Our Jekyll and Hyde July

Through the first three weeks of July, as of Thursday morning the 21st, only 0.45” of rain had been recorded at O’Hare Airport.  Had July ended with no additional rainfall, this would have been the third driest July in about 140 years of record keeping at Chicago.

  • Three days later, by Sunday afternoon, this July ranked as the second wettest on record for Chicago…with a week still left to go.  What a difference three (wet) days make.
  • Total rainfall through the 24th now is 9.04 inches while the record for the month is 9.56 inches (set in July 1889).
  • So in a three day period we moved from potentially the third driest July to the second wettest!

(Lawnmowers are being taken back out of storage.)

A brief summary of facts regarding the record rainfall measured on Saturday, July 23:

  • The all-time Chicago daily record rainfall of 6.86 inches was set during the pre-dawn hours this past Saturday, July 23.  Never had Chicago’s official climate station (presently O'Hare Airport) measured more rainfall in a single calendar day. 
  • The previous daily record for Chicago was 6.64 inches on September 13, 2008.  The previous record for July 23 itself was set just one year ago…with a total of 2.79 inches on 7/23/2010.
  • A total of 8.20 inches of rain fell during the 24-hour period from 7:00 AM Friday to 7:00
    AM Saturday. This fell shy of the all-time 24-hour record rainfall set on August 13-14, 1987.
  • As shown by the blue line in the graph below, this record setting rainfall actually took place over just about a 3-hour period!
  • If Chicago had not received a single drop of rain this month outside that 3-hour window early Saturday, this would still rank as one of Chicago's top ten wettest Julys on record (8th overall)


rainfall rates on July 23, 2011
Rainfall graphic provided by Daryl Herzmann of the Iowa Environmental Mesonet.

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