Winter Lightning and Heavy Frozen Precipitation in the Southeast United States

Abstract

This study addresses winter season lightning by examining synoptic-scale circulations, cloud-to-ground (CG) lightning patterns, and frozen precipitation. Specifically, locations, frequencies, and polarities of CG flashes are related to the location, intensity, and type of heavy frozen precipitation (snow, freezing rain, or ice pellets) for seven winter storms affecting the southeast United States from 1994 through 1997. The results suggest two distinct phases of winter storm development, each producing different patterns of CG lightning and frozen precipitation. These phases are termed the arctic front (AF) and migratory cyclone (MC) types. Analysis was performed on 27 periods within the seven cases. In several periods, there were significant numbers of CG flashes within or near a subfreezing surface air mass and frozen precipitation when a quasi-stationary arctic front existed. These periods were classified as AF phases. This flash pattern indicates a connection between the intensity of convection (associated with CG flashes) and downwind frozen precipitation. In these situations there was strong southwesterly flow aloft, which may have advected ice particles from these convective clouds into stratiform clouds near the frontal surface. This process resembles the ?seeder?feeder? mechanism of precipitation growth. The AF phases eventually developed into MC phases, and the latter were more common in this study. The MC phases in general exhibit a different spatial relationship between CG lightning and heavy frozen precipitation; that is, CG flashes retreat toward the warm sector of the cyclone and thus are not proximal to the 0°C surface isotherm. There appears to be little connection between convection and frozen precipitation in most of these situations. The distinction between AF and MC phases, in conjunction with CG lightning monitoring, may aid forecasts of the duration and amount of frozen precipitation during winter storms.