Damaging Wind in North Carolina, August 1, 2018

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
318 PM EDT Wed Aug 1 2018

.SYNOPSIS...
A broad area of low pressure will persist across the Tennessee
Valley through at least Friday. This low will transport deep
moisture from the Gulf of Mexico and produce abundant cloud
cover and continued rounds of precipitation, which will hold
high temperatures below normal.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 245 PM EDT Wednesday: At the top of our agenda remains the
severe weather threat for the afternoon and evening. The midday
update to the Day 1 Convective Outlook split the Slight Risk and
kept parts of the Upstate and metro Charlotte in the risk area,
and it seems reasonable to be concerned about the area along and
south/east of Interstate 85. The latest mesoanalysis shows the
breaks in the cloud cover have allowed that region to destabilize
to about 2000 J/kg of sfc-based CAPE. We are in a gradient of
effective bulk shear, but part of the area still had over 40 kt
with 0-3km storm relative helicity around 150 m2/s2. The 12Z run
of the HREF still suggested some rotating storms, so it would be
wise to not give up on a few HP supercells. Ultimately, our tornado
potential might depend on whether or not any boundaries will be
present to locally enhance the shear/helicity, and for the time
being my confidence is not particularly strong that it will be the
case. So, don't completely disregard the severe thunderstorm threat
while we concentrate mainly on the flash flood threat. Speaking
of which...now that we are seeing some lines/clusters beginning to
organize in the direction of the deep layer shear, our flash flood
threat will ramp up into the late afternoon and evening. Temps
need an upward adjustment over the east where the clouds have
scattered out.

The latest model guidance, thankfully, continues to play along with
our ongoing forecast with no surprises. The upper level pattern
remains locked in place with a trof axis over the MS River valley
and a large anticyclone over the wrn Atlantic. The pattern will
continue to focus a plume of deep tropical moisture from the Gulf
of Mexico to the srn Appalachians and western Carolinas thru the
near term period. Precipitable water should remain at or above the
upper end of the PW climatology (i.e. well above normal), while
the atmosphere will be characterized by a deep warm cloud layer,
and our meso-beta element vectors remain small. All this is to say
that we have many of the necessary ingredients for flash flooding,
so the ongoing Flash Flood Watch remains in good shape. Precip prob
will remain likely to categorical into the evening while we work
thru the diurnal cycle. There may be something of a relative lull
late tonight/early Thursday morning, but the lull might be more
of a dropoff in intensity, not coverage. We ramp back up after
daybreak on Thursday as we continue to bring mid-level PVA across
the region, add some daytime heating, and bring some increased upper
divergence to bear. That should increase our flood threat thru the
day, perhaps higher than today as we continue to pile up the rain
and soak the ground. As for severe thunderstorms, we cannot rule
them out once again over the eastern fringe of the fcst area in the
afternoon as we once again destabilize to 1500 J/kg of sfc-based
CAPE and retain seasonally strong wind shear. Temps should be on
the cool side of normal where clouds and extensive precip linger.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 245 PM EDT Wednesday: At the start of the forecast cycle our
area (FA) still sits in a blocking pattern. Once again the key
players: the upper level ridge in the west, troffing from the Great
Lakes to the Gulf of Mexico, and the western Atlantic high pressure
system.

The "wave train" continues Thursday night with embedded pockets of
energy shifting through the region in a southwesterly flow aloft.
The right entrance region of the upper level jet continues to show
its hand allowing lifting mechanisms to continue.

It looks like we have to wait for this upper level low in the
Bahamas to rotate around the western periphery of the Atlantic high
pressure system. Once this happens the upper level high will shift
slowly west, and the upper level trough will deamplify considerably.

Meanwhile, precipitable water values remain elevated Thursday night,
at 2.0 inches or greater in spots. Various mechanisms of forcing
will allow for the potential of additional heavy rain. As a result
we will keep high POPS going Thursday night.

For Friday we kept POPS elevated with lingering precipitable waters
still high, and the last vestiges of the upper trough lifts out. At
this point hard to pin point whether any one area would need an
extension of the Flash Flood Watch at this time. The mountains could
be candidates, but not enough evidence at this point

As we start the weekend, although heights will be on the rise,
diurnal showers and thunderstorms should erupt. The higher
elevations look to have the better involvement, but other areas are
still possible.

Once again we kept temperatures in range with the suite of guide,
with less diurnal range than usual.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 155 PM Wed:  The Bermuda High will exert more of an influence
on our weather during the weekend with a good southerly flow of air
into our region. From late Saturday to late Sunday the center of the
Bermuda High gets closer to the Carolina coast. As a result, the
weak 5 to 10 kt southerly 925mb flow becomes even lighter on Sunday
and shifts more toward the west to start the week. Less moisture
transport through time. Precipitable water levels drop from 1.8 in
the lower Piedmont Saturday evening to 1.5 to 1.6 across the area on
Monday. Instability  around 2000 CAPE in piedmont Saturday evening
then 2000 to 2500 late Sunday along the I-85 corridor. The next
trough crosses the Upper Mississippi Valley Monday and Monday night
with the cold front having a roughly 200 mile wide area of frontal
convection.  Height falls across our region in mid week as the
trough becomes established over the Eastern Half of the nation.
Frontal convection expected over our region on Wednesday with the
greater cloud cover.Temperatures will be near normal

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
At KCLT and Elsewhere: Another mixed bag this afternoon. Clouds
continue to scatter out at the lowest level east of the mtns while
boundary layer heating raises the cloud base up thru the MVFR
category. With the exception of KAVL, most places will be in and
out of a low-end VFR ceiling with occasional MVFR as showers pass
overhead. The stronger convection will have brief IFR ceiling
and visibility. Thunderstorms will become more numerous thru
the late afternoon and the fcst becomes an exercise in picking
the most likely time. We begin with a four hour window in the
late afternoon and early evening and will amend from there. More
restictions will continue with widespread rain this evening and
into the overnight hours. At some point we should see a lull early
Thursday, during which time confidence is high that an IFR stratus
deck will develop. Once formed, it will persist through at least
late morning on Thursday. Details of its demise are left out for
now. We finish with a PROB30 for convection that ramps back up with
daytime heating. Wind will be south to southeast thru the period,
with stronger gusts near thunderstorms.

Outlook: A wet pattern will remain in place over the region
through late week. Numerous SHRA/TSRA will develop across the
area, especially each afternoon and evening, along with associated
restrictions. Limited drying may occur over the weekend.

Confidence Table...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       High 100%     High  90%     High  81%     High  86%
KGSP       Low   51%     High  84%     Med   74%     High  86%
KAVL       High  83%     High  90%     Med   77%     High  96%
KHKY       Med   67%     Med   74%     High  82%     High  86%
KGMU       Med   64%     Med   79%     Med   76%     High  85%
KAND       Med   71%     High  86%     Med   76%     High  88%

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

&&

.HYDROLOGY...
The current hydrology situation this afternoon is comprised of
two primary areas of concern.  The first is over the far western
mountains including Graham, Haywood, Jackson, Macon, Rabun, and
Swain counties, where instability is poor (SBCAPE <500 J/kg) but low-
level covergence closer to the proximity of the surface front and
overall upslope flow suggest some forcing exists.  This combined
with high PWs of 1.7-1.9" suggest efficient, warm-layer rain
processes are still in play. However, at this time, rainfall rates
are generally less than 1"/hr in the SW mountains; therefore, the
flash flood threat here is not imminent but antecedent conditions
are priming if higher rainfall rates materialize later today into
tonight.

The second area of concern is along and east of the Blue Ridge
Escarpment into the Foothills and Piedmont of the Carolinas and NE
GA where instability is greater (SBCAPE >1500 J/kg) and PW values
are still near climatological maxes (1.8-2.1"). Also, Flash Flood
Guidance values are lower here, especially along the Escarpment, due
to previous activity (<2"/hr). Therefore, the concern for localized
flash flooding is greater in this area as ongoing activity is
producing rainfall rates of 1-3"/hr and some brief anchoring has
been occurring, producing 1-2" of rainfall in as little as 30-45
minutes.  Over urbanized areas, this will produce quick
street/parking lot/underpass flooding and will need to be closely
monitored.

As rainfall continues area wide, antecedent conditions will continue
to deteriorate as we approach the best chances for heavy rainfall
tonight into Thursday.  Therefore, the flood risk will continue to
increase into Thursday before tapering off (but not disappearing
completely) into Friday and the weekend. Meanwhile, as basin-average
rainfall amounts increase into tomorrow, mainstem river flooding
becomes a greater possibility, especially in the climatologically
favorable areas of the upper French Broad River, but rapid response
along the lower Tuckasegee, Swannanoa, South Fork Catawba, and
Pigeon River basins is also possible. At this time, Minor flooding
(i.e., flooding of low-lying areas, greenways, boat-access ramps,
recreational areas) is the primary concern.  Monitor the latest
forecasts and stream levels at:

https://water.weather.gov/ahps2/index.php?wfo=gsp.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Flash Flood Watch through Friday morning for GAZ010-017-018-
     026-028-029.
NC...Flash Flood Watch through Friday morning for NCZ033-035>037-
     048>053-056>059-062>065-068>072-082-501>510.
SC...Flash Flood Watch through Friday morning for SCZ001>014-019.

&&

SYNOPSIS...DEO
NEAR TERM...PM
SHORT TERM...TS
LONG TERM...DEO
AVIATION...PM
HYDROLOGY...JMP

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
553 PM EDT Wed Aug 1 2018

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-021200-
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-
553 PM EDT Wed Aug 1 2018

...FLASH FLOOD WATCH IN EFFECT THROUGH FRIDAY MORNING...

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.

   Flash Flood Watch.

Additionally, scattered thunderstorms will be capable of dangerous
cloud-to-ground lightning. A few storms could producing damaging wind
gusts, primarily in the evening.

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

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

   Flash Flood Watch.

Even following the end of the Flash Flood Watch, conditions will
remain favorable for localized heavy rainfall each afternoon into
Sunday. Meanwhile, the thunderstorms will be capable of dangerous
cloud to ground lightning.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to forward any reports of hail, damaging
winds, or flash flooding to our office.

ACS

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
546 PM EDT WED AUG 1 2018

SCZ013-014-012230-
Union SC-Chester SC-
546 PM EDT WED AUG 1 2018

...A STRONG THUNDERSTORM WILL IMPACT WESTERN CHESTER AND UNION
COUNTIES UNTIL 630 PM EDT...

At 545 PM EDT, Doppler radar was tracking a strong thunderstorm 11
miles north of Newberry, or 4 miles southeast of Whitmire, moving
north at 30 mph.

Locations to be impacted include...
Union, Monarch Mill, Lockhart, Carlisle, Rose Hill State Park,
Buffalo, Leeds, Adamsburg and Santuc.

Wind gusts up to 40 mph 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.

&&

LAT...LON 3449 8157 3453 8162 3453 8164 3456 8169
      3486 8166 3483 8147 3482 8147 3482 8142
      3481 8134 3457 8141 3457 8142 3450 8144
      3449 8144 3449 8149 3445 8154
TIME...MOT...LOC 2145Z 195DEG 27KT 3445 8158

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
558 PM EDT WED AUG 1 2018

NCZ057-072-012230-
Rowan NC-Cabarrus NC-
558 PM EDT WED AUG 1 2018

...A STRONG THUNDERSTORM WILL IMPACT NORTHEASTERN CABARRUS AND
SOUTHWESTERN ROWAN COUNTIES UNTIL 630 PM EDT...

At 558 PM EDT, Doppler radar was tracking a strong thunderstorm 7
miles northeast of Downtown Concord, or 5 miles northwest of Mt
Pleasant, moving north at 30 mph.

Locations to be impacted include...
Salisbury, Downtown Concord, Kannapolis, China Grove, Spencer,
Landis, Granite Quarry, Rockwell, Mt Pleasant and Faith.

Wind gusts up to 40 mph and very heavy rainfall rates of 1 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.

&&

LAT...LON 3539 8037 3539 8059 3578 8066 3578 8050
      3577 8049 3578 8048 3577 8047 3573 8045
      3572 8042 3573 8039 3572 8038 3572 8034
TIME...MOT...LOC 2158Z 178DEG 26KT 3547 8049

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
625 PM EDT WED AUG 1 2018

SCZ009-013-014-012300-
York SC-Union SC-Chester SC-
625 PM EDT WED AUG 1 2018

...A STRONG THUNDERSTORM WILL IMPACT WESTERN CHESTER...SOUTHWESTERN
YORK AND EAST CENTRAL UNION COUNTIES UNTIL 700 PM EDT...

At 625 PM EDT, Doppler radar was tracking a strong thunderstorm 10
miles southwest of Chester, or 6 miles east of Carlisle, moving
northeast at 25 mph.

Locations to be impacted include...
Chester, Lowrys, Chester State Park, Carlisle, Leeds, Bullock Creek
and Cornwell.

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

LAT...LON 3457 8142 3461 8150 3490 8138 3477 8102
      3456 8125
TIME...MOT...LOC 2225Z 216DEG 23KT 3462 8136

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
643 PM EDT WED AUG 1 2018

NCZ057-072-012315-
Rowan NC-Cabarrus NC-
643 PM EDT WED AUG 1 2018

...AN AREA OF THUNDERSTORMS WITH TORRENTIAL RAINFALL WILL IMPACT
NORTHWESTERN CABARRUS AND CENTRAL ROWAN COUNTIES UNTIL 715 PM EDT...

At 641 PM EDT, Doppler radar was tracking a line of training
thunderstorms with torrential rainfall from Kannapolis to Salisbury
and Spencer moving north at 50 mph.

Locations to be impacted include...
Kannapolis, Downtown Concord, Salisbury, West Concord, Harrisburg,
China Grove, Spencer, Landis, Granite Quarry and Rockwell.

Torrential rainfall rates up to 3 inches per hour will be possible in
these areas.

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.

&&

LAT...LON 3528 8046 3532 8068 3582 8059 3581 8056
      3578 8051 3578 8050 3577 8049 3578 8048
      3573 8045 3572 8042 3573 8039 3572 8038
      3572 8033
TIME...MOT...LOC 2241Z 190DEG 44KT 3555 8053

JMP

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
656 PM EDT WED AUG 1 2018

NCZ037-057-012330-
Rowan NC-Davie NC-
656 PM EDT WED AUG 1 2018

...A STRONG THUNDERSTORM WILL IMPACT DAVIE AND NORTH CENTRAL ROWAN
COUNTIES UNTIL 730 PM EDT...

At 654 PM EDT, Doppler radar was tracking a strong thunderstorm 5
miles northwest of Salisbury, moving north at 20 mph.

Locations to be impacted include...
Mocksville, Salisbury, Spencer, Bermuda Run, Cooleemee, High Rock
Lake, Fork Church, Advance, Farmington and Woodleaf.

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

LAT...LON 3565 8035 3573 8063 3602 8064 3601 8041
      3599 8042 3596 8038 3589 8037 3588 8042
      3587 8039 3585 8039 3585 8042 3583 8043
      3583 8046 3584 8047 3583 8049 3581 8047
      3579 8048 3577 8045 3573 8045 3572 8034
TIME...MOT...LOC 2254Z 187DEG 17KT 3573 8052

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
659 PM EDT WED AUG 1 2018

SCZ009-014-012345-
York SC-Chester SC-
659 PM EDT WED AUG 1 2018

...A STRONG THUNDERSTORM WILL IMPACT NORTH CENTRAL CHESTER AND
EASTERN YORK COUNTIES UNTIL 745 PM EDT...

At 658 PM EDT, Doppler radar was tracking a strong thunderstorm 9
miles north of Chester, or near Mcconnells, moving northeast at 25
mph.

Locations to be impacted include...
Rock Hill, York, Chester, Clover, Newport, Lesslie, Mcconnells,
Lowrys and Edgemoor.

Wind gusts up to 40 mph 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.

&&

LAT...LON 3466 8115 3481 8134 3514 8122 3492 8087
TIME...MOT...LOC 2258Z 211DEG 22KT 3484 8120

SGL