Determining Chicago’s average temperature

Dear Tom,
Why doesn’t the Chicago National Weather Service take the average of the high and low temperatures of Midway, O’Hare and the lakefront and consider it the official Chicago temperature for a given day? Wouldn’t that eliminate some of the biases reported at a given location?
Alexander Zazi, Chicago

Dear Alexander,
By definition, an average temperature at a given location is exactly that: the average temperature at that spot. Temperatures at any given moment vary, sometimes significantly, across a geographical area as large as Chicago. Averaging temperatures at several locations to create a new “average” would destroy the characteristics of each of the individual locations (characteristics that you have referred to as “biases”). This might seem desirable, but the question then becomes: What locations should be selected in determining the new average?

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