near the area into Tuesday morning.

KJB


Tuesday Afternoon through Sunday:

A majority of the guidance does scour out the areas of fog and
drizzle Tuesday afternoon, though at this time of year, can`t say
that`s a sure thing. It will otherwise be continued cloudy and
mild with highs in the lower to locally mid 50s.

Attention then turns to the powerful cold front sweeping across
the area Tuesday evening into the overnight. The front will be
driven by a potent and amplifying northern Plains short-wave
taking on a negative tilt as it reaches the Northern Lakes
Wednesday morning (and its associated surface low quickly deepens
as well). While deep layer moisture will be limited, the magnitude
of large scale and frontal forcing will likely overcome the
after sunset timing for a fast moving arc of showers to push
across the area ahead of the front. Can`t rule out a few showers
over the western half or third of the CWA just prior to sunset
Tuesday, but the bulk of the measurable rain (up to 1/10")
should be centered on 6pm to midnight Tuesday.

By far the bigger story will the post cold frontal passage strong
winds and plummeting temperatures amidst robust cold air
advection (CAA). The progged 990-995 mb surface low slowly
tracking across the northern Lakes as 1030-1035 mb high pressure
tries to build east from the Plains is a pretty classic pattern
for strong synoptic winds in the cold season. Very steep low-level
lapse rates from the strong CAA will help tap into 40-50 knots of
westerly flow aloft. Given the consistency of the signal for
strong winds on Wednesday, continued to nudge up the forecast
gusts to up to 45 mph, and there`s a pretty good chance we`ll end
up needing a Wind Advisory for much of if not the entire area.
While moisture is lacking in forecast soundings once solidly above
the -10C level, some wind-whipped flurries or light snow showers
are possible for roughly the northeast half of the CWA.
Temperatures will probably struggle to rise much if at all and
stay in the 30s through the day, keeping wind chills in the 20s.

Blustery but not quite as windy conditions will continue through
Wednesday night and Thanksgiving Day (gusts to 30-40 mph), with
temps only recovering to the lower to locally mid 30s Thursday
afternoon following morning lows in the 20s. Wind chills will be
as low as the the upper single digits to lower teens, "rebounding"
to the teens to around 20F during daylight hours. Keep this in
mind if you have any outdoor activities planned on Thanksgiving
Day. Thursday night into Friday will be much less windy and cold
(lows in the teens and 20s and highs in the 30s) as surface high
pressure transits the area.

Late Friday night through Saturday, a potentially prolonged
period of warm advection driven precipitation paired with
sufficiently cold temps aloft and at the surface may set the stage
for an accumulating snow event. While there`s a large spectrum of
plausible outcomes amongst ensemble members, the multi-ensemble
probability for 1"+ (10:1) snowfall in 24 hours centered on
Saturday-Saturday evening is >=60% even at this extended lead
time. The ECMWF/EPS depiction has been generally more robust than
the other guidance suites, but ultimately it`s much too far out
for specifics, aside from feeling comfortable with ~60% PoPs in
the gridded forecast. Our main message is to keep a close eye on
subsequent forecast updates as this timeframe draws closer for the
potential for winter weather impacts to post-Thanksgiving travel.

Forecast uncertainty grows considerably into Sunday and beyond.
The potential exists for continued precip as warmer air moves
into the region, represented by still sizable ensemble membership.
On the other hand, the active baroclinic zone may be shunted
far enough southeast for a period of quiet but cold weather into
early next week. Maintained broad-brushed chance PoPs with rain-
snow mention given the large spread in solutions.

Castro

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1128 AM CST Mon Nov 24 2025

The primary aviation concerns include:

- Quickly deteriorating ceilings and visibilities overnight,
  with LIFR conditions expected by daybreak Tuesday.

- A period of VLIFR cigs and visibilities in drizzle and fog
  Tuesday morning potentially dropping below airport minimums,
  especially between 14-18Z.

Discussion:

Over the next 24 to 36 hours, a low pressure system currently
centered over central Oklahoma will lift northeastward and move
directly over the terminals leading to inclement weather.

As the low pressure system approaches this evening, ongoing low
cigs of 200 to 400 feet across Iowa and central Illinois will
quickly shift northeastward and spread over the terminals
during the overnight hours. Confidence is high that cigs will
tank into IFR and LIFR overnight, but only medium on exact
timing. With that said, conditions may take longest to
deteriorate at ORD/MDW/GYY (potentially holding off until just
before daybreak). Increasing isentropic ascent ahead of the low
will encourage scattered shower and drizzle development this
evening and overnight as well, with perhaps the highest coverage
of showers expected from midnight through mid Tuesday morning.
Visibilities should gradually lower toward the 1-3 mile range
through the overnight hours as well owing to abundant moisture
and low-level lift across the region (which will lead to
drizzle and fog). Finally, southwest winds this evening will
gradually back southeasterly overnight, before becoming light
and variable by daybreak Tuesday.

The center of the low will move directly over the terminals
generally between 14 and 18Z as coverage of showers tapers,
leading to the worst aviating conditions. Slackening winds in
the column, abundant low-level moisture, and lift afforded by
the passing low meet conceptual models for a 4 to 6 hour period
of LIFR to VLIFR visbys and cigs in drizzle and fog occurring at
all terminals. In fact, do have concern that minimums will be
met at RFD/DPA where column winds will be weakest, but certainly
cannot rule out such conditions occurring at ORD/MDW/GYY, as
well. Will go ahead and introduce targeted TEMPO groups for
1/2SM VV001 FG at RFD/DPA and relegate to PROB30s at ORD/MDW/GYY
for 3/4SM OVC003 during the morning hours keeping in mind
adjustments are likely in later TAF packages. Winds through the
morning hours will be light and variable.

As the center of the low pulls away, winds will adopt a
southwesterly component and increase toward 5 kt. As a result,
will cautiously advertise modestly improving cigs and visbys
toward the very end of the TAF period, but would not be
surprised if conditions remain VLIFR to LIFR all the way into
Tuesday afternoon ahead of an approaching cold front from the
next system.

Borchardt

&&

.MARINE...
Issued at 337 AM CST Mon Nov 24 2025

A powerful cold front trailing from deepening low pressure
across the Northern Great Lakes will sweep across the lake
Tuesday night. In the wake of the frontal passage, westerly
winds will quickly increase, likely to gale force. The strongest
winds, with gales possibly as high as 45 kt at times, look to
occur during the day on Wednesday, with lower end gales then
possibly persisting through Thanksgiving Day. A Gale Watch has
been issued for all the waters of southern Lake Michigan, and
is in effect from the pre-dawn hours of Wednesday through early
Thursday evening.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Watch from late Tuesday night through Thursday afternoon
     for the IL and IN nearshore waters.

&&

$$

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