Tornado Environments, Metrics, and Warnings: Lessons from a Ten-Year Climatology

To ensure public safety during tornadic storms, forecasters are tasked with issuing timely and accurate tornado warnings based on information from radar and spotters, as well as the forecaster's knowledge of the environment. While it is desirable to have warnings on all tornadoes, simply issuing more warnings in order to reduce the chance of missing a tornado tends to increase the number of false alarms, unless improvements are made in our scientific understanding and/or our ability to apply this knowledge through technological advancements. Environmental conditions for which the probability of detection is low while the false alarm rate is high indicate that further understanding is needed for tornadoes occurring in these conditions. In this study, we highlight the regions of the environmental parameter space having low warning skill in various geographical locations and during different portions of the diurnal cycle.

This work makes use of the 40,357 tornado warnings and 15,771 tornado reports issued between 2003 and 2013 across the continental United States, coupled with warning verification data and proximity sounding data from the Rapid Update Cycle model, to create a 10.5-year tornado environment climatology and to evaluate tornado warning performance over this time to see which environmental conditions are associated with the lowest warning skill.

We use a kernel density estimation approach to plot and compare distributions of tornado warnings and reports across two parameter spaces known for their ability to discriminate between various types of severe and non-severe weather: the most-unstable convective available potential energy vs. 0—6 km vector shear magnitude, and the height of the mixed-layer lifted condensation level vs. 0—1 km storm-relative helicity. We also group these reports and warnings by time of day, geographical region, and storm morphology in order to highlight regional, diurnal, and geographical differences in both warning skill and in what makes up a "typical" tornadic environment.