What is Colorado’s ‘Indian Summer’ and When Does it Happen?

It's officially Fall! Then again, this is Colorado. The Autumnal Equinox for this hemisphere rolled around Sunday, September 22, 2024, marking the first day of fall.

Before you hang up your shorts and flip-flops, please keep in mind we do have this matter of "Indian Summer." What is that, and when does it happen?

Read More: The Most Scenic Fall Color Drives in Colorado

What is Indian Summer, and Have You Seen It Lately?

According to the Colorado Vacation Directory, the first known usage of the term "Indian Summer" can be attributed to a 1778 essay by 18th-century French-American writer John Hector St. John de Crevecoeur (1735-1813). He wrote:

Then a severe frost succeeds which prepares it to receive the voluminous coat of snow which is soon to follow; though it is often preceded by a short interval of smoke and mildness, called the Indian Summer.

Crevecoeur was born in France, as a young man moved to England, then Canada, and ultimately rural New York.

Crèvecoeur ultimately published a manuscript he had produced while in America. Annenberg Learner reports his book, Letters from an American Farmer (1782), was "...an account of rural life and travels through America told in the voice of a naive, rustic narrator." The letters of “Farmer James” became popular in France and England, and Crèvecoeur became a minor celebrity.

Definition of 'Indian Summer'

According to the Merriam-Webster dictionary, Indian Summer is defined as "A period of warm or mild weather in late autumn or early winter." It appears there's another definition, "A happy or flourishing period occurring toward the end of something."

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When Does Colorado Experience 'Indian Summer'?

Colorado Vacation Directory describes Indian Summer as "...a period of considerably above normal temperatures, accompanied by dry conditions, usually after there has been a killing frost. Depending on latitude and elevation, it can occur in the Northern Hemisphere between late September and mid-November."

Denver7 offers its own definition of Indian Summer, describing it as ".. loosely defined as the warm, dry, quiet period of weather that follows the first killing frost. This weather pattern usually occurs during late September or the first two weeks of October and is especially delightful because it coincides with the peak of the aspen leaves."

The Causes of Indian Summer

Denver7 adds there is no meteorological significance to Indian Summer. So, aside from a nice stretch of warm weather, what is it?

The Farmers' Almanac says, "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."

The Farmers' Almanac adds that for the warmer temperatures to qualify as a "true second summer," the following criteria must be met:

• Temperatures must be above 70 degrees Fahrenheit for at least seven days or more after the fall equinox.
• The heatwave must occur after the first frost.

When It's All Said and Done

Ultimately, Indian Summer is not an indication of the upcoming winter or a reminder of the summer recently passed. As Denver7 puts it, "Indian Summer is simply a time to try to slow down and savor the good fortune of living in Colorado."