Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
456 PM EDT Thu Aug 2 2018

.SYNOPSIS...
A broad area of low pressure will persist across the Tennessee
Valley through at least Friday. This low will transport deep
moisture from the Gulf of Mexico and produce abundant cloud cover
and continued rounds of precipitation, which will hold high
temperatures below normal. A slow increase in temperatures and
decrease in precipitation is expected over the weekend as high
pressure builds back in.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 450 PM EDT Thursday: Mesoscale analysis shows CAPE over 2000
J/kg across much of the Piedmont of the Carolinas this afternoon.
Effective bulk shear is around 25 kts across this same area. A
boundary appears to be developing across the Piedmont as well.
Helicity values are 50 or less however. KGSP and TCLT VWP both show
westerly winds in the low levels just above the surface. This is
keeping the helicity values muted despite the forecast for surface
winds to turn easterly this evening ahead of a mesolow. Of course,
will have to keep an eye on storms through the evening for severe
and flash flooding. Any severe storms should remain isolated given
these conditions unless some organization occurs along the weak
boundary or cold pools. Flash flood threat remains high as the cells
are beginning to line up and training of cells will develop.
However, it's uncertain if the cells train over the exact same
areas. Have updated the forecast for current and expected near term
conditions.

Subtle changes over the next 24 hrs will begin the process of
turning down the precip potential across the fcst area. The strong
southerly moist flow of this afternoon, due to the favorable
position of an upper trof axis over the MS Valley region and an
upper anticyclone over the wrn Atlantic, should weaken on Friday
and become more southwesterly as the trof axis acquires a more
positive tilt. Before we get to that point, we still have the
potential for additional heavy rain this evening and overnight
as a weak sfc wave lifts across the region. Slightly backed low
level flow may bring a bit more upslope flow to bear near the Blue
Ridge Escarpment. Needless to say, the entire Watch will continue,
as will categorical precip probs. The main axis of vorticity will
eject northeast on Friday morning while a jet streak also lifts out
to the northeast during the middle part of the day. The weakening
synoptic support should diminish the potential for additional heavy
rain as we work through the day, with a corresponding decrease
in precip chances from the SW as a dry slot of sorts works in
behind the weak low. There is some concern that flood potential
will linger beyond daybreak Friday across the nrn tier of zones,
so we will extend through the afternoon across the nrn mtns/nrn
foothills/nw Piedmont until 00Z Saturday based on coordination
with neighboring offices.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 230 PM EDT Thursday: A large subtropical ridge over the North
Atlantic will begin to retrograde into the Southeast. This will be
in the wake of the sheared out upper trough that has persisted just
to our west. As this trough lifts north and weakens, it will leave a
stalled front across the area. This front will wash out over the
weekend, but will leave an axis of enhanced RH/PWATS. So we can
expect to see scattered to numerous diurnally forced showers and
tstms both Saturday and Sunday. The sbCAPE will generally max out in
the 1500-2500 J/kg both days with weak bulk shear. As a result, the
storms that develop will be of pulse mode and slow-moving. So there
will be an isolated flash flood threat lingering thru the weekend,
along with the usual pulse downburst threat that we see in the late
summer. Aftn temps will trend warmer each day, as we see heights
rise and less cloud cover across the area. It will also feel more
humid, as dewpts will remain in the upper 60s to lower 70s across the
area. Highs Sunday will return to near normal. Lows both nights will
be near or slightly above normal.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 150 PM EDT Thursday: Starting Sunday evening, The Bermuda high
drifted west to be centered over GA or SC to start this forecast.
Lingering moisture from washed out frontal boundaries remain over
our area. Height falls will begin again over the Ohio Valley Monday
as the next trough drops down in the longwave flow. CAPE values in
the range of 2000 to 2800 over NE GA and southern parts of Upstate.
CAPE values on the GFS forecast to be a bit lower and little more
stable late Tuesday and even more stable late Wednesday. By then,
the weak cold front associated with the shortwave crossing the Ohio
Valley will cross TN and reach our area late Wednesday and be west
to east across NE GA and Upstate early Thursday. PWaT values
forecast to be near 2 inches just south of the front and be slowly
suppressed toward Florida late in the week. Therefore, an increase
in POPs associated with the front in the mountains late Tuesday,
over the forecast area Wednesday and remaining as the front slows
down toward stalling.  By late Thursday night, the front and
associated shortwave will be crossing the mid Mississippi Valley
with impact on our weather the following weekend.  Max Temperatures
around or just above normal Monday and Tuesday, then with increased
cloud cover temps just below normal by Thursday. Min Temps a couple
degrees above due to the clouds cover.

&&

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
At KCLT and Elsewhere: Still a rough go of it today. Plenty of VFR
over the eastern Upstate and western Piedmont of NC outside of deep
convection, so KCLT starts out prevailing VFR. The breaks will allow
for plenty of destabilization, so thunderstorms will become more
numerous as we work into the middle part of the afternoon. Will
keep a four hour window for the late afternoon...then a period of
prevailing thunder into the early evening as the models show the
best coverage. The main band of moisture/light precip is expected
to translate slowly eastward tonight. All sites keep a prevailing
restriction for MVFR based on low ceiling and visibility...then
it goes downhill from there. We have another very good chance
for widespread IFR ceilings developing once again tonight. The
passage of an upper wave in the mid/late morning should begin
the process of bringing some slightly drier air in from the SW,
which should improve flight conditions beginning around 15Z into
the early afternoon. Wind will generally remain southerly and
light outside of stronger storms.

Outlook: A slow improving trend will begin over the weekend, and
coverage of afternoon SHRA/TSRA will slowly decrease through the
beginning of the work week. Associated morning restrictions will
be possible each day, especially across the mountains.

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       High  85%     Med   74%     High  87%     High  93%
KGSP       Med   70%     High  98%     High  86%     High  88%
KAVL       Med   74%     High  90%     High  81%     High  84%
KHKY       Med   73%     High  89%     High  93%     Med   79%
KGMU       Med   66%     High  92%     High  88%     High  88%
KAND       Low   55%     High  96%     High  82%     High  93%

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

&&

.HYDROLOGY...
Through Friday morning, QPF totals range from 2-3: with isolated
4" in the upslope areas. WPC Moderate Risk remains in place for a
good chunk of the area today, and Marginal for Friday. Meanwhile,
as basin-average rainfall amounts increase into tomorrow, mainstem
river flooding becomes a greater possibility, especially in the
climatologically favorable areas of the upper French Broad River,
but rapid response along the lower Tuckasegee, Swannanoa, South Fork
Catawba, and Pigeon River basins is also possible. At this time,
Minor flooding (i.e., flooding of low-lying areas, greenways,
boat-access ramps, recreational areas) is the primary concern.
As always, monitor the latest forecasts and stream levels at:

https:/water.weather.gov/ahps2/index.php?wfo=gsp.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Flash Flood Watch through Friday morning for GAZ010-017-018-
     026-028-029.
NC...Flash Flood Watch through Friday evening for NCZ033-035>037-
     049-050-056-057-072-501>506.
     Flash Flood Watch through Friday morning for NCZ048-051>053-
     058-059-062>065-068>071-082-507>510.
SC...Flash Flood Watch through Friday morning for SCZ001>014-019.

&&

SYNOPSIS...DEO
NEAR TERM...PM/RWH
SHORT TERM...ARK
LONG TERM...DEO
AVIATION...PM
HYDROLOGY...

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
329 PM EDT Thu Aug 2 2018

GAZ010-017-018-026-028-029-NCZ048-051>053-058-059-062>065-068>071-
082-507>510-SCZ001>014-019-031930-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Madison-Swain-Haywood-
Buncombe-Graham-Northern Jackson-Macon-Southern Jackson-Transylvania-
Henderson-Cleveland-Lincoln-Gaston-Mecklenburg-Union-
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-Chester-Greenwood-
329 PM EDT Thu Aug 2 2018

...FLASH FLOOD WATCH IN EFFECT THROUGH FRIDAY MORNING...

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

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flash Flood Watch.

In addition to the flash flood threat, scattered thunderstorms this
afternoon and evening will be capable of dangerous cloud-to-ground
lightning. A couple of the storms could also produce severe weather,
in the form of a brief damaging wind gust, mainly over the Piedmont.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flash Flood Watch.

Even following the end of the Flash Flood Watch Friday morning,
conditions will remain favorable for localized heavy rainfall each
afternoon Friday through Sunday.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to forward any reports of damaging winds or
flash flooding to our office.

NCZ033-035>037-049-050-056-057-072-501>506-031930-
Avery-Alexander-Iredell-Davie-Yancey-Mitchell-Catawba-Rowan-Cabarrus-
Caldwell Mountains-Greater Caldwell-Burke Mountains-Greater Burke-
McDowell Mountains-Eastern McDowell-
329 PM EDT Thu Aug 2 2018

...FLASH FLOOD WATCH IN EFFECT THROUGH FRIDAY EVENING...

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

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flash Flood Watch.

In addition to the flash flood threat, scattered thunderstorms this
afternoon and evening will be capable of dangerous cloud-to-ground
lightning. A couple of the storms could also produce severe weather,
in the form of a brief damaging wind gust, mainly over the Piedmont.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flash Flood Watch.

Even following the end of the Flash Flood Watch Friday morning,
conditions will remain favorable for localized heavy rainfall each
afternoon Friday through Sunday.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to forward any reports of damaging winds or
flash flooding to our office.

ARK

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Special Weather Statement
National Weather Service Greenville-Spartanburg SC
557 PM EDT THU AUG 2 2018

SCZ013-022230-
Union SC-
557 PM EDT THU AUG 2 2018

...THUNDERSTORMS WITH TORRENTIAL RAINFALL WILL IMPACT UNION COUNTY
UNTIL 630 PM EDT...

At 556 PM EDT, Doppler radar was tracking a thunderstorm with
torrential rainfall near Union, or near Buffalo, moving north at 20
mph.

Locations to be impacted include...
Union, Monarch Mill, Buffalo, Jonesville, Rose Hill State Park,
Lockhart, Cross Keys, Sedalia and Adamsburg.

Wind gusts up to 40 mph and very heavy rainfall rates up to 2 inches
per hour will be possible in these areas.

LAT...LON 3460 8185 3485 8177 3491 8171 3490 8165
      3488 8163 3489 8159 3487 8156 3488 8153
      3487 8153 3488 8152 3487 8148 3484 8146
      3482 8149 3481 8147 3477 8145 3473 8149
      3472 8145 3470 8146 3458 8164 3457 8178
TIME...MOT...LOC 2156Z 177DEG 16KT 3474 8166

CSH