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

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986 FXUS64 KMRX 171933 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 233 PM EST Sun Dec 17 2017 .SHORT TERM...(Tonight and Monday)... Isentropic ascent to the north of a warm front is leading to widespread light rain across the area. Rainfall amounts have been light and do not expect to see anything over a tenth of an inch. Current water vapor imagery and RAP upper air analysis indicate a mid-level shortwave trough moving to the east across the Ohio River valley and Great Lakes with a ridge across the Florida Peninsula. At the surface, a warm front stretches W-E across South Alabama and Georgia. Current radar imagery indicates that the back edge of the precipitation is moving into the Plateau. Due to this, have decreased PoPs throughout the remainder of the afternoon and into the evening hours. The isentropic lift is forecast to move to the southeast during this timeframe. The lift will exit the region tonight but the low level moisture will remain with the boundary to the south. Due to this, expect fog and drizzle to develop overnight. Not forecasting dense enough fog for an advisory at this point but conditions will need to be monitored throughout the evening and overnight hours. Have also increased low temperatures overnight with widespread cloud cover lows will generally be in the upper 30s to mid 40s. On Monday, the upper level ridge will expand slightly to the north with the front to the south nudging to the northeast. The clouds will slowly dissipate late tomorrow morning. With the higher heights aloft and partly sunny skies by the afternoon, highs will warm into the mid to upper 50s. The boundary will not be too far to the south but the lack of a lifting mechanism aloft and PW values in the 0.4- 0.5 inch range will keep the forecast dry. .LONG TERM...(Monday night through Saturday)... Fairly active pattern will bring three precip episodes into the forecast area during the extended period, first on Tues night/Wed, second on Friday night/ Sat, and the third potentially on Sunday. Model solutions for the late portions of the forecast, around Christmas Eve, continue to fluctuate wildly. The 12Z EMCWF just arrived, showing a fairly warm Christmas Eve and Christmas Day with the frontal boundary and rain field to our north over the Ohio Valley, while the GFS is cooler and wetter with the frontal boundary near us, but still not cold enough to produce wintry precip. We will have to wait and see what comes of this epic battle of model solutions. But as it stands presently, this week looks to be warmer than normal, continuing into the holiday weekend. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 42 59 46 61 / 20 10 10 60 Knoxville McGhee Tyson Airport, TN 41 57 43 60 / 20 10 0 40 Oak Ridge, TN 40 57 43 59 / 20 10 10 40 Tri Cities Airport, TN 38 55 39 59 / 30 20 10 30 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ MA/GC

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