Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
151 PM EDT Sat Aug 21 2021

.SYNOPSIS...
An upper level low over the Mid-Atlantic states will gradually lift
northeast into New England this weekend into early next week while a
ridge of high pressure in the southern United States gradually
builds into the southeastern United States. This upper-level pattern
will lead to only isolated shower and thunderstorm activity this
weekend into early next week across northeast Georgia and the
western Carolinas. Meanwhile Hurricane Henri will remain out in the
western Atlantic tracking north towards New England throughout the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1030 am EDT: A few showers have developed in the Lakelands
area of the Upstate had have updated pops accordingly. Otherwise,
grids are in pretty good shape this morning for a seasonally hot and
muggy day across the area with typical summertime pops mainly across
the mountains in the NW flow.

Otherwise, an H5 closed low center over the central Appalachians
will continue to spin north of the region, with various spokes of
vorticity moving through the southern Appalachians and crossing the
forecast area today. Forcing from these vorticity lobes may be
better in the northern tier today, but moisture and instability will
be better in the southern half, and that is where the better chance
PoPs will be featured during peak heating as sbCAPE values climb to
2500+ J/kg. Initiation should get started near the mountains again,
especially the southern escarpment area, but with a secondary focus
along a weak lee surface trough. Maximum temperatures should be
comparable to yesterday.

Tropical System Henri will remain well east of the Carolinas today
through tonight, with no impact to the region expected. Otherwise,
any diurnal convection will die out quickly this evening, with
another night of patchy fog along with some dense fog in the
mountain valleys. Mins remain above climo.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 100 AM EDT Saturday: Dry air advection from NW-ly flow
aloft and weak high pressure over the southern Appalachians will set
the stage for very limited convective coverage on Sunday. A closed
upper low over the mid-Atlantic will continue to lift northeast,
while pulling TS Henri further west and potentially stalling over
New England and portions of the Northeast. In our neck of the woods,
subsidence aloft and rising heights will filter into the area from a
deepening upper ridge over the Southern Plains and Lower Mississippi
Valley, which allows for mostly dry conditions across the CFWA
outside of isolated ridgetop convection and a pop up storm or two
east of the mountains for Sunday. With ~590 dm thicknesses
continuing to set up shop over the region, expect for the very warm
and humid airmass to persist through the short term period. With
little change in the overall synoptic pattern and mesoscale
processes during the early part of the upcoming week, expect a very
similar forecast for both Sunday and Monday. The main difference
between both days will be temperatures. With the upper ridge
extending further east into the southeastern CONUS on Monday,
temperatures should uptick a few degrees from Sunday to Monday.
Either way, temperature values will run above normal for both days.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 230 AM EDT Saturday: Summertime Bermuda High pattern will
begin to set up shop during the medium range. The Bermuda high will
gradually bring a return flow back into the CFWA by the middle
part of the upcoming week. Two areas of upper ridges will leave
the CFWA hot and humid with high heights continuing to linger over
the area. Diurnal convection will make a return on Tuesday due
to the Atlantic fetch from the Bermuda High. PoPs will still run
below climo due to the stagnant subsidence aloft. By Wednesday and
Thursday, model guidance shows the upper high to the west
retrograding as the subtropical ridge over the western Atlantic
pushes towards the southeastern CONUS. An open tropical wave will
ride the southwestern peripheral of the subtropical high as the wave
pushes through the Bahamas. The track of the tropical wave will be
influenced by the western Atlantic subtropical high. Deterministic
models have pushed this into the western Carolinas and northeast
Georgia over the last couple of model runs by Wednesday and
Thursday. If this trend continues, expect PoPs and PWAT values to
surge as the atmospheric column becomes saturated from the
relatively deep tropical moisture. The GFS and ECMWF also introduce
the potential for the aforementioned tropical wave to stall over the
CFWA and develop a closed low. There are a lot more questions than
answers at this time, but the quiet pattern that is forecasted
during the short-term could come to an abrupt end during the
extended period if this scenario ends up playing out as it is
currently being displayed. Temperatures will start out above normal
for Tuesday, but values will likely decrease to near-normal readings
through the rest of the forecast period due to the uptick in
precipitation chances and cloud cover.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
At KCLT and elsewhere: VFR this afternoon, with some pockets of MVFR
Cu as convection is expected to begin firing this afternoon, but at
this time not widespread enough to introduce TEMPO; have left VCSH
in TAFs at this time. Expect typical mountain valley fog again
tonight with MVFR to IFR conditions expected again at KAVL. Slightly
better chances for afternoon convection Sunday but too early to
introduce PROB30 at this time. Winds are generally lgt/vrb in the
weak pressure pattern but by tomorrow should be favoring the S/SW.

Outlook: A typical, diurnal summertime convective pattern is
expected to prevail the rest of the weekend through the middle of
next week, with scattered coverage at best. Mountain valley fog will
be possible each morning, as well as at sites that receive heavy
rainfall the previous afternoon.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High  99%     High 100%     High 100%
KGSP       High 100%     High 100%     High  80%     High  92%
KAVL       High  93%     High 100%     Low   51%     Med   79%
KHKY       High 100%     High  95%     Med   79%     High  91%
KGMU       High 100%     High 100%     High  81%     High  89%
KAND       High 100%     High 100%     High  99%     High  82%

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...HG
NEAR TERM...HG/TDP
SHORT TERM...CAC
LONG TERM...CAC
AVIATION...TDP

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
503 AM EDT Sat Aug 21 2021

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-220915-
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-
503 AM EDT Sat Aug 21 2021

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

.DAY ONE...Today and tonight.

Isolated to scattered showers and thunderstorms are expected this
afternoon and evening. The main threats will be cloud-to-ground lightning
and locally heavy rainfall. One or two storms may become strong to
severe.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
239 PM EDT Sat Aug 21 2021

NCZ504>506-508-211930-
McDowell Mountains NC-Greater Rutherford NC-Greater Burke NC-
Eastern McDowell NC-
239 PM EDT Sat Aug 21 2021

...A THUNDERSTORM WILL IMPACT SOUTHEASTERN MCDOWELL...NORTH CENTRAL
RUTHERFORD AND SOUTHWESTERN BURKE COUNTIES UNTIL 330 PM EDT...

At 238 PM EDT, Doppler radar was tracking a thunderstorm near Marion,
moving southeast at 10 mph.

Locations to be impacted include...
Marion, Lake James State Park, Lake James, Nebo, Sugar Hill, Thermal
City, Pleasant Gardens, Glenwood, Fero and Dysartsville.

Very heavy rainfall rates up to 2 inches per hour will be possible in
these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall may flood areas with poor drainage, such as
ditches and underpasses. Avoid these areas and do not cross flooded
roads. Water levels of small streams may also rise rapidly. Seek
higher ground if threatened by flood waters.

&&

LAT...LON 3563 8215 3578 8202 3568 8174 3545 8192
TIME...MOT...LOC 1838Z 304DEG 8KT 3567 8202

JPT