How often is late February colder than the month’s first half?

Dear Tom,
Because of February’s lengthening daylight, it’s unusual for the month’s back half to be colder than its front half. I know that happened in 2015, but the last time I can recall a similar occurrence was in the 1960s. Were there any instances in between the two dates?
— Brian Beecher
Dear Brian,
There were. In most years, as Chicago transitions from winter to spring, the normal warming cycle dictates a warmer end to February than its start, but with Chicago’s wild temperature swings, that is not always the case. The February 2015 temperature reversal was quite dramatic, with temperatures averaging 19.4 degrees in the first half of the month and a frigid 9.7 in the back half. We had Chicago climatologist Frank Wachowski check recent Februaries and he found at least eight other such occurrences dating back to the mid-1960s.
How often is late February colder than the month’s first half?