Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
241 PM EDT Sat Jul 17 2021

.SYNOPSIS...
An upper-level trough of low pressure, and an associated surface
cold front, will approach from the northwest over the weekend. The
trough and front will slowly settle southeast of the area on Monday,
with modest drying from the north Tuesday through Wednesday.
Increasing clouds will keep maximum temperatures below normal
through Tuesday before temperatures rebound above normal late in the
week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 200 pm Saturday: Isolated to widely scattered convection has
developed across the forecast area this afternoon within an
environment characterized by sbCAPE values in the 2000-3000 J/kg
range. Coverage will continue to expand through the afternoon, with
additional activity possibly pushing into the area from East
Tennessee. Likely to categorical PoPs continue to appear warranted
across mainly the NC mtns and foothills. However, mean cloud-bearing
winds from the SW will carry convection much of this convection away
from the Upstate and northeast Georgia, so a sharp gradient in PoPs
is forecast , such that chances are around 30% in these areas.
Buoyancy is such that a few brief strong to severe pulse storms will
be possible. Perhaps more concerning is that more vigorous cells
have shown a tendency to backbuild, so a locally excessive rainfall
threat certainly appears to be on the table, especially in urban
areas.

While convection will diminish in coverage and intensity this
evening, increasing forcing and deep layer moisture associated with
an approaching region of height falls will warrant maintaining small
chances for convection across roughly the western third of the area
through the night. Min temps will again be a couple of degrees above
climo.

Aforementioned height falls and attendant weak frontal zone will be
the primary influencer of sensible weather across the region on
Sunday. Likely to categorical PoPs will be advertised across the
entire area Sunday afternoon. With the expectation of abundant
mid/high level cloud cover throughout the day, instability is should
be somewhat muted (max temps forecast to be a good 5 degrees below
today's readings...actually a couple of degrees below normal). Thus,
the threat for severe storms appears to be sub-marginal. However,
with PWATs forecast to increase to around 1.8" across much of the
forecast area, and deep SW quasi-unidirectional flow suggesting some
potential for cell training and/or backbuilding, locally excessive
rainfall will remain a concern.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 300 pm EDT Saturday: An active pattern will be in place during
the short term forecast period thanks to a positively tilted trough
tracking across the region. This potent trough will help breakdown
the Bermuda High across the western Atlantic allowing the trough to
become the main influence of the weather pattern. At the start of
the forecast period the cold front associated with the upper trough
will be just to our northwest. Ahead of the front the 850 mb flow
will be southwesterly streaming in plentiful moisture from the Gulf
of Mexico. Model soundings depict profiles gradually moistening
Sunday night into Monday evening. Instability could be limited
somewhat by the amount of cloud cover this cold front will bring
throughout the short term. However, upper level forcing associated
with the trough could lead to isolated strong to severe storms
Sunday evening into Monday. The main impacts with any strong to
severe storm look the be isolated damaging wind gusts and the
potential for isolated flash flooding due to PWATs to ranging from
1.5 to 2.0 inches and the potential for training thunderstorms. WPC
has our CWA in a marginal risk Sunday and Monday for excessive
rainfall. The FROPA should push through the northern zones Sunday
night into Monday before stalling across the northern SC Upstate and
central NC Tuesday. Showers and thunderstorms will remain likely
Sunday evening dropping down to the chance category overnight due to
the diurnal trend. Monday afternoon into Monday evening PoPs will
return to likely for the northern zones and categorical for the
southern zones as the front will be draped across the forecast area.
Monday night into Tuesday PoPs will decrease from north to south as
the front slowly sinks southward. Since the front is expected to
stall across the southern zones on Tuesday, these areas will have a
chance for showers and thunderstorms. The northern zones will only
have a slight chance for showers and thunderstorms as the 850 mb
flow turns more northerly behind the FROPA leading to drier
conditions. Despite the cold front stalling, the upper level trough
will track east of the CWA Tuesday afternoon. In response, PWATs
should gradually decrease from north to south throughout Tuesday.
The cloud cover mentioned above will lead to much cooler and below
normal temps throughout the short term. Highs should range from the
mid 60s to low 80s across the mtns and low to mid 80s outside the
mtns.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 300 pm EDT Saturday: Through much of the extended period the
aforementioned cold front will stall across the southern zones
transitioning into a stationary front. This will keep a slight
chance of showers and thunderstorms around Tuesday night into
Wednesday. Thursday into Friday looks much drier as the 850 mb flow
turns NW'ly, WNW'ly and W'ly. Only slight chance for isolated
diurnal showers and thunderstorms, especially for the western CWA
Thursday and Friday. Sunshine returns for much of the extended
forecast period allowing temps to rebound back to above normal. An
upper level trough looks to approach the region late Friday into
early Saturday bringing another cold front into the forecast area.
This could result in another round of showers and thunderstorms late
next week into next weekend, however capped PoPs at slight chance to
chance due to this system tracking through towards the end of the
period.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
At KCLT and Elsewhere: Convection will continue to increase in
coverage and intensity through the afternoon, with at least
VCSH/VCTS warranted at all sites. The best chances for convection
will exist across western NC, and tempos for TSRA are included at
KAVL/KHKY/KCLT this afternoon/evening. Convection will diminish this
evening, but can't rule out a shower or two wandering near KAVL
tonight, as an upper air disturbance approaches from the northwest.
Despite robust low level moisture, increasing mid and high level
clouds are expected to preclude development of any widespread
overnight/early morning restrictions. However, spotty fog/low
stratus may be seen in locations that see heavy rainfall today
and/or the mountain valleys. Convection will redevelop over the area
Sunday afternoon, with more widespread coverage expected than has
been seen in recent days. SW winds will generally persist in the
5-10 kts range.

Outlook: Active convective weather is expected o continue through at
least Monday, with a steady decrease in activity expected through
the middle of next week. Overnight/early morning fog/low stratus
will be possible each day.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High  95%     High  91%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
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...AP
NEAR TERM...JDL
SHORT TERM...AP
LONG TERM...AP
AVIATION...JDL

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
401 PM EDT Sat Jul 17 2021

GAZ018-026-028-029-NCZ070>072-082-SCZ004>014-019-182015-
Stephens-Franklin-Hart-Elbert-Gaston-Mecklenburg-Cabarrus-Union NC-
Greater Oconee-Greater Pickens-Greater Greenville-Spartanburg-
Cherokee-York-Anderson-Abbeville-Laurens-Union SC-Chester-Greenwood-
401 PM EDT Sat Jul 17 2021

This Hazardous Weather Outlook is for northeast Georgia, Piedmont
North Carolina and Upstate South Carolina.

.DAY ONE...This afternoon and tonight.

Scattered thunderstorms will continue to develop through this
evening. The main threats associated with these storms will be the
potential for heavy downpours, resulting in localized flash flooding
for areas with poor drainage and locations affected by multiple
storms. A stray severe storm or two cannot be ruled out, and even any
non-severe storms will be capable of producing gusty winds and
frequent cloud- to- ground lightning strikes. Storm activity should
diminish after sunset, though showers may continue into the night.

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

Coverage of heavy rain-producing showers and thunderstorms will
increase Sunday through Monday. The isolated flash flooding threat
will gradually increase as earlier storms saturate the ground and set
the stage for possible flooding with any later storms that move over
the same areas.

.SPOTTER INFORMATION STATEMENT...

None.

GAZ010-017-NCZ033-035>037-048>053-056>059-062>065-068-069-501>510-
SCZ001>003-182015-
Rabun-Habersham-Avery-Alexander-Iredell-Davie-Madison-Yancey-
Mitchell-Swain-Haywood-Buncombe-Catawba-Rowan-Graham-
Northern Jackson-Macon-Southern Jackson-Transylvania-Henderson-
Cleveland-Lincoln-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-
401 PM EDT Sat Jul 17 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.

Numerous to widespread thunderstorms will develop this afternoon and
evening. The main threat with the thunderstorms will be the
potential for heavy rainfall to produce isolated flooding in areas
affected by multiple rounds of storms. Any of the thunderstorms may
produce gusty winds, and one or two of the storms could become
severe, with damaging wind gusts the main threat - especially along
and north of Interstate 40 in the Piedmont. Dangerous cloud-to-
ground lightning will be possible with any thunderstorm as well.

Shower and thunderstorm coverage will continue to increase this
afternoon, with coverage becoming widespread by early evening. The
main threat will be heavy rain, leading to a risk for localized flash
flooding, especially for areas affected by multiple rounds of storms
or in areas with poor drainage. A few storms may become severe,
producing damaging winds. The greatest risk for severe storms will be
along the I-40 corridor and points west. Any of these storms will be
capable of producing frequent cloud- to- ground lightning strikes.
Storm activity should decrease after sunset, though scattered showers
may continue into the night.

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

Coverage of heavy rain-producing showers and thunderstorms will
increase Sunday through Monday. The isolated flash flooding threat
will gradually increase as earlier storms saturate the ground and set
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
105 PM EDT Sat Jul 17 2021

NCZ035-056-171730-
Alexander NC-Catawba NC-
105 PM EDT Sat Jul 17 2021

...A STRONG THUNDERSTORM WILL IMPACT NORTH CENTRAL CATAWBA AND
SOUTHERN ALEXANDER COUNTIES UNTIL 130 PM EDT...

At 104 PM EDT, Doppler radar was tracking a strong thunderstorm 5
miles south of Taylorsville, or 5 miles east of Bethlehem, moving
northeast at 20 mph.

Locations to be impacted include...
Taylorsville, Stony Point, Bethlehem, Lake Hickory, Hiddenite,
Millersville and Oxford.

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

LAT...LON 3587 8104 3582 8106 3581 8108 3576 8123
      3582 8130 3595 8112
TIME...MOT...LOC 1704Z 236DEG 16KT 3584 8119

LANE

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
130 PM EDT Sat Jul 17 2021

NCZ035-036-056-171800-
Iredell NC-Alexander NC-Catawba NC-
130 PM EDT Sat Jul 17 2021

...A STRONG THUNDERSTORM WILL IMPACT NORTH CENTRAL CATAWBA...
SOUTHEASTERN ALEXANDER AND WEST CENTRAL IREDELL COUNTIES UNTIL 200 PM
EDT...

At 129 PM EDT, Doppler radar was tracking a strong thunderstorm 6
miles south of Taylorsville, or 5 miles northwest of Lookout Shoals
Lake, moving northeast at 15 mph.

Locations to be impacted include...
Taylorsville, Stony Point, Lookout Shoals Lake, Lake Hickory,
Hiddenite, Millersville, Scotts and Oxford.

Wind gusts up to 50 mph, dime size hail and torrential rainfall rates
up to 3 inches per hour 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.

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 3576 8119 3583 8126 3598 8109 3584 8098
TIME...MOT...LOC 1729Z 237DEG 12KT 3583 8116

LANE

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
221 PM EDT SAT JUL 17 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0140 PM     HAIL             5 ENE ST. STEPHENS      35.80N 81.19W
07/17/2021  E0.75 INCH       CATAWBA            NC   PARK/FOREST SRVC

            SOME DIME SIZED HAIL IN THE RIVERBEND PARK AREA. ALSO HAD
            STRONG WIND BUT NO TREES OR LARGE LIMBS DOWN NEAR THE
            PERSON WHO REPORTED THE HAIL.

&&

OUTLAW

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
401 PM EDT Sat Jul 17 2021

NCZ501>504-172030-
Caldwell Mountains NC-Burke Mountains NC-Greater Burke NC-
Greater Caldwell NC-
401 PM EDT Sat Jul 17 2021

...A STRONG THUNDERSTORM WILL IMPACT WESTERN CALDWELL AND
NORTHWESTERN BURKE COUNTIES UNTIL 430 PM EDT...

At 401 PM EDT, Doppler radar was tracking a strong thunderstorm 12
miles northwest of Morganton, or 4 miles north of Table Rock, moving
northeast at 15 mph.

Locations to be impacted include...
Lenoir, Gamewell, Table Rock, Edgemont, Globe, Collettsville, Upton
and Jonas Ridge.

Wind gusts up to 45 mph and pea size hail will be possible in these
areas.

LAT...LON 3610 8170 3587 8154 3578 8184 3587 8191
      3591 8191 3594 8193 3598 8188 3598 8184
      3596 8181 3607 8174 3608 8173
TIME...MOT...LOC 2001Z 239DEG 11KT 3590 8183

RWH