Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
804 FXUS62 KGSP 011046 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 646 AM EDT Mon Sep 1 2025 .SYNOPSIS... High pressure will remain over the East Coast through Tuesday, then gradually weaken midweek. It will be mostly dry, until greater coverage of the showers and storms returns across mostly the mountains and adjacent foothills into Wednesday and Thursday as a cold front approaches from the northwest. Temperatures remain below seasonal normals through the week. && .NEAR TERM /THROUGH TONIGHT/... As of 1141 PM EDT Sunday: A closed upper low is forecast to meander around the Mid-Atlantic as it remains trapped beneath a blocking high just to the north. Broad and weak northwest flow aloft extends from the Central Plains to the southeast states. Meanwhile, at the surface, a large sprawling high extends from the Great Lakes region into New England. Ageostrophic response to low-level flow has resulted in the development of a CAD surface pattern with high pressure ridging down the Appalachians. Dry northeast flow has advected 50s dewpoints into the area which will continue to filter south overnight. This will be a dry CAD event with a dearth of upper forcing and lack of isentropic ascent atop the shallow cool air. The exception will be across the southwest mountains and Smokies farther removed from the influence of the CAD. Here, a pinched off area of higher moisture will yield non-zero surface-based instability and the potential for a couple isolated to widely scattered diurnally driven showers and thunderstorms. Otherwise, temperatures will be below average again today with highs in the mid to upper 70s. Quiet weather continues tonight with lows in the low to upper 50s. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 1230 AM EDT Monday: A deep upper-level longwave trough will remain anchored across the eastern CONUS. Sfc high pressure will linger along the East Coast, with a relatively stable, dry NELY low-level flow persisting across the Carolinas. A very deep upper low will dive into the Upper Midwest and bring a cold front SE into the OH Valley Wednesday. The sfc high will weaken and low-level flow will begin to turn out of the S/SW. The flow will remain fairly light, only tapping into a little moisture and increasing PWATs atop the CWFA into the 1.0-1.25" range for Wednesday. There should be enough instability for increased diurnal convection, mainly across the mountains. Most of this will likely be scattered showers and a few isolated general tstms. The Piedmont should stay largely dry thru the short term. Temps will continue to be below normal, with highs mainly in the 70s to lower 80 and lows in the 50s to lower 60s. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 125 AM EDT Monday: A blocking pattern out west will keep a persistent deep upper trough across the eastern CONUS thru the period. A large upper vortex will set up over central Ontario, but the southern periphery of the circulation will extend all the way into the Southeast. This will allow a cold front to push thru the OH Valley and across the Appalachians Thursday into early Friday. The front never attains a deep moisture tap, and the better upper forcing looks to pivot north of the forecast area. With that said, guidance has trended a little wetter and more unstable with the fropa. At this point, cannot rule out a few strong storms along/ahead of the front, especially if it crosses the area during peak heating, given 1500+ j/kg of sbCAPE and 30-40 kt of 0-6 km bulk shear. The flow increases enough to limit the heavy rain potential, and dry air starts working in from the west by 12z Friday. The latest NBM still has just chc to low-end likely PoPs in the mountains and slight chc to low-end chc east, which is quite a bit lower than the latest model consensus, especially east of the mountains. If the model trends hold, these PoPs may increase for Thursday into Thursday night. Guidance has also trended warmer behind the fropa for Friday and Saturday, with highs possibly back to normal or even a degree or two above normal. The eastern upper trough axis begins to drift east from the OH Valley to the Appalachians Sunday, which may allow another cold front to cross the area Sunday. This front looks dry, but might bring temps back down a little below normal. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... At KCLT and elsewhere: VFR conditions will prevail at all terminals through the TAF period. Clouds have lingered across the mountains early this morning and have hampered the development of valley fog. A few isolated instances of fog cannot be ruled out through sunrise, but confidence is too low to warrant mention in any TAFs. Otherwise, mainly high clouds will stream across the area today with light northeast winds. Outlook: At least scattered afternoon/evening convection will return for much of the area Wed and Thu before diminishing again late in the week. Nocturnal valley fog and/or low stratus will also be possible each night and early morning, especially at mountain terminals. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...ARK NEAR TERM...TW SHORT TERM...ARK LONG TERM...ARK AVIATION...TW