Calculating heat index and why we feel sticky on a muggy day

July 28, 2023
It's a long equation to calculate heat index, but here is a simple way
Published: Jul. 28, 2023 at 6:06 PM CDT
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HASTINGS, Neb. (KSNB) - You don’t need me to tell you it’s been hot and muggy this week. The air temperature may be 98 degrees Fahrenheit, but it feels more like 110. So, how is the heat index calculated and why does it feel like you are wearing the air when you step outside? You may be familiar with the heat index chart that correlates relative humidity with the air temperature. How do we get these feel like temperatures? Let’s bring out my dry erase board. The equation for calculating heat index looks like this.

It's complicated
It's complicated(KSNB)

Where T equals temperature and R equals relative humidity. Yeah. It’s a bit complicated. To skip the math, there is a heat index calculator on the National Weather Service website. You just punch in the air temperature and either the dew point or relative humidity and, voila, the math is done for you. Or we could simply go back to the chart and pinpoint the heat index.

The math is done for you
The math is done for you(KSNB)

For the example above, if the humidity is 55 percent and the air temperature, in the shade mind you, is 96 degrees Fahrenheit, you can calculate the heat index where the row and column intersect. In this scenario, the feel-like temperature would be 112 degrees. As if 96 degrees isn’t bad enough. Now to answer why we feel sticky.

When our bodies get hot, they sweat to cool down
When our bodies get hot, they sweat to cool down(KSNB)

Our body wants to stay near 98.6 degrees. When it gets hot outside, our body heats up. Our bodies sweat in order to cool back down to it’s normal temperature. It does this by a process known as evaporative cooling. As the sweat evaporates from our skin, it draws heat away from our body. On muggy days, however, sweat fails to evaporate efficiently due to the air being filled with so much water vapor. The sweat remains on your skin making you feel wet and muggy. It can be just down right oppressive.