Torrential downpours descended upon the Chicago region as repeat waves of thunderstorms "trained" over areas from Rockford to Chicago's North Side. When the rains finally ended more than 17 hours later, 9.35 inches of rain had inundated the O'Hare area, making it an inaccessible island for nearly 24 hours. Three people died and flood damage exceeded $220 million.
The worst flood in the history of Chicago, Illinois, struck on August 13 as a result of a succession of thunderstorms that produced excessive rainfall. An official measurement of 9.35 in. in 8 hours (National Oceanic and Atmospheric Administration, 1987) was the greatest for 116 years of record collection. The northern and western metropolitan areas of Chicago bore the brunt of the storm. Significant flash flooding occurred along with general riverine flooding that persisted for many days. Maximum discharges of record occurred at several streamflow-gaging stations on the Des Plaines River and its tributaries. Ponding developed in areas that were normally drained by storm sewers. Areas of northwestern metropolitan Chicago were transformed into large shallow lakes as standing water accumulated to depths of 1 to 3 ft.