textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated for 12z aviation discussion.

KEY MESSAGES

1. Above normal temperatures with daily chances for showers and thunderstorms continues through Saturday. 2. Cold front Sunday could increase chances for more appreciable rainfall followed by cooler conditions early next week.

DISCUSSION

Key message 1: Above normal temperatures with daily chances for showers and thunderstorms continues through Saturday.

Broad and flat upper ridging extending from the Atlantic across the southeast states into the Gulf will remain in place for the next several days as we close out the week and head into the weekend. An active southern stream will be displaced west of the region with several shortwave troughs lifting across the Mississippi Valley and climbing the western flank of the ridge into the Midwest and Great Lakes. As such, the vast majority of forcing for ascent will pass by well west and north of the Southern Appalachians as H5 heights hover around 582-585 dam. At the surface, sprawling high pressure extends from off the Carolina coast into the southeast states with continued moisture advection into the area within broad southerly flow. This overall synoptic regime will support a continued stretch of above average temperatures with daily chances for showers and thunderstorms. Afternoon highs will range from the upper 70s to low 80s each day. Mainly diurnal convection will also be possible with the greatest coverage generally focused over the mountains. Weak deep-layer vertical wind shear will preclude a threat for severe thunderstorms, but modest instability and seasonably steep lapse rates could support a few stronger cores with any deeper updrafts.

Key message 2: Cold front Sunday could increase chances for more appreciable rainfall followed by cooler conditions early next week.

By Saturday night, guidance spins up a surface low across the midwest and a trailing cold front. Ahead of the front, the CWA remains in an open warm sector as the persistent high off the coast continues to advect moisture into the southeast. This increases PWATs for the entire area. This is the first signal for much needed rainfall that could actually be helpful. At this time, guidance shows a 15-30% chance for rainfall amounts exceeding 1" from Saturday night into Sunday. Though a lower chance that is highly dependent on a FROPA, it's the best signal seen in a while. Additionally, pre-frontal showers and thunderstorms are possible which could increase rain chances for isolated locations. At this time, severe weather cannot be ruled out, but is too far out to pinpoint the details. Looking at long range modeled soundings, there could be enough instability and shear to promote such strong or severe storms, especially with the front. So for now, expect a few showers and thunderstorms Saturday afternoon/evening with another chance for possible severe with a line of storms ahead of a cold front Saturday night.

Behind the front, drier conditions return and cooler temperatures that are closer to normal for this time of the year.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: VFR conditions will prevail through the TAF period at all terminals. Scattered VFR stratus has developed across portions of the Blue Ridge escarpment as high clouds gradually fill east. No restrictions are expected with VFR continuing. Isolated to scattered showers and thunderstorms will be possible this afternoon, especially across the mountains. Brief reductions in visibility and ceiling can be expected with any of this activity before it dissipates later this evening. Otherwise winds will be generally light out of the southwest with a few sporadic low-end gusts possible.

Outlook: Daily chances for showers and thunderstorms with associated restrictions through the weekend. A cold front will bring greater chances for restrictions Saturday night into Sunday morning.

GSP WATCHES/WARNINGS/ADVISORIES

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