383 FXUS64 KMRX 212350 AAA AFDMRX AREA FORECAST DISCUSSION...UPDATED National Weather Service Morristown TN 750 PM EDT Sat Aug 21 2021 .UPDATE... FOR 00Z AVIATION. && .SHORT TERM...(Today through Sunday)... Key Messages: 1. Scattered showers and thunderstorms today and tonight, perhaps with some moderate to heavy rainfall at times tonight. 2. Falling rain chances and clearing skies from the north on Sunday with increasing temperatures amidst improved insolation. Discussion: The pattern this afternoon is highlighted by a large H5 vortex rotating atop the central Appalachians to the west of Hurricane Hurricane Henri over the western Atlantic, all of which is east of amplified ridging across the lower OH and Mid MS valleys consequent of anticyclonic flow atop the Arklatex. At the surface, an old stalled moisture axis is laid across KY/TN in a nw/se orientation generally from the Land Between the Lakes region se across Middle TN into southeast TN near Chattanooga. Earlier convection to the west across Middle TN in association with this moisture axis has finally shifted southeast toward/into northern AL, but not before dropping historic rainfall in it's wake. The deeper moisture continues to remain just west of the plateau with only some iso/sct convection out ahead across the plateau and central/southern TN valley. Outside of Marion County TN where previous day's rainfall has lowered FFGs a bit, most areas have relatively high FFG thus not expecting any current convection to present any hydro issues. Moving into/through tonight, the above noted moisture axis will shift east across the plateau into the TN valley bringing PWATs in excess of 2.25" as well as banded frontogenesis thanks to H3 Q Vector convergence associated with the jetmax rounding the trough. With that, guidance tends to favor some banded convection across the central/southern valley (generally south of I40) tonight into Sunday morning. Profiles overnight reveal deep saturation with 15kft frz levels and mean cloud winds of around 10kts, which are all signals for efficient rainfall. However, coverage seems sparse which favors lower confidence on any heavier convective rainfall tracks with residence time being much less than was observed this morning over Middle TN. Therefore, given the elevated FFGs in this region (which will likely lower some with the 00Z issuance given current rainfall) will just mention isolated moderate/heavy rainfall possible which could lead to localized flooding, all with pops in the chance range. Outside of the rain covered areas, guidance was also hitting fog pretty hard tonight where some increased radiational cooling is favored north of the I40 corridor, which was added. On Sunday the moisture axis finally looks to slowly exit the region as the primary upper vortex shifts east and heights begin to rise over East TN and southwest VA/NC. This will favor only lower end pops, peaking at chance levels over the southern valley. Overall, expecting decreasing cloudiness with temperatures surging into the upper 80s for the valley, lower 80s over the higher terrain. CDG .LONG TERM...(Sunday night through Saturday)... Key Messages: 1. A ridge will build into the region by Monday. Monday and Tuesday look fairly dry. 2. Mid and late in the week, showers and thunderstorms increase significantly as the ridge weakens and low level moisture increases. Activity will be mainly in the afternoon and evening hours. Discussion: A strong ridge will build into the region by Monday. With increased subsidence early in the week, POPs will be low around 15 percent or less on Monday. On Tuesday, POPs will be slightly higher around 20 to 25 percent in and near the mountains. Elsewhere, POPs will be around 15 percent or less. On Wednesday, the ridge will weaken and high pressure over the Atlantic will bring southerly winds and increasing low level moisture. This pattern will hold through the workweek and into the weekend. Scattered showers and thunderstorms are expected every afternoon and evening Wednesday, Thursday, Friday and Saturday. Temperatures will be hot through Wednesday with highs in the lower 90s and mostly sunny skies. Late in the week highs will be in the upper 80s as increased rain and clouds are expected. McD && .AVIATION... 00Z TAF DISCUSSION. Main concern for the 00z cycle is the possibility of TSRA affecting either KCHA or KTYS, and also fog and low ceilings mainly at KTRI. Best chances for TSRA at a terminal look to be KCHA, beginning around 02z as a complex of storms moves southeast from middle TN. Have a TEMPO for this. Another band may affect KTYS during that time but less confident there. Later on in the wake of this convection, fog and low clouds will be a concern. Lowest flight categories will be at KTYS and especially KTRI where some clearing may occur and promote fog development. CD && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 72 88 71 92 71 / 40 40 0 10 0 Knoxville McGhee Tyson Airport, TN 70 89 69 91 70 / 30 30 0 10 0 Oak Ridge, TN 70 89 68 91 70 / 30 30 0 10 0 Tri Cities Airport, TN 65 88 65 90 67 / 10 10 0 10 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$