What the Heck is “Indian Summer?”
by Mark McGinnis
Apple picking, pumpkin carving, costume shopping, football, hayrides, raking leaves and getting lost in a corn maze. Those are activities or memories that many of us relate to fall. It is a great time of year, when the nights are crisp and the weather is very changeable. Monday can be sunny and 70 degrees, only to be followed by a cloudy, windy, cool and wet Tuesday. In the northern United States and Canada, that scenario can happen in September and October. In the southern United States, that type of change can occur in November or December. Fall keeps us on our toes. Each morning we have to pay attention to the weather forecast to know what to wear. Have you dressed for the wrong weather — shorts on a cold day, long sleeves on a hot day? My children have because they didn’t check with their dad, the meteorologist. However, there are stretches of weather in the fall that are briefly warm and quiet: Indian summer.
The History of the Term
According to the American Meteorological Society Glossary of Meteorology, the term “Indian summer” dates back to at least 1778. It mentions that Native Americans — referred to at the time as Indians — typically used this type of weather as an “extra opportunity to increase their winter stores.” According to the glossary, there are comparable periods in Europe known as “Old Wives’ summer.”
So, on at least two continents, there is reference to nice weather in fall. In meteorological terms, the glossary defines Indian summer as “a period, in mid- or late autumn, of abnormally warm weather, generally clear skies, sunny but hazy days, and cool nights.” However, in the United States it is commonly understood that Indian summer cannot happen until after the first frost or killing freeze of the season.
We know that Indian summer occurs in “mid- to late autumn” but after a frost or freeze. Well, frosts and freezes occur at different times of the year for different locations. As a result, Indian summer can’t occur at the same time across the United States and Canada. Below is a map of the United States with average first frost. This map also marks the average earliest time Indian summer could occur in these locations.
According to Figure 1, the Rockies, Northern Plains, Great Lakes and New England have an average first frost between mid-September and mid-October. The central and southern United States, however, averages a first frost from mid-October to mid-November. As such, the first Indian summer will occur at different times during autumn. However, there can be more than one round of Indian summer. Mild autumns can be host to several rounds of Indian summer.
In North America and Europe, mild fall weather is notable and almost regular and has been occuring for several hundred years and probably longer. This period of late season warmth had been used to increase food supplies for the upcoming winter. By definition, Indian summer is a period of above-average temperatures with sunny, if not hazy, skies. This warm weather has to occur after a killing frost or freeze.
In most of Canada and the northern United States, Indian summer is possible as early mid- to late-September but more typical in October. In the southern United States, Indian summer is more typical in November and December.
So take advantage of the next burst of warm, sunny weather this fall and note that your ancestors used that time to work and build up supplies for the winter. If we are fortunate, we can have more than one round of Indian summer. You can use that time to rake leaves, do some home repairs or take the family to pick pumpkins and get lost in a corn maze.
Mark McGinnis is a Certified Consulting Meteorologist, Certified Broadcast Meteorologist and owner of Fair Skies Consulting. He has over 20 years of experience protecting people from weather, with extensive experience forecasting severe weather, hurricanes, blizzards, heat waves and arctic cold.