172
FXUS62 KCHS 241605
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1205 PM EDT Mon Jun 24 2024

.SYNOPSIS...
High pressure will remain over the western Atlantic this week
while occasional surface troughing prevails over the Southeast.

&&

.NEAR TERM /THROUGH TONIGHT/...
This Afternoon: A few changes were needed for the noon update.
First, dewpoints are not mixing out as quickly as expected and
heat indices are already at Heat Advisory criteria in some
locations. While the combination of scattered convection and
some dewpoint mixing should keep inland areas from reaching
advisory criteria, the Heat Advisory has been expanded to
include Charleston and Coastal Colleton as the onset of
convection is still a few hours out. As of noon, heat indices
had reached 104 at KCHS, 106 at KLRO and 108 at KJZI. It is
still possible the advisory may be cancelled early for some
locations pending how convection evolves. Second, incoming
high-res convective models suggest tstm coverage may not be as
great as what was expected earlier. Pops were nudged down about
10% in some areas given this trend, but any further adjustments
will wait until the arrival of the first few runs of the WoFS
which are scheduled to start around 17z.

Scattered showers and tstms are expected to impact much of the
area this afternoon as a surface trough to the northwest
approaches. A few of these storms could be strong to marginally
severe with damaging winds and frequent cloud-to-ground
lightning being the primary hazards.

Tonight: Initial showers/thunderstorms will move off the coast
by early evening. But of note, recent high-res guidance runs
show another cluster of showers/storms developing across the
Midlands late this afternoon along the stalling surface trough,
then advancing down through portions of southeast South Carolina
this evening and off the coast overnight. Will see how that
plays out, but forecast will hold on to showers/thunderstorm
chances through the evening into early overnight, particularly
for southeast SC. Lows largely in the middle 70s anticipated,
warmer at the beaches.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
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 across our far inland counties or just north of them at
daybreak. It`s forecasted to slowly shift southward during the day,
moving 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 could still exceed 1.75" closer to the coast, which is a
bit above normal for this time of year. 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.
Afternoon convection is expected with the front and afternoon sea
breeze as forcing mechanisms. The models differ on the convective
coverage. 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. MLCAPEs should approach 2,000-2,500 J/kg across portions
of our area with some shear. With DCAPEs exceeding 1,000 J/kg, a few
marginally severe storms with damaging winds are possible just about
anywhere. Additionally, there will be the potential for locally
heavy rainfall underneath the thunderstorms due to 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 our region. A cold front should approach from
the northwest overnight. Though, it`s not expected to reach our area
during that time frame. Higher PWATs should gradually creep into our
area as time progresses, especially along the coast. Similar to
Tuesday, high temperatures are expected to reach well into the 90s
for most areas. 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. Afternoon convection is expected with the
sea breeze. Though, the synoptic models point towards isolated
coverage, which may be underdone. Scattered coverage seems more
reasonable given the setup and time of year. Instability, DCAPEs,
and sheer should be similar to Tuesday, so a few marginally severe
storms with damaging winds can`t be ruled out. Additionally, there
will be the potential for locally heavy rainfall underneath the
thunderstorms due to fairly 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.

Thursday: Mid-level troughing initially over the East Coast will
shift offshore. A cold front located to our northwest at daybreak
should slowly move across our area later in the day. There will be a
plume of deep moisture ahead of the front. Forcing from the front
and afternoon sea breeze are expected to generate convection.
Though, the coverage will depend on how much instability is in place
and the amount of shear. So this aspect of the forecast will need to
be adjusted. Similar to the previous two days, high temperatures are
expected to reach well into the 90s for most areas. Dew points well
into the 70s near the coast will cause heat indices to rise as high
as 108-110 degrees along the coast, which could prompt Heat
Advisories. But they may be brief as the convection would quickly
cool temperatures.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
Mid-level troughing initially over the East Coast will eventually
transition to ridging over the Southeast U.S. by the weekend.
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. Additionally, heat indices could
approach 108 degrees along the coast each day.

&&

.AVIATION /16Z MONDAY THROUGH FRIDAY/...
24/18z TAF Discussion:
KCHS/KJZI/KSAV: Best chances for tstm impacts this afternoon
will be at KSAV and possibly a far north as KJZI. VCTS will be
highlighted at both terminals from roughly 19-21z with a TEMPO
for MVFR conditions in TSRA at the same time at KSAV. Risk for
showers/tstms could increase at KCHS by mid-evening as some
interaction with an approaching surface trough and inland moving
sea breeze occurs. VCSH was highlighted 02-05z for now to
trend. Otherwise, VFR through the period.

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

&&

.MARINE...
The Small Craft Advisory was allowed to expire at 11 AM.

Through tonight: South to southwest winds 15-20 kt will persist
into tonight. Seas will average 3-5 ft.

Tuesday through Friday: A typical summertime pattern is
expected with High pressure in the western Atlantic and
occasional surface troughing over the Southeast. Each day,
expect gradually backing winds. 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.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 6 PM EDT this evening for GAZ117-119-139-
     141.
SC...Heat Advisory until 6 PM EDT this evening for SCZ048>051.
MARINE...None.

&&

$$