With a 140 m.p.h. jet stream directly overhead, a strong influx of warm, moist air from the Gulf of Mexico, and a warm front just to the west and south of Chicago, all the ingredients were set for a severe storm outbreak late Friday afternoon. Heavy downpours hit in eastern Kane, northern DuPage, and northern Cook counties. St. Charles and Mount Prospect reported over 3 inches of rain in an hour and a half. Those areas and many others reported flooded streets and paralyzed traffic. O’Hare’s 1.73 inch total far exceeded the previous record (1.09 inches in 1965) for Sept. 22. Aided by instability created by the diverging jet stream flow aloft on top of the converging winds at the warm frontal boundary below, towering storms built to 58,000 feet tall. Downdrafts resulted in widespread hail and wind damage (70 m.p.h. reported at Hanover Park and 60 m.p.h. near West Chicago). Funnel cloud reports and Doppler radar signatures prompted at least seven tornado warnings.
--By Paul Dailey, WGN Weather Center Meteorologist
WGN-TV Chief Meteorologist Tom Skilling and the WGN Weather Center staff provide daily coverage of weather in the Chicago area.
