729
FXUS62 KCAE 111349
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
949 AM EDT Sun Aug 11 2024

.SYNOPSIS...
Hot temperatures and high humidity are likely to lead to triple
digit heat indices again today. Scattered afternoon and evening
thunderstorms are also likely this afternoon. River flooding is
expected to continue over the next several days. Temperatures then
cool off slightly early this week with daily chances of afternoon
showers and thunderstorms continuing.

&&

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

- Heat indices likely reaching triple digits this afternoon.
- Isolated flash flooding and severe thunderstorm potential
  this afternoon.

9:45 AM Update: Most of the low clouds and fog have been able to
mix out now that daytime heating is in full effect. A boundary
with relatively dry air behind it is currently moving through
the Pee Dee, which is scouring out the remaining low clouds out
of that area for the time being. Dew points ahead of this
boundary are in the upper 70s, while dew points behind this
boundary are in the low 70s with a few upper 60s mixed in just
across the border into North Carolina. This boundary has also
kicked of a few showers over our far eastern portions of the
forecast area this morning, but should move out of the area in
the next hour or two. The forecast for another round of showers
and thunderstorms with isolated strong to severe storms and
flash flooding remain possible. Read the early-morning
discussion below for more details.

Early-morning discussion: Much of our weather will be similar
to Saturday. Upper level winds will be relatively zonal with a
weak and diffuse surface boundary nearly stationary across the
area. Temperatures are expected to rise into the mid 90s, with
dewpoints steady in the mid to upper 70s. We will still have
some minor concerns around the heat index values, but they
should remain at or below 105 degrees for the most part, and no
headlines have been issued. This robust heating combined with
copious moisture (PW values of 1.8" to 2.2") is expected to
generate moderate to strong instability, with SBCAPE values over
2000 J/kg. Despite the moist atmosphere, we are also expecting
some mid level dry air to filter in, and DCAPE values at or
greater than 1000 J/kg will raise concerns for strong to severe
thunderstorm winds. Some additional organization is possible for
any storms which develop across the northern Midlands, as
forecast shear values in that area are slightly higher. The
surface boundary and perhaps sea breeze will likely serve as the
main areas for convective initiation, and PoPs are generally
lower in the western Midlands and slightly higher in the eastern
Midlands. Additionally, WPC has maintained a slight risk of
excessive rainfall for the eastern Midlands and a marginal risk
in the western Midlands due to saturated antecedent conditions.
So we will be on the lookout for any slow moving and/or training
storms which could pose an elevated Flash Flooding threat this
afternoon into this evening. HREF members are generally in good
agreement regarding this scenario.

The boundary should sink to our south tonight, and convection is
expected to diminish after sunset. Some lingering clouds tonight
could inhibit cooling, but generally we can expect overnight lows in
the mid 70s once again.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Key Message(s):

- Showers and storms expected across the eastern half of the forecast
  area on Monday, with chances decreasing on Tuesday.

Nearly zonal flow aloft will develop throughout Monday as deep
ridging builds to our west and the trough over the Mid-Atlantic
slides east. The diffuse surface trough that has lingered over the
Southeast since the departure of Debby will remain in place for
another day, with a broad moisture gradient across SC. PWAT`s will
remain above 2.0" for our forecast area and dew points will float
around in the mid-70`s. Instability will be a bit weaker on Monday
compared to the weekend, primarily due to relatively "cool" surface
temps around 90; generally lower heights, weak northeasterly flow at
low levels, and some persistent cloud cover are the primary
cause for the cooler temps. PoP`s and convective potential in
general in the GEFS, EC, and HREF are mostly consolidated to the
eastern Midlands and coastal plain, which makes sense given the
weaker instability inland and lack of true forcing outside of
sea breeze convergence.

The pattern begins to amplify on Tuesday as ridging builds further
in the south-central US, positioning the fa under northwest flow
from 700-250 mb. Drier air will then filter in aloft and help drop
PWAT`s a bit by the afternoon. Overall, the convective potential
looks to be the lowest on Tuesday since Debby thanks to weaker
instability, lower PWAT`s, and no trigger of note. High temps like
Monday will struggle to get much above 90 as surface high pressure
to our north drives north-northeast flow.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Key Message(s):

- Relatively "cool" but seasonably dry weather expected
  throughout the middle part of the week.

Deepening of the trough across the northeastern US on Wednesday and
Thursday will help strengthening the associated surface high and
drive stronger northwest flow over our area. These will both combine
to yield relatively dry air, both aloft and near the surface, and
cooler temps for much of next week; NAEFS and EC ensemble output
shows consistently unremarkable heights, moisture, and temps
Wednesday through Saturday with anomalously strong northwesterly flow.
This in turn will yield slightly below average temps and PoP`s,
thanks to the positioning the surface high to our north in
conjunction with the northwest flow aloft. High temps should
therefore run a few degrees below average and dew points should drop
down into the 60`s consistently.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
Generally VFR conditions through the remainder of the TAF
period, with afternoon and evening convection possible.

The fog and stratus from this morning has generally lifted,
leaving VFR conditions at the terminals. As the morning goes
on, expect a cumulus field to develop with bases in the 5k-6k
range. The air mass should become moderately to strongly
unstable in the afternoon, with scattered thunderstorms expected
after 11/18z. Confidence is still a bit low for TEMPO groups at
the terminals, so used VCSH for now. Winds generally light and
variable increasing S/SE this afternoon around 8 kts or less.
Thunderstorms may produce erratic and gusty winds to 40 kts.
Convection clears late this evening with winds returning to
light and variable.

EXTENDED AVIATION OUTLOOK...Afternoon and evening convection
and associate restrictions will be possible through Thursday.
Early morning fog and stratus could occur, especially at fog-
prone AGS/OGB.

&&

.HYDROLOGY...
Key Message(s):
- Area rivers have crested and are falling. The Pee Dee at Cheraw
and the Wateree River at Camden are currently at moderate flooding
levels, but will fall into the minor category shortly. Minor
flooding will continue on the Congaree River south of Columbia in
the Congaree National Park through tomorrow morning.

&&

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

&&

$$