textproduct: Chicago

KEY MESSAGES

- Chance of showers east of Interstate 57 overnight.

- Isolated to widely scattered showers and storms possible Saturday night into Sunday, though many areas will remain dry.

- Above normal temperatures expected next week.

DISCUSSION

Issued at 226 AM CDT Fri May 22 2026

Surface high pressure in eastern Canada will keep fairly quiet conditions over the forecast area today. Winds will remain out of the northeast and high temperatures are expected in the mid 60s north of Interstate 80, low 70s south of the Interstate, and upper 50s/low 60s along the immediate lakeshore. A parent upper level short wave currently analyzed over the northern Plains is expected to lift northeastward through the day toward the Minnesota Arrowhead through the overnight into Saturday morning. A second southern impulse wave is expected to lift from the lower Mississippi Valley toward southeast Michigan. There is still some uncertainty on the exact track of this wave, but model guidance has been showing good continuity in having the core of the wave (and the reflected surface low) focus its path through central Indiana (east of our forecast area). While there is a slight chance for some northwestward development, highest chances remain east of Interstate 57 in northwest Indiana. Instability with this wave remains non-zero and forcing appears fairly weak and it is expected to pass over the area in a unfavorable time of day. An isolated thunderstorm is possible, better chances remain east of the forecast area. Lastly, steering flow aloft with this wave is fairly weak (thus leading to slow storm motions). At the risk of sounding like a broken record, the higher modeled QPF is expected east of the area, but still around or just over an inch of precipitable water is forecasted in northwest Indiana. If a stronger shower were to develop, slow storm motions would increase the concern for downpours and localized flooding. For now, considering models are focused east of the area, this remains a low confidence threat, but certainly one to monitor in the overnight.

As the wave exits Saturday morning, drier conditions over the area can be expected during the daytime hours. Midlevel winds will turn to the west-southwest allowing for warmer temperatures to advect in, nudging afternoon high temperatures into the 70s across much of the forecast area, though still cooler at the lakeshore due to onshore flow.

The parent upper level wave will slowly move east over the western Great Lakes Saturday night through Sunday. Isolated to widely scattered showers and storms may pass over the region Sunday. Forcing looks weak with this wave as well, and while it does not look favorable for severe weather, the best chances for storms appears to be south and east of Interstate 55. Coverage of storms could be impacted by the speed of the wave. There are some models that have this wave passing east of the area by early afternoon.

An upper level ridge is expected to build early next week keeping the forecast dry for not just Memorial Day but through the early part of next week. 850 mb temperatures start reaching 15C with chances surface temperatures climb above normal into the low to mid 80s early next week. Models are showing the potential for another upper level trough to approach the area midweek that could provide the next chance for precipitation.

DK

AVIATION /12Z TAFS THROUGH 18Z SATURDAY/

Issued at 651 AM CDT Fri May 22 2026

Key aviation forecast messages:

- MVFR to near IFR CIGs develop late evening-early Saturday AM.

- A period of rain may occur overnight for part of the area (30% chance at GYY). Confidence in the western extent remains low (20% chance at ORD/MDW).

East to northeast winds are expected through the period around 15 kt during daylight hours with occasional lower 20 kt gusts. An expansive but thin ~4000-6000 ft cloud layer remains overhead this morning. This may scatter out later this morning before filling back in late afternoon ahead of our next weather system lifting toward the region. Expect gradually lowering ceilings thereafter through the evening and overnight hours to MVFR and potentially near IFR. Guidance has trended a bit farther northwest with the area of showers tonight into early Saturday morning. Opted to introduce a PROB30 at GYY to account for this. Have held off for the Chicago area TAF sites for now but a precip mention may become warranted if this trend persists, including the potential for associated MVFR visibilities and IFR ceilings.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

IL...Beach Hazards Statement through Saturday afternoon for ILZ006- ILZ103-ILZ104.

IN...None. LM...Small Craft Advisory until 4 AM CDT Saturday for the IL nearshore waters.