Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
226 PM EDT Wed Aug 25 2021

.SYNOPSIS...
An upper ridge will become dominant over the region Thursday through
the weekend, with periods of Atlantic moisture brought into our
region.  A cold front will approach from the north early next week.
Above normal temperatures are expected through the first half
of next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 224 PM EDT Wednesday: Deep convection well underway as of
fcst issuance time. The SPC mesoanalysis shows 1500-2500 J/kg
mlCAPE and sfc-based values about 500 J/kg higher, while also
showing 900-1200 J/kg of dCAPE. Fcst soundings show sfc-delta
theta-e to be around 30K, and weak shear. This suggests a good
environment for wet microbursts, thus the Marginal Risk for the
whole fcst area for the Day 1 Convective Outlook is warranted,
especially over the I-85 corridor and south/east. Expect a busy
radar into the early evening as multicells develop and fire
along outflow boundaries. Relatively slow movement of storms
will raise the risk of isolated flash flooding.

Although there is some indication that convection could linger
into the late evening hours, the severity should taper off around
sunset. Assuming convective debris dissipates in the early morning
hours, that should set the stage for fog/low stratus development
around areas where rain falls this past afternoon, probably
locally dense in the mtn valleys. Low temps will remain seasonally
warm. The weakness in the pattern aloft will linger into Thursday
before the Atlantic subtropical ridge starts building westward,
so expect Thursday to play out very similar to Wednesday. PW might
be slightly less and mid level temps slightly warmer, but there
should be a good chance of convection at least over the higher
terrain in the afternoon. The trend east of the mtns will be more
toward climo, however, as drier air filters in from the east over
the I-77 corridor at least. Temps will be a bit above normal over
the east, but close to normal elsewhere.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 100 PM EDT Wednesday: A 595dm subtropical ridge will be
situated over the Atlantic coast Thursday night into Friday morning.
Only meager synoptic forcing will be available, perhaps over the
lower SC Upstate.  In response to the building subtropical ridge,
the Bermuda High will retrograde westward through Saturday,
and low-level flow will turn from almost due southerly, to more
southeasterly, allowing surface moisture to tick slightly upward.

Friday, isolated to widely scattered convection is possible given
favorable SBCAPE (~1000-1500 J/kg) and PWATs in the 1.5-1.7" range.
Better coverage should be limited by a growing subsidence inversion
owing to deep high pressure at the surface and aloft.  Saturday,
model soundings indicate a strengthening subsidence inversion,
less favorable instability, and increasingly dry air aloft, which
should once again hinder widespread convection.  Nonetheless,
the presence of dry air aloft means any storms that do break
out could be capable of producing downbursts.  Both afternoons,
convection will be most active over the western part of the CWA,
where terrain effects will enhance lifting.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 130 PM EDT Wednesday: Ridging will persist throughout much
of the medium range forecast.  For the most part, this means a
continuance of diurnally-driven showers and thunderstorms, and
above-normal temperatures each afternoon.  The mid-levels look
to remain dry, as the subtropical ridge funnels moisture around,
rather than over, the Carolinas.  A trough axis should pass well
north of the area on Monday and Tuesday, with the attendant weak
cold front pushing across the area Tuesday afternoon or evening.

For now, the track of an approaching tropical system in the Gulf
of Mexico is unclear.  Global models currently suggest that the
blocking ridge set up over the Carolinas should steer such a
system to the west by Wednesday or beyond; however, the details
are unclear, and even if this situation plays out, some tropical
moisture might be able to filter into the area midweek.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
At KCLT and elsewhere: Looks like a good setup for wet microbursts
across the region this afternoon, with ample buoyancy, mid level
dry air, and a deep well mixed boundary layer. Guidance shows
the development of scattered thunderstorms during peak heating,
so all TAFs get a TEMPO with variable gusty winds. Flight category
should be VFR outside of storms with a light SE wind. Overnight,
expect fog to develop where storms move this afternoon. Most places
get at least a TEMPO for some MVFR vis in the pre-dawn hours, but
the mtns get LIFR for valley fog/stratus. This should mix out by
13Z to 14Z. Thursday should be very similar.

Outlook: Conditions for storms become less favorable for the late
part of the week. Overnight restrictions can be expected in the
mountain river valleys and in any areas that receive heavy rainfall
the previous day.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High  90%     High  80%
KGSP       High 100%     High 100%     High  93%     High  90%
KAVL       High  98%     High  95%     Med   61%     High  85%
KHKY       High 100%     High  98%     High  85%     High  87%
KGMU       High 100%     High 100%     High  94%     High  93%
KAND       High 100%     High 100%     High 100%     High  94%

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...PM
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...PM

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
1118 AM EDT Wed Aug 25 2021

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-261530-
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-
1118 AM EDT Wed Aug 25 2021

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

.DAY ONE...This afternoon and tonight.

Scattered to numerous showers and thunderstorms will develop this
afternoon and evening. Any of these thunderstorms may produce
dangerous cloud-to-ground lightning, locally heavy rainfall, and
gusty winds. A few storms may become severe, with damaging wind
gusts
possible.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

MPR

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
329 PM EDT Wed Aug 25 2021

NCZ082-252000-
Union NC-
329 PM EDT Wed Aug 25 2021

...A strong thunderstorm will impact portions of southeastern Union
County through 400 PM EDT...

At 329 PM EDT, Doppler radar was tracking a strong thunderstorm 13
miles east of Monroe, or near Sturdivants, moving west at 5 mph.

HAZARD...Winds in excess of 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Wingate, Marshville and Sturdivants.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3484 8032 3481 8046 3482 8049 3508 8048
      3505 8029
TIME...MOT...LOC 1929Z 092DEG 6KT 3495 8031

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

ARK

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
358 PM EDT Wed Aug 25 2021

GAZ029-SCZ010-011-252030-
Elbert GA-Anderson SC-Abbeville SC-
358 PM EDT Wed Aug 25 2021

...Strong thunderstorms will impact portions of northeastern Elbert,
southeastern Anderson and western Abbeville Counties through 430 PM
EDT...

At 357 PM EDT, Doppler radar was tracking strong thunderstorms along
a line extending from 11 miles southeast of Anderson to 9 miles west
of Abbeville. Movement was west at 10 mph.

HAZARD...Winds in excess of 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Calhoun Falls, Iva, Lake Secession, Starr, Lowndesville, Russell
State Park, Lake Russell, Antreville and Rock Branch.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with these storms and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3443 8268 3420 8280 3405 8269 3409 8243
      3428 8251 3447 8243
TIME...MOT...LOC 1957Z 060DEG 13KT 3438 8253 3425 8258 3413 8253

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

ARK

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
401 PM EDT Wed Aug 25 2021

NCZ049-252030-
Yancey NC-
401 PM EDT Wed Aug 25 2021

...A THUNDERSTORM WITH TORRENTIAL RAINFALL WILL IMPACT CENTRAL YANCEY
COUNTY UNTIL 430 PM EDT...

At 400 PM EDT, Doppler radar was tracking a thunderstorm with
torrential rainfall near Burnsville. This storm was nearly
stationary.

Locations to be impacted include...
Burnsville, Green Mountain, Ramseytown, Micaville and Poplar.

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 3603 8234 3603 8231 3604 8230 3602 8227
      3600 8227 3599 8225 3601 8225 3601 8220
      3600 8219 3600 8220 3595 8220 3593 8218
      3593 8215 3592 8215 3591 8214 3589 8215
      3582 8235 3598 8247 3608 8235
TIME...MOT...LOC 2000Z 237DEG 4KT 3595 8228

ARK