The summer of 2025 is shaping up to be one of the most humid on record across the U.S. Midwest, and corn sweat is playing a leading role. While meteorologists anticipated potential drought in many parts of the country earlier this year, states in the Corn Belt have experienced an overabundance of rain, moisture, and unbearable heat.

According to meteorologist Ryan Maue, the heat index soared to 115°F in Iowa on a recent July evening. What's extraordinary is that 20°F to 25°F of that stifling heat was attributed to cornfields alone. This is not just about temperature; it's about a surge in atmospheric moisture unlike anything typical for the region.

Corn Sweat: The Biological Humidifier

So what exactly is corn sweat? It's a form of plant transpiration, a biological process where corn draws water from the soil and releases it through tiny pores in its leaves. This water vapor then enters the atmosphere, contributing to local humidity.

"Each acre of corn can evaporate an additional 4,000 gallons of water into the atmosphere," says Eric Snodgrass, principal atmospheric scientist at Nutrien. "That might not sound like much, but multiplied over 95 million acres of corn, it adds up fast."

The impact is not merely theoretical. High levels of dew point humidity - such as the low 80°F readings reported by Maue - have coincided with areas of intense corn cultivation. These levels aren't unheard of, but they are relatively rare and highly uncomfortable, adding to livestock heat stress and complicating fieldwork.

The Gulf's Endless Pipeline

Corn isn't working alone. This year, the Midwest has had nonstop access to Gulf moisture, according to Snodgrass. The atmosphere has essentially been wide open for storm systems riding along a persistent high-pressure ridge centered further south.

"There's just been nothing turning that off," says Snodgrass. This access to Gulf moisture has enabled the development of large, slow-moving storm systems, including the recent ones that triggered flash flooding across Iowa, Illinois, and Missouri.

These systems, known as ridge-riders, skim the edge of high-pressure zones and feed off high atmospheric moisture. With a saturated landscape, even modest rainfall rates can lead to flooding, erosion, and delays in field operations.

Agricultural Impacts and Forecasts

While the current wet pattern poses short-term challenges such as delayed fungicide applications and harvest scheduling, it also brings some potential benefits. Crops in many areas have avoided drought stress, and the ample moisture could support above-average yields - assuming dry-down occurs in time for harvest.

Looking ahead, Snodgrass suggests the weather pattern is likely to persist. "If you ask me, the smartest forecast going longer term is probably persistence," he notes. This implies continued humidity and storm potential until a significant atmospheric shift occurs.

However, there is hope on the horizon. As corn reaches full maturity, its transpiration rates decline. That means the Midwest is now in peak 'corn sweat' season, and the worst of the dew point intensity may soon ease.

For now, agriculture professionals across the Midwest are urged to monitor weather patterns closely, adjust field schedules accordingly, and prepare for continued moisture and storm risks in the coming weeks.