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Longer Heat Streaks Across the U.S.

By Climate Central

We're in the final weeks of meteorological summer, usually a time when heat has worn out its welcome. Fortunately, for many in the Plains, Midwest, and the East, this August is providing a break from the sweltering heat. But over the long term, as the planet continues to warm from the increase in greenhouse gases, extended streaks of heat are getting longer. In our analysis this week, we examine the number of consecutive hot days annually for these cities. While there’s a lot of variation from year to year in the length of these hot spells, the trend suggests more prolonged periods of high heat in the majority of locations.


Longer streaks of 85°F, 90°F, 95°F, 100°F, 105°F and 110°F in these cities

Exposure to prolonged hot spells can raise the risk of heat-related illnesses like heat stroke, especially in urban areas where the impacts are compounded by the urban heat island effect. Late summer activities can further heighten the risk of heat-caused illness. High school and college football, for example, usually begin practices in pads at this time of year. When exercising, the body produces up to 20 times more heat than when at rest, and the risk of heat-related illness rises after 3 percent of the body’s weight is lost through fluids.

Economically, extended hot streaks increase the electricity demand from air conditioning, raising cooling costs and putting added stress on the electrical grid. They also increase the risk of wildfires, such as the ones that devastated northern Montana last month with multi-million dollar impacts on ranching communities and beef production.

NOTE: Although the term "heat wave" is sometimes used to indicate a stretch of abnormally hot weather, we opted not to use that word here since heat waves have a specific definition that varies across the country.

METHODOLOGY: To find heat streaks, we used the highest temperature (at 5°F intervals) that occurred an average of at least 5 consecutive days per year and at least once a year. Stations that did not meet both criteria or were missing data were evaluated at a lower threshold temperature. Let us know if you would like to see the data calculated at a different threshold temperature.