An assessment of key aspects of warm and cool season severe flash flooding in the Southern Appalachians

Flash flooding kills more people in the United States than any other weather phenomenon. One of the most vulnerable areas for flooding is the Appalachians. These mountains lie in a geographical location that place them near the Atlantic Ocean and the Gulf of Mexico, two major moisture source regions. This ample supply of moisture, mid-latitude circulation patterns, and orographic lifting leads to annual precipitation totals in the Appalachians that are comparable to locations along the Gulf coast.

The present study investigates flash flood events that are not influenced by tropical storms. We have considered eight such events. Four of these events occurred in the cool season and four occurred in the warm season. For example, during the afternoon of June 22, 2001, nearly stationary thunderstorms produced as much as four inches of rain on Skyland, North Carolina. On the other hand, a large mid-latitude cyclone resulted in up to four inches of rain on large portions of the southern Appalachians on January 26, 1996. This research shows the role of synoptic and general meso-scale settings and their forcings on the evolution of these extreme hydrometeorological events. Results suggest a significant difference in moisture advection between the cool season and warm season events. Wind profiles of the lower, middle, and upper troposphere of each system demonstrate the different roles of jet streams in precipitation movement.