Heat Index… is it really a thing?

Columbus (WCMH) – It is a discussion in many weather departments all over the country, are heat index and wind chills real things?

Well, ask anyone that lives in a climate that enjoys these two things and they will tell you it is real.  But what exactly is it?

 

Heat index is a value that is calculated using the air temperature and moisture content of the air:

According the National Weather Service, below is how to calculate the Heat Index outside

HI = -42.379 + 2.04901523*T + 10.14333127*RH – .22475541*T*RH – .00683783*T*T – .05481717*RH*RH + .00122874*T*T*RH + .00085282*T*RH*RH – .00000199*T*T*RH*RH

There are some adjustments however to this to make up for hotter and cooler temps, also lower humidity.

How heat index impacts you:

In a nutshell, heat index impacts humans, and how our bodies cool off.  So if the outside temperature is 95° and the heat index is 115° we are not going to see an egg cook outside.

But, your body will have difficulty trying to cool itself off.

To understand how this works, first you have to understand what sweating does to you. (I put this rough drawing together to explain)

 

When your body gets heated up, your body will sweat (blue splotches on arms on drawing above), and this sweat will appear on your skin, and hopefully if things work correctly, that sweat will evaporate (light blue lines coming off arms in diagram above) off your skin.

This process of the sweat evaporating is an “endothermic process” meaning it takes energy, or heat, away from your body as it occurs.  This makes your body feel slightly cooler!

When it is hot, your body gets hot and it sweats to cool itself.  If it is hot and dry, the air around your body is very accepting of moisture, and will evaporate the sweat easily.  If the humidity is high on a hot day (high heat index), the air around your body is already pretty full of moisture so evaporation will be slow to stopped.

This means the process of sweating will only make you (and your clothes) more wet, but not too much cooler.

 

Something else to remember about hot weather:

If it is hot and dry, or hot and humid, when you sweat, you are losing fluids and nutrients in your body through your sweat.  While your body is trying to cool itself, it is also dehydrating itself.  So always make sure to stay hydrated when outside on hot days, and taking frequent breaks can be the difference in keeping your body “cool”  this summer!

 

Next time someone claims heat index is not a real thing, you can reference this page.  If they ever claim wind chill isn’t real, just invite them over on a windy January afternoon!  🙂

 

If you ever have questions about heat, humidity, heat index, wind chills, or any other weather question, email me: dmazza@wcmh.com

-Dave

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