How is it possible to break a weather temperature record at O’Hare International Airport when it did not exist in the 1930s?

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Dear Tom,
How is it possible to break a weather temperature record at O’Hare International Airport when it did not exist in the 1930s?
— Chester Jaskiewicz

Dear Chester,

You are correct to note that weather observations from O’Hare did not exist in the 1930s. They began there in late 1958. However, records of Chicago’s official weather observations began Nov. 1, 1870, in downtown Chicago. The observation site has been relocated several times since then, but a continuous stream of data exists from then until the present.

Weather observations were taken at several locations in the Loop until a transfer to the University of Chicago in 1925, then to Midway Airport in 1942 and to O’Hare in 1980. Daily temperature records, such as highest and lowest temperatures, are compiled from the entire set of data from Nov. 1, 1870, to the present.

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