Descending and Nondescending Tornadic Vortex Signatures Detected by WSR-88Ds

Abstract

Tornadic vortex signatures (TVSs) of 52 tornadoes were identified and analyzed, then characterized as either descending or nondescending. This characterization refers to a known tendency of radar-observed tornadic vortices, namely, that of their initial detection aloft and then of their subsequent descent leading to tornadogenesis. Only 52% of the sampled TVSs descended according to this archetypal model. The remaining 48% were detected first near the ground and grew upward or appeared nearly simultaneously over a several kilometer depth; these represent primary modes of tornado development that have been explained theoretically. The descendingnondescending TVSs were stratified according to attributes of the tornado and TVS. Significantly, tornadoes within quasi-linear convective systems tended to be associated with nondescending TVSs, identification of which provided a mean tornado lead time of 5 min. Two case studies are presented for illustrative purposes. On 1 July 1997 in southern Minnesota, nondescending TVSs and associated tornadogenesis were revealed in the leading edge of a squall line, with a squall linesupercell merger, and later during that day, with the cyclonic bookend vortex of a bow echo. On 22 June 1995 in southern Colorado, a low-topped supercell storm produced a tornado that was associated with a descending TVS.

Morphology and evolution of cold‐frontal misocyclones

“…Our results, also obtained in a non-idealized modelling setting, extend the prevalence of this phenomenon to the regime of strongly forced systems in weakly unstable environments in the 'maritime' environment of the United Kingdom. Trapp et al (1999), McAvoy et al (2000) and Lane and Moore (2006) have drawn attention to the challenges posed to operational meteorologists by tornadoes and straight-line winds along QLCSs and NCFRs. Forecasting and nowcasting of such phenomena is a test of the limits of current modelling and operational radar capabilities.…”

Rapid Sampling of Severe Storms by the National Weather Radar Testbed Phased Array Radar

“…Of greater interest is the descending nature of the cyclonic rotation that the PAR captures. The potential capability to diagnose the evolution of these velocity signatures may be particularly advantageous in studies of storms exhibiting nondescending vortex development such as those described in Trapp et al (1999).…”

NWS Tornado Warnings with Zero or Negative Lead Times

“…Other studies have shown some impact of storm type on tornado warning lead time. Trapp et al (1999) found tornadoes resulting from nondescending vortices, often associated with quasi-linear convective systems, were associated with shorter warning lead times. Guillot et al (2008) found higher tornado warning lead times for isolated supercells and strong convective lines but less lead time for weaker, less-organized systems.…”