The Development and Accuracy Assessment of Wet Bulb Globe Temperature Forecasts

Abstract

Abstract Heat is the leading cause of weather-related death in the United States. Wet bulb globe temperature (WBGT) is a heat stress index commonly used among active populations for activity modification, such as outdoor workers and athletes. Despite widespread use globally, WBGT forecasts have been uncommon in the United States until recent years. This research assesses the accuracy of WBGT forecasts developed by NOAA’s Southeast Regional Climate Center (SERCC) and the Carolinas Integrated Sciences and Assessments (CISA). It also details efforts to refine the forecast by accounting for the impact of surface roughness on wind using satellite imagery. Comparisons are made between the SERCC/CISA WBGT forecast and a WBGT forecast modeled after NWS methods. Additionally, both of these forecasts are compared with in situ WBGT measurements (during the summers of 2019–21) and estimates from weather stations to assess forecast accuracy. The SERCC/CISA WBGT forecast was within 0.6°C of observations on average and showed less bias than the forecast based on NWS methods across North Carolina. Importantly, the SERCC/CISA WBGT forecast was more accurate for the most dangerous conditions (WBGT > 31°C), although this resulted in higher false alarms for these extreme conditions compared to the NWS method. In particular, this work improved the forecast for sites more sheltered from wind by better accounting for the influences of land cover on 2-m wind speed. Accurate forecasts are more challenging for sites with complex microclimates. Thus, appropriate caution is necessary when interpreting forecasts and onsite, real-time WBGT measurements remain critical. Significance Statement This research assesses the accuracy of wet bulb globe temperature (WBGT) forecasts. WBGT is a heat stress index that accounts for impacts of air temperature, humidity, wind, and radiation. It is widely used in occupational, athletic, and military settings for heat stress assessment, yet WBGT forecasting in the United States is a relatively new development. These forecasts can be used by decision-makers to better plan activities. We found that WBGT forecasts by NOAA’s Southeast Regional Climate Center and Carolinas Integrated Sciences and Assessments were within 0.6°C of observations overall in North Carolina and less biased than forecasts based on methods used by the U.S. National Weather Service, which had larger, colder biases that present potential safety issues in planning.