588
FXUS62 KGSP 281401
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1001 AM EDT Fri Jun 28 2024

.SYNOPSIS...
Seasonable temperatures are expected today and tomorrow as shower
and thunderstorm activity increases ahead of an approaching cold
front.  Hot and humid conditions on Sunday will precede the front,
which will usher in drier and cooler conditions Monday and Tuesday.
The summer heat will return Wednesday and beyond.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM...Plenty of cloud cover atop the forecast area this
morning, but not as much as this time yesterday. Overall, expect
a little more sunshine, allowing for scattered showers with a few
mainly garden-variety thunderstorms this afternoon. Warming aloft
will make for weak mid-level lapse rates and thus severe storm
potential will remain low. Only minor tweaks to the grids for this
update, but did lower the PoPs and thunder chances slightly given
the model trends.

Over the next 24 hours, a subtle weakness aloft will linger between
the old upper anticyclone over the srn Plains and the reflection of
the Atlantic Subtropical High off the Southeast Coast...or maybe
what we see in the model guidance is just the result of the moist
southeasterly low level flow toward the srn Appalachians. Either
way, coverage of showers and storms is expected to be a bit greater
this afternoon than the past few days. That being said, expectations
are tempered somewhat by our recent lack of widespread rain, and
wondering if the models are...a little over-enthusiastic. The
precip probs were kept fairly close to the old forecast, but
if anything might be overdone. Severe weather chances appear to
be low. High temps should stay close to normal. For tonight, the
persistence of the weak low level moist flow from the south should
support a continued rain chance with a focus on the Blue Ridge
Escarpment. Isolated and locally heavy rain would not be a surprise,
but confidence is low. Min temps look a bit warmer than normal.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 249 AM EDT Friday: A moist subtropical airmass will continue
to advect into the forecast are on Saturday as ill-defined upper
flow over the immediate forecast area does little to interact with
deep SSE flow at the low levels.  Forecast profiles on Saturday
appear moist through the depth of the troposphere, especially
during the afternoon hours.  Operational guidance depicts some
1000-1500 J/kg sbCAPE developing during the afternoon and evening
across most of the forecast area...but with anemic lapse rates that
should hinder more robust updrafts from developing.  And, without
much synoptic forcing, it`ll be tough to trigger initiation en
masse, which should once again limit convective coverage.  So,
despite juiced-up PWs exceeding 2" in some areas, the threat
of either severe weather or heavy rainfall appears limited.
Temperatures Saturday afternoon should climb into the upper 80s
or lower 90s along the I-77 corridor.  With profiles as moist as
they are, any amount of diurnal mixing will do little to lower
dewpoints, so afternoon heat index values may surge into the
upper 90s...possibly hitting 100 in isolated locations along the
southeastern fringe of the forecast area.

On Sunday, z500 troughing over the Great Lakes will sharpen, and
a shortwave will dig across the central Midwest and Ohio Valley,
pushing a surface cold front into the Cumberland Plateau and upper
/ central Tennessee Valley through afternoon.  Oddly, guidance
depicts a W wind developing at the low levels Sunday morning in
response to a subtle shortwave crossing the region...which will
both boost temperatures and lower dewpoints, as well as have an
initial suppressive impact on convection east of the mountains
where normally the dynamics might support better initiation
and stronger updrafts.  Instead, the mountains still look like a
focus for afternoon showers and thunder...although the Piedmont and
Upstate zones should eventually catch up and destabilize despite the
transient downsloping effect.  Forecast sbCAPE values range from
<1000 J/kg in ensemble members that depict a stronger downsloping
effect, to over 2000 J/kg in the more aggressive guidance.  A dry
slot aloft may support some limited downburst threat...but no
widespread severe risk is expected.

Like Saturday, there will be limited dry air aloft to mix down
on Sunday afternoon, so dewpoints will struggle to lower during
peak heating.  With temperatures expected to soar into low- to
mid-90s on Sunday afternoon, and dewpoints ever soupier...wide
swaths of the Upstate and Piedmont can expect to see heat index
values in excess of 100 degrees, with some potential for values
of 104-106 degrees, mostly south of I-85.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 311 AM EDT Friday: By Monday, the cold front should be pulling
east of the forecast area and ushering in somewhat cooler and drier
air in for the start of the new week.  Temperatures on Monday and
Tuesday will only climb into the mid/upper 80s...particularly on
Tuesday, which will boast an almost CAD-like pattern with high
pressure drifting off the New England coast and driving NE flow
across the Carolinas.  The latest cycle of ensemble guidance has
trended away from much active weather on Monday afternoon, depicting
a stronger subsidence inversion across most of the area and very
limited moisture.  So, maintained token PoPs across the southeastern
tier and across the mountains, where some widely scattered showers
will be possible.  Further quiet conditions are expected on Tuesday,
with an even more robust subsidence inversion in place.

By midweek, temperatures will be on the rise again as high
pressure slides off the Atlantic coast and winds turn back around
out of the south.  Deep ridging will once again develop over the
Southeastern CONUS, maintaining suppressed profiles across the
western Carolinas...so although some diurnally-driven afternoon
showers can`t be ruled out, the case for robust afternoon convection
appears weak through the end of the seven day forecast.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: A light southeasterly low level upslope flow
has been established across the region, and in response we are
seeing some sct/bkn low clouds forming in patches, mainly closer
to the Blue Ridge Escarpment. This could result in a temporary
MVFR ceiling restriction in some locations, while KAVL deals with
low stratus in the Fr Broad Valley that dropped the ceiling to
LIFR. The low clouds in the valleys should mix out by 14Z at the
latest. Expect the wind direction to come up from the SE once we
begin to mix out the morning inversion. Can`t rule out another
brief MVFR condition as cumulus form early in the day. The big
question will be the extent of deep convection this afternoon. Most
of the CAMs have fairly sparse coverage that suggests we stick to
PROB30s for this issuance. Hopefully the next few runs of the HRRR
lend confidence to go with a TEMPO at some terminals. The threat
for thunderstorms should taper off in mid-evening. Thereafter,
the guidance is hitting the low cloud development before daybreak
Saturday, so all terminals will get at least an MVFR. There are
some indications that a more widespread IFR could materialize,
but this was left out for now.

Outlook: Another cold front approaches the area Sunday night,
keeping unsettled weather around through early next week.

&&

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

&&

$$

SYNOPSIS...MPR
NEAR TERM...ARK/PM
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...PM