textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 06z TAFs.

KEY MESSAGES

1. Above-average rain chances and at or below-normal temperatures continue the rest of the week and into the weekend. Isolated flash flooding and a strong storm or two will be possible across the area each day through Saturday. 2. A return to seasonably hot conditions and typical coverage of afternoon and evening showers and storms is expected starting Sunday and continuing through early to mid next week.

DISCUSSION

Key message 1: Above-average rain chances and at or below-normal temperatures continue the rest of the week and into the weekend. Isolated flash flooding and a strong storm or two will be possible across the area each day through Saturday.

The synoptic pattern remains relatively unchanged, at least in regards to the location and evolution of key synoptic features. A persistent upper ridge has been parked over the Desert Southwest while a Bermuda high builds off the east coast. Between these two features, a broad longwave trough has enveloped the northern half of the country into Canada. A pesky upper low that was spinning over the Southern Appalachians has since opened into a shortwave trough and been absorbed into the mean longwave. As such, the continued wet pattern with above normal rain chances is being driven by the large scale trough with the trough axis extending down the Mississippi Valley. This will keep moist south/southeast return flow in place across Georgia and the Carolinas with PWATs ranging from 1.72-2.25". At least scattered to numerous diurnally driven showers and thunderstorms can be expected each day through Saturday, especially across the mountains. As we've seen the last several days, storms may eventually congeal into loosely organized segments along composite outflow boundaries with the strongest storms capable of locally gusty and perhaps damaging winds. In addition, clusters of storms with very efficient rainfall rates could drop a quick couple inches of rain leading to isolated flash flooding. Temperatures start off below normal again today before warming back to around normal with highs in the mid 80s to low 90s on Saturday.

Key message 2: A return to seasonably hot conditions and typical coverage of afternoon and evening showers and storms is expected starting Sunday and continuing through early to mid next week.

By Sunday into next week, the large scale upper trough progresses east into New England and helps to shunt the Bermuda high farther south. At the same time, the ridge is forecast to build west into the southeast states with rising heights. This will foster a warming trend with afternoon highs creeping back into the upper 80s to low 90s and heat indices near the low 100s. The convective portion of the forecast remains a bit trickier with guidance split as to the placement of a frontal boundary. A front will likely sag south into the Ohio Valley, but will become oriented parallel to the upper flow, which will stunt southward progression. How far south the front makes it will have implications on daily thunderstorm chances with the area residing on the northern fringe of the subtropical Bermuda ridge. For now, the forecast will reflect more traditional late summer climo PoPs with the best coverage focused over the mountains. Should the boundary placement reside farther south, a wet pattern may continue further into the week as bouts of convection make runs at the area from the Ohio Valley.

AVIATION /06Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Lingering showers and thunderstorms late this evening will push out of the area within the next hour or two with no additional convective concerns through the remainder of the overnight. Another round of mountain valley fog and stratus is expected at KAVL, but stratus coverage east of the mountains remains more uncertain. Any stratus that develops may remain more spotty in nature and likely anchored closer to the foothills, but cannot be ruled out at any given terminal. Where it does occur, however, ceilings could be as low as LIFR. Patchy fog also cannot be ruled out, but will also be patchy in coverage. An active pattern continues tomorrow with another round of afternoon and evening showers and thunderstorms with restrictions possible at any location. More low stratus and fog, especially in the mountain valleys, returns into Friday morning.

Outlook: Scattered to numerous diurnal showers and thunderstorms, with associated flight restrictions, are expected each day through early next week. Patchy fog and low stratus will be possible each morning, especially in the mtn valleys and anywhere that received significant rainfall the previous day/evening.

GSP WATCHES/WARNINGS/ADVISORIES

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