textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No significant changes for this forecast cycle.

KEY MESSAGES

1. Near-normal temperatures with unseasonably low humidity and no diurnal convection expected through Friday. 2. Another frontal system is expected to arrive from the west this weekend, possibly stalling across our area early next week, bringing back high rain chances, below-normal temperatures, and some potential for locally heavy rainfall.

DISCUSSION

Key message 1: Near-normal temperatures with unseasonably low humidity and no diurnal convection expected through Friday.

Deep, relatively weak ridging will continue to influence the weather over the East through Friday. This will result in relatively low humidity, resulting in larger-than-normal diurnal temperature ranges: max temps near normal and tonight's low temps around 5 degrees below climo. Afternoon surface dewpoints mostly in the 50s/ minimal instability will result in a very low...if not 0 chance of diurnal convection.

Key message 2: Another frontal system is expected to arrive from the west this weekend, possibly stalling across our area early next week, bringing back high rain chances, below-normal temperatures, and some potential for locally heavy rainfall.

Deep layer ridging will shift off the East Coast Fri night/early Sat, as large scale height falls overspread the TN and OH Valleys, with an upper low possibly closing off to our west by the end of the weekend. Resultant deep SW flow will advect a plume of deep moisture...characterized by precipitable water waters of over 2"...into our area ahead of an attendant frontal zone by the end of Saturday. In the interim, increasing low level moisture is forecast to allow for sufficient destabilization to support scattered diurnal convection, mainly across the western half of the area Saturday afternoon. Instability may be just enough to support the threat of an isolated pulse severe storm or two.

With the increasing moisture and relative low level jet developing ahead of height falls, some degree of convective activity is likely to continue well into Saturday night/early Sunday, with some threat of locally heavy/perhaps excessive rainfall lingering through the night in light of favorable environmental factors. The frontal boundary will likely enter the forecast area by Sunday afternoon, with continued high moisture levels and some instability (albeit tempered by widespread cloud cover) supporting the potential for widespread convective development and a continued locally heavy/isolated excessive rainfall threat Sunday afternoon/evening.

Beyond Sunday, global models diverge on the fate of upper troughing and the frontal zone/moisture plume over the East, although there is a weak consensus that the best ingredients for convection/heavy rainfall will shift to our east by Monday afternoon. Even in that scenario, scattered diurnal convection would be expected to develop Monday. While the global models agree that the deeper moisture will be to our east by Tuesday, there is also a broad consensus that a weak upper low will remain closed just west of the CWA into mid-week, possibly supporting climo+ PoPs for diurnal convection (i.e., scattered coverage across the mountains; isolated-to-widely scattered elsewhere) Tue through Thu.

Under widespread clouds and solid convective coverage, max temps are forecast to be a solid 5 degrees below normal each day from Sunday through Tuesday, with a gradual warming trend expected to begin Wed. Min temps will be right around climo during this time frame.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

At KCLT and elsewhere: An unseasonably dry air mass will support convection-free weather across the Terminal Forecast Area through Friday, with VFR conditions expected to continue at the TAF sites through this forecast period. Some mountain valley fog/low stratus is again expected in the mountain valleys, albeit less widespread (mainly confined to the valleys west of KAVL) and of shorter duration than on Thu morning. Winds will mostly favor a N direction through much of the period, with speeds mainly in the 4-7 kts range expected...except slightly higher and perhaps gusty at KAVL this afternoon.

Outlook: Dry and VFR through Friday, with shower and thunderstorm chances and associated restrictions returning this weekend into early next week. Low stratus and/or fog will be possible each morning starting Friday, mainly in the mtn valleys.

GSP WATCHES/WARNINGS/ADVISORIES

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