Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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959 FXUS62 KGSP 240609 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 209 AM EDT Tue Sep 24 2024 .SYNOPSIS... A moist and cooler airmass will remain in place across the forecast area through mid-week. A tropical system is expected to strengthen over the Gulf of Mexico, making landfall late Thursday and affecting the Carolinas on Friday. && .NEAR TERM /THROUGH TODAY/... As of 12:25 AM EDT Tuesday: We`re still seeing some isolated showers over the NC Piedmont (just west of the CLT area) and near the NC/TN border. The showers/cells near CLT have grown taller over the past half hour or so, but have yet to produce any lightning. The latest CAMs still have some shower activity lingering thru the overnight hours, mostly across our NC zones. Another round of low stratus and patchy fog will also likely develop from NE to SW across the area overnight. This will help keep lows around 10 degrees above normal. Otherwise, Tuesday should see a similar scenario as today with morning stratus slowly eroding and lifting from SW to NE through the day. Moderate instability with up to 35 kts of effective bulk shear expected as well. There may be better DCAPE Tues afternoon though. Expect good diurnal convective coverage during the aftn with a few severe thunderstorms. Highs will see a similar pattern as well with cooler temps where the stratus burns off latest. Highs will be around 5 degrees above normal. && .SHORT TERM /TONIGHT THROUGH THURSDAY/... As of 155 PM EDT Monday: By Tuesday evening, a potent upper low will be in place over the Ozarks, with the western Carolina sandwiched between its eastern periphery and a deteriorating ridge off the Atlantic coast. On the east side of a narrow baroclinic zone stretching from the Mississippi Delta region up into the Tennessee Valley, moisture will stream into the forecast are out of the southwest, maintaining cloud skies and at least scattered afternoon on Wednesday. As low-level flow turns around out of the ESE late Wednesday and into Thursday, moisture will gradually diminish, resulting in a brief reprieve from the wet conditions. For what showers do develop on Wednesday, some thunder will be able to mix in, given 1000-1200 J/kg sbCAPE. 20kts or so of deep layer shear may support some loosely-organized multicell clusters, and, especially as dry air begins to build in aloft, perhaps some downburst wind threat. Thursday will feature the slow approach of the remnants of Potential Tropical Cyclone 9. Models are in good agreement at this time on the low moving inland over the Florida Panhandle and tracking NNE into central Georgia through late in the day Thursday. The first upper-level moisture associated with PTC 9 will arrive as early as Thursday morning...but in terms of the deeper moisture needed to spur heavy rain...that`s not depicted arriving earlier than late Thursday afternoon, or possibly past the end of the short term period Thursday night. Thus, more appreciable rainfall doesn`t appear likely through the end of the day Thursday. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 204 PM EDT Monday: Thursday night and the first part of Friday will give us our taste of whatever impacts PTC 9 brings. Long-range ensembles remain split into two camps. The dominant group of LREF members curve the post-tropical low westward as it interacts with the preexisting upper low still churning over the Ozarks. This results in generally lower QPF response for the western Carolinas, and weaker winds. The secondary group of LREF members, however, depicts either less interaction with the low, or a low shifted a little farther eastward, bringing the remnant low directly over northeast Georgia and the western Upstate. Such a solution would result in potentially significant rainfall across parts of the Upstate. Forecast soundings for the Upstate, from both the operational GFS and GDPS, also feature low-level winds in excess of 45kts. The 850mb charts are even more dire. Although the configuration won`t be favorable for mixing this wind down to the surface in its entirety, it`s a hint that strong winds may also be a problem Thursday night and Friday. The current NHC forecast calls for no more than a 10% chance of tropical-storm force winds for the Upstate...and that seems quite reasonable at this time. Friday night, whatever is left of the post-tropical low will either deteriorate in a zone of unfavorable dynamics over central Virginia, or be absorbed into the preexisting Ozark low (depending on whether the eastern or western track pans out). Behind it, an extensive layer of dry air aloft is progged to push into the area from the south, associated with weak ridging. Despite this, weekend temperatures look to stay in the low- to mid-70s. The Ozark low, meanwhile, should remain in place somewhere over the Deep South. Consensus is, though, that it`ll remain far enough west as to preclude any impacts for our area. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... At KCLT and elsewhere: Patches of sct showers will likely linger thru the overnight hrs, especially across western North Carolina. This was handled with VCSH at the NC terminals for the next few hrs. We may need to extend the VCSH if shower activity continues for longer. Winds should remain light to calm across the area thru much of the morning. Another round of IFR to LIFR low stratus is expected overnight and thru the morning, with the lower cigs likely lingering into the early afternoon for KCLT and KHKY, but probably not quite as long for the Upstate terminals or KAVL. There`s a de- cent chance that patchy fog will develop as well but confidence is not as high as it is for lower cigs, so any IFR/LIFR visby was han- dled with TEMPOs. Fog should mix out by 14z or so, with the lower cigs likely to linger a few hrs longer. Another round of sct showers and thunderstorms is expected this aftn/evening, so I have PROB30s for TSRA at all taf sites from roughly 18 to 24z with TEMPOs for lingering showers after 00z. Winds will pick up modestly this aftn from the S to SW, and become light again later this evening. Outlook: A slowly approaching weak cold front will stall west of the fcst area on Wednesday, keeping the chance for diurnal showers and thunderstorms around. Fog/low stratus may develop each morning, especially in the mtn valleys. Confidence is increasing that a tropical cyclone will bring heavy rain and strong winds Thursday into Friday before moving out of the area Friday night into Sat. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...MPR NEAR TERM...AR/JPT SHORT TERM...MPR LONG TERM...MPR AVIATION...JPT