Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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047 FXUS62 KGSP 212152 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 552 PM EDT Sat Sep 21 2024 .SYNOPSIS... High pressure will linger across the region through the weekend, with balmy temperatures today and tomorrow. A more moist airmass will arrive early this week, lingering through at least mid-week. && .NEAR TERM /THROUGH SUNDAY/... As of 550 PM: Made some minor tweaks to PoPs and thunder chances through the early evening hours based on the latest KGSP radar loops. Otherwise, no major changes were needed this update. Despite an upper ridge extending from an anticyclone over Texas settling over the area, a weak short wave has led to enough forcing to allow for some isolated showers to develop, mainly over western NC. With instability and shear lingering through evening hours, isolated convection should continue. Have retained the isolated convection near and along the Blue Ridge given the upstream convective activity. This feature moves across the NC Piedmont this evening into the overnight bringing the potential for isolated convection there. Should be another round of mountain valley fog with patchy fog elsewhere. Lows will be 5 to 10 degrees above normal. The upper ridge remains over the area Sunday with increasing thickness values. Warming mid levels should limit instability and put a lid on convection. Have a dry forecast for now. Highs will be around 10 degrees above normal. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 140 PM EDT Saturday: No major changes to the short term forecast this afternoon. Ensembles are coming into somewhat better agreement that on Monday, the z500 ridge axis over the Carolinas will be nudged east of the forecast area, permitting a steady increase in upper-level moisture streaming into the area from the west. On Tuesday, it`ll become further suppressed, as a lobe of shortwave energy translates up the Ohio Valley and over the ridge. This`ll also have the effect of driving a weak cold front across Tennessee and northern Alabama. The bulk of guidance depicts this feature stalling west of the Appalachians by Tuesday evening, which will keep the Carolinas locked into a warmer, moisture air mass. So, expect lots of cloud cover through the period. High temperatures will be in the mid to upper 80s in most locations both afternoons, and on Monday, a few spots across the lower Savannah River Valley may even hit 90. This would be a little on the high side of model consensus, but given the setup, it`s not unreasonable. Models also depict scattered shower coverage both afternoons, and a plume of afternoon instability to the tune of 1000 J/kg sbCAPE...enough to support some embedded thunder, at the very least. Forecast profiles aren`t especially impressive in terms of shear, lapse rates, or overall updraft strength on Monday...so severe risk doesn`t look especially notable. By Tuesday, there`s considerably more disagreement among long-range ensembles in terms of features like dry air aloft, the location of the frontal circulation, and mid-level lapse rates, so for now suffice to say there`s a potential for some thunder, with details on the nature of that thunder hopefully becoming clearer with future model cycles. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 155 PM EDT Saturday: By Wednesday, even the new 12z suite of operational guidance begins to diverge on important synoptic forecast details. Like yesterday, ensemble guidance basically falls into two camps: first, those depicting a weaker trough passage that leaves a stronger ridge in place over the Atlantic coast, and second, those depicting a stronger trough that nearly or completely scours out the remnant upper ridge on Wednesday and early Thursday. The first solution, with a stronger ridge, remains the dominant one, and would drive a cold front through the region by Thursday, ushering in drier weather on the whole as we move into the end of the medium range. The second solution, which also develops an upper low over the Ozarks and central Great Plains, would result in no frontal passage an instead a strong mid-level moisture return over the Deep South, resulting in rainier conditions late next week. Of note is the development of a tropical system over the Gulf in most guidance towards the end of the medium range. Should the first solution above play out, remnants of this system could impact the Carolinas toward the end of D7 and beyond; the second solution`s deep upper low would potentially steer any remnant low away from the Carolinas or absorb it entirely. Confidence in the overall track and timing of this system, as well as any potential impacts, remains very low at this point. && .AVIATION /22Z SATURDAY THROUGH THURSDAY/... At KCLT and elsewhere: Low VFR Cu, along with cirrus, will remain over the area this afternoon. Isolated convection is expected this afternoon and evening, but coverage will again be too sparse to warrant a TAF mention at any site. A generally light SW wind becomes calm to light and variable overnight. Expect fog and low stratus again in the mountain valleys with patchy coverage elsewhere. Have MVFR TEMPO IFR Vsby/LIFR cigs again at the most likely locations of KAVL and KHKY. This should dissipate before mid morning with some low VFR Cu again developing. Light W to NW wind on Sunday. Outlook: A weak frontal system approaches the area and stalls over or near the area through Thursday bringing the potential for diurnal convection. Daybreak restrictions could recur each morning especially in mountain valleys. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...MPR NEAR TERM...AR/RWH SHORT TERM...MPR LONG TERM...MPR AVIATION...RWH