Marine Weather and Tide Forecast for Walhalla, SC

NEAR TERM /THROUGH SATURDAY/
As of 1047 PM Friday: A line of thunderstorms continues to make steady eastward progress across northeast to central GA, now entering the western part of the Upstate. A small pool of sfc-based CAPE remained over northeast GA, on the order of 500-1000 J/kg, just outside our fcst area, but once you get east of the river, the sfc-based CAPE is much lower and more inhibition has set in. Thus, while the line of storms probably has enough fuel to persist across most of the Upstate, think the chances of severe weather are greatly diminished as we get further east. Have updated the precip probs to account for the movement of the line across the fcst area for the next several hours. Temp/dewpt trend was actually in good shape still.

Otherwise...water vapor satellite imagery depicts a weak upper trough over the Lower Mississippi Valley. Guidance is in excellent agreement that this feature will lift northeast across the Southern Appalachians this evening into the overnight hours. Convection will weaken with waning instability with a broken band of showers progressing east of I-26 into the overnight. An accompanying modest cold pool may prove to be sufficient for a few embedded strong wind gusts, mainly west of I-26, but an otherwise unfavorable environment both thermodynamically and kinematically will limit any severe weather threat.

A few scattered showers may linger east of I-77 Saturday morning, but should quickly push out of the area shortly after sunrise. A more potent northern stream trough swinging across the Great Lakes region will send a surface cold front towards the area during the day with the boundary sliding into the mountains and towards the foothills/Piedmont late Saturday afternoon. By this point, the region will reside behind the trough axis of the original trough with dry mid-level air arriving within the northwest flow regime.
Flow will also have a downslope component off the mountains, which will further prove detrimental to the development of pre-frontal convection. The result has been a continued down tick in PoPs Saturday with only isolated to widely scattered showers and perhaps a couple thunderstorms ahead of the front, generally along and south of I-85. Afternoon highs will recover nicely ahead of the front with temperatures climbing back into the low 80s.

SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/
As of 100 PM Fri: Sfc cold front looks to have cleared the CWA by Saturday evening, although the trailing secondary push of cooler and drier air may still be near the Appalachian spine at that time, taking until Sunday morning to expand southeast across the whole CWA Remaining PoPs diminish overnight as the upslope layer dries out along the NC/TN border, and as more stable air reaches the Piedmont and any lingering convection fizzles. Behind the secondary front, sfc high centered near Lake Erie will nose into the CWA thru Sunday, shifting to the Mid-Atlantic coastal plain by Monday morning in advance of the upper ridge axis. Max temps return to about normal Sunday but moderate a little above normal for Monday. Low RH at or below 30% is possible in our northern NC foothills and the eastern portion of our Piedmont zones on Sun and Mon.

For the NE half of our CWA, more or less NE of I-26, pretty high confidence that subsidence will totally inhibit any convection Sunday and Monday, under profiles dry enough to warrant PoP near zero during that timeframe. Return flow however will set up on the periphery of the sfc high, ahead of the ridge, producing a midlevel moist layer and very weak upglide Sun night into Monday morning which leads some models to produce spotty QPF. That is not entirely out of the question although the forcing and lift are so weak it warrants only a slight-chance PoP, mainly in the Smokies, Balsams and vicinity.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
As of 130 PM Fri: Sfc high will continue to shift southeastward Mon night; ridge axis will tilt toward the East Coast as upper pattern turns more progressive. To wit, cyclogenesis occurs in the central Plains as a shortwave shears off the Western trough; those features track across the northern Great Lakes Tuesday and the sfc high moves fully offshore. South to southwesterly flow from the surface to 700mb will promote a warming trend over the CWA through late week and also bring back springlike sfc dewpoints. Temps will run around 10 above normal Wed and Thu.

The Appalachians look to be on the upstream side of the ridge by Tuesday, and subsidence inversion weakens to the point deep ridgetop convection again appears possible. The front associated with the Great Lakes low is generally shown to stall to our north Wednesday, keeping us more or less in the warm sector. Forcing generally looks weak, aside from diurnal instability. PWATs will rise to near the 90th percentile of climo. The return of sfc moisture does support at least seasonable diurnal instability of 500-1000 J/kg each day.
Coverage is expected to be better Wednesday compared to Tuesday as profiles become slightly more favorable for convection. Chances increase further Thursday as the southern shortwave moves into the lower MS Valley.

Convection Tue-Wed looks most likely to be garden-variety with actual thunder likely remaining isolated. Locally heavy rain may however lead to a localized flash flood threat each day. Deep shear increases as the shortwave approaches Thu, increasing the likelihood of at loosely organized multicell convection and a slightly better chance of severe winds and flash flooding.

AVIATION /03Z SATURDAY THROUGH WEDNESDAY/
At KCLT and elsewhere: VFR at all terminals this evening away from any convection that is ongoing, with a light SW wind. The main concern will be a broken band of convection moving in from the west this evening. The guidance continues to depict this band moving steadily east across the region thru the early morning hours. All terminals get a period of mainly MVFR restrictions in a TEMPO group to handle the passage of this broken band. At this point, the timing looks unfavorable to thunderstorms, so we include this as showers and will amend accordingly. In the wake of the band of convection, there should be a period of MVFR residual stratus until daybreak. Wind comes back around to SW after daybreak and we should break out to scattered by late morning.

Outlook: A few isolated to scattered showers and storms will be possible Saturday afternoon ahead of an advancing cold front, but coverage will be much less compared to the last few days. Dry high pressure returns Sunday into early next week.

GSP WATCHES/WARNINGS/ADVISORIES
GA...None.
NC...None.
SC...None.