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Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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616 FXUS62 KGSP 160200 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1000 PM EDT Thu Aug 15 2024 .SYNOPSIS... High pressure will drift off the East Coast Friday as a cold front approaches from the northwest this weekend, bringing better coverage of showers and thunderstorms. Drier conditions will return behind the front as well as near normal temperatures early next week. && .NEAR TERM /THROUGH FRIDAY/... Evening Update...A rather quiet overnight in store with a broad p/grad in place keeping winds weak to calm across the FA. Upper ridging remains strong with only few/sct Ci passing overhead. All in all good rad cooling with lows dropping to right arnd normal. Not a great threat for dense fog, but a few locales across the NC mtns may see VSBY lowering to a half mile or less before daybreak. As of 245 PM EDT Thursday: Some enhanced cu have been bubbling over top of the ridges early this afternoon, with some radar returns over the higher peaks, so that part of the forecast appears to be in good shape. The latest mesoanalysis shows sfc-based CAPE on the order of 500-1000 J/kg, so a thunderstorm won`t be ruled out, but with poor lapse rates and shallow profiles, lightning seems unlikely. Still seeing a patch of remnant cloudiness moving southeast over the western Upstate and northeast GA, so those locations might be kept a deg or two cooler than expected. Otherwise, the fcst was in good shape. Showers should dissipate this evening with the loss of heating, without much in the guidance to indicate that any of it would persist, unlike last night. Could be some mtn valley fog once again. Low temps should be close to normal. Moving on to Friday...the sfc ridge that we have enjoyed for the past few days should slide off to the east as the upper pattern remains slowly progressive. In this pattern, an upper ridge axis will make slow eastward progress, moving overhead during the day, thus allowing upstream moisture and convection to make a run for our borders. Most of the guidance has a weak short wave helping to organize some convection upstream during the day, then driving it east or southeast toward us with varying degrees of success, probably because of instability east of the mtns by Friday afternoon. Over the mtns looks like no problem, with a general agreement that we should destabilize to the tune of 1000-2000 J/kg of CAPE in the afternoon, but east of the mtns, not so much. That will be the limiting factor as to whether or not any convective outflows can trigger storms into the Piedmont late in the day. One or two of the CAMS do just that, so precip probs will be extended a bit further east than shown in the synoptic guidance. However, the main threat will be on the west side of the mtns for any strong linear convection that can survive through the TN Valley and not dive off to our southwest. High temps will be close to normal. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... As of 225 PM EDT Thursday: A long wave trough builds over the East Coast through the period as an upper low traverses the Great Lakes and a series of short waves cross our area in the developing trough. An associated cold front slowly moves into the area Saturday then across the area Sunday. A moderately unstable air mass is expected to develop Saturday and continue into Sunday. Around 30 knots of bulk shear is expected both days as well. Despite PW values approaching 2 inches, there is mid level dry air with quite a bit of dCAPE and sfc delta theta-e. SPC currently has us in a Marginal Risk of severe storms, and this looks reasonable. Sunday is a little more uncertain and there could be less overlap of instability, shear, and mid level dry air. Locally heavy rainfall is also possible both days. Temps will be near to slightly above normal Sunday and near to a few degrees below normal Monday. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 155 PM EDT Thursday: The medium range guidance shows the deep long wave trough over the East Coast now lingering through Tuesday as a series of short waves move through the trough Monday and Tuesday. The trough slides east Wednesday with a weak ridge beginning to move in from the west Thursday. At the surface, enough low level moisture remains over the area Monday with a front stalled along the coast for scattered diurnal convection mainly over the mountains dropping off to isolated across the NC Piedmont. Drier air moves in for Tuesday and Wednesday ending the convective threat. Moisture return begins again on Thursday to increase the potential of isolated to scattered diurnal convection, but the day could end up dry if the moisture return is slower. Temps will be a few degrees below normal through the period. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... At KCLT and elsewhere: A quiet evening is in store with little chance of showers at any TAF site with VFR conds continuing into the overnight. Before daybreak, KAVL and KHKY could see IFR/MVFR VSBY respectively as guidance has trended down due to good rad cooling and calm winds expected. Afternoon showers and thunderstorms will be most likely at KAVL as an upper disturbance pushes in from the west. However, some indications are showing KHKY possibly seeing tstms by the later afternoon as well. Kept a VCSH at KCLT aft 22z as there remains some uncertainty to storm strength and coverage with the incoming convec activity. Winds remain rather weak thru the period with a general s/ly to sw/ly direction at all TAF sites. Outlook: A cold front will track over the forecast area this weekend keeping convection around. Drier conditions return behind the front early next week. Patchy fog and low stratus will be possible each morning in the mountain valleys and in any locations that received heavy rainfall the day prior. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...PM/SBK SHORT TERM...RWH LONG TERM...RWH AVIATION...SBK