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

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845 FXUS64 KMRX 182017 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 317 PM EST Thu Jan 18 2018 .SHORT TERM...
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(Tonight and Friday)... A shortwave ridge is moving across the Appalachian Mountain region with a trough off the Atlantic Coastline. There is another trough across Texas that will drift slowly eastward throughout the short- term forecast. At the surface, high pressure is centered across the Lower Mississippi Valley with the ridge axis extending northeastward along the Appalachians. Quiet weather is forecast to continue tonight. Ideal radiational cooling conditions will setup again with clear skies and light winds. Temperatures will not be as cold as the pattern begins to shift. Overnight lows will still below normal and range from the teens to low 20s. Expect the colder locations will be in those sheltered valleys with remaining snow cover. On Friday, the surface high shifts further to the east across the Northern Gulf Coast with weak southerly flow returning to the forecast area. PW values will be near the minimum values observed for mid-January and the forecast calls for dry conditions with sunny skies. Temperatures will begin to moderate with plenty of insolation and weak southerly flow. Highs will generally be in the 40s. .LONG TERM...(Friday night through Wednesday)... An upper level low pressure system moves across the Gulf states through the day on Saturday. Low level flow continues to be from the southwest...bringing moisture and warm air to the area. NAM tries to bring enough lift and convergence in the low levels for scattered light showers across the area...though GFS and ECMWF keep the area dry and mostly clear. Have leaned towards the NAM with the amount of moisture available and included mostly cloudy skies through the day. Moisture and cloud cover will continue to increase across the area through Sunday...with a frontal boundary approaching the area Monday. Models have been slower on the approach of this bringing rain into the area beginning early afternoon Monday...through the overnight hours Monday night. Little to no instability is present with this front...though PW values are in the 90th percentile for this time of year. With the amount of upper level forcing...would expect widespread moderate showers...with only an isolated rumble of thunder expected in areas south of I40. Monday evening...a mid level jet moves through the area long with the front...with winds gusting 30 to 40 mph. The front is expected to be east of the Appalachians by mid Tuesday morning...with weak northwest flow setting up behind the front. Temperatures will only cool slightly with dry air and mostly clear skies expected through Thursday. A weak low pressure system will pass across the Gulf states late Wednesday through Thursday.
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Chattanooga Airport, TN 19 48 27 53 / 0 0 0 10 Knoxville McGhee Tyson Airport, TN 18 46 24 50 / 0 0 0 10 Oak Ridge, TN 17 46 25 49 / 0 0 0 10 Tri Cities Airport, TN 15 44 21 48 / 0 0 0 10
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