Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1134 AM 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 early next week before temperatures rebound above normal
late in the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1120 AM EDT Saturday: The upper ridge that has dominated the
region the past few days will become increasingly suppressed through
the near term as an upper trof and associated sfc front approach the
area. This will allow the lingering mid-lvl capping to weaken, which
combined with strong insolation and seasonably high dewpoints will
yield moderate instability across the forecast area through the
afternoon. Meanwhile, some minimal uptick in upper level support is
anticipated by the end of the day as the trough draws nearer.
Scattered convection is forecast to develop across the mountains
during early afternoon, with isolated activity also expected by that
time in the more unstable air mass across the Piedmont, where a cu
field was already bubbling late this morning.

Coverage will steadily increase such that numerous showers and
storms should occur across the mountains and NC foothills, with
scattered convection across the Piedmont. Overall, the severe
potential still looks minimal today, although a few isolated strong
to severe pulse cells are (as usual) possible. Compared to the past
few days, we are expecting more widespread showers/thunderstorms
with training convection and heavy downpours increasing the flash
flooding potential thru the period. As such, WPC continues to carry
a Marginal Risk for excessive rainfall over our higher terrain,
which lines up well with our higher area PoPs and QPF. Temperatures
will be right around normal for mid-July.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 215 am EDT Saturday: The short-term portion of the forecast is
shaping up to be quite active, with abundant moisture in place and
deep-layer forcing crossing the region Sunday through Monday. By
daybreak Sunday, a positive-tilt trough axis will be in the process
of carving out height falls across the Ohio River Valley. Meanwhile,
a leading shortwave rounding the developing trough will cross the
region during the morning hours to possibly provide for ongoing or
early developing showers and thunderstorms in our region well ahead
of the main forcing. In addition, a weak surface cold front will
begin to lay over into the area during the day on Sunday but likely
make only slow progress to the southeast through Monday. By Sunday
night, the main trough axis will have sharpened up just west of the
southern Appalachians before it moves slowly east over the area
through Monday and Monday night. Robust upper-level divergence on
the east side of the trough is indicated in and near the southern
Appalachians Sunday through Sunday night, with another round
possible on Monday. Cloudiness may limit instability somewhat during
peak heating Sunday, but profiles are plenty moist for solid
thunderstorm coverage with precipitable water values 1.5 to 2 inches
across the region. Shear profiles are more questionable, with plenty
of spread in the magnitude of the 850 mb winds as the system crosses
the region. Cannot argue with the SPC general risks at this point,
but a couple of severe thunderstorms seems likely, as does isolated
flooding with any training thunderstorm cells. Coverage should be
best in the mountains on Sunday, but more across the foothills and
Piedmont on Monday as the upper forcing migrates east. Anticipate
maximum temperatures running one to two categories below climo
with all the cloudiness, while minimum temperatures run slightly
above climo.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 230 am EDT Saturday: The location of the main axis of the
eastern trough is uncertain for Tuesday, with the GFS a bit more
progressive than the ECMWF and most ensembles. In addition, the
passing surface boundary will likely be along or near the
southwest fringe of the forecast area, and these two features
will work to keep above-climo PoPs in the forecast - especially
for the south/southeast tier. Modest, slow drying is anticipated
to begin for the northern tier by late Tuesday, but will still
feature continued scattered PoPs there as boundary layer
moisture lingers. Nevertheless, precipitable water values in
profiles should begin to fall from the northwest by late Tuesday
and continue falling Tuesday night into Wednesday.

The next upstream wave dropping south from the eastern Great Lakes
into the eastern trough axis on Wednesday will likely keep most of
the associated dynamics north of the region. However, the stalled
surface front in the vicinity will keep scattered diurnal PoPs
going, especially for southeast sections. Another surface cold front
should arrive with the upper wave by Wednesday night, with the
boundary pushing southeast of the area on Thursday. Despite any
falling thicknesses, better insolation will push maximum
temperatures back up toward climo. Yet another reinforcing system
will sink southward from the Great Lakes on Friday, but continued
good insolation will permit above climo temperatures.

&&

.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and Elsewhere: A few scattered showers continue to move
over far western NC, but elsewhere is dry. Mountain valley fog/
stratus has finally begun to develop, but it's looking less likely
that it will reach/impact KAVL this morning. Some brief patchy fog
could still develop elsewhere, but chances are too low to mention
in TAFs. Overall, the chances for convection are higher today than
yesterday with more forcing and increasing moisture. Have PROB30s
and/or TEMPOs with prevailing showers and VCTS developing during
the afternoon. Winds will continue to favor a SLY to SWLY direction
thru the taf period.

Outlook: An unsettled pattern, with afternoon/evening showers
and thunderstorms and morning fog/low stratus, will persist into
early next week.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High  91%     Med   69%
KHKY       High 100%     High 100%     High 100%     High  83%
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...HG
NEAR TERM...JDL/JPT
SHORT TERM...HG
LONG TERM...HG
AVIATION...JPT

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
425 AM EDT Sat Jul 17 2021

GAZ018-026-028-029-NCZ070>072-082-SCZ004>014-019-180830-
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-
425 AM EDT Sat Jul 17 2021

This Hazardous Weather Outlook is for northeast Georgia, Piedmont
North Carolina including the Charlotte Metro Area, and Upstate South
Carolina.

.DAY ONE...Today and tonight.

Scattered 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. Dangerous cloud-to-ground lightning will be
possible with any thunderstorm as well.

.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>003-180830-
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-
425 AM EDT Sat Jul 17 2021

This Hazardous Weather Outlook is for the mountains of northeast
Georgia, the mountains, foothills, and northwest Piedmont of
western North Carolina, and the mountains of Upstate South Carolina.

.DAY ONE...Today 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.

.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.

HG

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