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

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000 FXUS64 KMRX 170708 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 308 AM EDT Tue Jul 17 2018 .SHORT TERM (Today and Tonight)...
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With a weakly unstable air mass in place...a few isolated thunderstorms have continued over the region through the night into the early morning. Early morning coverage will be limited. a weakening cold front settles south and into the Southern Appalachian Region today...additional lift and low level moisture will increase and allow for widespread thunderstorm activity for the late morning and afternoon. The front should continue to weaken as it pushes through the area late today into this evening. As a result... thunderstorm activity will decrease this evening...ending for the overnight hours. As for temperatures ...highs today will reach into the mid 80s to around 90 across most valley locations and fall into the 60s to around 70 for the overnight lows. .LONG TERM (Wednesday through Monday)...The extended range fcst period kicks off on Wednesday morning amidst passage of an upper trough axis over the Appalachians, while at the surface drier high pressure will be building in from the north in the wake of an earlier fropa. With that, Wendesday into Thursday looks fairly dry across the region as instability is limited thanks to dewpoints in the upper 50s to lower 60s, as well as rising heights amidst shortwave ridging. The pattern looks to remain progressive into late week as another northern stream upper low/trough dives east/southeast across the lower Great Lakes and into the OH Valley by late day Friday. However, diffluent flow over the southern Appalachians out ahead combined with veered sly return flow (and thus rising dewpoints) looks to favor increasing chances for convection Friday afternoon and overnight, some of which could be strong. At that point the fcst becomes a bit less uncertain given range, however guidance does hint at a large nearly 600dm H5 anticyclone over the Atlantic providing some blocking of the mean flow aloft. Thus, the aforementioned trough and closed/stacked system is progged to slow/stall over the Appalachians and Mid- Atlantic through the weekend, which could result in prolonged periods of showers and thunderstorms and possible heavy rainfall. In summary, the fcst will remain dry on Wednesday with increased pops over higher terrain on Thursday. Pops will increase further for Friday and through the weekend into the high chance to likely range. Temperatures through the period will remain at or slightly below normal levels.
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Chattanooga Airport, TN 90 70 91 69 / 50 30 10 0 Knoxville McGhee Tyson Airport, TN 88 68 89 68 / 60 30 10 0 Oak Ridge, TN 88 68 89 67 / 50 30 10 0 Tri Cities Airport, TN 84 65 85 63 / 70 30 10 0
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