1. 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

2. 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

3. 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

4. Study Area Southern Appalachian Mountain (SAM) Region
Southeast US States of GA, SC, NC, TN, VA, WV, KY
Elevation Range: m
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)

5. 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)

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

7. Microwave Rain Radar
Reflectivity
Velocity

8. 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 cm snowfall

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

10. 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

11. 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

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

13. Statistics by Synoptic Event Type

14. 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

15. 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.

16. 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.

17. 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

18. 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%)

19. 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 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.

20. 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