645
FXUS62 KCHS 071342
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
942 AM EDT Sun Jul 7 2024

.SYNOPSIS...
High pressure will remain over the western Atlantic while a
weak surface trough exists just inland of the area through the
upcoming week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Mid-Morning Update: No major changes made, forecast is on track.

Morning: Latest 500 mb hand analysis from 07.00z revealed a
broad trough axis centered across the central United States with
a strong mid-level ridge located over California. Compared to
24 hrs earlier, the mid-level ridge over California is more
amplified with mild height rises observed across the west coast
of the United States. As such, the mid-level trough is also
slightly more amplified and nudged east towards South Carolina
and Georgia. This is reflected in the 500 mb wind field with
winds at Atlanta now being out of the southwest. Weak height
falls were also analyzed at Atlanta and Charleston. The other
item of note was the sharp moisture gradient across the region.
The 07.00z KCHS sounding recorded a PWAT of 1.71" with the
Atlanta sounding recording a PWAT of 2.16". This moisture/ PWAT
gradient is further supported by the CIRA ALPW product which
shows a pronounced 700 - 500 mb dry slot in the shape of an
inverted V just off of the coast of Charleston. This is due to
the eastward moving trough in the central United States and the
retrograding mid-level low near Bermuda. The ALPW product shows
the core of the dry slot finally being shunted south this
morning with an axis of dilatation oriented north-south.
Simultaneously, a remnant MCV from the convection on Saturday is
currently over Orangeburg county (seen on the KCLX radar)
progressing east. The general thought for today is that this MCV
will continue to move northeast and approach the North
Carolina/ South Carolina state line by late this morning. Some
convective development along and south of the MCV is possible,
which would be mainly across the Tri- County of South Carolina.

Afternoon: Showers and thunderstorms will form along an inland
moving sea breeze with slight convective suppression occurring
on the immediate backside of the exiting MCV. More of the region
will likely see precipitation than did Saturday with PWATs
being 2.00" + across all zones. However, the best coverage again
looks to be near the Savannah River and southwest where the
best instability is forecast (ML CAPE values ~2000 J/kg) and
maximum distance from the exiting MCV. Temperatures will also be
a degree or two lower today compared to Saturday with 1000/ 850
mb thicknesses falling to 1420/ 1425 m along with plentiful
clouds. Dewpoints have also fallen a degree or two across the
board and this is forecast to continue. The data above all
points to high temperatures in the low to mid 90s with heat
index values in the 105 to 108 degree range this afternoon (or
just shy of Heat Advisory criteria). Mean cloud bearing winds
are also forecast to be around 10 kt this afternoon which should
keep storms moving slightly more than Saturday. As such, HREF
exceedance probabilities are much less today compared to
Saturday. Only a few locations in Georgia are showing
probabilities of greater than 50% for 3" of rainfall. As is the
case most times in the summer though, a few isolated totals
greater than 3" are possible.

Tonight: Showers and thunderstorms will persist into the early
evening hours thanks to the remaining islands of instability and
finally come to an end around midnight. Expect low temperatures
in the mid 70s (near 80 degrees along the beaches).

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
A weak mid-level ridge will remain over northern Florida Monday
into Tuesday, then weaken in response to the approaching upper
low that has been gradually moving through the western Atlantic.
Additional upper ridging will occur on Wednesday from the
western Atlantic. Despite the continued influence of the ridge,
guidance continues to indicate a few weak shortwaves will move
through the local area during this period. At the surface, the
main sources of convergence will be a persistent lee trough
across the SC/GA Piedmont and a robust daily sea breeze that
pushes well inland during the afternoons. An incredibly moist
airmass will set up over the area early in the week, with
surface dewpoints in the upper 70s to around 80 and PWATs
ranging from 2.3 to 2.5". Scattered to numerous mainly diurnal
showers and thunderstorms are expected each day. The greatest
coverage will likely be farther inland, closer to the lee
trough. Convection could continue into the overnight hours,
though it should generally trend downward with the loss of
daytime heating. The main concern from the thunderstorms will be
torrential rainfall and localized flooding.

High temps will mainly be in the lower 90s. Typically these
temperatures would not produce excessive heat concerns, but with
forecast dewpoints approaching 80 degrees, we could be dealing
with pockets of 108+ heat indices, particularly Tuesday and
Wednesday. Heat Advisories may be needed.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
Shortwave ridging is expected on Thursday with a slightly drier
airmass. Less coverage of afternoon convection is expected,
though there should still be enough moisture and forcing for
scattered showers/tstms. A wetter pattern is possible Friday
into Saturday due to upper disturbances moving in from the
Atlantic, deeper moisture spreading in, and a weak surface
trough over the area.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
This morning: Convection that has since decayed from Saturday is
now moving across central SC as an MCV. Along and behind the
MCV/ remnant cold pool MVFR cigs have developed, but this
appears to be rather transient as KJZI has already gone SCT.

Today: Behind the MCV, weak subsidence will occur which will
limit convective coverage at the Charleston terminals again.
Towards KSAV, PWATs will be much higher (~2.4") and will have a
higher chance of observing thunder today. Convective initiation
will likely occur around 2-4 PM with an inland moving sea
breeze. As such, have left the mention of thunder out of the
KCHS/ KJZI terminals and added a tempo group of TSRA to KSAV.

Tonight: Showers and thunderstorms will persist into the
evening hours once again and slowly come to an end by early
Monday morning. Mostly VFR conditions are forecast.

Extended Aviation Outlook: Brief flight restrictions possible
in showers and thunderstorms, particularly during the afternoon
and early evening.

&&

.MARINE...
Today and Tonight: Southerly flow across the waters will begin
to back from the southeast this afternoon with an uptick in
speed near the land thanks to an inland moving sea breeze.
Expect gusts in the various harbors and inlets 15 - 20 kt this
afternoon. Seas 2 to 3 ft. Winds will then slowly decrease this
evening as the sea breeze circulation relaxes.

Monday through Friday: Typical summertime conditions expected
with southerly flow at or below 15 kt and seas mainly 2-3 ft.

&&

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

&&

$$

NEAR TERM...CPM/Haines
SHORT TERM...JRL
LONG TERM...JRL
AVIATION...Haines/JRL
MARINE...Haines/JRL