569
FXUS62 KGSP 190012
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
812 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 THURSDAY/...
As of 756 PM...With the loss of daytime heating, the boundary layer
has started to lose instability, and shower activity has sharply
dropped off in coverage, more or less as expected. We still have
some remaining weak buoyancy around 500 J/kg of sfc-based CAPE,
so that will fuel the remaining showers for another hour or two,
but the downward trend should continue. The swirl in the low clouds
seen in the IR satellite imagery shows the location of a cutoff low
over the northern Upstate. Won`t rule out a stray thunderstorm in
the northwest Piedmont east of I-77 where the CAPE is just a bit
deeper and a few lightning strikes have been observed.

Otherwise...the upper low will lose any connection with the sfc
pattern overnight and slowly shift east of the forecast area thru
the day on Thu. Still expect a good amount of low level wrap around
moisture in the wake, which will be able to develop isolated to
scattered pulse showers and possibly a few thunderstorms with
increasing instability during the afternoon. Overall, an improving
pattern as far as lessening cloud cover and temps will respond to
arnd 80 F outside the mtns, a few degrees warmer toward northeast
GA, and u70s mtn valleys. A dense fog threat is possible arnd
daybreak across the NC mtn valleys as better radiational cooling
conditions interact with a rather moist sfc layer. Lows will
generally be held a couple degrees abv normal.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 157 PM Tuesday: As we head into Friday and Saturday, upper
ridging will slowly drift east from the Southern Plains into the
Lower Mississippi Valley. Heights will rise through the period
across the Southern Appalachians with increasing subsidence. At the
surface, high pressure will extend down the spine of the
Appalachians form a parent high centered near the Hudson Bay.
Guidance still indicates the presence of a backdoor cold front
oozing into portions of the Carolinas from Virginia. A noticeable
change, however, is that guidance is less aggressive with clearing
the boundary through the area, thus keeping dewpoints in the low to
mid 60s. The airmass will be drier, relatively speaking compared to
the tropical origins of the current airmass, but PWATs may not fall
as appreciably. While a stray shower or two cannot be ruled out,
increasing subsidence from the building upper ridge will generally
preclude mentionable PoPs outside of the Blue Ridge escarpment on
Friday. Temperatures will continue to warm through the period with
highs back into the low to mid 80s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 206 PM EDT Wednesday: A warming trend will continue Sunday
into early next week as the axis of the upper ridge becomes centered
over the Appalachians. Warming H85 temperatures and deep/efficient
mixing of the boundary layer will promote high temperatures in the
mid to upper 80s on Sunday, which will likely be the hottest day of
the period. A few locations may even reach the 90 degree mark across
the Upper Savannah Valley. The forecast will remain dry, however, as
a stout subsidence inversion present on forecast soundings deters
any convection. By Monday into Tuesday, a shortwave trough swinging
across the Midwest will drag a cold front towards the area. Timing
of the trough and attendant front remains elusive at this time
range, but a gradual uptick in PoPs will be warranted across the
mountains as the boundary nears.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: Prevailing VFR at issuance time, but some
MVFR-level stratocu persisted over the western part of Upstate
SC that will require a TEMPO at some of the terminals. Otherwise,
shower activity has been on a quick downward trend, as has low cloud
coverage. An upper low was identified in the satellite imagery over
the northern Upstate, and that feature should continue to rotate
off to the east overnight. The guidance continues to strongly
suggest that a new cloud layer will develop late tonight across
the region, initially at the MVFR, and then lowering to IFR across
most terminals. This seems reasonable given the lingering high
moisture in the boundary layer. The ceiling should be the primary
restriction, but some vis problems could also develop. Note that
in the mtn valleys, the fog could drop the vis down into the LIFR
category and VLIFR is not out of the question. Wind will be light
N/NE or calm. The fog/low stratus may take until the middle part
of the morning to mix out. When it does, we will likely retain a
ceiling restriction into the early afternoon, which will eventually
lift to VFR. Some shower activity is possible once again over the
mtns, but the chances look too small to include a PROB30 at KAVL
at this time.

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...DEO
NEAR TERM...PM/SBK
SHORT TERM...TW
LONG TERM...TW
AVIATION...PM