A Comparison of Significant Tornadoes in North Alabama since 2008
Carcione, Brian ; Darden, Chris ; Lee, Jennifer L

Since 1 February 2008, North Alabama has experienced five significant (EF3 or greater) tornadoes including two with path lengths exceeding 25 miles. During the previous 13 year period, the same area only experienced two such tornado occurrences. There are certainly multiple reasons for this recent increase, but attention must focus on the mesoscale environment. Comparable conditions have been observed in the recent past, but the resulting tornadoes were generally weaker.

This study consists of a mesoscale analysis of the near-storm environment, with special emphasis on measures of instability and shear in the lowest three kilometers, which multiple studies indicate are useful predictors for tornadogenesis. While strongly sheared environments were present for each of the five tornadoes, conditions were only modestly unstable (100 hPa mixed-layer Convective Available Potential Energy less than 500 J kg-1) for all but one storm. The role of mesoscale boundaries and quasi-linear convective systems in low-level vorticity enhancement was a significant factor, and a possible prerequisite for significant tornado development.

Trends in the parent supercell thunderstorms of each tornado will also be analyzed using two methods of remote sensing. Velocity data from the dual-polarimetric Doppler Atmospheric Radar for Meteorological and Operational Research from the University of Alabama in Huntsville will be compared to National Weather Service WSR-88D radars at Hytop, Alabama, and Columbus, Mississippi. Total lightning information from the North Alabama Lightning Mapping Array will also be analyzed and compared, as past research in the Tennessee Valley has shown that a rapid increase in the lightning source densities is often a precursor to tornadogenesis.