-- Discussion containing changed information from previous version are highlighted. --
915
FXUS62 KGSP 202201
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
601 PM EDT Thu Jun 20 2024

.SYNOPSIS...
Strong high pressure will keep the area dry through Friday and cause
a heat wave to build across the region through early next week.
More typical summertime shower and thunderstorm activity will
gradually return to the area Saturday through Monday as a weak cold
front approaches from the north.

&&

.NEAR TERM /THROUGH FRIDAY/...
-- Changed Discussion --
As of 600 PM: The forecast is on track, with fair wx cu starting
to dissipate, while temps are still in the mid to upper 80s across
the lower elevations. No changes needed with this update.

Otherwise...The center of an upper anticyclone is forecast
to retrograde from the central Appalachians/Mid-Atlantic this
afternoon to the lower MS Valley by the end of the period, with an
overall weakening/breakdown of the ridge expected in response to
a series of short wave trough lift west-through-north around its
periphery. Despite this, heights aloft will remain anomalously high
and upper flow anticyclonic across our region, while a persistent,
albeit weakening easterly low level flow will support a relatively
dry/low theta-E air mass over our area through the period. Diurnal
destabilization will therefore remain meager, although a slight
uptick in instability is expected Fri afternoon...primarily near
the TN/NC border. This may be good enough to allow for a few
afternoon showers to initiate across the ridgetops of the Smokies
and vicinity, warranting spotty 20% chances across the NC mtns.
Otherwise, conditions will remain dry and increasingly (albeit
slowly) hot. Partial thickness progs support a warmup of a couple
of degrees above today`s readings on Friday afternoon...with max
temps of 90-92 expected to be widespread across the foothills
and Piedmont. Min temps tonight are again expected to be close
to normal.
-- End Changed Discussion --

&&

.SHORT TERM /FRIDAY NIGHT 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 /22Z THURSDAY THROUGH TUESDAY/...
At KCLT and elsewhere: VFR flight conditions and convection-free
weather is forecast to persist across the Terminal Forecast Area
through the period, as the lower levels will remain relatively dry
and the air mass stable. Can`t rule out a brief period of low
stratus and/or BR in the mountain valleys around sunrise, but
confidence in this is low at this time. Otherwise, winds will
generally be light, favoring a E/NE direction, although occasional
excursions to E/SE can be expected, esp this afternoon.

Outlook: Mostly dry/VFR conditions are expected to persist through
at least Saturday morning, although some potential for patchy mtn
valley fog and/or low stratus will persist. 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...DEO
NEAR TERM...ARK/JDL
SHORT TERM...PM
LONG TERM...PM
AVIATION...JDL