Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
240 PM EDT Fri Jun 11 2021

.SYNOPSIS...
Daily afternoon and evening thunderstorms are expected through the
weekend, and with subtropical moisture lingering over the region,
they will pose a threat of localized flash flooding. A front will
settle across the region early next week, promoting a slight chance
for showers Monday and Tuesday. Hot and humid conditions can be
expected those days, but somewhat drier and cooler high pressure
will return by midweek.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 150 pm: An upper trough/associated speed maxima and attendant
diffuse frontal boundary will sag slowly across the area through the
period. The atmosphere will remain anomalously moist through the
period, with PWATs hovering around 1.8. This setup combined with a
moderate;y unstable air mass will allow convective coverage...
currently widely scattered at most...to increase throughout the
afternoon into the evening, with likely PoPs still seemingly
warranted across much of the forecast area. Heavy/locally excessive
rainfall remains the primary concern, especially across the
Tennessee border counties, where persistent W/NW upslope flow will
provide a favorable scenario for training cells and antecedent
conditions are wet owing to heavy rainfall over the past 24 hours.
Having said that, the flash flood threat remains too localized to
warrant a Flash Flood Watch at this time. One or two pulse severe
storms also remain possible into the evening, esp in the more
unstable air across the Piedmont. Convective coverage will diminish
through the evening, but persistent W/NW flow should result in
occasional showers developing near the TN border through the
night.

With the upper trough positioned over the area tomorrow and the
diffuse frontal zone expected to sag into western NC, convection
should again blossom across the CWA Saturday afternoon, with likely
PoPs again advertised in all areas. In terms of hazards: more of the
same, with the threat of locally excessive rainfall persisting.
There may be a slight uptick in the threat of pulse severe storms,
particularly over the upper Savannah River Valley and Lakelands,
where guidance suggests an increase above the modest levels of
instability over that of the past several days. Temps will remain
around normal.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
As of midday Fri: As front continues to slowly sag south across SC/GA
Saturday night into Sunday morning, a weak coastal low is expected to
develop via the shortwave near the NC/SC coast. That development,
along with sfc high over the Mid-Atlantic, still looks to bring an
easterly component to the low-level flow, which leads multiple
guidance sources to show some continuing convection near the Blue
Ridge Escarpment into the night, in addition to what develops near
the front. The 12z HRRR and NAMNest however are not too excited by
this possibility, so will keep PoPs low; the concern would be for
possible anchoring of cells along the Escarpment in that scenario;
MBE vectors are very short as it is.

The weak easterly flow will continue into Sunday, but diminishing
and/or backing to a less upslope direction as the low drifts
offshore. The shortwave looks to be south and east of the CWA;
heights should rise as it is replaced by an extension of the deep
ridge over the Rockies/Plains. Dewpoints probably will be a tad lower
but still and most likely remaining in the 60s. Midlevel height rises
imply poor lapse rates above the PBL which, given lack of a trigger,
suggests PoPs close to climo. Still looking at a bit of a wildcard
with models depicting an unstable warm sector across the upper OH/TN
Valleys ahead of a seasonally respectable cold front.  Earlier runs
suggested that the resultant activity could impinge on our mountain
zones late Sunday or Sunday night, but this depiction has generally
diminished. Deep shear and weak forcing just don't look all that
supportive of an MCS threat. Profiles will be somewhat drier Sunday
than Saturday, so heavy rainfall potential may be slightly reduced
although soils may be wetter after still another day of storms, so
can't say we won't exactly be out of the flash-flood threat window.
Sfc-midlevel theta-e lapses will be a bit stronger, so pulse storm
wind damage threat may be a bit greater. Max temps will trend a
little warmer compared to Saturday, near to slightly above climo.

By Monday, the front appears to reach the CWA, as it picks up a
little bit of a boost from a shortwave approaching from the Great
Lakes and deepening the trough across the NE CONUS. With winds
turning northwesterly through much of the mid to upper levels, deep
drying does occur on the "cool" side of the front. Most of the models
depict a convergence zone across the Carolina/Georgia Piedmont, and
small PoPs will follow. Similar to the trend noted for Sunday, flood
threat may diminish a bit in lieu of improving microburst threat
where the drier air is able to work in. Downsloping and increasing
thicknesses still look to produce max temps in the lower 90s for much
of the Piedmont, but despite dewpoint pooling potentially keeping
values in the upper 60s there, heat index concerns are not expected.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 200 PM Fri: The drying trend will continue Monday night as cold
front continues to push south and east, and dewpoints/PWATs continue
to tumble across the CWA into Tuesday, looking likely to remain low
thru the remainder of the period. A shortwave will swing across the
area Tuesday on the periphery of a cutoff low over Quebec; the
combination of this feature and the front leads to model QPF response
mostly to our east, but we will maintain small PoPs over the eastern
half of the area. Above-normal temps persist in downsloping flow Tue.
Unmentionably low PoPs are fcst from Tue night to at least early
Friday as continental sfc high migrates across the eastern CONUS, and
max temps fall back to near normal. Various models depict a
tropical/subtropical low approaching the Gulf Coast late in the week,
but any moisture associated with it looks to affect our area after
the end of the period, if at all.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Convection remains somewhat isolated across
the Terminal Forecast Area so far this afternoon, but the influence
of an upper trough just to our west will combine with moderate
instability to allow for steady expansion of coverage throughout the
afternoon, and tempos for TSRA are warranted at most sites into the
early evening hours. Convection will likely linger, although with
decreasing coverage past the tempo expiration, so those may need to
be extended by an hour or two at some point. After this evening, low
level moisture is expected to result in clouds filling in and
lowering, mainly at the NC terminals, with low MVFR or IFR cigs
expected at the NC terminals by sunrise. MVFR/possible IFR fog is
also expected in the mountain valleys. Convection should begin
redeveloping Sat afternoon, warranting Prob30s at all sites. SW
winds at 5-10 kts will continue at most sites through the afternoon,
before weakening and gradually turning toward the NE by the end of
the period, as a diffuse frontal boundary sags across the area.

Outlook: Modest drying moves in Sunday into next week. This will
result in less coverage of diurnal convection each day, such that
little in the way of convection is expected Tue and Wed. The
potential for overnight/morning fog/low cigs should become
increasingly confined to the mtn valleys next week.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High  99%     High 100%     High  85%     High  83%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  96%     High  94%     Med   71%     High  84%
KHKY       High  98%     High 100%     High  83%     High  85%
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...Wimberley
NEAR TERM...JDL
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...JDL

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
331 AM EDT Fri Jun 11 2021

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-120745-
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-
331 AM EDT Fri Jun 11 2021

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

.DAY ONE...Today and tonight.

Numerous to widespread showers and thunderstorms will develop across
the western Carolinas and northeast Georgia today, with the greatest
coverage during the afternoon and early evening hours. The
thunderstorms will have the potential to produce torrential
downpours in affected areas and localized flooding may develop in
any locations that see repeated thunderstorms in a short period of
time. The thunderstorms will also produce dangerous cloud-to-ground
lightning and gusty winds.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

MPR

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
458 PM EDT Fri Jun 11 2021

NCZ065-507>510-112130-
Greater Rutherford NC-Henderson NC-Polk Mountains NC-
Rutherford Mountains NC-Eastern Polk NC-
458 PM EDT Fri Jun 11 2021

...A THUNDERSTORM WITH TORRENTIAL RAINFALL WILL IMPACT WEST CENTRAL
RUTHERFORD...NORTHEASTERN HENDERSON AND CENTRAL POLK COUNTIES UNTIL
530 PM EDT...

At 458 PM EDT, Doppler radar was tracking a thunderstorm with
torrential rainfall 7 miles northeast of Hendersonville, or 5 miles
east of Fletcher, moving east at 20 mph.

Locations to be impacted include...
Hendersonville, Columbus, Mountain Home, Lake Lure, Chimney Rock
Village, Chimney Rock State Park, Bat Cave, Fletcher, Mill Spring and
Edneyville.

Wind gusts up to 40 mph, pea size hail and very heavy rainfall rates
up to 2 inches per hour will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

The combination of gusty winds and saturated soil conditions will
cause scattered trees and power lines to fall. Seek shelter inside an
interior room.

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 3550 8209 3524 8215 3534 8251 3545 8249
      3545 8246 3547 8242 3546 8237 3548 8237
      3549 8236 3549 8235 3550 8233 3546 8225
      3547 8224 3551 8223
TIME...MOT...LOC 2058Z 280DEG 16KT 3542 8241

RWH

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
528 PM EDT Fri Jun 11 2021

NCZ507>510-112200-
Greater Rutherford NC-Polk Mountains NC-Rutherford Mountains NC-
Eastern Polk NC-
528 PM EDT Fri Jun 11 2021

...A THUNDERSTORM WITH TORRENTIAL RAINFALL WILL IMPACT CENTRAL
RUTHERFORD AND CENTRAL POLK COUNTIES UNTIL 600 PM EDT...

At 528 PM EDT, Doppler radar was tracking a thunderstorm with
torrential rainfall 10 miles west of Rutherfordton, or 4 miles
southeast of Lake Lure, moving east at 20 mph.

Locations to be impacted include...
Rutherfordton, Forest City, Spindale, Lake Lure, Chimney Rock State
Park, Shingle Hollow, Green Hill, Mill Spring, Lake Adger and Union
Mills.

Wind gusts up to 40 mph and very heavy rainfall rates up to 2 inches
per hour will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

The combination of gusty winds and saturated soil conditions will
cause scattered trees and power lines to fall. Seek shelter inside an
interior room.

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 3532 8225 3550 8221 3548 8184 3522 8190
TIME...MOT...LOC 2128Z 280DEG 16KT 3540 8215

RWH