Heat is par for summertime around here, but 100^oF days are actually pretty rare. Wilmington only had nine 100^oF days in the last 40 years - one of those was last year on July 19th.

In Wilmington, the temperature has reached 100^oF as early in the summer as June 1st - that happened way back in 1895. In Philadelphia, the earliest 100^oF reading occurred on this date back in 1925. By 7 that morning the temperature was already 82 degrees, and by noon it had climbed to 96. The century mark was reached around 2:30 in the afternoon.

By far, the most 100^oF days have occurred in July, with June and August distant seconds. There've even be a few 100^o days in September, as late as September 7 in Philadelphia and September 11 in Wilmington.