The climatology, convective mode, and mesoscale environment of cool season severe thunderstorms in the Ohio and Tennessee Valleys, 1995-2006

Although the primary severe convective weather season is in the spring and early summer, a secondary increase in severe weather occurs in the fall and winter across parts of the southeastern U.S., including the Ohio and Tennessee River Valleys. This study's purpose is to gain a better understanding of cool season (i.e. October-March) severe thunderstorms across this region by examining the severe report climatology, convective mode of storms producing severe weather, and their associated mesoscale environments. This was achieved by examining all severe reports (6,293) (tornado-311, hail-1,931, wind-4,051) during the 1995-2006 cool seasons in the Ohio and Tennessee Valleys. Storms responsible for severe reports were then classified by convective mode (i.e. supercell, quasi-linear convective system (QLCS), and single/multicell) using available radar data. Additionally, mesoscale environments associated with severe storms were also analyzed.

Most severe events in the region during the cool season are characterized by a high frequency of wind reports compared to hail and tornado reports. All severe report classes (i.e. tornadoes, hail, and wind) displayed a frequency tendency to remain relatively high into the late evening and early overnight hours, and the majority of tornadoes were associated with a tornado outbreak. QLCS were associated with the majority of severe weather reports whereas supercells were the convective mode most associated with significant tornadoes (F2 and greater). A radar-verified supercell database was compiled in order to examine supercell characteristics further. Preliminary findings indicate cool season supercells exhibited a mean east-northeast motion around 45 mph and tornadic supercells traveled nearly double the distance of non-tornadic supercells.