WX Blog: Heat Index and You


Beckley, WV (WVNS) — Are you prepared for the heat? More importantly, do you understand what it means when someone says the ‘Heat Index’ is approaching X°?

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RELATED: Weather 101: What is the heat index?

The ‘Heat Index,’ simply put, is the polar opposite of ‘Wind Chill’. ‘Wind Chill’ is a function of wind speed and air temperature that is used when the apparent, or ‘feels like’ temperature, is less than the actual temperature. ‘Heat Index,’ on the other hand, is a function of relative humidity (i.e. the percentage of water vapor in the air in relation to its saturation point), and the air temperature, this is used in situations in which the apparent temperature is higher than the actual temperature.

Courtesy: National Weather Service/NOAA

Above is a chart from the National Weather Service depicting how different levels of relative humidity and temperatures interact and the respective ‘Heat Index’ value that corresponds with it. You’ll notice how there seem to be different levels depicted on the chart and the legend that corresponds with each color at the bottom. These colors correspond to the likelihood of developing a ‘heat disorder’, also referred to as either Heat Exhaustion and Heat Stroke.

Courtesy: National Weather Service/NOAA

According to the CDC from 1999 to 2010 more than 8,000 people lost their lives to a heat related illness, the group with the highest percentage of that list was adults 65 and older. When dealing with situations where excessive heat will be an issue here are some tips from the National Weather Service to make sure you can stay safe:

  • Dress for summer. Wear lightweight, loose fitting, light-colored clothing to reflect heat and sunlight.
  • Drink plenty of water (not very cold), non-alcoholic and decaffeinated fluids, even if you don’t feel thirsty.
  • Use portable electric fans to exhaust hot air from rooms or draw in cooler air.
  • Do not direct the flow of portable electric fans toward yourself when room temperature is hotter than 90°F. The dry blowing air will dehydrate you faster, endangering your health.
  • Minimize direct exposure to the sun. Sunburn reduces your body’s ability to dissipate heat.
  • Check on older, sick, or frail people who may need help responding to the heat. Each year, dozens of children and untold numbers of pets left in parked vehicles die from hyperthermia. 
  • Touch a child’s safety seat and safety belt before using it to ensure it’s not too hot before securing a child
  • Never leave a child unattended in a vehicle, even with the windows down, even for just a minute

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