404 FXUS64 KMRX 112304 AAA AFDMRX AREA FORECAST DISCUSSION...UPDATED National Weather Service Morristown TN 704 PM EDT Sat Sep 11 2021 .UPDATE... FOR 00Z AVIATION. && .SHORT TERM...(Tonight and Sunday) Key Messages: 1. Dry weather expected again tonight and Sunday as upper level ridging strengthens over the region and surface high pressure remains in control. Temperatures increase back to above normal Sunday. Discussion: Upper level ridging over the southwest and south central states has now begun shifting east and is now covering much of the Tennessee Valley. Surface high pressure has now become centered east of the Appalachians as well. As a result winds were shifting to the south and southwest around the high and rising heights have allowed temperatures to climb into the lower 80s at most low elevation sites. With light southerly flow overnight lows will be slightly warmer tonight...mostly mid 50s to mid 60s. Patchy fog locally dense should form across some area rivers and lakes again by early morning with slight increase in low level moisture but does not look like it will be widespread. A warming trend will continue Sunday as the upper high strengthens. Dew points will begin to rise as well from the 50s into the lower 60s. Apparent temperatures will be in the mid to upper 80s Sunday afternoon with a few spots to about 90. Cloud cover should still be scattered and not affect high temperatures. TD .LONG TERM...(Sunday night through Saturday) |Key Messages: 1. Increasingly hot, humid, and mainly dry through Tues. 2. Chances for afternoon/evening showers/storms increase Wed through Sat, but temps will remain very warm and humid. Discussion: Sunday Night through Tuesday... Quasi-zonal flow will be found across the country Sun night and Mon with H5 heights over 591 DAM over the SE CONUS and broad surface high pressure retreating into the western Atlantic. This will maintain WAA, and with plenty of sunshine continuing and 850 mb temps around 18C, highs Mon will warm into the upper 80's to near 90 after morning lows staying in the low/mid 60's. By Mon night, a potential tropical cyclone will be approaching the TX coast with a landfall likely to occur sometime during the day Tues. Mid/upper ridging will continue to hang on over the SE CONUS through Tues with the broad surface high still over the western Atlantic as well, but the southerly flow will begin to advect the tropical moisture from the cyclone into the TN Valley. This increase in low-level moisture combined with strong heating will allow for isolated diurnal convection over the S Valley, Plateau, and Smokies Tues, so blended NBM slight chance PoPs. Most areas will stay dry with morning lows in the low/mid 60's and highs Tues around 90 once again. Tuesday Night through Saturday... The potential tropical cyclone will slowly move into the Delta region Tues night and Wed while a northern stream shortwave trough progresses rapidly from the N Plains through the Great Lakes. This shortwave will push a weak cold front into the OH Valley Wed, but the front will quickly wash out as a piece of the shortwave cuts off and dives into the S Plains and merges with the tropical system. This will result in a slow moving, cut off low that will gradually rotate through the Mid South Wed and Thurs advecting deep tropical moisture into the TN Valley and S Appalachians beneath large scale mid/upper ridging that rebuilds to the north. Have chance PoPs areawide both Wed and Thurs for diurnal convection as PWATs should be increasing to nearly 2 inches, and this combined with heating will build up appreciable diurnal instability. Too early for details, but slow moving convection with locally heavy rainfall is possible. Uncertainty increases Thurs night through Sat regarding how fast the cut off low will eject to the NE. The deterministic CMC and ECMWF are much more progressive with another northern stream shortwave kicking the low northeastward, while the GFS keeps it spinning over the deep South as another potential tropical system develops in the western Atlantic. The GEFS/Euro/Canadian ensemble means show big differences too, so kept NBM chance PoPs each afternoon Fri and Sat. Temps from Wed into next weekend will remain very warm and humid in this tropical airmass with highs in the mid/upper 80's and lows in the mid/upper 60's. Garuckas && .AVIATION... 00Z TAF DISCUSSION. Clear skies are forecast at all sites through the TAF period, but there is some uncertainty regarding fog at TRI. For now, signs point to no fog, similar to last night. Dewpoints dropped to the lower 50s this afternoon, and with forecast lows in the mid 50s, fog seems unlikely. But it's TRI, so you never know. Could see quarter mile vis develop if fog rolls in off the nearby lake. DGS && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 63 88 65 89 67 / 0 0 0 10 0 Knoxville McGhee Tyson Airport, TN 61 87 65 89 67 / 0 0 0 10 0 Oak Ridge, TN 61 86 63 88 66 / 0 0 0 10 0 Tri Cities Airport, TN 56 86 62 88 63 / 0 0 0 0 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$