Flash Flood Warning 9, NWS Columbia, SC

Area Forecast Discussion
National Weather Service Columbia SC
303 PM EDT Sun Aug 27 2023

.SYNOPSIS...
A weak cold front is expected to remain draped across the
region through the first half of the week resulting in several
days of unsettled weather. The rain may be moderate to heavy at
times resulting in localized flash flooding. Recently upgraded
Tropical Storm Idalia will be pulled north towards the forecast
area with possible impacts during the mid-week period. Much
drier air will move in behind the system to close out the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Broad upper trough in the northeast CONUS, with ridge out west.
Cut off upper low along the Deep South/north Gulf of Mexico
enhancing southerly moisture flux into area although mainly
focused in GA/AL. Plume of deep moisture in TN ahead of a mid
level short wave trough spreading east as seen on water vapor.
Precipitable water is around 2 inches and deep shear weak so
heavy rain threat. A weak frontal boundary appears to be located
across the SC Piedmont into the north Midlands. Low level
convergence will be enhanced near this front and heavy rain
possible there. Scattered showers and thunderstorms now
developing at 18z. Thunderstorms in the CSRA being forced by
weak short wave trough moving northwest from near SAV. CAMS and
global deterministic models suggest thunderstorms will increase
in coverage late this afternoon into the evening as short wave
trough over west TN moves east. The air mass is a little more
moist today than yesterday. Instability is about the same given
the increase in low to mid level moisture. Expect moderate to
strong instability with mixed layer CAPE around 2000 J/kg and
surface based CAPE 3000-4000 J/kg...lower in the north Midlands.
The DCAPE is elevated in northeast GA into the Piedmont
SC/north Midlands at the moment, but expect moisture to increase
later this evening. However, model soundings showing lower LFC
and a less pronounced inverted V. So severe threat appears
lower than yesterday, although isolated severe damaging wind
possible...mainly in area of enhanced DCAPE into the early
evening. Overall strong lift expected and GFS shows strong upper
divergence through this evening. Went with likely to
categorical pops near the front and chance to the southeast.
Convection expected to linger overnight especially near the
frontal boundary, so kept highest pops northwest/north and lower
southeast after Midnight. Threat for flash flooding highest
near the front as some of the storms may train along
front...even after Midnight. After highs in the low to mid 90sw,
lows tonight in the low to mid 70s. Patchy fog possible tonight
with low cloudiness in the morning.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Upper trough remains in place over the Eastern United States on
Monday deepening further Tuesday. Meanwhile a remnant surface
boundary lingers across the region. Latest guidance on Monday
continues to favor a drier solution with the best rain chances
expected along and to the north and west of I-20. Opted to put
Chance PoPs across the entire forecast area during the late
afternoon and early evening hours since at least isolated
convection should develop given the moist environment (PWATs
around 2 inches) and boundaries, both mesoscale and Synoptic, in
the area. While conditions don't look as favorable for severe
weather on Monday, any robust convection could once again
produce damaging wind gusts. The Day 2 SPC outlook continues a
regionwide Marginal (1/5) risk for severe weather. The rain may
be heavy at times which is reflected in the Day 2 WPC ERO where
much of the FA is in a Marginal (1/5) risk for excessive
rainfall and a Slight (2/4) risk in the northwest. Highs will be
in the mid 80s to around 90 degrees. Rain chances should
decrease Monday night but the clouds may linger for much of the
night with temperatures falling into the lower 70s. The
unsettled weather pattern continues as tropical moisture ahead
of Tropical Storm Idalia is drawn north. Showers and
thunderstorms are likely to develop during the afternoon and
evening hours and could once again produce heavy rainfall,
especially Tuesday night as Idalia approaches the coast.
Temperatures will be similar to Monday.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
The focus during the long term will of course be Tropical Storm
Idalia. The latest NHC forecast track takes the center into the
Big Bend area of Florida as a hurricane Wednesday morning
passing through South Carolina Wednesday night into Thursday
morning as a tropical storm. The primary hazard will be related
to heavy rainfall, especially given the antecedent conditions.
However, specific impacts will be dictated by the track and
intensity of the cyclone as traverses the region. After the
tropical cyclone exits the area, cooler and drier air moves in
with temperatures anticipated to be well below normal Wednesday
through Friday before rebounding next weekend.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
Restrictions expected in convection from this afternoon into the
overnight hours.

A weak frontal boundary across the SC Piedmont into the north
Midlands and will focus scattered to numerous showers and
thunderstorms through the evening...aided by an approaching
upper trough from the west. Brief restrictions possible with
these storms through the evening. Best chance for convection
21z-04z. The showers could linger after 06z but expect a
diminishing trend. The guidance is suggesting low clouds/fog
development late tonight so went with MVFR although IFR ceilings
possible. Low clouds should mix out around 15z Monday.

EXTENDED AVIATION OUTLOOK...Increasing potential for
restrictions in early morning fog/stratus along with with
afternoon/evening showers and thunderstorms each day.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.

&&

Hazardous Weather Outlook
National Weather Service Columbia SC
352 AM EDT Sun Aug 27 2023

GAZ040-063>065-077-SCZ016-018-020>022-025>031-035-037-038-041-115-
116-135>137-280800-
Lincoln-McDuffie-Columbia-Richmond-Burke-Chesterfield-McCormick-
Newberry-Fairfield-Kershaw-Edgefield-Saluda-Lexington-Richland-Lee-
Aiken-Sumter-Barnwell-Calhoun-Clarendon-Bamberg-Northern Lancaster-
Southern Lancaster-Northwestern Orangeburg-Central Orangeburg-
Southeastern Orangeburg-
352 AM EDT Sun Aug 27 2023

This Hazardous Weather Outlook is for the Midlands of South Carolina
and the Central Savannah River area of Georgia.

.DAY ONE...Today and tonight.

Thunderstorms will again develop this afternoon and continue into
tonight across the Midlands and CSRA. A few thunderstorms may become
severe with damaging winds. Heavy rain will also be possible with
potential for localized flooding.

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

Scattered showers and storms continue through midweek. A few storms
on Monday could be strong to severe with gusty winds. Heavy rain will
also be possible Monday and Tuesday, leading to localized flooding
potential. A tropical system is forecast to affect the area midweek,
bringing additional threat for heavy rain and flooding potential.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

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