How often does a day’s actual high and low temperatures equal the normal high and low temperatures for that date?
— Bill Wilson, Dyer, Ind.
It doesn’t occur very often. We used Midway Airport data for the period 1929 through 2017, the years for which complete high and low daily temperatures are available. That’s 88 years of data. A computer check of observed daily high and low temperatures against Midway’s normal daily high and low temperatures revealed only 83 occurrences on which all four numbers were exactly the same, or slightly less than one day per year.
Chicago’s temperature climate usually consists of swings (sometimes rather large swings) around the daily normals, and it’s not often that a day’s high and low readings are exactly equal to the normals on a given date.