THE EVOLUTION OF A SEVERE MESOSCALE CONVECTIVE SYSTEM - CLOUD-TO-GROUND LIGHTNING LOCATION AND STORM STRUCTURE

Cloud-to-ground lightning-location data are correlated with the Doppler-radar-observed structure of the evolution of a severe mesoscale convective system in Oklahoma on 23 May 1981. While many of the results are not new, this study is unique in that the evolution of electrical activity in a severe storm is compared to storm structure for most of the storm's life. The first storm formed ahead of a mesoscale low pressure area located at the intersection of a front and a dryline, and developed into a tornadic supercell in an environment of locally enhanced vertical shear. Ordinary cells subsequently formed both to the southwest and northeast of the supercell along the dryline and the front, respectively, and merged with the supercell to form a squall line having a trailing stratiform precipitation region with midlevel rear inflow. It is shown that the cloud-to-ground flash rate in the convective region is related to the apparent strength of the updraft. Before the storm became a supercell, the lightning strikes, which were relatively infrequent, emanated from the anvil west of the core. When the supercell was producing its first tornado, most lightning strikes occurred around the edge of the most intense core and under the anvil south of the core. As the supercell weakened, ground strikes clustered closer to the core. During the squall-line stage, most cloud-to-ground lightning strikes were found to the rear of the core of the remnants of the supercell, and in the core of the cells to the southwest, which were less mature. The overall ground-strike rate peaked during the middle portion of the squall-line phase. The area of the midlevel radar echo associated with the most intense reflectivity core was well correlated with the ground strike rate. The area of midlevel radar echo representing the weaker portion of the core, however, lagged the ground-strike rate.