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

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000 FXUS64 KMRX 240855 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 355 AM EST Fri Feb 24 2017 .SHORT TERM /Today and Tonight/... A strong frontal system is poised to impact the region over the next 24 hours, bringing with it the potential for strong to severe thunderstorms later tonight -- and a much cooler air mass heading into Saturday in it`s wake (addressed in the next section). Ahead of the front, breezy gradient winds from the south will help bring Gulf moisture into the region. In addition, this warm air advection and the insolation from the sun will help to warm us to near or above record high values by the afternoon. Most areas will peak in the mid to upper 70s, though I would not be shocked if a few areas across the southern Valley and along the immediate valleys near the foothills of the Smokies hit the 80 degree mark (thanks to downslope warming). The area will remain capped through the afternoon and evening as the front remains well to the west. Then between 00-06z an intensifying 850 mb jet will rotate across the Plateau and Valley in association with a prefrontal trough. These features will play a big role in whether convection will develop late in the evening and linger after the midnight hours across the eastern Tennessee Valley. Some modest instability will develop by 21-03z, with plenty of wind shear to provide lift and organization to any thing that does develop. The combination of around 800-1200 j/kg of ML CAPE and the 40-50 kts of bulk shear will allow a line of organized storms to develop and remain strong to severe as they move across the region between 03-09z. The primary threat with this activity will be damaging straight line winds and some marginally severe hail. Although a brief tornado or two cannot be ruled out, the presence of a pre-existing boundary will play a big role in realizing this threat. More veered/unidirectional wind profiles do favor line segments and damaging straight-line winds much more so over tornadoes at this time. In addition, as the LLJ ramps up overnight, strong gradient winds will be felt over the Great Smoky Mountain zones of Cocke, Sevier, and Blount Counties. Thus, we have issued an Advisory for those zones from 00-12z on Saturday. .LONG TERM /Saturday through Thursday/... Cold front will be pushing east of the forecast area by Saturday morning. High pressure builds in Saturday, bringing sunshine and generally dry conditions. West winds will be steady at 10-15kt and will help usher cooler air and more seasonable temperatures into the Tennessee Valley. Highs on Saturday will be 10-20 degrees cooler than Friday, ranging from the upper 40s across the Cumberland Plateau to the mid 50s in the Tennessee Valley. Very minimal lingering moisture behind the cold front combined with upslope flow may keep some light showers possible across the NE higher elevations through Saturday night. As cooler air rushes in behind the frontal passage and temperatures drop below freezing after sunset Saturday, a few snowflakes may even mix in, but no accumulation is expected. High pressure remains in place for Sunday with another day of sunny skies and seasonable temperatures. High pressure slides off the east coast Sunday night, and upper level flow becomes more southwesterly, helping to advect warmer air back into the region ahead of a fast-moving shortwave that will bring the next chance for showers. There`s still some differences in model solutions, but the general picture is a short wave lifting out of the Southern Plains, bringing scattered showers to mainly the southern half of the forecast area Monday afternoon. A warm frontal boundary will lift north and cross our area Tuesday/Tuesday night. It`s still a few days out and details will better resolve themselves as the days pass, but at this point it looks like this could bring another round of potentially severe thunderstorms to the area Tuesday into Tuesday night. The warm front would provide a focus for convection, and the GFS is currently showing a 50kt+ 850mb jet, CAPE values of 500-1000 J/kg, and PWATs maxing out at 1.3". For now, it`s something we`ll be keeping our eyes on, and thunder`s been added to the grids. The cold front is progged to push through the area on Wednesday, and should spark a more organized line of thunderstorms as it moves through. High pressure builds back in for Thursday, bringing drier, cooler conditions and mostly sunny skies. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 78 50 55 30 / 10 70 20 0 Knoxville McGhee Tyson Airport, TN 78 51 54 29 / 10 80 40 10 Oak Ridge, TN 77 49 53 27 / 10 80 30 10 Tri Cities Airport, TN 76 51 54 26 / 10 80 60 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...Wind Advisory from 7 PM this evening to 7 AM EST Saturday for Blount Smoky Mountains-Cocke Smoky Mountains-Sevier Smoky Mountains. VA...None. && $$ AMP/EMH is the U.S. government's official web portal to all federal, state and local government web resources and services.