Diurnal and Seasonal Patterns of Harmful Convective Weather Hazards Across Tennessee from 1996–2022

Tennessee is prone to meteorological hazards across the state, including three prevalent severe convective hazards: floods, tornadoes, and nontornadic thunderstorm winds. The frequency of these hazards differs across the state, seasonally, and diurnally. Compared to tornadoes, flash floods and, especially, thunderstorm winds are less studied. Thus, work that demonstrates the frequency of these three separate hazards in a specific area is a worthwhile contribution to the literature. This research aims to assess the frequency of hazards and harmful hazards (hazardous events that result in one direct injury and/or fatality) across the state of Tennessee and determine how their frequency varies seasonally and diurnally. Data between 1996 and 2022 from the National Centers for Environmental Information Storm Events Database were used to gather temporal, injury, and fatality information for the three hazard types across Tennessee. Hazardous events were divided into the four meteorological seasons: spring (MAM), summer (JJA), fall (SON), and winter (DJF); and two diurnal periods: day (sunrise to sunset) and night (sunset to sunrise). Temporal analysis was done in R with descriptive statistics, chi-square tests, and Cramer’s V test. Spatial analysis was done through ArcGIS Pro to map the frequency of hazards and harmful hazards across Tennessee. Results showed that thunderstorm winds were the most frequent of the three hazards in Tennessee, making up 80.0% of the events, while only 5.1% were tornadoes. However, tornadoes accounted for 47.2% of harmful hazardous events and flash floods accounted for 13.2% of harmful hazardous events. Tornadoes were the most frequent harmful hazard; however, due to the significant amount of thunderstorm winds, the harmful hazard patterns were heavily influenced by both tornadoes and thunderstorm winds. Results showed the type of hazard significantly affected whether it was a harmful event. Whether a hazard occurred was not significantly dependent upon the type of hazard, and instead was strongly dependent upon the season. The spatial analysis found that the three hazards, as well as the three harmful hazards specifically, were distributed differently across Tennessee. Understanding the spatial and temporal patterns of the frequency of severe convective hazards, including those that were harmful, across Tennessee will hopefully help forecasters, broadcasters, emergency management, and Tennessee residents better prepare for severe weather, and realize that the frequency of hazardous events and harmful hazardous events do not always agree, spatially or temporally, and that seasonal and diurnal timing can affect both frequency in hazards and their likelihood of causing harm.