Analyses of Quasi-Linear Convective System Tornado Characteristics, Environments, and Genesis Mechanisms
Abstract
Quasi-Linear Convective Systems (QLCSs) primarily produce straight-line winds and flash flooding but are also known to produce tornadoes. QLCS tornadoes often form rapidly with little, if any, advanced warning operationally. Our overarching hypothesis is that the potential warning lead time depends on the tornadogenesis mechanism. Specifically, we hypothesize that tornadogenesis via the release of horizontal shearing instability -(HSI) and stretching of subsequent vertical vorticity (H&S) will occur relatively more rapidly and over a shallower layer than tornadogenesis via tilting of environmental and internally generated horizontal vorticity and stretching of subsequent vertical vorticity (T&S). We also hypothesize that the HSI-associated tornadoes are more likely to occur during the cool season, and during the overnight hours, compared to the tilting-associated tornadoes. To test these hypotheses, tornado reports and corresponding NEXRAD data were examined during the years of 2016-2018 to objectively identify tornadic QLCS. These events were then separated by tornadogenesis mechanisms using NEXRAD data and application of simple criteria. Specifically, the presence (absence) of a midlevel mesocyclone at least three radar volume scans (~15 minutes) prior to tornado occurrence was required for T&S- (H&S-) type tornadogenesis. The characteristics of these events, including time of day, season, tornado intensity, and basic environmental parameters will be compared between these tornadogenesis mechanisms. Further analysis of lead time of radar-based circulations prior to tornadogenesis will also be compared between these tornadogenesis mechanisms. Our hope is that the results of these analyses will help improve operational forecasting of QLCS tornadoes.
