EAPS

Title: Changes in the statistics of U.S. tornado reports

Abstract: Tornadoes damage property and kill people each year. Recent observational studies have noted changes in the statistics of tornadoes reported in the U.S. While there is believed to have been no changes in the annual number of reliably reported tornadoes, year-to-year variability has increased and more tornadoes are occurring in clusters (outbreaks). A natural question is whether a changing climate might be responsible for these trends. The length, variability and quality of the U.S. tornado record make answering that question difficult. An alternative approach is to examine large-scale meteorological features such as vertical wind shear and convective available potential energy that are associated with increased likelihood of severe thunderstorm activity. These associations can be summarized in indices which are functions of the local environment and whose values indicate the likelihood of severe thunderstorms. Here we compare variability in tornado reports to observed changes in meteorological environments, as well as those expected under climate change.