textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation forecast updated for the 00Z TAF issuance.

KEY MESSAGES

1. Increased moisture will lead to greater shower and thunderstorm coverage through the end of the work week.

DISCUSSION

Key message 1: Increased moisture will lead to greater shower and thunderstorm coverage through the end of the work week.

An upper level trough axis is positioned just east of the area, resulting in a northwest flow aloft. Meanwhile at the surface, high pressure continues to build in from the Ohio Valley, with more of a northeasterly flow along the lee of the Appalachians. This pattern is responsible for the relatively dry airmass in place tonight.

The pattern will begin to change on Wednesday however, as another upper trough axis approaches from the west and a previously stalled front lifts northward as a warm front into the area. An influx of low and mid level moisture will cause precipitable water values will increase to 1.25-1.75 inches across the area, leading to a greater potential for showers and thunderstorms in the afternoon and evening. The greatest coverage should be in the higher elevations due to topographic forcing/convergence. The atmosphere will become weakly to moderately unstable, so a few stronger storms are possible.

On Thursday, a southerly flow advects more moisture into the area, pushing precipitable water values upwards of 1.75-2.00+ inches in the Piedmont and 1.50-1.75 inches in the Foothills based on the LREF. Meanwhile, a potent short wave disturbance will cross the area during the afternoon and evening, triggering numerous showers and thunderstorms. Given plentiful atmospheric moisture and the potential for some slower moving/training cells, there is a risk for localized flash flooding and the most of the area is outlooked in a Marginal Risk for Excessive Rainfall by WPC, with a Slight Risk for the Upper Savannah River valley. There is also at least an isolated threat for some severe thunderstorms capable of producing damaging winds with ample surface-based instability in place.

Not much change to the airmass on Friday, and although the greater upper level forcing should be displaced east of the area, a cold front crossing the area should maintain the potential for numerous showers and thunderstorms once again.

Shower and thunderstorm chances should diminish over the weekend as some drier air tries to filer in behind the departing cold front. Ensembles then generally support a strengthening ridge late in the weekend into early next week. This should limit the coverage of convection (mainly focused in the higher terrain) and lead to temperatures rising well above normal.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: Some VFR Cu lingers over the mountains and along an outflow boundary across the I-85 airfields. There is also an increase in SE winds with the boundary as well. Have a SE wind becoming NE this evening as the nocturnal inversion develops. Light N to light and variable wind for KHKY and KAVL. Expect mountain valley fog that doesn't reach KAVL overnight as well. Winds pick up from the S to SW by afternoon with VFR cumulus. Scattered convection expected so PROB30s in place for all but KCLT where chance is more isolated. That's enough to not mention convection there for now.

Outlook: A better chance of SHRA/TSRA is forecast through Saturday with a lower chance on Sunday. Mountain valley fog and low stratus is possible each morning.

GSP WATCHES/WARNINGS/ADVISORIES

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