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Heat Home • Heat Basics • Responding to Heat
During periods of excessive heat, it is essential to listen to a NOAA weather radio or your local TV or radio station to monitor weather conditions, especially if you work outside. Make sure you know what the following terms mean.
Heat Watch: Excessive heat is possible in the next few days.
Heat Advisory: High and potentially dangerous heat index temperatures occurring, imminent or highly likely. Prolonged exposure or strenuous activity might result in a heat-related illness.
Heat Warning: Life-threatening heat is occurring, imminent or highly likely. Take precautions.
Heat Wave: Prolonged period of excessive heat and humidity with temperatures that hover 10 degrees or more above the average high temperature for a specific region. The National Weather Service frequently alerts the public during these periods of high heat and humidity.
Heat Index: A temperature that tells you how hot it really feels when relative humidity is added to the actual air temperature. Exposure to full sunshine can increase the heat index by as much as 15°F.
Mean Heat Index: Fully implemented in May 2002, this National Oceanic and Atmospheric Administration index is a measure of how hot the temperature actually feels to a person over the course of the day. Unlike the traditional Heat Index, it is an average of the Heat Index from the hottest and coldest times of each day. It combines surface and ambient heat with humidity and other environmental factors.
Urban areas are especially susceptible to the way excessive heat affects air quality. Stagnant atmospheric conditions during high temperatures can trap ozone and other pollutants near the ground. Because pollutants are concentrated in urban areas, people living in or near cities are particularly susceptible. Health risks associated with decreased air quality ("ozone days") include difficulty breathing and, in extreme cases, asthma attacks.
Local broadcast and newspaper ozone alerts generally correspond to the federal standards described below.
| Ozone Index Value | Precaution | |
|---|---|---|
| 0-50 Green: good |
Best for outdoor activity. | |
| 51-100 Yellow: moderate |
Unusually sensitive people should consider limiting prolonged outdoor exertion. | |
| 101-150 Orange: unhealthy for sensitive groups |
Active children and adults, and people with respiratory disease such as asthma, should limit prolonged outdoor exertion. | |
| 151-200 Red: unhealthy |
Exercise early/late; indoors when possible. Everyone, especially children, should avoid (if sensitive) or limit prolonged outdoor exertion. | |
| Above 200 Purple: very unhealthy |
Active children and adults, and people with respiratory disease such as asthma should avoid all outdoor exertion. Others should limit outdoor exertion. |
More information on ozone alerts can be found at the National Institute of Environmental Health Sciences Web site. 
Seniors, small children, chronic invalids, individuals taking certain medications or drugs (especially tranquilizers and anticholinergics) and persons with weight and alcohol problems are particularly susceptible to heat reactions. Some common heat-related illnesses include sunburn, heat exhaustion and sunstroke. Read more about heat-related illnesses and how to treat them.