Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 270715
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
315 AM EDT Tue Jul 27 2021

.SYNOPSIS...
The cold front draped across the forecast area will bring another
round of widespread showers and thunderstorms this afternoon into
this evening. Main concerns with this system are excessive rainfall
leading to the potential for isolated flooding or flash flooding and
isolated strong to severe storms bringing the potential for damaging
wind gusts. High pressure nudges into the area middle to late this
week leading to dry and hot conditions. Heat indices could climb
near or above 100 degrees across the far southern and southeastern
zones. Another cold front impacts the area this weekend increasing
shower and thunderstorm chances again.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 am: Widespread low stratus will continue in the mountain
valleys this morning, with stratus and fog likely becoming
widespread in many areas outside the mountains in response to a
moist environment and lots of wet ground. Stratus will likely
persist through much of the morning, somewhat delaying
destabilization. Weak, increasingly diffuse frontal zone is expected
to sag south of the I-85 corridor by this afternoon, convergence and
differential heating along this boundary will provide a focus for
deep convective development during early/mid afternoon, while
terrain effects will also support initiation across the mountains
during the same time frame. Likely...if not categorical PoPs are
again warranted across much of the forecast area this afternoon into
the early evening.

Instability is forecast to be a bit lower this afternoon than on
Monday, but still expect a couple of pulse severe storms to develop.
The larger concern will again be heavy/locally excessive rainfall/
flash flooding. Several areas came very close to experiencing flash
flooding yesterday, and with deep warm cloud layers and slow cell
movement/cell backbuilding potential persisting, a similar situation
can be expected today. If anything, the potential may be a bit
higher, if for no other reason that short term antecedent conditions
are ripe for localized runoff problems in some areas.

The bulk of any convection should again move southeast of and/or
dissipate over the forecast area through the evening, with only
token chances for convection lingering, mainly across the southern
zones through the overnight. Temps will be around normal through the
period.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 300 AM EDT Tuesday: The ridge of high pressure remains in
place across much of the CONUS with troughing present across the
Northeast throughout the duration of the short term period. The
southeastern periphery of this ridge will extend into the
Southeastern United States Wednesday and Thursday. As a result,
subsidence will suppress convection allowing for dry conditions
across northeast Georgia and the western Carolinas. PWAT values will
continue to decline Wednesday as this high pressure system decreases
moisture content. Although northerly and northwesterly flow will be
present across the region, high temps will climb into the low to mid
90s outside the mtns and mid 80s to low 90s in the mtns. Higher
elevations will see highs ranging from the low 70s to low 80s.
Triple digit heat indices look most likely across the extreme
southern and southeastern zones of the CWA middle of the week. As of
right now, not planning to issue a heat advisory as heat indices
look to remain less than 105 degrees. Although we get a much needed
break from heavy rainfall, the trade off unfortunately seems to be
hot and humid conditions. A cold front will track out of the Ohio
Valley and is expected to be draped along or near the NC/VA state
line towards the end of the short term.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 300 AM EDT Tuesday: Throughout the extended forecast period,
the ridge of high pressure that extended into the southeastern CONUS
will be forced to retreat westward as an upper-level trough
amplifies and digs across the eastern US.

At the sfc, a cold front should be draped along or near the NC/VA
border early Friday, sinking southward across the CWA throughout the
day. This front has the potential to lift back north slightly over
the weekend. This will keep a slight chance to chance for diurnal
showers and thunderstorms late this week into the weekend. Despite
northerly and northwesterly flow on Friday, temps will remain hot
ahead of the FROPA. Highs in to low to mid 90s outside the mtns and
mid 80s to upper 90s across the mtns are expected. Higher elevations
will likely see slightly cooler highs. Heat indices have the
potential to remain near triple digits across the far southern and
southeastern zones. Westerly and northwesterly flow continues into
the weekend and with the frontal passage to our south, high temps
will be noticeably cooler ranging from the upper 80s to low 90s
outside the mtns and low 70s to mid 80s in the mtns.

Another cold front looks to track across the forecast area early
next week bringing below average temps and keeping shower and
thunderstorm chances around.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: Low stratus has become widespread in the
mountain valleys early this morning, and will most likely persist at
KAVL until after sunrise. Visby should eventually diminish to IFR
(or worse) over the next couple of hours as well. Considering the
heavy rain that fell at most terminals Mon afternoon suggests that
it`s a foregone conclusion that restrictions will eventually develop
at the other TAF sites, although timing and magnitude of these
restrictions remains uncertain. At least tempo IFR/LIFR conditions
are advertised at all sites for a couple of hours centered around
sunrise. Gradually improving conditions are expected later this
morning, with VFR expected by early afternoon. Convection will
redevelop across the area this afternoon, warranting VCSH/VCTS and
Prob30s for TSRA at all sites into the early evening. Winds will
generally be light/vrbl through the period.

Outlook: Drier air filtering into the area is expected to result in
a lull in convective activity Wednesday and Thursday. Diurnal
convection is expected to return Friday and continue through the
weekend. Early morning fog and low stratus will remain possible,
mainly Friday and Saturday morning.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High  95%     High  95%     High 100%     High 100%
KGSP       Med   68%     Med   79%     High 100%     High 100%
KAVL       Med   64%     High  87%     High 100%     High 100%
KHKY       High  89%     High  95%     High 100%     High 100%
KGMU       Med   78%     High  83%     High 100%     High  95%
KAND       Med   76%     High  82%     High 100%     High  95%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables are available at
the following link:

www.weather.gov/gsp/aviation

&&

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

&&

$$
SYNOPSIS...AP
NEAR TERM...JDL
SHORT TERM...AP
LONG TERM...AP
AVIATION...JDL


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