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Extreme heat warning
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Extreme heat warning
An extreme 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.
Extreme 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.
On March 10, 2025, the National Weather Service updated the Excessive Heat Warning and Watch, and renamed it to the Extreme Heat Warning and Watch, based on a public survey results in 2018.
Local offices, particularly those where extreme heat is less frequent or in areas with deserts or mountainous terrain, often have their own criteria.
Due to the extreme illnesses that can occur, athletes should limit their physical activity when an extreme heat warning is issued. According to the National High School Sports Related Injury Surveillance System, High School RIO, an estimated number of 51,943 excessive heat illnesses occurred in nine of the high school sports observed between 2005, 2011, and 2020.[full citation needed]
The following is an example of an extreme heat warning and a heat advisory issued by the National Weather Service office in San Antonio, Texas on May 13, 2025 during a heat wave.
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Extreme heat warning
An extreme 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.
Extreme 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.
On March 10, 2025, the National Weather Service updated the Excessive Heat Warning and Watch, and renamed it to the Extreme Heat Warning and Watch, based on a public survey results in 2018.
Local offices, particularly those where extreme heat is less frequent or in areas with deserts or mountainous terrain, often have their own criteria.
Due to the extreme illnesses that can occur, athletes should limit their physical activity when an extreme heat warning is issued. According to the National High School Sports Related Injury Surveillance System, High School RIO, an estimated number of 51,943 excessive heat illnesses occurred in nine of the high school sports observed between 2005, 2011, and 2020.[full citation needed]
The following is an example of an extreme heat warning and a heat advisory issued by the National Weather Service office in San Antonio, Texas on May 13, 2025 during a heat wave.