An extreme heat warning is a notice issued by the U.S. National Weather Service when dangerously hot conditions are expected, typically within 24 to 36 hours. On March 10, 2025, the agency renamed it from "Excessive Heat Warning" to "Extreme Heat Warning" based on a 2018 public survey. These warnings are critical because extreme heat can cause life-threatening conditions like heat stroke and exhaustion—indeed, over 51,000 high school sports-related heat illnesses were recorded between 2005 and 2020. Criteria vary significantly by region, as seen in a May 13, 2025 warning for San Antonio, Texas, where temperatures were forecast to reach 105–108°F (and near 115°F along the Rio Grande). The NWS advises staying in air-conditioned spaces, drinking fluids, and taking frequent rest breaks, while related measures like the heat index and wet-bulb globe temperature help assess the risk.