In the fall, it seems that almost any warm day is referred to by most people as “Indian summer.”
“Indian summer” is a phrase most North Americans use to describe an unseasonably warm and sunny patch of weather during autumn. In U.S. states that experience enough seasonal variation for a brief warming trend to be noticeable, the phenomena is generally observed anywhere from mid-October to early November and normally occurs after the first frost. The warm temperatures are usually accompanied by dry, hazy conditions.
An Indian summer is typically caused by a sharp shift in the jet stream from the south to the north. The warm weather may last anywhere from a few days to over a week and may happen multiple times before winter arrives for good.
To be a true Indian summer, the following generally agreed upon criteria must be met:
- Temperatures must be above 70 degrees Fahrenheit for a period of at least seven days or more after the autumnal equinox.
- In the Northeastern U.S. and Canada, the heat wave must occur after the first frost.
No one really knows how “Indian summer” came to describe such periods. One theory suggests that early American settlers mistook the sight of sunrays through the hazy autumn air for Native American campfires, resulting in the name “Indian summer.” Others speculate that Native Americans recognized this weather pattern and used the opportunity to gather additional food for the winter. Some say it comes from the early Algonquian Native Americans, who believed that the condition was caused by a warm wind sent from the court of their southwestern god, Cautantowwit.
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 go at the settlers. “Indian summer,” the settlers called it.