Dear Tom,

Often in October the day starts frosty, but the temperatures quickly warm into the 60s and 70s in the afternoon. Does October have the largest temperature swings?

Barb R.  Skokie

Dear Barb,

It does not. While October does produce its fair share of days with large temperature ranges, the city’s largest recorded daily temperature changes have occurred in late winter and early spring. The city’s largest one-day temperature increase, one that spanned 49-degrees, occurred on March 29, 1895, when the mercury soared from an early morning low of 31 to an afternoon high of 80. On February 8, 1900, the mercury plunged 52 degrees, from an unseasonably mild early high of 62 to a midnight low of 10 following the passage of an arctic cold front.

This October’s large diurnal temperature swings that you noted attest to abnormally dry conditions that existed over the first 10 days of the month. Frosty fall mornings followed by sunny, warm afternoons are typically dominated by continental high pressure which brings clear skies, light winds, and very dry air. Air with low water vapor content heats and cools more readily and more efficiently than humid air.