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

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381 FXUS64 KMRX 251925 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 325 PM EDT SUN SEP 25 2016 .SHORT TERM (This Afternoon through Monday)...
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Another hot day across the area with the upper level ridge stretching northward from the Southern Appalchians into the Great Lakes. Temperatures as of 3 pm are in the upper 80s and low 90s across most valley locations with record highs in jeopardy once again. A stationary boundary is analyzed across SW VA and E TN along the higher elevations. Current radar imagery indicates a few shower/storms along the higher elevations along the TN/NC line and across the Plateau. Therefore, continued PoPs for there areas through the remainder of the afternoon. Mid-level winds will respond as an upper level trough tracks into the Great Lakes region tonight. These southerly to southwesterly winds will aid in lifting the front to the north as a warm front. Isentropic lift in the vicinity of this boundary will lead to an increase in cloud cover and some light precipitation overnight. For now, expect the majority of this will occur to the east of the mountains but did leave a slight chance mention of showers throughout the overnight mainly across the high terrain along the TN/NC line. Expect patchy fog will be possible in this vicinity as well with low level moisture remaining elevated. On Monday, a cold front will race across the Mid-Mississippi River Valley into the Tennessee River Valley. PW values ahead of the boundary will be in the 1.3-1.5 inch range during the morning hours. The best synoptic lift will be to the north as the trough swings through the Great Lakes and Ohio River Valley. For now, not seeing much lift tomorrow morning and have decided to lower PoPs some. By the afternoon, the front is moving into the Plateau with PW values building into the 1.6-1.8 inch range. With the delay in the precipitation arrival, temperatures will once again rise into the 80s to potentially low 90s. SBCAPE values will build into the 1000- 2000 J/Kg range. However, the lack of any substantial deep layer shear should keep storms below strong/severe limits. The lack of lift will also lead to modest rainfall amounts of a tenth to three quarters of an inch. It looks as though the highest amounts will be over the terrain in SW VA and NE TN where there will be a bit more lift. Not exactly the drought buster that is needed. The good news is that the front will usher in much more seasonable air hopefully ended the 90 degree weather for the remainder of the year. .LONG TERM (Monday Night through Sunday... Big weather pattern change still on tap for the upcoming work week. A cold front will be moving thorugh the area to start the long term period on Monday night. There will still be minor amounts of instability present to begin the night so will leave mention of chance thunder in the forecast for the first few hours. Highest pops come at the start of the period with low-end likely pops in place across areas east of I-75 and chance pops west of I- 75. Pops will drop from west-to-east through the night as the front progresses eastward. By early Tuesday morning most areas should be precip free, will hold on to pops longest across the far eastern areas until the front pushes through.. This front is accompanied by a long wave trough that will dive down into the Eastern U.S. The parent low will eventually become cut off and will spin and wobble across the Southeast through most of the long term. This will allow for much cooler and drier air to move into our region resulting in more fall-like weather. Highs and lows will be near normal on Tuesday. Temps continue to fall and will drop below normal by Wednesday and further more on Thursday and Friday. Highs and lows will run 5 to 10 degrees below normal on Thursday and Friday. Previous model runs have showed the potential for clouds and precip to possibly drop down into our northeastern areas Wednesday through Friday as spokes of energy go round and round the low, whereas the rest of our area remained cloud and precip free. The 12z Euro came in and crashed that party though. While the Euro still shows the same cut off low it is quite a bit further west than the GFS. If this is the case it would mean a much cloudier and wetter week for most of our area. Will continue to lean toward the GFS as the 12z superblend data supports the drier and sunnier GFS solution, for now. With all that said, we can still count on a much cooler week with below normal highs and lows for several of the long term days. The finer details are still up in the air at this point so stay tuned.
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Chattanooga Airport, TN 70 88 61 81 / 0 50 40 10 Knoxville McGhee Tyson Airport, TN 69 86 60 78 / 0 50 60 10 Oak Ridge, TN 69 85 58 79 / 0 40 50 10 Tri Cities Airport, TN 64 82 57 75 / 0 60 70 20
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