An Observational Study of Warm Season Southern Appalachian Lee Troughs. Part II: Thunderstorm Genesis Zones

Abstract

The thunderstorm genesis regions during warm seasons lee-trough episodes in the southern Appalachians are examined in this study. A composite of cloud-to-ground lightning data during 1985 lee trough cases indicates that the time of maximum activity is the late afternoon. A stratification of cases by the strength of the large-scale forcing indicated that both the strength and location of afternoon convection depended on synoptic, and subsynoptic-scale process. Days with strong or moderate cyclonic forcing produced the most lightning, but the strong forcing days produced convection primarily in the coastal plain, while moderate forcing days spread convection from the mountains to the coast. Conversely, days with relatively little cyclonic forcing were dominated by mountain convection. Nocturnal convection tended to weaken in general, except when storms passed over Chespeake Bay or approached the coast of the Carolinas. Examples from individual cases used in the composite are used to demonstrate the role of surface fronts and lower troposphic troughs in setting up the convective regime seen in the lightning climatology.