Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
734 PM EDT Tue Aug 7 2018

.SYNOPSIS...
Weak high pressure will persist over the area into Wednesday. Then
a cold front will approach from the northwest and settle just
southeast of the area by Thursday. Seasonally warm temperatures and
scattered to numerous afternoon and evening showers and
thunderstorms will continue through the end of the week. The front
will persist in the vicinity through the weekend, with deeper
moisture returning from the south.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 4:45p EDT Tuesday:  Updated forecast to account for near term
convective trends.  Activity is fairly widely scattered and has been
declining earlier than usual over the last hour.  Blend of CAMs was
used as basis for POPs in first 6 hours.  Some fairly strong
updrafts have been seen so far this evening, with some continuing
chance for severe hail or wind, especially with cluster moving
southeast out of Pickens/Northern Greenville Counties.

A seasonably weak pressure field exists over the Southeast, with a
lobe of the Bermuda High extending onshore, while a trough extends
down the northern half of the Eastern Seaboard. A corresponding low-
amplitude upper ridge is present overhead, with light southwesterly
winds. Dewpoints remain exceptionally high at many obs sites, in the
lower to mid 70s, but may mix out a bit in the next couple of hours.
As has occurred the past couple of days, SBCAPE values have shot up
past 2500 J/kg, and storms fired over the mountain ridges around
noon.

Flat upper ridging will prevail over the region tonight into
Wednesday. As the upper trough advects east the flow becomes more
zonal, but heights do not fall appreciably across the Carolinas
or north Georgia. Low-level flow thus responds little and remains
west-southwesterly. In advance of the cold front moving thru the
Ohio/Tenn valleys, the trough east of the mountains does become a
bit better defined during the day Wed. Lapse rates manage to improve
a wee bit, and under slightly warmer sfc conditions, SBCAPE values
are progged to be a little higher at peak heating Wed. Given the
trough and better instability, we will advertise likely PoPs over
the mountains and chance values in the Piedmont. Height contours do
become a little better packed aloft tomorrow, and accordingly 0-6km
and 0-3km shear are slightly better. However, those are not strong
enough to suggest a significant enhancement to severe threat beyond
that posed by the large SBCAPE and marginally strong sfc-midlevel
delta-theta-E. Max temps will be normal across most of the area,
but perhaps a category above in the lower Piedmont zones.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 210 pm Tuesday: Broad upper trough will remain in place across
much of the East through the period, with attendant weak frontal
zone and associated deep moisture plume expected to ooze into the
forecast area through the end of the week. As such, very typical
mid-summer weather is expected to end the week, with much of the
area expected to see near-normal temps and near-climo pops for
primarily diurnal convection through the period. A possible
exception to this trend will be the NC mtns, particularly closer to
the TN border, where pops are advertised in the 50-60% range Thu and
Fri afternoon/evening to account for potential impacts from
convection developing along the frontal zone across the TN Valley
and wandering into the southern Appalachians by the end of the day.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 145 PM EDT Tuesday: An upper trough will close off into a low
over the Great Lakes over the weekend. The models are in decent
agreement on the depth and position of the low, but the GFS is just
a little SW of the ECMWF and more elongated N-S. Overall, the
differences do not have much impact on our sensible weather
forecast. A frontal boundary will remain draped across the
Southeast, from the Arklatex region thru the I-85 corridor of the
Carolinas. This should be a focus for enhanced convective coverage
thru the weekend, still mostly diurnally driven. The upper low will
quickly pivot NE and allow another front to drop in from the NW.
This front should push thru by Tuesday and bring some drier air into
the CWFA. The highest PoPs look to be Sunday and Monday, with
possibly a dry day on Tuesday. Temps will be near to slightly below
normal for afternoon highs, but still above normal for overnight
lows due to the expected enhanced moisture across the area. The 12z
Guidance doesn't seem to be hinting at much of a widespread heavy
rain threat. Although, isolated excessive rainfall/flooding will be
possible thanks to our we antecedent conditions.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere:  Showers have mostly ended this evening with
only a few widely scatter showers remaining that are unlikely to
directly impact a TAF site.  Chances for thunderstorms go up again
Wednesday afternoon in the same diurnal pattern with initiation over
higher terrain and southeastward movement into piedmont areas.  CAMs
produce more coverage in afternoon thunder on Wednesday, and have
included a PROB30 for each TAF site as a result.  Morning fog is
also expected to follow recent patterns, with IFR possible for a few
hours in mountain valleys and areas prone to fog (as KAVL).  Surface
winds also increase slightly with less VRB and more prevailing
southwesterly flow of around 5 kts.

Outlook: Typical mid-summer conditions are fcst the next several
days. Diurnal, scattered thunderstorms will continue mainly
in the afternoons, with coverage tending to increase toward the
weekend. Associated morning restrictions will be possible each day,
especially in mountain valleys.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High  83%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High  83%     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...ARK
NEAR TERM...Wimberley/WJM
SHORT TERM...JDL
LONG TERM...ARK
AVIATION...WJM

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
529 PM EDT Tue Aug 7 2018

NCZ033-048>053-058-059-062>065-501-503-505-507-509-082130-
Avery-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-Graham-
Northern Jackson-Macon-Southern Jackson-Transylvania-Henderson-
Caldwell Mountains-Burke Mountains-McDowell Mountains-
Rutherford Mountains-Polk Mountains-
529 PM EDT Tue Aug 7 2018

This Hazardous Weather Outlook is for western North Carolina.

.DAY ONE...Tonight.

Isolated to widely scattered thunderstorms will continue across the
mountains into the evening. Any of these thunderstorms may produce
cloud-to-ground lightning, locally heavy rainfall, and briefly gusty
winds.

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

Thunderstorm coverage will increase from Wednesday onward,
especially during the afternoon and evening periods. Primary impacts
will include cloud-to-ground lightning, heavy rainfall, and gusty
winds.

.SPOTTER INFORMATION STATEMENT...

None.

GAZ010-017-018-026-028-029-NCZ035>037-056-057-068>072-082-502-504-
506-508-510-SCZ001>014-019-082130-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Alexander-Iredell-
Davie-Catawba-Rowan-Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-
Union-Greater Caldwell-Greater Burke-Eastern McDowell-
Greater Rutherford-Eastern Polk-Oconee Mountains-Pickens Mountains-
Greenville Mountains-Greater Oconee-Greater Pickens-
Greater Greenville-Spartanburg-Cherokee-York-Anderson-Abbeville-
Laurens-Chester-Greenwood-
529 PM EDT Tue Aug 7 2018

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

.DAY ONE...Tonight.

Isolated to widely scattered thunderstorms will continue across the
Piedmont and foothills into the evening. While the main threats will
be from cloud-to-ground lightning and locally heavy rainfall, one or
two storms could produce brief severe weather in the form of
damaging winds.

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

Thunderstorm coverage will increase from Wednesday onward,
especially during the afternoon and evening periods. The main
impacts will include cloud-to-ground lightning, heavy rainfall, and
gusty winds.

Heat Index values of 95 to 100 will be likely once again on
Wednesday and Thursday. A few lower piedmont locations may see
values as high as 102 on Wednesday afternoon.

.SPOTTER INFORMATION STATEMENT...

None.

Lane

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
511 PM EDT TUE AUG 7 2018

GAZ010-SCZ001-004-005-072145-
Rabun GA-Greater Pickens SC-Greater Oconee SC-Oconee Mountains SC-
511 PM EDT TUE AUG 7 2018

...STRONG THUNDERSTORMS WITH INTENSE LIGHTNING WILL IMPACT
SOUTHWESTERN RABUN...SOUTHERN PICKENS AND OCONEE COUNTIES UNTIL 545
PM EDT...

At 511 PM EDT, Doppler radar indicated strong thunderstorms with
intense lightning along a line extending from 8 miles north of Seneca
to 3 miles southwest of Walhalla to 9 miles north of Toccoa, and
moving east at 15 mph.

Locations to be impacted include...
Clemson, Seneca, Walhalla, Easley, Central, Liberty, Westminster,
Norris, Six Mile and Lake Rabun.

In addition to intense lightning, wind gusts up to 45 mph and pea
size hail will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent lightning is occurring with these storms. If outdoors, try
to get indoors or into a hard topped vehicle. Otherwise, stay away
from open areas and isolated high objects such as trees. When
indoors, stay away from windows and doors and avoid using wired
electronic devices. Do not take a shower or bath. Try to unplug
unnecessary appliances before the storms approach.

&&

LAT...LON 3485 8294 3485 8290 3481 8290 3484 8284
      3480 8252 3468 8278 3463 8283 3455 8311
      3458 8316 3461 8316 3461 8322 3468 8334
      3473 8338 3473 8341 3475 8343 3474 8345
      3480 8356
TIME...MOT...LOC 2111Z 286DEG 15KT 3481 8295 3473 8310 3472 8338

RWH

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Special Weather Statement
National Weather Service Greenville-Spartanburg SC
651 PM EDT TUE AUG 7 2018

GAZ017-018-072315-
Stephens GA-Habersham GA-
651 PM EDT TUE AUG 7 2018

...A CLUSTER OF THUNDERSTORMS WITH INTENSE LIGHTNING WILL IMPACT
STEPHENS AND HABERSHAM COUNTIES UNTIL 715 PM EDT...

At 651 PM EDT, Doppler radar indicated the leading edge of a cluster
of thunderstorms with intense lightning along a line extending from 6
miles northeast of Cleveland to near Clarkesville to 5 miles
northwest of Toccoa, and moving east at 10 mph.

Locations to be impacted include...
Toccoa, Clarkesville, Cornelia, Baldwin, Demorest, Mount Airy, Alto,
Batesville, Turnerville and Hollywood.

In addition to intense lightning, wind gusts up to 45 mph and pea
size hail will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent lightning is occurring with these storms. If outdoors, try
to get indoors or into a hard topped vehicle. Otherwise, stay away
from open areas and isolated high objects such as trees. When
indoors, stay away from windows and doors and avoid using wired
electronic devices. Do not take a shower or bath. Try to unplug
unnecessary appliances before the storms approach.

&&

LAT...LON 3454 8362 3460 8365 3462 8364 3465 8366
      3473 8362 3476 8363 3478 8365 3481 8360
      3479 8356 3476 8356 3474 8353 3473 8349
      3473 8346 3454 8311 3447 8334 3446 8340
      3449 8354 3446 8358 3446 8361 3451 8367
TIME...MOT...LOC 2251Z 248DEG 11KT 3467 8370 3461 8352 3463 8341

RWH