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Why You Should Sweat the Heat Index

Gabriel Cristóver Pérez
Revelers enjoy Willie Nelson's 4th of July Picnic at the Austin360 Amphitheater at Circuit of the Americas.

It's summer in Texas. That means it's hot, but just how hot? That depends on what temperature you pay attention to.  In our reporting, we often provide two different numbers. There's  the air temperature – that's the temperature of the outdoor air in the shade. Then, there's the "heat index" – that's how hot it's supposed to feel outside, when you take humidity into account.  

Some skepticsargue that reporting those two numbers is unnecessary or even misleading. "Why bother tacking on a few extra degrees whenever you read the weather?" they might argue. "Hot is hot!"

But the heat index is about more than just adding extra degrees to the outdoor temperature, says Meteorologist Rich Segal with Time Warner Cable News. He says when the heat index  is high, people have a harder time cooling off. 

"What happens is when the body starts to get too hot, it starts to perspire sweat to cool itself off," says Segal. "But, if the perspiration is not able to evaporate (in high humidity), then the body's temperature cant be regulated, and some people do suffer from heat fatigue.

Credit Chart Courtesy of NOAA

When looked at that way, reporting on the heat index becomes a public health service. 

How high can the heat index go? Segal says it adds about five to seven degrees on average during humid summer days in Austin. But in East Texas heat the heat index can go even higher.

"In Houston, Galveston, Beaumont on certain days you'll get heat index values of anywhere from 108 to 115," says Segal. "That's when they'll issue heat advisories for the area."

Mose Buchele focuses on energy and environmental reporting at KUT. Got a tip? Email him at Follow him on Twitter @mosebuchele.
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