259
FXUS63 KLOT 110134
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
834 PM CDT Thu Sep 10 2026

.KEY MESSAGES...

- Quieter conditions with near to slightly above normal
  temperatures through the weekend.

&&

.UPDATE...
Issued at 834 PM CDT Thu Sep 10 2026

Evening forecast adjustments made for ending precip, and fog
potential overnight.

Several lingering boundaries (cold front, lake breeze and
differential heating) became the focus for scattered convective
showers this afternoon, also producing a few funnel clouds
between I- 80 and U.S. 24. All of that activity has dissipated
with the loss of diurnal instability at sunset. Attention for
the overnight and early morning hours then shifts to fog/low
stratus potential, as the western periphery of a surface high
pressure ridge settles across the area. Most likely area to be
affected is across our southern cwa where low-level moisture
lingers in the wake of the southward drifting cold front, and
where cloud cover and earlier precipitation had limited
warming/mixing. Guidance does depict some low-level drying later
tonight across our southeastern counties however, as high
pressure centered east of the area develops northeast winds and
dry advection above the boundary layer. Have expanded patchy fog
mention after midnight tonight for areas well west/south of
Chicago based on this (and where a variety of high-res guidance
depicts lower visibilities) and will continue monitor trends.
Can`t rule out some dense fog potential across mainly our
south/southwestern cwa.

Otherwise, only made tweaks to temps/sky cover based on
observational trends overnight, with a period of quiet and
pleasant weather expected Friday.

Ratzer

&&

.DISCUSSION...
Issued at 114 PM CDT Thu Sep 10 2026

Through Sunday Night:

Ongoing rain showers are being observed south of the Kankakee
River Valley this afternoon ahead of a mid level wave that is
passing over the area. There has been an increase in shower
coverage over the area, being located under the right entrance
region of a 300 mb jet. However, lapse rates are fairly poor
with the better well of instability south of the forecast area.
A rogue lightning strike or two may occur, but confidence is
low. This mid level wave should continue to pass south and east
over the forecast area through the afternoon with chances for
showers diminishing toward sunset.

Cloud cover over the area today has help mute temperatures
slightly. Clearing behind the wave should allow for temperatures
northwest of the Fox Valley to increase quickly, but opted to
lower this afternoon`s high temperatures else by a degree or
two. As the wave exits to the east, clearer skies can be
expected through the overnight north of I-80 (with lingering
cloud cover to the south). Winds are expected to become light
and variable overnight. With better radiational cooling due to
the lack of cloud cover, there is a chance for another round of
fog to develop toward daybreak tomorrow morning. Better chances
remain north and west of Chicago`s urban core, but satellite and
observations will need to be monitored through the night for
any fog development.

Surface high pressure will build tomorrow under the influence
of a weak ridge passing overhead. Sunny conditions are expected
with light winds to provide quite an ideal weather day
tomorrow. As the ridge passes east overnight into Saturday
morning, models are projecting a very weak shortwave to pass
over Wisconsin. There is a non-zero chance that there could be
some light showers/sprinkles on Saturday morning as the wave
passes over, but models are a.) keeping the track of the wave a
little farther north in Wisconsin and into western Michigan and
b.) struggling to penetrate a drier air mass over Illinois.
Models are suggesting that the surface cold front associated
with the wave could potentially slow and wash out over I- 80 by
Sunday morning. Perhaps some light showers develop along the
front on Sunday morning, but again, the drier air and weak
forcing should limit coverage, assuming it happens at all.
Otherwise, this weekend is looking fairly pleasant. Southerly
winds on Saturday will help drive temperatures back up into the
80s. There is a little more uncertainty with temperatures on
Sunday due to the timing of the frontal passage. An early
arrival will turn winds to the northwest and usher in cooler,
more seasonable temps in the 70s. But areas ahead of the front
south of I-80 have another chance of warming back up into the
80s.

DK

Monday through Thursday:

The first half of next week continues to look like it will turn
more active as we get into more of a southwesterly flow aloft.
There will be multiple opportunities for showers and
thunderstorms Monday-Wednesday as several shortwave troughs
ripple through the southwesterly flow. It remains too early to
pinpoint timing or rainfall amounts, but there is better chances
for a transition to a generally wetter, more unsettled pattern
next week.

Izzi/DK

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 635 PM CDT Thu Sep 10 2026

The only forecast concern this period is the potential for fog
early Friday morning. Confidence is too low for any mention of
fog in the terminals, with a low chance for fog at RFD and then
better chances west and southwest of the terminals.

Easterly winds generally under 10kt are expected to become light
and variable later this evening and then become southeast under
10kt Friday morning, with speeds possibly increasing to 10-12kt
by mid/late Friday afternoon. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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