Dear Tom,
What time of day is usually warmest during the winter?
— Marty Samual, Chicago
Dear Marty,
It’s the early afternoon. During the winter, Chicago’s daily high temperature occurs between 1 and 4 p.m. on 40 percent of the days (and in the summer the percentage rises to 65 percent in the same period). Surprisingly, however, on 13 percent of the days, or on 1 day in 8, the maximum temperature occurs at midnight — midnight either at the beginning or at the end of the 24-hour calendar day. Frequently in winter, during a warm-up after a cold spell, temperatures will continuously rise, with the day’s high being reached at midnight at the end of the day. Or, if a strong cold front passes during the previous night, the day’s high will be recorded at midnight at the beginning of the calendar day, with temperatures falling the rest of the day.
