An Analysis of Cold Season Supercell Storms Using the Synthetic Dual-Doppler Technique

Abstract

old season tornadic outbreaks occur with regularity in the southeastern United States; however, detailed analyses of parent supercell storms in the cold season environment (often low CAPE, high shear) are scarce. This is often because storms do not always move close enough to radars for a comprehensive single-Doppler analysis and significant topography or trees in the Southeast make it difficult for mobile radars to operate, thus limiting dual-Doppler coverage. However, during the Super Tuesday tornado outbreak of 5?6 February 2008, two tornadic supercell storms passed within 30?40 km of the Weather Surveillance Radar-1988 Doppler (WSR-88D) sites in Memphis and Nashville, Tennessee (KNQA and KOHX, respectively). The relative steadiness of these storms during passage, along with the large motion vector (from the southwest at 20?25 m s?1), allowed the application of a synthetic dual-Doppler (SDD) analysis. As such, a detailed analysis of these storms was completed, including examinations of low-level circulations, updraft strength and location, as well as retrievals and evaluations of perturbation pressure and the vertical pressure gradient. This study presents one of the first comprehensive analyses of cold season supercells using only one Doppler radar. Additionally, the relative success and failures of using the SDD technique on supercell storms are discussed. Major findings for the primary case include the updraft maximizing at a very low height (3.0 km AGL), and weak pressure forcing within the rear flank resulting in a nonexistent rear-flank downdraft (RFD).