Friday, August 13, 2010

What the Heat Index is all about

Over the past couple of weeks, you have heard us talk about the dangerous heat levels across East Texas. Even though the air temperatures have only been around 100, it is the heat index, or feels like temperature, that has made it very uncomfortable to be outdoors.

The heat index is what we call the "apparent" temperature in addition to the feels like temperature. This value is calculated by taking into account both the actual air temperature and the humidity.

When you go outside, your body is trying to cool down, not from the air temperature, but from the heat index all-together. Our heat indices have been running from 107-112° during the heating of the day.

Anyting over 105° is dangerous and anything over 110° is when it becomes a reality that heat fatigue and possible heat exhaustion could set in.

The chart above is a heat index chart, calculating the feels like temperature when taking into account the air temperature and relative humidity.

To show you just how important the humidity plays a role in our feels like temperatures, take this scenario. If we had an air temperature of 96° with 50% humidity, it would give us a heat index value of 108°. On the other hand, let's say the temperature was 100° with 40% humidity. The heat index in this case would be about the same.

The bottom line is it can be just as dangerous to have temperatures a few degrees lower, but with slightly higher humidity values than higher temperatures and lower humidity values.

That is why when we show you the heat index on the air, it is a better representation of what your body has to go through in order to cool itself down.