548 
FXUS62 KGSP 062208
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
608 PM EDT Mon Sep 6 2021

.SYNOPSIS...
Another cold front is expected to cross our area late Wednesday and 
bring more showers and possibly a few thunderstorms. Drying high 
pressure will spread back over the region in the front's wake and 
linger into the weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 600 PM EDT Monday: No big changes to the overall forecast. 
Showers and thunderstorms persist in the southern tier, but should 
slowly diminish through the evening. Lingering convective debris 
could put a damper into the temperature forecast for tonight across 
the southern tier. Elsewhere looks to remain on track. 

A cold front is draped over the southern tier of the CWA attm, at 
the leading edge of an upper trough over the NE CONUS. That area is 
highlighted by the CAMs depicting a few cells thru early evening 
along/south of the current frontal position, in addition to what 
already has formed, we will boost PoPs to high chance in the 
southernmost zones but sharpen up the gradient a bit heading north 
through the rest of the evening hours.

The trough will progress eastward tonight and heights will rise
slightly overhead. A weak surface high will fill in behind it; the
resultingly weak low-level flow is progged to veer to easterly across
most of the CWA, and the front will stall just south of our area by
early morning. Upslope flow and/or the usual Savannah Valley
convergence zone may be responsible for some of the QPF response seen
after sunset, so a slow decline in PoP is fcst thru evening. Some
degree of stratus should materialize near the front and near the
east-facing Escarpment, but not confident it will be extensive enough
to preclude mountain valley fog/stratus, so those are still reflected
in the fcst. Over the course of Tuesday, heights will flatten and
then begin to fall again as another trough rotates into the Great
Lakes. Winds thus will continue to veer to southerly, and very weak
isentropic lift looks to occur over the front. While generally drier
air looks to settle into the northern CWA by tomorrow, raising CCLs
and most likely precluding deep convection, the southern half of the
CWA will remain pretty humid. Temps will rebound a few degrees
compared to today. Furthermore, lapse rates actually look to
improve a bit compared to today. Slight-chance to chance range PoPs
remain warranted for the southern two-thirds of the FA.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 1:30 PM EDT Monday: Throughout the duration of the short term 
forecast period a ridge of high pressure will be the main synoptic 
feature over the western United States while a trough tracks east 
and digs across the Great Lakes and Northeast United States. A small 
area of low pressure in the Gulf of Mexico will track northeast 
towards the Alabama coast and Florida panhandle Tuesday night into 
Thursday. Meanwhile at the sfc, a stationary front will be draped 
across the central Carolinas Tuesday evening before dissipating 
early Wednesday. This stalled front will act to keep shower and 
thunderstorm chances around Tuesday evening and rain chances around 
early Wednesday morning. Capped PoPs to a slight chance towards the 
beginning of the forecast period. A cold front associated with the 
upper-level trough mentioned above should track across the area 
Wednesday into Thursday. Overall models have been slowing down the 
progression of this front. The majority of the guidance has the 
front tracking across the CWA late Wednesday afternoon into 
overnight Wednesday before pushing out of the area early Thursday 
morning. However, the ECMWF is the slowest solution with the FROPA 
pushing through overnight Wednesday into Thursday afternoon and 
finally clearing the area Thursday evening. For now, still have the 
highest PoPs occurring Wednesday afternoon into early Wednesday 
evening. Did cap PoPs at chance during this time frame. Model 
soundings have SBCAPE values ranging from 500 to 1500 J/kg Wednesday 
afternoon and early evening so thunderstorms can be expected. Severe 
threat looks minimal as as 0 to 6 km bulk shear values remain below 
20 kts. Thursday morning the FROPA should be southeast of the CWA, 
however this front could allow for isolated showers and 
thunderstorms to develop Thursday afternoon, mainly across the far 
SE zones. High temps Wednesday will be a few to several degrees 
above normal. Highs will be cooler Thursday and will be near normal 
or just a few degrees above normal. Low temps will 4 to 7 
degrees above normal.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 2:00 PM EDT Monday: The upper-level trough over the Northeast 
United States will lift northeast Thursday night into Friday night 
before tracking off US coast early Saturday. Another trough digs 
south out of Canada into the northern US while tracking east across 
the Midwest and Ohio Valley Saturday into early Sunday. This trough 
then lifts northeast into eastern Canada and the northeastern US at 
the end of the forecast period. Throughout the extended the ridge of 
high pressure will continue to dominate in the western US. The area 
of low pressure in the eastern Gulf of Mexico will continue moving 
northeast, eventually tracking across northern Florida then along 
the southeastern coast of the United States. The ECMWF is has the 
low tracking faster and farther east of the Carolina coast than the 
GFS. The GFS has the low tracking northeast and hugging the Carolina 
coast this weekend. Sfc high pressure is expected to build in behind 
the departing FROPA, (mentioned above in the short term), so the any 
moisture from the low along the SE coast should remain well south 
and east of the western Carolinas and NE GA. This area of high 
pressure will keep us dry throughout the duration of the extended 
forecast period. Temps will gradually warm throughout the period.

&&

.AVIATION /22Z MONDAY THROUGH SATURDAY/...
At KCLT and elsewhere: VFR conditions continue to prevail at all TAF 
sites with low-end VFR cu unfolding at some of the western sites. 
Haze is being reported at the KAVL and the reason is unknown at this 
time, but did include a TEMPO for haze vsby restrictions through 00Z 
Tuesday at KAVL. Cold front sagging thru the far southern tier of 
the CWA attm, on track to stall south of the region tonight. 
Moisture pooling in its vicinity has allowed cu to break out at MVFR 
level in parts of the Upstate. SCT SHRA/TSRA are possible on the 
warm side of the front this afternoon, but with wind shift having 
already occurred all the TAF sites, chances at the sites are too 
small to mention today except for VCSH at KAND being farthest south. 
Northerly winds should prevail thru tonight, eventually veering to 
NE in the Piedmont. Weak upglide developing over the front will 
potentially produce low VFR or MVFR stratus near KAND/KGSP/KGMU/KAVL,
but most guidance depicts VFR conditions aside from potential 
mountain valley fog/stratus. The latter will more likely if the 
higher cloud decks don't materialize, so IFR in TEMPO at KAVL. 
Another humid day with cu bases starting off on the low end, 
warranting MVFR at KAND. Isold-sct SHRA/TSRA will develop 
diurnally but not worthy of mention except at KAND.

Outlook: A second cold front entering from the NW may bring
scattered convection Wednesday into Thursday. Generally
settled weather and high pressure expected in the wake of that
front. Mountain valley fog and stratus will remain possible each
morning.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...DEO
NEAR TERM...CAC/Wimberley
SHORT TERM...AP
LONG TERM...AP
AVIATION...CAC/Wimberley