548 FXUS62 KGSP 062208 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 608 PM EDT Mon Sep 6 2021 .SYNOPSIS... Another cold front is expected to cross our area late Wednesday and bring more showers and possibly a few thunderstorms. Drying high pressure will spread back over the region in the front's wake and linger into the weekend. && .NEAR TERM /THROUGH TUESDAY/... As of 600 PM EDT Monday: No big changes to the overall forecast. Showers and thunderstorms persist in the southern tier, but should slowly diminish through the evening. Lingering convective debris could put a damper into the temperature forecast for tonight across the southern tier. Elsewhere looks to remain on track. A cold front is draped over the southern tier of the CWA attm, at the leading edge of an upper trough over the NE CONUS. That area is highlighted by the CAMs depicting a few cells thru early evening along/south of the current frontal position, in addition to what already has formed, we will boost PoPs to high chance in the southernmost zones but sharpen up the gradient a bit heading north through the rest of the evening hours. The trough will progress eastward tonight and heights will rise slightly overhead. A weak surface high will fill in behind it; the resultingly weak low-level flow is progged to veer to easterly across most of the CWA, and the front will stall just south of our area by early morning. Upslope flow and/or the usual Savannah Valley convergence zone may be responsible for some of the QPF response seen after sunset, so a slow decline in PoP is fcst thru evening. Some degree of stratus should materialize near the front and near the east-facing Escarpment, but not confident it will be extensive enough to preclude mountain valley fog/stratus, so those are still reflected in the fcst. Over the course of Tuesday, heights will flatten and then begin to fall again as another trough rotates into the Great Lakes. Winds thus will continue to veer to southerly, and very weak isentropic lift looks to occur over the front. While generally drier air looks to settle into the northern CWA by tomorrow, raising CCLs and most likely precluding deep convection, the southern half of the CWA will remain pretty humid. Temps will rebound a few degrees compared to today. Furthermore, lapse rates actually look to improve a bit compared to today. Slight-chance to chance range PoPs remain warranted for the southern two-thirds of the FA. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... As of 1:30 PM EDT Monday: Throughout the duration of the short term forecast period a ridge of high pressure will be the main synoptic feature over the western United States while a trough tracks east and digs across the Great Lakes and Northeast United States. A small area of low pressure in the Gulf of Mexico will track northeast towards the Alabama coast and Florida panhandle Tuesday night into Thursday. Meanwhile at the sfc, a stationary front will be draped across the central Carolinas Tuesday evening before dissipating early Wednesday. This stalled front will act to keep shower and thunderstorm chances around Tuesday evening and rain chances around early Wednesday morning. Capped PoPs to a slight chance towards the beginning of the forecast period. A cold front associated with the upper-level trough mentioned above should track across the area Wednesday into Thursday. Overall models have been slowing down the progression of this front. The majority of the guidance has the front tracking across the CWA late Wednesday afternoon into overnight Wednesday before pushing out of the area early Thursday morning. However, the ECMWF is the slowest solution with the FROPA pushing through overnight Wednesday into Thursday afternoon and finally clearing the area Thursday evening. For now, still have the highest PoPs occurring Wednesday afternoon into early Wednesday evening. Did cap PoPs at chance during this time frame. Model soundings have SBCAPE values ranging from 500 to 1500 J/kg Wednesday afternoon and early evening so thunderstorms can be expected. Severe threat looks minimal as as 0 to 6 km bulk shear values remain below 20 kts. Thursday morning the FROPA should be southeast of the CWA, however this front could allow for isolated showers and thunderstorms to develop Thursday afternoon, mainly across the far SE zones. High temps Wednesday will be a few to several degrees above normal. Highs will be cooler Thursday and will be near normal or just a few degrees above normal. Low temps will 4 to 7 degrees above normal. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 2:00 PM EDT Monday: The upper-level trough over the Northeast United States will lift northeast Thursday night into Friday night before tracking off US coast early Saturday. Another trough digs south out of Canada into the northern US while tracking east across the Midwest and Ohio Valley Saturday into early Sunday. This trough then lifts northeast into eastern Canada and the northeastern US at the end of the forecast period. Throughout the extended the ridge of high pressure will continue to dominate in the western US. The area of low pressure in the eastern Gulf of Mexico will continue moving northeast, eventually tracking across northern Florida then along the southeastern coast of the United States. The ECMWF is has the low tracking faster and farther east of the Carolina coast than the GFS. The GFS has the low tracking northeast and hugging the Carolina coast this weekend. Sfc high pressure is expected to build in behind the departing FROPA, (mentioned above in the short term), so the any moisture from the low along the SE coast should remain well south and east of the western Carolinas and NE GA. This area of high pressure will keep us dry throughout the duration of the extended forecast period. Temps will gradually warm throughout the period. && .AVIATION /22Z MONDAY THROUGH SATURDAY/... At KCLT and elsewhere: VFR conditions continue to prevail at all TAF sites with low-end VFR cu unfolding at some of the western sites. Haze is being reported at the KAVL and the reason is unknown at this time, but did include a TEMPO for haze vsby restrictions through 00Z Tuesday at KAVL. Cold front sagging thru the far southern tier of the CWA attm, on track to stall south of the region tonight. Moisture pooling in its vicinity has allowed cu to break out at MVFR level in parts of the Upstate. SCT SHRA/TSRA are possible on the warm side of the front this afternoon, but with wind shift having already occurred all the TAF sites, chances at the sites are too small to mention today except for VCSH at KAND being farthest south. Northerly winds should prevail thru tonight, eventually veering to NE in the Piedmont. Weak upglide developing over the front will potentially produce low VFR or MVFR stratus near KAND/KGSP/KGMU/KAVL, but most guidance depicts VFR conditions aside from potential mountain valley fog/stratus. The latter will more likely if the higher cloud decks don't materialize, so IFR in TEMPO at KAVL. Another humid day with cu bases starting off on the low end, warranting MVFR at KAND. Isold-sct SHRA/TSRA will develop diurnally but not worthy of mention except at KAND. Outlook: A second cold front entering from the NW may bring scattered convection Wednesday into Thursday. Generally settled weather and high pressure expected in the wake of that front. Mountain valley fog and stratus will remain possible each morning. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...CAC/Wimberley SHORT TERM...AP LONG TERM...AP AVIATION...CAC/Wimberley