Corn sweat is making Iowa feel even hotter

A map showing the expected high temperatures on June 30, not counting the heat index. Des Moines is at 96 degrees. Map: National Weather Service

Iowa's first prolonged heat wave of the year has arrived just in time for July Fourth.

Driving the news: A large, stagnant high-pressure area over Tennessee is driving the heat across much of the country, and Iowa is on the outer edge of that system, National Weather Service meteorologist Andrew Ansorge tells Axios.

How it works: Think of it like a lid on a pot.

The high pressure traps heat and moisture near the surface with nowhere to go, and because the system isn't moving, neither is the heat.

By the numbers: The heat index on Monday and Tuesday is around 100–110° in central Iowa.

Wednesday and Thursday will be up to 105°.

Things will cool slightly over the weekend, with a heat index of 100° on July 3 and the upper 90s on July 4, Ansorge says.

What they're saying: "The unusual thing this year is this is the first prolonged heat wave we've had at this magnitude, so maybe it's a little delayed, but overall, it's not uncommon," Ansorge says.

🌽 The intrigue: "Corn sweat," scientifically known as evapotranspiration, is also starting to contribute to the Midwest's high humidity, he says.

Corn sweat is the process by which corn releases vapor into the air after absorbing water through its roots.

It occurs every summer, starting around this time.

The bottom line: Stay hydrated, take shade breaks and double-check your back seats for kids and pets, Ansorge says.