Severe Thunderstorm Warning 189, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1039 AM EDT Sat Jul 15 2017

.SYNOPSIS...
Hot and humid conditions will persist through the weekend, with
scattered to numerous afternoon and evening thunderstorms each day.
A cold front will move into the region from the northwest on
Saturday and stall in or near the area through Sunday. Another cold
front will approach on Monday and move southeast of the area on
Tuesday, with drier and warmer conditions arriving by the middle of
next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1030 AM EDT Saturday: Morning update is mainly to increase
mixing of dewpoints in southern zones and delay onset of precip
across the Upstate, with a few other adjustments in pops through the
afternoon but overall trends are fairly similar. We remain in
Marginal Risk for Day1 but dCAPEs aren't really all that impressive
today, nothing like yesterday, so we'll see how this plays out with
the front working into the area.

Otherwise, a sharp upper trough is working its way from the Great
Lakes to the Mid-South, with upper ridging over the Southeast and
Carolina coasts. The attendant front is draped down the Ohio Valley,
with lee troughing in place across the western Carolinas, as it
pushes through the area today. As the front moves through, we should
see an increase in convective coverage today across the fcst area,
with the Day 2 Marginal Risk covering almost the entire CWFA, with
sbCAPEs progged between 1500-2000 J/kg, limited by increasing cloud
cover. Severe threat is mainly a low-end wind threat with the steep
low-level lapse rates, but some larger hail cannot be ruled out.
Temperatures won't respond much to the fropa, and should rise again
to normal levels today with the continued low-level WAA to our south.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 300 am Saturday: The upper trough will persist across the East
through the period, with the axis of the trough expected to
oscillate over and east of our forecast area in response to short
wave activity. On Sunday, the deep moisture and effective surface
boundary are expected to be east through south of the area.
Nevertheless, the lack of any substantial moisture gradient along
the boundary will result in plenty of instability developing across
the forecast area by Sunday afternoon. In fact, forecast soundings
depict some rather robust buoyancy and downdraft potential energy
Sunday afternoon. While there will be a pronounced forecast pop
gradient (from 20% across the extreme north to 50-60% nearer the
boundary across the southeast zones), diurnal convection will be
possible in all areas, especially from the southern Blue Ridge
escarpment and points southeast. Isolated pulse severe convection
will be possible, if not likely, especially in the form of
microbursts.

By Monday, the upper trough axis is expected to retrograde into our
area, as a short wave digs from the Ohio Valley into the southern
Appalachians. This feature and its attendant weak surface boundary
should support another day of above-normal coverage of pm
convection, with all areas receiving 40-60% chances. Slight
improvement in wind shear values resulting from the increasing
height gradient (esp in the lowest 3km) could support more in the
way of small scale organization/clustering Monday afternoon,
possibly increasing the overall coverage above what is reflected in
the current pop, and also increasing the potential for strong cold
pools/damaging microbursts. Underneath the influence of the upper
trough, max temps are expected to be slightly below normal through
the period, while persistently high dewpoints should support normal
to slightly above normal mins.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 315 am Saturday: As an anomalously strong upper high/ridge over
the central Conus starts nosing its way into the East, the medium
range will see steadily rising heights, with the upper trough
gradually weakening/getting squeezed...eventually evolving into a
weak upper low across the Southeast. For our area, this will spell
increasing temps, which are expected to return to above normal
(i.e., the mid/upper 90s across much of the Piedmont and foothills)
by the end of the period. Coverage of diurnal convection is also
expected to gradually diminish through the period, with daily
coverage expected to be around to slightly less than normal through
the period.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and Elsewhere: Winds have veered at KCLT so have
adjusted the 15z KCLT AMD to start WNW winds. Also adjusted TSRA
timing to 19z based on latest CAM guidance. Otherwise, expect mostly
VFR conditions thru the 12z TAF period with some brief IFR visby and
cigs likely at KAVL again tomorrow morning. More widespread
convection is anticipated this afternoon/evening, as a cold front
pushes into the fcst area from the northwest. VCTS and/or prevailing
TSRA will be carried from roughly 20z to 00z at all sites with
PROB30 for lingering convection for another 4 to 6 hours after that.
Winds will go from mostly SWLY this morning to more WLY this
afternoon, except at KAVL which is expected to maintain more of a
NWLY direction thru the period.

Outlook: Scattered to numerous afternoon and evening thunderstorms
are expected each day through Monday across the area, with higher
coverage in the mountains. Morning fog development can be expected
in the mountain valleys and in areas that receive rainfall the
previous afternoon/evening.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  95%     High 100%     High  95%     Med   79%
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...JPT/TDP
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...JPT/TDP

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
507 AM EDT Sat Jul 15 2017

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-160915-
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-
507 AM EDT Sat Jul 15 2017

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

.DAY ONE...Today and Tonight.

Scattered to numerous thunderstorms are expected to develop over the
area this afternoon and evening. A few of the storms are expected to
become briefly severe, with damaging downburst winds being the main
threat, although hail to the size of quarters could also occur.
Locally heavy rainfall and frequent cloud to ground lightning can
occur with any thunderstorm.

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

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

.SPOTTER INFORMATION STATEMENT...

None.

LANE

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1256 PM EDT SAT JUL 15 2017

NCZ064-065-507-509-510-SCZ003-151745-
Transylvania NC-Henderson NC-Polk Mountains NC-
Rutherford Mountains NC-Eastern Polk NC-Greenville Mountains SC-
1256 PM EDT SAT JUL 15 2017

...A STRONG THUNDERSTORM WILL IMPACT NORTHEASTERN TRANSYLVANIA...
HENDERSON...WESTERN POLK AND NORTH CENTRAL GREENVILLE COUNTIES UNTIL
145 PM EDT...

At 1255 PM EDT, Doppler radar was tracking a strong thunderstorm 7
miles south of Hendersonville, or near Flat Rock, moving east at 20
mph.

Locations to be impacted include...
Hendersonville, Brevard, Columbus, Mills River, Flat Rock, Etowah,
Mountain Home, Laurel Park, Tryon and Saluda.

Wind gusts up to 45 mph, half inch hail and very heavy rainfall rates
up to 2 inches per hour will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

The combination of gusty winds and saturated soil conditions will
cause scattered trees and power lines to fall. Seek shelter inside an
interior room.

This storm may intensify, so be certain to monitor local radio and tv
stations, as well as local cable tv outlets for additional
information and possible warnings from the National Weather Service.

&&

LAT...LON 3520 8219 3519 8222 3514 8222 3512 8262
      3514 8276 3534 8282 3538 8279 3541 8274
      3545 8226
TIME...MOT...LOC 1655Z 265DEG 17KT 3522 8243

CARROLL