Large swaths of the US Midwest are experiencing extreme humidity, with meteorologists describing the conditions as a 'zone of sweaty despair.' In parts of Illinois and Iowa, humidity levels are rivaling and even exceeding those found in the Amazon rainforest due to a combination of a powerful heat dome and the natural process of corn evapotranspiration.
The National Weather Service (NWS) has issued Extreme Heat Warnings for much of Illinois and Iowa, forecasting heat index values up to 110°F. This oppressive weather is attributed to a persistent high-pressure system over the Tennessee River Valley, coupled with a significant influx of atmospheric moisture.
Corn fields, particularly during their peak growth phase, are contributing substantially to the humidity. According to climate scientists, a single acre of mature corn can release between 2,000 and 4,000 gallons of water vapor daily through evapotranspiration, a process colloquially referred to as 'corn sweat.' This released moisture becomes trapped near the ground, pushing dew point temperatures into the high 70s in affected areas.
Forecasters noted that the highest recorded dew point in the Amazon rainforest is 79°F, indicating that parts of the Midwest could briefly experience even higher humidity. Experts describe the phenomenon as 'thick and oppressive,' likening it to being in a sauna or steam room, especially when there is little wind.
This intense humidity is further exacerbated by a 'mega' or 'double heat dome' – a merging of two separate high-pressure systems, one originating from the Southwest and another influenced by the subtropical Atlantic. This massive dome acts like a lid, trapping hot air at the surface, suppressing cloud formation, and intensifying sunlight.
In Illinois, the Extreme Heat Warning covers nearly the entire state. Central and southeastern regions, including cities like Springfield and Peoria, anticipate heat index values between 105°F and 110°F. Northern Illinois, encompassing areas around Chicago, is also under a warning with expected afternoon heat index values around 105°F. Some relief from thunderstorms is possible in northern Illinois by Thursday afternoon or evening, but dangerous heat is expected to persist.
Iowa faces similar conditions. Southern and southeastern parts of the state, including Des Moines, are under an Extreme Heat Warning with heat index values projected to reach 104°F. Central and eastern Iowa are under warnings through Wednesday night, while northwestern Iowa is experiencing heat index values up to 102°F.
The prolonged nature of this heat wave is a significant concern, with overnight temperatures expected to remain in the mid- to upper 70s. This offers little respite, making it difficult for individuals without air conditioning to cool their homes and recover from the daytime heat.
The NWS has emphasized that heat-related illnesses increase significantly under extreme heat and humidity. Residents are urged to drink plenty of fluids, stay in air-conditioned environments, and avoid strenuous outdoor activities during peak heat. Those who must work outdoors should take frequent breaks and limit exertion to the cooler parts of the day. Officials also issued a critical warning against leaving children and pets unattended in vehicles, as interior temperatures can become lethal within minutes.
With the heat wave projected to last several more days, authorities are advising residents in Illinois and Iowa to check on vulnerable individuals, including the elderly and those without access to cooling, to prevent heat-related fatalities.