Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
451 PM EDT Sun Aug 6 2017

.SYNOPSIS...
A warm front will move north of the fcst area this evening and
remain north of the area on Monday as low pressure moves from
Texas across the Ohio Valley. The low pressure will move off the
New England Coast and pull the front back over the forecast area
as a cold front on Tuesday. The front is expected to stall again
across our region and remain through the end of the week, with
deep moisture and periods of heavy rain likely.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 450 PM EDT Sunday:  Southerly moisture flux is slowing
getting underway as flow veers and dewpoints increase across the
Midlands/Lakelands.  As such, latest SPC Meso Analysis indicates
an instability axis in association with the old washed out front.
Said instability combined with pockets of H5 vort associated
with the approaching trof look to favor continued development of
shra/tsra along the quasistationary front.  With the front expected
to slowly lift northward with time, pops were adjusted up a bit
along/south of I85 through the evening to favor likely levels
over the Lakelands through the immediate near term, increasing
to likely levels westward across portions of northeast GA, the
western Upstate, and southwest NC.  Otherwise, mid/high chance
pops prevail elsewhere.  Given poor lapse rates and thus weak
instability, think the primary hazard with any of these storms will
be prolonged heavy rainfall that could lead to iso flash flooding,
as well as cloud to ground lightning.

Previous Discussion:  Radar remains clear with a few showers having
popped-up south of the CWA in the last hour.  Main features of
near-term synoptics are the approach of an upper trough and the
advance of surface moisture.  These 2 things should combine for
showers tonight and Monday morning, and thunderstorms Monday
afternoon.

Latest surface analysis has some convective instability over
northeast GA and far western NC, with most better moisture confined
to the south of the CWA.  As poorly defined surface boundary to the
south washes-out this afternoon and a weak surface trough forms
over the mountains, surface winds will become more southerly and
moisture will move northward.  Surface dewpoints are expected to
advance 15 degrees between now and this time on Monday, with PWAT
values doubling from 1 inch now to 2 inches tomorrow.  PVA from an
upper long-wave trough over the Eastern CONUS will also pass over
the area on Monday.  These ingredients will give increasing chances
for rain this evening, with widespread rain and thunderstorms
on Monday.  Heavier rain amounts are expected in the mountains,
but thunderstorms are more likely over the piedmont as instability
will be better to the south.  Despite the advance of moisture,
forecast CAPE is still modest at 500 to 1000 j/kg of MLCAPE Monday
afternoon.  Windshear, however, will be improving with up to 30kts
of 0-1km shear over western NC, which is also an area of low CAPE.
Surface delta-thetae from BUFKIT are also subdued through Monday,
so chances for severe are questionable. A quarter inch to an inch
of rain is anticipated on average with activity on Monday, with a
lot of variability depending on location of convective elements.
As rest of forecast has considerable rain in it, hydro concerns
will increase over time.

High temperatures Monday will be reduced due to extensive cloud
cover and precipitation.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 210 PM Sunday: The broad upper trough over the eastern Conus
will be reinforced early in the period by a short wave digging from
the Ohio Valley through the Mid-Atlantic. Attendant wavy cold front
is expected to be in, or at least just west of the forecast area at
the start of the period, supporting scattered to numerous coverage
of deep convection through Monday night. CAPE and deep-layer shear
are progged to be modest at best by mid-evening. Thus, whatever
severe convective threat exists Monday afternoon should diminish
quickly Monday evening. The front will slowly sag south through the
area on Tuesday, providing a focus for scattered to numerous showers
and thunderstorms. The buoyancy forecast for Tue afternoon is highly
uncertain at this point, as destabilization will be highly dependent
upon the extent of clouds and showers at the start of the day. (And
in fact, model guidance is all over the map regarding CAPE progs).
Therefore, it's about as clear as mud what the extent of any
convective threats will be Tuesday, but very high PWATs and
potential training of showers and storms along the slow-moving
boundary should yield at least a marginal threat of localized flash
flooding.

Abundant moisture remains in place across the area through the end
of the short term period. And although a slight diurnal trend
appears warranted due to the absence of strong forcing, at least
some degree of shower coverage should persist well into Tue night.
By the start of Wednesday, model guidance is in very good agreement
in moving the center of a 1024-ish mb surface high into the upper
Mid-Atlantic, with resultant ridging down the Eastern Seaboard now
expected to push the boundary south of the forecast area by that
time. The result will be a definitively more stable air mass for
Wed. However, guidance tends to develop a moist upslope/upglide flow
above the surface, warranting continued good chances for showers and
perhaps a few thunderstorms through Wednesday. Max temps will be
below normal and mins near to slightly above climo through the
period.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 2 PM EDT Sunday: the extended fcst picks up at 00z on Thursday
with a very broad upper trof centered over Eastern Canada and upper
ridging persisting over the Western CONUS and well to our east over
the sub-tropical Atlantic. A few weak, upper shortwaves will likely
pass over the fcst area early in the period with little change in the
large-scale pattern otherwise. As we move into the weekend, a more
amplified upper trof begins to dig down over the Northern Plains and
Western Great Lakes as the upper ridge persists over the Western CONUS.
At this point, the upper trof axis is not expected to reach our area
until early next week, which is beyond day 7.

At the sfc, a lingering frntl bndy is expected to move back northward
across the CWFA on Thursday as a warm front. Simultaneously, reinforcing
high pressure will be moving offshore putting us back under a moist, SLY
return-flow pattern for the end of the work week and into the weekend.
By the end of the period on Sunday, the models try to develop a low to
our NW and move its associated cold front towards the fcst area, however
it doesn't appear to reach the CWFA until late Sunday/early Monday.
As for the sensible fcst, precip chances will remain elevated thru the
period with high-end chance to low-end likely PoPs each day and broken
to overcast cloud cover thru the period. The potential for isolated to
widespread flooding remains elevated with Precip Water fcst values 1 to
2 standard deviations above normal thru the period. With the ample cloud
cover expected, high temps will start out at least a category below normal
and gradually warm thru the period with values just below climatology
by the end of the period.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
At KCLT and Elsewhere: Currently there is no precip. around the area
with some cells to the south where some instability exists.  Winds
have been variable, but will gradually become more southerly this
evening as a low pressure trough gains some definition over the
mountains.  Once southerly flow commences and an upper trough
approaches the area Monday morning, the chances for precipitation
will increase as, with a good chance for rain Monday morning and
possible thunderstorms Monday afternoon, with a greater chance over
higher terrain.  MVFR CIGS and VIS are anticipated in areas of
rain.  Winds should remain 5 to 10 kts (despite wind shifts) through
Monday morning, after which increasing low pressure over TN will
increase southwesterly flow.

Outlook: The boundary will continue its northward trek through
Monday. Moisture will steadily return over the region. Unsettled
conditions will then set up through most of the week as the boundary
remains nearby, moisture pools overhead, and a series of upper level
waves pass by. Restrictions will be possible with any showers and
thunderstorms. Fog and low clouds may develop each morning around
daybreak, mainly in the mtn valleys but also in areas that receive
heavy rainfall the day before.

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       High 100%     High 100%     High  90%     High 100%
KGSP       High 100%     High 100%     High  93%     High 100%
KAVL       High 100%     High  88%     Low   58%     Low   58%
KHKY       High 100%     High 100%     Low   47%     High  84%
KGMU       High 100%     High 100%     High  93%     High 100%
KAND       High 100%     High 100%     High  84%     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 and ensemble forecasts
are available at the following link:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

SYNOPSIS...JPT
NEAR TERM...CDG/WJM
SHORT TERM...JDL
LONG TERM...JPT
AVIATION...WJM

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
539 PM EDT Sun Aug 6 2017

GAZ010-017-018-026-028-029-NCZ048-051>053-058-059-062>065-SCZ001>014-
019-072145-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Madison-Swain-Haywood-
Buncombe-Graham-Northern Jackson-Macon-Southern Jackson-Transylvania-
Henderson-Oconee Mountains-Pickens Mountains-Greenville Mountains-
Greater Oconee-Greater Pickens-Greater Greenville-Spartanburg-
Cherokee-York-Anderson-Abbeville-Laurens-Union-Chester-Greenwood-
539 PM EDT Sun Aug 6 2017

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

.DAY ONE...Tonight.

Scattered to numerous thunderstorms will continue to develop across
the area through the overnight hours. Any of these storms will be
capable of producing cloud-to-ground lightning and locally heavy
rainfall. However, a couple of the storms may produce severe weather
in the form of damaging wind gusts this evening.

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

..Monday...Heavy rain possible. Scattered thunderstorms are expected
to develop within a very moist subtropical airmass. The potential
exists for these storms to produce torrential rainfall. Furthermore,
some areas may experience multiple rounds of such storms, resulting
in locally significant accumulation.
..Tuesday...No hazardous weather is expected at this time.
..Wednesday...No hazardous weather is expected at this time.
..Thursday...No hazardous weather is expected at this time.
..Friday...No hazardous weather is expected at this time.
..Saturday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

NCZ033-035>037-049-050-056-057-068>072-082-501>510-072145-
Avery-Alexander-Iredell-Davie-Yancey-Mitchell-Catawba-Rowan-
Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union-
Caldwell Mountains-Greater Caldwell-Burke Mountains-Greater Burke-
McDowell Mountains-Eastern McDowell-Rutherford Mountains-
Greater Rutherford-Polk Mountains-Eastern Polk-
539 PM EDT Sun Aug 6 2017

This Hazardous Weather Outlook is for piedmont North Carolina and
western North Carolina.

.DAY ONE...Tonight.

Scattered to numerous thunderstorms will continue to develop across
the area through the overnight hours. Any of these storms will be
capable of producing cloud-to-ground lightning and locally heavy
rainfall.

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

..Monday...Heavy rain possible. Scattered thunderstorms are expected
to develop within a very moist subtropical airmass. The potential
exists for these storms to produce torrential rainfall. Furthermore,
some areas may experience multiple rounds of such storms, resulting
in locally significant accumulation.
..Tuesday...No hazardous weather is expected at this time.
..Wednesday...No hazardous weather is expected at this time.
..Thursday...No hazardous weather is expected at this time.
..Friday...No hazardous weather is expected at this time.
..Saturday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

LANE

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
358 PM EDT SUN AUG 6 2017

SCZ019-062045-
Greenwood SC-
358 PM EDT SUN AUG 6 2017

...THUNDERSTORMS WILL PRODUCE VERY HEAVY RAINFALL OVER EXTREME
SOUTHEASTERN GREENWOOD COUNTY THROUGH 445 PM EDT...

At 354 PM EDT, Doppler radar was tracking a series of thunderstorms
and rain showers repeatedly producing heavy rainfall over
southeastern Greenwood County, generally east of a line from Dyson
to Kirksey. These thunderstorms were moving northeast at 5 to 10
mph, but back-building to the southwest to keep the heavy rainfall
locked in place.

Radar indicated rainfall rates of 1 to 2 inches per hour in the
heaviest downpours. Localized flooding of low-lying and poor
drainage areas will be possible in the vicinity of Kirksey and
Dyson.

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 3398 8205 3398 8211 3420 8193 3418 8192
      3418 8191 3416 8191 3415 8190 3413 8187
      3410 8190 3409 8192 3404 8194 3400 8199
      3397 8201 3395 8205
TIME...MOT...LOC 1954Z 208DEG 9KT 3403 8200

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
646 PM EDT SUN AUG 6 2017

NCZ082-062315-
Union NC-
646 PM EDT SUN AUG 6 2017

...A STRONG THUNDERSTORM WILL IMPACT SOUTHERN UNION COUNTY UNTIL 715
PM EDT...

At 645 PM EDT, Doppler radar was tracking a strong thunderstorm 10
miles northeast of Lancaster, or 8 miles south of Mineral Springs,
moving northeast at 20 mph.

Locations to be impacted include...
Monroe, Wingate, Mineral Springs, Unionville, Indian Trail, Trinity
and Jaars.

Wind gusts up to 40 mph 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 3493 8033 3481 8046 3482 8077 3509 8060
TIME...MOT...LOC 2245Z 216DEG 17KT 3482 8065

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
651 PM EDT SUN AUG 6 2017

SCZ006-010-062315-
Anderson SC-Greater Greenville SC-
651 PM EDT SUN AUG 6 2017

...A STRONG THUNDERSTORM WILL IMPACT SOUTHWESTERN GREENVILLE AND
NORTHEASTERN ANDERSON COUNTIES UNTIL 715 PM EDT...

At 651 PM EDT, Doppler radar was tracking a strong thunderstorm 10
miles northeast of Anderson, or over Williamston. This storm was
moving northeast at 5 to 10 mph.

Locations to be impacted include...
Powdersville, Piedmont, Belton, Williamston, West Pelzer, Donaldson
Center and Fork Shoals.

Wind gusts up to 40 mph and very heavy rainfall rates of 1 to 2
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.

&&

LAT...LON 3461 8263 3482 8249 3466 8228 3450 8246
TIME...MOT...LOC 2251Z 217DEG 3KT 3462 8250

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
713 PM EDT SUN AUG 6 2017

NCZ082-062345-
Union NC-
713 PM EDT SUN AUG 6 2017

...A STRONG THUNDERSTORM WILL IMPACT SOUTHEASTERN UNION COUNTY UNTIL
745 PM EDT...

At 713 PM EDT, Doppler radar was tracking a strong thunderstorm 7
miles southeast of Monroe, or 6 miles south of Wingate, moving
northeast at 20 mph.

Locations to be impacted include...
Monroe, Wingate, Marshville, Sturdivants and Trinity.

Wind gusts up to 40 mph and very heavy rainfall rates of 1 to 2
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.

&&

LAT...LON 3484 8032 3481 8038 3482 8053 3492 8062
      3515 8032 3511 8029
TIME...MOT...LOC 2313Z 235DEG 19KT 3489 8049

HG