Positive ground flashes produced by low-precipitation thunderstorms in Oklahoma on 26 April 1984

Abstract

A group of thunderstorms developed in western Oklahoma during the afternoon of 26 April 1984. Two of these storms initially exhibited characteristics of low-precipitation (LP) thunderstorms. Lightning ground flashes produced by these storms were mostly positive. These storms split, with one right-moving component evolving into a tornadic supercell. Ground flashes produced by the supercell, however, were predominantly negative. The highest rate of positive ground flashes (1.5 min-1) occurred during LP storm splitting and merging, when about 84% of ground flashes were positive. The maximum total ground-strike rate was 3.4 min-1 and occurred during the tornadic supercell phase and when all but one of 136 ground flashes were negative. Analyses of soundings in the environments of the LP and supercell thunderstorms on this day show that the magnitude of the vector-averaged shear vector within the cloud-bearing layer was 4.8 × 10-3 and 3.8 × 10-3 s-1, respectively. -from Authors