Snowfall Event Characteristics from a High Elevation Site in the Southern Appalachian Mountains Daniel T. Martin and L. Baker Perry Appalachian State University 70th Eastern Snow Conference Huntsville, Ontario 05 June 2013

Background Accurate assessment of remote snowfall patterns is essential to providing climatological boundary conditions Southern Appalachian Mountain (SAM) region unique due to low latitude, proximity to moisture-rich Gulf of Mexico Sparse reliable high-elevation climatological records exist in the Appalachians

Societal Impacts: The 1998 Roan Mountain Flood Deadly flooding (7 lives lost) attributed to heavy rainfall, relatively deep snow pack at highest elevations (i.e., Roan Mountain > 30 cm). Highlights importance of understanding characteristics of antecedent snowfall/snowpack

Study Area Southern Appalachian Mountain (SAM) Region Southeast US States of GA, SC, NC, TN, VA, WV, KY Elevation Range: 183-2037m Exposed to a variety of synoptic regimes Northwest flow snowfall Isentropic precipitation from Miller A/B lows Cold Air Damming SAM Region (From Perry and Konrad 2006)

Data Suite of instrumentation in northwestern North Carolina Mobile Precipitation Research and Monitoring (MOPRAM) surface observations (Roan Mountain) Micro Rain Radar (MRR, Poga Mountain) Corroborative wind speed/direction (Poga Top, Grandfather Mountain)

Roan MOPRAM Suite Precipitation type sensor Sonic Snow Depth Temp/RH Pluvio liquid precip w/shield

Microwave Rain Radar Reflectivity Velocity

Case Study: Hurricane Sandy Remnants In late October, Hurricane Sandy makes landfall in New Jersey Phasing with longwave trough initiates prolonged period of upslope snowfall, unseasonably cool temperatures Storm total estimated, 79.5 mm liquid equivalent precipitation 71-89 cm snowfall

Methods Overview Manually determine snowfall events through systematic approaches Compare MOPRAM data with Vertically Pointing Radar Seek low fall speeds indicative of solid precipitation

Methods Overview Generate characteristics for determined event catalogue Seasonal wind direction histograms Precipitation statistics by synoptic event type Derive parameters Lapse rates Seasonal snowfall estimates Orographic enhancement of precipitation Snow cover days

Summary Statistics Temporal Range: 30 September 2012 – 04 April 2013 Number events: 25 Average event duration (hr): 18.92 Event Totals Snow Liquid Equivalent Precipitation: 364 mm Event Hours: 473

Wind Direction West-northwest winds dominate majority of events ~69% (328 event hours) include direction between 270, 360 degrees Modal wind direction: ~280 degrees

Statistics by Synoptic Event Type

Lapse Rates Derive lapse rates from T_Poga (1115 m) and T_R0an (1915 m) at event maturation Maxima occur during beginning, end of season Minima associated with E/SE winds, cold air damming Average Lapse Rate: 9.59 C/km Absolutely unstable (10.29 C/km) excluding outliers

Seasonal Snowfall Estimates Estimate seasonal snowfall at Roan using a variety of metrics Max/Min: Sum of differentials between event maximum and minimum snow depth recorded by sensor 6-hr: Sum of differentials between 6 hourly time periods (e.g., 0, 6z) Poga: Uses product sum of SLRs reported at Poga, roan liquid equivalent. When unavailable, 5:1 “warm” ratios assumed.

Orographic Enhancement Factor Ratio of Roan to Poga liquid precipitation amounts Average enhancement: 2.25 for 900 meter height differential Additionally consider exposure to NW flow.

Precipitation Distribution by Type Compare SWE total with seasonal precipitation to determine fraction of solid precipitation Derive freezing rain on Roan as function of sub-freezing, non snowfall accumulating precipitation

Seasonal Snow Depth Days snow cover >1 cm: 104 (53%) Manual reports of SWE (mm), Density (kg/m3) shown 65, 232 88, 203 34, 193 44, 219 99, 244 141 , 292 ~ 50 cm 66, 200 Days snow cover >1 cm: 104 (53%) Days snow cover > 25 cm: 43 (22%)

Conclusions Installation of an automated precipitation station in a high elevation location favorable for snowfall in SAM region allows new snowfall characteristics to be determined for the first time Majority of snowfall events during 2012-2013 season dominated by west, northwest winds Location receives further enhanced precipitation being on NW escarpment of NC/TN border. Lapse rates are commonly indicative of an unstable air mass despite synoptic-scale subsidence Orographic enhancement remains a key influential factor and is a relatively consistent way of determining snowfall amounts in remote, high elevation locations.

Questions? Acknowledgements The authors would like to thank Mike Hughes, Dana Greene, and the College of Arts and Sciences as well as the Office of Student Research. Dr. Sandra Yuter of North Carolina State University. Special thanks to Jonathan Welker for assistance with site installation. Steve Keighton, Laurence Lee, Douglas Miller for assistance with synoptic event classifications This material is based upon work supported by the National Science Foundation under Grant # EAR 0949263.