What is the wet bulb temperature? And why is it so important?
...A better metric, according to Ward, is the wet-bulb globe temperature, which was developed by the US military after World War II in response to a rash of heat-related deaths during training. According to the US Marine Corps, WBGT is “the most effective means of assessing the effect of heat stress on the human body.”It’s often described as the reading on a thermometer with a damp sock around it, though the devices are a bit more sophisticated than that. WBGT integrates three distinct measurements: It measures open-air temperatures with a conventional thermometer. It measures temperatures inside a black globe to indicate what it’s like under direct sunlight. And yes, it measures temperatures with a thermometer wrapped in a wet cloth.The point of the damp thermometer is to simulate how well sweat can evaporate under the present conditions. The longer the thermometer stays wet as temperatures rise, the more humid the surrounding air, and thus the more difficult it is to cool off by sweating.These measurements are then plugged into a formula: The WBGT equals 10 percent of the air temperature plus 70 plus of the natural wet bulb temperature plus 20 percent of the black globe temperature. There aren’t as many WBGT monitoring stations as there are conventional thermometers, and coverage can be spotty. The National Weather Service has a prototype tool that can estimate WBGT near you.