Illinois and Iowa are under Extreme Heat Warnings as a high-pressure system drives heat indices to 110°F across large parts of both states.

Dew points have climbed near 80°F, pushing conditions more humid than typical readings in the Amazon rainforest.

The combination of temperatures in the upper 90s and moisture from agricultural sources has created dangerous “feels-like” values that threaten public health through the end of the week.

The National Weather Service issued the warnings for nearly all of Illinois and much of Iowa, with the most intense heat expected through Thursday night. Overnight lows in the mid to upper 70s will provide minimal cooling, increasing the risk of heat-related illnesses for those without air conditioning.

Corn Fields Add to Regional Humidity

Mature corn crops in the Corn Belt release 2,000 to 4,000 gallons of water vapor per acre daily through evapotranspiration.

This process, often called corn sweat, contributes measurable moisture to the lower atmosphere, especially under a heat dome that traps air near the surface.

A single high-pressure system over the Tennessee River Valley, combined with broader moisture from the south, has merged into what forecasters describe as a double heat dome covering much of the central United States.

In Illinois, cities including Springfield, Peoria, Champaign, and Chicago suburbs face heat indices between 105°F and 110°F. Similar conditions grip Des Moines and other Iowa communities, with peaks at 104°F.

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The phenomenon occurs as corn reaches peak growth. The added water vapor raises dew points, making the air feel thicker and reducing the effectiveness of natural cooling through perspiration.

Warnings Cover Wide Areas

The National Weather Service warned that heat-related illnesses rise sharply in these conditions. Central and southeast Illinois remain under warnings through Thursday night. Northern Illinois, including areas near Rockford and Joliet, faces similar risks until thunderstorms possibly arrive later in the week.

In Iowa, southern and southeast portions including Des Moines stay under warnings through Thursday evening. Central and eastern counties face elevated risks through Wednesday night, with northwest areas seeing heat indices near 102°F.

Forecasters noted that prolonged exposure, even indoors without cooling, can lead to exhaustion, heat stroke, and other complications. Young children, older adults, and outdoor workers face higher vulnerability.

Health Risks and Local Impacts

High humidity prevents efficient sweat evaporation, causing core body temperatures to rise faster than in drier heat. Officials reported increased emergency calls during similar past events.

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The current pattern offers little relief at night, preventing recovery for residents in older housing or without reliable power.

Thunderstorms may bring temporary breaks in northern Illinois, but the overall heat dome is expected to persist for several days. Agricultural regions feel the dual pressure of extreme weather on both people and crops.

How to Protect Yourself

To protect yourself, Americans are advised to drink water regularly, even before feeling thirsty. Stay in air-conditioned spaces during peak afternoon hours. Avoid strenuous outdoor work; schedule necessary tasks for early morning or evening.

Take frequent breaks if working outside. Wear lightweight, loose clothing. Check on neighbors, especially the elderly or those with medical conditions. Never leave children or pets in vehicles, where temperatures can become lethal within minutes.

The National Weather Service recommends monitoring local forecasts and using fans alongside other cooling methods. For those without home air conditioning, seek public cooling centers or community facilities.

Residents should prepare for continued heat through the weekend. Simple steps such as limiting activity and maintaining hydration can prevent serious outcomes in these record-challenging conditions.