Corn Sweat Pushed Heat Index To 128F In Missouri; 100s Of Temp Records To Fall Or Be Matched As Heat Moves East

Sultry air over the central United States — fueled by a heat dome, corn sweat and tropical winds from warmer than average Atlantic Ocean temperatures — will spread eastward in the days ahead, bringing record temperatures to parts of the U.S. Over the past several days, dew points, a direct measure of humidity, were just a few degrees short of national records in the Corn Belt. The combination of heat and humidity exacerbated by corn fields caused heat index values to surge to 128 degrees in southern Missouri, 117 degrees in western Kentucky and 116 degrees in central Iowa this week. Now, that heat will spread into other states.

On Thursday, the most oppressively hot conditions will be found in the Midwest and Great Lakes before surging Friday into the Northeast and Mid-Atlantic, where temperatures will near 100 degrees in some places. Dangerous and long-duration heat will settle in the Southeast and redevelop in the Corn Belt into next week — with heat indexes of up to 120 degrees possible. Over the next week, more than 180 temperature records will be challenged or broken, especially at night, as 100 million people are covered by heat alerts and a more humid than normal summer continues.

Meteorologists use dew point thresholds to describe and communicate humidity; values above 75 degrees qualify as rainforest-like — or in this case, cornfield-like. The dew point is the temperature at which air becomes fully saturated with moisture, causing water vapor to condense into dew.

EDIT

Corn can release up to 4,000 gallons of water per acre into the lower atmosphere each day, a process known as evapotranspiration, contributing to extreme humidity and flooding rainfall. The 88-degree dew point observed in southern Missouri — where a heat index of 128 degrees occurred around midday Wednesday — was measured at an airport, where Herzmann noted there are stricter rules around clearing vegetation near weather instrumentation. In more populated places in Missouri, such as St. Louis and Kansas City, heat indexes reached 107 degrees.

EDIT

https://www.washingtonpost.com/weather/2025/07/24/corn-sweat-heat-humidity-east-forecast/