Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 242140 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 540 PM EDT Mon Sep 24 2018 .SYNOPSIS... A wedge of moist high pressure will persist across the area into Tuesday. A cold front will then move across the mountains Wednesday and become stationary thru Thursday. This front will maintain a chance of showers and thunderstorms each afternoon until dry high pressure builds in Friday and lingers through the weekend. && .NEAR TERM /THROUGH TUESDAY/... As of 520 PM EDT: Breaks continue to occur in the overcast around the edges of the wedge, but there`s not enough insolation to really destabilize things. So thunder chances look close to zero at this point and will be removed from the forecast. Otherwise, minor tweaks to the hourly temps and sky thru this evening were made. Otherwise, weak cold air damming will remain over the area tonight. Despite some breaks in the clouds around the edge of the wedge, expect clouds to return during evening and continue overnight. The best coverage of showers this afternoon and early evening will be west of the French Broad Valley and south into the Upper Savannah River Valley where weak instability has developed. Shower coverage will increase along and near the Blue Ridge escarpment overnight in the continued moist upslope flow. Coverage decreases elsewhere. Lows will be around 10 degrees above normal. The low level flow turns more south then southwest through the day Tuesday allowing the cold air damming to slowly erode and mixing begin. Shower activity will continue to favor the mountains where PW values and instability will be higher. Drier conditions will linger outside of the mountains where a moisture minima develops and weak subsidence moves in ahead of the weak tropical systems approaching the Carolina coast. Low level thickness values increase with the eroding wedge. This will combine with drier conditions and some sunshine for highs to rise a few degrees above normal. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... As of 215 PM EDT Monday: With troughing over the central US and ridging over the Atlantic, latest guidance continues to suggest a weak sfc ridge across the Carolinas will be in the process of retreating off to the northeast Tuesday evening, ahead of an approaching cold front. Situated in between these two synoptic features, SWly flow will allow for moisture to be infiltrated into the Southeast as fcst soundings continue to suggest PWATs ranging between 1.50-1.75", possibly increasing to near 2 inches. Anticipate lingering isolated showers and thunderstorms Tuesday night into Wednesday morning, mainly across the mountains, with coverage becoming more widespread Wednesday into Thursday across the entire FA, as the upper trough axis shifts eastward and becomes more elongated, pushing the cold front into the FA from the NW. Some guidance highlights dynamic support increasing on Thursday as the now upper trough axis moves overhead and the cold front becomes somewhat stationary over the Carolinas. With increasing noteable instability and lower end shear values, would not entirely rule out a few strong to severe tstorms throughout the short term forecast period. Though, do anticipate more favorable conditions for severe weather will remain well of to the north, as noted by the latest SPC Convective Outlook. Temperatures throughout the forecast period will remain above normal. With SWly flow keeping dewpoints in the 70s, it will continue to feel more like Summer than Fall. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 245 PM EDT Monday: The extended forecast period kicks off Thursday night as a cold front remains nearly stationary across the area with lingering showers and thunderstorms. Per latest guidance, anticipate this boundary to finally push out of the area on Friday as the upper longwave trough continues to broaden and expand eastward. Behind the front, flow becomes nearly zonal as an upper ridge builds in over the Atlantic/Southeast, expanding westward into the Gulf of Mexico through the weekend. With lower confidence on the placement of the sfc high between the model guidance, will keep the inherited trend of low end PoPs throughout the weekend - but am not expecting activity to be as widespread/higher PoP as is expected Wednesday and Thursday. Temperatures will remain slightly above normal, but dewpoints will drop into the 60s Saturday and Sunday. && .AVIATION /22Z MONDAY THROUGH SATURDAY/... At KCLT and elsewhere: Conditions only slowly improving this afternoon with some MVFR but quite a bit of IFR. Should see MVFR cigs for all but KHKY later this afternoon. Expect MVFR to continue into the evening with IFR and even LIFR developing overnight. Showers most likely at KHKY and KAVL this afternoon and overnight and this afternoon at the SC sites. Vsby will generally be VFR except possibly MVFR is showers. IFR to LIFR vsby overnight at KAVL. Any vsby restrictions quickly improve after daybreak Tuesday. However, cigs will remain low with IFR for most of the morning and MVFR into the afternoon. Winds generally ENE, with SE at KAVL. Outlook: A cold front moving in from the west will then bring higher chances of showers and storms Wednesday thru the end of the work week. Confidence Table... 21-03z 03-09Z 09-15Z 15-18Z KCLT High 81% High 90% Med 79% High 80% KGSP High 82% Med 64% Med 63% Med 79% KAVL High 98% Med 74% High 87% High 93% KHKY High 85% Med 70% High 94% Med 76% KGMU Med 73% Med 68% Med 67% Med 79% KAND High 91% High 94% Med 76% High 85% The percentage reflects the number of guidance members agreeing with the scheduled TAF issuance flight rule category. Complete hourly experimental aviation forecast consistency tables and ensemble forecasts are available at the following link: && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...SBK NEAR TERM...ARK/RWH SHORT TERM...SGL LONG TERM...SGL AVIATION...RWH is the U.S. government's official web portal to all federal, state and local government web resources and services.