National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Greer, SC

-- Discussion containing changed information from previous version are highlighted. --378FXUS62 KGSP 131847AFDGSPArea Forecast DiscussionNational Weather Service Greenville-Spartanburg SC247 PM EDT Tue Aug 13 2024.SYNOPSIS...Dry high pressure gradually builds in from the north throughThursday, pushing a stalled front further south of the area. Thehigh will drift east off the East Coast Friday, as a cold frontapproaches from the west over the weekend. The front will bring areturn of better chances of shower and thunderstorms through Sunday,then lower chances early next week.&&.NEAR TERM /THROUGH WEDNESDAY/...-- Changed Discussion --
As of 240 PM EDT Tuesday: A curious, almost-weak-wedge-likescenario was seen in the satellite imagery and suggested by thesfc observations, which should impact the weather for the rest ofthe daylight hours. Two boundaries were noted on the imagery. Oneboundary has recently slipped down farther into northeast Georgiaand was clear of the lower Piedmont/Lakelands, where mesoanalysisindicates pooled moisture has allowed for sfc-based CAPE on theorder of 1500-2000 J/kg. The dCAPE is also modest in that samearea in northeast Georgia, with values almost high enough tosupport strong downdrafts and outflows. That the boundary hasslipped out of the fcst area might suggest our opportunity foran isolated strong/severe storm has passed, but there is a secondboundary noted, slowly sagging south across the Upstate. Along andsouth of this boundary, some weak instability remains in place togo along with modest 35 kt deep layer shear. Thus, an isolatedstrong/severe storm can`t be totally ruled out. We also mighthave an outside chance at some heavy rain and localized flooding,as we retain a very moist air mass that has precipitable waterapproaching two inches. The orientation of the boundary looksfavorable for storms to move/train W-to-E, thus the small threat.We should lose all of this around sunset as the boundary layerstabilizes. We`ll keep our eyes on that, but don`t get your hopesup. As for temps, a large area of rain-cooled air covered by lowstratus/stratocu has temps trapped well down into the 70s over NCeast of the mtns. So, it looks like well below normal high tempsare going to prevail in that area, while the rest of the fcst areastays below normal as well with the light NE sfc flow.For tonight, improving NW flow aloft in the wake of a short waveshould keep it quiet. Some of the guidance has been hitting the fogdevelopment after midnight, with some of it locally dense. Thissort of makes sense given the ample remaining low level moistureacross the region. If we can manage to dry out aloft, the fogcould become a problem. Otherwise, low temps have been lowered abit because of the cooler start this evening over the nrn tier.For Wednesday, the NW flow aloft is maintained by the modelguidance, with no mid/upper forcing to speak of. Meanwhile,weak high pressure will ridge down from the north to give us adecent day, with more sun across more of the area. Fcst soundingsare generally unfavorable with only shallow instability over themtns. All of the CAMs manage to develop shower activity on the Eside of the mtns, so a chance will be included near the Blue RidgeEscarpment for the afternoon hours. Seems like a good bet. Thehigh temp fcst looks more uniform, with a nice rebound over theNC foothills and western Piedmont, maybe five degrees warmer,but maybe five degrees cooler over northeast Georgia.-- End Changed Discussion --&&.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...-- Changed Discussion --
As of 200 PM EDT Tuesday: NW flow will be in place across the areaas we move into the short term Wednesday night, with upper troughingdown the East Coast. Upper ridge will be building up the MS Valley,and surface high pressure in place over the Carolinas and Mid-Atlantic. Fairly quiet, seasonable temperatures on Thursday with low-end pops mainly in the mountains due to the light upslope flow. Asthe wavetrain moves east for Friday, the ridging will push east andover the Appalachians and an upper trough will begin to work intothe upper Midwest, dragging a front through the OH Valley.Temperatures will increase somewhat in response to the buildingridge, and forcing from the approaching wave and attendant surfacefront warrants increased pops at least in the mountains by Fridayafternoon, with less confidence further south.-- End Changed Discussion --&&.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...-- Changed Discussion --
As of 215 PM EDT Tuesday: The aforementioned front will be on ourdoorstep as we move into the extended, pushed by an upper lowworking its way from the Upper Midwest across the Great Lakesthrough the weekend. The front pushes through during the weekendwhile it will be strongly occluded with limited moisture, upperforcing and and hints of some deep layer shear as it passes towarrant keeping an eye on to provide some organization to theconvective potential especially for Saturday. The longwave troughsets up over the Appalachians in the wake of the front but guidanceis in disagreement on whether or not our area is still on theupslope and unsettled side or on the downslope and drier side. Fornow, temps remain just above normal with low-end pops mainly in themountains.-- End Changed Discussion --&&.AVIATION /19Z TUESDAY THROUGH SUNDAY/...At KCLT and elsewhere: An almost-wedgelike configuration is observedin the satellite imagery, with a large area of low cloudinesscovering most of the foothills and northwest Piedmont. Thus, KCLTand KHKY will be in-and-out of a low cloud MVFR ceiling through theafternoon (mostly IN), with a light northeast wind. The Upstateterminals will also have some low clouds developing through theafternoon, but will remain mostly OUT of the restriction. Precipprobs are looking less and less based on the recent outputof the CAMs, so we will amend by watching radar trends. Thus,KCLT and the Upstate terminals get a TEMPO for shower activityand associated restrictions, but the others don`t. Most of thelowest cloud deck will finally mix out late in the day, leading toa period of VFR in the evening and early overnight. Wind shouldgo light/variable. Tricky forecast overnight. Previous guidancesuggested prevailing VFR, but the last model run before issuancemade a major change to widespread IFR/LIFR restrictions at mostterminals in the pre-dawn hours. Rather than jump on the big change,preferred to wait to see some consistency over the next few runsbefore adding it in. Be on the lookout for changes, though. Windshould come back up from the ENE in the morning owing to highpressure to our N. We could easily pop up a low cloud ceilingrestriction with minimal heating, but this was left out for thetime being.Outlook: Expect mostly diurnal isolated to scattered diurnalconvection through Thursday. Coverage of convection increases Fridayinto Saturday as a cold front approaches out of the west. Patchy fogand low stratus will be possible each night in the mountain valleysand in any locations that received heavy rainfall the day prior.&&.GSP WATCHES/WARNINGS/ADVISORIES...GA...None.NC...None.SC...None.&&$$SYNOPSIS...DEONEAR TERM...PMSHORT TERM...TDPLONG TERM...TDPAVIATION...PM