753
FXUS62 KGSP 210608
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
208 AM EDT Fri Jun 21 2024

.SYNOPSIS...
Strong high pressure and relatively dry easterly winds should keep
the weather quiet and humidity on the low side for today. More humid
subtropical air will return Saturday and remain into early next
week, resulting in more typical summertime shower and thunderstorm
activity, as heat builds over the region. and cause a heat wave
to build across the region through early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 145 AM: No major changes this cycle, as far as the near
term. Deep upper anticyclone still expected to retrograde slightly
through early Saturday morning. Sfc high will remain more or less in
the same position off the East Coast but will weaken slightly. PBL
winds will remain quite weak thru the morning and patchy fog looks
to develop in the mountain valleys by dawn. Initially NE to E winds
will veer slightly to SE with the retrogression of the upper high
and perhaps as the influence of the offshore high weakens. Moisture
flux remains minimal thru the afternoon and dewpoints should mix
out a little bit. Thus, despite temps warming slightly further
compared to Thu, subsidence aloft again should cap off deep
convection even over the ridgetops; just shallow convective noise
on CAM output. Flow will remain weak tonight although the fetch
becoming more southeasterly, maritime air looks to make more of
a run into the area from the SC coast, and a few pockets of low
stratus may develop southeast of I-85 by daybreak Sat.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
As of 134 PM EDT Thursday: The weekend looks like it will be a slow
transition into something more active and more typical of summer, as
an upper anticyclone migrates/retrogrades from the TN Valley region
on Friday night to the srn Plains Sunday afternoon. As this happens,
our flow aloft will switch from anticyclonic at the start of the
weekend to broadly cyclonic on Sunday as a nrn stream system moving
from the Great Lakes to ern Canada exploits a weakness between the
aforementioned anticyclone and the Atlantic Subtropical Ridge. The
wildcard in all this will be how much a weak easterly wave/sfc low
can hold together after it moves onshore across north FL/south GA
Friday night. Of note is the compact swirl maintained in the 12Z NAM
Nest over southeast GA through Saturday afternoon, but still too far
away to directly affect our area. Instead, the model trend continues
with bringing in more low level moisture faster, which stands to
reason given the westward-moving wave bringing the moisture from
the Atlantic coast. The typically wetter NAM raises dewpoints
high enough that we would end up with a breakable cap Saturday
afternoon. That seems reasonable at least over the higher terrain,
so elevation-based precip probs ramp up there midday. Outside the
mtns, confidence is lower, but the guidance seems to be on the
right track with at least some small chance on the south/southeast
fringe. Temps will climb a few deg above average. By Sunday, the
old capping inversion breaks down and gets mixed out, which should
allow for at least a climatological precip prob distribution in
the afternoon, with what looks for now like just garden-variety
thunderstorms. Temps may creep upward another deg or two, but the
dewpoint will be rising further, altho not to the point where the
heat index would get close to Advisory criteria. Now that it is
summer, we can say it just looks like typical summer.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 243 PM EDT Thursday: Once we get out into next week, the
situation looks more active and summerlike, thus at the same
time a bit more uncertain, particularly with what days might
have the better chances of diurnally-enhanced thunderstorms. The
expectation is for above normal precip chances and above normal
temps, provided by a weak WNW flow aloft that brings some remnant
short wave activity and weak downslope flow. Confidence is probably
best in the temperatures being on the order of five degrees above
normal Monday through Wednesday, which means highs mostly around
90 in the mtn valleys and in the middle 90s east of the mtns,
with some upper 90s sprinkled in. Humidity will be high enough to
bring the heat index into the low triple digits in some places,
but not yet to Heat Advisory levels. We shall continue to mention
the heat in the HWO for the time being. There is some indication
that a weak boundary may cross the region Monday night, which
could render Tuesday as the quietest day of the stretch, but any
significant reduction in the precip chance is smeared out in the
model guidance blends that we typically use. Wednesday/Wednesday
night might be the busiest time of the stretch, as some of the
guidance shows a more coherent wave/vort lobe coming down from
the NW and crossing the region, which should be sufficient to
trigger/organize thunderstorms. It stands to reason that we should
have a good shot at a few pulse-severe storms with some locally
heavy rain. The boundary may cross the region and bring the precip
chances and RH back down on Thursday, but that is uncertain.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: VFR expected to prevail at the TAF sites
this morning; despite generally clear skies crossover temps
from yesterday afternoon are low. Some of the rural areas of
mountain valleys could develop fog but likely somewhat variable
in magnitude. An occasional NE to ENE wind may blow until after
daybreak; a slow veering trend is expected around the region as
high pressure retrogrades slightly. Winds most likely will remain
N of E at KCLT until late afternoon but then should go into the S
half and remain there into Sat. Diurnal cu may develop as low as
040 but more likely in the 050-060 range. SE winds tonight could
allow low stratus to creep in very late, warranting a FEW mention
at MVFR level at KCLT.

Outlook: Patchy mtn valley fog and/or low stratus also possible Sat
morning. Isolated diurnal convection will be possible over the mtns
on Saturday, with a return to more sct convection expected across
the region Sunday and Monday.  Slight drying may follow for Tuesday.

&&

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

&&

$$

SYNOPSIS...Wimberley
NEAR TERM...Wimberley
SHORT TERM...PM
LONG TERM...PM
AVIATION...Wimberley