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Update 7/7/2022: In July 2022, in an effort to be more consistent with calculations from NOAAs National Weather Service,the SCO implemented the method used by the Meteorological Development Laboratory at NOAA to calculate natural wet bulb temperature (Boyer 2022). You can read more about their methods here. These methods are identical to the National Digital Forecast Database outputs for WBGT, and will enable easier comparison of WBGT values across multiple weather data sources and products. ECONet stations directly measure black globe temperature and air temperature, while natural wet bulb temperature is calculated. Natural wet bulb temperature can be calculated in a number of ways. Previously, the SCO was using methodology from Stull (2011) to calculate natural wet bulb temperature. However, Stull's method only takes into account temperature and relative humidity, which alone does not equate to a natural wet bulb temperature.

Wet Bulb Globe Temperature (WBGT) is a measurement of heat stress that takes into account air temperature, relative humidity, wind speed, and solar radiation. WBGT is a function of Wet Bulb Temperature, Air Temperature, and Black Globe Temperature. In the 1950s, the US Military started measuring WBGT to help determine heat stress on recruits during training. A flag system was then created to easily alert people of potential hazardous conditions. Today's categories differ per region, but in North Carolina, we will use the levels determine by the National Weather Service and from Grundstein et al. (2014). In 2018, the NC ECONet started installing black globe thermometers at its stations to more accurately calcuate WBGT.

WBGT values from the ECONet were used to assist researchers at the North Carolina Institute for Climate Studies and the National Centers for Environmental Information (NCEI) to validate WBGT values nationally through the US Climate Reference Network (USCRN). You can read more about that study here.

For more information, questions, or comments, please email climate-office@ncsu.edu

References Cited

• Boyer, T. 2022. NDFD Wet Bulb Globe Temperature Algorithm and Software Design. https://vlab.noaa.gov/documents/6609493/7858379/NDFD+WBGT+Description+Document.pdf/fb89cc3a-0536-111f-f124-e4c93c746ef7?t=164279547129
• Grundstein, A., C. Williams, M. Phan, and E. Cooper. 2014. Regional Heat Safety Thresholds for Athletics in the Contiguous United States. Applied Geography. 56, 55-60. DOI: 10.1016/j.apgeog.2014.10.014
• Rennie, J.J., M. A. Palecki, S. P. Heuser, and H. J. Diamond. 2021. Developing and Validating Heat Exposure Products Using the U.S. Climate Reference Network. Journal of Applied Meteorology and Climatology. 60, 543-558. DOI: 10.1175/JAMC-D-20-0282.1
• Stull, R. 2011. Wet-Bulb Temperature from Relative Humidity and Air Temperature. Journal of Applied Meteorology and Climatology.50,2267-2269. DOI: 10.1175/JAMC-D-11-0143.1.