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FXUS62 KGSP 051431 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1031 AM EDT Sun May 5 2024

SYNOPSIS
A general summertime pattern sets up today through Wednesday, keeping scattered thunderstorm chances around each afternoon. A strong cold front will approach out of the west on Thursday before tracking across the western Carolinas on Friday, leading to better coverage of thunderstorms towards the end of the workweek. Highs will remain above normal through the workweek but will climb well above normal Tuesday through Thursday.

NEAR TERM /THROUGH TONIGHT/
As of 1025 AM EDT Sunday: The latest water vapor imagery indicates a slow-moving short wave trough has cleared the CWA this morning with only a few light showers east of I-77. Additional precip should hold off until afternoon convection begins.

12Z RAOBs show a moderately unstable air mass at KFFC with a low wetbulb zero level. Instability hadn't reached KGSO with a relatively moist profile. Still expect drying aloft and periods of sunshine/good insolation for the afternoon which will result in max temps returning to above-normal levels while also allowing for some destabilization even over the eastern forecast area. Continued poor mid-level lapse rates will limit the degree of instability, but sbCAPE of around 1500 J/kg is likely across much of the area by mid- afternoon. Differential heating should result in scattered convection developing along ridgetops...esp near the Blue Ridge escarpment by mid-afternoon, which will then drift southeast on outflows and W/NW mean cloud-bearing winds into the foothills and Piedmont during late afternoon/early evening. Afternoon PoPs will range from likely along the escarpment to 20-40% across much of the remainder of the area. Shear parameters will remain weak, while modest instability will limit the depth of updraft cores, but can't completely rule out an isolated microburst, especially given the potential for DCAPE values to approach 1000 J/kg.

Diurnal convection should wind down across the Piedmont this evening. However, the next short wave trough/associated occluding cyclone is forecast to eject from the southern Great Plains this evening, with associated remnant warm conveyor belt/moisture plume forecast to overspread the CWA from the west between 09-12Z Monday.
This will increase the potential for convection...primarily SHRA to move into western areas by daybreak, warranting an increase to chance PoPs. Min temps will again be almost 10 degrees above normal.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/
As of 230 AM EDT Sunday: Weak upper ridging will be in place over the Southeast Monday before an upper shortwave trough tracks over the Carolinas Monday evening into daybreak Tuesday. Embedded shortwaves will track overhead the western Carolinas during this timeframe keeping shower and thunderstorm chances around. Have likely PoPs area-wide on Monday, with chance PoPs Monday night.
Shear will remain fairly weak, ~15-20 kts, so slow storm motions will continue the first half of the short term. 850 mb flow will remain SW'ly through the the period keeping the 90th percentile PWATS around. This may lead to locally heavy rainfall, especially for areas that received heavy rain over the weekend. Overcast skies should limit daytime heating somewhat on Monday so the severe wx potential should remain low. However, with SBCAPE from ~1000-1500 J/kg expected Monday afternoon, a few strong storms cannot be ruled out. Highs on Monday will end up around 2-4 degrees above climo, with lows Monday night expected to be ~10-13 degrees above climo thanks to mostly cloudy skies.

Weak upper ridging builds back across the Southeast Tuesday into Tuesday night, kicking off a warming trend. Temps Tuesday afternoon should climb into the lower to mid 80s across the mtn valleys and east of the mtns, which will be ~7-9 degrees above climo. Diurnal convection is expected on Tuesday, with generally lower coverage expected compared to Monday. Thus, have likely PoPs confined to the western NC mtns with chance PoPs elsewhere. Shear values will increase slightly on Tuesday, ranging from 25-35 kts, allowing for an increase in storm motion. Higher shear along with guidance depicting 1500-2000 J/kg of SBCAPE Tuesday afternoon may lead to isolated severe storms during the afternoon and early evening hours.
The main potential impacts would be damaging wind gusts and locally heavy rainfall. Have PoPs winding down Tuesday evening but maintained chance PoPs across the western zones as global models shows convection lingering into the overnight hours. Lows Tuesday night should remain around 10-13 degrees above climo.

LONG TERM /WEDNESDAY THROUGH SATURDAY/
As of 300 AM EDT Sunday: Upper level ridging flattens out on Wednesday while a cold front draped from the eastern Great Lakes to the Southern Plains makes little eastward progress. This will lead to another warm day and another round of diurnal convection.
However, the 00Z GFS and ECMWF show convective chances increasing from the west Wednesday night. With the 00Z Canadian still showing drier conditions Wednesday night, capped PoPs to chance Wednesday into Wednesday night for most locations. The exception is areas along the NC/TN border where low-end likely PoPs are in place.
Wednesday will also feature similar shear and SBCAPE values as Tuesday, so isolated severe storms will remain possible once again.
Damaging winds still look like the main potential impact with any severe storms that develop. Highs on Wednesday will climb into the mid to upper 80s east of the mtns and across the mtns valleys which would be ~9-12 degrees above climo. The CLT metro area may even see highs flirt with 90! Lows Wednesday night will remain ~13-15 degrees above climo thanks to increasing cloud cover well ahead of the aforementioned cold front.

The cold front will push into the TN Valley on Thursday before tracking across the western Carolinas and northeast Georgia late Thursday into early Friday. With model runs being inconsistent with the timing of the front, confidence remains low on when exactly the front will track across the forecast area. Nevertheless, shower and thunderstorm activity is expected well ahead of the main FROPA on Thursday, with convection likely lingering across portions of the forecast area on Friday. However, with models not in agreement on the exact timing/coverage of convection, confidence on PoPs will also be low towards the end of the workweek. Went with likely to low- end categorical PoPs across the western half of the CWA on Thursday, with chance PoPs across the eastern half of the CWA Capped PoPs to likely across the western zones on Friday and chance across the eastern zones. Shear values should climb to 40-50 kts on Thursday and 50-60 kts on Friday, with SBCAPE values up to 2500 J/kg on Thursday and up to 1500 J/kg on Friday across portions of the forecast area. This combined with the 00Z GFS showing an 850 mb jet tracking overhead the Carolinas on both Thursday and Friday will lead to the concern for severe weather both days. Thursday looks like the main day to watch for now, but Friday could be another day to watch depending on how fast the FROPA pushes east. Temps will remain well above climo Thursday into Thursday night, with temps becoming near climo to a few degrees above climo Friday into Friday night behind the cold front. Below climo temps and drier conditions return on Saturday, but NW flow convection may linger across the NC mtns.

AVIATION /15Z SUNDAY THROUGH THURSDAY/
At KCLT and elsewhere: SHRA have ended but IFR to LIFR cigs and patchy vsby restrictions remain. Expect the vsby to improve before noon, but cig restrictions could linger into early afternoon.
Scattered convection is expected to develop across the mountains during early/mid afternoon and move E/SE. Prob30s for afternoon/early evening TSRA are warranted at all sites, while a tempo for TSRA appears prudent at KAVL beginning at 18Z. Convection will diminish this evening, followed by lowering cigs again overnight. Most sites should see at least VFR conditions by daybreak Monday. Showers may redevelop from the west toward the end of the forecast period, but this remains uncertain.

Outlook: Enhanced moisture will combine with a weak/stalled front through the middle of next week, resulting in a period of active/mainly diurnal convective weather each day. There will also be the potential for restrictions associated with widespread fog and/or low clouds each morning.

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

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