Comparison of Radar-Observed Tornadic and Nontornadic MCS Cells Using Probability-Matched Means

Forecasting tornadogenesis remains a difficult problem in meteorology, especially for short-lived, predominantly nonsupercellular tornadic storms embedded within mesoscale convective systems (MCSs). This study compares populations of tornadic nonsupercellular MCS storm cells with their nontornadic counterparts, focusing on nontornadic storms that have similar radar characteristics to tornadic storms. Comparisons of single-polarization radar variables during storm lifetimes show that median values of low-level, midlevel, and column-maximum azimuthal shear, as well as low-level radial divergence, enable the highest degree of separation between tornadic and nontornadic storms. Focusing on low-level azimuthal shear values, null storms were randomly selected such that the distribution of null low-level azimuthal shear values matched the distribution of tornadic values. After isolating the null cases from the nontornadic population, signatures emerge in single-polarization data that enable discrimination between nontornadic and tornadic storms. In comparison, dual-polarization variables show little deviation between storm types. Tornadic storms both at tornadogenesis and at a 20-min lead time show collocation of the primary storm updraft with enhanced near-surface rotation and convergence, facilitating the nonmesocyclonic tornadogenesis processes.

Automated summary

This study compares the characteristics of tornadic and non-tornadic storms, and finds that low-level azimuthal shear values are the most distinguishing factor between the two. By analyzing single-polarization data, the study shows that it is possible to accurately differentiate between tornadic and non-tornadic storms, while dual-polarization data shows little deviation between storm types. The study also reveals that tornadic storms exhibit enhanced near-surface rotation and convergence, collocating with the primary storm updraft, during tornadogenesis and at a 20-minute lead time.