-- Discussion containing changed information from previous version are highlighted. --
721
FXUS62 KCHS 231724
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
124 PM EDT Sun Jun 23 2024

.SYNOPSIS...
A typical summertime pattern with High pressure in the western
Atlantic and diurnal convection will prevail this week.

&&

.NEAR TERM /THROUGH TONIGHT/...
This morning: Surface low pressure remains near the Jasper/
Colleton county line this morning with showers primarily focused
across the Charleston TriCounty. Taking a look at surface
observations shows weak surface theta-e advection occurring
across the area, with weak stabilization on the western flank of
the surface low (supported by the disappearing cu field on
visible).

This afternoon: On the backside of the decaying surface low,
winds will briefly back west/northwesterly and there may be some
drier air (lower dewpoints) that edges into the western reaches
of the CWA through the afternoon. But with lingering low level
moisture nearer the coast, very warm temperatures, broader scale
low level convergence and potential for differential heating
boundaries, some additional showers and thunderstorms will be
possible, particularly along and east of the I-95 corridor, with
decreasing chances further westward. Daytime highs will again
reach the upper 80s to lower 90s along and east of the I-95
corridor, to the middle 90s well inland with less cloud cover.
Where higher dewpoints linger (closer to the coast), heat index
values might climb into the 100-105 range this afternoon...below
advisory criteria but it will need to be watched.

Tonight: Mid level troughing begins to dig into the mid Atlantic
region along with a surface trough that develops on the lee of
the Appalachians and advances into the southeast states. No
precipitation anticipated through tonight. But enhanced south to
southwest flow will develop and may lead to marine headline
concerns. Lows will again span the 70s to around 80 at the
beaches.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
Monday: The mid-levels will consist of a trough initially over the
East Coast. It`ll gradually shift offshore as time progresses.
Meanwhile, broad High pressure centered over the Southern Plains
will try to creep its way towards our region. At the surface,
troughing will be over the Southeast during the day, with High
pressure in the western Atlantic. A cold front will slowly approach
from the north, becoming located just north of our area late at
night. A band of deep moisture appears to get pushed offshore in the
morning. But then another band of deep moisture should move over our
area well in advance of the front. Some models now indicate that
PWATs could exceed 2" across our area in the afternoon. If that
occurs, it would be above the 90% mark for CHS per SPC Sounding
Climatology and be nearly 2 standard deviations per NAEFs. The heat
will be the main concern due to 850 mb temperatures, low-level
thickness values, and compression ahead of the front. Highs should
peak in the mid to maybe upper 90s, except cooler at the beaches.
But dew points rising into the 70s near the coast will cause heat
indices to rise to ~106 degrees. This is just short of Heat Advisory
criteria. But the heat will generate a decent amount of instability
that should generate afternoon convection, causing temperatures to
drop. The models differ on the convective potential. The synoptic
models point towards isolated coverage while the long-range CAMs
point towards scattered or greater coverage. Given the setup and
time of year, we leaned heavily with the long-range CAMs. So
afternoon convection will form well ahead of the front and along the
sea breeze. While a stronger or marginally severe storm with
damaging winds is possible just about anywhere, the bigger concern
will be the potential for locally heavy rainfall underneath the
thunderstorms. Though, ~15 kt of steering flow should limit QPF if
no training develops. Convection will gradually decrease during the
evening and overnight, but remain closer to the coast. Lows will
generally be in the 70s.

Tuesday: Mid-level troughing initially offshore will shift away as
time progresses. Meanwhile, broad High pressure centered over the
Southern Plains tries to make its way towards our region. But it`s
not expected to make much progress. A weak cold front should be
located just to our north at daybreak. It`s forecasted to slowly
shift southward during the day and move across our area. After
briefly transitioning to a stationary front over our area, it should
reverse direction and head back to the north during the evening and
overnight while weakening. The front will keep the highest PWATs
south and offshore of our area. But they still should exceed 1.5"
closer to the coast, which is near normal for this time of year.
Once again, the heat will be the main concern due to 850 mb
temperatures, low- level thickness values, and compression near the
front. Highs are expected to reach the mid to upper 90s across most
of our area, except cooler at the beaches. Dew points well into the
70s near the coast will cause heat indices to rise to ~106 degrees,
which is just short of Heat Advisory criteria. Once again, another
round of afternoon convection is expected. Surprisingly, the models
have isolated coverage at worst, despite having a lot of
instability. With the front and afternoon sea breeze as forcing
mechanisms, we expected scattered or greater convective coverage in
the afternoon and have POPs higher than what some of the models
would indicate. A stronger or marginally severe storm will be
possible, especially with hints of higher DCAPE nearby. But the
concern remains the potential for locally heavy rainfall underneath
the thunderstorms due to very weak steering flow and the potential
for training. Convection should quickly decrease during the evening,
with the overnight being mainly dry. Lows will be in the 70s.

Wednesday: The mid-levels will consist of troughing developing over
the East Coast. At the surface, a weak stationary front should be
located to our west and north at daybreak. It`s forecasted to
dissipate into the afternoon. Though, surface troughing should
remain in place across the region. Higher PWATs should gradually
creep into our area, especially along the coast. Similar to the
previous two days, high temperatures are expected to reach well into
the 90s for most areas and even make a run for 100 degrees in some
spots. Dew points well into the 70s near the coast will cause heat
indices to rise to 105-110 degrees, which could prompt Heat
Advisories along the coast. But they may be brief as convection is
expected along the afternoon sea breeze. Hence, we have chance
POPs.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
Mid-level troughing initially over the East Coast will eventually
transition to ridging by the end of the week. Surface troughing or
weak fronts will be impacting the Southeast U.S. while High pressure
is near Bermuda. This summertime pattern will yield diurnal
convection. The highest POPs are each afternoon and evening, then
trending lower overnight. High temperatures will be well into the
90s each day. Heat indices could rise to 108 degrees along the coast
Thursday, which would prompt Heat Advisories if realized.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --
KSAV: The center of the surface low is now located over western
Charleston county this afternoon with most of the shower
formation being towards the Charleston terminals. Behind the
surface low, winds have veered around from the northwest with
not much in the way of precipitation expected. A sea breeze will
push inland later this afternoon with winds turning around from
the south/ southeast. Overnight, only some high and mid clouds
will remain with VFR conditions expected. No fog is forecast
tonight as the pressure gradient remains elevated which should
keep winds up. Late Monday morning, winds will again turn from
the west and be 10 to 15 kts. No precipitation is expected
through the morning hours of Monday.

KCHS/KJZI: The center of the surface low is now located over
western Charleston County this afternoon with most of the shower
activity occurring in close proximity to KCHS and KJZI. A sea
breeze will push inland later this afternoon with winds turning
around from the south/ southeast. Showers will likely come to an
end very soon with coverage decreasing through the afternoon
hours. Overnight, only some high and mid clouds will remain
with VFR conditions expected. No fog is forecast tonight as the
pressure gradient remains elevated which should keep winds up.
Late Monday morning, winds will again turn from the west and be
10 to 15 kts. No precipitation is expected through the morning
hours of Monday.

Extended Aviation Outlook: Mostly VFR. However, convection will
bring brief flight restrictions, mainly each afternoon and
evening.
-- End Changed Discussion --

&&

.MARINE...
Southerly winds will remain elevated (gusts 20-25 knots) across
the coastal waters this morning and remnant surface low
pressure migrates up through southeast South Carolina, with
winds weakening some heading into the afternoon. However,
pressure gradient will tighten through tonight as a surface
trough/boundary approaches the southeast states heading into
Monday. This will result in increasing southwest flow across the
waters tonight with gusts possibly reaching Small Craft Advisory
levels and seas building to 4 to 6 feet. Borderline, but Small
Craft Advisories may eventually be needed for tonight.

Extended Marine: A typical summertime pattern is expected with High
pressure in the Atlantic and occasional surface troughing over the
Southeast. Monday morning the pressure gradient will be elevated,
leading to gusty SW winds. Winds should surge into Monday late
afternoon and evening, then decrease Monday night. Gusts could
approach 25 kt and we can`t rule out Small Craft Advisories for our
ocean zones during this time period. Otherwise, from Tuesday onward
expect gradually backing winds each day. They`ll be strongest along
the land/sea interface and the Charleston Harbor with the formation
of the afternoon sea breeze. Each night, winds will gradually veer,
possibly surging closer to the coast. Seas will average 2-4 ft.

Rip Currents: A moderate risk continues through today due to
onshore winds and a moderate southeast swell.

&&

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

&&

$$

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