What is 'corn sweat' and why is it making heat, humidity worse in Midwest?

MADISON, Wis.- It's a common saying in the Midwest: "it's not the heat that gets you, it's the humidity." But turns out with this late August heatwave, it's not the heat that gets you, it's the corn -- or rather, "corn sweat."

Moisture given off by corn and other green vegetation like soybeans evaporates into the atmosphere, increasing the humidity.

"It's called evapotranspiration, but I kind of like corn sweat better," News 3 Now Chief Meteorologist Alex Harrington said Tuesday.

One acre of corn gives off approximately 3,000 gallons of water into the atmosphere. According to the USDA, roughly 4 million acres were planted in Wisconsin in 2023.

So no, the corn doesn't actually "sweat" like humans do, but it left some pretty noticeable pit-stains on the t-shirt that is America Monday and Tuesday.

On Monday, the National Weather Service's map of Dewpoints, or the measure of moisture in the atmosphere, showed up highest and darkest on the Southern Coast and, sure enough, the Corn Belt of the Midwest.

"Dewpoints in the upper 70s and in a few local instances, the lower 80s -- that's about as high as a dewpoint value can get," Harrington said.

"A lot of folks would be very surprised that the upper Midwest, the Corn Belt -- Iowa, Southern Minnesota, Wisconsin, Illinois, Ohio, Indiana -- that we can build humidity levels that near that of the deep jungles, local here in the upper Midwest, all because of the corn."

But when high dewpoints and temperatures mix so well it creates a jungle of high energy in the atmosphere ripe for some beastly storms.

"Some of the storms that we see when we have this extreme amount of instability in the atmosphere, all owing to their corn, could lead to high end severe weather that term," Harrington said.

But across social media other Midwesterners were surprised to learn the reason why working in or near a cornfield in the dog days of summer can feel like a sauna.

"Growing up on the farm I had no inclination that something is simple behind me in the cornfield, all this water giving off is moisture for thunderstorms, moisture to make an incredibly uncomfortable environment," Harrington.

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