Dear Tom,
How often do we see drastic temperature changes of 25 degrees or more from one day to the next in Chicago? I believe in June it was 95 degrees one day and 60 the next.
—Jack Daoud, Niles
Dear Jack,
You're close. Chicago's high temperature June 8 was 95 degrees; cool air surged in and June 9 registered a high of only 69, a 26-degree drop. Despite Chicago's vigorous, changeable weather, day-to-day temperature changes of 25 degrees or more do not occur very often: only five times per year on average. That's the result of a computer sweep of the city's official temperature data set that covers 140 years (1871-2010). The sweep found 477 instances of day-to-day high temperature declines of at least 25 degrees and 192 instances of day-to-day increases of at least 25 degrees. The greatest changes: 48 degrees (from 32 degrees to 80 on March 28-29,1895, and from 61 degrees to 13 on Jan. 18-19, 1996.
