Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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743 FXUS62 KGSP 181723 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 123 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 TONIGHT/... 1000 AM Update...No sigfnt changes made the fcst grids. A cutoff upper low continues to provide enuf lift to produce periods -ra/dz over most areas and expect little improvement thru the next update. Temps and td/s are holding nearly steady-state in this moist environ with only slow warming thru the remainder of the morning due to widespread downcast conds. The upper low should support a little more mixing and some breaks in the clouds later in the day, which will help high temps to rebound from yesterday`s readings. The warmer temps and still cool temps aloft will support at least a few hundred J/kg sbCAPE by midafternoon, especially around the edges of the low (that is, the northern and eastern parts of the forecast area). So isolated to scattered showers may develop before the end of the day (most CAMs show at least some diurnal convection). Instability and forcing will likely be too weak for thunder, but cannot rule out one or two general thunderstorms in the I-40 and/or I-77 corridors. The western and southern parts of the FA will be on the more stable side of the low. Temps are forecast to top out a few degrees below normal under mostly cloudy skies. Tonight, the low will continue to drift east, allowing for most of the mid and upper moisture to exit stage right. However, lingering low-level moisture will likely support an increase in low stratus overnight, with patchy fog possible, especially in the mountain valleys. Lows will a few degrees above normal. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 135 AM EDT Tuesday: The weak closed upper low will open up into a shortwave trough by the beginning portion of the forecast period and lift into the northeast CONUS Thursday night into Friday as the associated trough axis gradually shifts east of the CFWA. Upper anticyclone over northern Mexico and Southern Plains slowly pivots higher heights into the southeastern CONUS in response to a digging upper low that moves into the southwestern CONUS. Lingering mid/low-level moisture should keep isolated to scattered showers across the CFWA on Thursday with a focus on the mountains and drier conditions becoming more evident elsewhere. The upper anticyclone axis will begin to encroach the region from the west as weak high pressure begins to settle in across the area. Dry air entrainment in the upper and mid-levels of the atmosphere will essentially shutoff any shower chance outside of a small chance over the mountains where convergence is maximized. Temperatures Thursday will be a few ticks below normal for afternoon highs as cloud cover will be more extensive and that will carry over into Thursday night as well, with overnight lows a few ticks above normal. More insolation Friday will result in temperatures rising to near normal values for highs and better radiational cooling conditions Friday night leading to near normal temperatures. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 300 AM EDT Wednesday: Upper ridge axis gradually slips east from the MS Valley to the eastern CONUS over the weekend into the early part of next week. Surface high stretching from Atlantic Canada down the Appalachians will control the sensible weather during this timeframe and allow for a much drier airmass to settle over the region. Operational models try to send a cold front in from the west as a shortwave trough travels across the northern CONUS, but some form of moisture return is evident as the surface high slips offshore ahead of the front. Mentionable PoPs return to forecast by D7 as the front inches closer to the area, but of course uncertainty resides this far out. Temperatures will be near-normal for mid to late September through much of the forecast period. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... At KCLT and elsewhere: A tricky TAF set in store as an upper low continues to produce low clouds and VSBY issues. Expect some improvement to VFR this afternoon, esp at KCLT. The wrn sites could remain socked in (MVFR/IFR CIGs) for a while with deeper moisture continuing to train and lift over the area. All sites will likely drop to IFR, mainly due to CIGs, overnight with MVFR VSBY probable as well. At KAVL, a good signal for a drying column as the low shifts east thereby setting up a possible dense fog threat arnd daybreak. Expect improving conds late period all sites to either MVFR or VFR. Winds remain light thru the period favoring a ne/ly direction. 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...ARK NEAR TERM...ARK/SBK SHORT TERM...CAC LONG TERM...CAC AVIATION...ARK/SBK