Using the standard deviational ellipse to document changes to the spatial dispersion of seasonal tornado activity in the United States

Abstract Recent studies have documented possible ongoing changes to the climatology of tornadoes in the United States. Observed changes include increasing tornado counts in the Southeast and Midwest Regions, decreasing tornado counts in the Great Plains, and increased clustering of tornadoes on fewer days of the year. This study illustrates that the spatial dispersion of tornadoes in the United States is also changing. The dispersion of tornadoes decreased between 1954 and 2017, most notably in spring, summer, and fall. Furthermore, tornadoes tended to be less spatially dispersed in seasons with more tornadoes and with multiple days on which 20 or more tornadoes occur. This suggests that the increased occurrence of tornado outbreaks is contributing to the decrease in dispersion.