268 FXUS62 KGSP 211047 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 647 AM EDT Sat Aug 21 2021 .SYNOPSIS... An upper level low or trough will persist over the eastern seaboard, as Tropical System Henri moves over the offshore waters. Weak surface high pressure will set up over the southern Appalachians, with a lee trough persisting in the Piedmont. The upper-level pattern will remain relatively unchanged through most of the period. Isolated showers and thunderstorms will remain possible this weekend into early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 630 am EDT: Nighttime microphysics enhanced satellite imagery shows plenty of lower clouds floating around the region near daybreak this morning, but any widespread fog issues are impacting mainly the mountian river valleys. An SPS has been issued there for patchy dense fog through 9 am. 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 /12Z SATURDAY THROUGH WEDNESDAY/... At KCLT and elsewhere: Scattered MVFR-level bases are floating around the foothills and Piedmont this morning in NE flow, but with any ceilings rather transient in nature. The main exception is KAVL, with lower stratus and fog filling up the mountain valleys and likely to impact the airfield for a couple of hours past sunrise. Expect FEW to SCT VFR cumulus to develop quickly with heating throughout today, with PROB30 TSRA or VCSH/TS for the mid to late afternoon hours at all but KHKY and KCLT where profiles will be drier. Light winds will favor a northerly direction early in the period and then a southerly direction the second half of the TAF period, except mainly NW at KAVL. Any afternoon convection will diminish quickly this evening. Other than early morning valley fog, any restrictions through the period will be confined to the immediate vicinity of thunderstorms. 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... 10-16Z 16-22Z 22-04Z 04-06Z KCLT High 95% High 100% High 100% High 100% KGSP High 100% High 100% High 100% High 100% KAVL Low 40% High 100% High 100% High 100% KHKY High 100% High 100% High 100% High 100% KGMU High 100% High 100% High 100% High 100% KAND High 100% High 100% High 100% High 100% 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 SHORT TERM...CAC LONG TERM...CAC AVIATION...HG