textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

A slight increase in PoPs today, and a marginal risk of severe thunderstorms has been added to most of the NC mountains this afternoon and evening.

Aviation discussion was updated for the 12z TAFs.

KEY MESSAGES

1. Isolated thunderstorms possible this afternoon through early evening, mainly near the Blue Ridge Escarpment and in the mountains near the Tennessee border later this evening. A few storms may become severe, with damaging wind gusts being the main threat. 2. Drier weather returns Sunday through early next week, with afternoon shower and thunderstorm chances returning by midweek.

DISCUSSION

Key message 1: Isolated thunderstorms possible this afternoon through early evening, mainly near the Blue Ridge Escarpment and in the mountains near the Tennessee border later this evening. A few storms may become severe, with damaging wind gusts being the main threat.

Convection has finally waned, leaving plenty of stratus that will linger thru mid to late morning. A digging upper trough over the western Great Lakes into the Ohio Valley will increase NWLY bulk shear across the Ohio Valley and into the Southern Appalachians later today. Drier air is starting to filter in behind yesterday's frontal passage, but enough moisture will remain to allow for at least isolated thunderstorms to develop this afternoon across the mountains and adjacent foothills. The latest CAMs are not too excited about coverage or intensity with this activity. The bigger concern may be with anything that develops upstream over the Ohio Valley. Some of the CAMs show loosely organized multicell clusters diving SE toward the NC mountains. There is some concern that some of these storms could be strong to severe as they cross the TN/NC line this evening. The new Day 1 Convective Outlook has expanded a marginal risk into the NC mountains to account for this potential. Whether any of this would survive east of the mountains remains in doubt. CIN should be increasing this evening, and MUCAPE will be decreasing. Despite this, some of the CAMs, along with the ECMWF and Canadian, suggest some activity may track into the NC NW Piedmont late evening. The NBM PoPs do not reflect this, and are on the low side overall. Otherwise, it should be a typical late August day with highs near normal with muggy dewpts.

Key message 2: Drier weather returns Sunday through early next week, with afternoon shower and thunderstorm chances returning by midweek.

An upper low closes off over the Great Lakes Sunday, then wobbles slowly east into Quebec thru the first half of next week. This will result in a deep trough axis persisting roughly along the Appalachians to the East Coast, which will put the forecast area in a drier W/NW flow pattern. Dewpts should dip into the 50s to lower 60s Sunday and Monday, combined with temps in the 80s will be a refreshing break from the hot, humid weather we've been experiencing. The pattern will gradually modify, with another trough digging into the Midwest and allowing return flow to bring moisture back into the region by the middle of next week. Some diurnal convection may return Tuesday and Wednesday, then more substantial coverage of convective activity on Thursday with an approaching cold front from the NW. Temps will remain near normal thru the week, but humidity will gradually increase, with dewpts back into the upper 60s to lower 70s by Thursday.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: IFR to MVFR stratus should start to scatter out and lift later this morning to VFR by around midday at all sites. Most restrictions are due to cigs rather than vsby this morning. Isolated to widely scattered convection may develop again this aftn, mainly along the Escarpment. Latest guidance has trended a little higher in coverage in the NC foothills and NW Piedmont, so have added a PROB30 to KHKY. Otherwise, only KGSP and KGMU have high enough confidence for PROB30s for some TSRA in the roughly 20-24z time frame. There is about a 20% chance of some TS around KCLT, so not high enough to mention in the TAF at this time. Drier air filters in tonight, which should keep most fog and stratus potential to the mountain valleys. Winds will be light thru the period, mainly out of the SW east of the mountains and NNW at KAVL.

Outlook: No significant chance of convection until Wednesday. Mountain valley fog and low stratus is possible each morning.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...None. SC...None.