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FXUS62 KGSP 030329 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1029 PM EST Sat Dec 2 2023

SYNOPSIS
A moist airmass will continue over the region tonight into Sunday morning before drier air arrives with a cold frontal passage late Sunday. Reinforcing cold fronts will cross the region late Monday and then again Tuesday night, with a brief increase in moisture along the spine of the southern Appalachians early Wednesday. Dry high pressure will then allow temperatures to return to near normal by Thursday and rise to 5 to 10 degrees above normal through next Saturday.

NEAR TERM /THROUGH SUNDAY/
Evening Update...Rainfall amounts continue meager across the FA this evening as moisture robbing convec continues upstream. A frontal zone is beginning to nudge east into the wrn NC mtns where pockets of moderate rain will fall over the next few hours with low-end amts expected thru the next update. Otherwise, the llvls remain quite saturated and areas of dense fog have formed along and southeast of the escarpment. A dense fog advisory is in effect for these areas thru 13z. The hires models, mainly the HRRR, continue to show an uptick in rainfall across the srn half of the FA aft 10z or so, and this would help scour out the fog where the heavier rain falls, if at all. With the area remaining in a warm sector and high cloud cover, expect temps to drop little overnight with lows remaining 15- 20 degrees abv normal.

As for latest CAMs and operational QPF forecasts, the latest trends are for the best coverage of showers to be this evening into the early overnight, as isentropic lift and some upper level divergence increases across the region. So have the hourly PoPs trend upward from late aftn thru the evening, then start to taper back off toward daybreak Sunday. QPF will still be limited due to lack of good moisture transport and synoptic forcing. Temps will be mild tonight, with lows mainly in the mid to upper 50s. The wedge should be basically gone by tonight, and a light sfc SW wind should persist across the area. But some guidance is hinting at fog development again near the escarpment and adjacent foothills, along with sheltered mountain valleys.

A sfc cold front will slip through the area during the day Sunday, as an upper level trough axis shifts east across Lower-MS Valley to the TN Valley. There may be some lingering light showers/sprinkles/drizzle across mainly the eastern third of the forecast area after daybreak. But precip should end pretty quickly. Forecast soundings show that morning fog and low stratus will be a little slow to clear out Sunday morning, but should mostly scatter out by early aftn. With increased mixing, breezy W to SWLY winds are expected to ramp up by midday. Not expecting anything approaching advisory-level. Despite the fropa, temps will be warm, thanks to a warm start to the day and some downslope warming negating the CAA. Highs will be 60s in the mountain valleys and generally 70-73 east of the mountains.

SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/
As of 145 pm EST Saturday: A departing cold front will move east of the area Sunday night, with drier air spilling in across the region.
A reinforcing cold front and slowly deamplifying upper shortwave will then cross the southern Appalachians on Monday, but with very limited attendant moisture in light of the short airmass recovery period from the previous fropa. Shallow northwest flow moisture and breezy to windy conditions will affect the NC mountains into Monday evening, but any upslope-induced precipitation should dwindle quickly through the nighttime hours given the limited low-level moisture. Expect mainly isolated to scattered western mountain showers PM Monday, with a mixover/changeover to snow at the higher elevations and TN border area before the precipitation tapers off Monday evening. Downslope warming, on the other hand, will keep maxes in the 60s east of the mountains Monday afternoon.

Transient high pressure will cross the region the rest of Monday night into Tuesday before yet another cold front approaches from the northwest in the active northern stream flow pattern. Will keep the Tuesday period dry throughout, with temperatures within a category of climatology.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
As of 150 pm EST Saturday: Another cold frontal passage is expected Tuesday night. Slightly colder and deeper northwest upslope flow moisture should occur post fropa Tuesday night into Wednesday morning, with a bit better snow shower potential compared to the late Monday system given the deeper boundary layer moisture and amplifying upper wave. Upstream Froude numbers west of the mountains are rather modest during the peak upslope, indicating limited instability in the northwest flow moisture, and this should cap any light snow accumulations along the ridges and near the immediate Tennessee border areas to around a half-inch or less in all but highest peaks. Gusty winds will also occur during the peak of the cold advection, but the anticipated pressure gradient should keep max speeds below advisory levels except along the highest ridges.

Dry high pressure, with an embedded lee trough of low pressure, will then dominate the region Thursday through Friday. Another cold front will lay over to the north of the area on Saturday, likely moving southward through the region in cold air damming fashion just beyond the current forecast during the latter half of next weekend.
Temperatures will continue to warm ahead of this backdoor front as the airmass in place over the region modifies.

AVIATION /04Z SUNDAY THROUGH THURSDAY/
At KCLT and elsewhere: The sfc layer will remain quite moist thru most of the TAF period. Expect lowering CIGS all sites to IFR or lower aft midnight, persisting thru daybreak. Dense fog is also possible and have included mention across all SC terminals and at KHKY. Dense morning fog will be trickier at KCLT as that area will receive some measure of rainfall longer than the other TAF sites.
IFR CIGs will linger thru noon, especially at KCLT as a remnant llvl ridge axis is slower to break down ahead of an incoming cold front.
Areas west of CLT will likely see a return to MVFR/VFR by early afternoon as winds strengthen and become aligned sw/ly to nw/ly with low-end gusts probable.

Outlook: Dry conditions will return Sunday afternoon and persist into early next week as high pressure builds back into the Carolinas.

GSP WATCHES/WARNINGS/ADVISORIES
GA...Dense Fog Advisory until 8 AM EST Sunday for GAZ010-017-018.
NC...Dense Fog Advisory until 8 AM EST Sunday for NCZ035>037-056- 057-064-065-068-069-502-504-506>510.
SC...Dense Fog Advisory until 8 AM EST Sunday for SCZ101>106.

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