Investigating the Environments of Null Tornado Cases in North Alabama and Southern Middle Tennessee

Various synoptic and mesoscale parameters taken from SPC Mesoanalysis data were cataloged for environments of both 1) unverified tornado warnings and 2) confirmed tornadoes in the Huntsville County Warning Area (CWA) from 10/2007-6/2015. The database of environments of unverified tornado warnings was analyzed to try to identify any cases of contamination of those environments by nearby tornadic environments. Any contaminated cases were removed from the unverified warning database, resulting in one database of 83 truly non-tornadic (“null case”) environments, and another of 172 tornadic environments. These datasets were filtered to avoid skewing of data towards one or two prolific tornadic or null case events, and sorted by season, to yield 49 filtered tornadic and 40 filtered null cases. The data were compared against each other to determine meaningful differences between the datasets, for potential use to NWS Huntsville forecasters. Many of the 37 different parameters proved significant, the most evident being that mixed-layer CAPE was greater for null cases, low-level lapse rates for tornadic cases were never below 5 °C/km, and various composite parameters (EHI, SCP, and SIGTOR) showed weaknesses in diagnosing cool season tornadic environments.