Evaluating Precursor Signals for QLCS Tornado and Higher Impact Straight-Line Wind Events

Abstract

Tornadoes produced by quasi-linear convective systems (QLCS) present a significant challenge to National Weather Service warning operations. Given the speed and scale at which they develop, different methods for tornado warning decision making are required than what traditionally are used for supercell storms. This study evaluates the skill of one of those techniques—the so-called three-ingredients method—and produces new approaches. The three-ingredients method is found to be reasonably skillful at short lead times, particularly for systems that are clearly linear. From the concepts and science of the three-ingredients method, several new combinations of environmental and radar parameters emerge that appear slightly more skillful, and may prove easier to execute in real time. Similar skill between the emerging methods provides the forecaster with options for what might work best in any given scenario. A moderate positive correlation with overall wind speed with some radar and environmental variables also is identified. Additionally, mesoscale convective vortices and supercell-like features in QLCS are found to produce tornadoes at a much higher rate than purely linear systems.

Regional to Mesoscale Influences of Climate Indices on Tornado Variability

“…Additionally, the mesoscale study areas had very few days with one or more tornadoes after the exclusion of EF0s. If using only days that met a specified minimum number of tornadoes or high-magnitude tornadoes, the resulting datasets for the mesoscale study areas would be too small for statistical tests to be reliable [30,31]. To keep the testing process similar for the regions and mesoscale study areas and to reduce confounding variables, tornado activity throughout each study area's tornado season was analyzed.…”

“…The entire EUS was compared with the other three regions to determine whether and to what degree the correlation between specific climate indices and tornado frequency varies between the primary region and its subregions. Pearson correlation coefficients were considered significant at a 95% confidence interval (α < 0.05) [30]. This interval was used to evaluate the significance of all tests, both at the regional scale and mesoscale.…”