Here’s How Much Longer Summer Is Lasting In Illinois

ILLINOIS — It doesn’t just feel as if the steamy temperatures of summer are lasting longer in Illinois, they are, according to an analysis of historical weather data over the past 30 years conducted by climatologist Brian Brettschneider and shared with The Washington Post.

According to Brettschneider’s analysis, summer in cities across the Chicago area lasts anywhere from 10 days to 15 days beyond the calendar definition of the season — the 93 to 94 days between the summer solstice and the fall equinox, this year on Sept. 22.

In Chicago, summer is 13 days longer than it was 30 years ago. In Joliet, summer is five days longer than it was 30 years ago; and in Elgin, summer is 12 days longer than it was 30 years ago.

The forecast for the Chicago area through Labor Day, the unofficial end to summer, calls for milder temperatures. Sunny and dry weather is expected through Monday, with temperatures in the 70s all weekend.

Brettschneider examined the hottest 90 days of the year from 1965 to 1994 and compared their frequency to the years between 1995 and 2024.

Overall, cities in the southern U.S. and California are gaining the most summer days. The Mid-Atlantic and Pacific Northwest have seen a more moderate expansion of summer and the Midwest has seen the least lengthening of summer, according to Brettschneider’s analysis.

Cities where summer lasts the longest include:

• San Francisco, 42 more days
• Miami, 39 more days
• McAllen, Texas, 36 more days
• New Orleans, 30 more days
• Houston, 29 more days
• Tampa, 24 more days
• Los Angeles, 23 more days
• Austin, 23 more days
• El Paso, 23 more days
• Reno, Nevada, 23 more days

You can use The Washington Post’s tool to see just how much summer is increasing in your city here.

Yuping Guan, a physical oceanographer at the Chinese Academy of Sciences, who was not involved in the analysis, told The Post the rate of change over the past 30 years “is faster than anticipated.”

He and his team conducted a global study in 2021 that showed summer heat is lasting a few more days each decade in the Northern Hemisphere. Although the study used slightly different datasets, “the trends are consistent,” Guan told The Post.

Last year and the past decade have been the hottest on record, according to the National Oceanic and Atmospheric Administration. Earth’s average surface temperature has been rising because of human-produced greenhouse gases, which trap heat in our atmosphere, according to NOAA.