Heat Index Explained

Heat Index Chart Dewpoint

The summer heat is taking over and the heat index has become a big part of the weather forecast lately. So what is the heat index and how is it determined?

The heat index is calculated by combining the air temperature with the relative humidity. This helps determine the human-perceived equivalent temperature – or how hot it actually feels to us. Simply put, if the humidity is high and so are the temperatures, then the heat index will be higher as well. You can take a look at the attached chart and play around with some of the numbers.

The chart shows air temperature at the top (x-axis) and the dew point temperature on the left (y-axis). Dew point is another way of measuring humidity and is the best way to assist in determining the heat index. For example, on the chart, if the temperature is 92° and the dew point is 76°, the heat index will be 105°. The National Weather Service will issue Heat Advisories if the heat index gets to 105° and they’ll issue Excessive Heat Warnings if the heat index reaches 110°. These advisories and warnings are meant to help the public stay safe and aware of the dangers of heat exhaustion and heat stroke.

The heat index is an important factor during the summer because our bodies have a hard time cooling off when the humidity is high. We sweat for a reason, and that is to remove heat and cool us down. When the humidity is high, then the temperature feels hotter to us because the cooling process is reduced. Below is a look at some tips on how to stay cool this summer.

If you want some more information on the heat index, our very own meteorologist Ulises Garcia did a Weather Tidbits segment on it. You can watch it by clicking here:


Categories: Weather Blog