|Abstract:||The primary goal of this research was to quantify occurrence frequencies of the two main proposed mechanisms of tornadogenesis in quasi-linear convective systems (QLCSs), namely, tilting and stretching (T&S) and HSI and stretching (H&S). This research then sought to investigate differences and similarities between the characteristics of the T&S- and H&S- associated tornadoes and their supporting environments. A combined Doppler radar, tornado report, and environment dataset was compiled for this purpose. Lastly, this research aimed to quantify National Weather Service (NWS) warning performance for both mechanisms.
From a strict consideration of only the first tornado generated by a QLCS during 2016-2018, 152 QLCS tornado cases were identified. Of these, 145 where determined to be the result of T&S, and 7 where determined to be the result of H&S, indicating that T&S is far more likely to be the tornadogenesis mechanism of the first tornado in a QLCS. QLCS tornadoes tended to be focused in the southern U.S. during winter and spring and the northern U.S. during summer. Tornadogenesis through H&S occurred relatively earlier in the year and earlier in the day, and resulted in relatively weaker tornadoes than did tornadogenesis through T&S. Environmental analysis showed that H&S environments had relatively lower values of CAPE and relatively higher values of low-level shear compared to T&S. Analysis of NWS warnings showed that H&S tornadoes had relatively lower tornado warning frequencies than did T&S tornadoes, while having, on average, half the warning lead time. Finally, based on a consideration of pre-tornadic Doppler radar data, it was found that H&S low-level circulations tended to form more rapidly than did T&S low-level circulations, thus providing less potential lead time.