textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

PoPs have trended down slightly for Thursday, but up for Friday and Saturday.

The aviation discussion updated for the upcoming 12Z TAF issuance.

KEY MESSAGES

1. Daily shower and thunderstorm chances return today and continue through the weekend. Locally heavy rainfall will be possible. A drying and warming trend is expected early next week.

DISCUSSION

Key message 1: Daily shower and thunderstorm chances return today and continue through the weekend. Locally heavy rainfall will be possible. A drying and warming trend is expected early next week.

Shortwave energy will dive into the TN Valley today, deepening a longwave trough as its axis approaches from the west. In response to height falls across the region, return flow will increase and advect deep moisture back into the CWFA during the day today. Guidance is in pretty good agreement on a return of diurnal convection across the area, especially the high terrain with the added benefit of differential heating across the mountain slopes. The 00z CAMs keep coverage isolated to widely scattered, with activity peaking east of the mountains this evening. PWATs will climb into the 1.5-2.0" range, and combined with deepening warm-cloud layer and slow steering flow, may result in a localized heavy rain threat. The 00z REFS and HREF PMM QPF don't show much of a signal for heavy rain to be any more widespread. Guidance still hinting at convection lingering well into the evening and possible into the overnight, as SWLY low-level flow remains atop a lifting warm frontal zone and approaching upper wave rounding the base of the longwave trough. Severe threat looks to remain low, but probably not zero, as soundings become moist and shear remains weak.

Latest guidance has trended lower on PoPs Thursday, possibly due to a combination of more persistent cloud cover limiting insolation and instability, and a more pronounce gap between upper shortwaves crossing the area. Still expect an active day with high-end chc to likely PoPs. Temps will be near to slightly below normal with increased humidity. Friday now looks like the most convectively active day of the week, with likely to categorical Pops across the entire area. A cold front will approach from the west and a fairly pronounced upper shortwave will cross the area as it rounds the base of the longwave trough, providing enhanced forcing. PWATs will remain high both Thursday and Friday. So, there will be a marginal threat of excessive rainfall, with a slight risk in the Excessive Rainfall Outlook in the Upper Savannah Valley. I wouldn't be surprised if a slight risk gets expanded into the area on Friday, if the model trends hold.

A large upper ridge will begin to expand eastward from the Southern Plains over the weekend, and become centered over the Southeast early next week. PoPs will gradually decrease from Saturday thru the weekend, as the ridge builds and sfc high pressure pushes the weak front southeast of the area. Temps will remain near normal for highs and slightly above normal for lows in the moist air mass until Monday, when temps overall bump up above normal with heat indices pushing into the upper 90s to around 100 Monday and Tuesday.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: Patchy MVFR stratus has developed across KCLT area. Confidence remains low on how extensive the clouds will become before scattering out after sunrise. Have a FEW015 in the TAF, but amendments may be needed if the clouds really fill in. The MVFR clouds may also affect KHKY this morning, but should mainly stay FEW to SCT. Fog is also close to KAVL. Light and variable winds should toggle to S/SE by midday, and remain light. A more substantial Cu field is expected to form, with a return of aftn convection across the mountains, expanding into the Piedmont late aftn thru this evening. Coverage looks to be isolated to scattered, so will continue with PROB30 groups, including KCLT. Convection could linger thru late evening, but should dissipate overall overnight. Depending on how much rain falls today and how much mid clouds can clear out, there may be some IFR stratus and fog development across the area late tonight. But some guidance keeps low-VFR clouds around instead, making for a low-confidence forecast.

Outlook: More numerous to widespread SHRA/TSRA is forecast Thursday and Friday, then decreases to more isolated to scattered Saturday and Sunday. Mountain valley fog and low stratus is possible each morning.

GSP WATCHES/WARNINGS/ADVISORIES

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