A weak cold air damming (CAD) event occurred east of the southern Appalachians on Saturday, 14 December 2013. The evolution of the surface pressure pattern subsequent to the onset of precipitation suggested diabatic influences were active in the development of the CAD air mass. Frontal precipitation moved into the western Carolinas and Virginia from the west during the morning of 14 December. The surface pressure gradient supported a south to southeast wind (Fig. 1) across the foothills and Piedmont. During the next several hours, an axis of high pressure developed just east of the mountains from Upstate South Carolina into the mid-Atlantic region (Fig. 2). The formation of the small high pressure ridge occurred when the precipitation moved into the region and apparently initiated evaporative cooling east of the mountains. Other factors possibly contributing to the CAD development were weak cold air advection and the inland movement of a front along the coast that enhanced the definition of the narrow ridge of high pressure.
The NOAA ESRL/PSD HMT-SE Pilot Study 915-MHz wind profiling radar at Marion in McDowell County, North Carolina, provided a look at the vertical structure of the atmosphere as the CAD developed. A weak and ill-defined low-level wind was replaced by a well-defined northeast wind in the lowest 1 km at the onset of precipitation between 1300 and 1400 UTC (Fig. 3). The profiler data also captured the decreasing near-surface temperature when the precipitation began and the persistence of the cool air until the precipitation ended at approximately 1900 UTC (Fig. 4). The northeast wind in the shallow CAD air mass lasted for about six hours after the precipitation ended, but it gradually diminished as the CAD eroded from the top down to the surface.