Heat Index Information Online!

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heat index graph

In their June 24 blog post, the NC State Climate Office (SCO) discusses the history of the heat index and how it is calculated.  Basically, the heat index is a way to determine how warm the outside temperature feels when relative humidity is also considered. In eastern NC, the heat index can be an important consideration when planning summer outdoor activities.  To help people, the SCO has a website where you can see the current heat index (and other values) for sites across the state.  Be informed and stay safe this summer!

Terms:

Excessive Heat Watch:  Issued by the National Weather Service when heat indices in excess of 105ºF (41ºC) during the day, combined with nighttime low temperatures of 80ºF (27ºC) or higher, are forecast to occur for two consecutive days.
Heat Advisory:  Issued within 12 hours of the onset of heat index between 105°F – 114°F for less than three hours per day, or nighttime lows above 80°F for two consecutive days.
Excessive Heat Warning:  Issued within 12 hours of the onset of heat index of at least 105°F for more than three hours per day for two consecutive days, or heat index more than 115°F for any period of time.

The heat index values used in National Weather Service forecasts, warnings, and in heat index tables assume that the body is:

  • 5′ 7″ tall.
  • 147 pounds.
  • Caucasian.
  • At 98.6°.
  • Clothed in long trousers and a short-sleeved shirt.
  • In shade.
  • Walking at a speed of 3.1 mph.
  • In a breeze of 6 mph.
  • Not dripping with sweat.

If any of these factors are different (heavier, working in the sun, etc.), the heat index will feel different to that individual.  Exposure to full sun can increase heat index values by up to 15°F.

Written By

Photo of Dr. Diana RashashDr. Diana RashashArea Specialized Agent, Water Quality / Waste Management Serves 18 CountiesBased out of Onslow County(910) 455-5873 diana_rashash@ncsu.eduOnslow County, North Carolina
Posted on Jun 27, 2014
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This page can also be accessed from: go.ncsu.edu/readext?305298