Besides falling within specific dates, true Indian Summer must meet certain other criteria. It must be warm, of course. In addition, however, the atmosphere must be hazy or smoky, there must be no wind, the barometer must be standing high, and the nights must be clear and chilly.
The more controversial aspect of Indian Summer is the time of its occurrence – or whether there is a certain time. Most would agree that warm days in the fall do not of themselves constitute Indian Summer unless they follow a spell of cold weather or a hard frost. Beyond that, many references to Indian Summer in American literature indicate that it occurs in late fall.
For the past two hundred and twenty-two years, The Old Farmer’s Almanac has adhered to the saying, “If All Saints brings out winter, St. Martin’s brings out Indian Summer.” Accordingly, Indian Summer can occur between St. Martin’s Day (always November 11th) and November 20. If the conditions that constitute Indian Summer do not occur between those dates, then there is no Indian Summer that year. If a period of warm fall weather occurs at a different time, such a period could be correctly described as being like Indian Summer.
Finally, why is Indian Summer called Indian Summer? Some say the name comes from the Indians, who believed that the condition was caused by a certain wind emanating from their god Cautantowwit, or the southwestern god. Others say that the term evolved from the fact that around the time of Indian Summer, or shortly before it, the deciduous trees are “dressed” as colorful as Indians.
The most probable origin of the name, in our view, goes back to the very early settlers in New England. Each year they would welcome the arrival of cold, wintry weather late in October, knowing that they could leave their stockades without worrying about Indian attacks and could begin preparing their fields for spring planting. The Indians didn’t like attacking in cold weather. But then came a time, almost every year around St. Martin’s Day, when it would suddenly turn warm again and the Indians would decide to have one more go at the settlers. “Indian Summer” the settlers called it.