Alert archive / South Carolina / Severe Thunderstorm Warnings in 2017

Severe Thunderstorm Warning 274, NWS Greenville-Spartanburg, SC

September 20, 2017Oconee County, Pickens County, South Carolina; Transylvania County, North Carolina

NWS Greenville-Spartanburg, SC issued this severe thunderstorm warning at Sep 20, 2017, 4:59 PM EDT for Oconee County, Pickens County, South Carolina; Transylvania County, North Carolina. It was in force for 46 min. 2 reports came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued
Sep 20, 2017, 4:59 PM EDT (20:59 UTC)
Expired
Sep 20, 2017, 5:45 PM EDT
In force
46 min
Issued by
NWS Greenville-Spartanburg, SC
Area
Storm-based polygon
Hail
1.0 in
Wind
60.0 mph

Counties Transylvania County, NC, Oconee County, SC, Pickens County, SC

The radar

The Greer radar (KGSP), 77 km from the middle of the area, began a volume at 21:01 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

What was reported inside it

TimeReportWhereRemark
Sep 20, 5:30 PM EDTHAIL 0.58 Se Cashiers, SCBAD CREEK HYDRO REPORTED DIME SIZED HAIL.
Sep 20, 5:35 PM EDTTSTM WND DMG3 Nnw Salem, SCTREE DOWN ON RIDGE RD. TIME ESTIMATED FROM RADAR.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

Did it verify

Verified. The Iowa Environmental Mesonet's Cow matched 2 storm reports to this severe thunderstorm warning; the first came 4 minutes after it went out.

Cow counts a report within 15 km of the polygon while the warning was in force: a tornado for a tornado warning; hail of 1 inch or more, a gust of 58 mph or more or wind damage for a severe thunderstorm warning; a flash flood report for a flash flood warning.

The nearest sounding before it

Peachtre/Fal Fld, GA (KFFC), launched 12:00Z, 9.0 hours before the alert went out and 225 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-pSkew-T log-p diagram, Peachtre/Fal Fld, GA at 12:00Z on 2017-09-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 277 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Peachtre/Fal Fld, GA at 12:00Z on 2017-09-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 20 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
277 J/kg
Mixed-layer CIN
-85 J/kg
Mixed-layer LCL
1236 m above ground
0-6 km bulk shear
27 kt
0-1 km storm-relative helicity
20 m²/s²
0-3 km storm-relative helicity
33 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.1

Open this sounding in Storm Lab

The text

As transmitted.

871 
WUUS52 KGSP 202059
SVRGSP
NCC175-SCC073-077-202145-
/O.NEW.KGSP.SV.W.0274.170920T2059Z-170920T2145Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Greenville-Spartanburg SC
459 PM EDT WED SEP 20 2017

The National Weather Service in Greenville-Spartanburg has issued a

* Severe Thunderstorm Warning for...
  Southwestern Transylvania County in western North Carolina...
  Northwestern Pickens County in Upstate South Carolina...
  Northeastern Oconee County in Upstate South Carolina...

* Until 545 PM EDT

* At 457 PM EDT, a severe thunderstorm was located 17 miles north of 
  Walhalla, or 6 miles southeast of Cashiers, and was moving south 
  at 5 to 10 mph. Another severe thunderstorm cell was developing 
  over northwestern Pickens County, South Carolina, west of Rocky 
  Bottom, also drifting to the South.

  HAZARD...60 mph wind gusts and quarter size hail. 

  SOURCE...Radar indicated. 

  IMPACT...Minor hail damage to vehicles is expected. Expect wind 
           damage to trees and power lines. 

* Locations impacted include...
  Devils Fork State Park, Gorges State Park, Jocassee Gorges, Lake
  Jocassee, Bad Creek, Sapphire and Lake Keowee.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Scattered trees and power lines will be blown down in the warned
area. Seek shelter inside an interior room.

Lake Jocassee is in the path of this storm. Get away from the water 
and seek shelter in an interior room in the nearest shelter. If you 
can hear thunder, you are close enough to be struck by lightning.

Please report damaging winds, hail, or flooding to the National
Weather Service Greenville-Spartanburg by calling toll free, 1, 800,
2 6 7, 8 1 0 1, or by posting on our Facebook page, or Tweet it using
hashtag nwsgsp. Your message should describe the event and the
specific location where it occurred.

&&

LAT...LON 3494 8313 3494 8311 3495 8313 3496 8312
      3497 8312 3499 8310 3500 8310 3503 8301
      3505 8306 3508 8304 3509 8303 3511 8296
      3510 8283 3495 8282 3491 8315
TIME...MOT...LOC 2057Z 002DEG 4KT 3502 8304 

HAIL...1.00IN
WIND...60MPH
 
$$

MOORE
2 follow-up statements
766 
WWUS52 KGSP 202120
SVSGSP

Severe Weather Statement
National Weather Service Greenville-Spartanburg SC
520 PM EDT WED SEP 20 2017

NCC175-202129-
/O.CAN.KGSP.SV.W.0274.000000T0000Z-170920T2145Z/
Transylvania NC-
520 PM EDT WED SEP 20 2017

...THE SEVERE THUNDERSTORM WARNING FOR SOUTHWESTERN TRANSYLVANIA
COUNTY IS CANCELLED...

The storms which prompted the warning have moved out of the warned 
area. Therefore, the warning has been cancelled.

LAT...LON 3494 8313 3494 8311 3495 8313 3496 8312
      3497 8312 3499 8310 3500 8310 3503 8300
      3504 8294 3502 8283 3495 8282 3491 8315
TIME...MOT...LOC 2119Z 338DEG 6KT 3498 8293 3497 8307 

$$

SCC073-077-202145-
/O.CON.KGSP.SV.W.0274.000000T0000Z-170920T2145Z/
Pickens SC-Oconee SC-
520 PM EDT WED SEP 20 2017

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 545 PM EDT
FOR NORTHWESTERN PICKENS AND NORTHEASTERN OCONEE COUNTIES...

At 519 PM EDT, severe thunderstorms were located along a line
extending from 14 miles northwest of Pickens to 13 miles north of
Walhalla, moving south at 5 to 10 mph.

HAZARD...60 mph wind gusts and quarter size hail. 

SOURCE...Radar indicated. 

IMPACT...Minor hail damage to vehicles is expected. Expect wind 
         damage to trees and power lines. 

Locations impacted include...
Jocassee Gorges, Devils Fork State Park, Lake Jocassee, Bad Creek and
Lake Keowee.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Scattered trees and power lines will be blown down in the warned
area. Seek shelter inside an interior room.

Lake Jocassee is in the path of these storms. Get away from the 
water and seek shelter in an interior room in the nearest shelter. 
If you can hear thunder, you are close enough to be struck by 
lightning.

Please report damaging winds, hail, or flooding to the National
Weather Service Greenville-Spartanburg by calling toll free, 1, 800,
2 6 7, 8 1 0 1, or by posting on our Facebook page, or Tweet it using
hashtag nwsgsp. Your message should describe the event and the
specific location where it occurred.

&&

LAT...LON 3494 8313 3494 8311 3495 8313 3496 8312
      3497 8312 3499 8310 3500 8310 3503 8300
      3504 8294 3502 8283 3495 8282 3491 8315
TIME...MOT...LOC 2119Z 338DEG 6KT 3498 8293 3497 8307 

HAIL...1.00IN
WIND...60MPH
 
$$

MOORE
581 
WWUS52 KGSP 202139
SVSGSP

Severe Weather Statement
National Weather Service Greenville-Spartanburg SC
539 PM EDT WED SEP 20 2017

SCC073-077-202149-
/O.EXP.KGSP.SV.W.0274.000000T0000Z-170920T2145Z/
Pickens SC-Oconee SC-
539 PM EDT WED SEP 20 2017

...THE SEVERE THUNDERSTORM WARNING FOR NORTHWESTERN PICKENS AND
NORTHEASTERN OCONEE COUNTIES WILL EXPIRE AT 545 PM EDT...
    
The storms which prompted the warning have weakened below severe
limits, and have exited the warned area. Therefore the warning will
be allowed to expire.

LAT...LON 3494 8313 3494 8311 3495 8313 3496 8312
      3497 8312 3499 8310 3500 8310 3503 8300
      3504 8294 3502 8283 3495 8282 3491 8315
TIME...MOT...LOC 2139Z 002DEG 4KT 3496 8293 3495 8307 

$$

MOORE

What forecasters said that day

The local office's own words before this severe thunderstorm warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Greenville-Spartanburg, SC wrote its last area forecast discussion before this severe thunderstorm warning went out at Sep 20, 2:38 PM EDT, 2 hours 21 minutes earlier.

Area forecast discussion, Sep 20, 2:38 PM EDT, 2 hours 21 minutes before
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
238 PM EDT Wed Sep 20 2017

.SYNOPSIS...
A weak trough will move east of the area tonight and settle along
the southeast coast on Thursday. A gradual increase in more moist,
easterly flow is expected through the latter part of the work week.
Drier and stronger high pressure will settle across the region over
the weekend and likely persist through early next week, as Tropical
Systems Jose and Maria remain off the east coast.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 230 PM: A weak ridge of high pressure is still present
over the region, though a well-defined shortwave trough is
centered over SW VA. Vort lobes embedded within the trough are
expected to rotate through the area this aftn and evening. Warm
temps and good lapse rates within the trough have allowed
1500-2000 J/kg of SBCAPE to develop, per SPC mesoanalysis.
Initiation has been spotty so far, with deeper cumulus over the
mountain ridges but also in an area of enhanced convergence
southeast of I-85, just ahead of the trough. Meso models have
not done an especially good job so far today, being overdone
with convection for the most part, though the HRRR has done a
reasonable job of highlighting the two areas where radar echoes
have developed so far. Thus, the revised PoPs are close to the
previous values, blending in a bit of meso model output to
reflect the expected coverage. It is not out of the question
that the most vigorous couple storms could produce a damaging
microburst given the dry air wrapped into the shortwave. Shear
is just enough to expect storms to propagate slowly along
outflows. All this activity will diminish diurnally, despite the
shortwave taking its time moving southeast thru the region
tonight. Under partly cloudy to mostly clear skies, but
continued moist sfc conditions, min temps will remain 4-6
degrees above normal. Expect some fog in the mtn valleys and in
the more fog-prone areas of the Piedmont.

A sharp ridge of high pressure will build over the inland parts
of the eastern CONUS on Thursday, while the shortwave will remain
on our southeast flank. Though the high will bring N to NE flow,
thermal advection is basically neutral, so max temps will remain
6 to 8 degrees above normal. Lapse rates won't be quite as good in
the wake of the shortwave, but respectable instability still will
develop. Models mainly key on terrain as an initiation mechanism,
leading to chance range PoPs over the mountains and slight chance
in the Piedmont. Profiles feature a bit more moisture aloft but
sfc-midlevel theta-E lapses are progged to be sufficient for a tiny,
but nonzero, threat of damaging winds.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 155 PM EDT Wednesday: An upper level trough axis will settle
along the southeast coastline Friday and linger through Saturday, as
a 590 dm ridge axis sets up from the Great Lakes to the MS Valley.
Low level easterly flow continues Friday into Saturday which should
help to focus the highest chance PoPs along the eastern slopes of
the mountains. Thus anticipate mainly diurnal, scattered ridge
top/eastern mountain convection both days with weak forcing and
limited moisture. Drier air moves into the NC Piedmont on this flow
Saturday limiting precip chances there, with better chances
remaining over the mountains, western Upstate and NE GA. SBCAPE
values should steadily recover to 1000 to 1500 J/kg across the
mountains to support a scattered thunder mention. Instability will
be lower elsewhere but high enough for thunder. Highs will be nearly
steady around 5 degrees above normal both days. With lows around 5
degrees above normal Friday morning falling a couple of degrees
Saturday morning.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 155 PM EDT Wednesday: the extended fcst picks up at 00z on
Sunday with persistent and highly amplified upper ridging in place
over the Eastern CONUS and steep upper trofing over the west. The
trof will gradually slide eastward thru the period and will begin to
flatten the ridge by the end of the period. At the sfc, very broad
high pressure will be in place to start the period. The remnants of
TS Jose will still be lingering off the New England Coast while TS
Maria is currently forecast to be due east of the Bahamas by early
Sunday. Maria is still expected to remain far enough off the east
coast to not have significant impacts on our fcst area. We will
remain under broad high pressure thru day 7 with predominately dry,
N to NELY low-lvl flow expected to persist. A cold front is expected
to approach the fcst area just beyond the fcst period early Thurs.
As for the sensible fcst, no major changes were needed. The period
should be mostly dry with temperatures starting out about a category
above normal and warming a few more degrees by the end of the period.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
At KCLT and Elsewhere: Expecting some SHRA/TSRA this aftn in mainly
two areas, near the Blue Ridge as well as the lower Piedmont. A
TEMPO is included at KCLT and KHKY, and VCSH at KAVL. Otherwise
just low VFR cumulus will be seen; these and the precip will
diminish by sunset. Winds will be quite VRB this aftn, but as a
shortwave trough exits the area and is replaced by high pressure
from the north, they will tend to veer with time, becoming N by
late evening. Fog again is progged in the mtn valleys and outlying
areas of the Piedmont; TEMPO IFR is included at KAVL.

Outlook: Chances for diurnally favored showers and thunderstorms
remain in the fcst Thursday and Friday. Restrictions from early
morning fog across the northern NC Piedmont and foothills, as well
as in the mtn valleys, will also be a concern. Drier weather is
expected to return for the weekend.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High  97%     Low   51%     High  81%
KHKY       High 100%     High 100%     High  97%     High  97%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High  97%     High  91%

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...JPT
NEAR TERM...Wimberley
SHORT TERM...RWH
LONG TERM...JPT
AVIATION...Wimberley
Hazardous weather outlook, Sep 20, 4:53 AM EDT, 12 hours 6 minutes before
Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
453 AM EDT Wed Sep 20 2017

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-210900-
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-
453 AM EDT Wed Sep 20 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 will develop around the region
this afternoon and evening. The main threat with any thunderstorms
will be a few cloud-to-ground lightning strikes. A few of the
stronger thunderstorms could also produce briefly gusty winds and
small hail.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

..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.
..Tuesday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

HG

In the hours before

Special weather statement, Sep 20, 3:30 PM EDT, 1 hour 29 minutes before
Special Weather Statement
National Weather Service Greenville-Spartanburg SC
330 PM EDT WED SEP 20 2017

NCZ052-059-202000-
Haywood NC-Northern Jackson NC-
330 PM EDT WED SEP 20 2017

...A STRONG THUNDERSTORM WILL IMPACT NORTHEASTERN JACKSON AND
SOUTHWESTERN HAYWOOD COUNTIES UNTIL 400 PM EDT...

At 329 PM EDT, Doppler radar was tracking a strong thunderstorm 7
miles northeast of Sylva, or near Balsam. This storm was nearly
stationary.

Locations to be impacted include...
Balsam, B.R. Parkway-Balsam Gap To Black Balsam Area, B.R.
Parkway-Smoky Mountains To Balsam Gap, Tuckasegee and Sunburst.

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

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 3544 8323 3552 8312 3541 8293 3525 8312
TIME...MOT...LOC 1929Z 318DEG 3KT 3543 8312

MOORE
Special weather statement, Sep 20, 4:05 PM EDT, 54 minutes before
Special Weather Statement
National Weather Service Greenville-Spartanburg SC
405 PM EDT WED SEP 20 2017

NCZ064-202030-
Transylvania NC-
405 PM EDT WED SEP 20 2017

...A STRONG THUNDERSTORM WILL IMPACT NORTHEASTERN TRANSYLVANIA COUNTY
UNTIL 430 PM EDT...

At 405 PM EDT, Doppler radar was tracking a strong thunderstorm 4
miles northwest of Brevard, or near Looking Glass. This storm was
nearly stationary.

Locations to be impacted include...
Brevard, Looking Glass, Penrose and North Transylvania.

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

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 3526 8262 3517 8280 3532 8284 3532 8283
      3533 8283 3538 8272
TIME...MOT...LOC 2005Z 328DEG 3KT 3529 8276

MOORE
Special weather statement, Sep 20, 4:28 PM EDT, 31 minutes before
Special Weather Statement
National Weather Service Greenville-Spartanburg SC
428 PM EDT WED SEP 20 2017

NCZ063-064-202100-
Transylvania NC-Southern Jackson NC-
428 PM EDT WED SEP 20 2017

...A STRONG THUNDERSTORM WILL IMPACT SOUTHWESTERN TRANSYLVANIA AND
SOUTHEASTERN JACKSON COUNTIES UNTIL 500 PM EDT...

At 428 PM EDT, Doppler radar was tracking a strong thunderstorm 17
miles southwest of Brevard, or 4 miles west of Lake Toxaway. This
storm was nearly stationary.

Locations to be impacted include...
Lake Toxaway, Gorges State Park and Sapphire.

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

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 8305 3520 8290 3509 8285 3506 8289
      3505 8292 3504 8310
TIME...MOT...LOC 2028Z 359DEG 3KT 3513 8301

MOORE
Local storm report, Sep 20, 4:31 PM EDT, 28 minutes before
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
431 PM EDT WED SEP 20 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0430 PM     HAIL             LAKE TOXAWAY            35.13N 82.93W
09/20/2017  E0.50 INCH       TRANSYLVANIA       NC   TRAINED SPOTTER

            DIME SIZE HAIL REPORTED IN LAKE TOXAWAY

&&

LEC

The office that day

Everything else NWS Greenville-Spartanburg, SC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 20, 3:30 PM EDTSpecial Weather StatementGSPJackson30 min
Sep 20, 4:05 PM EDTSpecial Weather StatementGSPTransylvania25 min
Sep 20, 4:28 PM EDTSpecial Weather StatementGSPTransylvania32 min
Sep 20, 4:30 PM EDTSevere Thunderstorm WarningGSPJackson, Transylvania30 min
Sep 20, 5:01 PM EDTSevere Thunderstorm WarningGSPJackson14 min

Nearby

Severe Thunderstorm Warnings in South Carolina, 2017Severe Thunderstorm Warnings in North Carolina, 2017Every severe thunderstorm warning in 2017

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.