Ask Tom Why

Dear Tom,
If you review our annual average high and low temperatures, what day or days of the year most closely approximate a typical day in Chicago?
— Greg Foltz, La Grange
Dear Greg,
It’s difficult to define a “typical” Chicago temperature value because large temperature fluctuations characterize the city’s climate. Rarely will Chicago experience a day whose high and low temperatures are within a degree or two of the daily normals. Indeed, a case can be made that a “typical” Chicago day brings sizable departures from the normals rather than adherence to them. That said, Chicago’s annual average daily high and low temperatures are 60 and 42 degrees, respectively. The normal daily high/low temperatures on April 19 and 20, and on no other days, exactly match those values. It’s a stretch, but those April 19-20 are the “typical” days.