Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
238 PM EDT Thu Jul 15 2021

.SYNOPSIS...
A broad trough approaching from the west will slowly breakdown the
Bermuda high this weekend, supporting a gradual increase in coverage
of afternoon to evening convection. The trough and an associated
cold front may push through the region early next week, leading to
at least briefly cooler and drier conditions by the middle part of
next week.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 100 PM: Just not really a lot to get excited about
thru Friday. We will remain under a typical midsummer pattern
dominated by the Bermuda High. Convection has recently fired up
over the Appalachians, loosely along an axis from West Virginia
to N Georgia. Looks like a very weak vort ripple aloft may have
played a role in this. At any rate, activity should continue to
propagate slowly eastward thru evening, although light downsloping
flow across the mtns looks to limit coverage. This warrants isolated
to scattered PoPs, close to climatological chances. PWATs are
near or slightly above climo; overall weak shear is producing slow
storm motion vectors. Not really anything out of the ordinary for
July. Areas of fog or low stratus are expected in the mountain
valleys tonight, and some patches thereof may develop in the
Piedmont as well, wherever heavy rain falls this afternoon.

Height pattern aloft does amplify a little with time, as ridge
builds slightly and/or retrogrades inland from the Atlantic, and as
trough axis moves into the middle Mississippi Valley. Lapse rates
may improve slightly Friday afternoon; some guidance does depict a
bit of an uptick in convective coverage in response. Overall still
looking like chance PoPs are warranted across the CWA. 1000-850
and 1000-500mb thicknesses rise a bit with the building ridge,
so temps generally should top out a degree or two warmer Friday.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 100 PM Thursday: The subtropical high will continue to linger
overhead during the weekend, but a low-amplitude trough moving
in from the Midwest will slowly weaken the upper ridge. Slight
height falls will be accompanied with the upper trough as embedded
shortwaves help steepen mid-level lapse rates and produce modest
instability with the associated cooler air aloft. The Bermuda
High continues to pump in a moist southwesterly flow through
much of the forecast period. Deep layer southwesterly flow and
persistent embedded shortwaves will keep shower and thunderstorm
chances lingering into Friday and Saturday nights, especially in
the favorable slopes in southwest mountains of NC. The Bermuda High
will continue to produce moisture advection from the southwest as
lee troughing sets up shop over the Carolina piedmont/foothills
and thus, an uptick in PoPs and convective coverage will return
to the forecast yet again on Saturday, especially during the
afternoon/evening hours.

Convective coverage will likely grow on Sunday as the trough axis
and attendant frontal boundary inches closer to the CFWA. With deep
layer southwesterly flow nearly parallel to the front, training
showers and storms can't be ruled out. This could produce hydro
concerns across portions of the CFWA, especially with PWAT values
>1.50" and the slow progression of the front. Organized convection
will be possible ahead of the front on Sunday as effective bulk
shear will be on the order of 20-30 kts which is conducive to a
low-end severe threat, especially with steeper mid-level lapse
rates and upper-level support. Temperatures will run hot and humid
for Saturday, but will dampen a little bit Sunday with increasing
cloud cover and more widespread convective coverage.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 215 PM Thursday: Unsettled weather will continue into Monday
as the positively tilted trough continues to dig down over the East
Coast. The attendant frontal boundary looks to make a full passage
sometime Tuesday into early Wednesday, so scattered convective
coverage could continue into the Tuesday, especially for the
southern half of the CFWA. The aforementioned subtropical high
will become suppressed as the upper trough takes control. Model
guidance continue to produce a rare July fropa, but not before
producing an excessive rainfall and low-end severe threat before
the full fropa. With the expected activity during the short-term,
hydro concerns will increase with any additional heavy rainfall
during the early part of next week. The frontal boundary's very slow
progression will help produce more training cells to help raise
the cause of concern for localized flash flooding. With a full
fropa now expected, Wednesday and Thursday of next week could end
up being dry and cool for mid-July standards. With the uncertainty
still lingering during this potential post-frontal regime, decided
to keep chance diurnal PoPs for the middle part of next week as the
trough axis slowly passes over the CFWA. Model guidance differ in
the timing with the GFS being slightly more progressive with the
passage of the frontal boundary and trough axis, but the overall
synoptic setup is similar between the GFS and ECMWF. Temperatures
will likely run 5-10 degrees below normal for highs during the
early part of next week, while rebounding to near or slightly
below normal values by the latter half of the extended period.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
At KCLT and Elsewhere: Another seasonably humid and unstable
afternoon will bring isolated to widely scattered SHRA/TSRA across
the region. Expected coverage warrants TEMPOs at KAVL, KHKY, KAND;
elsewhere mention is retained as VCSH. IFR vsby would be likely
at any site that takes a direct hit. Light SW'ly winds except
NW at KAVL. The swaths of heavy rain that occur this afternoon
are more likely to see fog/stratus develop in the predawn hours;
with low confidence on the precip confidence on these restrictions
is also low, and not mentionable at any site. Valley fog however
should affect KAVL, though signal is not as strong as it was for
this morning, so only MVFR for now. Slightly better precip chances
tomorrow, but am not yet mentioning at any site.

Outlook: An unsettled pattern, with afternoon/evening storms and
morning fog/stratus restrictions, will persist for several more
days at least. A front near the region this weekend may enhance
afternoon convective coverage.

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  95%     High  87%     High 100%
KHKY       High 100%     High 100%     High 100%     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 are available at
the following link:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

SYNOPSIS...CAC
NEAR TERM...Wimberley
SHORT TERM...CAC
LONG TERM...CAC
AVIATION...Wimberley

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
343 PM EDT Thu Jul 15 2021

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-161945-
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 NC-
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-Union SC-Chester-Greenwood-
343 PM EDT Thu Jul 15 2021

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

.DAY ONE...This afternoon and tonight.

Showers and thunderstorms are expected to develop again this
afternoon across the western Carolinas and northeast Georgia, with
coverage ranging from patchy to scattered. The main threats from
these storms will be gusty winds, brief heavy rain, and the
occasional cloud- to- ground lightning strike. Storm activity should
diminish after sunset.

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

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

MPR

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
521 PM EDT Thu Jul 15 2021

NCZ064-152200-
Transylvania NC-
521 PM EDT Thu Jul 15 2021

...A HEAVY RAIN SHOWER WILL IMPACT SOUTHEASTERN TRANSYLVANIA COUNTY
UNTIL 600 PM EDT...

At 521 PM EDT, Doppler radar was tracking a heavy rain shower 6 miles
southeast of Brevard, or 4 miles northwest of Caesars Head State
Park, moving east at 10 mph.

Locations to be impacted include...
Brevard, Dupont State Forest, Connestee, Little River In Transylvania
County, Cedar Mountain and Sassafras Mountain.

Very heavy rainfall rates up to 2 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 3526 8260 3519 8260 3514 8258 3513 8263
      3513 8264 3512 8266 3513 8268 3510 8270
      3509 8273 3508 8274 3508 8275 3507 8275
      3507 8277 3520 8281
TIME...MOT...LOC 2121Z 269DEG 8KT 3516 8269

KRENTZ