HOUSTON – It’s been a hot week in Houston. Every day we’ve seen heat advisories with heat index values up to110° in the afternoon. This happens from time to time when Houston is in a heat dome, and every time there’s always a few viewers who don’t quite understand the heat index. Take this email the weather team received on Monday:
Viewer: “Why do y’all continue to emphasize the heat index? This is Texas in August and I believe our temperatures are normal but y’all focus on an extreme number instead of a normal number? I do recognize that precautions must be taken but DONT over use it. The sky isn’t falling but watch out and be prepared.”
First of all, thank you for the email. It’s always helpful for us to know how y’all are feeling! In this case I realized we haven’t explained the heat index much this year since this is our first big hot stretch.
So what is it? Why are we using it?
The heat index value is a combination of temperature and humidity. We use the heat index because this is what the outside feels like to our body. We want y’all to be prepared for the day.
How do we know what it feels like for you?
It’s a scientific calculation based on the human body! When we are hot, we produce sweat. This sweat evaporates from our skin, which is actually a cooling mechanism!
The human body has a hard time cooling down efficiently when we are so humid because evaporation slows down. This means we will feel much hotter, i.e. the feels like temperature (or heat index) is several degrees warmer than the actual air temperature.
Take a look at this chart from the National Weather Service. This is an easy way to determine what the heat index is using the relative humidity and temperature.
To circle back to the email, we use the heat index because it’s a more accurate representation of the conditions outside. We are not trying to scare anybody or make the heat seem worse than it is. The fact is, it just is that bad.
Our heat alerts are issued based on a list of criteria set by the National Weather Service. In order for a heat advisory to be issued we either need our air temperature to reach 103° or for our heat index to reach 108°. This week we reached the heat index criteria, which is why the heat advisory was issued and why our team has focused on the heat index.
We really do love to hear from y’all and answer your questions. If you have a question for our weather team, you can email us at weather@kprc.com .