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

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179 FXUS64 KMRX 221953 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 253 PM EST Thu Feb 22 2018 .SHORT TERM...
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(Tonight and Friday)... Another hot and humid day across the Southern Appalachians. All climate sites have already set record highs for the day with highs in the low 80s. So far the high of 81 degrees at Chattanooga makes it the all time warmest temperature observed in February. The portion of the front across the Tennessee Valley is making some progress to the east getting close to the Cumberland Plateau. Current radar imagery indicates an area of showers and storms stretching from Cumberland county southward into Marion county moving east. Due to this, have increased PoPs in the near-term for the Southern Plateau and Valley. The SBCAPE values are in the 500- 1000 J/Kg range with the high heat and humidity across the region. Overall, do not expect any organized convection with the lack of upper level support. Models indicate that 850 mb winds will become more southerly later this evening and overnight with the front pushing back to the north. This will also lead to decreasing PoPs across the forecast area during the overnight period. Expect records for maximum overnight low temperatures again tonight with lows ranging from mid 50s to low 60s. The cold front will be located near the Ohio River on Friday. Upper level to low level flow will be nearly parallel to the boundary from the southwest. Higher heights aloft and partly to mostly sunny skies will lead to record high temperatures again on Friday with highs generally in the mid to upper 70s. There is a shortwave trough that will approach the area late in the short-term forecast but expect any precipitation should hold off to just beyond 00z Saturday. .LONG TERM...(Friday night through Wednesday)... The upper ridge of high pressure that has nosed into the region will slowly drift south and east during the weekend. This will allow for a frontal boundary that has been stalled to our northwest to slowly push into the MRX CWA. Models continue to struggle with timing of this feature with the GFS the quickest...pulling the front through on Saturday and the NAM the slowest...waiting until Sunday. Prefer the slower timing and will trend the forecast towards a Saturday night/Sunday morning frontal passage. This will bring slight chance/chance POPs into the area late Friday night and Saturday with likely to categorical POPs Saturday night and early Sunday. The air mass ahead of the front will become weakly unstable and a few thunderstorms will be possible. Also...with a 50 to 60 KT jet at 850MB...can not rule out the potential for a stray strong storm. A few showers will linger into Sunday night as the front settles to our south. On Monday...a weak short wave riding along the frontal boundary be the focus of ongoing convection. Depending on how far south this boundary is...could see a few isolated to scattered showers move into at least southern areas on Monday. The boundary should continue to drop southward and by Tuesday...the front should be well south and surface high pressure will build in for a quiet and dry day. A low pressure system is expected to move in around the Wednesday/Thursday time frame...returning the area to an active and wet pattern for mid week.
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Chattanooga Airport, TN 62 78 59 75 / 10 10 30 40 Knoxville McGhee Tyson Airport, TN 61 77 57 73 / 20 10 30 40 Oak Ridge, TN 62 76 57 73 / 20 10 30 40 Tri Cities Airport, TN 56 76 54 71 / 20 10 30 30
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