textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The forecast was updated to reflect the recent 12Z TAF update.

KEY MESSAGES

1. Above average rain chances and below normal temperatures continue through the middle of the week. 2. A more typical late summer pattern returns late week into the weekend with warming temperatures and daily scattered afternoon showers and storms.

DISCUSSION

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

The synoptic pattern remains largely unchanged early this morning with a broad upper ridge parked over the Desert Southwest while a Bermuda high builds off the east coast. Pronounced northern stream flow is draped from the Northern Great Plains to New England. A closed and cutoff upper low remains sandwiched between the two ridges and continues to spin as it meanders over the Southern Appalachians. A weak surface reflection over central Georgia has fostered the development of east/southeast onshore return flow with a deep plume of moisture pivoting west across the Coastal Plain and into the North Carolina Piedmont and foothills and portions of the northern Upstate. The presence of the upper low and increasing moisture will instigate at least scattered to numerous afternoon showers and thunderstorms across much of the area both today and tomorrow. As with any summer storms in a moist environment locally heavy rainfall could result in isolated flash flooding. Additionally, a few strong to marginally severe storms cannot be ruled out, especially this afternoon. Modest instability is progged in guidance with 2000-3000 J/kg of surface-based instability. While tall/skinny CAPE profiles are still depicted in guidance, mid-level lapse rates nearing 6.5 C/km along with 500-700 J/kg of DCAPE and 20- 25 kts of deep-layer vertical wind shear will support the potential for locally damaging wind gusts with any deeper cores and loosely organized clusters of convection. Temperatures will remain at or several degrees below average.

Key message 2: A more typical late summer pattern returns late week into the weekend with warming temperatures and daily scattered afternoon showers and storms.

By late Wednesday into Thursday, a broad longwave trough will become established from the Central Plains into Canada and will slowly translate into the Great Lakes region. This will allow for the closed upper low over the Southern Appalachians to evolve into a weak open shortwave trough and become absorbed into the broader trough. The base of the trough and better height falls and forcing is forecast to remain displaced north of the region with height rises by Friday into the weekend as the Bermuda high tries to nudge onshore. In the absence of the upper low, diurnally driven rain chances will return to more typical climo values for late summer with the best coverage over the mountains with isolated to widely scattered elsewhere. Temperatures will also return to more seasonable values for early August with highs in the mid 80s to low 90s.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: A rather busy TAF period continues with a myriad of restrictions throughout the forecast. A widespread deck of IFR to LIFR stratus has developed this morning east of the mountains with ribbons of valley fog and low stratus across the traditional mountain valleys. Patchy fog is also common, but most visibilities remain above dense. Fog will mix out after sunrise with ceilings also slowly lifting through the morning with a return to VFR by the afternoon. Next up will be scattered to numerous afternoon and evening showers and thunderstorms across the region. Associated visibility and ceiling restrictions can be expected with any of this activity along with gusty and erratic winds with any stronger storms. Persistent low-level moisture will once again support the development of another low stratus deck tonight into Wednesday morning with more mountain valley fog/stratus.

Outlook: Daily showers and thunderstorms, and associated flight restrictions, will continue through most of the week. Patchy fog and low stratus will be possible each morning, especially in the mountain valleys and anywhere that heavier rainfall has developed the previous evening.

GSP WATCHES/WARNINGS/ADVISORIES

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