Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
757 PM EDT Tue Aug 10 2021

.SYNOPSIS...
High pressure will persist off the Southeast coast, resulting in
a typical summertime pattern across the region this week. Abundant
moisture ahead of an approaching cold front will enhance coverage
of showers and thunderstorms, mainly in the afternoons and evenings.
The front is forecast to stall over the area this weekend,
maintaining good chances for rainfall.  A tropical system could add
to our rainfall in the first half of next week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 730 PM EDT Tuesday: Thunderstorms have pushed out of the
mountains and into the Piedmont where DCAPEs are a little higher,
and we're seeing stronger wind gusts to go with them. Near term
update has tried to account for radar trends but CAMs are, as usual,
not handling the pulse convection well so have made a bunch of hand
edits. Highs today outperformed the forecast across the Piedmont and
so had to make adjustments for hourly trends into the night. Other
changes are for aviation-related parameters and expect that we
should see typical mountain valley fog overnight as guidance is
starting to hit that harder with recent updates.

Otherwise, a large upper low remains in place centered over Central
Canada, with a circulation that extends marginally down into the
Southern States. Dynamics over the GSP area are quite weak, with
scarcely any deep layer shear. Upper and lower high pressure lies
off the Atlantic Coast, giving light to variable mostly southerly to
southwesterly flow to the region. Synoptic features have small
changes over the next 24 hours, with upper North American low making
some slight eastward progress.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 100 PM EDT Tuesday: A deep trough over the upper Midwest will
persist through the short term, while the Bermuda high will nudge
slightly westward in response to a building subtropical ridge over
the eastern CONUS.  On Thursday, as the ever-weakening boundary
draped across the Southeast pushes northward, southerly surface
flow will strengthen, advecting a plume of moisture into the region.
PWATs should climb well into the 1.7"+ range by Thursday afternoon.
With SBCAPE in excess of 1000 J/kg across the Piedmont and Upstate,
we'll be in store for another round of diurnally-driven pulse
convection.  In the absence of any discernible lifting mechanism,
and with midlevel drying promoting higher LFCs, widespread
convection should be somewhat suppressed.  Still, we're likely to
see isolated to scattered showers and thunder across the forecast
area, and with increasingly dry midlevels, a few of these storms
could produce downbursts.  The latest guidnace doesn't suggest
surface-to-700mb delta-theta-e values will be quite high enough
for a serious microburst threat, but the potential for some gusty
straight-line winds is there.

Friday will be a similar, if somewhat enhanced, scenario.  Guidance
depicts a 500mb shortwave rotating across the deeper trough over
the course of the day, resulting in increased DPVA and driving
increased PoPs beginning Friday afternoon.  Coverage of convection
should be enhanced on Friday afternoon as well - model consensus
points to SBCAPE in the 800-1200 J/kg range, and profiles should
be moister in the midlevels than on Thursday, making them more
conducive to convective initiation.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 145 PM EDT Tuesday: PoPs continue to increase into Saturday as
a front pushes into the southeast CONUS.  By now, moister profiles
and falling heights should allow for widespread rainfall ahead
of the front; although cloud cover should be building Saturday,
somewhat hindering destabilization, it's likely we'll see some
embedded thunder in the afternoon.  Once again, localized heavy
rain will present a flooding concern.  As the frontal zone reaches
us on Sunday, we'll ramp up to ever-higher PoPs in the morning.

Early next week, all the global models agree we'll come under
the influence of PTC 6.  Although there remain significant track
differences between models and to some extent from run to run,
the general consensus is that the system will track up the west
Florida coast before turning more northward.  What local impacts
we'll face is unclear, though heavy rain and ensuing flooding
is certainly a possibility, especially as the extensive rainfall
we'll have received prior to PTC 6's arrival should have raised
soil moisture and primed the ground for flash floods.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: TSRA along and S of the I85 corridor
has pushed away from KGSP and generally KCLT as well, but have kept
VCTS for another hour at KCLT. Should still see convection in
vicinity of KAND. Otherwise TAFs should generally be clear of
convection for the evening barring a sunset surprise that will have
to be monitored. Expect mountain valley fog to form and have kept
previous trends at KAVL but added TEMPO for VLIFR conditions in the
pre-dawn hours. Winds should remain generally SW through the period
5kt or less, except in any TS that might develop tomorrow afternoon.
Expect another round of diurnal convection tomorrow, with greater
coverage than today, so kept trend of PROB30 for all sites tomorrow.

Outlook: Diurnal shower/thunderstorm activity remains in the
forecast the rest of the week.  Fog and low stratus will be possible
each morning, particularly over mountain valleys and areas primed
by rainfall from the previous evening.

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       High 100%     High 100%     High  99%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     Low   44%     Med   76%     Med   77%
KHKY       High 100%     High  95%     High  90%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High 100%

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...DEO
NEAR TERM...TDP/WJM
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...TDP

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
522 AM EDT Tue Aug 10 2021

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-110400-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Avery-Alexander-
Iredell-Davie-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-Catawba-
Rowan-Graham-Northern Jackson-Macon-Southern Jackson-Transylvania-
Henderson-Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union NC-
Caldwell Mountains-Greater Caldwell-Burke Mountains-Greater Burke-
McDowell Mountains-Eastern McDowell-Rutherford Mountains-
Greater Rutherford-Polk Mountains-Eastern Polk-Oconee Mountains-
Pickens Mountains-Greenville Mountains-Greater Oconee-
Greater Pickens-Greater Greenville-Spartanburg-Cherokee-York-
Anderson-Abbeville-Laurens-Union SC-Chester-Greenwood-
522 AM EDT Tue Aug 10 2021

This Hazardous Weather Outlook is for northeast Georgia, piedmont
North Carolina, western North Carolina and upstate South Carolina.

.DAY ONE...Today and tonight.

Scattered thunderstorms will develop across the area today, with the
greatest coverage during the afternoon. Any of these storms will be
capable of dangerous cloud-to-ground lightning as well as heavy
downpours. Localized flash flooding may result.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

Wimberley

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