The system produced widespread winds of 70 to more than 100 mph across northeastern Illinois and northwestern Indiana. Six tornadoes had been confirmed in that corridor.
Updated Aug. 14, 2026.
Update: The Aug. 11 severe weather threat described in the original forecast has ended. A separate flood watch now covers Des Moines, the Quad Cities and other parts of Iowa and Illinois through Saturday morning. Read the current flood-watch coverage.
DAVENPORT, IA — The storm system forecast to cross Iowa and the Quad Cities on Tuesday, Aug. 11, later produced its most destructive conditions farther east, where it developed into a derecho with widespread wind damage and tornadoes.
The strongest documented wind swaths extended across northeastern Illinois and northwestern Indiana. Winds reached 70 to more than 100 mph in parts of that corridor, while Gary/Chicago International Airport recorded a 99 mph gust.
The Quad Cities remained west of the area where the National Weather Service documented the event’s most extensive damage.
The most destructive winds developed farther east
The storm line moved through portions of the Midwest and Ohio River Valley during the morning and afternoon of Aug. 11.
Its broad area of damaging wind met the characteristics of a derecho, a long-lived line of thunderstorms capable of producing wind damage across a large region.
The forecast had identified winds above 70 mph as the main hazard for Iowa and the Quad Cities. That forecast described the potential along the storm’s path, but it did not mean every city would receive the same wind speeds.
As the system advanced east, northeastern Illinois and northwestern Indiana experienced the most widespread destructive winds. Some locations recorded major tree and structural damage.
Six tornadoes were confirmed in Illinois and Indiana
Six tornadoes had been confirmed within the National Weather Service Chicago coverage area as of its latest event update.
The list included an EF0 tornado near Oswego and EF1 tornadoes near Wilmington, from Mokena to Tinley Park, from Orland Park to Munster and from Glenwood to Lansing.
An EF2 tornado traveled from Monee, Illinois, toward Crown Point, Indiana. EF2 tornadoes have estimated winds between 111 and 135 mph.
Damage surveys remained underway, and the number or ratings could change as additional locations are examined.
The Aug. 11 forecast no longer applies
The severe thunderstorm watches and warnings connected to the Aug. 11 system expired after the storms moved out of the region.
The flood watch now affecting Des Moines, Davenport, Bettendorf, Moline and Rock Island is tied to later rounds of heavy rain and has a different timeline and primary hazard.
Keeping the two events separate preserves the historical record of the Aug. 11 derecho while directing readers seeking current conditions to the active flood-watch coverage.
Related coverage: State disaster assistance remains available in four Iowa counties after storms.
The National Weather Service continues documenting the Aug. 11 derecho. Confirmed tornado tracks, damage information and subsequent updates are available through the official Aug. 11 storm summary.
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