Examination of Tornadic and Non-tornadic Supercells in Southwest Virginia on 28 April 2002

On the afternoon of 28 April 2002, four isolated supercell storms moved across the Blue Ridge mountains and into the foothills and Piedmont areas of southwest Virginia, leaving swaths of wind damage and large hail in their wakes. Only one of these supercells, the northern most, produced tornadoes (two separate touchdowns of F1-F2 damage, resulting in 12 injuries and approximately $7 million in damage). While all four storms were comparable in terms of the strength and diameters of the mesocyclone signatures, as viewed in the Doppler velocity products, there were a few notable differences in terms of the vertical and horizontal size of the tornadic storm compared to the others. In addition, objective mesoscale analyses of the environment and close examination of surface observations suggest there were some subtle differences in several parameters previously shown to be correlated with tornadic environments, namely lifted condensation level, storm-relative helicity, energy-helicity index, the vorticity generation parameter, and others. Still, given the relatively subtle differences and the overall favorable values of most of these parameters, as well as the strong radar signatures and what appeared to be a favorable outflow boundary position from the northern-most storm, it would be difficult to suggest with any degree of confidence that the three non-tornadic supercells were unlikely to produce tornadoes.

We will use a series of radar reflectivity and storm-relative velocity images in a 4-panel mode to show the structure and evolution of the mesocylones with radar loops to supplement the static images. Time-height plots of mesocylone strength and diameter for each of the supercells will help compare and contrast potentially important differences in mesocyclone character, while IR satellite imagery will show the differences in the depths of these storms. Finally, RUC analyses of the parameters mentioned above along with plotted surface observations will illustrate the subtle differences in mesoscale environment across the region where the supercells tracked.