372
FXUS62 KGSP 211746
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
146 PM 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.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1130 AM: Not much reason to make any changes for the
afternoon. Temp/dewpt trends appear to be in good shape, and no
showers are expected to develop over the higher terrain.

Otherwise...a deep upper anticyclone is 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
a little. PBL winds will pick up in the aftn and veer slightly
to SE with the retrogression of the upper high and perhaps via
the diminished offshore high. Moisture flux remains poor thru
the afternoon and dewpoints should mix out a little bit. Thus,
despite temps warming another two or three degrees above Thursday`s
readings, subsidence aloft again should cap off deep convection
even over the ridgetops; only 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, resulting in a muggier night tonight
and a few pockets of low stratus may develop southeast of I-85 by
daybreak Sat. Deeper moisture associated with disturbance off the
GA coast is expected to remain south of our area.

&&

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

1) Warming Trend and Above Normal Temperatures Continue into the
Weekend

2) Heat Indices Should Reach the Upper 90s/Lower 100s East of the
Mountains Each Afternoon

3) Thunderstorm Chances Return for the Weekend

As of 230 AM EDT Friday: Upper anticyclone will continue
retrograding westward on Saturday, ending up centered over Texas by
the overnight hours on Saturday. The upper anticyclone will remain
over the Southern Plains and Desert Southwest through the rest of
the short term forecast period. Meanwhile, an upper trough will dig
across the East Coast and into the Carolinas Sunday into Sunday
night. At the sfc, high pressure will remain in place through
Saturday night while a cold front tracks across the Midwest. Diurnal
showers and thunderstorm chances are expected to return across the
mountains on Saturday but capped PoPs to chance (15%-25%) for now
per the latest CAMs showing only isolated activity. The cold front
will continue to approach from the north Sunday into Sunday night,
allowing shower and thunderstorm chances to increase in coverage
ahead of the main FROPA. Thus, have slightly higher chance PoPs (25%-
45%) in place across most of the area during this timeframe.
Temperatures will continue on a warming trend through the period and
will remain around 5-9 degrees above climo. Heat indices each
afternoon should climb into the upper 90s/lower 100s near the I-77
Corridor and in the Upper Savannah River Valley.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Key Messages:

1) Heat Indices May Climb Near Heat Advisory Criteria Monday
Afternoon for Some Locations East of the Mountains

2) The Lower to Mid 90s Stick Around East of the Mountains Through
Wednesday, with Slightly Cooler Temperatures Possible on Thursday

3) Thunderstorm Chances Linger Through Most of the Workweek

As of 300 AM EDT Friday: Upper troughing lingers over the area
through Monday night before upper ridging builds in late Monday
night into Tuesday night. At the sfc, a cold front will track across
the western Carolinas on Monday before stalling just south of the
area Tuesday into Tuesday night. This will keep shower and
thunderstorm chances around, mainly during the daytime Monday. Thus,
have chance PoPs (28%-50%) area-wide on Monday to account for the
FROPA. Sfc high pressure will build in behind the departing front
Monday night into Tuesday night leading to drier conditions per the
latest global model guidance. Did hang on to some low-end chance
PoPs (25% or less) Monday night into Tuesday night, but these will
likely need to be lowered (or even removed) in future updates if the
current dry trend holds. Temperatures will remain around 6-9 degrees
above climo through the period, with highs climbing into the low to
upper 90s each afternoon. Heat indices may reach near Heat Advisory
Criteria in the Upper Savannah River Valley and in the Charlotte
Metro area Monday afternoon. Heat indices should end up slightly
lower Tuesday afternoon thanks to lower dew points behind the
cold front.

Another upper trough will approach out of the west on Wednesday
before tracking across the forecast area on Thursday. At the sfc,
another cold front will approach out of the Midwest on Wednesday
before tracking across the forecast area on Thursday. This will bring
shower and thunderstorm chances back to the forecast area Wednesday
into Thursday. Thus, have chance PoPs (30%-50%) area-wide during
this timeframe. Highs will remain in the mid 90s again Wednesday
afternoon, with heat indices climbing back into the upper 90s/lower
100s along the I-77 Corridor and in the Upper Savannah River Valley.
We may finally see some relief from the mid 90s on Thursday, thanks
to the cold front and its convection. Highs on Thursday are
currently expected to only climb into the upper 80s and lower 90s
east of the mountains. Unfortunately this is not too much of a
relief from the heat, but it will be welcome nonetheless.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: High pressure at the sfc and aloft
should continue to keep things quiet and suppressed through the
period. For the remainder of the afternoon, enough moisture is
present to allow for stratocu to develop underneath the persistent
subsidence inversion, so all terminals will be in-and-out of a VFR
sct/bkn cloud deck around 050-060. The low clouds should dissipate
with the loss of heating this evening, so clear overnight with
light/variable winds. Some of the guidance would have a low cloud
deck moving northwestward from the coast, perhaps impacting the
terminals outside the mtns, but for now the chance is not great
enough to include. There remains the possibility of low cloud/fog
restrictions in the mtn valleys as well, but again the confidence
is too low. For Saturday, low clouds are more likely to develop
earlier in the day as low level moisture should be greater on
a developing light SE flow. There might be a few showers in the
afternoon as the cap could be breached, but that remains beyond
the scope of this forecast.

Outlook: Isolated diurnal convection will be possible over the
mtns on Saturday afternoon, 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...PM/Wimberley
SHORT TERM...AR
LONG TERM...AR
AVIATION...PM