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How the heat index works


Temperatures across Kansas have been well over 100° in the last several days bringing our first stretch of that Kansas summer heat we have grown accustomed to. Every weather report you watch or read talks about the heat index being well past the 100° mark causing some major issues for a lot of people. But the question remains; what is the heat index?

In a nutshell, the heat index is the 'feels like' temperature, or what the temperature feels like to our bodies regardless of what the thermometer shows. To understand the heat index you have to dive into how the human body works. Our body's natural air conditioning is sweat. That sweat evaporates from our bodies, which takes heat away from our skin and makes our bodies feel cooler.

But there's a catch. In order for our bodies to cool efficiently you really need dry air. The more water vapor there already is in the air, the harder it is for more vapor to be absorbed by the surrounding air. Our relative humidity (or the amount of moisture in the air) has been extremely high over the last couple of weeks. This makes it difficult for the sweat our bodies create to evaporate quickly enough to cool us down. When that happens, the perceived temperature for our bodies is actually higher than the actual air temperature.

You often hear the phrase, "Yeah, but it is a dry heat." That phrase actually does have credence. Areas like Arizona or Montana don't have an abundance of moisture like we do in the Midwest. That means that when you have extreme heat with no humidity, our bodies will cool efficiently and make it more comfortable than it would otherwise be in a extremely humid environment.

Here are a few tips to help beat the heat.

1) Drink plenty of water

2) Wear light-colored and loose-fitting cotton clothing

3) Take plenty of breaks in the AC or in the shade

4) Avoid alcohol or caffeinated drinks


Leslie Swearingen 8 years, 11 months ago

That is the best explanation I have read as to how the heat index works.

DeMontfort 8 years, 11 months ago

Ahh, but Matt...how exactly is it calculated?

Matt Elwell 8 years, 11 months ago

You asked for it!

Heat Index = -42.379 + 2.04901523T + 10.14333127R - 0.22475541TR - 6.83783x10-3T2 - 5.481717x10-2R2 + 1.22874x10-3T2R + 8.5282x10-4TR2 - 1.99x10-6T2R2

where T = ambient dry bulb temperature (°F) R = relative humidity (integer percentage).

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