An excessive heat warning is a notice issued by the National Weather Service of the United States within 12 hours of the heat index reaching one of two criteria levels. In most areas, a warning will be issued if there is a heat index of at least 105 °F (41 °C) for more than three hours per day for two consecutive days, or if the heat index is greater than 115 °F (46 °C) for any period of time.[1]
Excessive heat can pose a threat to human life and other animals, through conditions such as heat stroke, heat exhaustion, dehydration, and other heat-related illnesses.[1]