Your Local Heat Category

The most official guidelines around heat safety use the WBGT and identifies regional categories and standards for dealing with heat and physical activity.

The Wet Bulb Globe Temperature (WBGT) is the comprehensive measure that assesses heat stress by considering factors such as temperature, humidity, wind speed, and solar radiation.

The research article that is mostly widely referenced and used to set standards by region is called "Regional heat safety thresholds for athletics in the contiguous United States" by Andrew Grundstein.

It set three regions in order to establish heat safety guidelines in the US:

Per this study, the categories were established employing "a unique WBGT climatology for the contiguous U.S. to determine locally extreme WBGTs, defined as the 90th percentile warm season daily maximum value, for 217 stations. Three heat safety regions were identified based on local extremes:

1. Category 3 (90th percentile daily WBGTs ≥ 90.1 °F, 32.3 °C) - Category 3 encompasses much of the southeastern quadrant of the U.S. along with portions of the Southwest, and the Central Valley of California
2. Category 2 (90th percentile daily 86.2 °F- 90 °F, 30.1–32.2 °C) - Category 2 areas extend in an arc from the interior Northwest through Nevada and portions of the Midwest, Ohio Valley, and Northeast
3. Category 1 (90th percentile daily ≤ 86°F, 30 °C) - Category 1 locations include the Pacific Coast, New England, and the northern tier of the country.

Associated regional activity guidelines based on those developed by the ACSM and the Georgia High School Association (GHSA) were developed for each heat safety region.

It's important to note that WBGT thresholds can vary by region beyond what is listed in this chart. For instance, the California Interscholastic Federation (CIF) has specific WBGT guidelines tailored to different areas within the state

Review your region's recommendations and get familiar with how to cope with the heat during outdoor physical activity.

Sources

https://www.weather.gov/ict/WBGT

https://koreystringer.institute.uconn.edu/wet-bulb-globe-temperature-monitoring/