The Challenge of Forecasting Heavy Rain and Flooding throughout the Eastern Region of the National Weather Service. Part I: Characteristics and Events

Abstract

Heavy rain and flooding are of particular concern to forecasters throughout the eastern and southeastern United States. In this paper, the unique combination of synoptic-scale and mesoscale weather conditions and topographic factors that contribute to and enhance convectively produced flash flooding and river flooding are described and categorized. A classification system for synoptic-scale flooding events is developed, which is then used to identify the distribution (by month and synoptic-scale weather system) of major floods in the region of interest. Also, examples of flooding caused by synoptic-scale weather systems are presented. Characteristics of mesoscale heavy-rain events that result in flooding are discussed. Topographical and geographical factors in the region, which play a role in these events, are described, along with examples of mesoscale, flash flood events. Finally, floods produced by warm-top thunderstorms, which pose a unique and challenging forecast problem throughout the east and southeast, are described and an example is provided.