Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
259 PM EDT Thu Aug 19 2021

.SYNOPSIS...
A weak upper trough and abundant moisture will continue across the
region into Friday leading to scattered afternoon and evening
showers and thunderstorms. Saturday an upper-level low will meander
around the Ohio Valley and Mid-Atlantic region before lifting
northeast into New England late this weekend into early next week as
a ridge of high pressure to the south nudges eastward. This should
lead to drier conditions for the weekend with only isolated showers
and thunderstorms during the afternoon and evening hours expected.
Highs will remain above climo this week into next week.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 2:45pm EDT Thursday:  Round of typical diurnal thunderstorms
is underway this afternoon, expected to die out after dark.  Storms
are being enhanced by the passage of a weak upper wave. This shows
nicely as updraft strength in hi-res models. This wave will have
most of its energy east of the region by tomorrow, and while some
thunder will still be possible, the coverage and intensity will be
much reduced from today.  For today, forcing from the wave might
give some severe storms today, despite only 500-1000 j/kg of MLCAPE.
Bulk shear and hodographs are unimpressive, with pulse severe wind
gusts the main threat.  Storm motion is also eastward at 10 to
20kts, which should reduce the risk from hydro issues.  Should mid
and upper clouds clear behind weak surface boundary ahead of upper
wave later tonight, fog could become an issue overnight as surface
layer remains very moist from recent rains, but this is not clear.
Fading tropical air mass will have highs and lows near to a couple
degrees above normal tomorrow.  Winds are fairly light around weak
frontal boundary, and will be lighter on Friday as surface high
behind boundary moves in.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 215 PM EDT Thursday...A ridge of high pressure will continue
to dominate across the southern United States through the short term.
Meanwhile an upper-level closed low will meander around the Ohio
Valley and Mid-Atlantic region Friday night into Saturday. This low
will be forced to lift northeast into New England as the ridge of
high pressure in the southern CONUS nudges eastward Saturday night
into early Monday. As a result of this ridge pushing east into the
western Carolinas and northeast Georgia, flow will be mainly
northerly and northwesterly. This will lead to limited moisture
across the CWA this weekend. Capped PoPs to a slight chance to
chance for the entire period as only isolated showers and
thunderstorms look possible. Highs this weekend should be a couple
degrees above climo.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
As of 215 PM EDT Thursday...The closed low keeps lifting northeast
out of New England into Nova Scotia during the first half of the
extended term forecast period. This will allow the ridge to remain
over the southeastern CONUS through the middle of next week. Towards
the end of the forecast period, this ridge should start to
retrograde back west of the CWA. Meanwhile, a surface trough looks
to linger along the Southeast coast throughout the extended. Monday
and Tuesday are looking like the drier days as the eastern periphery
of the ridge will remain over the area. Capped PoPs to a slight
chance to chance for this reason. Wednesday into Thursday moisture
associated with this trough could push further inland as the high
retreats west. This would increase the moisture influx. Both the GFS
and ECMWF have PWAT values increasing Wednesday into Thursday. As a
result, have PoPs at chance for the end of the forecast period.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
At KCLT and elsewhere:  Thunderstorms now spreading across the area
from west to east.  Expect a typical diurnal pattern with storms
dying out just after sunset.  Upper trough crossing the area will
assist storm development today with some severe.  Weak surface
boundary has generally SW winds of 5 to 10 kts.  As this boundary
moves eastward, surface high comes in, and winds become light and
VRB overnight, becoming more NW to northerly on Friday.  Opted to
keep in some mention of fog at all locations as some possible
clearing overnight above a still moist surface layer and light
winds, will create good conditions for fog formation at some level.
For KCLT, have kept in a PROB30 for thunder tomorrow afternoon,
though storms will be much more widely scattered than today.

Outlook: A typical, diurnal summertime convective pattern is
expected to prevail into early next week, with coverage scattered at
best. Mtn valley low stratus and fog will be possible each morning.

Confidence Table...

            12-18Z        18-24Z        00-06Z        06-12Z
KCLT       High 100%     High 100%     High 100%     High  89%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High  92%     High 100%     High  84%
KHKY       High 100%     High 100%     High  95%     Med   76%
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 are available at
the following link:

www.weather.gov/gsp/aviation

&&

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

&&

SYNOPSIS...AP
NEAR TERM...WJM
SHORT TERM...AP
LONG TERM...AP
AVIATION...WJM

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
513 AM EDT Thu Aug 19 2021

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-200915-
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-
513 AM EDT Thu Aug 19 2021

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

.DAY ONE...Today and tonight.

Thunderstorms are expected to develop today as an upper level
disturbance moves through. After a few early morning storms, new
thunderstorms are expected to develop in the late morning and early
afternoon mainly over the mountains. The storms may become numerous
and organized as they move east across the Upstate, foothills, and
western Piedmont this afternoon and into the early part of the
evening. Some of the storms will become strong to severe, with
frequent cloud-to-ground lightning, damaging wind gusts, and large
hail. Heavy downpours are also possible. The storms will end in the
early to mid evening hours around the Charlotte metro area.

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

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

PM

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