Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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000 FXUS64 KMRX 071958 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 258 PM EST Thu Dec 7 2017 .SHORT TERM (Today through Friday night)...
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At the surface, a cold front marked by a wind shift and dewpoint gradient now over E KY and Middle TN will push across our area this evening. As a result, drier low level air in the TN Valley will be a factor in how far west precip will reach late tonight/Friday. Models have come into better agreement with the 12Z runs that the mountains and SW NC will see some snow. The NAM spreads precip farther west, along a line from CHA to TYS to TRI, while the GFS precip hugs the terrain more closely. The difference appears to be in their moisture profiles, with the GFS showing much drier air below 600 mb than the NAM. Will keep PoPs in the mountain zones and SW NC to account for the dry post-frontal air mass, more like the GFS, but will raise PoPs and QPF in those areas from the previous forecast. Both models indicate that forcing associated with the jet will be weak in our area, and remain to our SE. Thus, snow accumulations are expected to be light, with up to 1 inch expected in Clay Co. NC and the higher elevations of the Smokies. For timing, onset of snow is expected to be within a few hours of sunrise tomorrow, ending near midnight Friday night as the upper jet pushes moisture east of the area. .LONG TERM (Saturday through Wednesday)... Cold upper low over eastern Canada near Hudson`s Bay and northeast Canada will keep the eastern two thirds of the country in a longwave upper trough and bring a series of cold fronts across the region from the Great Lakes. The first system will move in late Saturday and Saturday night. Light snow flurries and showers possible across mainly southwest Virginia and northeast Tennessee higher elevations with one half to one inch accumulation possible. Another impulse late Sunday night early Monday looks dry. Then Monday night and Tuesday a stronger impulse which deepens trough will reinforce the cold air and bring a better shot of frozen precipitation late Tuesday into Wednesday morning. Orographic northwest snowfall will develop Tuesday with good cold air advection with even light snow or flurries possible at lower elevations. The deeper moisture and strong northwest flow brings a better chance for more significant high elevation snowfall. This is followed by another quick moving weaker system Wednesday night into Thursday. Cold temperatures will prevail Saturday and Sunday but high temperatures warm into the mid 40s to lower 50s ahead of the next system. Lows will be several degrees below freezing Saturday through Sunday but closer to freezing early Monday and Tuesday. Temperatures become much colder again Tuesday with a slow warming by Thursday. Night time lows stay below freezing through the end of the forecast period.
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Chattanooga Airport, TN 31 38 26 45 / 10 10 0 10 Knoxville McGhee Tyson Airport, TN 27 35 24 41 / 0 10 10 10 Oak Ridge, TN 27 38 24 41 / 0 0 0 10 Tri Cities Airport, TN 28 35 24 38 / 0 10 10 10
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ DGS/TD is the U.S. government's official web portal to all federal, state and local government web resources and services.