Wet Bulb Globe Temperature (WBGT)
Source: Wet Bulb Globe Temperature
Here is a link to the outlook for the US WBGT
Humans cool themselves by sweating: the ambient heat evaporates sweat from our skin, and that keeps us from getting too hot. If the relative humidity is already near 100 percent, the air simply cannot take any more. Our sweat does not get evaporated as easily, and we cannot cool down. This makes humid heat not just uncomfortable, but dangerous.
The WetBulb Globe Temperature is a measure of the heat stress in direct sunlight, which takes into account: temperature, humidity, wind speed, sun angle and cloud cover (solar radiation). This differs from the heat index, which takes into consideration temperature and humidity and is calculated for shady areas. For comparison, a wet-bulb temperature of 90 F is equivalent to a heat index of 130 F.
Even heat-adapted people cannot carry out normal outdoor activities past a wet-bulb temperature of 90 F. A reading of 95 F – equivalent to a heat index of 160 F – is considered the theoretical human survivability limit for up to six hours of exposure. Any hotter than that, and the body will start to overheat, even if given unlimited water and shade.
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