Missouri’s Heat Wave Meets ‘Corn Sweat’
Susan Smith Kline
In late July 2025, Missouri is experiencing an oppressive heat dome—a large high-pressure system that traps hot, tropical air over the Central Plains. Forecasts predict daytime high temperatures near or above 100°F, with humidity pushing heat index values into the 110–120°F range in areas like southern and central Missouri.
The term “corn sweat” may sound whimsical, but in Missouri, this late-July phenomenon is anything but trivial. It exacerbates already dangerous heat conditions, creating a summer climate filled with discomfort and risk. As global temperatures continue to rise, the Midwest is likely to face more frequent “sweaty” heat waves, making it essential for residents to stay informed, vigilant, and prepared.
This region of Missouri is part of the U.S. Corn Belt, and right now, cornfields are at their peak pollination stage, a process that involves the plants releasing moisture through evapotranspiration. Corn sweat refers to this process, during which corn absorbs water from the soil and releases it through its leaves, adding significant moisture to the air.
A single acre of mature corn can emit between 3,000 to 4,000 gallons of water per day. When this process is multiplied across millions of acres throughout Missouri, the impact on humidity is substantial.
As humidity levels rise, the dew point also increases, with regional weather stations reporting dew points nearing 88°F, among the highest ever recorded. This humid, swampy air prevents the human body from cooling effectively through sweat evaporation, leading to heat indices that often soar beyond 115°F, and sometimes approach 128°F in southern Missouri.
This oppressive air persists well into the night, with minimal cooling overnight further increasing health risks.
Extreme heat is the deadliest weather hazard in the U.S. Heat-related illnesses, such as heat stroke, dehydration, and aggravated heart conditions, pose serious threats, especially for vulnerable populations and outdoor workers.
Agriculturally, farmers face challenges due to accelerated plant growth, poor root development caused by early-season excess moisture, and an increased risk of crop diseases or reduced yields if rain does not arrive on time.
For cattle, the cumulative effect of two heat waves, combined with the humidity from cornfields, can be fatal, particularly when overnight temperatures remain above 70°F.
This extreme weather pattern is part of a larger warming trend: Missouri has already warmed by about 0.5–1°F over the last century and is projected to experience many more days above 95°F in the coming decades, with summers potentially resembling today’s climate in Arizona by 2100.
The current heat dome is expected to persist through early August. While a cool air mass from Greenland may arrive in early August to provide temporary relief, summer heat is forecasted to return around mid-August.
This dual threat of heat and humidity is likely to continue until harvest season, unless there are significant weather changes.
What You Can Do:
– Stay hydrated and wear lightweight, breathable clothing.
– Limit outdoor activities, especially during late morning to late afternoon.
– Use air conditioning or visit cooling centers. Missouri laws prohibit utility disconnection when forecast temperatures exceed 95°F or the heat index reaches 105°F.
– Check on vulnerable neighbors, particularly those without access to cooling.
