Just about every time there's a warm day in the fall, you'll hear most people mention the term "Indian Summer."
The saying has a wide variety of meanings all over the world, but is normally associated with late-October to mid-November warmth in the northeast and Mid Atlantic states.
Most don't realize, to be considered an "Indian Summer," the weather conditions have to meet some specific criteria.
The National Weather Service defines "Indian Summer" as weather conditions that are sunny and clear with temperatures above 70°, following a sharp frost
Similarly, the American Meteorological Society says, at least one killing frost and preferably a substantial period of normally cool weather must precede this warm spell in order for it to be considered a true "Indian summer."
It does not occur every year, and in some years there may be two or three Indian summers.
WHERE THE TERM CAME FROM
According to the Old Farmer's Almanac, the most probable origin of the term goes back to the very early settlers in New England. Each year they would welcome the arrival of a cold wintry weather in late October when they could leave their stockades unarmed.
But then came a time when it would suddenly turn warm again, and the Native Americans would decide to have one more attack on the settlers. The settlers called this warm spell, an "Indian summer."
The American Meteorological Society has a different thinking on the origin.
The AMS glossary says, "It dates back at least to 1778, but its origin is not certain; the most probable suggestions relate it to the way that the American Indians availed themselves of this extra opportunity to increase their winter stores. The comparable period in Europe is termed the Old Wives' summer, and, poetically, may be referred to as halcyon days."
In England, dependent upon dates of occurrence, such a period may be called St. Martin's summer, St. Luke's summer, and formerly All-hallown summer.