textproduct: Chicago

KEY MESSAGES

- Above normal temperatures (highs in the 80s) are expected much of this week with onshore winds keeping temperatures cooler near the Lake Michigan shore (60s and 70s). - Other than a low (20%) chance of showers and storms Wednesday afternoon near the WI/IL state line as well as near/south of US-24, dry conditions are favored through the end of the week.

DISCUSSION

Issued at 330 AM CDT Mon May 25 2026

Light and variable winds and mostly clear skies paired with increased low-level moisture from yesterday's widespread rainfall will set the stage for patchy fog development early this morning. Can't fully rule out locally dense fog into portions of northwest Indiana but this is mostly favored just east of the area.

Otherwise no major weather concerns are in store for today with surface high pressure in place across the region. Mostly sunny skies and southwesterly flow will allow temperatures to soar into the 80s today and tomorrow for much of the area. Daily lake breezes will keep temperatures cooler along the Lake Michigan shore, where forecast highs are only in the low to mid 70s, particularly on the Illinois side.

Heading into Wednesday, the local area will be situated between two separate mid-level features of interest. The first is a cut-off low expected to slowly lift toward the Ohio Valley through the day. The northern periphery of the associated showers and embedded thunderstorms has been trending farther south with each passing day. However, the latest guidance still suggests this could manage to lift into portions of the area, generally near and south of US-24 (20% chance). Meanwhile, a positively tilted mid-level wave is expected to dive southeast out of Ontario across the Great Lakes. An associated backdoor cold front extending across Wisconsin and Michigan will drop southwest across the area late in the day. Showers and storms will be possible along this front as it approaches the area, likely decreasing in coverage with southward extent as it encounters the locally drier airmass. There is a narrow window where a faster frontal passage could allow isolated storms to persist into far northern/northwest Illinois late in the afternoon where an axis of higher instability (MLCAPE to 1000-1500 J/kg) may exist prior to sunset (20% chance). Otherwise dry conditions are expected for the rest of the area with temperatures in the 80s inland and 70s near the lakeshore.

A 1020+ mb Hudson Bay surface high is expected to shift south and stall out across the western Great Lakes region midweek as a pseudo-Omega blocking pattern becomes established across the broader CONUS and Canada. The position of the surface high generally favors east to northeast wind directions here locally, potentially for several days. Accordingly, cooler conditions are likely to continue near the Lake Michigan shore with forecast highs only in the 60s through the upcoming weekend. The cooler onshore flow will also extend farther inland than earlier in the week with highs generally in the 70s to near 80.

Petr

AVIATION /06Z TAFS THROUGH 12Z TUESDAY/

Issued at 1230 AM CDT Mon May 25 2026

Key Aviation Messages for the current TAF period:

- Localized vis reductions from fog closer to the lake this morning, but confidence is low.

Mostly VFR and dry conditions are expected through the current TAF window. The only exception is localized fog in northern Indiana and over the lake that may ooze inland. Confidence in it reaching any specific terminal is low, and may just reduce things to 5 or 6 SM with some BCFG, but will be monitored closely. The only other impact to terminals are wind direction trends. Everything is light and southeasterly currently and expected to flip to the southwest after daybreak. A lake breeze is expected in the afternoon switching things to the southeast. Winds will diminish this evening and become more southerly if not southwest.

DK

LOT WATCHES/WARNINGS/ADVISORIES

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