Ever Heard Of Corn Sweat? It’s A Thing

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Hot temperatures in the Midwest this week have been made even worse by a phenomenon called "corn sweat" which sometimes gives a boost to humidity in the region during summer heat waves.

The Midwest "corn sweat" factor adds to already humid Gulf air. Southerly winds draw moisture from the Gulf of Mexico northward, leading to already higher dew points at times during summer in the Midwest.

Corn sweat gives a localized boost to dew points in the region when the crop is in full swing during midsummer, through what's called evapotranspiration (more on that below). That's especially the case in areas where the crop's production is largest, in the darker green shading below.

T​he dew point is the best way to tell how uncomfortable you'll feel in the summer. Dew points reached the upper 70s to low 80s in parts of Minnesota and Iowa Monday, partly due to the corn sweat factor. That's a level of mugginess more typically seen near the Gulf Coast.

A​s the chart below shows, a dew point that's generally 75 degrees or higher is considered oppressive.

Evapotranspiration is the key to how "corn sweat" works. As the root systems of plants like corn draw in water, the leaves of the plant then release water vapor (moisture) into the air through their stomata, according to agdaily.com. This is called evapotranspiration, essentially the plant's way of breathing.

A single acre of corn can give off 3,000 to 4,000 gallons of water per day, according to a post on X by the National Weather Service in Sioux Falls, South Dakota.

T​hat added moisture in the air then increases already high dew points, making it feel even more humid on a localized scale. The increased humidity can then help boost heat index temperatures even higher.

Chris Dolce has been a senior meteorologist with weather.com for over 10 years after beginning his career with The Weather Channel in the early 2000s.