How ‘corn sweat' can make a hot summer day even worse

The Hill

22-07-2025

(NEXSTAR) — Forget the dog days of summer — it's corn sweat season.
Through the end of July, the National Weather Service has warned that a large stretch of the country — from Louisiana to Minnesota and eastward — is expected to experience 'dangerous, prolonged heat' coupled with humid weather.
For those in the Midwest and across the Corn Belt, the high humidity can be attributed in part to the plethora of corn (and other crops) growing in the region.
As Ellen Bacca, chief meteorologist at Nexstar's WOOD, explains, corn and crops 'sweat' just like humans when they become hot. Unlike humans, plants bring water from their roots and release it into the air in a process known as evapotranspiration.
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Estimates from the U.S. Geological Survey say that a single acre of corn can release 3,000 to 4,000 gallons of water vapor daily. As Nexstar's WGN previously reported, in Illinois alone, the National Weather Service said a mature corn crop is capable of producing more than 35 billion gallons of water vapor in a day. That would be enough to fill over 52,500 Olympic-size swimming pools.
Iowa and other areas known for growing large expanses of corn can frequently be the most humid locations in the country.
That was true Tuesday: data from the National Weather Service shows dew points in the upper 70s across Iowa, Illinois, Missouri, Kentucky, and Tennessee. Only Florida and the southern portions of the Gulf states had higher early afternoon dew points.
The corn sweat effect has grown from a hyper-local event to a more expansive situation due to climate change, according to Brian James, chief meteorologist with the Nexstar Weather Center said Tuesday.
'The increased humidity caused by very large corn fields is a phenomenon that has become even more amplified due to climate change,' he explained. 'A warmer atmosphere can hold more moisture. That means as the summer heat builds and temperatures rise across the Corn Belt, the increased humidity is leading to heat index values above 110 degrees over a much larger area than what used to occur.'
The latest temperature outlook from NOAA's Climate Prediction Center shows that, across the Lower 48, only California and parts of Nevada, Wisconsin, Michigan and the Northeast are likely to see below-average temperatures during the final week of July. All other parts of the country — especially areas from the southern Plains, across the Gulf Coast and into the southern Ohio Valley — have a higher chance of seeing above-normal temperatures.
Any corn sweat that increases humidity will, of course, only last a few more months.