All of northern Illinois will be under an excessive heat warning on Tuesday, but a phenomenon known as “corn sweat” will make the conditions especially oppressive in areas away from the city of Chicago.
Heat indices could soar above 110 degrees and could even approach 115 degrees in some parts of the state on Tuesday, according to an excessive heat warning issued by the National Weather Service.
Since heat indices are calculated using dew points and temperature, anything that adds extra moisture into the air can impact them.
And that’s where “corn sweat” comes in.
According to the Weather Channel, “corn sweat” refers to a process by which plants exhale water, the technical term for which is “evapotranspiration.”
Officials say that process peaks between mid-July and late-August, with each acre of corn potentially giving off up to 4,000 gallons of water per day.
That is a lot of extra moisture being added into the atmosphere, and it can drive dew points up in areas where there is a lot of agricultural land.
Monday is a good illustration of that phenomenon. While the excessive heat warnings will only spread into eastern Illinois on Tuesday, areas of western Illinois, Iowa and Missouri are already seeing the impacts of the high humidity.
In the Quad Cities for example, the heat index reached nearly 110 degrees on Monday afternoon, with air temperatures in the low-90s and dew points reaching a steamy 80 degrees.
The entire state of Iowa was under an excessive heat warning on Monday and will see similar conditions on Tuesday as the high humidity couples with some of the hottest air temperatures of the season.
Iowa is ground-zero for “corn sweat” impacting conditions, but parts of Missouri, Minnesota, Wisconsin and Illinois can also be impacted.