Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
241 PM EDT Sat Aug 18 2018

.SYNOPSIS...
An upper level trough will persist over the eastern half of the
nation through Tuesday with abundant moisture coming up from the
Gulf. A strong and reinforcing trough will arrive early in the week
creating a greater boost to shower and thunderstorm activity around
Tuesday. The passage of the cold front on Wednesday will bring drier
air to start the second half of the week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 230 PM: A prominent upper trough stretching from Ohio to
Alabama this afternoon will cross the southern Appalachians tonight,
preceded by a few embedded lobes of stronger vorticity. Anticipate
peak right entrance region divergence associated with the upper
jetlet east of the trough to cross the forecast area during peak
heating late this afternoon/early this evening. A couple of rounds
of strong DPVA will pass overhead as well. KGSP radar shows
shower/thunderstorm coverage increasing ahead of the upper support
and anticipate the coverage and strength of the convection to
steadily increase through late afternoon. 850 mb winds will see a
brief uptick to 25 kt later this afternoon but deep layer bulk shear
will remain a modest 20 kt through 6 km. Despite the clouds today,
sbCAPE values have already reached 2500 to 3000 J/kg east of the
mountains and this will produce a marginal threat of severe
thunderstorms - mainly in the form of isolated damaging wind gusts.

Precipitable water values running about two standard deviations
above climo, along with deep warm cloud layers around 12 kft, should
permit very efficient rainfall processes to raise the risk of
isolated flooding from heavy rainfall. However, with 3-hr FFG values
at 3 to 4 inches in most areas, and stream levels not very high, do
not plan on any posting any Flash Flood Watches.

The trough will flatten out tonight with upper forcing diminishing
through Sunday. The trough may push a weak front into the region
from the northwest, but with the thermal contrast getting lost as it
drifts into the heart of the area on Sunday. Will keep mountain
showers going overnight in the persistent, moist southwesterly
upslope flow. Abundant moisture continuing in the profiles, and
especially in the boundary layer, along with the aforementioned weak
boundary, will permit well above climo PoPs again Sunday afternoon,
albeit a category less than today. Maximum temperatures will be very
near climate normals.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 230 PM EDT Saturday: As we begin the work week, the region
will be underneath a stubborn shortwave trough centered over the
Mid-Atlantic, but heights aloft will briefly build during the day
Monday as weak shortwave ridging arrives in the progressive flow.
A surface trough axis will persist and bisect the region on Monday
and should serve as a weak focusing mechanism for afternoon
activity.  There will be some warming and drying aloft due to
ridge-inducing subsidence for Monday, but the warming is not
significant enough to overcome low-level lapse-rates/instability
and the drying will not reduce low-level moisture content (max PW
values remain near 2 inches) as SWly GoMex moisture flux persists.
Therefore, afternoon convective coverage is expected to remain
scattered to numerous from east to west across the area with brief
periods of heavy rainfall possibly persisting just long enough in
isolated areas to cause minor flooding issues. Guidance is bullish
on remnant activity lingering into the overnight hours with the
ample moisture in place for light showers so chance PoPs persist.

The mid-level pattern quickly evolves late Monday into Tuesday
as another, more potent shortwave trough approaches the region.
The trough will be deamplifying as the primary energy lifts NE
into the Great Lakes area, however, an accompanying cold front
will also be approaching the area later Tuesday. The system
should enhance diurnal coverage especially over the mountains,
closer to the front and the support aloft with numerous showers
and storms forecast. The heavy rainfall potential may be
enhanced somewhat by upper-level diffluence ahead of the trough
axis.

The airmass will not change significantly through Tuesday and
with partly to mostly cloudy skies and above-normal precipitation
chances, max temperatures will remain near to perhaps 1-2 degrees
below normal west over the mountains and Foothills and 1-2 degrees
above normal east over the Piedmont.  Low temperatures will remain
2-5 degrees above normal as dewpoints/humidity remain high.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 150 PM EDT Saturday: Starting 00Z Wednesday.  At 00Z Wednesday
the axis of the upper trof is forecast to be from the eastern Great
Lakes to near Atlanta. The dynamics should support at least one or
two severe storms ahead of the approaching cold front Tuesday
evening. The high Precipitable Water values of 2 inches plus will be
moving east but still over CLT area at 00Z Wed. This will support
high rainfall rates in the prefrontal convection.  By Wednesday
morning, the high PWats are moving off the Carolina coast.

One last upper wave crosses on Thursday as the GFS has one big axis
aligned along the Appalachian Chain early Thursday. The air ahead of
this wave is generally dry and supported by cool surface high
pressure. This cooler high pressure transitions across the region
Thursday and Friday then moving off the East Coast Saturday. As this
high moves off the East Coast, low level wind flow will become
southerly again bringing a gradual increase in humidity for next
weekend. As the upper trof moves off the East Coast at the end of
the week, the ridge over the SW and Texas will build east toward the
Carolinas. Temperatures near normal Wednesday dropping to around 5
degrees below normal late in the week.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Showers and thunderstorms continue to slowly
build east of an approaching upper trough axis this afternoon.
Anticipate decent coverage of TSRA by late afternoon to warrant
TEMPO running to near 00Z, with continued showers through late
evening, and possibly overnight near KAVL. Ceilings are expected to
be mainly lower end VFR this afternoon and evening, but possibly
MVFR at times and certainly MVFR or worse in any thunderstorms.
Although the guidance hasn't been very consistent about the low
cloud and fog potential for early Sunday morning, recent history and
the potential for wet ground from the showers suggests that IFR to
MVFR restrictions look to be a good bet for most areas. Anticipate
mainly southwest winds through the period, with afternoon gusts
today during peak heating, except winds turning NW behind a weak
boundary at KAVL Sunday. Showers will start to build again toward
the end of the TAF period, but with less coverage expected Sunday
afternoon than this afternoon.

Outlook: Expect decent coverage of mainly diurnal showers and
thunderstorms from late Sunday through Wednesday. Drier high
pressure may build in behind a passing front on Thursday. Until
then, restrictions are expected mainly during the morning as low
clouds forms, and then under any afternoon/evening showers and
thunderstorms.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High  99%     Med   71%     High  84%
KGSP       High 100%     High 100%     Med   77%     High  90%
KAVL       High  98%     High 100%     Low   59%     High  81%
KHKY       High  80%     High 100%     Med   60%     High  85%
KGMU       High  95%     High 100%     Med   79%     High  93%
KAND       High  90%     High  98%     Med   72%     High  85%

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...DEO
NEAR TERM...HG
SHORT TERM...JMP
LONG TERM...DEO
AVIATION...HG

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
1129 AM EDT Sat Aug 18 2018

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-191530-
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-
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-Chester-Greenwood-
1129 AM EDT Sat Aug 18 2018

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 showers and thunderstorms will develop this
afternoon and linger into the evening hours. Any thunderstorms that
repeatedly affect the same location could generate localized
flooding of streams and creeks, as well as low-lying or poor
drainage areas. In addition, a few thunderstorms could become strong
enough to produce damaging wind gusts and small hail. The highest
chance of severe thunderstorms will be late this afternoon over the
piedmont.

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

On Sunday, thunderstorms will develop once again across the area and
produce high rainfall rates that could lead to localized urban and
small stream flooding. The flooding threat will be highest in and
near the mountains.

.SPOTTER INFORMATION STATEMENT...

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

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
321 PM EDT SAT AUG 18 2018

NCZ068-508-181945-
Greater Rutherford NC-Cleveland NC-
321 PM EDT SAT AUG 18 2018

...A STRONG THUNDERSTORM WILL IMPACT EAST CENTRAL RUTHERFORD AND
CENTRAL CLEVELAND COUNTIES UNTIL 345 PM EDT...

At 320 PM EDT, Doppler radar was tracking a strong thunderstorm 10
miles northeast of Forest City, or near Polkville, moving east at 25
mph.

Locations to be impacted include...
Shelby, Belwood, Lawndale, Fallston, Polkville, Ellenboro, Lattimore,
Waco, Kingstown and Mooresboro.

Wind gusts up to 35 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 3542 8146 3535 8139 3527 8139 3531 8180
      3549 8180 3551 8151
TIME...MOT...LOC 1920Z 269DEG 21KT 3541 8171

ARK