Early this week, I heard a weatherman say we were going to have an "Indian Summer". He was right about the weather, after a few weeks of fall, this week has been between seventy and eighty degrees every day. But his use of the term was not excruciatingly correct.
I did some searching and, in order for a day to technically be classified as an "Indian Summer" day, it has to happen after a killing frost. Since we haven't had a frost, it can't be Indian Summer.
Indian Summer is what's called a weather "singularity". A singularity (also called a calendaricity) is a discernable weather event that recurs around a specific calendar date each year.
But why is it called Indian Summer? According to a nice article in the Wisconsin Natural Resource Magazine
The term "Indian summer" is most often heard in the northeastern United States, but its usage extends throughout English-speaking countries. It dates back at least 200 years, but the origin is not certain; the most probable suggestions relate it to the way the American Indians availed themselves of the extra opportunity to increase their winter stores. According to New England Native American folklore, Indian summer is sent on a southwest wind from the spirit Countantowit.
European folklore has Indian summer equivalents: "Old wives’ summer" in central Europe, probably from the widespread existence of "old wives’ tales" concerning this striking feature of autumn weather; "halcyon days" also in central Europe, based on a period of fine weather described in Greek mythology; and "all-hallown summer," "St. Luke’s summer," and "St. Martin’s summer" in England, depending on when the autumn time the weather occurs.
So, bottomline, it hasn't been cold enough yet for the warm to count. But it's still nice.