A heat dome is bringing high temperatures to much of the Midwest this week and they’re being worsened by humidity that is, at least in part, caused by moisture being released from crops—or “corn sweat.”
“Corn sweat” refers to the moisture crops—especially corn—release when temperatures are high.
Much of the Midwest is under heat alerts, including Iowa, all of which is under an excessive heat warning—the National Weather Service’s most severe designation—due to heat index values between 105 to 115 degrees.
The eastern half of Kansas, southeast portion of Nebraska, northern Missouri, western Ohio, central Kentucky and most of Indiana, Illinois, Wisconsin, Minnesota and Michigan are also under either excessive heat warnings or heat advisories.
Des Moines, Iowa—near the epicenter of the heat wave Monday—hit 99 degrees in the afternoon, with a heat index of 111, while St. Louis also reached 99 and topped out with a heat index of 104, with Chicago hitting 95 and a heat index of 103.
The elevated heat indexes are being driven by high humidity, partially due to corn, soybeans and other crops letting out moisture because of heat, similar to the way humans sweat in high heat, Scientific American reported—a phenomenon known as “corn sweat.”
“Corn sweat” can result in “some of our higher moisture values of the year,” Chicago-based National Weather Service meteorologist Andrew Taylor told the publication.
Get Forbes Breaking News Text Alerts: We’re launching text message alerts so you'll always know the biggest stories shaping the day’s headlines. Text “Alerts” to (201) 335-0739 or sign up here.
One acre of corn can release 4,000 gallons of water a day, The Washington Post reported during a heat wave worsened by “corn sweat” in 2022.
How long the heat lasts. The heat risk—a forecast risk of heat-related impacts—is highest on Monday and Tuesday, according to the National Weather Service, with the heat wave pushing into the mid-Atlantic by mid-week and moderating by the weekend. The excessive heat warning for much of central Iowa and southern Minnesota expires Monday evening, while warnings farther east, covering parts of Wisconsin, central Illinois and the Chicagoland area, will continue through Tuesday night. The National Weather Service advises people to drink plenty of fluids and stay in air conditioning and out of the sun if possible as “heat related illnesses increase significantly during extreme heat and high humidity events.”
Dew point, or “the temperature the air needs to be cooled to” to achieve a relative humidity of 100%, is a more accurate measure of how “dry” or “humid” it will feel outside than looking at relative humidity alone, according to the National Weather Service. If the dew point is less than or equal to 55 degrees the air is generally “dry and comfortable,” not too muggy. Between 55 and 65 can become “sticky” and bring muggy evenings, and if the dew point is greater than 65 it may become “oppressive” with “lots of moisture in the air.” Scientific American reported the moisture from “corn sweat” during this heat wave is raising dew points as high as the 60s and 70s, with some areas reaching the low 80s.