019
FXUS62 KGSP 180631
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
231 AM EDT Sat May 18 2024

.SYNOPSIS...
A weak low pressure system will track east across North Carlina
today, bringing another rounds of showers and thunderstorms to the
area. The low exits off the Carolina Coast on Sunday, with weak
high presure building in from the north. Somewhat drier conditions
return early next week resulting in only isolated afternoon and
evening showers and storms. A cold front will bring better shower
and thunderstorm chances back into the forecast late in the week.

&&

.NEAR TERM /THROUGH TODAY/...
As of 200 AM Sat: Ill-defined pattern in place over the region
featuring very weak sfc high or cold pool, with synoptic warm front
seemingly near I-20. Southwesterly low-level flow continues between
flat ridge centered off the SE coast, and upper low now near the
Mississippi Delta region. Guidance had overdone evening convection,
but MUCAPE is expected to trend slowly upward thru the morning as
warm front lifts north. Lowering cloud ceilings and areas of -DZ
are developing in parts of the area as an indicator of the ongoing
isentropic lift, but deep convection and measurable showers look
unlikely to develop for several more hours. PoPs have been trimmed
back mainly to the Upstate and I-85 corridor mainly as a nod to
the light stratiform precip. 850-700mb lapse rates are shown to
increase with the warm front; along with sfc temps warming after
daybreak shower chances ramp up in the S half of the CWA by late
morning. CAMs are in reasonably good agreement on mainly just
spotty showers in that area during the late morning to midday,
but destabilization eventually will occur farther north via the
advecting front but also with height falls as the shortwave moves
in from the west. The same CAMs depict more potent convection
developing on the mountain ridges early to mid afternoon,
propagating eastward by evening.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
As of 200 PM EDT Friday: Short Term Key Messages

1) Models are trending drier Sunday into Monday.

2) The severe weather potential looks minimal through the period.

3) Highs on Monday are trending warmer.

An upper trough and associated upper low will gradually push
eastward across Georgia the Carolinas Saturday evening into Sunday.
12Z CAMs show shower and thunderstorm activity lingering over the
forecast area, especially the northern zones, Saturday evening into
late Saturday night before gradually diminishing in coverage through
daybreak Sunday. Thus, have the likely PoPs (55%-65%) confined to
the northern two-thirds of the CWA through midnight. Capped PoPs to
chance (40%-54%) across the southern third of the CWA through
midnight as coverage of convection is expected to be lower. The
locally heavy rainfall threat will continue through Saturday night
thanks to 90th percentile PWATs lingering over the region. 12Z CAMs
are trending towards much lower coverage of showers and
thunderstorms on Sunday, with any activity looking to be limited to
the mountain zones. Thus, have likely PoPs (55%-63%) across the
mountains with chance PoPs (40%-54%) elsewhere. PoPs may need to be
lowered further on Sunday if this trend of lower coverage of
convection continues. Drier air looks to filer into the forecast
area from the north throughout Sunday, allowing PWATs to gradually
lower. Thus, the heavy rainfall threat will be limited somewhat,
especially if the lower coverage of convection holds true. With much
lower deep shear values expected on Sunday, the severe threat should
be very low, if any. However, global models do show 1,000-1,500 J/kg
of SBCAPE over the mountains during peak daytime heating, so an
isolated strong storm or two cannot be entirely ruled out. The upper
trough and associated upper low will continue pushing eastward
Sunday evening into early Monday morning, eventually pushing
offshore. Sfc high pressure will build into the region behind the
departing low, leading to drier conditions Sunday night into Monday.
However, isolated showers and thunderstorms are expected to develop
Monday afternoon and evening over the mountains per the latest
global models. Thus, have chance PoPs (15%-25%) in place across the
mountain zones. The severe weather potential looks minimal, if any,
on Monday due to even lower deep shear values and SBCAPE values
generally at or below 1,000 J/kg. Lows Saturday night will end up ~5-
8 degrees above climo thanks to cloud cover and rain. Lows Sunday
night will end up near climo to a few degrees above climo thanks to
lower cloud cover and drier conditions. Highs on Sunday will be ~2-6
degrees below climo. Highs across the mountains on Monday will be a
few degrees above climo, with highs elsewhere near climo to a few
degrees below climo.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 230 PM EDT Friday: Long Term Key Messages

1) Mostly dry conditions should linger through Wednesday night.

2) Isolated diurnal convection is possible on both Tuesday and
Wednesday in the North Carolina mountains.

3) A cold front will bring better shower and thunderstorm chances
late next week, but timing differences remain between the global
models.

Sfc high pressure will remain over Georgia and the Carolinas leading
to mostly dry conditions through mid-week but isolated diurnal
convection will be possible each day. With global models generally
showing <1000 J/kg of SBCAPE and weak deep shear during peak
heating, the severe threat looks to be low, if any. A cold front
will approach out of the west Wednesday before pushing across the
forecast area late Thursday into early Friday increasing shower and
thunderstorm chances. The 12Z GFS shows precip pushing east of the
area by Friday afternoon with dry high pressure building in behind
the front. Meanwhile, the Canadian and ECMWF show a wave of low
pressure tracking along the stalled frontal boundary on Friday,
keeping shower and thunderstorm activity around. With models not in
agreement regarding on whether precip will linger through the end of
the work week, capped PoPS to chance (25%-45%) on Thursday and
Friday. Deep shear will increase in association with the front
towards the end of the workweek. This combined with 1,000-1,500 J/kg
of SBCAPE each afternoon, may lead to strong to severe storm
development. However, with this being towards the end of the long
term period, confidence will be low on the severe potential. Both
high and low temps through the period will remain a few to several
degrees above climo as a gradual warming trend is expected through
the workweek.

&&

.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Abundant low-level moisture beneath inversion
early this morning, but murky forcing regime, makes for tricky
TAFs. Weak warm front south of the terminal area. Some -DZ will
occur prior and accelerate decline to IFR which otherwise is likely
by 09-10z. Approach of shortwave from the west will activate warm
front in mid to late morning and focus light -SHRA development. The
front will also allow parcels to overcome the inversion aloft,
leading to lifting and perhaps partially scattering cigs by late
morning. With already favorable upper level lapse rates this also
will support development of TSRA during the afternoon, handled with
PROB30s. Southerly flow will continue today. Tonight, shortwave
will drift over the area while occluded front advances over the
Eastern Seaboard and weak sfc high builds in from the north. This
will induce a shift to northerly winds across the Piedmont in a
wedgelike scenario, with cigs again deterioriating from north to
south overnight. Elevated convection may be able to re-fire along
the backdoor front and persist in some fashion into Sunday.

Outlook: SHRA/TSRA remain possible Sunday and perhaps even Sunday
night until stronger high pressure settles over the region
Monday. Late night/early morning restrictions in low stratus
and/or fog will remain possible Sunday night; isolated mountaintop
convection still appears possible Monday.

&&

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

&&

$$

SYNOPSIS...ARK
NEAR TERM...Wimberley
SHORT TERM...AR
LONG TERM...AR
AVIATION...Wimberley