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FXUS62 KGSP 021930 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 230 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/
As of 230 PM EST Saturday: Areas of dense fog are stubbornly holding on across portions of the NC foothills and NW Piedmont, as an in situ wedge lingers. Light rain showers are breaking out across the western portions of the forecast area, as upglide and upslope wring out leftover moisture from upstream convection along the Gulf Coast. Updated the entire near term forecast with latest NBM/CONSshort to line up with the latest trends. Temps are warming a little more than expected across much of the southeastern portions of the forecast area with plenty of mid to upper 60s being reported.

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 /20Z SATURDAY THROUGH THURSDAY/
At KCLT and elsewhere: A residual wedge is eroding from south to north, resulting in improving vsby and cigs. The Upstate sites and KCLT may be mostly VFR this aftn, but could TEMPO into MVFR in cig/vsby due to scattered SHRA. KAVL looks to be mostly MVFR and KHKY mostly IFR this aftn. The highest coverage of showers and possibly an isolated TS or two, look to be this evening, but guidance is not in good agreement on the exact timing. Will go with prevailing SHRA to cover the most likely period. Whether the precip develops or not, all sites are expected to return to LIFR this evening and thru the overnight, with possibly some dense fog again early Sunday morning. Conditions should begin to improve late Sunday morning, as winds pick up out of the SW and dry air begins to work into the area.

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...None.
NC...None.
SC...None.

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