textproduct: Chicago

KEY MESSAGES

- Dry and warm today with highs in the mid-upper 80s.

- A corridor of heavy rainfall may occur somewhere in the region Thursday PM, though confidence in local impacts remains low. The strongest storms may be capable of gusty to locally damaging wind gusts, mainly south of I-80.

- Mainly dry, warmer weather expected this weekend through early next week.

DISCUSSION

Issued at 342 AM CDT Wed Jul 8 2026

Winds are light and variable to calm early this morning amidst an expansive area of surface high pressure. Radiational cooling under clear skies may lead to patchy fog development, mainly southeast of a Pontiac, IL to Valparaiso, IN line where dewpoints depressions are lowest. Can't fully rule out very shallow and locally dense fog over low-lying open areas and fields. Any fog that does develop will quickly erode after daybreak.

The mid-upper ridge axis will gradually shift east today allowing a return of southwesterly low-level flow to the area, which paired with mostly sunny skies will lead to a seasonably warm day with highs in the mid-upper 80s (upper 70s to lower 80s possible along the Lake County, IL lakeshore where winds lean southeast in the afternoon).

To our northwest a shortwave and associated trailing cold front will lead to thunderstorm development across IA/MN/WI this afternoon and evening. This activity may attempt to drift into northwest Illinois very late tonight, likely in a decaying phase. Nevertheless, can't fully rule out gusty outflow winds and a few lightning strikes northwest of a Dixon to Waukegan, IL line after midnight.

Looking ahead to Thursday through early Friday morning, the surface front and/or residual outflow boundary may stall over the area during the day. While there has been an overall southward trend in model guidance over the past 24 hours with respect to where the corridor of heaviest rainfall is most favored, there remains notable model spread in where this boundary ends up as well as the strength and position of a separate convectively augmented wave (and associated MCV) from the Central Plains that is expected to move across the region. Even with a southerly shift in its track, continue to have concerns that localized areas or even a narrow corridor of heavy rainfall may materialize within the vicinity of the aforementioned stalled boundary on the north side of the system (hinted at in the 6Z HRRR/NAMNest). Given the local susceptibility to flooding from recent heavy rains, will need to continue monitoring model and observational trends closely. The strongest storms will be capable of precip loaded gusty to locally damaging wind gusts, though the better potential for severe weather exists just south of the area into central and southern Illinois where the stronger mid-level flow is expected.

The forecast for Friday will be largely dependent on Thursday, though in general the greatest coverage of showers and storms is favored south of the area. Have maintained precip chances (20-40%) south of the Chicago metro to account for any showers and storms that develop on the northern edge of another wave expected to move across central and southern Illinois. North to northeasterly low-level flow will lead to slightly cooler temperatures, in the lower 80s for inland areas and 70s near the lakeshore.

While a few diurnally driven showers and storms can't be ruled out on Saturday, upper level ridging expands across the central CONUS over the weekend into early next week which should lead to mainly dry conditions into the first part of next week with temperatures in the upper 80s to around 90. Given we will be on the northeast periphery of the ridge we will have to monitor the potential for thunderstorm complexes rounding the ridge across the broader region toward midweek.

Petr

AVIATION /06Z TAFS THROUGH 12Z THURSDAY/

Issued at 1234 AM CDT Wed Jul 8 2026

No major forecast concerns expected for this TAF period as high pressure will remain in control. Light (speeds around 5 kt) and variable winds are expected tonight before directions settle into a southwesterly orientation by Wednesday morning. Speeds will increase on Wednesday into the 10-12 kt range with a chance for the occasional mid to upper teen kt gust. Any gusts that materialize Wednesday afternoon should diminish after sunset but with the high shifting east and a disturbance beginning to approach the area it looks like winds will stay elevated (around 10-11 kts) Wednesday night.

Otherwise, expect mostly clear skies tonight with diurnal cumulus clouds developing Wednesday afternoon resulting in scattered VFR skies. However, there has been some patchy 4000-5000 ft stratus developing across southern WI and northwest IL. While the expectation is for these clouds to remain transient, there is a signal for some of these clouds to thicken up and possibly mix down into some patchy fog near RFD. Since confidence on fog or low stratus is low confidence have opted to forgo a formal mention in the RFD TAF, but did add a FEW040 mention to tease the potential.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...Air Quality Alert until midnight CDT tonight for INZ001-INZ002- INZ010-INZ011.

LM...None.