229
FXUS62 KGSP 172356
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
756 PM EDT Fri May 17 2024

.SYNOPSIS...
A warm front and weak low pressure system will bring rounds of
showers and thunderstorms today into the weekend. 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 during
the middle of next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 755 PM Friday: Extensive cloud cover over the area has
lowered cloud bases. Area of precip stretching across the NC
Piedmont will continue to lift north and provide a lull in the
activity. Updated forecast based on current observations and latest
trends.

Otherwise, problem once again appears to be convection to the
south...this time a band of rain and thunderstorms across south
central AL/south central GA, to the north of a warm front stretched
out north of the FL Panhandle, which was contributing much of the
cloud cover that was limiting our buoyancy to 1000 J/kg or less.
Temp/Dewpt trends still look ok, but without much buoyancy or
forcing, and a lack of a trigger, it`s starting to look like even
scattered showers might be a stretch. Precip probs will be nudged
downward as a result.

The situation should change this evening as better forcing will
move up from the southwest, including improved upper divergence,
mid-level DPVA as a few ripples of vorticity lift northeast from
the upper system over the Arklatex, and low level isentropic lift
as the warm front also lifts northward. Precip probs are expected
to increase thru the evening in response, perhaps with some elevated
thunderstorms. However, the concentration of convection might never
be more than scattered. Any precip will help to keep/maintain a cool
pool across much of the region. If the precip fails to develop,
we could get areas of fog. Low temps should remain mild...and
generally five degrees above normal. That sets the stage for
Saturday, when we have some concern for severe storms. The upper
system will continue to approach from the southwest through the
afternoon with improved forcing, but it remains unclear as to
the severe storm potential. The CAMs look unimpressed and depict
mainly garden-variety thunderstorms in the afternoon, with the
environment characterized by 1500-2000 J/kg of sbCAPE and maybe
25-30 kt of effective shear, which is nothing to sneeze at, so we
will have to keep an eye on what develops. However, for now, agree
with the SPC Day 2 Marginal, as the better shear and instability
will stay to our southeast. High temps will be right around normal.

&&

.SHORT TERM /SATURDAY NIGHT 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 /00Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: VFR/MVFR cigs continue to roam the area
as rainfall became more widespread than expected and cloud bases
responded by lowering. Updated TAFs to include this mention with
more precip expected later this evening. Wind light S to SE.
Overnight, a surge of low level moisture is planned that brings a
ceiling restriction into the area along with any precip, then locks
in an IFR stratus deck and variable winds. If the precip coverage is
less than expected, we may get widespread fog. Once that gets locked
in, it should persist through the morning hours and not break up
until midday Saturday. Beyond that, convection may develop, but that
is beyond all but the period for KCLT. Added a PROB30 for
thunderstorms there.

Outlook: Periods of convection, which could be widespread at
times, are expected through the weekend. Late night/early morning
restrictions in low stratus and/or fog will also be possible. Drier
weather is expected to return early in the next work week.

&&

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

&&

$$

SYNOPSIS...AR/Wimberley
NEAR TERM...CAC/PM
SHORT TERM...AR
LONG TERM...AR
AVIATION...CAC/PM