832
FXUS62 KGSP 220719
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
319 AM EDT Sat Jun 22 2024

.SYNOPSIS...
A hot and humid subtropical airmass returns to the area this
weekend, lingering through much of next week. Isolated diurnal
showers and thunderstorms return to the mountains today, with
scattered activity possible area-wide Sunday into Monday as a weak
cold front tracks across the area. Drier conditions are expected
Tuesday into early Wednesday before a stronger cold front brings
better coverage of shower and thunderstorms late Wednesday into
Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 AM Sat: Mostly clear over the CWA at this hour under
influence of upper anticyclone in the lower MS Valley and weak
sfc high pressure centered off the Atlantic coast. Compact sfc low
sitting near St Simons Island GA remains too distant to have direct
impact in our area, but maritime airmass is spreading inland on
its north flank, evidenced by 70-74 dewpoints in the northern SC
Midlands. This air is creeping into the lower Catawba Valley and
Charlotte metro, and likely will bring some low cloud cover along
its leading edge, and radiation fog/stratus can`t be ruled out at
dawn. The moisture advection will continue today as the sfc low
drifts inland into South GA, but with the incumbent air being rather
dry through a deep layer, diurnal mixing will slow the moistening
trend from mid-morning through early afternoon. Subsidence is
still evident aloft, although inversion is a little more likely
to be overcome owing to the slightly warmer sfc T/Td, with SE sfc
flow still being the only real forcing. The models that correctly
depicted minimal coverage yesterday over the mountains are doing
so again today. Still think a mention of isolated showers and more
isolated thunderstorms is reasonable in that area, with overall
PoP pretty similar to previous fcst. Still not confident enough
to mention PoP for most of the Piedmont, except in our southeast
border areas where the more humid air will become established
earlier in the day, and a slight-chance is included. Max temps
will inch a degree or two warmer compared to Friday, ending up at
91-93 for most of the Piedmont and around 90 in the major mountain
valleys. Dewpoints should mix out into the upper 60s and this
should be enough to keep heat index below 100. Some models hint
that some patchy clouds and a few late showers could develop after
sunset in the foothills in the convergent area between the inland
high and subtropical/maritime airmass. Otherwise, tonight again
will be mostly clear aside from the possibility of fog/stratus
developing in the more humid air. Temps will be warmer also owing
to the moisture, 3-5 degrees above normal.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Key Messages:

1) Hot and Humid Conditions Continue into Monday, Especially East of
the Mountains.

2) Heat Indices may Flirt with Heat Advisory Criteria in the Upper
Savannah River Valley on Monday Afternoon.

3) A Weak Cold Front Increases Shower and Thunderstorm Chances
Slightly Sunday into Monday.

As of 130 AM EDT Saturday: No major changes to the short term
forecast period this update. A large upper anticyclone will remain
parked over the Southern Plains/Desert Southwest while an upper
trough digs south across the East Coast through the short term. At
the sfc, a weak cold front will track across the Midwest Sunday into
Sunday night before pushing across the western Carolinas Monday into
Monday night. This front should allow for at least scattered shower
and thunderstorm development Sunday into Monday. Capped PoPs to
chance (50% or less) for now as global models are still not in
agreement regarding the exact timing/coverage of convection. Drier
conditions are expected Monday night behind the front as sfc high
pressure builds into the region. Despite the cold front, hot and
humid conditions will linger through the period. Highs east of the
mountains should reach into the low to mid 90s with heat indices
climbing into the upper 90s/lower 100s each afternoon, especially
across the Upper Savannah River Valley and along I-77. Heat indices
should generally remain below Heat Advisory Criteria but may flirt
with criteria on Monday in the the Upper Savannah River Valley.
Highs will end up around 7-9 degrees above climo each day. Lows
Sunday night will be around 8-10 degrees above climo, becoming 4-7
degrees above climo Monday night.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Key Messages:

1) Hot and Humid Conditions May Now Linger Through Thursday,
Especially East of the Mountains.

2) Heat Indices may Flirt with Heat Advisory Criteria again in the
Upper Savannah River Valley on Wednesday Afternoon.

3) A Stronger Cold Front Brings Better Shower and Thunderstorm
Coverage Late Wednesday into Thursday.

As of 200 AM EDT Saturday: Upper riding briefly builds into the
region Tuesday into the first half of Wednesday leading to drier
weather and continued hot and humid conditions. Upper troughing will
approach out of the west throughout Wednesday while a cold front
tracks across the Midwest. Highs will climb into the mid 90s each
afternoon east of the mountains, remaining around 7-9 degrees above
climo. Heat indices will be a bit lower east of the mountains on
Tuesday afternoon thanks to slightly lower dew points behind a
departing front. However, heat indices may still climb into the
upper 90s/lower 100s in the Upper Savannah River Valley Tuesday
afternoon. Dew points are expected to recover on Wednesday, allowing
heat indices to rebound back into the upper 90s/lower 100s east of
the mountains during the afternoon hours. Thus, the Upper Savannah
River Valley may once again flirt with Heat Advisory criteria on
Wednesday.

Upper troughing will push across the Southeast overnight Wednesday
into Thursday, dragging a stronger cold front across the western
Carolinas and northeast Georgia on Thursday. This will allow shower
and thunderstorm chances to increase again the second half of
Wednesday and into Thursday. Capped PoPs to chance (30%-50%)
Wednesday afternoon into early Thursday evening due to global model
guidance inconsistencies regarding both the timing and coverage of
convection. Cloud cover and convection associated with the front
should lead to slightly cooler temps on Thursday but will keep lows
Wednesday night around 7-9 degrees above climo. Highs Thursday
afternoon should only climb into the upper 80s/lower 90s east of the
mountains but dew points will remain elevated. So, heat indices
should climb back into the upper 90s/lower 100s in the Upper
Savannah River Valley and near I-77 on Thursday. Guidance diverges
regarding the both the upper and low-level pattern Thursday night
into Friday but convection may linger through the end of the period.
Thus, maintained slight chance PoPs to low-end chance PoPs (25% or
less) Thursday night into Friday. Highs should be fairly similar to
Thursday`s but should generally be a degree or two cooler. Humidity
should lower a bit on Friday thanks to slightly lower dew points.

&&

.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Light SE flow will advect moist maritime
air to near KCLT by dawn and has prompted TEMPO for MVFR cigs, with
IFR not out of the question. Mountain valleys likely will develop
fog but once again not extensive enough to reach KAVL. Elsewhere
VFR this period. Sfc winds initially will be light/VRB at the
terminals aside from KCLT, but should pick up from the SE after
daybreak and veer toward S by afternoon. Low VFR cu will develop by
midday; some could linger or even develop anew after sunset owing
to weak sfc convergence near leading edge of maritime airmass. A
stray SHRA or even TSRA will be possible this aftn and evening
in the mountains but with such weak forcing this was not likely
enough to include at KAVL.

Outlook: Expect a return to more typical scattered convection across
the region Sunday and Monday.  Slight drying may follow for Tuesday.

&&

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

&&

$$

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