385
FXUS62 KCAE 211043
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
643 AM EDT Thu Aug 21 2025

.SYNOPSIS...
A retreating upper ridge breaks down today and allows Erin to
pass offshore of the United States. Increased chances of rain
today through the weekend with a heavy rain threat. Cooler
temperatures expected Friday and Saturday due to developing
upper troughing. Cold front late in the weekend will usher in a
drier and cooler air mass for next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Key Message(s):

- A weak front slides south through the forecast area this
  afternoon with increasing rain chances.

- Heavy rainfall possible

Erin is making its northeastward turn about 200 miles southeast
of Cape Hatteras while a weak upper trough and associated
frontal boundary slowly sink southeastward through the TN Valley
into the southern Appalachians. As Erin departs the region the
associated subsidence that was noted on Wednesday will also
shift away to the northeast allowing the weak upper trough to
our west to sink into the area and the weak frontal boundary
will move through the forecast area this afternoon. Atmospheric
moisture has already increased with satellite derived PWATs
already up to 1.7 in the western Midlands and expected to
continue to rise through the day to around 2 inches by this
afternoon. The combination of increase deep layer moisture and
weak upper forcing with weak to moderate instability should
yield scattered convection initiating by early afternoon and
initially favoring the western Midlands and CSRA. Severe storms
do not appear likely given weak northwesterly downsloping flow
and weak wind shear but slow storm motion and high PWATs will
provide an isolated localized flooding threat. WPC continues to
highlight much of the forecast area in a marginal risk for
excessive rainfall. Temperatures will be tricky with a bit of
weak downsloping northwesterly flow developing but also
expecting quite a bit of cloud cover this afternoon with
scattered convection but should be similar to yesterday with
highs around 90 degrees.

Expect showers and isolated storms to linger through the
evening into overnight with the frontal boundary stalling near
the CSRA and weak forcing associated with the upper trough
nearby. Overnight lows will be limited by extensive cloud cover
and lows should be in the lower 70s.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Key Messages:

- A weak frontal boundary stalls just south of the area Friday
  and remains there into Saturday.

- This front along with upper troughing should drive scattered
  to widespread showers and storms, especially in the southern
  FA.

- Heavy rainfall will be the primary risk from this activity
  each day, especially Friday.

On Friday weak upper troughing will continue to move into the
region as the weak front will continue through the FA before
likely stalling just south of the area. High PWAT`s (between
2.1-2.3") look to be in place through the day, especially into
the CSRA and Eastern Midlands. Generous cloud cover behind the
front should limit temperatures toward the low to mid 80s and
thus strong instability is not anticipated to build, though
skinny CAPE profiles with MLCAPE around 1000 J/kg is expected.
The GFS and other medium range models are showing a shortwave
approaching during the afternoon and evening, which should aid
in driving scattered to widespread convection, though the
highest coverage is expected in the southern FA, closer to the
front. Severe weather is not anticipated but deep layer shear on
the order of 20 kts could allow for a few loosely organized,
but strong clusters to develop. The main hazard will continue to
be heavy rainfall and possible areas of flooding from this
activity due to the substantial moisture in place, mean storm
motions around 5-10 kts, and the stalled boundary. The most
recent experimental REFS 24hr LPMM for rainfall Friday shows
pockets of 2-4" in the southern CSRA and into the eastern
Midlands, which is further supported in the 00z HREF 24hr LPMM
where even isolated spots of 5" are seen just outside of the
CWA. Due to this, WPC has upgraded the southern FA into a Slight
Risk (level 2 out of 4) for excessive rainfall. With shortwave
energy continuing to advect in the region overnight, some
isolated to scattered activity may carry into Saturday morning.

Saturday is expected to be fairly similar to Friday with the
main upper trough now moving into the Great Lakes region and a
more robust cold front approaching the western Appalachians by
the end of the day. More shortwave activity, deep moisture, and
the nearly stalled boundary just to our south should bring
another afternoon and evening with scattered to widespread
showers and storms. Like Friday, cloud cover should keep
temperatures toward the mid 80s and limit how much instability
can build, bringing a lower risk for isolated strong storms. The
axis of greatest PWAT`s should slowly shift toward the
southeast through the day, but the CSRA and into the Eastern
Midlands will remain where the greatest convective coverage is
expected and thus where the greater risk for locally heavy
rainfall and spots of flooding will reside. Some of this risk
will be dependent on where exactly the greatest axis of rainfall
falls on Friday. This activity is expected to slowly taper off
overnight as the axis of greater moisture pivots out ahead of
the main upper trough.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Key Messages:

- Stronger cold front pushes through the region Sunday, driving
  more showers and storms.

- Behind the front, drier conditions and cooler air moves in
  for the early week and into the mid week.

Ensemble guidance remains in good agreement that the deeper
upper trough should begin shifting over the eastern CONUS
Sunday, aiding in driving a fairly substantial cold front for
this time of the year into the region. Ahead of the front,
decent moisture should allow for more showers/storms throughout
the afternoon and evening on Sunday but by Monday, and
especially Tuesday-Wednesday, much drier air will filter in with
PWAT`s nearly 1-1.5 standard deviations below normal. This
drier air and the trough axis shifting overhead during the early
week should also usher in cooler air where temperatures Monday
may still be near to just below normal, but by Tuesday, will
begin falling below normal. Overall, this airmass modification
behind Sunday`s front toward the start of the week and into the
mid week should bring cooler/drier conditions to the area.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
Generally VFR conditions expected through the 24 hr forecast
period.

Some scattered stratocumulus noted on satellite but generally
above 3kft heights with some cirrus across the eastern Midlands.
Some intermittent river valley fog has occurred at AGS and will
include a tempo for restrictions through 13z. As Erin moves
away from the region northerly flow should shift more
northwesterly by this afternoon with wind speeds generally less
than 10 mph. Increased moisture today combined with a sinking
weak frontal boundary should provide isolated to scattered
convection favoring the CSRA so included a PROB30 group to
account for this generally in the 18z-24z time frame. Some
showers likely to linger into the evening hours at AGS/DNL
especially. Possible stratus expected to develop overnight but
mixed signals in guidance so decided to leave out at this time
but carry a SCT015 cig to indicate the potential.

EXTENDED AVIATION OUTLOOK...Restrictions become increasingly
likely Friday morning and into the weekend as deep moisture
returns to the region. Showers and thunderstorms are also
likely on Friday and Saturday.

&&

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

&&

$$