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

Abstract

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.

Relationships between aerosols and precipitation in the southern Appalachian Mountains

“…The synoptic classification scheme resulted in 183 precipitation events during the study period (Figure ) (Kelly et al ., ). There were 123 events during the two warm seasons in the study period, which included precipitation associated with cold, warm, and stationary fronts, as well as non‐frontal mechanisms involving shallow upslope flow and terrain‐induced convection.…”

“…There were 60 cool season precipitation events, which included frontal precipitation associated with cold, warm, and occluded fronts, as well as Gulf Lows and Nor'easters (Kelly et al, 2012). Non-frontal mechanisms, such as northwest upslope flow (e.g., Keighton et al, 2009;Perry et al, 2007) were also responsible for some events.…”

“…This study examines the synoptic controls of precipitation patterns and aerosols in the SAM based on a synoptic classification scheme described by Kelly et al . (, accepted for publication in Climate Research ).…”

“…Statistical relationships between aerosols and precipitation were examined in the southern Appalachian Mountains to determine the seasonal and synoptic influences on these relationships, as well as the influence of air mass source region. Precipitation events were identified based on regional precipitation data and classified using a synoptic classification scheme developed for this study and published in a separate manuscript (Kelly et al 2012). Hourly aerosol data were collected at the Appalachian Atmospheric Interdisciplinary Research (AppalAIR) facility at Appalachian State University in Boone, NC (1110 m asl, 36.215 • , -81.680 • ).…”

Winter climate variability in the southern Appalachian Mountains, 1910–2017

“…Miller A and Miller B cyclones that originate in the Gulf of Mexico before tracking along the Atlantic Coast are the primary contributors to heavy snowfall in the region (Miller, 1946;Perry et al, 2010). A variety of other synoptic patterns known to produce snowfall in the SAM includes upper-level cut-off lows, clippers, and northeastward tracking Colorado lows (Perry et al, 2010;Kelly et al, 2012). Spatially, Gulf lows contribute a majority of snowfall to eastern-facing slopes, whereas Northwest flow snow (NWFS) events contribute more than 50 percent of the annual snowfall to windward and high elevation locations (Perry and Konrad, 2006;Keighton et al, 2016).…”