textproduct: Chicago

KEY MESSAGES

- Periods of rain this afternoon through Saturday evening with a chance of thunderstorms.

- The potential exists for locally heavy rainfall with areas of 2"+ rainfall totals.

- High waves and dangerous swimming conditions at Lake Michigan beaches late tonight through Monday morning.

DISCUSSION

Issued at 151 AM CDT Fri Jul 31 2026

Low pressure will move southeast across IA today then across south/central IL tonight and across the Ohio River valley Saturday as it slows. Showers and at least a chance for thunderstorms will spread across the area this afternoon. As the low approaches later today, the southern cwa may remain in the warm sector allowing for a better chance of thunderstorms, a few of which may be strong to locally severe. Though it appears the best chance of any severe thunderstorms will remain southwest of the local area.

Periods of rain will continue tonight into Saturday morning along with a continued chance for thunderstorms, which current timing trends would suggest the best chance in the evening into the early overnight of Saturday morning. The rain during this time period will likely be moderate to heavy at times with precipitable water values in the 2 inch range. With the system slowing as it moves southeast, at least scattered showers are expected to continue Saturday and these may continue into Saturday night, especially across northwest IN. Models differ quite a bit for storm total rainfall but amounts in the 1 to 3 inch range look reasonable, highest amounts across the northern cwa. There may be some locally higher amounts as well.

A prolonged period of northeast winds is expected, gusting to 30-35 mph across southern Lake Michigan. This will allow for high waves and dangerous swimming conditions at Lake Michigan beaches late tonight through early Monday morning and plan to issue a beach hazard statement with this morning's forecast.

High pressure will bring dry weather back to the area early next week with precip chances possibly returning late next week. cms

AVIATION /06Z TAFS THROUGH 12Z SATURDAY/

Issued at 109 AM CDT Fri Jul 31 2026

Key Messages:

- SHRA develop west-to-east this afternoon.

- Increasing threat for embedded thunderstorms with heavy rain and MVFR to IFR conditions mid to late this evening through Friday night.

- SSE winds shift easterly and increase later today into tonight.

A weather disturbance across portions of the Dakotas early this morning will shift east-southeastward across the Midwest into the lower Great Lakes regions today into tonight. As it does, expect light rain do develop eastward across the northern IL terminals this afternoon (potentially as early as 18Z at RFD and ~20Z at the Chicago terminals). The rain showers will become more pronounced across the area this evening and tonight as the center of the system begins to shift into northwestern IL. Steepening mid-level lapse rates associated with the approaching mid-level system will also support increasing chances for embedded non-severe storms with heavy downpours into the overnight hours. Accordingly, we have opted to include a PROB30 mention for TS in the TAFs after 04Z at the Chicago terminals and after 02Z at RFD. The threat of rain and low flying conditions is likely to persist into Saturday (beyond the current 24 to 30 hour forecast period).

Otherwise, expect southeasterly winds to increase from the east later this afternoon and tonight, in association with the approaching area of surface low pressure.

KJB

LOT WATCHES/WARNINGS/ADVISORIES

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