653
FXUS63 KLOT 060150
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
850 PM CDT Sat Sep 5 2026

.KEY MESSAGES...

- Moderate to high swim risk expected through early Sunday
  during the final weekend of beach season.

- Relatively cooler Sunday and Monday, although remaining
  seasonably warm.

&&

.UPDATE...
Issued at 850 PM CDT Sat Sep 5 2026

A few minor adjustment were made to the going forecast through
tonight/early Sunday, mainly to bump winds up a bit through this
evening, and to increase cloud cover over northeast
IL/northwest IN especially through the early overnight hours. In
addition, had earlier cancelled the heat advisory for our far
southern counties.

Latest surface analysis indicates a cold front has pushed well
south of the forecast area at mid-evening, allowing northeast
winds to gradually bring cooler and initially somewhat less-
humid air into the region. A fairly expansive area of low-clouds
lingers across much of northeast IL/northwest IN in the cooler
northeast flow, and should continue to drift west-southwest
across the forecast area overnight before gradually eroding into
early Sunday morning. With surface high pressure building
across Ontario and the northern Great Lakes, the surface
pressure gradient has tightened a bit over the last few hours,
resulting in increasingly breezy conditions especially near Lake
Michigan where gusts around 20 kts have been occurring. These
breezy conditions should gradually ease after midnight, with
lighter east-northeast winds expected Sunday. Waves on Lake
Michigan (especially Illinois beaches) have increased into the
3-4 foot range as of 8 PM, supporting a solid moderate swim risk
which should gradually improve on Sunday with the
aforementioned easing of wind speeds and a slightly more
easterly fetch.

Otherwise, generally pleasant weather is expected through the
remainder of the holiday weekend, with seasonable and less humid
conditions and no precipitation expected.

Ratzer

&&

.DISCUSSION...
Issued at 137 PM CDT Sat Sep 5 2026

After an unseasonably hot and humid stretch to start September,
cooler conditions are beginning to filter over the area from
north to south today. Moisture pooling along a cold front draped
across the southern CWA combined with temps in the lower 90s
south of the front is leading to heat index values around 105F.
Those numbers have likely peaked as the front should clear the
remainder of the CWA over the next couple hours. While surface
convergence is fairly weak on the front, interactions with
residual outflow boundaries from earlier convection over Indiana
are providing an added focus early this afternoon. Cannot rule
out an isolated strong to briefly severe storm through 2-3pm
given a weakly capped, highly unstable, and slightly sheared
environment.

Surface high pressure will expand across the Great Lakes region
Sunday and Monday. Though temps will remain seasonably warm,
drier air will advect in from the east through the day Sunday,
with values falling into the 50s during the afternoon and
continuing through Monday.

Mid-level ridging will build back across the western Great
Lakes by Tuesday before deamplifying in response to a strong
mid-level system crossing southern Canada on Wednesday. Daytime
highs both days will push well into the 80s to perhaps near 90,
but dew points are expected to be lower (mid to upper 60s) than
the past few days.

A cold front associated with the southern Canadian system will
slowly drag across the area Wednesday into early Thursday
morning. Minimal deep-layer forcing and weak low-level
convergence on the front suggest that the coverage of showers
and embedded thunderstorms will be, at most, scattered. Would
not be surprised to see a mostly dry frontal passage.

Like Sunday and Monday, cooler (but seasonably warm) conditions
will follow the front late in the week before ridging again
builds over the area and results in unseasonably warm conditions
next weekend.

Kluber

&&

.AVIATION /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 626 PM CDT Sat Sep 5 2026

Forecast concerns include...

Low mvfr cigs, possible ifr cigs, this evening.
Gusty northeast winds this evening.

Low mvfr cigs continue moving southwest across the Chicago
terminals early this evening with ifr cigs across far northeast
IL and southeast WI. Expect low mvfr cigs to continue through at
least mid evening, possibly longer. Confidence for ifr cigs is
low but opted for scattered ifr mention and will need to monitor
trends. Eventually, this cloud cover should slowly lift and
scatter out overnight.

Some light/patchy fog will be possible overnight into early
Sunday morning, mainly west of the Chicago terminals. Only
medium confidence and made no changes to tempo fog mention for
DPA/RFD.

Northeast winds will continue through the period. Speeds in the
10-15kt range are expected this evening with higher gusts at
times and then speeds are expected to diminish under 10kts later
this evening and overnight. Speeds will increase back to 10kt on
Sunday, diminishing with sunset Sunday evening. cms

&&

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

&&

$$

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