The term "Indian Summer" refers to a period of above-average temperatures in mid or late autumn, with mainly sunny days and cool nights. Around here, a bona-fide Indian Summer usually has to follow at least one killing frost.

Given how variable our weather can be, and the wide range of time when Indian Summer can occur, it's really not that unusual for there to be an "Indian Summer" in the Delaware Valley. In fact, some years might have two or three "Indian Summers."

An example of a weather pattern that brings us Indian summer weather goes something like this: a sprawling area of high pressure sits just off the East Coast. This high brought chilly air days before when it moved out of Canada. But as the high settles along the East Coast, our winds locally start to blow from the south and southwest. This brings a warm-up which sometimes lasts a few days. And this scenario can play out several times before the winter chill sets in for good.