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FXUS62 KGSP 200730 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 330 AM EDT Mon May 20 2024

SYNOPSIS
Warm high pressure will persist across the region through the middle of the week. A cold front approaches from the northwest on Thursday, bringing a chance of showers and storms mainly to the mountains. The front will stall over the area Friday, keeping rain chances through weekend.

NEAR TERM /THROUGH TONIGHT/
As of 315 AM: Weak sfc high now centered over Virginia but extending thru our CWA, supported by positively tilted upper ridge. Sfc winds are very light or calm around the area owing to weak gradient and decoupling. Patchy stratocu are seen along the Appalachian foothills from WV to GA where weak low level flow bears an easterly component. Observed cloud heights suggest some of these are being generated by shallow convection beneath subsidence inversion; they generally look to persist in the NW half of the CWA thru daybreak, although likely variable in coverage. Dewpoint depressions are small across the board, but especially so along/SE of I-85 where skies have been clearest. NAMNest and HRRR depict some fog/stratus forming via radiation but so far have appeared overdone in their extent. Shallow nature of the moist layer suggests any fog will be similarly transient to the aforementioned cloud decks.

Today, flow will veer to SE as sfc high builds slightly further south and east. Max temps will rebound back to normal or even a couple degrees above. Some cumulus will break out beneath the weak inversion across the area. Despite that, most prog soundings over the mountains depict some skinny CAPE developing, perhaps a few hundred J/kg. With upslope flow some convection is expected to fire there. Tame PWATs of generally an inch or less, mostly via low to midlevel moisture. Profiles are quite dry above 700 mb. Dry air entrainment will keep coverage isolated or widely scattered at best. Not particularly concerned for severe wx or for flash flood threat, but will point out any cells will be slow-moving and fairly healthy accums still may be seen. This activity will wane diurnally. SE flow will result in some areas of cloud cover persisting near the Blue Ridge Escarpment, similar to what we're seeing this morning, and with dewpoints not expected to mix out much this aftn. Mins near normal.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/
As of 300 AM EDT Monday: An upper ridge axis extending from the Gulf of Mexico northeast along the Appalachians will keep the atmosphere rather suppressed atop the forecast area thru the short term. Isolated showers and perhaps a couple of garden-variety tstms may develop along the ridgetops with strong daytime heating. But otherwise, just some fair wx cu and temps continuing a warming trend. Highs will be in the mid 80s on Tuesday and mid to upper 80s Wednesday across the lower mountain valleys and the Piedmont. Lows will be mainly in the 50s in the mountains and lower to mid 60s elsewhere.

LONG TERM /THURSDAY THROUGH SUNDAY/
As of 315 AM EDT Monday: Thursday has the potential to be the hottest day of the week with highs approaching 90 degrees in parts of the lower Piedmont. However, convective debris clouds may spill over the area from the west, as upper flow begins to flatten out, and this may limit insolation. While shortwave energy works to flatten the eastern CONUS ridge, guidance still is in disagreement on how far east an approaching cold front will get to our area. The ECMWF continues to keep Thursday dry, while the NBM PoPs suggest at least scattered diurnal convection returns to the mountains and possibly the I-40 corridor east. The front should sag into the area Friday, as a more pronounced wave rides thru the upper flow across the region. This should provide for better diurnal convective coverage Friday, with more shear and instability for a few strong storms. Then the front basically stalls out across the Southeast, as it becomes oriented parallel to the upper flow. So above climo PoPs looks on tap for the weekend with temps remaining a few degrees above normal.

AVIATION /08Z MONDAY THROUGH FRIDAY/
At KCLT and elsewhere: NE PBL flow continues via weak sfc high centered over Virginia. Mountain valley fog and stratus expected to persist through daybreak, with generally LIFR to VLIFR at KAVL. Otherwise, stratocu are being generated apparently via weak convergence and/or upslope east of the Blue Ridge Escarpment, with distinct layers at 030-040 and 060-080. Think these clouds are likely to be seen over all the terminals at some point before 12z, with periodic cigs possible, but cigs not likely to last long enough to allow valley fog to dissipate. Some sources depict radiation fog in the Piedmont in the predawn hours but presently not expected to extend to TAF sites. The NE winds will continue until early afternoon, with diurnal cu forming at MVFR to low VFR level but probably not causing cigs. Winds go SE with aftn mixing and southward migration of sfc high. Ridgetop SHRA or even TSRA are possible but chance still not mentionable at KAVL. SE flow tonight will produce low stratus near the Escarpment, and MVFR is possible at KAVL after 06z, along with valley fog. Otherwise VFR tonight.

Outlook: High pressure remains dominant over our area thru Wed, but isolated mountaintop convection still expected each afternoon. Precip and restrictions possible with next front arriving late Thu or Fri.

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

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