Fox Q13 Iowa: “The farms of Iowa are the nation’s number one supplier of the nation’s corn. But this week, it’s exporting oppressive humidity in large quantities. A phenomenon known as ‘corn sweat’ is combining with a summertime heatwave in the Upper Midwest to make for some unbelievably humid conditions. Clarion, Iowa, reported a dew point of 90 degrees Wednesday afternoon at 2:15 p.m. Central time. The air temperature at that time was also 90 degrees, resulting in 100% relative humidity and a heat index of 132 degrees. Some 130 miles west of Clarion in Maurice, Iowa, an even higher dew point of 91 degrees was recorded Tuesday evening between 5-7 p.m. Central time. The 5 p.m. air temperature was 93 degrees, making the heat index an astounding 141 degrees.”

“Iowa has an abundance of corn fields around the state. Corn (or any plant) pulls moisture out of the soil, and some of that moisture escapes through the corn’s leaves and enters the surrounding air. This is called transpiration. Just as humans sweat, or perspire, to cool down, plants are no different. The higher the air temperature, the more the plant will sweat, or transpire. The transpired moisture will then evaporate off the plant’s leaves to cool it down, just like how sweat evaporates off human skin. Evaporation is a cooling process. Additional moisture also enters the air from lakes and other water sources in the area through evaporation. Combine all of this evaporation and transpiration, and you get evapotranspiration. ‘Corn sweat’ is simply a more colloquial way of referring to evapotranspiration in the vicinity of corn fields. This process of evapotranspiration leads to increased moisture in the air near corn fields as the corn ‘sweats’ to keep itself cool, ultimately leading to higher dew points in many areas surrounding the corn fields.”