textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated Key Message 2.

KEY MESSAGES

1. Relatively quiet weather will continue through Wednesday, with very low chances for afternoon showers and thunderstorms. Hot and muggy conditions will persist. 2. Afternoon showers and thunderstorm chances return Thursday and persist through Saturday. Lower humidity and near-normal temperatures return Sunday and Monday.

DISCUSSION

Key message 1: Relatively quiet weather will continue through Wednesday, with very low chances for afternoon showers and thunderstorms. Hot and muggy conditions will persist.

Our region will remain under weakly cyclonic upper flow through the midweek period. Temperatures and dewpoints are running slightly lower this afternoon than they were on Monday, keeping heat index out of Heat Advisory range. That said, it will remain muggy even for August. A weak capping layer remains above the PBL, and the lower temps/dewpoints also should have the effect of inhibiting deep convection over the area this afternoon. With abundant cumulus however a stray/brief shower is not out of the question in the lee of the Blue Ridge Escarpment, although the overall chance is only about 10%. Generally northerly low-level flow will continue into Wednesday which may bring dewpoints slightly lower still. Thus the coverage of afternoon cumulus is expected to be a little lower and PoPs remain near zero, and the afternoon may feel slightly less oppressive.

Key message 2: Afternoon showers and thunderstorm chances return Thursday and persist through Saturday. Lower humidity and near-normal temperatures return Sunday and Monday.

Upper flow will turn more cyclonic over the inland portion of the eastern CONUS Wednesday, as a vort lobe rounds the embedded closed low near James Bay. A cold front will advance across the Ohio Valley Wednesday night in conjunction with the vort lobe and may support development of an MCS to our west, and if so that could make a run at the Appalachians Thursday morning. Regardless, 850mb WAA and low level moisture advection strengthen over our area Wed night and Thursday ahead of the front. Assuming an MCS does not bring a cloud shield or cold pool over the area during the morning, the moisture advection should again make thermodynamic profiles favorable for deep diurnal convection. The vort lobe and front would appear timed to promote convective initiation in the mountains, and perhaps Thursday evening in the Piedmont; CAM response is greater to our east and southeast. The shear afforded by the fast 500mb flow and forcing along the front could result in at least loosely organized convective clusters at that time and perhaps at least an isolated threat of damaging wind. Temps and humidity increase Thursday and a few locations in the lower Piedmont could see heat index rise into the lower 100s, and a few spots may reach Heat Advisory criteria.

The front essentially stalls over the area Friday seemingly as a wave develops along it, due to interaction with the trough aloft. Moisture pooling and convergence in the vicinity of the front result in an uptick in precip chances for the area, with shear still supportive of loosely organized storms producing a nonzero severe threat. Cloud cover is expected to bring temperatures down a few degrees though dewpoints will remain high. The front gradually drifts east Friday night into Saturday, so PoPs trend lower and shift toward the coast, with temps also trending a bit cooler. Drier continental air will arrive behind the front; the mountains may see a dip in dewpoints as soon as Saturday afternoon while the remainder of the area sees the drying trend begin Saturday night and particularly Sunday. Temps may actually rebound a bit Sunday and Monday owing to clearer skies, but the drier air suggests suppressed diurnal convection those days and PoPs thus mostly remaining below slight-chance.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

At KCLT and elsewhere: Abundant low VFR cumulus this afternoon with light NW winds. Cumulus should dissipate by sunset leaving mostly SKC though FEW cirrus occasionally may be seen overnight. Winds remain light but veer to NE at all sites except KAVL. With expected good radiational cooling, valley fog appears likely enough to include TEMPO IFR at KAVL in the morning. Less coverage of cumulus expected Wed, with bases also more likely to remain at/above FL045 at KCLT.

Outlook: Scattered afternoon/evening convection Thursday through Saturday. Low stratus and fog will be possible each morning, especially in the mountain valleys.

GSP WATCHES/WARNINGS/ADVISORIES

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