Severe Thunderstorm Warning 251, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
738 PM EDT Sat Jul 21 2018

.SYNOPSIS...
A broad upper low will settle across the Deep South through early
next week. This low will remain nearly stationary through midweek
and support moist unsettled weather across the region.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 730 PM EDT Saturday: Several storms out there at update time
and have adjusted pops to account for current trends and CAM
forecasts over the next few hours. Increased pops for Sunday as well
based on updated trends along the Blue Ridge. Other updates this
evening are for aviation parameters.

Otherwise, water vapor imagery and RAP heights placed the 500 mb
closed low center near the IL/IN/MI border this afternoon, with
drier mid-level air wrapping around the associated trough and across
the western Carolinas and northeast Georgia. Very good insolation
developed late this morning into this afternoon behind the departing
daybreak rain areas, and LAPS surface based CAPE values have
gradually returned to 1500 to 2500 J/kg across northeast GA and the
western Upstate. RAP and NAM profiles are very unstable this
afternoon, especially across our southern parts, where sbCAPE values
reach some 3000 to 4000 J/kg. The convection-allowing models have
not been terribly consistent on placement or timing, but the general
consensus is that enough triggering will take place as vorticity
lobes round the trough axis to generate scattered to numerous
thunderstorms later this afternoon and this evening. These
thunderstorms will grow in an enviroment with 7+ deg C/km mid-level
lapse rates and approximately 30 to 35 kt of sfc-6 km bulk shear.
This should be sufficient to warrant a Slight risk of severe
thunderstorms across our southern half, with a Marginal risk across
the northern part. Rotating updrafts will support mainly a damaging
wind and large hail threat. The consensus HRRR/NAMnest solution has
mountain triggering overcoming a weak cap circa 19Z, with activity
then developing and spreading quickly east of the mountains through
evening, moving east of the I-77 corridor by midnight. PoPs will
generally follow this trend.

Otherwise, the vertically stacked low pressure system will slowly
pivot southward toward the Ohio River Valley later tonight through
Sunday. Q-vector divergence will continue east of the deepening
trough axis mainly along the I-40 corridor. Reasonably steep 6 to
6.5 deg C/km lapse rates continue on Sunday east of the upper
trough. This will warrant at scattered south to numerous north
coverage again, with mainly a diurnal focus Sunday afternoon.
Temperatures should be at least a category below climo Sunday
afternoon.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 130 PM EDT Saturday: Active weather is likely to continue for
the period from Sunday night through Tuesday. The synoptic scale
feature of interest acrs the eastern CONUS will be the slowly
filling and southward sinking closed upper low.  With the mean
southerly flow atop the region deepening on Monday, expect an influx
of higher PWAT values leading to numerous if not widespread
diurnally enhanced deep convection with a heavy rain possibility
especially from the Blue Ridge to the piedmont. Widespread clouds
and showers should aid in max temperatures topping out around 5 deg
F below climo. It does not look like the sensible wx will change
very much through Tuesday, lingering rich PWAT values and a broad
SSEly flow feeding moisture into the Southern Appalachians. Expect
another day of deep convection becoming numerous to widespread with
the ongoing chance of locally excessive rainfall.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 115 PM Saturday: A weakening ulvl trof will linger over the
region thru the first half of the ext range before becoming sheared
out Fri into Sat. This synoptic scenario is well agreed upon by the
op models with the GFS holding onto a pocket of stronger vort energy
a little longer into Fri. At the sfc...broad low pressure will allow
for continued e/ly Atl moist flux early Wed before the deep layered
flow calms and becomes sw/ly in the lower levels Wed night thru the
period. This will lower any flooding potential as sustained mech lift
is reduced...however PWAT values will remain quite high allowing for
high rainfall rates associated with afternoon pulse convec. With
high cloud cover and decent coverage of precip...max temps will
remain a cat or so below normal with normal levels likely returning
Fri/Sat. Mins will remain a little abv normal each morning.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
At KCLT and Elsewhere: Widespread convection coming off the Blue
Ridge this evening has so far missed most of the TAF sites, though
GSP is showing VCTS and got pretty close to KHKY. Have continued
VCTS or TEMPO TSRA for the next few hours, trending into VFR
overnight. Increasing moisture may lead to a brief period of MVFR
cigs around sunrise, but the bigger concern will be the increasing
chances of convection on Sunday. Have introduced PROB30s where there
wasn't one before and expanded the one previously introduced for
KCLT. Expect mainly southwest winds, with low end gusts at times,
and a shift to NW flow at KAVL late.

Outlook: An active/wet period is expected to continue from late
Sunday through the middle part of next week as a slow-moving storm
system impacts much of the East. Numerous showers and thunderstorms
are expected during this period. While there will likely be an
afternoon/evening peak in coverage on most days, higher-than-normal
chances will also exist during the overnight and morning hours.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       High 100%     High 100%     Med   66%     High 100%
KGSP       High 100%     High 100%     High  94%     High 100%
KAVL       High 100%     Med   75%     Med   64%     High 100%
KHKY       High 100%     High 100%     Med   75%     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...SBK
NEAR TERM...HG/TDP
SHORT TERM...CSH
LONG TERM...SBK
AVIATION...TDP

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
550 PM EDT Sat Jul 21 2018

GAZ010-017-018-026-028-029-NCZ068>070-507>510-SCZ001>014-019-222200-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Cleveland-Lincoln-
Gaston-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-Union-Chester-Greenwood-
550 PM EDT Sat Jul 21 2018

...SEVERE THUNDERSTORM WATCH 300 IN EFFECT UNTIL 2 AM EDT SUNDAY...

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

.DAY ONE...Tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Severe Thunderstorm Watch.

Thunderstorms will continue to develop and expand in coverage across
the region into this evening. Some of these storms may become
severe. The most likely hazards will be damaging winds, large hail,
frequent lightning, and minor flooding from heavy rainfall. An
isolated tornado will also be possible, mainly east of the Blue
Ridge.

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

..Sunday...No hazardous weather is expected at this time.
..Monday...Heavy rain possible. A persistent moist southeasterly
flow will increase the risk for heavy rainfall across the area
starting late Monday and continuing through Wednesday.
..Tuesday...Heavy rain possible.
..Wednesday...Heavy rain possible.
..Thursday...No hazardous weather is expected at this time.
..Friday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

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

NCZ033-035>037-048>053-056>059-062>065-071-072-082-501>506-222200-
Avery-Alexander-Iredell-Davie-Madison-Yancey-Mitchell-Swain-Haywood-
Buncombe-Catawba-Rowan-Graham-Northern Jackson-Macon-
Southern Jackson-Transylvania-Henderson-Mecklenburg-Cabarrus-Union-
Caldwell Mountains-Greater Caldwell-Burke Mountains-Greater Burke-
McDowell Mountains-Eastern McDowell-
550 PM EDT Sat Jul 21 2018

This Hazardous Weather Outlook is for piedmont North Carolina and
western North Carolina.

.DAY ONE...Tonight.

Thunderstorms will continue to develop and expand in coverage across
the region into this evening. Some of these storms may become
severe. The most likely hazards will be damaging winds, large hail,
frequent lightning, and minor flooding from heavy rainfall. An
isolated tornado will also be possible, mainly east of the Blue
Ridge.

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

..Sunday...No hazardous weather is expected at this time.
..Monday...Heavy rain possible. A persistent moist southeasterly
flow will increase the risk for heavy rainfall across the area
starting late Monday and continuing through Wednesday.
..Tuesday...Heavy rain possible.
..Wednesday...Heavy rain possible.
..Thursday...No hazardous weather is expected at this time.
..Friday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
716 PM EDT SAT JUL 21 2018

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

0650 PM     HAIL             1 SW BETHLEHEM          35.81N 81.31W
07/21/2018  E1.75 INCH       ALEXANDER          NC   BROADCAST MEDIA

            BROADCAST MEDIA REPORTED GOLF BALL (1.75 IN) SIZE HAIL
            IN BETHLEHEM. TIME ESTIMATED FROM RADAR.

0650 PM     TSTM WND DMG     1 S OAKWAY              34.58N 83.03W
07/21/2018                   OCONEE             SC   911 CALL CENTER

            911 CALL CENTER REPORTED A FEW TREES DOWN IN THE
            SOUTHERN PART OF THE COUNTY. TIME ESTIMATED FROM RADAR.

0640 PM     HAIL             HARRIS                  35.24N 81.88W
07/21/2018  E1.00 INCH       RUTHERFORD         NC   SOCIAL MEDIA

            SOCIAL MEDIA REPORTED QUARTER (1.00 IN) SIZE HAIL IN
            HARRIS. TIME ESTIMATED FROM RADAR.

0640 PM     HAIL             1 SW HICKORY            35.73N 81.34W
07/21/2018  E1.00 INCH       CATAWBA            NC   SOCIAL MEDIA

            SOCIAL MEDIA REPORTED QUARTER (1.00 IN) SIZE HAIL IN
            HICKORY. TIME ESTIMATED FROM RADAR.

0625 PM     HAIL             4 S SPINDALE            35.30N 81.94W
07/21/2018  E1.50 INCH       RUTHERFORD         NC   SOCIAL MEDIA

            SOCIAL MEDIA REPORTED PING PONG BALL (1.50 IN) SIZE
            HAIL IN THE SHILOH COMMUNITY. TIME ESTIMATED FROM RADAR.

&&

LEC

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