Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
742 PM EDT Sun Jul 18 2021

.SYNOPSIS...
An upper-level trough of low pressure, and an associated surface
cold front, will approach from the northwest and settle
slowly southeast across the region Monday through Tuesday. Increased
clouds and high rain shower chances will keep maximum temperatures
below normal through Tuesday before drier air arrives from the north
and temperatures rebound to normal or above mid to late week.

&&

.NEAR TERM /THROUGH MONDAY/...
600 PM Update...The atmos outside the mtns is beginning to become
more convectively active. Upper h3 div is shifting over the area and
enhancing tstm development along existing outflow bndrys. Available
CAPE remains on the low-end, so not anticipating real strong storms,
however high PWATS and precip rates may lead to localized hydro
issues thru the evening.

As of 205 pm Sunday: Widespread cloud cover has thus far limited
instability across the forecast area (generally to the tune of <
2000 J/kg) and this has limited convective coverage so far today.
The only exception to this is across the TN border counties, where
mechanical lift from SW flow has taken advantage of thinning of the
overcast to allow for initiation of numerous showers and isolated TS
across southwest NC, with more sparse coverage northeast of there.
As upper trough continues to approach from the northwest through
tonight, moisture and broad scale lift will continue to increase,
which combined with a few more hours of gradual heating should yield
scattered to numerous coverage of showers and storms before sunset.
Large scale lift will actually increase overnight, as unseasonably
strong upper jet streak passes through the Mid-Atlantic, placing
much of our area in the right rear quadrant for several hours.
Additionally, guidance agrees in developing an area of low level
speed convergence across the heart of the forecast area overnight.
These factors, along with PWATs increasing to AOA 1.8" should yield
increasing coverage of convection...mainly showers, but isolated/
scattered TS are also expected, with PoPs advertised in the 70-80
range across much of the area between 6 and 12Z Monday.

Showers and storms should generally diminish in coverage during the
morning, as the upper jet streak moves off the Mid-Atlantic coast.
If anything, instability will more difficult to come by on Monday,
as widespread low cloud cover that is expected to develop late
tonight will be slow to lift. (As a result, max temps are forecast
to be around 10 degrees below climo). Nevertheless, with the
environment expected to remain very moist...and guidance suggesting
another  enhancement in large scale lift by the end of the day,
likely to categorical PoPs appear warranted by the end of the day.
The main concern through the near term will remain the potential for
flash flooding, as slow-moving cells (esp this afternoon/evening)
along with potential for cell training and the likelihood of
efficient rainfall rates as the warm cloud depth deepens to more
than 10 kft poses the threat of excessive rainfall. At this point,
the threat appears to remain very localized.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 230 pm EDT Sunday: A positively tilted trough remains over the
eastern US while high pressure builds across the Desert Southwest
through the short term forecast period. The two main changes to the
short term are that the through tracking across the CWA has slowed
down a bit and now all global models are showing a low attempting to
cut off in the TN Valley just west of or along the southern
Appalachians on Tuesday. This slower movement of the trough will
lead to the weak sfc stationary front progressing slower across the
CWA. Despite the presence of this low in the models, forcing looks
to remain best across the SE zones Tuesday.

This frontal boundary will slowly sink southward Monday night before
stalling out across central NC and the northern SC Upstate Tuesday
into Wednesday. S'ly and SW'ly flow at 850 mb will be present ahead
of the front drawing in moisture from the Gulf. This will allow
PWATs to remain around 1.5 inches across the mtns and 1.5 to 2.0
inches outside the mtns Monday night into early Wednesday. These
PWATs combined with efficient warm rain processes, will allow for
heavy downpours at times, especially during peak daytime heating.
There's the potential for isolated flash flooding, especially for
locations that repeatedly see heavy downpours. Therefore, WPC has a
marginal risk for excessive rainfall in place for the entire CWA
Monday night into early Tuesday morning. A marginal risk will be in
place again Tuesday for the SW NC mtns, NE GA, and the majority of
the SC Upstate. The highest rainfall totals look to be confined to
portions of the NC mtns, NE GA, and SC Upstate. Rainfall amounts for
these locations could range from 1.5 to 3.0 inches. Elsewhere,
amounts could range from 1.0 to 1.50 inches. Locally higher amounts
are possible and will depend heavily on where the heaviest downpours
track. In regards to the severe wx potential, upper level forcing
from this trough could lead to isolated strong to severe storms
Monday evening into Tuesday, especially during peak heating hours.
Global models show 0-6 km bulk shear values ranging from 25 to 30
kts and SBCAPE values above 1,000 J/kg mainly SE of I-85. However,
the severe wx threat could be limited somewhat due to the amount of
cloud cover thanks to deep moisture in place. For now SPC has the
CWA in a general thunderstorm risk. High temps Tuesday will be
roughly 5 to 10 degrees below normal due to cloud cover remaining
over the region.

Tuesday night into Wednesday the moisture influx will gradually
decrease as winds turn more NW'ly and W'ly. This will lead to cloud
cover gradually decreasing during this time period. More insolation
Wednesday means high temps will rebound back into the mid to upper
80s outside the mtns and mid 70s to mid 80s across the mtns. Higher
elevations could see highs ranging from the mid to upper 60s.
Lingering moisture will remain in place as the stationary front
remains stalled over the northern SC Upstate and central NC. This
will allow the diurnal trend of showers and thunderstorms to return.
Right now capped PoPs at a slight chance to chance. The trough axis
is expected to clear the area Wednesday evening and as a result,
PWATs will gradually decline from north to south.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 230 pm EDT Sunday: The aforementioned trough axis will continue
pushing east Wednesday night and the stationary front will dissipate
early Thursday. For the rest of the extended forecast period a ridge
of high pressure will continue to dominate over the Desert Southwest
while a cutoff low develops over Texas. Meanwhile high pressure in
the Atlantic will nudge westward into the Gulf of Mexico while a
large low pressure system meanders around eastern Canada and the
Northeastern US. For the entire extended period it looks like W'ly
and NW'ly 850 mb flow will continue across our CWA. This will allow
daily diurnal showers and thunderstorms to continue. Capped pops at
a slight chance to chance for the end of the workweek and the
weekend. Insolation will continue through the extended allowing
highs to return to near normal or slightly above normal. Cloud cover
may increase slightly across the spine of the Appalachians during
the weekend. Originally it looked like we would get a backdoor cold
front dropping into the area Friday into Saturday, but now models
keep the upper-level trough and associated sfc frontal boundary well
to our north across the Ohio Valley and northeastern US.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
At KCLT and Elsewhere: Showers and thunderstorms have become
widespread across the FA and expect active weather to continue thru
the period as a frontal zone settles across the region. Thunder
chances remain fairly low for any given location, but enuf
confidence is had to include an early TEMPO TSRA at KCLT with
stronger cells currently developing to the SW of the terminal.
Expect lowering CIGs overnight to IFR all sites, while VSBY lowers
as well, yet likely remains in the MVFR range outside of showers due
to saturated llvls. Expect low CIGS to persist thru the late morning
over all sites in rather steady state conds as the stationary front
drapes across the area. Added PROB30 TSRA all sites late period as
embedded thunder will likely develop due to an increase in upper
forcing.

Outlook: An unsettled pattern is expected to continue into Tuesday,
with a steady decrease in convective activity expected during the
middle of the week. Overnight/early morning fog/low stratus will be
possible each day.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       High 100%     Med   65%     Low   53%     High  95%
KGSP       High 100%     Med   79%     High  82%     High  90%
KAVL       High  90%     Low   44%     Med   70%     High  80%
KHKY       High 100%     Med   79%     High  86%     Med   65%
KGMU       High 100%     Med   79%     Med   77%     High  90%
KAND       High 100%     Med   79%     Med   72%     High  95%

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...JDL/SBK
SHORT TERM...AP
LONG TERM...AP
AVIATION...SBK

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
348 PM EDT Sun Jul 18 2021

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-192000-
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-
348 PM EDT Sun Jul 18 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.

Showers and thunderstorms will continue to develop across the region
this afternoon and evening, with coverage increasing for the next
few hours, especially over the mountains and NC foothills. The
primary threat with these storms will be heavy and in some cases
long-lived rainfall, which will result in localized flash flooding in
locations affected by multiple thunderstorms or where drainage is
poor. Many of these storms will be capable of producing gusty winds
and frequent cloud- to- ground lightning.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Continued high coverage of heavy rain-producing showers and
thunderstorms will persist on Monday and Tuesday. The isolated flash
flooding threat will gradually increase as earlier storms saturate
the ground and raise stream levels, setting the stage for possible
flooding with any later storms that move over the same areas.

.SPOTTER INFORMATION STATEMENT...

None.

MPR

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
634 PM EDT Sun Jul 18 2021

NCZ035>037-056-057-502-504-182300-
Rowan NC-Davie NC-Iredell NC-Greater Burke NC-Greater Caldwell NC-
Alexander NC-Catawba NC-
634 PM EDT Sun Jul 18 2021

...THUNDERSTORMS WITH INTENSE LIGHTNING AND TORRENTIAL RAINFALL WILL
IMPACT CATAWBA...CENTRAL DAVIE...SOUTHERN ALEXANDER...IREDELL...
SOUTHEASTERN CALDWELL...NORTHWESTERN ROWAN AND EAST CENTRAL BURKE
COUNTIES UNTIL 700 PM EDT...

At 633 PM EDT, Doppler radar indicated thunderstorms with intense
lightning and torrential rainfall along a line extending from 10
miles southwest of Mocksville to 6 miles west of Statesville to 9
miles south of Lenoir, and moving northeast at 10 mph.

Locations to be impacted include...
Hickory, Statesville, Newton, Mocksville, Taylorsville, St. Stephens,
Conover, Longview, Sawmills and Granite Falls.

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...

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.

Frequent lightning is occurring with these storms. If outdoors, try
to get indoors or into a hard topped vehicle. Otherwise, stay away
from open areas and isolated high objects such as trees. When
indoors, stay away from windows and doors and avoid using wired
electronic devices. Do not take a shower or bath. Try to unplug
unnecessary appliances before the storms approach.

&&

LAT...LON 3589 8040 3588 8042 3587 8039 3583 8046
      3584 8048 3583 8049 3582 8047 3570 8068
      3557 8106 3573 8166 3587 8144 3595 8109
      3593 8037 3591 8038 3589 8037
TIME...MOT...LOC 2233Z 238DEG 10KT 3581 8071 3580 8101 3577 8151

RWH

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
700 PM EDT Sun Jul 18 2021

NCZ035>037-056-057-502-504-182330-
Rowan NC-Davie NC-Iredell NC-Greater Burke NC-Greater Caldwell NC-
Alexander NC-Catawba NC-
700 PM EDT Sun Jul 18 2021

...THUNDERSTORMS WITH INTENSE LIGHTNING AND TORRENTIAL RAINFALL WILL
IMPACT CENTRAL CATAWBA...DAVIE...ALEXANDER...IREDELL...SOUTHEASTERN
CALDWELL...NORTHWESTERN ROWAN AND EAST CENTRAL BURKE COUNTIES UNTIL
730 PM EDT...

At 659 PM EDT, Doppler radar indicated thunderstorms with intense
lightning and torrential rainfall along a line extending from 8 miles
east of Lenoir to near Statesville to 5 miles southwest of
Mocksville, and moving northeast at 15 mph.

Locations to be impacted include...
Hickory, Statesville, Mocksville, Taylorsville, Newton, St. Stephens,
Conover, Longview, Sawmills and Granite Falls.

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...

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.

Frequent lightning is occurring with these storms. If outdoors, try
to get indoors or into a hard topped vehicle. Otherwise, stay away
from open areas and isolated high objects such as trees. When
indoors, stay away from windows and doors and avoid using wired
electronic devices. Do not take a shower or bath. Try to unplug
unnecessary appliances before the storms approach.

&&

LAT...LON 3589 8040 3588 8042 3587 8039 3585 8039
      3585 8042 3583 8043 3583 8046 3584 8047
      3584 8048 3581 8047 3578 8047 3571 8062
      3561 8097 3577 8155 3599 8126 3595 8073
      3596 8038 3589 8037
TIME...MOT...LOC 2259Z 246DEG 14KT 3586 8139 3578 8087 3583 8060

RWH

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
710 PM EDT Sun Jul 18 2021

SCZ009-014-182345-
York SC-Chester SC-
710 PM EDT Sun Jul 18 2021

...A STRONG THUNDERSTORM WILL IMPACT NORTHWESTERN CHESTER AND WESTERN
YORK COUNTIES UNTIL 745 PM EDT...

At 710 PM EDT, Doppler radar was tracking a strong thunderstorm 11
miles southwest of York, or 5 miles south of Sharon, moving northeast
at 15 mph.

Locations to be impacted include...
York, Sharon, Mcconnells, Lowrys and Bullock Creek.

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 3485 8106 3476 8139 3487 8147 3489 8147
      3490 8148 3491 8147 3493 8147 3509 8121
TIME...MOT...LOC 2310Z 241DEG 15KT 3488 8137

RWH

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
839 PM EDT Sun Jul 18 2021

NCZ056-068>070-504-506-508-190115-
Greater Rutherford NC-Gaston NC-Cleveland NC-Lincoln NC-
Greater Burke NC-Eastern McDowell NC-Catawba NC-
839 PM EDT Sun Jul 18 2021

...A CLUSTER OF THUNDERSTORMS WILL IMPACT CATAWBA...SOUTHEASTERN
MCDOWELL...NORTHEASTERN RUTHERFORD...LINCOLN...CLEVELAND...GASTON AND
SOUTHEASTERN BURKE COUNTIES UNTIL 915 PM EDT...

At 838 PM EDT, Doppler radar indicated the leading edge of a cluster
of thunderstorms along a line extending from 12 miles east of Marion
to 7 miles southeast of Morganton to 9 miles southwest of Newton to 6
miles northwest of Gastonia, and moving east at 20 mph.

Locations to be impacted include...
Gastonia, Hickory, Shelby, Newton, Lincolnton, Kings Mountain,
Conover, Cherryville, Bessemer City and South Gastonia.

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...

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 3575 8158 3576 8128 3565 8099 3516 8109
      3522 8132 3527 8166 3545 8174 3561 8195
TIME...MOT...LOC 0038Z 269DEG 18KT 3563 8180 3566 8160 3559 8135 3530
8127

RWH