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

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537 FXUS64 KMRX 141946 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 246 PM EST Thu Dec 14 2017 .SHORT TERM...(Tonight and Friday)... The cold front is now to the south and east of the area with a reinforcing shot of cold air arriving across the Southern Appalachians. PW values remain low behind the front with values in the 0.3-0.4 inch range. There is an area of low-level post frontal clouds across NE TN and SW VA. Expect these will persist throughout the afternoon and into the evening hours. The heart of the cold air advection will arrive late tonight into Friday and overnight lows will generally be in the 20s as surface high pressure builds in behind the departing front. This cold and dry airmass will continue into Friday with highs in the upper 30s to mid 40s. .LONG TERM...(Friday night through Wednesday)... Models continue to be in good agreement early in the long term period with diverging solutions late in the period. Surface ridging on Saturday will keep things dry with low boundary layer moisture resulting in large diurnal temperature variation through the day. As a shortwave trough moves eastward across the Southern Plains on Saturday night, southerly flow and moisture will increase ahead of it on Sunday. Model soundings indicate very dry air within the boundary layer on Sunday morning even though mid-levels are nearly saturated. This will likely limit precipitation on Sunday, especially during the early onset of precipitation. Cannot rule out a slight chance of brief light mixed precipitation early on Sunday morning with lingering cool air in the valleys and evaporational cooling. However, temperature profiles show warm air advection will keep any mixed precip brief and switch to all liquid rain by mid- morning Sunday. We stay in a southwesterly flow on Monday and Tuesday with most moisture expected to remain to our south. A cold front sweeps through late Tuesday with lingering moisture across the higher elevations of the mountains and northeast TN on Tuesday night. Surface ridging expected to keep us dry on Wednesday and Thursday. Model solutions diverge late week with increased uncertainty regarding strength and position of trough and expected position of the surface cold front. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 29 44 28 53 / 0 0 0 0 Knoxville McGhee Tyson Airport, TN 27 42 27 52 / 0 0 0 0 Oak Ridge, TN 27 42 27 51 / 0 0 0 0 Tri Cities Airport, TN 25 40 24 50 / 0 0 0 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ MA/JB

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