September 2008 Heavy Rains in Northeast Illinois: Meteorological Analysis and Impacts

During 12-14 September 2008, an unlikely combination of abundant atmospheric moisture associated with the remnants of two tropical storms (Lowell from the Pacific Ocean and Ike from the Gulf of Mexico) and frontal lifting associated with a slow-moving cold front draped across the upper Mississippi River valley, produced record rainfall over parts of northern Illinois. Chicago’s O’Hare airport set its all-time 24-h (midnight to midnight) rainfall record with 6.64 in. on 13 September. The heavy rains created historical flooding along most rivers in northern Illinois and northwestern Indiana, closed regional interstates, cancelled flights out of Chicago’s Midway and O’Hare airports, placed many corn and soybean crops under water, and were linked to four deaths in the metropolitan area. A meso-/synoptic-scale analysis of the three-day period identified that heavy rains occurred over similar locations for extended periods. The unusual aspect of this event was the record-breaking 24-h precipitation totals in the absence of thunderstorm activity.