699
FXUS62 KGSP 100217
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1017 PM EDT Thu May 9 2024

.SYNOPSIS...
A cold front will continue to push east of the area, before another
system approaches Friday. Showers and thunderstorms are possible
Friday afternoon, before dry high pressure builds in from the north
through the weekend.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 1000 PM: The forecast is on track. Temps are falling
slightly faster than expected, thanks to clear skies. But clouds
will quickly spread back in from the west due to ongoing convection
over MS/AL. The clouds should slow the downward temp trends. Latest
guidance hasn`t really trended up or down much on fog potential. So
no significant changes made with the evening update.

Otherwise, mostly clear skies this evening should permit good
radiational cooling for a time. Some dry advection will begin
overnight as weak sfc low passes by to our north, pulling very weak
sfc front through the area. This will promote just enough drying to
maintain a dewpoint depression of a few degrees in the foothills and
upper Piedmont, and furthermore some gradient wind is expected to
persist. Thus, the likelihood of radiation fog/stratus looks small
in those areas and mins will remain several degrees above normal.

Mountain valleys are likely to see some fog, along with the
SE CWA border where that weak front doesn`t reach and instead
may serve to pool moisture. A couple hundred joules of CAPE may
persist there thru daybreak. An MCV or other remnant of convection
looks to round the base of the main trough in the morning and some
guidance depicts a round of showers passing thru the Piedmont at
that time. Partly cloudy skies will permit the return of warmer
temps, again being a few degrees above normal. 700-500mb lapse rates
will increase as main shortwave swings in, and isolated convective
development is not out of the question over the mountains. For
the aforementioned Piedmont areas, guidance members differ as
to how soon low-level airmass change begins; GFS for example
maintains poor low level lapse rates above the PBL and develops
only small diurnal instability. The NAM depicts favorable lapse
rates thru a deep layer and develops 1000 J/kg or more of CAPE in
the afternoon. All models depict strong deep layer shear, perhaps
60+ kt, so if timing of the shortwave trends slightly slower or
the low level lapse rates improve, we could see an isolated severe
threat develop mainly southeast of I-85 or east of I-77. The setup
warrants only a chance PoP in our south and east; FV3 and HRRR
show short updraft helicity streaks from a lone cell.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 1245 PM Thursday...An upper shortwave axis continues to swing
east of the area Fri night as a cP air mass mixes into the lower
levels. This airmass will slowly modify warmer over the weekend as a
small scale ridge gives way to another diving Canadian h5 trof Sat
afternoon. This trof looks to bring it/s own moisture and will
probably produce some rain showers across the NC mtns Sat afternoon
into the evening. No good chance of thunder during that time as sfc
td/s drop into the 40s and potential instability remains nil or
quite low. Drier conds with warming temps across the FA Sun as a
broad sfc high builds over the area from the west. Generally, both
days will be rather pleasant with highs a couple degrees below
normal Sat, then back to normal levels on Sun. Mins will likely fall
a couple degrees below normal each night.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 120 PM Thursday...A more springtime pattern returns during the
ext range. The latest guidance contines to show a subs zone becoming
displaced by waves of srn stream energy while a mlvl trof/low
travseres the MS to OH valleys. The surface response indicates an
opening GOM flow, which will supply a good amt of moisture to a
broad frontal system each day. Onset precip timing Mon is suspect
with the majority of models indicating a later timeframe than the
moister insitu wedge pattern progged by the latest GFS. In any case,
thunder probabilty remains low with non-conducive llvl thermal
profiles. By Tue, expect a better chance of afternoon thunderstorms
as a wavy cold approaches from the west and sfc dewps rise into the
u50s to l60s. The pattern remains uncertain, yet possibly active
into Wed as another round of srn stream energy may be pushing east
across the GOM coastline by then. High Temps remain near normal Mon,
then drop abt 5 degrees below normal Tue with the best chance of
widespread precip and cloud cover. Highs rebound to normal values
Wed. Lows begin the period near climo, then warm abv normal Tue/Wed
nights.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Mainly just a few high clouds this
evening, with lingering light winds out of the SW (except for
NW at KAVL). Overnight, thicker mid and high clouds are expected
to stream in from the SW due to convection over the central Gulf
states, which combined with just enough mixing, could limit fog
potential. With that said, very moist soils and low levels may
combine to produce patchy fog or LIFR stratus across portions of
the lower Piedmont as well as the mountain valleys sheltered from
NWLY flow. Guidance is still not hitting cigs or vsby restrictions
all that hard, and with the mixed signals of clouds/wind/moisture,
will continue to just show few LIFR clouds and/or 6sm BR for the
early morning hours Friday. If trends in the clouds and wind trend
lower, potential for the stratus and fog will go up. Whatever does
develop, should dissipate early Friday morning. Spotty light rain
may cross the southern Upstate, but should stay mostly south of
the area and looks too low for any TAF mention. In the aftn, a
cold front will slip across the mountains and into the Piedmont,
which may trigger a few showers and isolated TS before pushing
east of the area. While better coverage of showers will be near
the TN/NC border. The NC TAF sites will feature PROB30 for the
SHRA potential. Given less confidence on TS, will not mention for
now. The Upstate sites look largely dry Friday aftn. Winds should
toggle from SW to WNW behind the front with gusts generally in
the 18-22 kt range.

Outlook: Drier and likely VFR conditions can be expected this
weekend. Moisture returns late Monday with active weather possible
by Tuesday.

&&

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

&&

$$

SYNOPSIS...SBK
NEAR TERM...ARK/Wimberley
SHORT TERM...SBK
LONG TERM...SBK
AVIATION...ARK