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

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430 FXUS64 KMRX 241913 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 213 PM EST Tue Jan 24 2017 .Short Term (Tonight through Wednesday Night)... Quiet night tonight as our low clouds erode this afternoon. Ridging aloft moves in tonight...and cold front will move through TN from west to east during the day Wednesday...keeping our area in the warm sector all day...so expect high temps in the TN valley to generally reach the 60s. Chances of rain move in from the west after lunch...peaking with likely category pops or higher Wednesday evening. Front will begin to clear precip from the area from west to east after midnight Wednesday night...with only isolated to scattered showers left east of I-81 by sunrise Thursday. H5 flow will be wsw`erly by sunrise Thurs and temps will not quite get to freezing at most places...so not expecting any issues when the cold air moves in behind the tapering precip. .Long Term (Thursday through Tuesday)... A cold front will be approaching the Atlantic Seaboard to start the extended portion of the forecast with cold air advecting in behind the departing front. A long-wave trough across the Eastern CONUS will prevail throughout much of the long-term forecast. Several shortwave troughs will rotate through the area during this portion of the forecast. The challenge will be the amount of lift and moisture with each passing system. The GFS continues to be the most bullish with each passing wave producing at least some measurable precipitation across the region. Cooler air will be in place with a reinforcing shot of cold air with each passing system. Thursday night into Friday it appears the best chances for precipitation will be in the higher elevations and locations north of I-40. The much more conservative ECMWF even shows some light QPF during this timeframe as well. For now, have mentioned 20-30 PoPs due to the uncertainty and low amounts forecast. Due to the cold air would expect much of this to be snow with any accumulations mostly limited to the higher elevations with light amounts expected there as well. Saturday looks to be a dry day as there is a brief break between system. Large discrepancies exists in the models on Sunday into Monday with the strongest of the upper level troughs forecast. The GFS and Canadian both indicate a phase between a northern trough diving southward out of the Northern Plains into the Tennessee River Valley and a southern wave moving across the Central Plains into the Northern Gulf. This phases allows the trough to dig across the region brining the heart of the cold air across the area. In addition, light precipitation will spread across the region. The GFS is the most bullish with QPF amounts of around 0.1-0.3 inches across the area with the Canadian being around half of that. Meanwhile, the ECMWF does not indicate this phase and the trough doesn`t dig as far south. The southern extent of the trough occurs Monday morning across the Mid-Atlantic. This puts the forecast area on the western periphery of the cold air advection with the moisture remaining well to the north and east. This latest run of the ECMWF is much different than the last run which was more in line with the current GFS. For the forecast, have included around 30-40 PoPs Sunday into Sunday night with mostly snow expected with 850 mb temps well below zero Celsius even on the warmer ECMWF. Again, there is still a good bit of model uncertainty and the forecast is likely to change over the next several days. Monday and Tuesday morning will be the coldest mornings throughout the forecast period with widespread upper teens and lower 20s. A moderating temperature trend is forecast on Tuesday as a ridge builds in from the southwest. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 39 65 42 47 / 0 30 70 10 Knoxville McGhee Tyson Airport, TN 37 64 42 45 / 0 20 70 20 Oak Ridge, TN 38 61 41 45 / 0 30 70 20 Tri Cities Airport, TN 33 62 42 44 / 0 10 60 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ GC/MA

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