Nocturnal Tornado Outbreak Climatology

Research investigating tornado outbreaks has primarily focused on events that have occurred during daylight hours. While nocturnal events tend to be less significant in terms of spatial extent and severity than daytime outbreaks, they still pose a serious threat to the general public owing to the increased difficulty of conveying risk information during nighttime hours. Additionally, the meteorological conditions driving these events are less well established, increasing forecast difficulty. It is important that a climatology of nocturnal tornado outbreaks is created in order to better understand these events. The goal of this research is to establish a climatology of purely nocturnal tornado outbreaks. A nocturnal outbreak was defined as 6 or greater tornadoes within one synoptic-scale system that occurred between sunset and sunrise east of the Rocky Mountains. For an event to be nocturnal, no tornadoes could occur during the day, limiting the impact of events that transition from afternoon outbreaks to overnight events. From this subset of events, characteristics of path length, intensity, fatalities, time of night, number of tornadoes, geographical location, and month of occurrence were assessed using percentile statistics. The results showed trends in nocturnal outbreak activity that should be considered for future research.