The Short and Long-Term Variability of Selected Midwestern Tornadoes. (Atmospheric Science Section).

Chambers, M.D. and A.R. Lupo. Department of Soil and Atmospheric Sciences, 109 Gentry Hall, University of Missouri-Columbia. THE SHORTAND LONG-TERM VARIABILITY OF SELECTED MIDWESTERN TORNADOES. Predicting the occurrence of tornadoes has proven to be one of the most difficult aspects of severe weather forecasting. The isolated nature and short duration of these destructive events not only makes forecasting them difficult, but also makes studying them a challenge. Despite these challenges, recent studies have shown that certain weather events across the Midwest exhibit impressive interannual variability that can be related at least in part to the El Nino and Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) phenomena. Thorough knowledge of the characteristics of this variability, and other relationships like it, can be extremely useful for long-term forecasting applications. In the hopes of furthering the general understanding of interannual variability and its importance in forecasting severe weather, this study focuses on selected Midwestern U.S. tornadoes. This climatological study considers all tornadoes of intensity F2 (according to the Fujita Scale) or greater that occurred in Iowa, Kansas, Missouri, and Nebraska from 1950 through 1999. Once all applicable tornadic events were collected and organized, statistical calculations were examined to find trends in the data and to investigate the interannual variability and its relation to ENSO and PDO. Several flow regimes conducive to tornadic activity in the Midwest were also determined. Results thus far have shown an increase in tornadic activity during the La Nina phase and during PDO2. Downward trends in tornadic activity were also evident over the 50-year period in all four states.