Sumter, South Carolina 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

519
FXUS62 KCAE 290814
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
414 AM EDT Thu May 29 2025

.SYNOPSIS...
Temperatures returning to more seasonal values for rest of the week.
Showers and stronger storms possible today and again Friday,
followed by a return to drier weather through the weekend.

&&

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

- Patchy fog continues through dawn.

- Scattered strong to severe thunderstorms this afternoon and
  evening, particularly in the southern Midlands and CSRA.

Plentiful moisture remains entrenched over the region despite the
break up of the wedge yesterday. SPC mesoanalysis indicates
PWAT values over the area between 1" and 1.2" this morning.
Thus, some low clouds and patchy fog have developed even with
increasing high clouds from the west. Despite decoupled winds,
the cloud cover is keeping temperatures on the mild side, with
most locations in the mid to upper 60s. Keeping an eye on some
decaying thunderstorms to the south which have been poorly
modeled by CAM guidance, but confidence is low that anything of
significance will survive long enough to cause any issues across
the CSRA or southeast Midlands this morning.

The rest of today is a little more interesting, as a fairly robust
shortwave will eject across the Deep South and into the Carolinas
this afternoon. Deep southwest flow will continue to infuse moisture
into the region, with PWATs increasing back up above 1.5", perhaps
as high as 1.75". Regardless of increasing cloud cover, daytime
heating should generate at least moderate instability, with
forecast soundings indicating 1500-2000+ J/kg of SBCAPE by
midday with little capping. The shortwave will provide mid-level
support for convection, in addition to upper divergence that
will aid in storm organization. There should also be plenty of
deep layer shear, around 30-40 kts from 0-6km, but shear and
helicity below 3km is extremely lacking.

That said, CAM solutions are in good agreement that scattered strong
to severe storms will develop this afternoon and continue into early
this evening, mainly along and especially south of I-20. There are
also some hints of two waves of convection in a few of the models,
one earlier in the afternoon followed by another lesser wave around
30/00z this evening. Other solutions favor one stronger wave of
activity later in the afternoon and early evening, with just perhaps
some lingering showers in the the later evening hours. In both
cases, it seems the CSRA is a hot spot, and SPC has increased the
Day 1 convective outlook to highlight a Slight Risk east of I-20,
with a Marginal Risk maintained across the rest of the forecast
area. Threats will be primarily for wind and hail with a low end
tornado threat across the Coastal Plain.

Temperatures may be a bit tricky given cloud cover, but still should
warm up into the low to mid 80s. Overnight lows don`t fall too far,
only into the mid to upper 60s with some stratus and/or patchy fog
possible once again.

&&

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

- A line of strong-severe storms ahead of a cold front is
  expected Friday afternoon into the early evening.

- Primary threats appear to be damaging wind gusts, heavy rain,
  and some hail.

- Drier conditions begin to take grip late Friday into
  Saturday.

Friday`s Severe Environment: The deepening upper trough now
impinges on the region Friday as 90kts of southwesterly flow
aloft and upper divergence overspread the FA by the afternoon
hours with a prefrontal trough moving in ahead of the surface
cold front. Mainly unidirectional southwesterly flow is seen
across all levels of the atmosphere, with a 35-40 kt LLJ likely
developing by the mid afternoon. This enhanced southwesterly
flow brings strong moisture transport into the FA with PWAT`s
surging near 1.70-1.80" and temperatures into the mid 80s.
Strong 500 mb height falls associated with the deepening trough,
bring additional forcing for ascent as well as steepening mid-
level lapse rates. With strong flow throughout most of the
atmosphere (near the NAEFS 99th percentile from 200mb to 850mb),
shear will plentiful in this environment as nearly 50 kts of
0-6km Bulk Shear is expected and between 25-40 kts of 0-3km
shear. This favorable environment also looks to yield in excess
of 1500 J/kg of MLCAPE and strong low level instability with
3km CAPE up to 100 J/kg possible.

Timing/Potential Hazards: As more high res guidance has reached
Friday, the overall timing and mode of convection is in decent
agreement. The main outlier in the model suite in terms of
timing is the RAP, which brings an organized line of convection
closer to the late afternoon, but the bulk of high-res guidance
has the line entering the northern FA from the west closer to
the early afternoon with the prefrontal trough. In terms of
storm organization, the experimental RRFS depicts a bit more of
a broken/segmented line of convection while the HRRR, NSSL`s WRF
model suite, RAP, and the mean HREF solution depict an organized
convective line across the bulk of the CWA with minimal
convection ahead of it to hinder it`s potential intensity. Now
for potential hazards. Luckily, the line of storms should be
fairly quick moving and thus widespread flash flooding is not
expected, but with parts of the CSRA and the eastern Midlands
seeing between 5-10" of rainfall over the past 3 weeks,
localized flooding cannot be ruled out here. All severe hazards
appear possible, with a non-zero tornado risk as fixed layer STP
values between 0.5-1.0 are seen, though 0-1km helicity is on
the lower end due to the minimal veering of winds in the low
levels. Damaging wind gusts and possible severe hail would be
the main hazards expected with the likely strong cold pool
associated with the line and steeper mid-level lapse
rates/cooler temperatures aloft. Due to these threats, the SPC
has maintained the CWA in its Slight Risk (level 2 out of 5) for
severe weather at this time.

This line is expected to clear the FA by the early evening with
drier air and conditions being ushered in behind the surface
cold front with PWAT`s quickly falling to near 1".

&&

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

- Drier conditions continue to be expected in the extended with
  near average temperatures, that possibly become slightly
  above average early next week.

Ensemble guidance is in good agreement that the troughing over
the eastern CONUS is slowly replaced by upper riding into next
week. PWAT`s generally look to be near or under 1" for much of
the period and thus mostly dry conditions are expected each day
in the extended. The main chance for low end PoPs appear to be
late Sunday and into Monday as guidance has picked up on a
potential shortwave rounding the base of the upper trough before
it departs. After this, strong ridging and surface high
pressure slide into the region, maintaining the expected mostly
dry conditions. Temperatures over the weekend stick to near
average, but may rise to just above average into early next
week.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
Satellite imagery showing some higher clouds moving into the region
from the west with some fog stratus developing in a few locations as
per surface observations. This is leading to periodic restrictions,
particularly at AGS/OGB. More minor restrictions, mainly MVFR, are
possible over the next few hours at the remaining terminals. Expect
this to continue through about 29/13z before a return to VFR at all
sites. Winds should be light and variable to calm through sunrise
before picking up from the SW/W around 5 to 10 knots. Another
disturbance will approach this afternoon, increasing chances for SCT
-TSRA/-SHRA, which could bring some periodic restrictions and gusty
winds. At this time, AGS/DNL/OGB appear more favored than CAE/CUB
but included a PROB30 at all terminals. Precip should then clear
from west to east late this evening, with some CIG restrictions
possible again tonight as winds diminish to less than 5 kts.

EXTENDED AVIATION OUTLOOK...Chances of diurnal showers and
thunderstorms through Friday with the potential for periodic
restrictions. VFR expected this weekend into early next week.

&&

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

&&

$$