Relationship of Low-Level Instability and Tornado Damage Rating Based on Observed Soundings

Abstract

A database of upper-air soundings was collected for weak (EF0/EF1), significant (EF2/EF3), and violent (EF4/ EF5) tornadoes that occurred within 100 km and 6 h of the rawindsonde observation. After case filtering and quality control, a total of 50 proximity soundings for violent tornadoes and randomized samples of 100 proximity soundings for significant tornadoes and 102 for weak tornadoes were obtained. Key convective parameters were analyzed between the tornado datasets. Low-level instability parameters (0-3-km lapse rates and 0-3-km mixed-layer convective available potential energy) were noteworthy predictors of the highest tornado damage rating, whereas mixed-layer lifted condensation level, wind shear, and effective storm relative helicity displayed little predictive skill distinguishing significant and violent tornado environments. The ability of the significant tornado parameter (STP) to discriminate between significant and violent tornadoes also was analyzed. This analysis found that STP does statistically discriminate between violent and significant tornadoes, with mixedlayer convective available potential energy the best discriminator of its variables. Because of the skill in the lowlevel instability parameters, this study also offers a new violent tornado parameter that includes the low-level instability fields in order to better differentiate between significant and violent tornado environments.