Synoptic-scale Precursors and Characteristics of High-end Tornado Outbreaks in the Southeastern Region of the United States

The atmospheric conditions and patterns preceding high-end tornadic outbreaks (HETO) are important to understand as such events often lead to loss of life and property. This study examines the synoptic conditions in the days surrounding a HETO to identify large-scale atmospheric structures that can be used to improve forecasts of HETOs. Tornadic events were ranked for these times by number of tornado reports and the top 75 are defined as HETOs. Generally, there are four ingredients needed for severe weather: lift, moisture, instability, and vertical wind shear. For HETOs, strong vertical wind shear, low lifted condensation levels and veering wind profiles typically are present as well. These variables are taken into consideration when analyzing large-scale patterns of mass fields such as 500hPa heights, 250hPa winds, total wind shear, equivalent potential temperature, etc. The domain for the HETOs in this study includes Alabama, Georgia, Kentucky, Mississippi, the Carolinas, and Tennessee. Tornadic events are examined using NCEP reanalysis from January 1st to May 31st, years 2001-2014, as this period best describes the primary severe weather season for the Southeast. The goal of this study is to compare HETOs to lesser tornadic outbreaks and to events that consist of severe, non-tornadic weather; these results can then be implemented into pattern recognition techniques for short to medium range forecasts of severe weather events.