171
FXUS63 KLOT 062330
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
630 PM CDT Sun Sep 6 2026

.KEY MESSAGES...

- Seasonably warm conditions through Monday, although cooler and
  more comfortable than recent days.

&&

.DISCUSSION...
Issued at 114 PM CDT Sun Sep 6 2026

Surface high pressure continues to expand over the Great Lakes
early this afternoon, providing the area with cooler east-
northeasterly surface winds. While dewpoints started the day
around 70, a persistent influx of a drier low-level airmass has
continued to drop values through the 60s this morning. The
remainder of the day will be rather pleasant, with mostly sunny
conditions and temperatures peaking from around 80 inland to the
mid and upper 70s closer to the lake. Similar conditions are
expected for Labor Day, as the Great Lakes surface high remains
dominant.

East-northeasterly onshore winds across southern Lake Michigan
are not terribly strong (10-15 knots). However, the fetch has
allowed waves to become choppy across southern Lake Michigan,
with wave heights generally in the 2 to 4 foot range along the
northeastern Illinois shores. These conditions are expected to
persist tonight, making for a Moderate Swim Risk at northeastern
Illinois Lake Michigan beaches.

Late Monday into Tuesday, the mid/upper Pacific Northwest
trough/low is expected to eject east-northeastward across the
northern Rockies. As it does, models and ensembles remain in
general agreement regarding the development and northeastward
shift of a seasonably strong surface low across Manitoba. While
this system will remain far removed from our area, it will act
to drive the mid-level ridge axis residing over the Plains back
eastward into the western Great Lakes for Tuesday. An
accompanying shift back to southerly low-level flow will thus
result in warming weather across our region into midweek.
Temperatures for Tuesday into Wednesday are expected to climb
back well into the 80s (potentially near 90 in some locations).
Humidity will also be on the increase, though it is not expected
to reach the magnitude experienced a couple of days ago.

This period of warmer weather is expected to remain short-
lived, as the cold front associated with the potent Canadian low
begins to sag southward across our area Wednesday into early
Thursday. A period of showers and thunderstorms will be possible
(50%+) with this front from late Tuesday night through
Wednesday night. However, the better synoptic-scale forcing does
not look to coincide with the surface front until potentially
later Wednesday night into Thursday morning. By this time, the
front should be shifting south of much of our area into central
Illinois and Indiana. For this reason, shower and thunderstorm
activity could remain more scattered in coverage in our area on
Wednesday.

Surface high pressure will build back into the region for
Thursday and Friday in the wake of Wednesday`s cold frontal
passage. This will result in a return to cooler, more pleasant
weather through the end of the workweek. As we head into next
weekend, there is a signal for a larger-scale mid-level trough
and surface cold front to shift into the central CONUS later in
the weekend. However, specifics regarding the pattern remain
largely unclear at this time owing to increasing ensemble
spread. Nevertheless, chances for showers and thunderstorms
return to the forecast for next weekend.

KJB

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 630 PM CDT Sun Sep 6 2026

No significant aviation weather concerns for this TAF period.
The forecast area will remain within the western periphery of
expansive surface high pressure drifting slowly southeast across
the Great Lakes region through Monday night. While there may be
some light/variable winds during the night away from the Chicago
metro, the pattern will generally maintain modest easterly
winds (with a slight afternoon lake-breeze push for ORD/MDW/GYY),
with VFR conditions (mainly high cirrus from convection well
west/northwest of the area) prevailing.

Ratzer

&&

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

&&

$$

Visit us at weather.gov/chicago