Performance Evaluation of National Weather Service Heat Metrics in Central North Carolina

According to the National Weather Service (NWS), heat is the leading cause of weather-related fatalities (1993-2022 average) in the US. While the connection between heat and morbidity/mortality has been established rigorously in literature, the most effective heat metric is widely debated. Most NWS offices use the heat index (HI) as a trigger for Heat Advisories and Excessive Heat Warnings, but the new NWS HeatRisk has shown promise in the western half of the United States. Separately, wet bulb globe temperature (WBGT) has long been used by the military and has become a popular tool in athletic and labor settings. This project investigates the three heat metrics to compare and contrast their effectiveness and capabilities. Using data from the NWS and the North Carolina State Climate Office’s Environment and Climate Observing Network (ECONet) stations, as well as a review of relevant literature, HI, WBGT, HeatRisk, and other meteorological variables are analyzed at four stations in central NC for 2019-2022 for the month of July. WBGT flagged the most number of days as the top 3 categories of heat danger, while HeatRisk flagged around half of these same days as the top 3 categories. The effectiveness of HI was limited due to wide threshold values, properties of the metric, and errors in calculation found in literature. In consideration of the NWS Unified Heat Strategy, recommendations for improvement of these heat metrics include refinement of thresholds, explicit documentation of use case scenarios, and further localized research on metric efficacy.