Heat Index – What Is It?

Have you ever walked outside on a 90-degree day and it “feels like” the upper 90s and possibly the triple digits? That “feels like” temperature is known as the heat index.

One way to calculate heat index temperatures starts with air and dew point temperatures. For example, if the air temperature on a given day is 95 degrees and dew point temperature is at an uncomfortable 70 degrees, then the resulting heat index would be a scorching 102 degrees. 

Another way of finding heat indices would involve the air temperature once more on a given day but instead pairing it with the relative humidity. Similar to the previous example, if the air temperature is 95 degrees and the relative humidity is 50 percent, then the resulting heat index would be a toasty 105 degrees. 

The National Weather Service issues heat-related alerts once heat index temperatures are expected to exceed 100 degrees for consecutive days (at least 2). One wild card with these calculations is how much wind is blowing on a given day. If there is a calm wind, then heat indices will be virtually unaffected. However, strong and warm winds could result in heat indices being inflated by 15 degrees. This is especially true if there is no shade available. 

It is of the upmost importance to check your WeatherBug app and local weather forecast, especially during the summer months. Heat-related illnesses can result from over exposure to dangerously high heat indices. Those more susceptible to heat-related illnesses include animals, small children and elderly. Be sure to limit heat-sensitive groups outdoor exposure and make sure to stay hydrated during the sweltering summer months!

Source: National Weather Service (NWS)

Image:  NWS Heat Index chart. (National Weather Service)