Severe Thunderstorm Warning 161, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1011 AM EDT Thu Aug 1 2019

.SYNOPSIS...
A persistent trough of low pressure will support showers and
thunderstorms at times over much of the next seven days. Deeper
tropical moisture will likely push into the region by Friday and
linger into the weekend, supporting a more widespread threat for
heavy rain and isolated flooding.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM EDT Thursday: Fog is kind of slow to dissipate this
morning across the mountain valleys but should start picking up
shortly. Updates this morning are mainly to delay the moistening
trend in dewpoints this afternoon (new guidance is slowing this
down) and make adjustments to hourly temperatures to reflect a
slightly earlier afternoon high due to expected expanding cloud
cover later this afternoon as convection blossoms. Pop trends still
look good for now with thoughts from earlier this morning.

Otherwise, troughing between dueling anticyclones across the central
Conus and the western Atlantic will continue to get squeezed/weaken
through the near term, with increasingly moist low level S/SW flow
persisting around the western periphery of surface Bermuda high.
Increasing dewpoints and strong insolation should allow for
destabilization to the tune of around 2000-2500J/kg of sbCAPE across
much of the area by mid-afternoon. Differential heating and ridge
top convergence acting on this instability will allow deep
convection to begin firing across the high terrain by early
afternoon, with 50-70 pops appearing to be a good bet across the
mtns by mid/late afternoon. East of the mtns, forecast soundings,
despite being moderately unstable are somewhat inhospitable to
initiation, at least through mid-afternoon or so, as a rather dry
boundary layer (PWATs still forecast to remain below climo until at
least this evening) with relatively high LFCs is depicted. In fact,
while the CAMs (namely the HRRR) blows up scattered convection
across the entire forecast area by mid-afternoon, traditional
operational guidance keeps it confined to the high terrain until
this evening. Above-climo pops (generally 40-50%) will still be
advertised for the first period across the Piedmont and foothills,
but not until this evening.

If anything, the highest Piedmont near term pops may exist after 00Z
Friday as LFCs lower and deep layer moisture begins increasing . By
that time, deep layer moisture is increasing across the region as
mid-level energy digging into the weakness in the subtropical ridge
shows some signs of carving out an upper-level cyclone. All guidance
is in rather good agreement in flaring up convection across roughly
the eastern half of the area btw 00-06Z, and this is when likely
pops will be advertised in those areas. As was the case on Wed,
conditions will be favorable for a few storms to produce brief
microbursts. Continued good steering flow (around 15 kts) should
render any excessive rainfall threat highly localized to cells
anchoring along terrain features this afternoon. However, heavy rain
may become more of a concern this evening, as PWATs increase to more
respectable levels for the time of year.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 315 AM Thursday: The short term will be characterized by
humid, tropical like conditions in response to a tropical
disturbance moving into the coastal waters off of the Southeast
coast. The main concern with this setup is the potential for heavy
rainfall with localized flooding. As of now it appears the I-77
corridor northwestward into the North Carolina foothills are the
areas of greatest concern with model guidance showing the potential
for around an inch of rain with locally 2+ inches over a relatively
short period of time. The ingredients for the heavy rainfall
includes deep tropical moisture, light steering currents, decent
instability, with synoptic enhancement. A low level jet may also
become just strong enough for orographic enhancement over the North
Carolina foothills. However, the amount of thunderstorm activity is
in some question as extensive cloud cover with the tropical moisture
could limit daytime destabilization, at least somewhat limiting the
concern for flooding. Model guidance diverges somewhat for Saturday
as some guidance shunts the deeper moisture eastward, while the GFS
for instance, hangs onto it for one more day. Forecast reflects a
blend of the guidance with maybe one more day for a heavy rain
threat, especially for eastern areas and near stronger
thunderstorms. Drier air working in aloft, especially for western
areas could support a renewed threat for damaging winds in stronger
thunderstorms due to microbursts. Highs will generally be 5 to
locally 10 degrees below normal (upper 70s to mid 80s) due to all of
the cloud cover and rainfall, with near normal lows.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 330 AM Thursday: Fairly consistent weather is expected in the
extended with a piece of energy acting to reinforce the trough in
place over the eastern half of the nation by mid-week. This feature
may provide an extra oomph in thunderstorm activity during the early
to middle part of next week with otherwise fairly typical afternoon
to evening thunderstorm activity. The weak trough overhead with
cloud cover at times will likely support near to below normal
temperatures through the period.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: Fog and low stratus remains widespread in the
mtn valleys, with KAVL having reported occl VLIFR conditions since
09Z. This will remain possible through about 13Z, although the bulk
of that time will see LIFR. VFR conditions are advertised beginning
at 13Z, but with a tempo for LIFR carried through 14Z.

Otherwise, the other terminals should see VFR continue through at
least this morning. Convection will develop again this afternoon,
with coverage likely being similar to what was seen Wed, albeit with
a later initiation time. All sites receive a VCTS/Prob30 for TSRA by
mid-afternoon (except early afternoon at KAVL), continuing through
the evening. In fact, most of the terminals are expected to see
their highest chances during the evening (esp KCLT). Winds will
generally be light and vrbl this morning, becoming light S/SW during
the afternoon. Redevelopment of fog/low stratus is likely again early
tomorrow morning, mainly in the mtn valleys, but how widespread it
will be will depend at least in part upon how much falls this
afternoon/evening. Due to the inherent uncertainty, restrictions
are limited to MVFR at KAVL.

Outlook: The cold front will stall across the area, leading to
elevated chances for scattered diurnal showers and storms/associated
restrictions later this week, as well as an increasing potential
for morning low stratus and/or fog.

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  95%
KAVL       High 100%     High 100%     High  87%     High  91%
KHKY       High 100%     High 100%     High 100%     High  83%
KGMU       High 100%     High 100%     High 100%     High  95%
KAND       High 100%     High 100%     High 100%     High  95%

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...Munroe
NEAR TERM...JDL/TDP
SHORT TERM...Munroe
LONG TERM...Munroe
AVIATION...JDL

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
441 AM EDT Thu Aug 1 2019

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-020845-
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-
441 AM EDT Thu Aug 1 2019

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

.DAY ONE...Today and tonight.

Scattered thunderstorms are expected across the western Carolina's
and northeast Georgia this afternoon to evening. A few of the storms
will be strong to severe with small hail and damaging wind possible.
Heavy rainfall with localized flooding will also be possible,
especially this evening into tonight.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Scattered to widespread showers and thunderstorms are expected Friday
afternoon into Friday night and again Saturday. A tropical airmass in
place will support periods of heavy rain with localized flooding
likely, especially from the I-77 corridor, including Charlotte,
northwest into the North Carolina foothills.

.SPOTTER INFORMATION STATEMENT...

None.

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1242 PM EDT Thu Aug 1 2019

NCZ064-011715-
Transylvania NC-
1242 PM EDT Thu Aug 1 2019

...A STRONG THUNDERSTORM WILL IMPACT CENTRAL TRANSYLVANIA COUNTY
UNTIL 115 PM EDT...

At 1241 PM EDT, Doppler radar was tracking a strong thunderstorm 7
miles southwest of Brevard, or near Rosman, moving east at 10 mph.

Locations to be impacted include...
Rosman, Balsam Grove and Connestee.

Wind gusts up to 45 mph and torrential rainfall rates up to 3 inches
per hour will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Gusty winds can blow down trees that are dead, or that have weakened
root systems. Outdoor furniture and similar items can be tossed
around if not anchored. Seek shelter indoors.

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 3516 8291 3523 8292 3528 8276 3513 8274
TIME...MOT...LOC 1641Z 267DEG 8KT 3519 8286

08

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1250 PM EDT Thu Aug 1 2019

NCZ033-501-011715-
Caldwell Mountains NC-Avery NC-
1250 PM EDT Thu Aug 1 2019

...A STRONG THUNDERSTORM WILL IMPACT NORTHWESTERN CALDWELL AND EAST
CENTRAL AVERY COUNTIES UNTIL 115 PM EDT...

At 1249 PM EDT, Doppler radar was tracking a strong thunderstorm 5
miles south of Foscoe, or near Grandfather Mountain State Park. This
storm was nearly stationary.

Locations to be impacted include... Blowing Rock, Grandfather
Mountain State Park, B.R. Parkway between Linville Falls and
Grandfather, Upton and Globe.

Wind gusts up to 55 mph, dime size hail and torrential rainfall rates
up to 3 inches per hour will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Gusty winds can blow down trees that are dead, or that have weakened
root systems. Outdoor furniture and similar items can be tossed
around if not anchored. Seek shelter indoors.

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 3612 8167 3600 8169 3605 8184 3612 8182
      3612 8181 3611 8181 3612 8169
TIME...MOT...LOC 1649Z 280DEG 2KT 3609 8176

08

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