textproduct: Chicago

KEY MESSAGES

- Showers and sprinkles through tonight with locally heavy rainfall potentially south of US 24.

- A few thunderstorms are possible Saturday night into Sunday morning, mainly west of the Fox Valley.

- Dangerous heat will build across the area next week, with afternoon heat index values over 100 degrees each day beginning Monday.

DISCUSSION

Issued at 205 PM CDT Fri Jun 26 2026

Ongoing showers will continue through the evening and overnight. Most of the rain thus far has been fairly minimal. Light rain can be expected as far north as Interstate 90, but the better coverage will remain closer to the higher moisture plume south of Interstate 80 with localized heavier downpours possible along and south of US 24. The better instability remains well to the south and out west near the area of surface low pressure. Thus, pulled the chances for thunder for the rest of today for much of the area, with any lingering (less than 24 percent) chance around US 24.

The surface low, currently in western Missouri, will slowly move northeast and pass just south of the forecast area overnight. The models slowing the progression of the low gave confidence in maintaining chance PoPs for areas southeast of I-57 Saturday morning, though overall drier conditions are expected tomorrow. Winds will remain out of the northeast through the day on Saturday. High temperatures are expected in the 70s to low 80s inland with cooler upper 60s to low 70s along the lakeshore.

While Saturday is looking to shape up as a nice day locally, the overall atmospheric pattern will be changing tomorrow. An upper level low out over the Rocky Mountains will continue to deepen and sink farther south over the western CONUS. Subsequently, an upper level ridge will amplify northward from the Gulf and deepen. This amplified pattern will set up broad southwest flow over the Plains and Mississippi River Valley. A weak wave is expected to eject out of the upper level low and move toward Wisconsin. Decent mid-level lapse rates could support thunder and the presence of a slug of moisture with warm air advection and isentropic upglide could support showers and a few thunderstorms in the overnight hours. However, this will be moving in toward a drier and less favorable air mass, and models are already responding giving confidence to lower PoPs. Perhaps a few showers fester into Sunday morning, but generally drier (and more humid conditions) are expected during the day.

More concerning, starting on Sunday, is the potential for dangerous heat next week. A strong upper level ridge will sit east of the Mississippi River through the week. Southwest flow will continue to advect in warmer air as 850 mb temps increase over the area from 15 to 20C on Sunday to around 25C on Tuesday (the current expected highest temperature forecast of the stretch). Temperatures are expected to climb into the 90s for most of the forecast area, and with overnight lows only in the mid to upper 70s, little relief can be expected at night. Additionally, the southwest winds will bring the afternoon temperatures all the way to the traditionally cooler lakeshore. Dew points climbing into the 70s will make for humid conditions and drive heat index values up to around 105 F.

Setting a record high temperatures is not a guarantee (especially for any records that are 100+, like much of KRFD), but a Climate section has been created below for interested individuals. Two big questions for this heat event will focus on the center of the upper level high embedded in the ridge: 1.) where will its location be? And 2.) how strong will it remain? Monday and Tuesday look to be a good chance for these hot temperatures to set up, but there is greater uncertainty for mid-week and after. If the high were to weaken or even set up along and south of the Ohio River Valley, there could be a convective complex that could ride over the top of the ridge and bring not just showers and storm chances to the area, but also some relief from the temperatures. So no changes were made to the splotchy chance PoPs that the NBM provided for the middle and end of the week. However, recent models have trended towards a slightly stronger high. If that were to materialize, the region could be set up for not just drier conditions, but an extended period of heat indices over 100F. It's still far too early for any headline (e.g. Watch, Warning, Advisory), but there is growing confidence in the first heat wave of the year leading into the holiday weekend.

DK

AVIATION /18Z TAFS THROUGH 00Z SUNDAY/

Issued at 1152 AM CDT Fri Jun 26 2026

Intermittent sprinkles/light showers will continue through the afternoon, mainly south of RFD. Have continued VCSH mentions at the Chicago-area terminals, stair stepping towards later end times at MDW and GYY. May need AMDs for TEMPO -SHRA through the day, but vsby reductions should be limited to 6sm or greater. Some FEW-SCT MVFR filaments may attempt to build west off the lake this afternoon. Cigs should then lower towards 030-050 this evening and overnight, and some patchy light BR can't be ruled out. Winds will be ENE/NE around 6-10 kts through the rest of the TAF period.

Carlaw

......Daily Record High Temperatures.....

Chicago (KORD) Rockford (KRFD) June 28 101F (1951) 103F (1934) June 29 97F (1954) 103F (1931) June 30 99F (1913) 102F (1954) July 1 103F (1956) 101F (1931) July 2 99F (1970) 99F (1910)

DK

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.