Every summer, it happens.
You step outside expecting another warm July afternoon, but instead you’re greeted by air so thick it almost feels like you could wear it. You immediately start sweating before you’ve even made it to your car. The air feels heavy. Sticky. Oppressive. You look at your weather app and think, “It’s only 91 degrees. Why does it feel so much worse?”
Believe it or not, the answer may be growing just a few miles down the road.
As I travel throughout eastern Missouri and southern Illinois, one thing is impossible to miss this time of year: corn. It stretches for miles in every direction, standing tall under the summer sun. To many, it’s simply another crop. To a farmer, it’s a livelihood. But to a meteorologist, it’s something else entirely.
It’s part of the forecast.
Yes, corn sweats.
The scientific term is transpiration, but “corn sweat” has become the nickname because it paints a pretty accurate picture. Corn absorbs water from the ground through its roots and moves that moisture throughout the plant as it grows. During hot summer days, tiny openings on each leaf release water vapor into the atmosphere. It’s the plant’s natural way of regulating itself, much like our bodies sweat to cool down.
One plant doesn’t make much difference.
One field certainly does.
During peak growing season, an acre of mature corn can release 3,000 to 4,000 gallons of water into the atmosphere every single day. When you consider there are millions of acres of corn across the Midwest, that’s an incredible amount of moisture being added to the air around us. Nature has essentially created one giant humidifier.
It’s one reason why Midwest summers feel so different than summers in many other parts of the country.
People often ask me whether corn sweat actually makes the temperature hotter. The answer is no... at least not directly. What it does is increase the humidity, and that’s what makes the heat feel so much more uncomfortable.
As meteorologists, we pay close attention to something called the dew point, which tells us how much moisture is in the atmosphere. Once dew points climb into the 70s, the air begins to feel tropical. Your body’s cooling system becomes less efficient because sweat can no longer evaporate as quickly from your skin. Instead of cooling you, it simply sits there.
That’s why a day with an actual temperature of 92 degrees can easily feel like 102 or even 107 degrees.
It’s also why we issue Heat Advisories and Extreme Heat Warnings based on the heat index, not just the air temperature. Heat doesn’t have to break records to become dangerous. Add enough humidity, and the human body begins working much harder just to stay cool.
Corn sweat also plays a role after the sun goes down.
Have you ever noticed how some summer nights never seem to cool off? You wait for relief after sunset, but by 10 or 11 o’clock it still feels warm and muggy outside. That’s because moisture acts like a blanket in the atmosphere, slowing the rate at which temperatures fall overnight. Those warm nights are more than just uncomfortable. They don’t allow our bodies enough time to recover from the daytime heat, especially during extended heat waves.
There’s another interesting piece to this story.
That extra moisture can also become fuel for thunderstorms. Corn doesn’t create storms by itself, but when a cold front, upper-level disturbance, or other lifting mechanism arrives, all of that added humidity provides another ingredient for developing showers and thunderstorms. Weather is rarely influenced by just one thing. It’s a constant interaction between the atmosphere, the land, the water, and yes, even the crops growing in our fields.
That’s one of the reasons I’ve always loved meteorology. The deeper you look, the more you realize weather isn’t just happening thousands of feet above our heads. It’s happening all around us. Rivers influence it. Lakes influence it. Cities influence it. Forests influence it. Even the ground beneath our feet plays a role.
And every July, so does the corn.
The next time you’re driving through the countryside and pass those endless rows of green stretching toward the horizon, remember you’re looking at more than this year’s harvest. You’re looking at millions of living plants quietly exchanging moisture with the atmosphere, helping shape the weather we all experience.
It’s another reminder that some of the most fascinating weather stories aren’t always found inside a tornado, hurricane, or snowstorm. Sometimes they’re hiding in plain sight, right outside our window.
Until next week, keep looking up... because there’s always something new to discover about the weather.
This is Dr. Nick, and that’s today’s Weather from My Window.
