Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
256 AM EDT Fri Jun 11 2021

.SYNOPSIS...
Daily afternoon and evening thunderstorms are expected today through
the weekend. With abundant moisture remaining over the region, these
storms will pose a threat of localized flash flooding. A cold front
settles across the region early Tuesday, promoting a marginal chance
of showers on Monday and Tuesday, before high pressure builds in
midweek.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 250 am EDT: Southwest to west winds at low-levels will provide
a mountain upslope flow component through daybreak. This will
combine with arriving vorticity embedded in the 500 mb trough moving
into the southern Appalachians to yield scattered to numerous
coverage of mountain showers through the early morning hours.
Reasonably steady steering flow, and the lack of any significant
anchoring, should keep hydro concerns at a minimum throughout the
morning hours.

The upper forcing will transit the forecast area today and it may
catch up to better instability along the I-77 corridor, and
southeast of I-85, by the afternoon hours. Piedmont locations should
see 1500 to 2000 J/kg of sbCAPE during the late day. Weak upper
jetlet divergence is also indicated. Meanwhile, low-level westerly
flow will provide continued upslope triggering across the spine of
the NC mountains near the Tennessee border. This could permit a
localized maximum of higher QPF in and near the western part of the
northern mountains, however, forcing throughout and better
instability farther southeast makes it very difficult to pin down
the area of greatest hydro threat today. Will thus highlight the
localized flooding potential in the HWO and forego any Flash Flood
Watches at present since hydro issues in the 1.75 to 2 inch PWAT air
will be possible just about anywhere training showers/storms set up.
Persistence looks good for maximum temperatures.

The base of the H5 trough will cross the mountains tonight, with
modest mid-level drying arriving from the west. However, continued
low-level westerly upslope flow will allow scattered nocturnal
showers to continue in the western mountains overnight. Persistence
is good for min temps too in this airmass.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 200 AM EDT Friday: By daybreak Saturday, an upper trough axis
is just east of our CWA and mid/upper forcing is rapidly
diminishing.  Accordingly, PoPs drop off through the first part of
Saturday.  At the surface, northerly flow sets in and leads to some
drying, though elevated PoPs could hang on especially in the
mountains.  Should continue to see enough moisture for scattered
clouds on Saturday, with perhaps a few stray showers as some DPVA
ripples across the CWA in association with a de-amplifying shortwave
aloft.

Weak CAA aloft promotes steepening midlevel lapse
rates through Saturday, keeping thunder in the forecast.  Although
lifting will be minimal with the cold frontal boundary well to our
south, we should still see a few cells pop up in the afternoon.  The
GFS/NAM are pushing afternoon winds turning more north-
northeasterly, which could induce a slight upslope component and
enhance convective initiation.  Excessive rainfall appears to be a
continuing threat with these storms: weak steering flow and minimal
shear will likely lead to slow-moving or near-stationary cells,
especially in the NC Foothills and SC Upstate.  Otherwise, severe
threat should be minimal, although as always a rogue severe storm
can't be ruled out.

Sunday, a more robust cold front pushes through and surface flow
shifts to a more pronounced northwesterly direction.  Downsloping
will promote drastically lowered RHs, while aloft, the continued de-
amplification of the Saturday's shortwave will lead to dwindling
synoptic forcing.  Clearing skies and better surface heating will
promote a deeper PBL than on Saturday, thus as noted in previous
discussions, mixing should allow dewpoints to drop a bit more on
Sunday than on Saturday.  So, convection will be fairly suppressed
on Sunday compared to Saturday, and the only area with much risk of
thunder will be the mountains, where terrain enhancement could drive
a few convective cells to break out.  Although flooding risk on
Sunday will be much lower than on Saturday, a few rogue severe cells
can't be ruled out in light of drier profiles generating a few
damaging winds.

Temps still on track to stay right around normal both Saturday and
Sunday - downsloping off the Appalachians combined with good solar
insolation should compensate for the weak CAA with Sunday cold
frontal passage and prevent a notable drop in temps.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 230 AM EDT Friday: The elongated 500mb trough over the
northeastern CONUS slowly creeps eastward through the medium range.
As another weak cold front pushes across the CWA on Tuesday, surface
convergence along the Appalachians should allow for a few showers
there on Monday, while the rest of the CWA will see mainly fair
weather.  Widespread subsidence limits active weather on Wednesday,
apart from a few isolated showers still possible in the mountains.
Northwesterly flow ushers in high pressure past Tuesday, and as
heights gradually rise we should see continued clear and dry
conditions through Friday morning, as the frontal boundary settles
to our south.

Anticipating temps on Monday and Tuesday to be several degrees above-
normal, before falling to near-normal the rest of the week in the
wake of Tuesday's frontal passage.

&&

.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Spotty showers will continue to pare back
toward the western mountains early this morning in low-level
southwesterly to westerly upslope flow. The main impact east of the
mountains early this morning will be the arrival of lowering MVFR
cigs, which will be slow to lift and scatter through mid to late
morning. Mountain valleys could see IFR cigs at times around
daybreak as well. Will reintroduce showers from west to east late
morning through early afternoon with the arrival of an upper
shortwave, with PROB TSRA timed to the better instability and
passing upper support later today. Winds will pick up from mainly
the southwest this afternoon, with low end gusts most likely at the
Upstate SC TAF sites with better mixing. Winds will remain more
northwesterly on average at KAVL. Showers will taper off this
evening with mainly higher VFR cigs persisting before overnight
restrictions return in the moist boundary layer just beyond the
current TAF period.

Outlook: Scattered to numerous diurnally-driven thunderstorms and
associated flight restrictions will continue through at least
Saturday before modest drying moves in on Sunday and in early next
week. Overnight/morning fog/low cigs are possible each day,
especially over the mtn valleys and at any locations that receive
heavy precipitation each day.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High 100%     High  88%     High 100%     High 100%
KGSP       Med   71%     High  96%     High 100%     High 100%
KAVL       Med   61%     Med   78%     High  93%     High  91%
KHKY       Med   65%     High  81%     High 100%     High 100%
KGMU       Med   68%     High  96%     High 100%     High 100%
KAND       High  82%     High  97%     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...MPR
NEAR TERM...HG
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...HG

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
331 AM EDT Fri Jun 11 2021

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-120745-
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-
331 AM EDT Fri Jun 11 2021

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

.DAY ONE...Today and tonight.

Numerous to widespread showers and thunderstorms will develop across
the western Carolinas and northeast Georgia today, with the greatest
coverage during the afternoon and early evening hours. The
thunderstorms will have the potential to produce torrential
downpours in affected areas and localized flooding may develop in
any locations that see repeated thunderstorms in a short period of
time. The thunderstorms will also produce dangerous cloud-to-ground
lightning and gusty winds.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

MPR

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
548 AM EDT Fri Jun 11 2021

NCZ051-111045-
Swain NC-
548 AM EDT Fri Jun 11 2021

...A SERIES OF HEAVY RAIN SHOWERS WILL IMPACT SWAIN COUNTY
THROUGH DAYBREAK...

A series of heavy rain showers crossing the Great Smoky mountains
from the west has been producing one inch per hour rainfall rates in
a few locations across Swain County. Additional rainfall of one-half
to one inch will be possible in and around the Smokies through 7 am
EDT.

Locations to be impacted include...Bryson City, the Great Smoky
Mountains National Park, Newfound Gap, Fontana Lake, Luada, and
Alarka.

Deep standing and running water will develop in low-lying areas.
Rises to near bankfull will be possible along Hazel Creek, Roaring
Creek, and Bone Valley Creek in northwest Swain County.

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 3556 8377 3557 8363 3558 8360 3556 8358
      3556 8350 3560 8345 3561 8335 3535 8341
      3539 8359 3543 8359 3543 8361 3544 8364
      3543 8365 3545 8373 3544 8376 3545 8380
      3545 8383
TIME...MOT...LOC 0943Z 279DEG 5KT 3551 8355

HG