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NOAA Heat Index Measures Risk of Heat Illness

High heat and humidity increases risk of dangerous heat illness, including heat stroke

The National Oceanic and Atmospheric Administration (NOAA) has developed a heat index chart parents and coaches can use to determine when heat and humidity have reached the point where athletes are at serious risk of heat illnesses, such as heat cramps, heat exhaustion or even heat stroke. 


National Oceanic and Atmospheric Administration
("NOAA") Heat Index


This heat index chart is designed to provide general guidelines for assessing the potential severity of heat stress. Individual reactions to heat will vary. In addition, studies indicate that the susceptibility to heat disorders tends to increase with age. Exposure to full sunshine can increase Heat Index values by up to 15° F.

How to use Heat Index:

  1. Locate on the chart above the current Air Temperature down left side
  2. Locate the current Relative Humidity across the top
  3. Follow across and down to find Apparent Temperature (what it feels like to the body)
  4. Determine heat stress risk on chart below

Heat Illness Risk
Apparent Temperature Heat Stress Risk with Physical Activity and/or Prolonged Exposure
80° to 90° Exercise caution; dehydration likely if athlete fails to drink adequate fluids

91° to 103°

Exercise extreme caution: Heat cramps or heat exhaustion possible

104° to 124°

Danger: Exertional heat cramps or heat exhaustion likely, heatstroke possible

125° and up

Extreme Danger: Exertional Heatstroke highly likely


Note: All of the information in this article is available in a helpful iPhone application called iHydrate TM, which calculates the heat index at your location and provides the heat illness risk.