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

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000 FXUS64 KMRX 240727 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 327 AM EDT Wed May 24 2017 .Short Term (Today and Tonight)...
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An active day across the Tennessee Valley and southern Appalachians. A deep upper trough will dig southeast into the Tennessee Valley with jet dynamics moving across the Region. First wave of energy is currently moving across northern Alabama. This wave will move northeast across the area this morning with showers and embedded thunderstorms. As another jet streaks moves across the Region late this morning and afternoon, pressure falls are expected across the lower Ohio/northern Tennessee Valleys with a surface low moving northeast into east Kentucky/southern Ohio. The pressure falls will help induce a boundary layer jet of 35kts across the Region improving the shear profile. A surface boundary will move across the area late this morning and afternoon with moist and unstable air ahead of the frontal boundary. Main question is if there will be enough breaks in the cloud cover today allowing the low-level airmass to destabilize. Latest high resolution models, such as the HRRR model do show individual strong convection developing. Due to the expected shear, low- topped supercell structures are anticipated later today with the SPC HRRR Browser depicting good updraft helicity for the storms across the eastern/northern counties between 16-20Z. Given the above isolated tornadoes are a concern Today for areas mainly along and east of interstate 75. Besides the tornado threat, cold air aloft and low-level jet may produce hail and damaging winds with the stronger storms. Frontal boundary will move east of the area by early evening with shower coverage diminishing for tonight. A cool night is in store. .Long Term (Thursday through Tuesday)... Confidence in forecast through Saturday is fairly high with models in good agreement on a largely amplified wave pattern aloft. GFS Ensemble as well as GFS and ECMWF begin to diverge slightly Sunday through Tuesday as next fairly broad 500 mb low begins to drive SE across the Great Lakes area. By Thursday morning, 500 mb low over central Ohio extends trough axis south over East TN. As trough axis swings eastward through Friday morning expect to see some showers and thunderstorms particularly over the northern half of the area that will diminish with sunset Thursday night as a broad ridge builds over the area on Friday. Shortwave trough is fcst to move across the broad ridge on Saturday. With it, expect chance for some showers and thunderstorms Saturday afternoon. Greatest threat for strong storms on Saturday will likely lie in SW Virginia and NE Tennessee where nose of 300 mb jet pushes across the ridge axis late Saturday. Next front approaches the area Sunday before moving through on Monday. Digging 500 MB trough coupled with surface dewpoint climbing back into the upper 60s across a large portion of the area, will result in greater coverage of showers and thunderstorms on Sunday with potential for more strong to severe storms by afternoon. Broad trough aloft dominates the eastern third of the US on Monday into Tuesday with instability on Monday holding up chance POPs into Tuesday before significant dry air aloft lowers chances on Tuesday. Thursday`s temperatures expected to be on the cool side with cloudy skies and the upper trough swinging over the area. However, temperatures will rebound nicely on Friday to near seasonal norms through the remainder of the forecast.
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Chattanooga Airport, TN 72 55 75 56 / 90 50 30 0 Knoxville McGhee Tyson Airport, TN 73 54 70 54 / 90 40 50 10 Oak Ridge, TN 72 54 71 55 / 90 40 40 10 Tri Cities Airport, TN 73 53 64 52 / 90 60 70 30
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