Flash Flood in North Carolina, September 23, 2018

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
816 PM EDT Sun Sep 23 2018

.SYNOPSIS...
A wedge of moist high pressure will persist across the area into
Tuesday. A cold front will then move into the forecast area from the
west on Wednesday. This front will become stationary and increase
the chance for showers and thunderstorms through the end of the week.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 800 PM EDT...So far little convection has developed
along/behind the slow-moving backdoor cold front. Latest SPC
mesoanalysis shows about 1000-1500 J/kg and is on a decreasing
trend. Updated PoPs to mainly highlight the high terrain, where SELY
upslope flow will continue to force shower activity. Confidence in
any thunderstorms is decreasing. Steering currents from the S/SW at
10-15 mph will limit the localized heavy rainfall potential.
However, some training of cells will be possible along the eastern
escarpment roughly parallel to the flow.

CAMs are in pretty good agreement (and have shown strong run-to-run
consistency) in allowing convection to continue developing into at
least the early part of the overnight near the NC Blue Ridge, where
weak but deep SE flow will focus upslope lift through much of the
period. Pops therefore peak at 60% across the northern foothills and
mountains by late evening, then gradually diminish through the
night.  Otherwise, the leading edge of the back door front will
continue its S/SW ooze (possibly picking up a little bit of speed)
to warrant 20-30 pops expanding to include much of the area. Min
temps will remain above climo, but slightly cooler than in previous
days.

Weak cold air damming is expected to impact much of the forecast
area on Monday, with persistent/stubborn low clouds expected to hold
max temps in the 75-80 range across much of the area (a little lower
across the mountains and north of I-40, a little higher across
southern Piedmont areas). Weak instability and lack of a source of
lift other than terrain effects will limit the most notable pops
(40-50%) to the high terrain and adjacent foothills.

&&

.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY/...
As of 300 PM EDT Sunday: A muggy and mild night is in store under
the clouds on Mon night. The NErn high pressure dome will be
centered over the Canadian Maritimes during the short term period,
but it's influence will still be felt here. Cool, moist air dammed
up against the mountains will allow the clouds to expand again and
cover most of the CWA by morning. Most of the area should be dry,
but will carry low chc PoPs to allow for a bit of drizzle or a very
light-brief shower overnight. The winds then veer enough to the east
to bring in some drier air to mix out much of the clouds by mid-aftn
Tues. Some instability is generated where it gets sunny, but the
CAPE is thin, and we can't see putting in higher PoPs than what is
going for Mon. Temps go back above normal for Tues aftn where the
clouds break up. Some southern towns may get near 90F.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
As of 300 PM EDT Sunday: A cold front will advance in from the
west/northwest later Wed and Wed night. Numerous showers and
thunderstorms should result, but coverage does not look to be total.
Highest PoPs will be painted highest over the mountains. By sunrise
Thurs, the front should be splitting the CWA in two. But, it will
also be dragging it's feet and probably lay out W-E, causing a delay
to the end of showers. The weak anti-cyclone behind the front just
about gives up as it runs into the upper ridging over the Atlantic.
Heights do fall a little, but forcing generally weak overhead. Next
weekend does look dry/rain-free for the most part with NW flow.
Dewpoints will be more comfortable in the m50s mtns to m60s S.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Weak back door cold front continues to work
its way slowly S/SW across the area and is about halfway between
KCLT and KGSP as of 00z. This front is not triggering much
convection, except along the eastern escarpment, where upslope is
enhancing lift. Will keep VCSH at KAVL and KHKY thru most of the
night, due to lingering showers in the SELY upslope flow. The
Piedmont sites look to only see isolated SHRA, so no mention at this
time. Winds will shift to NE behind the front (except SE at KAVL), and
low cigs are expected to develop from NE to SW thru daybreak Monday.
I went with the latest LAMP for the cig trends. All sites are
expected to go to the LIFR to MVFR range thru Monday morning. Some
improvement is expected Monday aftn, but confidence is low that much
of the cloud deck will mix out. A few showers possible across the
Upstate and southern NC mountains early Monday morning and thru the
aftn.

Outlook: Weak cold air damming may support restrictions and
occasional showers/light rain during the day Monday thru possibly
Tuesday. A cold front moving in from the west will then bring higher
chances of showers and storms Wednesday thru the end of the workweek.

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       High  80%     High  91%     Med   76%     High  94%
KGSP       High  95%     Med   74%     High  84%     High  87%
KAVL       High  86%     Med   78%     High  90%     High 100%
KHKY       Med   74%     Med   76%     High  80%     High  98%
KGMU       High  92%     Med   74%     High  80%     High  81%
KAND       High 100%     High  84%     High  84%     High  89%

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...DEO
NEAR TERM...ARK/JDL
SHORT TERM...MMD
LONG TERM...MMD
AVIATION...ARK

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
918 PM EDT Sun Sep 23 2018

GAZ010-017-018-026-028-029-NCZ035>037-048-051-052-056>059-062>064-
068>072-082-508-510-SCZ001>014-019-250130-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Alexander-Iredell-
Davie-Madison-Swain-Haywood-Catawba-Rowan-Graham-Northern Jackson-
Macon-Southern Jackson-Transylvania-Cleveland-Lincoln-Gaston-
Mecklenburg-Cabarrus-Union-Greater Rutherford-Eastern Polk-
Oconee Mountains-Pickens Mountains-Greenville Mountains-
Greater Oconee-Greater Pickens-Greater Greenville-Spartanburg-
Cherokee-York-Anderson-Abbeville-Laurens-Chester-Greenwood-
918 PM EDT Sun Sep 23 2018

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

.DAY ONE...Tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

NCZ033-049-050-053-065-501>507-509-250130-
Avery-Yancey-Mitchell-Buncombe-Henderson-Caldwell Mountains-
Greater Caldwell-Burke Mountains-Greater Burke-McDowell Mountains-
Eastern McDowell-Rutherford Mountains-Polk Mountains-
918 PM EDT Sun Sep 23 2018

This Hazardous Weather Outlook is for western North Carolina.

.DAY ONE...Tonight.

Scattered to numerous showers will continue to develop along and near
the eastern Blue Ridge Escarpment the rest of the this evening into
the overnight hours. Some showers may produce heavy rain and isolated
flooding will be possible.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

ARK