Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1049 AM EDT Sat Jun 12 2021

.SYNOPSIS...
Abundant moisture will persist over the region again today as a back
door cold front arrives from the northeast late this afternoon. The
front will settle just south of the area through Sunday, and provide
a focus for active weather through the day.  Another cold front
approaches from the northwest on Monday and crosses to the Atlantic
coast on Tuesday. High pressure will return from the northwest mid
to late next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1030 am: Today continues to look rather active across the
region, with high precipitable water values of ~1.7 to 2 inches
persisting. Scattered showers have already developed this morning,
mainly north of I-40 in response to speed maxima passing through the
H5 trough overhead in addition to NW upslope flow. The trough will
continue to pass slowly over the region throughout the day, while
boundary layer convergence ahead of a backdoor cold front
approaching from the northeast will provide a low-level focus for
convective initiation. Best convergence/moisture pooling is expected
from the NC foothills across Charlotte metro, which should result in
intensification and increasing coverage above and beyond the current
activity during early/mid afternoon. Outflow boundaries and terrain
effects will then allow convective development to increase to the
southwest within a stronger region of instability across upstate SC
and northeast GA. Will thus feature solid likely to categorical PoPs
across much of the CWA. The moist environs along with training cell
potential will again yield a threat of localized excessive rainfall
and flash flooding just about anywhere. Meanwhile, there is a slight
uptick in the threat of brief/pulse severe storms above recent
days...mainly across southwest zones where sbCAPE is expected to
peak in the 2500-3000 J/kg range this afternoon.

Temperatures ahead of the boundary in SW parts should be comparable
to recent days, but with NW NC piedmont temps a bit cooler with more
clouds and then weak late day cold advection on NE surface winds.
The H5 trough axis will move just east/southeast of the area
tonight, with the surface boundary making a stronger push southward
across the region. This will lead to a gradual dropoff in PoPs from
N to S through the late evening and early overnight hours. Min temps
should be at least a category cooler early Sunday morning than this
morning, and perhaps a touch cooler than that in the northern tier.
This will be mitigated by continued clouds in the NE flow.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 230 AM EDT Saturday: At daybreak Sunday, surface winds retain
a bit of an easterly component, as a weak coastal low traverses the
stalled boundary to our south.  As this easterly component
diminishes, we should see a lull in PoPs.  The incipient shortwave
should be east of our CWA by Sunday afternoon, so synoptic forcing
will be lacking, with more stable profiles and a lack of any
discernible lifting mechanism; SBCAPE will be well below 1500
J/kg across the CWA, and midlevel lapse rates struggle to get
above 5 K/km or so. Thus, convection on Sunday afternoon will be
suppressed compared to Saturday. Any pulse storms which do
form, however, will have some potential to produce isolated
flooding, as PWATs are still near 1.5" and potential is high for
backbuilding.

Sunday night, a deeper trough finally pushes into the east CONUS out
of the Midwest, and the attendant cold front approaches the
Appalachians.  Previous model guidance had suggested some mountain
precip beginning Sunday night, but the latest GFS/ECMWF runs are
holding off until early Monday morning.  So, have dialed back PoPs
accordingly on Sunday night.

Ahead of the front, we'll see modest surface convergence on Monday,
prompting precip beginning in the mountains, and spreading across
the rest of the CWA throughout the day.  The NAM is pushing SBCAPE
in excess of 2000 J/kg Monday afternoon, so convection will be
possible across much of the CWA.  Luckily, with shear struggling to
crest 10-15 kts, severe potential is low, and the primary threat
will be another day of localized flash flooding - PWATs are by this
time dropping back down to 1-1.25", but warm cloud layers greater
than 10 kft across the NC Foothills and SC Upstate point to
efficient precip generation, and MBE vectors under 5 kts mean
backbuilding is a concern as well.  Additionally, the drier
profiles, while reducing the flood threat compared to previous days,
create a slightly better environment for damaging winds in any
storms that crop up.

Behind the front, northwesterly flow and overnight clearing should
lead to rapid stabilizing and drying profiles, cutting off
convection and allowing temps to drop from a bit above-normal on
Sunday to near- or slightly below-normal starting Monday night.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 245 AM EDT Saturday: We remain dry for most of the medium
range.  From Tuesday onward, dry high pressure will dominate the
surface pattern, and although a weak shortwave is depicted as
traversing the CWA in multiple model runs late Tuesday, the lack of
available moisture should keep PoPs negligible except perhaps for
the eastern NC Piedmont.  Through Friday, PoPs remain low, before
the GFS and ECMWF indicate a potent upper trough brings additional
chances for active weather.  This feature is conspicuously absent in
the latest CMC.  Temps from Tuesday through Friday night should
remain at- or slightly above-normal.

Notably, models are converging on the possibility of a tropical low
moving out of the Gulf of Mexico next weekend.  For now, this
appears to take place outside our period, but this system could
interact with the midlatitude features in place late next week to
produce more active weather on Saturday and beyond.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and Elsewhere: Spotty showers around daybreak this
morning will steadily grow from the west with a passing upper trough
axis. Showers and thunderstorms will become more robust at the
terminals from midday onward with the continued progress of the
upper trough but mainly from the arrival of a backdoor cold front
from the northeast. Anticipate plenty of IFR visibilities, MVFR
cigs, heavy rainfall, and gusty winds with any thunderstorms ahead
of the front. Will feature TEMPO TSRA at most sites with generally
18Z to 00Z being the peak period. W to NW surface winds early today
will turn northeasterly today into tonight. Anticipate low clouds
returning in the NE flow overnight, with lowering MVFR to IFR bases
at times, becoming more solidly IFR late.

Outlook: Modest drying moves in Sunday into next week, however a
brief uptick in showers and thunderstorms will return with a passing
cold front late Monday into Tuesday. The potential for overnight and
morning fog and low cigs should become increasingly confined to the
mtn valleys next week.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       Med   66%     High 100%     Med   65%     High  83%
KGSP       High 100%     High 100%     Med   72%     High  85%
KAVL       High  95%     High 100%     High  81%     Med   69%
KHKY       Med   73%     Med   73%     Med   69%     Low   59%
KGMU       High 100%     High 100%     High  83%     High  87%
KAND       High 100%     High 100%     Med   77%     Med   78%

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...MPR
NEAR TERM...HG/JDL
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...HG

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
433 AM EDT Sat Jun 12 2021

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-130845-
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-
433 AM EDT Sat Jun 12 2021

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

.DAY ONE...Today and tonight.

Showers and thunderstorms will develop across the region today,
primarily this afternoon and early this evening. The thunderstorms
will move slowly and produce torrential rainfall in affected
locations. Any areas experiencing repeated thunderstorms in a short
period of time may see flooding of low-lying areas and stream beds.
Any of the thunderstorms will have the potential to produce
dangerous cloud to ground lightning and gusty winds. A few of the
thunderstorms may produce damaging wind gusts.

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

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

MPR

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
115 PM EDT Sat Jun 12 2021

SCZ012-121745-
Laurens SC-
115 PM EDT Sat Jun 12 2021

...A STRONG THUNDERSTORM WILL IMPACT WEST CENTRAL LAURENS COUNTY
UNTIL 145 PM EDT...

At 114 PM EDT, Doppler radar was tracking a strong thunderstorm 6
miles west of Laurens, moving south at 10 mph.

Locations to be impacted include...
Laurens and Waterloo.

Half inch hail will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Heavy 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.

&&

LAT...LON 3437 8219 3449 8220 3452 8206 3435 8199
      3435 8217
TIME...MOT...LOC 1714Z 347DEG 8KT 3446 8214

KRENTZ

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
138 PM EDT Sat Jun 12 2021

SCZ011-121815-
Abbeville SC-
138 PM EDT Sat Jun 12 2021

...A STRONG THUNDERSTORM WILL IMPACT SOUTHWESTERN ABBEVILLE COUNTY
UNTIL 215 PM EDT...

At 137 PM EDT, Doppler radar was tracking a strong thunderstorm 14
miles west of Abbeville, or near Lowndesville, moving south at 10
mph.

Locations to be impacted include...
Lowndesville, Lake Russell and Lake Secession.

Wind gusts up to 40 mph and pea size hail will be possible in these
areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Gusty winds can blow down trees that are dead, or that have weakened
root systems. Outdoor furniture and similar items can be tossed
around if not anchored. Seek shelter indoors.

&&

LAT...LON 3420 8274 3428 8262 3427 8256 3408 8262
TIME...MOT...LOC 1737Z 016DEG 8KT 3424 8262

KRENTZ