


Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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921 FXUS62 KGSP 151327 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 927 AM EDT Thu May 15 2025 .SYNOPSIS... Warm high pressure settles over our area today through Friday. A cold front will approach from the northwest and may bring a line of showers and storms into the NC mountains late Friday night into early Saturday. The front will push through to our south and stall over the weekend, ushering in slightly cooler, but still above-normal temperatures into early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 924 AM Thursday: Latest satellite observations depict continued erosion of locally dense fog along and north of the I-40 corridor from Marion to Mocksville. The area of dense fog will shrink as the edges mix out with daytime heating with all fog expected to be gone within the next hour or so. Otherwise, the remainder of the forecast remains on track and no substantial changes were needed. Now that we finally have the old mid/upper trof well to our northeast today, we should enjoy an amplifying upper ridge building in from the west with sfc high pressure building up from the south. The main story will most likely be warmer temps...some five degrees warmer than yesterday...and feeling summerlike because of all the humidity that will be in the air from evaporation off the wet ground we have in most places. Most of the region will be effectively capped off from deep convection this afternoon/evening, including northeast GA/Upstate SC/central and southern mtns of NC. In theory, that would also include the rest of the fcst area, but there looks like some sneaky potential to break the cap along/N of I-40 into the NW Piedmont as it will probably be weaker there. Certainly that potential is much greater farther to the northeast into the RNK/RAH fcst areas, and the plan is for the building ridge to nudge the cap farther north and keep the storms out of the GSP forecast area, but we will have to keep an eye out for it. The potential will certainly wane with the loss of heating, and after sunset we will keep an eye out to the west. As the upper ridge axis moves overhead late tonight, there will be an avenue by which upstream convection could reach the mtns after midnight. However, the CAMS for the most part kill it off before reaching the mtns and leave us only with some scattered remnant showers. Overnight low temps will be warm. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 330 PM Wednesday, key messages: 1. Friday still looks largely capped, but some guidance hints at one or two storms developing in the northern part of the CWA in what is a very concerning environment for severe weather. 2. Organized convection will likely develop in the lower OH or TN valleys Friday, and could track into or across the Appalachians at some point between Friday evening and Saturday morning. 3. Muggy Friday with temperatures about 10 above normal. A little cooler and less humid Saturday but still above normal. Height falls aloft expected from the Mid-MS Valley to the Carolinas, as a potent upper low tracks east across the Great Lakes. The associated sfc low will be occluded, but with an active cold front extending south across the Midwest. Forecast soundings show a pronounced elevated mixed layer (EML) atop the forecast area Friday, with steep lapse rates resulting 3000+ J/kg of sbCAPE by early aftn. There will also be 0-6km shear 50-60 kt. This is concerning for any convection that can break the capping inversion caused by the EML. Some of the CAMs now go thru 00z Sat, and show a few isolated supercells popping along/near the Blue Ridge escarpment roughly along or north of I-40 in the aftn. These depicted cells manage to track east across the Northwest NC Piedmont. If this happens, these storms could produce very large hail and damaging wind gusts. With that said, a lot of guidance still keeps our entire CWA capped. Will introduce some slight chc to low-end chc PoPs along/north of I-40. The other story Friday will be the muggy conditions. Despite dewpts mixing out into the 60s, highs in the upper 80s to around 90 will feel more like the low to mid 90s across most of the Piedmont. Highs overall about 8-12 deg above normal. Friday night, the NAMnest and High-Res FV3 go thru this period and show strong convection upstream of the forecast area going upscale and entering the NC mountains as a pretty solid line of convection before 12z Saturday. The activity will likely be on a weakening trend. But the environment may support damaging wind gusts as the line first enters the mountains from TN. The new Day 2 SPC convective outlook only has a marginal risk right along the border. But I wouldn`t be surprise if later outlooks bring the marginal or even slight further east into the area. The convection still only has a 20-30% chance of surviving across the mountains to the Piedmont per latest consensus PoPs. This is mainly due to lingering CIN from the EML, and the early morning hour minimum in MUCAPE. Even if the line completely falls apart, an outflow/wind shift looks to push thru the southeast edge of the forecast area by early Saturday aftn. If for some reason the line is slower, it could tap into some diurnal instability before completely exiting the forecast area. With the uncertainty in the timing of the potential line of convection, will keep PoPs in the slight chc to low-end chc range east of the mountains Saturday. The new Day 3 convective outlook has the entire CWA in a marginal risk, with a slight risk just to our east. The passing cold front will also result in deeper mixing and breezy conditions Saturday aftn. Temps will remain around 10 deg above normal, with downslope flow helping offset any cooling from the front. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 300 AM Thursday...An upper ridge will amplify across the lower and mid-MS Valley Sunday thru Tuesday, with the axis drifting east to the OH/TN Valley, then crossing to our east Wednesday. A sfc front will stall out across the Southeast, oriented roughly from the Central Plains east to the I-20 corridor of AL/GA. The latest guidance still suggests it will be far enough south to allow Sunday to be a dry day. But from there, the front begins to activate as a warm front and nudge northward. This may place the forecast area within an MCS track for Monday and/or Tuesday. But the deterministic guidance does not show strong instability over the area. So any convection that tracks toward us may struggle to maintain intensity. The best chances will be in the NC mountains, with a west-northwesterly downslope flow largely capping the atmosphere east of the mountains. A deep and well-organized low pressure system may form in the Midwest Wednesday, and bring a chance of showers and storms to the forecast area. The environment may even support a severe weather threat. Temps will be slightly above normal thru the medium range. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... At KCLT and elsewhere: VLIFR vis has developed around KHKY early this morning so that is our trouble spot. Now that the sun is up, the vis should improve by 9 am or thereabouts. Otherwise, fog restrictions are noted around metro Charlotte but not at KCLT, and given their greater dewpt depression, think KCLT will stay VFR and out of the fog. Once that`s out of the way, today looks relatively quiet as the old upper low/trof has finally moved away and a warm layer aloft keeps a lid on the deep convection. Wind will come up from the SW and could be occasionally gusty in the afternoon. We should lose the gusts and any low clouds at dusk, after which we watch the radar for upstream convection making a run at the mtns early Friday morning. Outlook: In general, a summertime pattern is expected thru the end of the week with diurnally-driven convective storms possible each day. In addition, fog and low stratus will be possible each morning, primarily in the mtn valleys and in areas that receive appreciable precip the previous day. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...ARK NEAR TERM...PM/TW SHORT TERM...ARK LONG TERM...ARK AVIATION...PM