Last updated October 15, 2021
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Midwestern Heat Wave September 2017

United States

A vast area of high pressure brought unusual heat and humidity to the Great Lakes and Ohio Valley after the end of astronomical summer. This late-season heat wave occurred the same year and in much of the same region that experienced record hot and unseasonably early temperatures in February. Formal attribution work has identified the fingerprint of global warming in February's record hot temperatures, as climate change increased the likelihood of such heat by threefold.[1]

Chicago had seven days in a row of record daily high temperatures, with the mercury reaching or passing the 92 degree-mark each day from September 20th to 26th.[2][3] This is the latest stretch of seven consecutive 90-degree days on record in Chicago.[3] Further east, Cleveland had a five-day streak of daily record highs,[4] and Lansing, Michigan had a five-day streak of highs that tied or broke the previous records set in 1891 and 1895. A handful of other cities saw their highest temperatures on record for this late in the year, and Burlington, Vermont warmed above 90°F for the first time since 1939.[4]

The fingerprint of global warming has been firmly identified in the increasing intensity, duration and frequency of extreme heat events globally. Heat waves exacerbate the risks associated with heat exposure, and urban residents are particularly vulnerable to threats of heat waves due to the urban heat island effect.

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A hot yellow sun rises on Lake Michigan at Montrose Avenue Monday Sept. 25, 2017 as a jogger takes advantage of the cool early morning temperatures. Although still cool at sunrise another record-breaking hot day was expected for the Chicago area.  Photo: Nancy Stone / Chicago Tribune

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