The Role of an Upper-level Potential Vorticity Anomaly in a Severe Weather Outbreak During MPEX
The purpose of this presentation is to characterize the influence of the aforementioned potent PV anomaly on the 12-13 June 2013 severe weather outbreak with the aid of high-density dropsonde observations provided by MPEX. A preliminary analysis shows enhanced upper-level winds on both the PV anomaly's poleward and equatorward sides produced a coupled jet structure, which created enhanced upper-level divergence and allowed for modest cyclogenesis on 12 June 2013. Enhanced vertical motion associated with the resulting surface cyclone in conjunction with favorable dynamic and thermodynamic parameters allowed convection to flourish along the cyclone's warm front. The convection was initially discrete in nature but later organized into a bowing progressive derecho with a well-defined bookend vortex on its poleward side. Particular attention will be paid to the vertical structure of the atmosphere in and around the PV anomaly leading up to convective initiation. A companion presentation by Bosart and Guastini (separate abstract) will document the life of the aforementioned PV anomaly from its incipient stages as a PV streamer over the Pacific to its interaction with the Rocky Mountains as a closed vortex.