Synoptic classification of 2009-2010 precipitation events in the southern Appalachian Mountains, USA

Precipitation processes and patterns in the southern Appalachian Mountains (SAM) are highly complex and varied due to the considerable diversity of synoptic-scale circulation patterns and associated orographic effects. Whereas frontal activity associated with extratropical cyclones is responsible for a large fraction of the annual precipitation in the region, 500 hPa cutoff lows, tropical cyclones, non-frontal air mass thunderstorms, and moist SE or NW low-level flow also produce considerable precipitation. This paper classifies the synoptic patterns associated with precipitation in the SAM over the course of a 16 mo period in 2009 and 2010. Precipitation events were identified using National Weather Service cooperative observer, Community Collaborative Rain, Hail, and Snow (CoCoRaHS), and other selected automated meteorological stations across the region. A combination of manual and automated approaches was used to create a synoptic classification of precipitation events in the SAM. Antecedent upstream air trajectories provided information on moisture source regions and low-level flow. Warm season precipitation events were influenced by air masses originating over the Gulf of Mexico and the Atlantic Ocean. These events were characterized by short periods of high-intensity precipitation that was primarily convective in nature. Cool season precipitation was associated with a variety of frontal types, as well as non-frontal mechanisms, characterized by longer, wetter, low-intensity events. These events were largely influenced by air masses originating over the Gulf of Mexico and to the northwest of the study area. In both seasons, precipitation events associated with frontal activity produced greater amounts of precipitation per event when compared with non-frontal activity.