textproduct: Chicago

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.