936 FXUS64 KMRX 111717 AAA AFDMRX Area Forecast Discussion...UPDATED National Weather Service Morristown TN 117 PM EDT Mon Sep 11 2023 ...New AVIATION... .UPDATE... Issued at 1041 AM EDT Mon Sep 11 2023 Clouds in the northern TN Valley and SW VA have been slow to lift with the lowering sun angle and light/calm winds through the bounary layer. Some locations under the cloud cover have been slow to warm, and temperatures will need to be adjusted for this. As for rain chances today, the CAMS are showing some isolated development in the Plateau, which seems overdone given the lack of instability and dry air aloft seen in forecast soundings. Will maintain the slight chance PoP along the NC border, with a dry forecast elsewhere. && .SHORT TERM... (Today and tonight) Issued at 257 AM EDT Mon Sep 11 2023 Key Messages: 1. Patchy dense fog early this morning. 2. Mostly dry today and tonight with temperatures not far from normal. Discussion: Patchy fog to start with some locally dense. Will issue an SPS to highlight the fog. Heights will rise across our area today as brief ridging ahead of the next upper trough builds in. Model soundings show a drier profile with very limited convective energy. Best chance for some isolated convection will be across the eastern mountain terrain, and will keep slight chance PoPs in place there. Otherwise, expect a dry day with plenty of sunshine once any morning fog/low clouds dissipate. Temperatures will be near to slightly above normal. Some patchy fog is expected to develop again late tonight, although models suggest a bit more cloud cover may help to keep the fog from being as extensive as early this morning. && .LONG TERM... (Tuesday through Sunday) Issued at 257 AM EDT Mon Sep 11 2023 Key Messages: 1. Showers and thunderstorms expected Tuesday into Wednesday associated with a cold front. 2. Below normal temperatures expected the second half of the week. Discussion: On Tuesday, an upper level trough will be located across Ontario and the Great Lakes, just downshear of a ridge axis across the Rockies and into Saskatchewan/Manitoba. At the surface, area of low pressure will be centered over the Great Lakes with an associated cold front extending through the Ohio Valley and into the midsouth. High pressure will be centered across Ontario. Southwest flow aloft and isentropic ascent will bring increasing clouds and rain showers/storms ahead a cold front that is progged to sweep through the area Tuesday afternoon into Tuesday night. Weak advection and increasing cloud cover may tend to limit instability, with most guidance depicting MUCAPE's upwards of to 1000 J/kg. Not expecting much in the way of severe weather, but 30-35 kts of bulk shear may accompany the stronger h50 flow Tuesday afternoon so it will be something to keep an eye on. Any stronger storms could contain gusty winds. This system looks progressive enough to keep the threat of widespread flash flooding low but with antecedent conditions, it may not take much rainfall to cause isolated flash flooding. Majority of precipitation moves out late Tuesday, although isolated showers may hang around through early Wednesday. Main upper trough moves through the Ohio Valley Wednesday into Thursday with an airmass change behind the fropa. Cooler and drier conditions are expected through the end of the week and even into the weekend. Operational guidance starts to diverge late in the period though with Hurricane Lee's northward progression. How Lee impacts the synoptic flow is still in question and that may bring some minor changes to the forecast. && .AVIATION... (18Z TAFS) Issued at 114 PM EDT Mon Sep 11 2023 VFR conditions are forecast through this TAF period. Overnight, some scattered to broken clouds are expected to spread into the area from the west ahead of a low pressure trough, which should prevent widepsread fog development. Should this cloud cover arrive later than expected, or is less extensive than expected, then fog will be possible, mainly at TRI. Some showers may develop late in the TAF period, but confidence it too low to mention in the TAFs at this time. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 88 68 85 65 / 10 10 40 20 Knoxville McGhee Tyson Airport, TN 85 65 83 64 / 10 10 60 30 Oak Ridge, TN 86 65 81 61 / 10 10 60 20 Tri Cities Airport, TN 81 60 81 62 / 10 10 60 50 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...DGS LONG TERM....Diegan AVIATION...DGS