Winter lightning and heavy frozen precipitation in the southeast United States

This study addresses winter season lightning by examining synoptic-scale ci rculations, cloud-to-ground (CG) lightning patterns, and frozen precipitati on. 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 di stinct phases of winter storm development, each producing different pattern s of CG lightning and frozen precipitation. These phases are termed the arc tic front (AF) and migratory cyclone (MC) types. Analysis was performed on 27 periods within the seven cases. In several per iods, there were significant numbers of CG flashes within or near a subfree zing surface air mass and frozen precipitation when a quasistationary arcti c front existed. These periods were classified as AF phases. This flash pat tern indicates a connection between the intensity of convection (associated with CG flashes) and downwind frozen precipitation. In these situations th ere was strong southwesterly flow aloft, which may have advected ice partic les from these convective clouds into stratiform clouds near the frontal su rface. This process resembles the "seeder-feeder'' mechanism of precipitati on 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 degreesC surface isotherm. There appears to be little con nection between convection and frozen precipitation in most of these situat ions. The distinction between AF and MC phases, in conjunction with CG ligh tning monitoring, may aid forecasts of the duration and amount of frozen pr ecipitation during winter storms.