Vol. 63: 171–190, 2015 CLIMATE RESEARCH Published online May 20 doi: 10.3354/cr01291 Clim Res Snowfall event characteristics from a high-elevation site in the Southern Appalachian Mountains, USA Daniel T. Martin1, L. Baker Perry1,*, Douglas K. Miller2, Peter T. Soulé1 1Department of Geography and Planning, Appalachian State University, Rankin Science West, 572 Rivers Street, Boone, NC 28608, USA 2Department of Atmospheric Sciences, University of North Carolina at Asheville, Robinson Hall, Asheville, NC 28804, USA ABSTRACT: Accurate assessment of snowfall patterns in high-elevation remote areas is essential to providing a foundation for further climatological analyses. The Southern Appalachian Moun- tain (SAM) region of the eastern US provides a unique study area due to its low latitude and prox- imity to the Gulf of Mexico and Atlantic Ocean. Major snowstorms, such as the remnants of Hur- ricane Sandy in October 2012, can result in heavy snowfall of 100 cm or greater in favorable upslope regions. Understanding the behavior of these precipitation patterns is important due to flooding threats caused by a combination of factors including deep snowpack exposed to heavy rainfall, cloud immersion, and high dew point temperatures, further exacerbating flooding threats. To contribute to this understanding, we installed the Mobile Precipitation Research and Monitor- ing (MOPRAM) station at Roan Mountain (1875 m) on the Tennessee/North Carolina border in October 2012. MOPRAM allowed us to analyze liquid equivalent precipitation, new snowfall, snow depth, air temperature, and relative humidity at high temporal resolutions during the 2012−2013 snow season. We present the observed snowfall event characteristics (e.g. new snow- fall, liquid equivalent precipitation, atmospheric conditions, and synoptic patterns) along with how these characteristics compare to other sites in the SAM. In our 25 event dataset, we observed the following patterns: conditionally unstable upstream lapse rates; predominantly northwest winds; high-to-low elevation precipitation enhancement near a factor of 3; and 364 mm of snow liquid equivalent on Roan Mountain. An estimated 391 cm of snow fell at Roan during the 2012−2013 season using nearby snow liquid ratios as an estimate for snowfall. KEY WORDS: Orographic snowfall · New snowfall properties · Southern Appalachian Mountains Resale or republication not permitted without written consent of the publisher 1. INTRODUCTION — on the order of kilometers or less — current atmos- pheric models cannot easily resolve precipitation The dynamic multiscale forcings governing snow- patterns for a wide variety of snowfall regimes such fall rates and amounts in mountainous terrain can be as synoptically driven flows (e.g. Miller-style sys- especially difficult for forecasters and climatologists tems) or mesoscale-forced flows (e.g. upslope precip- to diagnose due to complex interactions between itation). At the climatological level, understanding physical barriers and a poorly observed atmosphere. how these fine spatial patterns are reacting to cli- What sampling does exist suffers complications from matic shifts is important for predicting the outcome of instrumentation challenges, especially when meas- many important hydrological resources. While com- uring snowfall (Rasmussen et al. 2012). Because the prehensive studies of mountain meteorology such as spatial scale of mountain influences is often very fine the Mesoscale Alpine Programme (MAP) have made *Corresponding author: [email protected] © Inter-Research 2015 · www.int-res.com 172 Clim Res 63: 171–190, 2015 important contributions (Medina et al. 2005), the cation and reliable winter weather climato logy (John- atmospheric processes and patterns in mountainous son 1987). While not dependent on natural snowfall areas remain poorly understood because of low pop- due to a high capacity for snowmaking, cold weather ulation densities and associated limited observa- and natural snow enhance the experience and often tional networks due to inaccessible locations when lead to larger crowds on the slopes. Additionally, the compared to valley, coastal, or plains regions (Barry presence of perennial snow cover in remote areas 2008). such as Roan Mountain and along the Blue Ridge One reason the Southern Appalachian Mountain Parkway often provides an environment conducive (SAM) region of the US serves as a unique test bed for cross-country skiing that attracts visitors. for the analysis of snowfall climatology is the high The diverse terrain and climate of the SAM also frequency of events at higher elevations from a vari- make possible a number of natural hazards such as ety of synoptic regimes, such as Gulf and Atlantic flooding, landslides, and potent winter storms. In lows, 500 hPa cutoff lows, and Alberta Clippers 2004, torrential rainfall, attributed to the remnants of (Perry et al. 2010). Additionally, this region is charac- Hurricanes Frances and Ivan, triggered multiple terized by considerable topographic relief leading to landslides claiming 5 lives and 16 homes (Wooten et high spatial variability of precipitation. The most al. 2008). In 1998, deadly flooding affected the town extreme of these spatial gradients is associated with of Roan Mountain; this was ultimately associated northwest flow snowfall (NWFS), which is often char- with the combination of heavy rainfall and melting of acterized by orographically enhanced precipitation the existing deep snowpack on Roan Mountain on northwest slopes in the wake of synoptic-scale (1916 m), and resulted in 7 fatalities (Hunter & Boyd subsidence behind a surface cold front (Perry 2006). 1999). While such natural phenomena cannot be pre- With an elevation range between 183 and 2037 m, vented, the appropriate warning and response can the SAM region has the greatest topographic relief in be enhanced through effective study and under- the eastern US. Key features of this domain include standing of orographic precipitation regimes in the the southeast-facing Blue Ridge Escarpment in North region. Carolina (NC), the Great Smoky Mountains National Observation networks in the SAM such as the Coop- Park (GSMNP) and Unaka Range on the borders of erative Observer (COOP) and NC Environment and NC and Tennessee, and the Black Mountains of NC, Climate Observation Network (ECONet) have grown home to Mount Mitchell, the highest point east of the in recent years (Holder et al. 2006). However, auto- Mississippi River (2037 m). Annual average snowfall mated representation of favorable upslope snow fall in the region can range from <10 cm in the southeast sites remains lacking. To address this lack of sites, we foothills to >250 cm in high-elevation windward installed the Mobile Precipitation Research and escarpment regions such as Mt. LeConte in the Monitoring (MOPRAM) station on Roan Mountain GSMNP (Perry & Konrad 2006). just south of the Tennessee border (elevation This dramatic spatial variability makes the SAM a ~1875 m) on 30 September 2012 (Fig. 1). We chose unique region in the southeastern US when com- Roan Mountain for 2 primary reasons. First, the com- pared to Piedmont regions with substantially more bination of elevation and exposure results in fre- uniform climate patterns. Consequently, understand- quent snowfall events from multiple storm tracks ing of meteorological processes in the SAM remains (Johnson 1987). Second, the site has no known clima- an integral part of the culture for both the support of tological observations at the summit (nearby COOP tourism and the prevention and assessment of natu- sites are ~1000 m or more lower in elevation). The ral hazards. The 755 km Blue Ridge Parkway spans MOPRAM station now provides hourly observations from north-central Virginia to the GSMNP in western of temperature, relative humidity, liquid precipita- NC. In 2012, over 17 million visitors travelled the tion, and snow depth within a sparsely instrumented Parkway primarily for recreation (National Park region. Service 2012). This extensive road network extends We present results from the first year of MOPRAM to elevations over 1850 m in the western portion and data, exploring in detail lesser understood contribu- as a result is subject to frequent closures due to snow tors to snowfall in the SAM such as lapse rates, wind and ice (Meyers 2006). direction, and antecedent air trajectories. Character- While the ski resorts of the western US boast istics rarely sampled in the SAM such as orographic greater acreage, trail lengths, and vertical ascents, enhancement, lee drying, and event-scale variability the SAM has remained an important winter recreation are of particular interest, and are addressed in our destination for citizens of the East due to its nearby lo- analysis. In addition, we explore 2 case studies in Martin et al.: High-elevation snowfall characteristics 173 Fig. 1. Roan Mountain Mobile Precipitation Research and Monitoring (MOPRAM) site in North Carolina, USA, with sec- ondary monitoring stations; up- stream lapse rate locations are starred. MRR: Micro Rain Radar; GSMNP: Great Smoky Mountains National Park detail — the remnants of Hurricane Sandy and a pro- 2. BACKGROUND longed late-March snowstorm — in order to analyze the atmospheric processes and associated snowfall 2.1. Observations of snowfall in mountainous patterns involved with events having relatively high regions societal impacts. The research project was largely motivated by the inter-event mesoscale variability of Mountain regions are characterized in part