Wet Bulb Globe Temperature (WBGT)
The Wet Bulb Globe Temperature (WBGT) index was developed by the U.S. military to model the stress on the human body in hot, humid environments. A calculated WBGT, based on National Weather Service data, is used by Heatline. Four evironmental factors affect thermal stress on the body: wind, temperature, humidity, and radiation from the sun and nearby hot surfaces.
WInd and radiation are very much influenced by the immediate surroundings. Buildings and trees can block air flow and artificial surfaces like basketball courts can make a local setting warmer. The calculated WBGT provided on this site is a generalized guide, light winds and fairly sunny conditions are assumed. Consider your location when planning activities. Below are guidelines relating to the WBGT index. These guidelines have been modified from adult recommendations to levels more appropriate for children.
| WBGT | Flag Color | Heat Guidelines |
| < 78 |  |
Normal Activity Drink throughout the day for full hydration |
| 78.0 - 82.0 |  |
Normal Activity Take longer rest periods in the shade Drink 3-9 ounces every 20 minutes of activity Wear weather appropriate clothing |
| 82.1 - 86.0 |  |
Limit intense excercise to 2 hours Limit total outdoor exercise to 4 hours Use discretion in planning intense physical activity Rest after 20-25 minutes of activity Hydrate regularly 3-9 ounces after every 20 minutes of activity Wear light summer-weight clothing Pay special attention to at-risk individuals |
| 86.1 - 89.9 |  |
Limit exercise to 1 hour Limit total exercise to 3 hours Rest after 15-20 minutes of activity Hydrate regularly 3-9 ounces every 20 minutes of activity Wear as little clothing as possible Be on high alert: watch for early signs and symptoms Consider moving activity to early or late in the day |
| > 90 |  |
Cancel all outdoor exercise involving physical exertion Move activities to an air-conditioned space If event cannot be canceled or rescheduled use extreme caution as the risk of heat illness is very high Closely monitor for signs of heat illness and withdraw any athletes who show symptoms |
The Wet Bulb Globe Temperature is obtained daily from National Weather Service temperature and humidity readings taken under normal conditions at area airports. Please understand that this number can vary depending on location. Guidelines summarize approaches for the prevention of the detrimental effects of children's activity in hot or humid climates, including the prevention of exercise-induced dehydration.