241
FXUS62 KGSP 170010
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
810 PM EDT Mon Sep 16 2024

.SYNOPSIS...
A semi tropical low will move inland over the Carolinas
tonight and Tuesday bringing heavy rain and gusty winds. The low
will weaken through mid week with less wind and rain. By Wednesday,
the remnant low will stall out over the Mid-Atlantic, while high
pressure begins to build into the region from the north and west
late in the week.

&&

.NEAR TERM /THROUGH TUESDAY/...
Key Messages:

1) Potential Tropical Cyclone 8 Will Bring Heavy Rain and Gusty
Winds to the Western Carolinas

2) A Flood Watch for Flash Flooding is in Effect for the Charlotte
Metro Area this Evening through Tuesday Morning

3) A Wind Advisory is in Effect for Locations Along I-77 through
Late Tonight

As of 250 PM EDT Monday: Active near term forecast period thanks to
Potential Tropical Cyclone (PTC) 8 pushing towards the South
Carolina Coast. Already seeing some light to moderate rain and
widespread cloud cover across the eastern half of the forecast area
this afternoon. Gusty winds are also in place and are expected to
increase through late tonight as the pressure gradient tightens
between PTC 8 and a sfc high to the north. Thus, a Wind Advisory
remains in effect through 2am EDT for most locations along I-77 as
high-res models show wind gusts reaching 40-45 mph in these areas.
Gusts could be strong enough to knock down a few trees, which may
result in isolated power outages. PTC 8 is expected to push onshore
this evening before tracking farther inland across the Carolinas
overnight. This will allow both cloud cover and precip associated
with the system to gradually expand westward through late tonight.
The system will stall over the Carolinas on Tuesday allowing cloud
cover and rain chances to linger through the end of the forecast
period. Rainfall amounts look to be lowest (~0.25-0.50 inches)
across northeast GA, the SW NC mountains, and the western SC Upstate
based on the latest track for PTC 8. Better rainfall amounts (~1-3
inches) are expected across the eastern SC Upstate, NC Piedmont, and
the northern and central NC mountains. The highest amounts (~3-5
inches) look to fall along the Blue Ridge Escarpment and higher
elevations of the NC mountains, although locally higher amounts from
6-7 inches cannot be entirely ruled out in these locations thanks to
upslope flow. With this amount of rainfall leading to the potential
for flash flooding, have a Flood Watch for Flash Flooding in effect
for the Charlotte Metro area from this evening into early Tuesday
morning as these locations have wetter antecedent conditions thanks
to Tropical Cyclone Debby last month. Highs this afternoon and
tomorrow afternoon will end up a few to several degrees below climo
thanks to both precip and cloud cover limiting daytime heating.
Cloud cover and precip overnight will limit radiational cooling,
allowing lows to end up a few degrees above climo.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 208 PM Monday: By tomorrow night, the remnants of a weak
tropical cyclone are forecast to be centered over the forecast area,
but a surface reflection will be hard to come by. The remnants will
instead manifest as a weak closed upper low that will slowly fill
through the day on Wednesday before opening into a shortwave trough
and lifting into New England on Thursday. A broad area of showers
will likely be ongoing tomorrow night, especially across the western
foothills and mountains, with at least scattered showers expected to
linger through the rest of the night across much of the area. The
presence of the upper low in concert with 1.5-1.75" PWATs will
promote above normal coverage of showers on Wednesday with
temperatures several degrees below average. Rain chances will begin
to decrease on Thursday as the evolving upper trough lifts away from
the area, but at least isolated to scattered showers look like a
good bet across much of the area.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 228 PM Monday: The large scale pattern finally becomes more
progressive by Friday into the weekend as persistent
blocking/troughing over the eastern CONUS breaks down. A tall upper
ridge that has been parked over the Great Plains will shift east
with heights rising across the Southern Appalachians as the ridge
axis nudges into the Tennessee Valley. At the same time, a sprawling
surface high will become centered over the Hudson Bay with high
pressure oozing down the spine of the Appalachians. This will send a
backdoor front through the area on Friday that will quickly scour
out low-level moisture with both PWATs and dewpoints falling.
Resulting intrusion of dry will bring an end to any lingering
showers with dry and pleasant weather through the weekend. Deep and
efficient mixing of the dry airmass will promote healthy diurnal
temperature swings of 20-25 degrees as morning lows in the upper 50s
to low 60s rebound into the upper 70s to low 80s during the day.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: What`s left of PTC 8 will gradually push
farther inland across the Carolinas tonight before stalling over
the fcst area on Tuesday. Widespread rain from this system will
continue to expand westward tonight and overnight, while precip
intensity gradually increases. Have prevailing RA/+RA for all
terminals by late tonight as the system is expected to stall over
our area. The precip shield should allow visby to range from IFR
to MVFR levels, although the heaviest bands of rain may allow cigs
to drop to LIFR levels at times. BKN to OVC cigs should also expand
westward thru late tonight with values gradually lowering thru the
overnight hrs with IFR to LIFR restrictions expected for most sites.
KAND, however, will likely remain MVFR. Gusty winds will continue
into the overnight before tapering off around daybreak Tues. Low-
level wind shear may also be an issue, mainly late tonight and into
the overnight. Still expect cig restrictions to linger thru much of
Tues, although visby should return to VFR by the afternoon, outside
of any lingering showers. I kept PROB30s and/or VCSH for any linger-
ing showers tomorrow aftn/evening. Wind direction will generally be
N to NE east of the mtns thru early Tuesday morning. Winds at KAVL
should gradually toggle more N/NW tonight and into Tuesday and then
back to NLY by Tuesday afternoon. Winds at KCLT and KHKY should gra-
dually turn more E/ESE Tuesday morning into Tuesday afternoon while
the Upstate sites will see winds favoring a NLY direction thru the
period.

Outlook: A weak upper low will linger over the Carolinas into Wed-
nesday before gradually weakening and lifting NE late Wednesday into
Thursday. This will keep precip chances and possible restrictions
around thru Thursday. On Friday, sfc high pressure builds into the
area from the north allowing drier weather and VFR conditions to
return.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Wind Advisory until 2 AM EDT Tuesday for NCZ057-070>072-082.
     Flood Watch until 8 AM EDT Tuesday for NCZ070>072-082.
SC...Wind Advisory until 2 AM EDT Tuesday for SCZ009-014.
     Flood Watch until 8 AM EDT Tuesday for SCZ009.

&&

$$

SYNOPSIS...DEO
NEAR TERM...AR/JPT
SHORT TERM...TW
LONG TERM...TW
AVIATION...JPT