Beat the Heat: Intra-Hour Heat Metric Variability

According to the National Weather Service (NWS), heat is the leading cause of weather-related fatalities (1993-2022 average) in the United States. While the connection between heat and morbidity/mortality has been established rigorously in literature, the most effective heat metric to use is widely debated. One such metric, wet bulb globe temperature (WBGT), has been extensively used in military, athletic, and outdoor labor settings and is often preferred over the traditional heat index as it accounts for solar radiation and wind effects. Yet, research gaps exist in characterizing WBGT sub-hourly changes and quantifying their importance, consequently posing issues in translating WBGT to NWS heat advisories and warnings. This project investigates the intra-hour variation in WBGT, seeking to inform best practices in using WBGT for potential heat alerts. Using data from the North Carolina State Climate Office’s Environment and Climate Observing Network (ECONet) stations, WBGT and other meteorological variables are analyzed at four stations in central NC for 2019-2022 for the month of July. The research reveals that WBGT can be highly variable within an hour, but this variability can change across any given day. On average, midday hours have an hourly range greater than 4°F, which often spans multiple WBGT thresholds. Hours with higher maximum WBGT are correlated with increased WBGT variability, although this relationship is minimal when exclusively examining midday hours. Understanding intra-hour WBGT variability and the most effective averaging technique can improve efficacy in determining WBGT threshold levels and in turn enhance NWS heat alerts.