What is the earliest date of a sub-30-degree high in Chicago?

Dear Tom,
What is the earliest date of a sub-30-degree high in Chicago?
— Chuck Kennell
Dear Chuck,
Considering the fact that over the course of a year, the city’s lowest average maximum is just 31 degrees occurring during most of January, a day with a sub-30-degree high can truly be classified as a wintry day. We had Chicago climatologist Frank Wachowski check the archives, and he determined that the average date of the season’s first sub-30 day is Nov. 19, and in a typical year the city logs 33 such days. The most ever recorded in a cold season was 66 in the winter of 1903-04 and the least just four in 1877-78. The city’s earliest on record occurred 130 years ago with a 29-degree high Oct. 25. So far this autumn, the lowest official high temperature has been 30 degrees recorded at O’Hare International Airport on Nov. 10.