Synoptic Classification of Snowfall Events in the Great Smoky Mountains, USA

Perry, L; Konrad, Charles; Hotz, David; Lee, Laurence

Mean annual snowfall in the Great Smoky Mountains National Park (GSMNP) exhibits considerable spatial variability, ranging from 30 cm in the valleys to 254 cm at higher elevations. Snowfall can be tied to a variety of synoptic classes (e.g. Miller A or B cyclones, 500 hPa cutoff lows), but the frequency and significance of different synoptic classes have not been fully understood, particularly at higher elevations. In this paper, we manually classify all snowfall events during the period 1991 to 2004 according to a synoptic classification scheme, calculate mean annual snowfall by 850 hPa wind direction and synoptic class, and develop composite plots of various synoptic fields. Hourly observations from nearby first-order stations and 24-hr snowfall totals from five sites within the GSMNP are used to define snowfall events. NCEP/NCAR reanalysis data are used to develop composite plots of various synoptic fields and to compare differences in synoptic field values between heavy and light snowfall events for Miller A cyclones. Results indicate that over 50% of the mean annual snowfall at higher elevations occurs in association with low-level northwest flow and that Miller A cyclones contribute the greatest amount to mean annual snowfall at all elevations. Heavy Miller A events are characterized by lowlevel northwest upslope flow, longer durations, lower 500 hPa heights, lower 850 hPa temperatures, and stronger mid- and upper-level dynamics.