Wet Bulb Globe Temperature Is Great For Heat Warnings – Why Don’t We Use It?

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This story was born from a casual chat with my Weather Channel colleague and meteorologist, Jen Carfagno. She asked my opinion on why Wet Bulb Globe Temperature is not utilized more often as a standard for warning the public about excessive heat. The context for the question is that parts of the Atlanta area and southeast United States experienced some of its hottest weather of the year this week. WSB-TV Atlanta is reporting that, according to its sources, a high school basketball player died this week after doing conditioning outdoors. The youth football association that my son plays for canceled practice and rightfully so. Heat index values approached 110 degrees F. In the state of Georgia and some other places, Wet Bulb Globe Temperature (WBGT) is used as the metric for assessing “go/no go” for high school sports practices. The U.S. Occupational Safety and Hazard Administration (OHSA), military agencies, and other nations also use WBGT. Why doesn’t everyone else use it?

At this point, you might be saying, “It would help if you explain what it is Dr. Shepherd.” According to the National Weather Service website,

The WetBulb Globe Temperature (WBGT) 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. If you work or exercise in direct sunlight, this is a good element to monitor.

NWS website

The heat index, which was referred to as “humiture” in earlier times, accounts for what the “temperature and humidity” feels like to our bodies. It was developed in the late 1970’s by NOAA and is widely used today. However, researchers, including some of my colleagues at the University of Georgia, have found that WBGT is better at accounting for the direct heat load on an athlete exerting themselves in extreme heat conditions. The basic components are: WBGT = 0.7 Tw+0.2 Tg+0.1 Td. Tw is something we use in meteorology called the wet bulb temperature. It provides an indication of the humidity. Td is the dry air temperature. Radiant heat or globe temperature, Tg, attempts to account for the radiant heat load from the sun.

The WBGT may be a new term for you, but it has actually been around for several decades. The Kory Stringer Institute is a leading organization advocating for safe athletic performance under extreme heat conditions. Their website notes,

The use of WBGT as an environmental monitoring measure during exercise in the heat was invented in the early 1950’s in response to the number of heat casualties occurring in the United States armed services that occurred during the 1940’s and 1950’s. For example, from 1942-1944, 198 soldiers died due to heat illness during military training.
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Korey Stringer Institute website

The state of Georgia has been a leader and uses the guidelines in the graphic below to inform decisions on high school sports practices. My colleague, Dr. Andrew Grundstein at the University of Georgia, has published thresholds for other states at this link.

Ah, these guidelines may actually be part of the answer to the initial question in this piece. Why isn’t the use of WBGT more common? Weather Channel meteorologist Stephanie Abrams, who hosts the AMHQ morning show with Carfagno, also weighed in on the conversation. Abrams argues that numbers in the WBGT may not sound “ominous” enough with critical values “only” in the upper 80 to lower 90 degrees F range. The graphic below is a comparison of WBGT and heat index for August 14th, 2019 in the Tulsa area. WGBT are lower but in the dangerous range. Abrams does have a point. Recently, I overheard someone say something to the effect of “the temperature is only 95 degrees F, it’s summer, what’s the big deal.” That day the heat index was actually 108 degrees F.

Carfagno agrees that perception is reality for many people and suggested that some type of flag or color warning system might be the answer rather than numbers. She told me, “I am not even opposed to an entirely new index or scale, but I think WGBT should be utilized more than it is.”

The fact that two of the most popular voices in television meteorology are having this conversation is important. Extreme heat is the most deadly form of weather in the United States each year according to the National Weather Service (see this link). Yet, I am convinced that people don’t react to heat advisories and extreme heat warnings in the same way that they would a tornado warning. Go figure.

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