264
FXUS63 KLOT 111109
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
609 AM CDT Fri Sep 11 2026

.KEY MESSAGES...

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

- Waves of heavy rain producing thunderstorms possible in the
  general region early to mid next week.

&&

.DISCUSSION...
Issued at 310 AM CDT Fri Sep 11 2026

Surface high pressure is centered overhead across the western
Great Lakes early this morning. Light winds under this high may
support patchy fog development before dawn, particularly west-
southwest of the Chicago metro area. However, the main threat
for dense fog will remain to the southwest across portions of
northern Missouri into west-central Illinois. Any fog that
develops will quickly burn off after sunrise.

The western Great Lakes surface high will slide eastward into
New England through tonight. As it does, the surface synoptic
flow will favor a south-southeasterly direction. However, wind
directions are likely to turn more easterly across northeastern
Illinois this afternoon as the flow becomes augmented by a lake
breeze. Overall, today will be a pleasant early fall day for
the area. Mostly sunny skies should warm inland locations to
around (or just above) 80F this afternoon, with slightly cooler
conditions expected lakeside. Humidity levels are expected to
remain comfortable.

Warm air advection is forecast to ramp up across the area
Friday night into Saturday as the low-level synoptic flow shifts
south-southwesterly ahead of an approaching cold frontal
trough. This will support a temporary bump in temperatures (into
the mid-80s) and humidity on Saturday. The front should slide
across the area late Saturday afternoon and evening. Currently,
rain chances with this front look low (<20%) due to weak frontal
and larger-scale forcing.

Northerly low-level flow behind Saturday evening`s cold front
will push a cooler air mass across the region for Sunday.
Increased cloud cover and a chance of afternoon showers tied to
an approaching mid-level impulse should keep high temperatures
in the 70s across most locations. Rain chances then look to
shift south and southwest of the area Sunday night as surface
high pressure builds over the Great Lakes. While the current
gridded forecast maintains 20-40% shower chances Sunday night,
these may need to be lowered or removed if guidance trends hold.

The first half of next week continues to look active across the
region. Upper-level ridging will expand eastward over the
southeastern CONUS while a shortwave trough axis migrates east-
northeastward across the northern tier. As this occurs, a
trailing surface cold front is expected to become quasi-
stationary somewhere over the lower Great Lakes region through
midweek, favoring multiple rounds of heavy rain-producing
showers and thunderstorms. This pattern could result in a Maddox
frontal heavy rain setup Tuesday into Wednesday, so this period
will need to be monitored closely over the coming days.

KJB

&&

.AVIATION /12Z TAFS THROUGH 18Z SATURDAY/...
Issued at 609 AM CDT Fri Sep 11 2026

VFR through the period with no significant concerns.

Winds will become steady southeast by mid morning today. Expect
lake influence to turn winds more easterly near the lake during
the afternoon. There may be a brief period of closer to due
south winds at ORD and MDW prior to the shift to east-southeast.
Winds will then become light southerly tonight and southwest
around 10 kt after sunrise on Saturday.

Castro

&&

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

&&

$$

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