Flash Flood and Flooding in North Carolina, May 27 to 28, 2020

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
237 PM EDT Wed May 27 2020

.SYNOPSIS...
The remnant low from Tropical Storm Bertha will move north tonight
and Thursday across central North Carolina and into Virginia.
Warming southerly flow will develop Thursday through Friday ahead of
the next approaching cold front, but with continued moist conditions
over the area. The cold front will move into the region from the
northwest on Saturday, and settle southeast of the area through
Sunday. Drier and cooler air will arrive from the northwest for the
early part of next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 225 PM EDT Wednesday: Tropical Storm Bertha is currently
making its way farther inland over South Carolina. Showers will
continue to expand across the area as the system tracks northward,
however most of the more significant impacts are still expected
to remain just to our south and east. The main concern for our
fcst area remains the potential for flooding in the vicinity of
the I-77 corridor. Most of the guidance remains in good agreement
on the center of the low tracking thru Eastern SC and then Central
NC. This places a deformation zone on the NE side of the weak
circulation that tracks right along and east of I-77. Staying with WPC
preference, we're still forecasting 1-2" of rain over these areas,
with a very sharp gradient just west of I-77. The rest of the CWFA
looks to only get a couple tenths of an inch at most. One saving
grace is that the system should track fairly fast, which should
help limit really high rainfall totals. The rain should taper off
south to north this evening. Based on the wet antecedent conditions
and high stream levels, flooding potential remains elevated over
these areas. Otherwise, a large closed upper low will persist to
our west over the ArkLaTex region thru the near-term period.
Tropical Storm Bertha will steadily track northward and become more
disorganized the farther north it drifts. By the end of the period
Thursday evening, what's left of the tropical system will get absorbed
by a larger Canadian low tracking eastward. Later tonight, there
should be a lull in activity with some drier air on back side of
the departing low into VA. There will likely be some convection
across the TN Valley approaching the western edge of the forecast
area. But only expecting a few weakening showers possibly getting
in before daybreak Thursday. Lows will be about a category above
normal under mostly cloudy skies.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 227 pm EDT Wednesday: Some of the details are coming more
into focus with regard to the evolution of the old upper low to
our west that is still expected to open up Friday and then lift
out across our region on Saturday. In particular, the guidance
has taken on a decidedly diurnal scenario through the period. The
operational model runs are now in agreement that precip will be
convective and will diminish greatly in coverage both Thursday night
and Friday night, to the point where the radar might be largely
quiet during the early morning hours both days. The forecast was
moved in that direction with regard to the precip probability
distribution. Each day, daytime heating will flare up numerous to
widespread showers and storms, with a lingering flash flood threat
during the afternoons and evenings. Strong to severe storms won't
be ruled out during the diurnal peak both days, but the generally
poor overlap in buoyancy and shear in space and time suggests that
our chances right now don't look overly fantastic.  The best threat
might be Friday, but the GFS has the shear and not the buoyancy,
while the NAM has the sbCAPE but not the shear. Saturday might
have the best focus with the cold front moving in late in the day,
but again shear looks minimal. The front is now expected to move
through earlier Saturday night, so precip chances finally come to
an end for awhile before daybreak Sunday. Temps should stay above
normal until the front passes Saturday night.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 1253 pm EDT Wednesday: After the week that we have had, we
will be rewarded with a period of cooler and drier weather during
the first half of next week. The model guidance is still on board
with moving a cold front off the east coast by daybreak Sunday and
building a large continental sfc high into the region on a deep NW
flow aloft. The slowly progressive and amplifying upper pattern
will keep the NW flow in place through Monday and Tuesday, with
the sfc high center finally moving past on Tuesday afternoon. Temps
during this part of the period should be at or below normal, but the
lower humidity will make it seem even better. Would never rule out
an isolated shower on the ridgetops during peak heating each day,
but the chance is too small to mention at this time. On Wednesday,
the upper ridge axis finally moves east of the MS River, pushing
the high far enough off the east coast to start pumping the warmer
and more humid air back up from the SW. Temps will climb quickly
above normal as a result...and the chances of showers and storms
will start to increase.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
At KCLT and Elsewhere: Tropical Storm Bertha is currently making its
way inland over South Carolina with tropical moisture and showers
spreading northward across the area. Still expecting bands of
moderate to heavy rain to affect CLT this aftn and into the evening
keeping IFR to low MVFR visby and cig restrictions. Winds have
picked up a bit out of the NE, with the most gusts in the 15 to 20kt
range expected. Winds should favor an ELY to SELY direction at KAVL
before going light and vrb later tonight. The rest of the sites
should see more intermittent and light showers thru the aftn/evening,
with VCSH carried at those sites, with a TEMPO group for the most
likely window of heavier precip. Lower stratus and patchy fog is
expected later tonight and early tomorrow, as winds become light
and skies begin to clear aloft behind the departing low.

Outlook: A return to a more typical early summer pattern is expected
tomorrow and Friday, with shower/thunderstorm chances peaking in the
aftn to early evening. A cold front will slowly push into the area on
Saturday, resulting in another day of widespread showers/thunderstorms.
Dry high pressure will finally start to push into the region on Sunday.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High  85%     Med   70%     High  85%     High  89%
KGSP       High  83%     High  86%     High  89%     High  96%
KAVL       High  83%     Med   79%     Med   65%     High  83%
KHKY       Med   75%     Med   63%     Med   79%     High  81%
KGMU       Med   78%     High  86%     Med   77%     High  86%
KAND       Med   79%     High  97%     Med   72%     High  81%

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...Flash Flood Watch until 2 AM EDT Thursday for NCZ035>037-056-
     057-069>072-082.
SC...Flash Flood Watch until 2 AM EDT Thursday for SCZ009.

&&

SYNOPSIS...DEO
NEAR TERM...JPT
SHORT TERM...PM
LONG TERM...PM
AVIATION...JPT

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
212 PM EDT Wed May 27 2020

GAZ010-017-018-026-028-029-NCZ033-048>053-058-059-062>065-068-
501>510-SCZ001>008-010>014-019-281815-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Avery-Madison-Yancey-
Mitchell-Swain-Haywood-Buncombe-Graham-Northern Jackson-Macon-
Southern Jackson-Transylvania-Henderson-Cleveland-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-Anderson-Abbeville-Laurens-
Union SC-Chester-Greenwood-
212 PM EDT Wed May 27 2020

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

.DAY ONE...This afternoon and tonight.

As Tropical Storm Bertha, or its remnants, move north through the
central Carolinas today and this evening, tropical moisture will fuel
showers and a few thunderstorms. Heavy rain will be the main threat
from any storms that develop, in addition to cloud to ground
lightning. Isolated flooding of low-lying and poor drainage areas
will be possible this afternoon and evening.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

NCZ035>037-056-057-069>072-082-SCZ009-281815-
Alexander-Iredell-Davie-Catawba-Rowan-Lincoln-Gaston-Mecklenburg-
Cabarrus-Union NC-York-
212 PM EDT Wed May 27 2020

...FLASH FLOOD WATCH IN EFFECT UNTIL 2 AM EDT THURSDAY...

This Hazardous Weather Outlook is for piedmont North Carolina and
upstate South Carolina.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flash Flood Watch.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

PM