As we draw closer to Thursday afternoon a strong upper level system will near the southeastern US. This storm will draw in copious Gulf of Mexico and Atlantic moisture. Many model projections forecast close to 2 inches of QPF in the southeast over the next 36 hours. Due to the nature of upper lows, cold air aloft can be tapped into under the right circumstances. As this upper low tracks across the deep south tomorrow and the Carolinas tomorrow night, this cold air will dynamically be driven to the surface via heavy precipitation rates
Rain will change to snow from NW to SE. First this will take place over the mountains Thursday morning and into the foothills and Piedmont by late afternoon. Further east into the coastal plain, rain will change to snow by early evening. In these situations, strong dynamics can lead to erratic accumulations. Some areas could see very little in the way of accumulations, while 15 miles away several inches could fall. Especially further south as you get closer to the intense dynamics.
The 500mb low will travel across central Georgia into central SC and over eastern NC. The reason we have seen favorable trends over the last few days is because of a known American model bias of shearing out upper lows too quickly in these scenarios. The EuroENS mean actually maintains a cutoff 500mb upper low all the way to the coast of NC. A very rare scenario and one which could prove to spark a very solid and unusually consistent deformation zone over the southeast. These deformation snows are much more commonplace further west and over the plains, however, much less so over the southeast and southern mid-atlantic. With the 850mb low taking a similar track, this will allow the deformation zone (aka comma head) to pivot from eastern Tennessee into western NC and eventually the piedmont.
Warmer ground temperatures and boundary layer temperatures in the mid 30's will limit excessive accumulations over some areas. Further north near the NC/VA border, especially over S-Central VA and far N-Central NC, colder boundary layer temps will all more favorable conditions for accumulations. See the attached forecast map for details.
-Brandon
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