Millions under threat of extreme heat. Do you live in the 'danger' zone? See heat map
Extreme heat warnings, advisories and watches are in effect across several states Wednesday, July 23, as a powerful heat dome tightens its grip over the Mississippi Valley. The National Weather Service says the dome will slowly expand eastward through the week, pushing dangerous temperatures and stifling humidity into new regions.
In many areas along and east of the Mississippi River, heat index values could soar to between 110 and 115 degrees — the kind of oppressive heat that can quickly turn dangerous without proper precautions.
By Thursday, July 24, the dome's reach is expected to stretch into the Great Lakes and Northeast, bringing the intense summer scorch with it.
"While this is not really a record-breaking air mass in terms of high temperatures, some towns and cities will struggle to drop below 80 degrees at night due to the high humidity levels and retention of heat by vast areas of concrete and pavement," AccuWeather Senior Meteorologist Brett Anderson said Wednesday. "For those that only have a fan or open window to keep cool, sleeping will be difficult for some, with a high risk of dehydration."
And in Texas, summer doesn't just hit harder — it sticks around longer. The first 90-degree days are arriving earlier, and stretches of triple-digit heat are lasting longer than ever, a USA TODAY analysis found.
National heat index map: How hot is it in your city?
The map below identifies areas where the heat index is forecasted to reach NWS-defined levels from "Caution" (80 degrees Fahrenheit) to "Extreme Danger" (above 125 degrees).
The heat index measures how hot it actually feels when factoring for humidity. Prolonged exposure to a heat index above 80 degrees can lead to fatigue, as previously reported by USA TODAY. As it gets hotter, the risk continues to increase − potentially resulting in heat stroke or even death. Older adults, children, and outdoor workers are generally at higher risk of heat-related incidents.
Search the heat index in your area
Is your city getting hotter? It's possible! You can check the heat index forecast here to find out!
What's the difference between temperature and heat index?
The temperature is the actual air reading — what a thermometer records in the shade. The heat index, on the other hand, represents what it feels like to the human body when both temperature and humidity are factored in, according to the National Weather Service.
When humidity is high, sweat doesn't evaporate as easily, making it harder for your body to cool down. That's why the heat index is often higher than the air temperature, and why it's used to gauge the risk of heat-related illness.
This article originally appeared on Austin American-Statesman: Extreme heat scorches US. Are you in the 'danger' zone? See map
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