History of Extreme heat warning in Timeline

By Popular Timelines Editorial Team · Updated: March 15, 2026

An extreme heat warning is issued by the National Weather Service in the US when the heat index is forecast to reach critical levels. Generally, a warning is triggered when the heat index is at least 105°F (41°C) for over three hours a day for two consecutive days. A warning is also issued if the heat index exceeds 115°F (46°C) for any duration. These warnings alert the public to potentially dangerous heat conditions.

2005: Tracking of Heat Related Illnesses Begin

Beginning in 2005, the National High School Sports Related Injury Surveillance System, High School RIO, tracked excessive heat illnesses in high school sports. From 2005, 2011, and 2020, an estimated 51,943 cases were reported in nine sports.

2011: Tracking of Heat Related Illnesses

In 2011, the National High School Sports Related Injury Surveillance System, High School RIO, tracked excessive heat illnesses in high school sports. From 2005, 2011, and 2020, an estimated 51,943 cases were reported in nine sports.

2018: Public survey regarding Excessive Heat Warning and Watch

In 2018, a public survey was conducted, resulting in the update and renaming of the Excessive Heat Warning and Watch to the Extreme Heat Warning and Watch on March 10, 2025.

2020: Tracking of Heat Related Illnesses Continued

In 2020, the National High School Sports Related Injury Surveillance System, High School RIO, tracked excessive heat illnesses in high school sports. From 2005, 2011, and 2020, an estimated 51,943 cases were reported in nine sports.