127
FXUS63 KLOT 242342
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
542 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.

&&

.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 /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 542 PM CST Mon Nov 24 2025

Primary forecast concerns include...

Lifr/vlifr cigs/vis with fog/drizzle overnight/Tuesday morning.
Scattered showers through midday Tuesday.
Ifr cigs Tuesday afternoon, mvfr cigs Tuesday night.

Scattered showers will be possible through midday Tuesday with
perhaps the best time period for prevailing showers from late
this evening through mid morning Tuesday. There will be another
chance of showers mid/late Tuesday evening ahead of a strong
cold front. Areas of drizzle will also be possible overnight
through midday Tuesday.

Ifr cigs west of the Chicago terminals will slowly move east
this evening, likely not reaching ORD/MDW until late this
evening or in the early overnight hours, possibly as a low mvfr
deck to start. Current forecast has this trend handled well and
made no changes. As a broad area of low pressure moves across
the area around and just after daybreak, cigs and vis are
expected to drop into lifr/vlifr which current prob/tempo groups
have covered for now. Cigs/vis will slowly improve during the
late morning and early afternoon with vis improving by early
afternoon. At least ifr cigs are expected by Tuesday afternoon
and its possible cigs may lift to low mvfr during the afternoon
with mvfr cigs continuing Tuesday evening.

South/southeast winds may briefly be in the 10-12kt range early
this evening, but are expected to diminish under 10kts and turn
south/southeast and possibly more southeast later this evening.
Winds will likely become light and variable overnight, possibly
light easterly. Winds will shift back to the southwest as the
low moves east of the area. Gusts into the 15-20kt range are
expected to develop Tuesday evening and then much stronger winds
are expected early Wednesday morning, just after the end of the
current 30 hour ORD/MDW taf period. 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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