Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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301 FXUS62 KGSP 202130 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 530 PM EDT Fri Sep 20 2024 .SYNOPSIS... High pressure will linger across the area today, though we could see some widely scattered showers and storms through this evening. High pressure will remain through early next week, with hot temperatures expected over the weekend, before a wetter pattern arrives after Tuesday. && .NEAR TERM /THROUGH SATURDAY/... As of 525 PM: No major changes this update. Isolated showers continue along/east of I-77 in area of higher dewpoints and lower LCLs/CCLs, but cu development has slowed or ended over areas further west. Revised PoPs to continue the mention near I-77 thru mid-evening, but remove any mention toward the west. Made slight adjustments to T/Td trends this evening but think min temps are on track. Still expecting heights to gradually rise through the period as a ridge extending from an upper anticyclone over Texas nudges into the region. Weak surface high pressure remains over the area through the period as well. Expect mostly clear skies overnight as the afternoon cumulus dissipates through the evening. This combined with light winds and low level moisture, expect another round of mountain valley fog, some dense, and patchy dense fog outside of the mountains. Lows will be up to 5 degrees above normal. Instability looks to be lower Saturday with warming mid levels. Still there my be enough to combine with differential heating for isolated convection along and near the Blue Ridge during the afternoon, but overall chance is lower. Highs will be around 5 degrees above normal. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... As of 136 PM EDT Friday: Fairly good agreement on the forecast for the latter half of the weekend and into Monday. Subtropical ridging will build over the southern US and Gulf of Mexico through the period, sharpening on Monday in response to increased troughiness over the Continental Divide and points west. This`ll maintain mostly dry and suppressed conditions over the area on Sunday, before a broad and ill-defined baroclinic zone arrives in the Ohio Valley Monday. Ripples of shortwave energy aloft will ride up and over the ridge, lending a little synoptic forcing to anotherwise murky setup. So, increasing PoPs are warranted through the end of the period Monday evening. Temperatures will likely hit the upper 80s to lower 90s on Sunday, with the highest temperatures to be found across the Savannah River Valley; on Monday, they`ll fall back into the upper 80s in most locations in response to the weakening ridge and enhanced cloud cover. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... As of 148 PM EDT Friday: Lower-than-typical confidence as we look out into the medium range. Another round of more focused shortwave energy will arrive on Tuesday, further suppressing the ridge over the eastern CONUS; it`s unclear, though, how strong this effect will be. The latest operational GFS depicts the ridge remaining in place, if perhaps migrating even farther east and exposing the Carolinas to better deep-layer SW flow and accompanying moisture flux. The most recent two runs of the ECMWF depict a complete dissolution of the ridge, with a massive upper low developing over the Mid-Atlantic by Wednesday. The 12z GDPS, comparatively, depicts an open trough and associated surface front arriving on Wednesday and Thursday and scouring out the remnants of the ridge. The broader ensemble envelope of solutions clearly favors the more progressive solutions depicted by the GFS and GDPS, but there`s around 25% support for a more EC-like upper low solution as well. That is to say, predictability is fairly low past Tuesday or so, but most solutions will result in some sort of more active/rainy setup through the medium range...and the more GFS-like solutions would even introduce some afternoon instability each day, resulting in at least some isolated thunder chances! && .AVIATION /22Z FRIDAY THROUGH WEDNESDAY/... At KCLT and elsewhere: Low VFR cumulus and isolated SHRA will continue through the afternoon. No mention of SHRA in the TAFs at this time as chance of moving over an airfield is low. Light N to NE wind this afternoon becomes light and variable overnight. Expect another round of mountain valley fog and patchy fog elsewhere. Chance high enough for MVFR TEMPO LIFR at KAVL and KHKY, where VLIFR is possible. MVFR at KCLT and KGSP/KGMU with IFR possible there. Chance too low at KAND for now. VFR returns by mid morning with more low VFR Cu/Stratocu. Winds become light SW, NNW at KAVL. Outlook: No appreciable return of moisture or precip chances expected until early to middle of next week. Daybreak restrictions could recur each morning especially in mountain valleys. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...MPR NEAR TERM...RWH/Wimberley SHORT TERM...MPR LONG TERM...MPR AVIATION...RWH