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

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847 FXUS64 KMRX 270756 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 356 AM EDT WED JUL 27 2016 .SHORT TERM...
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(Today and Tonight)...Upper level ridging refusing to budge along the southeast US coast into the Tennessee Valley today. Some convection was continuing overnight across northern middle Tennessee possibly along an outflow boundary and this may spread into the northern plateau before sunrise. Otherwise the beginning of the day will be mostly sunny with a few areas of patchy fog early. Fog not widespread enough to put in forecast. Weak frontal boundary stays to the north over the Ohio Valley today. Temperatures were again very warm yesterday in the mid and upper 90s. With current temperatures early this morning in the lower 70s northeast and mostly upper 70s south and central. Another hot day is in store. GFS brings in more convection south and NAM northeast. Think GFS is trying to cool temperatures down too much so will go closer to warmer NAM with highs again mid 90s in most lower elevations. Hopefully a couple degrees cooler than Tuesday as there should be a little better coverage of showers and storms. Weak mid to upper level low over lower Mississippi Valley begins to move east overnight and should bring a surge of moisture west toward the forecast area late wednesday night into Thursday. Will keep rain chances up overnight and then increase in the west late. Models now not showing as much coverage or as much rainfall late tonight so lowered pops some from earlier forecast. .LONG TERM...(Thursday through Tuesday)...Middle level low over the MS Delta tonight continues to drift northward around the western periphery of the Atlantic subtropical ridge. Guidance in good agreement on this low merging with the Westerlies N of the subtropical ridge over West TN by Thursday morning, then drifting E over Middle TN by Thursday night. This break in the subtropical ridge will allow for ample deep layer moisture to flow northward out of the Gulf Of Mexico into the East TN Valley on Thursday with PWS reaching to near 2 inches over the Southern and Central portions of the area. Combination of slow moving middle level trough and ample deep moisture will bring good rain chances to the area on Thursday with prospects of some locally heavy and sustained rains for portions of the area in need of it. With SFC-6KM shear on the order of 20-25 kt and MLCAPE values of 1000-1500 J/Kg, there is a possibility that some of the tstm activity may be strong to severe. Given precipitation and cloud cover expected, temperatures should fall back to near climatological normals for Thursday. As the broad middle level trough remains over the area through the weekend, a series of weaker middle level disturbances will propagate through bringing increased rain chances during maximum daytime heating. First of these shortwaves looks to move through the area on Friday. Although deep layer moisture will be cut off by that time, there is still enough instability, particularly over the southern half of the area to generate diurnal shower and thunderstorm activity. Trough then begins to shift East on Monday and Tuesday with decreasing chances for pcpn and a return to slightly above normal temperatures across much of the area. Building middle level ridge begins to shift E over the Ohio Valley by late Tuesday.
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Chattanooga Airport, TN 95 74 89 73 / 30 40 70 50 Knoxville McGhee Tyson Airport, TN 94 73 88 72 / 30 40 70 50 Oak Ridge, TN 93 73 86 72 / 30 40 70 50 Tri Cities Airport, TN 93 70 87 69 / 30 30 70 50
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