####018009784#### FXUS62 KGSP 160302 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1102 PM EDT Thu May 15 2025 .SYNOPSIS... Warm high pressure settles over our area through Friday. A cold front will approach from the northwest and may bring a line of showers and storms into the North Carolina mountains late Friday night into early Saturday. The front will become stationary over our region into early next week as the next storm system organizes over the plains states. && .NEAR TERM /THROUGH FRIDAY NIGHT/... As of 10:25 PM EDT Thursday: Over the past hour or so, one lone thunderstorm has developed over far western NC and is currently making its way SE over the far western Upstate. Otherwise, we remain shower free across our area. An upper ridge will continue to build over the region into the overnight with a notable capping inversion lingering well into Fri morning. This should help keep convection at bay with the exception of maybe a few more stray showers and/or thunderstorms. With increasing high clouds, temps overnight should remain roughly 8 to 12 degrees above climatology. The fcst becomes more complex on Friday, as the upper ridge axis shifts offshore and subtle height falls return as a potent shortwave slowly moves across the Mississippi Valley. This will allow for a period of quasi-zonal mid-level flow to become established over the Southern Appalachians downstream of the base of the mean trof. A pronounced Elevated Mixed Layer (EML) will get advected into the region, which should largely keep most of the area capped. The latest near-term CAM guidance continues to depict a wide range of solutions ranging from too capped with no convection to the potential for vigorous deep convection across northern portions of our CWA during the afternoon. Overall, it's still looking like more likely that the stronger storms will remain just north of our CWA where the cap will be somewhat weaker. Nonetheless, should any storms develop over our CWA, they could become severe quickly. Model profiles continue to depict sfc-based CAPE on the order of 3000 to 4000 J/kg along with steep mid-level lapse rates of 7 to 8 C/km tomorrow afternoon. Deep- layer wind shear of 40 to 60 kts with straight hodographs will support clusters of splitting supercells within the robust thermodynamic environment. Thus, any storms that are able to develop, will likely become severe with the potential for large hail and very strong down- drafts. Again, this is a conditional severe threat and it's certainly possible that no storms impact our area because of the strong cap. Nonetheless, close attention will need to be paid if any storms do develop on Friday. && .SHORT TERM /SATURDAY/... As of 100 PM Thursday, key messages: 1. Confidence has increased for organized convection to move from KY/TN into the southern Appalachians late Friday night into early Saturday morning, translating to a nonzero threat of severe weather at that time. 2. Per the above, confidence is slightly higher for a cold pool to overspread the area and suppress convection Saturday. The cold pool also would bring lower humidity to much of the area Saturday, although temperatures will remain above normal. As a mature low pressure system crosses the upper Mississippi Valley Friday night and Saturday morning, a shortwave will cross the lower Ohio Valley. A convergence axis, arguably a dryline, will move into a strongly unstable and sheared environment invof western KY/TN Friday evening. It looks likely at least one linear MCS--maybe two depending on how well the forcing mechanisms overlap--will take shape and progress to the western slopes of the Appalachians overnight or early Saturday morning. That suggests a widespread threat of damaging wind across the lower OH and TN valleys with potential for large hail as well. The track of the first MCS shown on some runs has generally been such that it misses us to the north. However, the dryline activity continues to be depicted as pushing across the TN/NC border between 06-12z Sat, with the earlier timing more likely given the potential for the cold pool to be driving development. We will be coming off a remarkably unstable afternoon, but MUCAPE still is likely to be greater than 1000 J/kg over our mountain zones. Thus it is plausible the line will at least make it partway into the CWA before weakening enough for the severe weather threat to diminish. SPC has included our mountains in the Day 2 Marginal Risk area. Many aspects of the forecast for Saturday remain contingent on how the convection plays out during the early morning, but with that looking more likely than it had been, confidence is not as low as before. PoPs will be retained over a good portion of the area Saturday morning as the convection decays along the edge of the cold pool and stratiform rain fizzles. Most models show little to no QPF response east of the mountains Saturday, The NAM shows some scattered response seemingly progressing with the cold pool thru the Piedmont late morning to afternoon, but that would be somewhat atypical; usually we experience a complete lull for a time with diurnally forced redevelopment late in the day, if the cold pool doesn't completely work us over. PoPs are being shown to taper from NW to SE during early to mid aftn. The cold pool is associated with an appreciable drop in dewpoints following the same trend; temperatures should be a few degrees cooler than Friday although potentially will be offset by downsloping. Maxes remain at least a few degrees above normal. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... As of 215 PM Thu: The actual cold front associated with the Great Lakes system should push into the CWA Saturday night. Still cooler conditions and lower dewpoints are forecast Sunday in the wake of the front. Ridge will be building in the lower MS Valley by that time, however, and the cold front stalls and gets reactivated to our west. Stable post-frontal airmass is most likely to persist over the NE half of the CWA. Seasonable CAPE of at least a few hundred joules will redevelop in the other half of the area, nearest the front; T/Td may actually be a little warmer in the Savannah Valley compared to Saturday. Furthermore, NW flow into the Appalachians will also provide weak forcing along the TN border so small PoPs extend along there. The ridge to our west and NW-SE oriented warm front may put us in the path of another MCS if one develops Sunday night or Monday. The deterministic global models, plus a number of members of the NAEFS and ECMWF ensembles, show precip developing variously in AR, MO, KY, TN Sunday and/or Monday and carry it into our area as an apparent MCV rounds the ridge. Per the pattern, that would appear possible Monday night or Tuesday as well, although there appears less support for that idea from the models. The MCS possibility notwithstanding, spotty diurnal convection may develop over the mountains Sunday, with climatological 20-40% chances Monday as dry air aloft should be less of a limiting factor that day. 0-6km shear will be supportive of at least an isolated severe threat if storms do develop either day. Early in the week, cyclogenesis is probable in the central CONUS as upper low moves across the Rockies. By late Tuesday we may enter the warm sector of that system if the front is able to shift far enough north. Shortwave/cold fropa potentially will occur Wednesday. Precip chances are highest those days but confidence on the extent of any severe threats is limited by spread in timing and the position of the front. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... At KCLT and elsewhere: Expect VFR conditions to prevail thru the 00z taf period at all terminals. Light sct showers are currently making their may into the NC mtns from the west and could poten- tially reach KAVL over the next few hrs, however my confidence that any showers will reach KAVL is too low to mention in the taf at this time. On the other hand, there is a decent chance that a fast-moving MCS could approach from the west, remain organized moving thru our northern zones and impact KAVL and KHKY during the late morning into the afternoon. As such, I have a PROB30 for TSRA for those 2 terminals from roughly 14 to 20z on Friday to account for this possibility. Chances are currently too low to mention convection at the other taf sites. Otherwise, sct to bkn high clouds will persist over the fcst area thru the taf period with few to sct cumulus expected again Friday afternoon. Winds will continue to favor a S to SWLY direction thru the taf period with speeds becoming light again by the overnight. The Upstate terminals will also likely see another round of low-end gusts Friday aftn/evening. Winds at KAVL are expected to remain light and VRB thru much of the overnight and morning and will eventually pick up from the SW again tomorrow afternoon. Outlook: A decaying line of robust storms is expected to move thru our fcst area early Saturday morning and could produce brief restric- tions as it move thru the area. Diurnal convection will be possible on Sunday and early next week as the synoptic pattern remains active. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...JPT SHORT TERM...Wimberley LONG TERM...Wimberley AVIATION...JPT