Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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569 FXUS62 KGSP 190012 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 812 PM EDT Wed Sep 18 2024 .SYNOPSIS... The remnants of the coastal low will gradually dissipate or move off the Mid Atlantic coast by Friday. Meanwhile, high pressure begins to build into the region from the north and west giving our region a dry weekend. Temperatures will be near normal. && .NEAR TERM /THROUGH THURSDAY/... As of 756 PM...With the loss of daytime heating, the boundary layer has started to lose instability, and shower activity has sharply dropped off in coverage, more or less as expected. We still have some remaining weak buoyancy around 500 J/kg of sfc-based CAPE, so that will fuel the remaining showers for another hour or two, but the downward trend should continue. The swirl in the low clouds seen in the IR satellite imagery shows the location of a cutoff low over the northern Upstate. Won`t rule out a stray thunderstorm in the northwest Piedmont east of I-77 where the CAPE is just a bit deeper and a few lightning strikes have been observed. Otherwise...the upper low will lose any connection with the sfc pattern overnight and slowly shift east of the forecast area thru the day on Thu. Still expect a good amount of low level wrap around moisture in the wake, which will be able to develop isolated to scattered pulse showers and possibly a few thunderstorms with increasing instability during the afternoon. Overall, an improving pattern as far as lessening cloud cover and temps will respond to arnd 80 F outside the mtns, a few degrees warmer toward northeast GA, and u70s mtn valleys. A dense fog threat is possible arnd daybreak across the NC mtn valleys as better radiational cooling conditions interact with a rather moist sfc layer. Lows will generally be held a couple degrees abv normal. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... As of 157 PM Tuesday: As we head into Friday and Saturday, upper ridging will slowly drift east from the Southern Plains into the Lower Mississippi Valley. Heights will rise through the period across the Southern Appalachians with increasing subsidence. At the surface, high pressure will extend down the spine of the Appalachians form a parent high centered near the Hudson Bay. Guidance still indicates the presence of a backdoor cold front oozing into portions of the Carolinas from Virginia. A noticeable change, however, is that guidance is less aggressive with clearing the boundary through the area, thus keeping dewpoints in the low to mid 60s. The airmass will be drier, relatively speaking compared to the tropical origins of the current airmass, but PWATs may not fall as appreciably. While a stray shower or two cannot be ruled out, increasing subsidence from the building upper ridge will generally preclude mentionable PoPs outside of the Blue Ridge escarpment on Friday. Temperatures will continue to warm through the period with highs back into the low to mid 80s. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... As of 206 PM EDT Wednesday: A warming trend will continue Sunday into early next week as the axis of the upper ridge becomes centered over the Appalachians. Warming H85 temperatures and deep/efficient mixing of the boundary layer will promote high temperatures in the mid to upper 80s on Sunday, which will likely be the hottest day of the period. A few locations may even reach the 90 degree mark across the Upper Savannah Valley. The forecast will remain dry, however, as a stout subsidence inversion present on forecast soundings deters any convection. By Monday into Tuesday, a shortwave trough swinging across the Midwest will drag a cold front towards the area. Timing of the trough and attendant front remains elusive at this time range, but a gradual uptick in PoPs will be warranted across the mountains as the boundary nears. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... At KCLT and elsewhere: Prevailing VFR at issuance time, but some MVFR-level stratocu persisted over the western part of Upstate SC that will require a TEMPO at some of the terminals. Otherwise, shower activity has been on a quick downward trend, as has low cloud coverage. An upper low was identified in the satellite imagery over the northern Upstate, and that feature should continue to rotate off to the east overnight. The guidance continues to strongly suggest that a new cloud layer will develop late tonight across the region, initially at the MVFR, and then lowering to IFR across most terminals. This seems reasonable given the lingering high moisture in the boundary layer. The ceiling should be the primary restriction, but some vis problems could also develop. Note that in the mtn valleys, the fog could drop the vis down into the LIFR category and VLIFR is not out of the question. Wind will be light N/NE or calm. The fog/low stratus may take until the middle part of the morning to mix out. When it does, we will likely retain a ceiling restriction into the early afternoon, which will eventually lift to VFR. Some shower activity is possible once again over the mtns, but the chances look too small to include a PROB30 at KAVL at this time. Outlook: On Friday, sfc high pressure builds into the area from the north allowing drier weather and VFR conditions to return into this weekend. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...PM/SBK SHORT TERM...TW LONG TERM...TW AVIATION...PM