Top line
A heat dome is bringing high temperatures to much of the Midwest this week, made worse by humidity caused at least in part by moisture released by plants, known as “corn sweat.”
“Corn sweat” is the name given to the moisture that crops – especially corn – give off at high temperatures.
Key data
Heat warnings are in effect across much of the Midwest, including Iowa, where an extreme heat warning is in effect due to heat index values between 40 and 46 degrees Celsius – the most severe designation from the National Weather Service.
The eastern half of Kansas, southeastern Nebraska, northern Missouri, western Ohio, central Kentucky and most of Indiana, Illinois, Wisconsin, Minnesota and Michigan are also under either extreme heat warnings or heat advisories.
In Des Moines, Iowa, which was near the epicenter of the heat wave on Monday, afternoon temperatures reached 99 degrees and a heat index of 111. In St. Louis, it was also 99 degrees and the heat index was 104 degrees. In Chicago, it was 95 degrees and the heat index was 103 degrees.
The elevated heat indices are due to high humidity, which is partly because corn, soybeans and other crops release moisture in hot weather, similar to how humans sweat in high heat — a phenomenon known as “corn sweat,” Scientific American reported.
“Corn sweat” could lead to “some of our higher humidity levels of the year,” Chicago-based National Weather Service meteorologist Andrew Taylor told the publication.
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Surprising fact
An acre of corn can release 4,000 gallons of water a day, the Washington Post reported during a heat wave made worse by “corn sweat” in 2022.
What you should pay attention to
How long the heat will last. 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 moving into the Mid-Atlantic by midweek and weakening by the weekend. The heat advisory for much of central Iowa and southern Minnesota expires Monday evening, while advisories farther east, covering parts of Wisconsin, central Illinois and the Chicago area, will remain in place through Tuesday night. The National Weather Service advises people to drink plenty of fluids and stay indoors and out of the sun if possible, as “heat-related illnesses increase significantly during extreme heat and high humidity.”
tangent
The dew point, or “the temperature to which the air must be cooled” to achieve 100% relative humidity, is a more accurate measure of how “dry” or “humid” it feels outside than relative humidity alone, according to the National Weather Service. When 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 degrees, it can become “mug,” bringing muggy evenings, and when the dew point is above 65 degrees, it can become “oppressive” because there is “a lot of moisture in the air.” Scientific American reported that moisture from “corn sweat” during this heat wave is pushing dew points up into the 60s and 70s, with some areas reaching just above 80s.
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