Dear Tom,
I live a few miles west of O’Hare International Airport, and I recorded a temperature of 20 degrees below zero on Jan. 16, when O’Hare went to 18 below. How many times has it been 20 below or lower in Chicago?
— Dan Klein
Dear Dan,
Twenty degrees below zero or lower is a rare occurrence in Chicago. In 138 years of official temperature records, (from 1871-2008, a period of 50,404 days), 20 below or lower has been recorded on only 15 days. That’s one day out of 3,360, or about once every nine years. However, the occurrences were not evenly distributed. Five of the minus 20 days occurred from 1872-1899, and then 83 years passed before the next one, 26 below in 1982. That initiated a “Little Ice Age” here, because eight of those frigid days came in rapid succession through 1985. The last and most recent was 21 below on Jan. 18, 1994.
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