168
FXUS62 KCAE 171816
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
216 PM EDT Sat Aug 17 2024

.SYNOPSIS...
A cold front approaches the Southeast US this weekend along with
increasing moisture and rain/thunderstorm chances. A few strong to
severe storms will be possible, with better chances on Sunday. Drier
air and cooler temperatures are then on tap for early to mid next
week. The next chance for rain arrives late in the work week

&&

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

- A few passing showers this afternoon.
- Additional showers and thunderstorms are expected to move
  through during the evening and early overnight period.
- A few thunderstorms could be strong to severe, especially
  closer to the Upstate.

Radar this afternoon shows a line of showers moving through the
southeastern Midlands and CSRA. This activity should depart the
forecast area during the next hour or two. Model guidance
continues to suggest that more robust convection will develop in
the Upstate later today, moving through the CWA during the
evening and early overnight hours. The CAMs also show the
possibility of two waves of showers and thunderstorms, with the
first more likely to produce strong to severe thunderstorms. The
latest SPC Day 1 Severe Weather Outlook placed much of the
forecast area in a Marginal (1/5) risk for severe weather
through 12Z Sunday, on a line that roughly stretches from
Augusta and Aiken to Sumter and then north to west of Cheraw.
The primary forcing mechanism today is expected to be the
combination of a pre-frontal trough with a supporting shortwave
which will promote lift. The main deterrent for thunderstorms
in our forecast area is that modeled soundings at CAE, AGS, and
OGB show a decent amount of CIN developing in the lowest levels
of the atmosphere, especially the farther east you go. The CIN
appears to be absent in the CLT sounding. This would suggest
that the thunderstorms will be more likely closer to the Upstate
with convection potentially weakening as it moves into the more
stable conditions to the south and east. Leaned PoPs towards
the 15Z HRRR with this update which seems to have the best
handle on convective evolution today. The clouds and showers
that we`ve seen so far today has limited warming so reduced
temperatures as a result with highs now in the upper 80s to
lower 90s. Temperatures tonight should fall into the lower 70s.

&&

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

- Scattered afternoon thunderstorms expected, a few of which
  could produce damaging wind gusts.

A bit of a tricky forecast for Sunday. Upper trough over the Great
Lakes region is expected to amplify and eject a rather robust mid-
level shortwave around its base. This disturbance is progged to
move through GA and the Carolinas Sunday afternoon and evening
in conjunction with a surface front. Adequate moisture will be
available, with PWATs around 1.5"-1.7". Convergence along the
approaching surface boundary is expected to be sufficient enough
for convective initiation. Given forecast temperatures in the
low 90s and dewpoints in the low 70s, SBCAPE between 1500 and
2500 J/kg should generate a broken line of storms along the
front. Potential for mainly severe wind gusts will exist, given
DCAPE values in excess of 1200 J/kg and 0-6km bulk shear of
25-35 kts aiding in organization. Some model discrepancies exist
with the timing of the frontal passage, and the extent of
thunderstorm coverage will likely depend on sufficient heating
as it moves through. Current thinking is that the eastern half
of the CWA is at greatest risk, or mainly east of I-20. This
area should have convective elements lining up the best in time
and location. HREF members are generally showing initiation in
this region, though its possible the strongest storms will be
reserved for the Coastal Plain. As the forecast stands now, SPC
has placed almost all of the Midlands and CSRA in a Slight Risk
for severe thunderstorms. Thunderstorms that do develop will
push southeastward along with the front. Behind it, drier air
will begin to filter into the area with falling PWAT values and
lows around 70.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Key Message(s):

- Dry through midweek before rain chances return for the end of
  the week.

Next week is relatively quiet compared to the first half of the
month. Upper level troughing will remain in place over the eastern
CONUS through midweek with drying northwest flow aloft. We`ll still
have some lingering moisture near the surface, but dewpoints will be
lower, generally in the 60s or perhaps upper 50s, while PWATS will
linger between 1" and 1.25". With this stagnant pattern, the front
that pushes through Sunday and Sunday night will linger just
offshore, with showers and thunderstorms south and east of our area
through midweek. Late in the period, deterministic and ensemble
solutions are in good agreement that surface high pressure will
strengthen over the Great Lakes and move eastward before ridging
down the coast. The breakdown of the upper trough is then expected
to assist in allowing the offshore front to move back toward the
coast. As such, there will be a slight increase in shower and
thunderstorm chances at the end of the week, particularly for the
eastern Midlands. Overall moisture will still be on the lower side
though, so maintained only slight chances for these areas.
Temperatures this week will be quite pleasant for August, in the mid
to upper 80s with lows in the mid to upper 60s.

&&

.AVIATION /17Z SATURDAY THROUGH WEDNESDAY/...
Monitoring for Potential Showers and Thunderstorms this
Evening...

VFR conditions are ongoing at all terminals this afternoon. A
few light showers are currently moving through OGB but should
not cause any restrictions and will move away from the airport
around 18Z. SCT clouds are expected for the remainder of the
day with the next chance for significant restrictions occurring
during the evening hours. Model guidance suggests that an area
of showers and thunderstorms will approach the terminals from
the northwest. However, it remains to be seen if the activity
will hold together and reach any of the airports. With this in
mind, have omitted shower and thunderstorm chances from the TAFs
for now. The Columbia and Augusta terminals are most likely to
be impacted by showers and thunderstorms which could result in
brief restrictions during their passage. Showers and
thunderstorms diminish towards daybreak. Surface winds outside
of thunderstorms will be south to southwest under 10 knots
through the TAF period.

EXTENDED AVIATION OUTLOOK...Scattered showers and thunderstorms
are expected Sunday afternoon and evening, possibly strong to
severe with restrictions possible.

&&

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

&&

$$