779
FXUS62 KCHS 080538
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
138 AM EDT Mon Jul 8 2024

.SYNOPSIS...
High pressure will continue over the western Atlantic while a
weak surface trough of lower pressure remains inland of the
area through the upcoming week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Showers and thunderstorms that were across the Midlands of SC
have continued to weaken early this morning with another MCV
having now formed near the SC/ NC border. This feature will
progress northeast through the overnight/ early morning hours. A
chance of precipitation will persist in Jenkins, Screven, and
Allendale counties through the early near term period. For the
second half of the early morning hours (3 AM - 6 AM) no
precipitation is expected. Lows will range from the mid 70s
well inland to the lower 80s at the beaches and Downtown
Charleston.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY/...
Monday through Tuesday Night: At upper levels, a large upper level
low well east of the region over the Atlantic, is shown my all
models to push west-southwestward and dissipate through the period.
Very high values of deep layer moisture will reside over the entire
southeast U.S., with PWs 2-2.5 inches. At the surface, a trough of
lower pressure will generally reside well inland. This trough, along
with any seabreeze and/or differential heating boundaries, will
likely be the main triggers for afternoon and evening convection.
With ample deep layer moisture and relatively slow storm motions,
locally heavy rainfall will be the main threat from any stronger
showers/thunderstorms. Models have been focusing the highest PoPs
along and west of I-95 through much of this period. Concerned that
guidance PoPs are too high for this time of year, and have tried to
taper PoPs down a tad for the afternoon/early evening periods. High
temperatures near to slightly above normal, but low temperatures
likely to continue 3 to 5 degrees above normal. Current grids keep
max Heat Indices in the 100-105 range. Thus, not concerned about
Heat Advisory conditions at this time, at least across widespread
areas.

Wednesday: The upper low center that was over the Atlantic is shown
by models to dissipate southeast of the region as a developing upper
trough moves into the central MS River Valley. This is the same
upper trough that appears to pick up the remnants of Beryl. Our
region will remain under the presence of ample deep layer moisture,
with PWs 2-2.5 inches. Given slightly better upper level troughing
and some vorticity reaching at least well inland locations, would
not be surprised if convective coverage was a bit higher than
current forecast shows. For now, have continued high chance/low end
Likely PoPs, mainly due to uncertainty. High temperatures slightly
above normal. Max Heat Indices may be a tad higher than previous
days, with marginal Heat Advisory conditions possible in some areas.
However, the amount of convective development will impact max Heat
Indices, which leads to a good amount of uncertainty. Will continue
to monitor the situation.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
In general, a deep layer Atlantic ridge of high pressure looks to
stay in place during this period. At the surface, an inland trough
of lower pressure will also persist, which along with the sea
breeze, will be the main initiator of afternoon/evening convection.
Again, concerned that model/guidance PoPs are a bit too high for
this time period and time of year. Climo PoPs are generally 30-40%,
but guidance has been going likely to categorical. Have again tried
to trim PoPs down a tad, while also keeping collaboration thresholds
in check with surround offices. Again, with ample moisture and weak
steering flow, will continue to watch the threat for locally heavy
rainfall with any stronger showers/thunderstorms. Temperatures,
especially low temperatures, are expected to remain above normal.
Afternoon Heat Indices of 100-105 each day, which is below Heat
Advisory criteria.

&&

.AVIATION /05Z MONDAY THROUGH FRIDAY/...
This morning: Showers and thunderstorms will continue to decay
across the Midlands of SC this evening with another MCV forming
near the SC/ NC border. Extending south and then southwest from
the MCV is a weak boundary (convectively reinforced cold pool)
with an MVFR stratus deck. KSAV has already gone MVFR this
morning and another round of morning stratus/ strato-cu appears
likely at the Charleston terminals as well. MVFR clouds will
then slowly start to rise by mid-morning with a return of VFR
clouds.

Afternoon: A very difficult forecast with low confidence for
this afternoon. The MCV mentioned above will be exiting the
region this afternoon with another round of weak subsidence on
the backside of the forcing. The latest runs of the high res
guidance continues to show redevelopment along a weak wind shift
(from the exiting MCV) that is pinned along coastal SC/ GA. The
sea breeze then collides with this boundary causing convective
initiation. However, the HRRR is again playing catch-up this
morning with the exiting MCV and appears to slow. The wind shift
on the high res guidance also appears to strong. The cold pool
will likely not be reinforced as much as at least the latest
HRRR indicates. This would favor less coverage and a more
dispersive/ less focused solution. For now, have maintained VCTS
at KSAV and not included the mention of thunder in the
Charleston terminals. This will likely need to be revisited by
or before the 12z TAF issuance.

Evening: Showers and thunderstorms will be coming to an end this
evening as daytime heating is lost. Mostly VFR conditions are
forecast.

Extended Aviation Outlook: Scattered to numerous afternoon
showers and thunderstorms each afternoon may produce brief
flight restrictions, especially for KSAV.

&&

.MARINE...
Tonight: Seas 2 to 3 ft. Winds will then slowly decrease this
evening as the sea breeze circulation relaxes, generally around
5 to 10 knots.

Monday through Friday: No highlights expected through the
period. An Atlantic ridge of high pressure will generally remain
centered well east of the waters, which is typical for this
time of year. The low level flow will be mostly southerly at 15
knots or less and seas 2 to 3 feet. This pattern also tends to
favor nighttime over daytime convection.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$

NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...Haines
MARINE...