Dear Tom,
To determine the capacity of a drain, I need to know the rate of heavy rainfall that sometimes occurs in Chicago. Can you help?
Don Ward, Glen Ellyn
Dear Don,
On an hourly basis, heavy rain is defined as that which falls at a rate greater than 0.30 inches per hour. However, rains of far greater intensity routinely occur across northeast Illinois. For example, early this month Midway Airport registered 0.51″ of rain in the 15-minute period that ended at 3:30 a.m. Sunday, June 3.
Chicago weather historian Frank Wachowski provides these extreme rainfall statistics from Chicago’s precipitation records: 0.67″ in three minutes (April 24, 1976); 2.35″ in 30 minutes (July 20, 1978); 3.34″ in 60 minutes (June 13, 1976); and 5.20″ in two hours (June 10, 1967).
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
