Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1059 AM EDT Tue Jun 13 2017

.SYNOPSIS...
Subtropical high pressure centered to our east will weaken through
mid week, allowing deeper moisture to spread over the forecast area
from the south. As it does, the chances for showers and
thunderstorms will increase each day through the work week, with
chances remaining elevated through the weekend. A cold front is
expected to approach the area early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
1045 AM Update: The lee trough that spawned the early morning
showers north of Charlotte extends southwest to near Greenville
attm. This had initially created a patch of stratocu that is now
dissipating with diurnal warming. A few towering cu are seen
across the foothills N and NE of GSP, with one radar echo now
seen as well. Interestingly HRRR has been doing nothing with this
activity, instead keying on the mountain ridges (a few stronger cu
are also forming there). Updated PoPs thru the aftn are initially
a bit higher along the I-85 corridor and points just N due to this
observed activity, though overall the best chances still are over
the mountains. Updated temp trends partially take into account
cool outflow spreading into the upper Piedmont as depicted by RAP.

Otherwise: A broad upper ridge continues to dominate the Southeast
this morning, however showing signs of weakening as expected,
while a Bermuda oriented surface high controls the flow down
low. Moisture advection over the last few days has allowed for
surface Tds to reach into the mid/upper 60s this morning, with Ts
holding in the upper 60s to lower 70s across much of the region.
Given expected/further weakening of the upper ridge axis, this
increased BL moisture will provide more favorable profiles for
convection than days past.  With that, NAM soundings exhibit
higher LFCs than yesterday as well as sbcapes in 1500j/kg range
this afternoon. CAM guidance favors spreading of mtn convection
along outflows into the Fthills/Piedmont of western NC as well as
the SC Upstate and northeast GA by late afternoon into the early
evening hours.  Therefore pops have increased to include high
chance to low likely levels atop the high terrain of NC/GA/SC,
tapering to mid/high chances eastward into the I77/I85 corridors.
With surface temps expected to reach into the upper 80s to near 90
yet again today, think this combined with ample mixing will yield
higher LFCs than yesterday presenting more favorable conditions for
modest dcape and thus downburst potential.  Therefore, although
widespread svr storms are not expected, wouldn't be suprised to
see a few reaching svr limits today with damaging downburst winds
and large hail being the primary threats.  Weak steering flow will
also likely result in slow storm motions, therefore brief heavy
downpours are also certainly possible.  Pops will taper regionwide
into the overnight hours as heating is lost.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 310 am Tuesday:  Increasing moisture and suppression of the
surface ridge associated with the Bermuda high to our southeast
should result in higher CAPE values across the Piedmont Wed
afternoon. Continued poor lapse rates will limit the extremity of
the buoyancy, but sbCAPE values of around 2000 J/kg appear likely
Wed afternoon. Short term guidance depicts better definition of a
lee side/thermal trough, and this along with terrain effects should
initiate convection across the area by mid-afternoon. Cells and
attendant outflow boundaries should subsequently propagate toward
the SE throughout the remainder of the afternoon and early evening,
warranting 50-60 pops across the mtns and foothills, and 30-40
across the Piedmont. The increased buoyancy will support a slightly
better probability of a few pulse severe storms, especially with any
cell mergers that occur.

The trend of a daily increase in diurnal convective chances
continues into Thursday, as thermal trough remains in place, while
the wind shift associated with a back door cold front moving south
across the Mid-Atlantic Piedmont could make its way into our
northern zones Thu afternoon, providing an additional source of low
level convergence. The synoptic pattern may also become more
supportive of convection by the end of the day, as heights fall
across the region in response to a short wave trough digging
southeast from the Ohio Valley. Likely pops will be focused across
all of western NC into the GA/SC mtns. Shear will remain weak and
instability moderate, so the severe storm threat will continue to be
limited to perhaps a handful of pulse severe updrafts.

The upper air pattern and increasing moisture content should support
at least isolated convection continuing into the overnight hours Thu
night/early Friday. Concerns for heavy rainfall/localized flash
flooding may increase by the end of the period after a couple of
afternoons of solid coverage of slow-moving showers and storms. This
will especially be the case of the leading edge of the back door
cold front pushes into our area as some guidance is suggesting,
which would seem to create a ripe situation for cell training.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 330 am Tuesday: The convectively active pattern should
continue through the medium range, as a mid-level shear axis is
progged to become established from the Deep South into the Tennessee
Valley early in the period, with resultant deep SW flow maintaining
plenty of heat and humidity across the western Carolinas and
northeast GA. This supports above-climo pops for afternoon/evening
convection Fri through Sunday.

By early next week, the global models indicate a strong short wave
will carve out an anomalously deep trough across the eastern Conus,
perhaps driving a more significant surface boundary across our
region on Monday. Thus, another day of solid chance to likely pops
is advertised for Monday, while there may be a better chance for
increased wind shear/organized convection as the height gradient
increases across the East. Max temps will be near to a category or
so above climo, while mins should be a solid 5 degrees warmer than
normal through the period. The good news is that some relief from
the active convective and hot/humid weather could be in the works
after Day 7.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
At KCLT/KHKY:  VFR expected through the period with the exception
of MVFR visb/cig restrictions by way of afternoon convection today,
as well as the possibility of ground fog at KHKY Wednesday morning.
Low/mid level debris clouds highlight the skies this morning
amidst weak sly sfc flow.  Deep layer ridging will weaken with
time as llv moisture continues to increase thanks to the flow
around the Bermuda high over the Atl.  With that, guidance favors
improved lapse rates today with weaker CIN to the east across
the NC Piedmont.  Thus, amending for TEMPO TSRA during peak
heating with MVFR stratocu mentioned amidst prevailing low VFR
cu; timing has been refined per consensus of recent HRRR runs.
Conditions will improve gradually into the early evening hours
with loss of heating, thus all wx was removed beyond 02-03z.

Elsewhere: Pattern very similar to that of KCLT above.  Mostly VFR
through the period aside for restrictions at MVFR levels associated
with afternoon/evening convection. Taf tsra timing was again based
on CAM guidance which favored early afternoon initiation across the
mtns to affect KAVL, then spreading east/southeast into the Upstate
to affect the SC sites by mid/late afternoon.  Prob30s remain in
all tafs with lengthy timing given slow nocturnal stabilization
this evening.  Did also include mention of MVFR fog at all sites
on Wednesday morning as any locales that receive precipitation
will likely be most susceptible to such.

Outlook: Improving boundary layer moisture combined with a weakening
upper ridge will lead to increasing chances for SHRA/TSRA each
day this week. Morning visibility restriction chances will also
increase, mainly in the mountain valleys, but also possible outside
of the mtns where any precipitation has recently occurred.

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%     Med   66%
KAVL       High 100%     High 100%     High 100%     High  97%
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 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...JDL
NEAR TERM...CDG/Wimberley
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...CDG/Wimberley

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
449 AM EDT Tue Jun 13 2017

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-140900-
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-
449 AM EDT Tue Jun 13 2017

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

.DAY ONE...Today and Tonight.

Isolated to scattered thunderstorms are expected to develop across
the area this afternoon into the evening. While the main threats will
be from cloud to ground lightning and locally heavy rainfall, a few
of the storms could produce brief severe weather in the form of
damaging wind gusts and hail to the size of quarters.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

..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.
..Sunday...No hazardous weather is expected at this time.
..Monday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

LANE

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Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1249 PM EDT TUE JUN 13 2017

NCZ063-064-131745-
Transylvania NC-Southern Jackson NC-
1249 PM EDT TUE JUN 13 2017

...THUNDERSTORMS WITH TORRENTIAL RAINFALL WILL IMPACT TRANSYLVANIA
AND SOUTHEASTERN JACKSON COUNTIES UNTIL 145 PM EDT...

At 1248 PM EDT, Doppler radar indicated slowly-moving thunderstorms
with torrential rainfall along a line extending from 4 miles west of
Brevard to 14 miles southeast of Franklin, and moving south at 10
mph.

Locations to be impacted include...
Brevard, Rosman, Cashiers, Lake Toxaway, Looking Glass, Gorges State
Park, Highlands, Balsam Grove, Connestee and Whiteside Mountain.

Very heavy rainfall rates of 1 to 2 inches per hour will be possible
in these areas. Low-lying and poor drainage areas may flood as a
result.

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. Do not drive across
flooded roads.

&&

LAT...LON 3512 8318 3533 8275 3513 8264 3512 8266
      3513 8268 3510 8270 3509 8273 3508 8275
      3507 8275 3507 8278 3509 8279 3500 8311
      3502 8313 3504 8313 3506 8317 3507 8317
      3508 8314
TIME...MOT...LOC 1648Z 348DEG 8KT 3524 8282 3508 8316

HG