textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 18Z TAFs.

KEY MESSAGES

1. Above average rain chances and below normal temperatures continue through much of the week.

DISCUSSION

Key message 1: Above average rain chances and below normal temperatures continue through much of the week.

Water vapor satellite continues to show the main northern stream upper trough lifting to the northeast, while a piece of it is left over the the southern Appalachians. At the same time, two upper/mid-level anticyclones will intensify with one remaining parked over the Four Corners region and the other over the western Atlantic. Model guidance continue to support the idea of the left over energy developing into a weak closed upper/mid-level low and meander over the area through mid-week. With the added forcing for ascent from this feature and anomalously high PWAT values (1.50"-2.00+"), expect for an enhancement in convective coverage each day throughout the week, especially during the typical diurnal period. By Wednesday through the end of the workweek, a digging longwave upper trough is noted across the northern/central Plains and may engulf some of the lingering energy as the close upper/mid-level low breaks down and lifts north. However, weak upper troughiness will still play a vital role in a synoptic pattern favorable for continued higher than normal diurnal PoPs through the end of the workweek and into the upcoming weekend. Each day will lead to scattered to numerous showers and thunderstorms across the region, especially Tuesday through the end of the workweek. Multiple days of this activity may lead to a few instances of localized flash flooding, especially in locations that receive multiple rounds of heavy rainfall or training thunderstorms over a short period of time. With how localized the hydro threat is expected to be and lower confidence on exact placement of the heaviest rainfall, decided not to issue a Flood Watch at this time, but conditions will need to be monitored throughout the week as this set up evolves. Can't rule out an isolated strong to severe thunderstorm or two each afternoon, with locally damaging wind gusts as the primary threat, but the environment is not conducive for organized convection or widespread severe weather throughout the week. Enhanced PoPs and cloud cover will allow for high temperatures to remain between normal and/or a category below normal through much of the forecast period.

AVIATION /18Z MONDAY THROUGH SATURDAY/

At KCLT and elsewhere: Low-end SCT/BKN VFR cu will continue through the afternoon and evening with showers and thunderstorms developing, mainly over the mountains, but a few isolated showers can't be ruled out over KCLT and KHKY. As a result, placed a PROB30 for SHRA/TSRA and associated restrictions for this afternoon for these TAF sites. Another round of low stratus and fog are expected overnight tonight, but will be more focused over the NC terminals. Placed a prevailing line mention for IFR/LIFR stratus at KCLT/KAVL/KHKY, with IFR/LIFR fog potential at KAVL for mountain valley development. Can't rule out fog and possibly MVFR stratus creeping into the Upstate sites, but confidence is too low for a TAF mention at this time. Another round of shower and storms is likely late Tuesday morning through the afternoon and evening, which is earlier than the typical Summertime timing. All TAF sites have a PROB30 for SHRA/TSRA and associated restrictions as the activity becomes more widespread across the area. Winds will generally be light through the period with southwesterly flow this afternoon, becoming light and variable overnight, and picking up a east to northeasterly component for Tuesday. KAVL will remain variable with a few instances of an up-valley component.

Outlook: Daily showers and thunderstorms, along with associated flight restrictions, linger through at least mid to late week. Patchy fog and low stratus possible in the mountain valleys each morning, and wherever heavier rainfall fell the previous evening.

GSP WATCHES/WARNINGS/ADVISORIES

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