Sunrise 6:51 AM   Sunset 8:07 PM Moonrise 3:25 PM   Moonset 4:01 AM

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FXUS62 KGSP 191435 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1035 AM EDT Fri Apr 19 2024

SYNOPSIS
Showers and thunderstorms are possible today as a cold front crosses the area, but unseasonably warm weather continues through Saturday.
Below-normal temperatures and widespread light rain is expected Sunday with cool but drier weather on Monday. Drier and warmer weather will return to the area Tuesday through Thursday of next week.

NEAR TERM /THROUGH TONIGHT/
As of 1030 AM Friday: Line of showers associated with a pre-frontal short wave will move east of the area before noon. An isolated TSRA will be possible over Chester County as this line moves east.
Westerly wind and clearing skies moving in behind the line. The clouds associated with the showers have slowed warming somewhat, but that should resume. Therefore, kept highs as is for now. Afternoon and evening convection still look on track, with the potential for strong to severe storms.

A lead short wave will move across the region this morning and will take weakening showers off to the east. After that, it might get a bit interesting across the fcst area, with the possibility of a few thunderstorms, one or two of which could be severe. Destabilization should occur in the middle part of the day as morning cloudiness shifts eastward with the passing wave. The RAP shows mainly 1000-1500 J/kg of sfc-based CAPE, with a few pockets upwards of 2000 J/kg. Shear should be enough to help organize whatever storms manage to develop, with effective shear 40-45 kt in places. This leaves us with a conditional prob of a few severe storms, if we can get a few storms to develop at all. Differential heating and convergence downwind of some of the higher mtns should be able to do that trick, not to mention a weak sfc boundary coming down from the WNW. Large hail would be one possibility as RAP profiles show some decent CAPE in the hail growth zone and relatively strong winds at the EL. Meanwhile, the dCAPE could get above 800 J/kg, suggesting some strong thunderstorm outflows. Some of the CAMs at 00Z had brief updraft helicity streaks downwind of the mtns. Make of that what you will, but it at least hints of some potential for briefly rotating updrafts that would improve severe weather chances. The entire fcst area is in a Marginal Risk on the Day1 Convective Outlook and this is reasonable. Temps should end up a category cooler than yesterday if we get the convection by peak heating. The weak front crosses the region this evening and takes most of the precip with it, save for some lingering upslope showers near the TN border. Temps should remain mild overnight.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
As of 200 AM EDT Friday: The near-term cold front is forecasted to be well south and east by the start of the forecast period as the frontal boundary stalls over the Gulf Coast. An active baroclinic zone will develop across the Deep South/Gulf Coast and help aid in widespread showers and thunderstorms in these regions as a series of surface waves develop and ride along the stalled front. Enough differential heating and a northward ripple of the boundary due to a passing surface wave could set the stage for isolated convection near the vicinity of the boundary Saturday afternoon, mainly in locations along and south/east of I-85.
Otherwise, dry air entrainment will gradually filter in behind the front and should allow for a pleasant day for most locations Saturday. Highs will be 4-8 degrees above normal for highs across the Piedmont, while near-normal values are expected across the mountains. Model guidance are in decent agreement with developing a weak coastal low along the boundary Saturday night into Sunday along the east-central Gulf Coast. The current track has this feature slipping across the S GA/FL Panhandle and offshore the Southeast Coast. Bizarre in-situ wedge will settle in as the parent surface high slides into the Southern Plains and a piece of this area of high pressure breaks off and sets up shop over the Mid-Atlantic Saturday night into Sunday. In this case, high temperatures will drop ~15-20 degrees on Sunday compared to Saturday. The precip shield associated with the coastal low will bring rainfall to the area Sunday and essentially lock in any kind of wedge that develops.
QPF response will be light to moderate, with the southeastern zones expected to receive the most rainfall.

The coastal low slips further offshore the Southeast Coast Sunday night as the aforementioned parent surface high propagates eastward and stretches from the Lower MS Valley through the Mid-Atlantic. Cooler thicknesses will move over the area Sunday night as a stout shortwave trough quickly shifts across the central CONUS and knocking on our front door by the very end of the period. Factor in continued north-northwesterly flow in the low-levels and weak CAA, overnight lows are expected to be in the 40s for most locations, with values flirting with the 30s in the higher elevations.

LONG TERM /MONDAY THROUGH THURSDAY/
As of 315 AM EDT Friday: Lingering in-situ wedge is shown eroding by Monday as the aforementioned surface high shifts across the Carolinas and into the northeastern CONUS, while the shortwave trough slips overhead and offshore by Monday night. This will keep temperatures ~10-15 degrees below normal for most locations Monday. Low-amplitude upper ridging will traverse across the CFWA Tuesday into Wednesday, which will allow for the airmass to modify as highs rebound to slightly below normal Tuesday to at or just a tad above normal for afternoon highs on Wednesday. A potent shortwave trough will move into the region later Wednesday into Thursday with an attendant frontal boundary. Model guidance are not excited about the potential impacts as the boundary will move into a moisture starved environment and lack thereof forcing as better forcing will reside north of the area. Best PoPs will stay confined to the immediate Tennessee border before rain chances dwindle east of the state line. Temperatures should remain near-normal through the end of the week, with a mainly quiet pattern in store to round out the extended forecast period.

AVIATION /15Z FRIDAY THROUGH TUESDAY/
At KCLT and elsewhere: The line of showers will move east of the area soon with no additional restrictions. Clearing skies and westerly winds are moving in behind the line. Winds should turn more NNW at KAVL and SW elsewhere for the afternoon. Restrictions are possible in showers and thunderstorms that develop this afternoon and early evening. The latest guidance shows scattered storms after 21Z, thus we employ the PROB30 to handle the possibility of MVFR in a 5-6hr window. The showers should get pushed east of the fcst area by the mid-evening as a frontal boundary moves in from the WNW.
Expect a wind shift to W or WNW with the boundary passage. Some upslope light precip could continue along the TN border after dark and into the early morning hours Saturday. Some of the guidance indicates the possible development of MVFR-level bkn ceiling around daybreak Saturday, but think only the mtns have a serious chance.

Outlook: As a cold front sags south across the area, another round of convection is possible Saturday, mainly during the afternoon.
Rain and possibly isolated thunderstorms are expected to develop north of the front on Sunday, likely resulting in restrictions for at least the southern part of the area. Drier conditions return Monday, continuing into Tuesday.

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

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