Coldest Day in Chicago History - 25 Years Ago

Coldest Day in Chicago History 25 Years Ago
January 20, 2010 marks the 25th anniversary of Chicago’s coldest day. On January 19, 1985 an arctic blast hit northern Illinois. Temperatures fell all day reaching a low of -23F by midnight. The temperature continued falling after midnight on January 20, eventually setting an all-time low temperature record for Chicago of -27F at 618 in the morning. The temperature began a slow recovery later in the day, reaching a high of -4F before midnight. The frigid weather was accompanied by 15 to 30 mph west to northwest winds, creating wind chill equivalent temperatures of -60F to -80F. The wind chill dropped to -77F at O’Hare Airport at 550 AM on January 20 when the temperature was -26 with a 21 mph wind.
Although the National Weather Service does not keep records of wind chill values, that is one of the coldest wind chills ever experienced in Chicago. The wind chill formula was changed in 2001. Using today’s table, the wind chill would be around -57F.  Frostbite can occur on exposed flesh in five minutes under those extreme conditions. The coldest known wind chill equivalent temperature for Chicago was -82F on December 24, 1983 when the temperature was -23F and the wind was 29 mph.
The January 20, 1985 arctic blast also set a record for the all-time lowest dew point temperature for Chicago. The dew point dropped to -39F at 450 AM and again at 618 AM.   
The low temperature at Midway Airport was -25F, while Rockford dropped to -26F. This was the second coldest temperature recorded at Rockford. The coldest was -27F on January 10, 1982.

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