709
FXUS63 KLOT 291931
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
231 PM CDT Sat Aug 29 2026

.KEY MESSAGES...

- Heat and humidity will return on Sunday and persist through
  much of the workweek.

- There may be a opportunities for showers and thunderstorms at
  times amidst plenty of dry hours.

&&

.DISCUSSION...
Issued at 231 PM CDT Sat Aug 29 2026

Rest of Today:

Despite the ominous upstream radar earlier today, drier air at
the lower levels has substantially eroded the rainfall footprint
this afternoon (as expected). Thus expect occasional sprinkles
and perhaps light showers sufficient to wet the ground in a few
spots, favoring near and north of I-80 until sunset. Mostly
cloudy skies will keep temperatures in the mid 70s to around
80F, coolest northwest.

Tonight through Sunday Night:

Following a mostly quiet evening, isolated to scattered showers
will likely blossom overnight (favoring near/north of the IL and
Kankakee Rivers) into Sunday morning. Forecast soundings are
unfavorable for anything more than isolated embedded
thunderstorms (slight chance/20% mention). Lows will be in the
mid 60s to around 70F.

Sunday will mark the start of the advertised very warm to hot
and humid pattern in store for much of the week. However,
relatively extensive cloud cover and a sharp lower level
inversion will keep temperatures in check somewhat (mid to
locally upper 80s). Breezy southwesterly flow below the
inversion will yield gusts up to 30 mph. A mid-level short-wave
will cross the mid-upper MS Valley in the afternoon, which will
bring another chance (20-30%) for elevated convection (widely
scattered showers and a few storms) to areas primarily north of
I-80. Fairly meager, skinny CAPE due to marginal mid-level
lapse rates rooted above the strong inversion down around 850
mb, and overall modest forcing will likely again serve to keep
thunderstorms isolated at most.

Additional isolated to scattered showers (20-30% chance) and a
few storms may then move across portions of far northern
Illinois late Sunday night/early Sunday.

Monday Onward:

Strong mid and upper level ridging will amplify northeastward
from the southern Plains and center over the Ohio Valley next
week. While we`re past peak crop evapotranspiration, it will be
a very warm to hot and generally uncomfortably humid week.
Monday still looks to have a good chance to be the first 90F
reading of August at Chicago and Rockford, on the last day of
the month! September and thus meteorological fall (already?!)
will get off to a summer-like start with additional 90+ temps
and daytime heat indices flirting with 100F in spots probable on
Tuesday and Wednesday. If the ridge flattens out sufficiently
later in the week, weak surface high pressure may enable a
backdoor cold front to sag south and bring some cooling,
particularly closer to the lake.

The ridging currently looks amplified enough to result in more
pronounced capping and a better chance for "ring of fire" type
convective activity to remain primarily north of the area until
perhaps later in the week, when the ridge may flatten out some,
as alluded to above. Northern Illinois (especially with
northward extent) is close enough to the precarious northern
periphery of the ridge to warrant occasional lower end (20-30%)
thunderstorm chances (focused at night) through midweek.
Ensemble guidance variance, even later in the week, is such that
periodic PoPs are still only in the 20-30% range.

Looking ahead to Labor Day weekend, central CONUS ridging will
likely remain in control, resulting in continued well above
normal temps. The exact position and orientation of the ridging
will modulate how warm temperatures will get, along with
convective chances.

Castro

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1228 PM CDT Sat Aug 29 2026

Forecast concerns include...

Chance of showers this afternoon into this evening, Sunday
morning and Sunday afternoon.
Possible low level wind shear overnight.
Gusty southwest winds Sunday.

There will be a chance of showers this afternoon into early this
evening but the low levels remain fairly dry and much of this
precipitation will likely fall as sprinkles/virga. There is a
better chance for scattered showers from the predawn hours
through mid morning Sunday. Have only included prob mention for
now, but tempo or prevailing showers may be needed with later
forecasts. There will be another chance of showers Sunday
afternoon, perhaps focused just north of the Chicago terminals
and an isolated thunderstorm is also possible. Confidence during
this time period is fairly low and maintained a dry ORD/MDW 30
hour taf for now.

South/southwest winds 10-15kt early this afternoon will turn
more southerly by late afternoon and south/southeast by early
this evening. A few higher gusts are possible but are not
expected to become prevailing. Directions will turn back to the
south/southwest overnight and as low level winds increase, there
may be a few gusts at times, mainly for ORD/MDW. These low
level winds may increase high enough for low level wind shear,
which currently looks more likely west of the Chicago terminals
across northwest IL and at RFD, but confidence is still too low
to include mention. Southwest winds will increase after daybreak
Sunday into the mid/late morning when gusts into the mid 20kt
range will be possible. These gusts may slowly diminish by mid/
late Sunday afternoon. cms

&&

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

&&

$$

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