515
FXUS62 KCAE 120947
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
547 AM EDT Mon Aug 12 2024

.SYNOPSIS...
Scattered showers and thunderstorms expected each afternoon
through Tuesday. Then drier air moves into the region allowing
for a few slightly cooler days with only isolated showers and
thunderstorms. Moisture returns to the region late this week and
into the weekend as a frontal system moves into the eastern US.

&&

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

- Patchy fog with reduced visibilities possible this morning.
- Showers and thunderstorms expected across the eastern half of the
forecast area this afternoon.

The forecast remains in good shape this morning. A surface boundary
remains quasistationary across the state from southwest to northeast
with zonal flow aloft. A weak shortwave upstream from the Carolinas
continues to provide some support for weak convection north of
Columbia. The CAMs have been consistently showing these showers and
storms, but they are beginning to show signs of weakening and moving
into NC - thankfully moving off to the northeast at a decent pace.
Low temperatures will be fairly similar to the past couple of nights
- generally mid 70s across the area.

Zonal upper level flow will persist overhead today. At the surface,
a weak and diffuse boundary will be over the Midlands and will
continue to provide a source of convective initiation. Moisture
remains entrenched over the region, with dewpoints in the mid to
upper 70s once again, and PW values from 1.8"-2.2", the highest
values toward the coast. Strong heating with highs in the low 90s
will yield moderate to strong instability, with 1500-2000 J/kg of
SBCAPE. This should be plenty to generate scattered showers and
thunderstorms during the afternoon and evening with much of the
anticipated activity along and south of I-20. Wind gusts will be the
main threat for severe thunderstorms as DCAPE values will again push
toward 1000 J/Kg. A few transient shortwaves may enhance activity
for a time, but widespread severe weather is not expected.

The other concern remains the potential for locally heavy rainfall
over already saturated or nearly saturated soils. WPC has maintained
much of the central and eastern Midlands in a marginal risk of
Excessive Rainfall. Expect the majority of convection to dissipate
with the loss of daytime heating, however any residual outflow
boundaries could interact to develop a few cells into the early
overnight hours. Steering flow should also be a bit faster, around
15-20 kts.

Lows tonight will be in the low to mid 70s.


&&

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

- Damaging wind gusts possible Tuesday afternoon and evening

An upper trough axis will be just east of the area on Tuesday.
Low level moisture should pool over the forecast area with PWAT
values between 1.75 and 2 inches. As the air mass destabilizes
in the afternoon, convection will develop in an environment with
deep-layer shear strong enough to support organized convection.
West-northwest winds aloft with easterly low level winds should
support 0-6 km shear values from 30 to 40 kts. Although 0-3 km
lapse rates will be steep, poor lapse rates aloft may limit
updraft strength and the overall severe threat. The HREF tends
to favor convection initiating in the higher terrain of the
Upstate progressing SE into the forecast area in the late
afternoon or evening. Steep low level lapse rates and moderate
shear could support damaging wind gusts with storms. The bulk of
the convective activity should move east of the forecast area
in the evening with a few lingering storms behind the main area.
Highs Tuesday will be in the upper 80s to low 90s with lows in
the low 70s.

&&

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

- Drier air moves into the region mid to late this week
- A frontal system may approach the area Friday into the weekend

The GEFS and ECMWF ensembles continue to favor the
amplification of a ridge over the central US this week with the
axis of an upper trough offshore of the East Coast. This will
direct northwest flow into the Southeast along with drier air
for Wednesday and Thursday. PWAT values of 1.4 to 1.6 inches and
weak lapse rates favor isolated to widely scattered convection
each afternoon.

Late week, models indicate the potential for an upper low to
move into the Great Lakes region. The associated frontal system
should swing into the Southeast near the end of the long term.
As warm, moist advection strengthens ahead of the front we
should expect to see PWAT values rise back to 1.75 to 2 inches
through the weekend. This will support at least a chance of
showers and thunderstorms. With troughing generally over the
area for much of the long term we should see afternoon high
temperatures slightly below normal in the mid to upper 80s.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
Generally VFR conditions expected outside of brief restrictions in
diurnally driven thunderstorms and early morning stratus/fog.

Convection is north of the terminals early this morning with mainly
mid and high level clouds across the area. With shallow low-level
moisture, near calm winds overnight and decreasing high clouds, fog
and low stratus may develop toward dawn. Have included a mention of
restrictions in the TAFs, possibly as low as LIFR/IFR but improving
by 12/14z. As the air mass becomes moderately to strongly unstable
this afternoon, scattered thunderstorms are expected to develop once
again. Outside of convection, sfc winds will be variable at 5 to 10
knots.

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

&&

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

&&

$$