textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 00z TAFs.

KEY MESSAGES

1. Above-average rain chances and below-normal temperatures continue the rest of the week and into the weekend. Isolated flash flooding 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 next week.

DISCUSSION

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

A weak upper low that has been spinning invof northern GA is finally starting to open up into a weak trough that will linger just to our west. The trough will be reinforced/merged with a digging longwave trough over the Northern Plains to the Great Lakes on Saturday. This will combine with a persistent Bermuda High to keep a deep-layered SWLY flow and elevated PWATs atop the forecast area thru the end of the week. Moist profiles and weak shear will keep severe thunderstorms chances low. However, efficient rain rates and slow storm motions will lead to an isolated flash flood threat from this aftn thru Saturday, mainly during the typical peak-heating/diurnal cycle. Highs will be a category or two below normal under plenty of cloud cover and lows near to slightly above normal.

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 next week.

Large subtropical upper ridge starts to build west from the Atlantic over the Southeast states Sunday into Monday, then becomes flattened by upper troughing over the Great Lakes to the Mid-Atlantic by the middle of next week. This will bring low-level flow more out of the west to west-northwest and usher in slightly drier air into the region. Overall, temps will return to normal Sunday and a couple degrees above normal Monday thru midweek. Diurnal convection should return to near typical early-mid August levels, with scattered to numerous in the mountains and isolated to widely scattered elsewhere. A few pulse severe storms and localized heavy rain will likely be a threat each day. The muggy conditions will result in heat indices pushing into the upper 90s to lower 100s each aftn across most of the Piedmont.

AVIATION /00Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Clusters of showers and thunderstorms continue to make their way from south to north over the fcst area this evening. Still expect convective coverage to peak over the next couple of hours and then diminish later this evening. As such, I have prevailing VCSH with either a PROB30 or TEMPO for TSRA at all TAF sites for the next few hours. Otherwise, a very moist air mass will remain in place and allow for another night of lower stratus and patchy fog de- velopment across the fcst area. The latest guidance generally agrees on widespread low-MVFR to IFR cigs around daybreak, with areas of fog in the mtn valleys and patchy fog over the Piedmont and Upstate. The lower stratus should gradually lift/sct to VFR by late morning. Similar (if not greater) coverage of showers and thunderstorms is expected Thursday aftn/evening. As such, I have VCSH with PROB30s for TSRA at all TAF sites beginning around 18z tomorrow. Winds will continue to favor a SLY direc- tion thru the TAF period. Most sites will go light to calm to- night, with speeds picking up again later tomorrow morning.

Outlook: Sct to numerous diurnal showers and thunderstorms, with associated flight restrictions, are expected each day thru 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.