Your Local Heat Category
Understanding your region’s typical heat conditions is a key part of making smart decisions during outdoor activity. Heat safety guidelines often use the Wet Bulb Globe Temperature (WBGT)—a comprehensive measure of heat stress that factors in temperature, humidity, solar radiation, and wind speed—to establish thresholds for training and competition.
WBGT and Regional Safety Categories
One of the most referenced studies for regional heat standards is titled:
“Regional Heat Safety Thresholds for Athletics in the Contiguous United States” by Andrew Grundstein.
This research used long-term WBGT data from across the U.S. to determine typical peak heat conditions and divided the country into three distinct categories:
- Category 3: WBGT ≥ 90.1°F (32.3°C)
- Includes: Southeast U.S., parts of the Southwest, and California’s Central Valley
- Category 2: WBGT between 86.2°F–90°F (30.1–32.2°C)
- Includes: Interior Northwest, Nevada, Midwest, Ohio Valley, and parts of the Northeast
- Category 1: WBGT ≤ 86°F (30°C)
- Includes: Pacific Coast, New England, and northern U.S. states
These categories are based on each region’s 90th percentile warm-season daily maximum WBGT values, helping identify areas where heat stress may be more frequent or intense.
Category Detail
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.
Why It Matters
Knowing your local heat category can help teams and athletes adjust expectations and preparation during hot weather. Several sports organizations use these thresholds to develop training modifications, hydration plans, and activity scheduling guidelines.
It’s also important to note that local guidelines may vary further. For example, the California Interscholastic Federation (CIF) has its own region-specific WBGT standards within the state.
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