291 FXUS62 KGSP 211751 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 151 PM EDT Sat Aug 21 2021 .SYNOPSIS... An upper level low over the Mid-Atlantic states will gradually lift northeast into New England this weekend into early next week while a ridge of high pressure in the southern United States gradually builds into the southeastern United States. This upper-level pattern will lead to only isolated shower and thunderstorm activity this weekend into early next week across northeast Georgia and the western Carolinas. Meanwhile Hurricane Henri will remain out in the western Atlantic tracking north towards New England throughout the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 1030 am EDT: A few showers have developed in the Lakelands area of the Upstate had have updated pops accordingly. Otherwise, grids are in pretty good shape this morning for a seasonally hot and muggy day across the area with typical summertime pops mainly across the mountains in the NW flow. Otherwise, an H5 closed low center over the central Appalachians will continue to spin north of the region, with various spokes of vorticity moving through the southern Appalachians and crossing the forecast area today. Forcing from these vorticity lobes may be better in the northern tier today, but moisture and instability will be better in the southern half, and that is where the better chance PoPs will be featured during peak heating as sbCAPE values climb to 2500+ J/kg. Initiation should get started near the mountains again, especially the southern escarpment area, but with a secondary focus along a weak lee surface trough. Maximum temperatures should be comparable to yesterday. Tropical System Henri will remain well east of the Carolinas today through tonight, with no impact to the region expected. Otherwise, any diurnal convection will die out quickly this evening, with another night of patchy fog along with some dense fog in the mountain valleys. Mins remain above climo. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 100 AM EDT Saturday: Dry air advection from NW-ly flow aloft and weak high pressure over the southern Appalachians will set the stage for very limited convective coverage on Sunday. A closed upper low over the mid-Atlantic will continue to lift northeast, while pulling TS Henri further west and potentially stalling over New England and portions of the Northeast. In our neck of the woods, subsidence aloft and rising heights will filter into the area from a deepening upper ridge over the Southern Plains and Lower Mississippi Valley, which allows for mostly dry conditions across the CFWA outside of isolated ridgetop convection and a pop up storm or two east of the mountains for Sunday. With ~590 dm thicknesses continuing to set up shop over the region, expect for the very warm and humid airmass to persist through the short term period. With little change in the overall synoptic pattern and mesoscale processes during the early part of the upcoming week, expect a very similar forecast for both Sunday and Monday. The main difference between both days will be temperatures. With the upper ridge extending further east into the southeastern CONUS on Monday, temperatures should uptick a few degrees from Sunday to Monday. Either way, temperature values will run above normal for both days. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 230 AM EDT Saturday: Summertime Bermuda High pattern will begin to set up shop during the medium range. The Bermuda high will gradually bring a return flow back into the CFWA by the middle part of the upcoming week. Two areas of upper ridges will leave the CFWA hot and humid with high heights continuing to linger over the area. Diurnal convection will make a return on Tuesday due to the Atlantic fetch from the Bermuda High. PoPs will still run below climo due to the stagnant subsidence aloft. By Wednesday and Thursday, model guidance shows the upper high to the west retrograding as the subtropical ridge over the western Atlantic pushes towards the southeastern CONUS. An open tropical wave will ride the southwestern peripheral of the subtropical high as the wave pushes through the Bahamas. The track of the tropical wave will be influenced by the western Atlantic subtropical high. Deterministic models have pushed this into the western Carolinas and northeast Georgia over the last couple of model runs by Wednesday and Thursday. If this trend continues, expect PoPs and PWAT values to surge as the atmospheric column becomes saturated from the relatively deep tropical moisture. The GFS and ECMWF also introduce the potential for the aforementioned tropical wave to stall over the CFWA and develop a closed low. There are a lot more questions than answers at this time, but the quiet pattern that is forecasted during the short-term could come to an abrupt end during the extended period if this scenario ends up playing out as it is currently being displayed. Temperatures will start out above normal for Tuesday, but values will likely decrease to near-normal readings through the rest of the forecast period due to the uptick in precipitation chances and cloud cover. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... At KCLT and elsewhere: VFR this afternoon, with some pockets of MVFR Cu as convection is expected to begin firing this afternoon, but at this time not widespread enough to introduce TEMPO; have left VCSH in TAFs at this time. Expect typical mountain valley fog again tonight with MVFR to IFR conditions expected again at KAVL. Slightly better chances for afternoon convection Sunday but too early to introduce PROB30 at this time. Winds are generally lgt/vrb in the weak pressure pattern but by tomorrow should be favoring the S/SW. Outlook: A typical, diurnal summertime convective pattern is expected to prevail the rest of the weekend through the middle of next week, with scattered coverage at best. Mountain valley fog will be possible each morning, as well as at sites that receive heavy rainfall the previous afternoon. Confidence Table... 18-24Z 00-06Z 06-12Z 12-18Z KCLT High 100% High 99% High 100% High 100% KGSP High 100% High 100% High 80% High 92% KAVL High 93% High 100% Low 51% Med 79% KHKY High 100% High 95% Med 79% High 91% KGMU High 100% High 100% High 81% High 89% KAND High 100% High 100% High 99% High 82% The percentage reflects the number of guidance members agreeing with the scheduled TAF issuance flight rule category. Complete hourly experimental aviation forecast consistency tables are available at the following link: www.weather.gov/gsp/aviation && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...HG NEAR TERM...HG/TDP SHORT TERM...CAC LONG TERM...CAC AVIATION...TDP