Record Rainfall and Flooding of July 17-18, 1996

A swath of heavy rainfall occurred across portions of south central Wisconsin, northeast Illinois, and northwest Indiana on July 17-18, 1996. The heaviest rainfall was observed near Aurora, Illinois, with a maximum point rainfall of 16.94 inches in a 24-hour period. The 24-hour rainfall measured near Aurora remains the statewide record (as of 2022). An observation of 10.99 inches of rainfall was recorded on the far west side of Chicago which remains the highest storm total observed in Chicago (as of 2022). These extreme rainfall totals led to widespread, significant flooding in the western suburbs of Chicago and areas just to the west. Flooding was observed on the Fox River, DuPage River, Des Plaines River, and tributaries including Blackberry Creek, Sawmill Creek, and Lemont Run. Many river crest records remain to this day (as of 2022). Damage estimates were on the order of $600-700 million ($1.1 to $1.3 billion in 2022 dollars). FEMA estimated that more than 35,000 residences were flooded.

A relatively large area experienced extreme rainfall amounts. It was estimated that an area of about 100 square miles near the heaviest rainfall averaged 16.3 inches and an area of about 1,000 square miles averaged about 12.6 inches.

Rainfall data was collected from hundreds of gauges to map the extent of the event. A contour map of rainfall published in a technical report created several months after the event is shown below (Angel et al 1997). In 2020, newer radar bias-correction techniques were used to create estimated rainfall maps using rain gauges and radar data combined. Updated analyses suggest that heavier rainfall than the recorded maximum may have occurred just to the southwest of Aurora. A large area experienced rainfall with less than a 1% chance of occurring in a given year.

Information on this page was collected from multiple sources, including contributions of Jim Angel, previously state climatologist for the state of Illinois. More information on this flood event can be found in the technical report "The Record Rainstorm of July 17-18, 1996 in Northern Illinois" (Angel et al 1997). Inflation adjusted damage numbers derived from the US Bureau of Labor Statistics CPI Inflation Calculator.