District Issues Protective Actions for Extreme Heat In the District, the heat emergency plan is activated when the heat index (an accurate measure of how hot it really feels when the effects of humidity are added to the high temperatures) reaches 95?.   In general, you should know the difference between an advisory and a warning.  An excessive heat ADVISORY means that extreme heat is likely and an excessive heat WARNING means that extreme heat is likely and can pose a threat to life if proper precautions are not taken. In the event of extreme heat, you should take the following precautions: Stay indoors as much as possible. Turn on the air-conditioner or fan. DO NOT leave children or pets in vehicles. Drink plenty of water. Wear light-colored, lightweight and loose-fitting clothes. Apply sunscreen at least 20 minutes before going outside (SPF 15-30 is best).  Limit exposure to the sun (the sun is most powerful between 10 am and 3 pm). Watch for heat cramps, heat exhaustion and heat stroke. If you do not have access to a cool-temperature location, visit one of the District’s “Cooling Centers” located throughout the city.