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

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610 FXUS64 KMRX 180909 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 409 AM EST Wed Jan 18 2017 .SHORT TERM...(Today and tonight)... Upper trough moving east across Ohio Valley this morning is pushing a cold front across eastern sections of the forecast area this morning. Light rain showers across eastern third of the region will move out by mid morning. Some drier air will move in behind the front with skies clearing by afternoon. The break in the clouds will be brief this afternoon and evening as surface low in Texas along the front moves into the lower Mississippi valley tonight. The front to the south will begin to move back north as a warm front with moisture overrunning it late tonight. A few showers will develop late across southeast Tennessee. Highs today will be several degrees cooler than Tuesday behind the front but still in the mild mid 50s to lower 60s. Tonight with partly cloudy to possibly clear skies early lows will drop to near freezing northeast and mid 30s to near 40 elsewhere except southern plateau and valley where clouds move in first lows will stay in the mid to upper 40s. .LONG TERM...(Thursday through Tuesday)... An active pattern is expected throughout the extended forecast with higher than normal PW values and temperatures expected throughout much of the forecast period. For the beginning of the extended period on Thursday morning an upper level trough will be moving eastward across the Central and Southern Plains. At the surface, a warm front will be located just to the south of the area with a cold front across the Lower Mississippi River Valley. Southeasterly downsloping flow around an exiting high pressure to the northeast will counteract some of the isentropic ascent ahead of the approaching warm front and pushed PoPs back a bit with highest chances Thursday afternoon and into the overnight hours. These downsloping winds will lead to the highest temperatures along the foothills with highs in the low to mid 60s. The upper level trough will take on a negative tilt later in the day as it moves into the Tennessee River Valley. At this point, there will be some weak instability and have mentioned a slight chance for thunderstorms in the forecast late Thursday afternoon into early Friday morning. Upper level drying moves into the region Friday as the trough axis passes to the east and a shortwave ridge moves into the area. Highs on Friday will still be well above normal with values generally in 60s. The next system will move in on Saturday as strong low level warm air and moisture advection continue into the weekend. A tropical jet will bring in a series of shortwave trough across the Southeastern U.S. over the weekend. Rain chances will increase through the day Saturday with strong warm air and moisture advection. Models depict a warm front lifting northward during the afternoon with a good directional shear along the boundary with SBCAPE values nearing 1000 J/Kg across the Southern Valley and Southern Plateau late in the afternoon. An upper level trough will close off across the Lower Mississippi River Valley early Sunday. The continued warm advection and moisture advection will push SBCAPE values up into the 500-1200 J/Kg range across the forecast area, however, there is a bit of a capping inversion on the GFS forecast soundings. Low level shear still remains decent around 150-250 m2/s2. The system is still several days away but will go ahead and add the mention for strong to severe storms to the HWO for Saturday and Sunday with the threat on Saturday limited to the Southern Valley and Plateau. Cooler temperatures are expected to start the work week as the upper level low moves overhead. This will keep chances for showers continuing late in the forecast period. Despite the cooler air aloft, all of the precipitation from the upper level low should be in the form of rain. The upper level low will eventually drift to the northeast Monday night into Tuesday with drier air moving in for the middle of the work week. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 62 47 63 55 / 20 30 70 100 Knoxville McGhee Tyson Airport, TN 58 39 62 51 / 10 10 40 90 Oak Ridge, TN 57 40 59 51 / 10 10 60 90 Tri Cities Airport, TN 55 33 61 47 / 10 10 20 100 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ TD/MA is the U.S. government's official web portal to all federal, state and local government web resources and services.