Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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360 FXUS62 KGSP 092355 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 755 PM EDT Thu May 9 2024 .SYNOPSIS... A cold front will continue to push east of the area, before another system approaches Friday. Showers and thunderstorms are possible Friday afternoon, before dry high pressure builds in from the north through the weekend. && .NEAR TERM /THROUGH FRIDAY/... As of 750 PM: Skies have mostly cleared out, making for a pleasant evening. Convection firing across central MS/AL will provide thickening mid and high clouds across the area overnight as anvils advect ENE. This combined with some dry advection in the low-levels should limit fog potential. But very moist soils from earlier rainfall and weakening sfc winds may allow for patchy fog and possibly some low stratus to form before daybreak Friday. Temps and PoPs look on track. Tonight, mostly clear skies this evening should permit good radiational cooling for a time. Some dry advection will begin overnight as weak sfc low passes by to our north, pulling very weak sfc front through the area. This will promote just enough drying to maintain a dewpoint depression of a few degrees in the foothills and upper Piedmont, and furthermore some gradient wind is expected to persist. Thus, the likelihood of radiation fog/stratus looks small in those areas and mins will remain several degrees above normal. Mountain valleys are likely to see some fog, along with the SE CWA border where that weak front doesn`t reach and instead may serve to pool moisture. A couple hundred joules of CAPE may persist there thru daybreak. An MCV or other remnant of convection looks to round the base of the main trough in the morning and some guidance depicts a round of showers passing thru the Piedmont at that time. Partly cloudy skies will permit the return of warmer temps, again being a few degrees above normal. 700-500mb lapse rates will increase as main shortwave swings in, and isolated convective development is not out of the question over the mountains. For the aforementioned Piedmont areas, guidance members differ as to how soon low-level airmass change begins; GFS for example maintains poor low level lapse rates above the PBL and develops only small diurnal instability. The NAM depicts favorable lapse rates thru a deep layer and develops 1000 J/kg or more of CAPE in the afternoon. All models depict strong deep layer shear, perhaps 60+ kt, so if timing of the shortwave trends slightly slower or the low level lapse rates improve, we could see an isolated severe threat develop mainly southeast of I-85 or east of I-77. The setup warrants only a chance PoP in our south and east; FV3 and HRRR show short updraft helicity streaks from a lone cell. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... As of 1245 PM Thursday...An upper shortwave axis continues to swing east of the area Fri night as a cP air mass mixes into the lower levels. This airmass will slowly modify warmer over the weekend as a small scale ridge gives way to another diving Canadian h5 trof Sat afternoon. This trof looks to bring it/s own moisture and will probably produce some rain showers across the NC mtns Sat afternoon into the evening. No good chance of thunder during that time as sfc td/s drop into the 40s and potential instability remains nil or quite low. Drier conds with warming temps across the FA Sun as a broad sfc high builds over the area from the west. Generally, both days will be rather pleasant with highs a couple degrees below normal Sat, then back to normal levels on Sun. Mins will likely fall a couple degrees below normal each night. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 120 PM Thursday...A more springtime pattern returns during the ext range. The latest guidance contines to show a subs zone becoming displaced by waves of srn stream energy while a mlvl trof/low travseres the MS to OH valleys. The surface response indicates an opening GOM flow, which will supply a good amt of moisture to a broad frontal system each day. Onset precip timing Mon is suspect with the majority of models indicating a later timeframe than the moister insitu wedge pattern progged by the latest GFS. In any case, thunder probabilty remains low with non-conducive llvl thermal profiles. By Tue, expect a better chance of afternoon thunderstorms as a wavy cold approaches from the west and sfc dewps rise into the u50s to l60s. The pattern remains uncertain, yet possibly active into Wed as another round of srn stream energy may be pushing east across the GOM coastline by then. High Temps remain near normal Mon, then drop abt 5 degrees below normal Tue with the best chance of widespread precip and cloud cover. Highs rebound to normal values Wed. Lows begin the period near climo, then warm abv normal Tue/Wed nights. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... At KCLT and elsewhere: Mainly just a few high clouds this evening, with lingering light winds out of the SW (except for NW at KAVL). Overnight, thicker mid and high clouds are expected to stream in from the SW due to convection over the central Gulf states, which combined with just enough mixing, could limit fog potential. With that said, very moist soils and low levels may combine to produce patchy fog or LIFR stratus across portions of the lower Piedmont as well as the mountain valleys sheltered from NWLY flow. Guidance is still not hitting cigs or vsby restrictions all that hard, and with the mixed signals of clouds/wind/moisture, will continue to just show few LIFR clouds and/or 6sm BR for the early morning hours Friday. If trends in the clouds and wind trend lower, potential for the stratus and fog will go up. Whatever does develop, should dissipate early Friday morning. Spotty light rain may cross the southern Upstate, but should stay mostly south of the area and looks too low for any TAF mention. In the aftn, a cold front will slip across the mountains and into the Piedmont, which may trigger a few showers and isolated TS before pushing east of the area. While better coverage of showers will be near the TN/NC border. The NC TAF sites will feature PROB30 for the SHRA potential. Given less confidence on TS, will not mention for now. The Upstate sites look largely dry Friday aftn. Winds should toggle from SW to WNW behind the front with gusts generally in the 18-22 kt range. Outlook: Drier and likely VFR conditions can be expected this weekend. Moisture returns late Monday with active weather possible by Tuesday. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...SBK NEAR TERM...ARK/Wimberley SHORT TERM...SBK LONG TERM...SBK AVIATION...ARK