329
FXUS63 KLOT 250450
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1050 PM CST Mon Nov 24 2025

.KEY MESSAGES...

- Light rain or drizzle expected tonight into early Tuesday,
  along with the possibility for a 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 conditions on
  Thanksgiving Day.

- There is a growing signal for accumulating snow and associated
  travel impacts in the region Saturday and into Sunday.

&&

.UPDATE...
Issued at 812 PM CST Mon Nov 24 2025

Bumped up pops for this evening`s initial round of light
rain/showers, though going forecast otherwise appears to have
trends well in hand. Will have to watch visibility trends
overnight however, with areas of fog likely to form especially
west/northwest of Chicago.

Regional radar mosaic currently depicts an area of light rain
especially near and east of the I-55 corridor at mid-evening.
This appears to be occurring in associating with a subtle mid-
level wave lifting northeast ahead of the main short wave trough
back toward the KS/MO border. This initial area of better
coverage rain/showers should continue to lift northeast across
the eastern parts of the cwa over the next few hours with a bit
of a lull likely by late evening, though spotty light
rain/drizzle should persist throughout the evening. High-res
guidance is then in pretty good agreement in bringing another
push of rain into the area after midnight, which also looks to
favor the southeastern 1/2 to 2/3 of the forecast area. This
second batch of rain should taper off to drizzle toward/just
after sunrise Tuesday morning with the passage of the main mid-
level trough axis.

Extensive low stratus has already developed into the mid-
Mississippi Valley this evening, and will continue to spread
across the forecast area over the next few hours. Also noting
1-3SM visibilities in fog developing upstream across western IL,
and this will likely continue to develop into the overnight
hours where rain persists. Plenty of guidance support exists for
some denser fog to develop after midnight, especially across
our west/northwest cwa where rain/shower coverage looks to be
lower. Already seeing a few <1/2SM obs into southwest WI, and
we`ll have to keep an eye on this later tonight into Tuesday
morning. Would not be surprised to eventually need a Dense Fog
Advisory for at least west/northwest parts of the forecast area
toward morning. Fog could linger for a decent part of Tuesday
morning prior to the surface reflection of the upper trough
moving off to the east.

Ratzer

&&

.DISCUSSION...
Issued at 225 PM CST Mon Nov 24 2025

Through Wednesday:

On early afternoon water vapor imagery, a couple of separate
impulses can be seen spinning over the central Plains each tied
to a broader upper trough. A feed of Gulf moisture extends all
the way to the upper Midwest in the system`s "warm sector" and
is responsible for the overcast skies hanging overhead today. To
our west and southwest, light rain, fog, and ceilings below
1,000 ft have been lingering nearer to the centers of
circulation. Such conditions will propagate into our area
tonight into tomorrow as low pressure approaches from the
southwest. Just as of around 1:30 PM, a few light radar returns
are showing what appears to be scattered virga showers, or
sprinkles at the most. Some patchy drizzle may start to fill in
from the west late this afternoon. The plume of deeper moisture
will lift into our area after 00Z allowing for a higher coverage
of light rain and drizzle. This will continue through the night
as a warm, moist upglide regime resides overhead. While we may
see largely drizzle through the night, there should be enough
moisture and forcing through the column to support true light
rain showers from time to time. The more appreciable light rain
potential should wrap up before mid-morning, and some drizzle
may linger through the rest of the morning.

We`ll find ourselves in a favorable location relative to the
low track for low stratus and fog tonight and into tomorrow. In
fact, we`ve been seeing periodic 3 mile visibilities in our west
and southwest most of the day, and there`s no reason that
shouldn`t maintain itself before conditions start dropping
further this evening. There is good agreement among guidance in
fog thickening across our west and northwest this evening and
expanding around the CWA through the night. Probs for dense fog
build after sunrise when we`ll see a bump in dewpoints and are
highest west of the city between the I-80 corridor and the WI
state line. There is a signal from a number of camps for
visibilities around Chicago to stay up near a couple of miles
while the thicker stuff remains outside of the city. However,
there is certainly a potential for dense fog to spread into and
around the city tomorrow morning. The nature of any
precipitation falling will also play a role in visibility
impacts. Plan on a soupy, slow-moving morning commute tomorrow.
Gradual improvements should take place after mid-morning, but
the whole day looks pretty gloomy with the low ceilings
continuing to hang overhead.

A digging upper wave will traverse the upper Midwest tomorrow
afternoon into Wednesday. The surface response will be a
deepening center of low pressure across northern WI and fast-
moving cold front which is progged to move across our CWA
tomorrow evening. Modest dynamic forcing ahead of the front
could stir up a few light pre-frontal showers as early as dusk
in our west, although precip chances are much higher along the
front during the evening. It should be a rather brief stint of
rain for any given area (maybe only a couple of hours). Being
largely katafrontal in nature, profiles dry out very quickly
behind the front. However, enough BL moisture may remain in
place to provide some lingering flurries or very light snow
showers amid the strong shear and cold advection tomorrow night
through Wednesday, especially north of I-80. No accumulations
are expected out of any this snow.

The bigger story regarding this front will be the strong winds
and much cooler air following it. The cold advection will keep
the boundary layer well mixed Tuesday night as a low level jet
builds off the deck featuring as much as 45 kt of flow at 925mb
and 50 kt beneath 850mb. Accordingly, we should be looking at
westerly gusts in excess of 40-45 mph for much of Wednesday. The
period of strongest winds appears to be between early morning
and mid-afternoon before the LLJ starts to ease, but expect
windy conditions to last into the evening. You might want to
hang onto your steering wheel a little tighter on Wednesday,
especially when traveling on open north-south roads. No decision
just yet to issue a Wind Advisory for Wednesday, but we do
appear to be heading in that direction.

These strong winds will advect a cold airmass into the region
from the northwest and usher in a stretch of much cooler weather
for the latter half of this week. 850mb temps are progged to
drop about 15C between Tuesday and Wednesday evenings (that`s
27F!). After surface temperatures fall into the lower and middle
30s in the wake of the front Tuesday night, the cold advection
should balance with diurnal heating and daytime temperatures on
Wednesday are expected to barely depart from morning lows. It`s
possible that we even cool a degree or two during the day.

Doom

Wednesday Night Through Monday:

Blustery conditions will continue Wednesday night through
Thanksgiving. Temperatures in the 20s with the potential for
single digit wind chills are possible through sunrise, where
daytime warming will only approach the freezing mark with wind
chills in the 20s. Winds will begin out of the west and turn to
the northwest through Thursday morning. With favorable fetch and
warm lake water temperatures supporting some lake induced CAPE,
lake effect snow is possible through Thursday evening. However,
it will likely be limited to just the far northeastern portion
of Porter County, Indiana. Otherwise winds will slowly diminish
Thursday evening. Weak surface high pressure will provide quiet,
albeit cold, conditions on Friday.

Models have been somewhat consistent in developing a shortwave
trough over southwestern Saskatchewan and eastern Montana early
Friday morning and have it approach the western Great Lakes
Saturday morning. As an inverted surface trough grows over the
southern Plains, warm air advection should overspread much of
Illinois and Indiana with much colder temperatures aloft.
Ensemble probabilities are keeping fairly consistent signal for
some amount of accumulating snow. However, models are still
disagreeing on the exact track of that trough and how far south
the colder temperatures will reach. GEFS models are suggesting a
much warmer solution that allows for some snow (with minimal
accums) on Saturday, before lifting and allowing for warmer
temperatures through the column to transition to (potentially)
all rain on Sunday. The EPS is far colder, allowing for
traditional warm advection snowfall before a new surface low
develops and allows for a cold conveyor belt of air to provide
for a healthier chance for additional snowfall. For now, there
was no need to change the PoPs the NBM provided. While it does
allow for "likely" snow on Saturday, how this all transpires
comes with a lot uncertainty and low confidence. That being
said, considering how many people will use this weekend to
travel following the holiday, it could provide a great deal of
impact depending on which solution plays out.

There is a lot of uncertainty beyond Sunday. The EPS keeps
things cold, while the GEFS warms afternoon temps. Both are
suggesting high pressure could grow behind the system. So it is
possible that PoPs are too high and drier conditions could in
store for early next week.

DK

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1050 PM CST Mon Nov 24 2025

Forecast concerns include...

Lifr/vlifr cigs/vis with fog/drizzle overnight/Tuesday morning.
Scattered showers through mid morning Tuesday.
Ifr cigs Tuesday afternoon, mvfr cigs Tuesday night.
Very strong/gusty southwest winds late Tuesday night/Wednesday.

A period of showers is expected overnight through mid morning
Tuesday. Outside of these showers, areas of drizzle are
expected, possibly lasting through midday Tuesday. There will be
another chance of showers Tuesday evening ahead of a strong cold
front. Toward the end of the new 30 hour ORD/MDW forecast, near
daybreak Wednesday morning, there is an increasing chance of
snow showers. Opted not to include these as they may be arriving
around 12z, but trends will need to be monitored for later
forecasts.

Ifr cigs have been as far east as DPA/06C this evening, but
continue to remain west of ORD/MDW. Guidance trends continue to
support low mvfr cigs developing in the next few hours for the
Chicago terminals and quickly lowering into ifr and then into
lifr and possibly vlifr for a time around/after daybreak.
Further west including RFD/DPA, lifr/vlifr cigs/vis look on
track. These lowest conditions will occur as a broad weak area
of low pressure moves across the area. As this passes,
visibilities should steadily improve with cigs lifting through
ifr by early afternoon and likely into low mvfr during the
afternoon with mvfr cigs continuing Tuesday evening into early
Wednesday morning.

Light southeast winds are expected to become light and variable
overnight and then shift light westerly by mid/late morning as
the low shifts east. Winds will turn back southwest late Tuesday
afternoon into Tuesday evening with speeds/gusts slowly
increasing. Once the cold front moves through, west/southwest
winds will quickly increase with gusts into the lower/mid 30kt
range. Higher gusts, possibly to 40kts will be possible around
and after daybreak Wednesday morning. cms

&&

.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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