209
FXUS63 KLOT 051837
AFDLOT

Area Forecast Discussion...RESENT
National Weather Service Chicago/Romeoville, IL
137 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.

&&

.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 /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1220 PM CDT Sat Sep 5 2026

Key Messages:

- Low MVFR cloud bases gradually improve through the afternoon.

- Threat for some ground fog at DPA and RFD around, daybreak
  Sunday morning.

A deck of IFR to low end MVFR stratus continues to shift into
the area on northeasterly winds early this afternoon. While
this cloud cover is expected to persist this afternoon, bases
are expected to gradually improve through the remainder of the
day, with VFR conditions potentially returning at most
terminals after 20Z.

Some patchy ground fog is then possible early Sunday morning at
DPA and RFD. Otherwise, expect quieter weather during the day
Sunday, with east-northeasterly surface winds.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory until 7 PM CDT this evening for ILZ032-ILZ033-
     ILZ039.

IN...Heat Advisory until 8 PM EDT this evening for INZ019.

LM...None.

&&

$$

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