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By Amanda Greenwood
Associate News Editor
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A sprawling heat wave is gripping large parts of the United States, with National Weather Service (NWS) offices issuing Extreme Heat Warnings across 19 states as dangerously high temperatures and oppressive humidity raise the risk of heat-related illness.
Warnings issued on Monday stretch from the deserts of California and Arizona to the Midwest and parts of the South, affecting millions of Americans as forecasters urge residents to “stay out of the sun” during the hottest part of the day, keep hydrated, and avoid prolonged sun exposure.
Which States Are Affected?
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Based on the NWS warnings, Extreme Heat Warnings are in effect for certain parts of the following 19 states:
- Arizona
- Arkansas
- California
- Illinois
- Indiana
- Iowa
- Kansas
- Kentucky
- Minnesota
- Mississippi
- Missouri
- Montana
- Nebraska
- Nevada
- Oklahoma
- Tennessee
- Texas
- Utah
- Wisconsin
The warnings cover hundreds of counties and numerous major population centers, including parts of the Phoenix metropolitan area, Las Vegas Valley, St. Louis region, Memphis area, Little Rock region and communities across Illinois, Iowa and Kansas.
How Hot Will It Get?
Temperatures vary by region, but some of the most extreme conditions are expected in the Southwest.
In Arizona, southeastern California and southern Nevada, afternoon highs are forecast to reach between 108 and 116 degrees Fahrenheit, with some lower-elevation areas of Death Valley potentially reaching 120 degrees.
Elsewhere, dangerous heat combined with high humidity is pushing heat index values—the "feels like" temperatures—to between 110 and 117 degrees across parts of Tennessee, Arkansas, Mississippi, Missouri, Illinois, Iowa, Kansas, Nebraska and Oklahoma.
Even northern states under warning are facing unusual heat. Parts of eastern Montana are expected to approach or exceed 100 degrees, while areas of Minnesota and Wisconsin could see heat index values near 110 degrees.
Forecasters warn that warm overnight temperatures, in some cases remaining in the 80s and low 90s, will provide little relief and increase cumulative heat stress.
What Is a Heat Dome?
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The widespread heat is being driven by what meteorologists commonly call a "heat dome."
According to NOAA, a heat dome develops when a large, strong area of high pressure becomes parked over a region for an extended period. The high-pressure system acts like a lid on the atmosphere, trapping hot air near the surface and preventing cooler air from moving in.
As the air sinks beneath the high-pressure system, it compresses and warms further. Day after day, temperatures build, and the longer the pattern persists, the more dangerous conditions can become.
Heat domes are often associated with prolonged heat waves and can affect multiple states simultaneously, especially during the peak summer months.
How Long Will It Last?
The duration varies by location.
Several warnings across California, Nevada, Utah and Nebraska are scheduled to expire Monday evening, while warnings covering parts of Arkansas, Tennessee, Missouri, Kentucky and Mississippi remain in effect through Tuesday.
In the Phoenix metropolitan area and nearby portions of Arizona, some warnings are set to continue through Wednesday evening.
Forecasters expect the most intense heat to gradually ease in parts of the Midwest during the first half of the week, though dangerous conditions could persist longer across portions of the Southwest and South.
Residents are advised to monitor local forecasts, as warnings may be extended if temperatures remain higher than expected.
How Can People Stay Safe?
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The NWS is urging people to take heat warnings seriously.
Officials recommend:
- Drinking plenty of water, even if not thirsty.
- Staying in air-conditioned buildings whenever possible.
- Avoiding strenuous outdoor activity during the hottest hours of the day.
- Wearing lightweight, loose-fitting clothing.
- Checking on elderly relatives, neighbors and vulnerable individuals.
- Never leaving children or pets in vehicles.
- Taking frequent breaks in shaded or cooled areas if working outdoors.
The agency repeatedly emphasized one key message across Monday's warnings: "Stay out of the sun" and seek cool environments whenever possible.
With temperatures reaching well above 100 degrees and humidity making conditions feel even hotter, officials say heat-related illnesses can develop rapidly, especially among older adults, young children, outdoor workers and people without reliable access to air conditioning.
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