🌽 Fast Facts: Corn Sweat
- What is Corn Sweat? The informal term for crop evapotranspiration—the process where corn plants absorb water from the soil and release water vapor through leaf pores to cool down and move nutrients.
- Moisture Output: A single acre of corn can evaporate an additional 4,000 gallons of water into the atmosphere every day (equivalent to about 0.15" of precipitation deep per acre).
- Heat Index Spike: Surrounding corn fields can add 20°F to 25°F on top of actual air temperatures, pushing local heat indexes past 115°F.
- The Scale Factor: With 95 million acres of corn planted, combined with historic July rainfall patterns, moisture levels are pinned at peak levels.
In a year when most meteorologists were watching signs of drought — especially across the western half of the country — the middle of the U.S. has been inundated with moisture. It’s not just been hot, but unusually humid — even for this time of year.
Several Midwestern states are reporting a July that ranks as one of the top 10 wettest on record. Eric Snodgrass, Nutrien’s principal atmospheric scientist, says you can look to the Gulf to understand what’s been pumping all this moisture into much of the Corn Belt this year.
“We’ve had nonstop access to Gulf moisture. So, there’s just been nothing turning that off. As a result, we’d been able to just generate huge storms on plenty of moisture,” he says.
What is Corn Sweat and How Does It Affect Humidity?
The other factor that’s pumping moisture into the atmosphere is something called “corn sweat” — the process where corn plants release water vapor into the atmosphere. As the corn plant absorbs water from the soil and releases it through the pores in its leaves, the plant can cool down and transport nutrients.
“Corn sweat shows up a lot in some of the news media,” Snodgrass says. “We just can’t forget that each acre of corn can evaporate an additional 4,000 gallons of water into the atmosphere. Now, that’s not a lot, believe it or not. If you precipitate it back out onto that acre, it’s only about 0.15" deep. But the reality is we expect to see more ridge-riding storms.”
| Corn Sweat Metric | Impact |
|---|---|
| Water Vapor Released | ~4,000 gallons per acre / day |
| Precipitation Equivalent | ~0.15" deep if rained back down onto that acre |
| Heat Index Increase | Adds 20°F to 25°F on top of actual air temperatures |
| Peak Heat Index Readings | Pushed local readings past 115°F (with dew points in the low 80s) |
| Total Crop Scale | 95 million acres of corn planted |
| Peak Season | Mid-to-late July (dew points expected to improve soon after) |
Snodgrass says last week’s rains that caused flash flooding across Iowa, Illinois and Missouri are proof of what the ridge-riding storms can do this time of year.
“We continue to see storms running the periphery of a ridge that’s going to probably live farther into the Southern Plains of the United States. But until you shut off the Gulf, we’re going have moisture coming through the country,” Snodgrass adds.
That “corn sweat” isn’t just aiding the recent ridge-riding storms. According meteorologist Ryan Maue, it’s also fueling some of the recent humidity.
At 7 pm ET, the corn fields 🌽were adding 20°F to 25°F on top of the actual temperature = heat index > 115°F 🔥
— Ryan Maue (@RyanMaue) July 28, 2025
Dewpoints in the lower-80s + temperatures in 90s = insane "feels like" readings 📈 pic.twitter.com/JP89U5qXzt
Maue said as of 7 p.m. ET on Sunday, the corn fields were adding 20°F to 25°F on top of the actual temperature, which means it felt like 115°F outside.
Much of that is because of the dew point, which according to Maue, reached in the low ‘80s. Dew points of 80°F or higher locally aren’t unusual, but they aren’t necessarily common either. It’s that high dew point creating such heavy humidity, and it’s no coincidence those dew point levels were highest around where there’s a lot of corn.
And we just can’t forget that each acre of corn can evaporate an additional 4,000 gallons of water into the atmosphere. Now, that’s not a lot, believe it or not. If you precipitate it back out onto that acre, it’s only about 0.15" deep.
With 95 million acres of corn planted in the ground this year, along with all the recent rains, it explains why the dew points and humidity has been so high.
The good news is the Midwest is currently in peak “corn sweat” time, which means the dew point should improve soon.
However, when it comes to moisture, Snodgrass thinks this wet weather pattern could continue over the next couple of weeks.
“If you ask me, the smartest forecast going longer term is probably persistence. In other words, what have we just seen? That will keep going until there’s some big overwhelming push to shove the atmosphere in a different direction,” he says.
Things should dry out for fall harvest. To understand the possible change in the weather pattern, watch Snodgrass’ full forecast from U.S. Farm Report.
