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What is the heat index, and why does it matter?

You've probably heard the meteorologist tell you the "heat index" or the "feels like" temperature, but what does that mean?

MEMPHIS, Tenn. — It's summertime in Memphis, which means you’ve probably heard something about the heat index or “feels like” temperature.

In fact, the heat index is often 10 to 15 degrees above the actual temperature this time of year in the Mid-South.

So, what gives? Well, you may already know the answer, even if you don’t realize it.

You’ve probably heard the phrase “it’s not the heat, it’s the humidity” when talking about summer in the Mid-South. And that’s where the heat index comes into play.


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♬ Intro - The xx

Thanks to our proximity to the Gulf of Mexico, the moisture content of our air is usually high. This gives our air a humid, soupy feel in the summertime.

When your body gets hot, it naturally produces sweat to cool you off. This works because evaporation is a cooling process. So, when your body produces sweat, it evaporates off your skin, and cools you down.

When it’s humid outside, sweat (or any liquid, for that matter) can’t evaporate as quickly. This means you don’t cool down as well as you would if that sweat were able to evaporate.

In drier climates like California or Nevada, sweat evaporates quickly, providing a little extra relief even though the actual temperature may be hotter.

The bottom line is, the more moisture in the air, the higher the humidity, the less sweat evaporates from your body, and the hotter your skin feels.

Typically, heat index values over 105 are considered dangerous, and you should limit time outdoors. If you have to be outside in extreme heat, stay hydrated and take frequent breaks in the shade.


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