A Three-Ingredients Approach to Anticipating Mesovortex Genesis

Quasi-linear convective systems (QLCSs) have been known to pose a significant threat to life and property given their propensity to produce large swaths of wind damage as well as embedded tornadoes. Over the past few decades, warning decision forecasters (WDFs) in the National Weather Service have shown an increase in warning skill and lead time for tornadoes, though this is likely associated with tornadoes produced by supercells. In contrast, studies have shown that tornadoes generated by mesovortices within QLCSs develop on average only five minutes following mesovortex genesis. Thus, the common practice of WDFs using a developing QLCS mesovortex circulation as the driving force for issuing tornado warnings often exhibits little to no lead time. In an effort to provide WDFs with guidance for detecting QLCS tornadoes with greater accuracy and lead time, Schaumann and Przybylinski (2012) examined several QLCS events and identified three co-existing characteristics that were associated with an increased probability for mesovortex genesis and subsequent rapid intensification. (1) A portion of the QLCS exists in which the system cold pool and ambient low-level shear are nearly balanced or slightly shear dominant. (2) The 0-3 km line-normal bulk shear magnitudes are equal to or greater than 15 m s-1. (3) A rear-inflow jet or enhanced outflow causes a surge or bow in the line. The primary purpose of this study is to provide statistical analyses on a collection of cases in an attempt to verify the utility of the three-ingredients method. The meaning of these results as they apply to WDFs and the issuance of timely and accurate tornado and severe thunderstorm warnings is discussed.