Non-supercell Tornadoes

Analyses of tornadoes that are not associated with supercells are presented. The database for this study was collected during CINDE (Convention INitiation and Downburst Experiment), a field project operated during the summer of 1987 in Colorado. A total of 27 visual vortices were studied. They appeared to form as shear instabilities along radar detected convergence lines. The circulations initiated at low levels generally in the absence of precipitation echo. Subsequently as these vortices propagated along the convergence line they appeared to strengthen to tornadic intensity when they became colocated with the updraft of a rapidly developing storm. It is hypothesized that vortex stretching is responsible for intensifying the initial rotation. Although these tornadoes were weaker than those accompanied by strong midlevel mesocyclones, estimates of their strength suggest damage capability as high as F2. The implications for operational radars to detect these types of phenomena were identified. The sensitivity of NEXRAD radars to detect motions in clear air, as well as an increased awareness of the radar observations at the lowest elevation angles, were found to be important.