textproduct: Chicago

KEY MESSAGES

- Scattered thunderstorms late this afternoon through early Sunday morning. A few storms could be strong to severe.

- Possible dangerous swimming conditions at Indiana Lake Michigan beaches Sunday.

- Cooler temperatures early next week with precipitation chances returning midweek.

DISCUSSION

Issued at 210 AM CDT Sat Jun 13 2026

Overall confidence remains low for convective/precip trends later today into tonight. This morning is expected to be dry areawide and then there will be a low chance (20%) for showers and thunderstorms mainly across the southern cwa this afternoon. As a cold front approaches the area this evening, that seems to be the best time window for thunderstorms, late afternoon across far northwest IL and then for areas along and north of I-80 during the evening. Showers may increase in coverage later this evening and into the overnight hours with perhaps just isolated thunderstorms at that time. The potential for a few storms to become strong to severe remains with the best timing in the late afternoon into the evening hours. Heavy rain and localized flooding would also be possible with any stronger storms. End time of the precipitation is also somewhat uncertain, ending from northwest to southeast Sunday morning with some shower activity still possible along/southeast of I-57 after daybreak Sunday morning.

With the expectation that much of the daylight hours today could be dry with at least some sunshine through early afternoon, high temps may make a run at upper 80s for many areas today and nudged temps up some. Southwest winds will also quickly increase after sunrise with gusts into the 30 mph range possible today.

A cold front will move across the area early Sunday morning, shifting winds northerly and bringing in much cooler air. High temps on Sunday may struggle to reach the lower 70s and likely be dependent on how long cloud cover persists on Sunday with some sunshine expected by afternoon. North/northwest winds may gust as high as 30 mph on Sunday and these stronger winds will allow waves to build across southern Lake Michigan, leading to dangerous swimming conditions at Lake Michigan beaches in Indiana and possibly some of the Illinois beaches depending on the exact wind direction.

No significant changes in the models for the pattern next week. An upper trough is expected to move across the Great Lakes region midweek bringing increasing precipitation chances by Wednesday and Wednesday night ahead of another cold front which may bring another short burst of cooler air for the end of the week. cms

AVIATION /18Z TAFS THROUGH 00Z MONDAY/

Issued at 1253 PM CDT Sat Jun 13 2026

Key Messages:

- Period of showers and thunderstorms this evening (00Z-04Z window).

- Breezy southwest winds this afternoon turn north-northwesterly tonight in wake of a cold frontal passage.

We continue to monitor the threat and potential timing of showers and thunderstorms late today into this evening as a cold front moves into the area. Confidence continues to increase that a period of at least widely scattered storms will develop across northern IL into early this evening. Accordingly, we have opted to convert the PROB30 group for TSRA to a tempo group in the latest 18Z tafs (all sites with the exception of RFD). The primary window for the these potential storms is generally looking to be in the 01-04Z timeframe. KRFD may remain displaced north of the better coverage of storms this evening, so we opted to hold on with the going PROB30 for now. A few lingering light showers may persist for a period overnight (following the main time window for storm potential highlighted in the tempo group). A more formal mention for these overnight showers may be needed in future TAF updates. This lingering activity is expected to move out of the area into early Sunday morning, with an otherwise dry Sunday with VFR conditions anticipated for the area.

Southwest winds will remain gusty (into the mid 20 kt range) in advance of the approaching cold front this afternoon. As the front passes, expect a shift to a northwest direction mid to late this evening, then north-northwesterly overnight. Gusty northwesterly winds (gusts of 20-25 kt) are then likely during the day Sunday.

KJB

LOT WATCHES/WARNINGS/ADVISORIES

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