283
FXUS62 KCHS 240825
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
425 AM 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/...
Overnight composite analysis reveals an upper level trough
diving through the eastern Great Lakes with lowering heights
down into the mid Atlantic region. Attending surface trough is
advancing into the western Carolinas/northern Georgia region
along with a cluster of showers and a few thunderstorms. Quiet
and very mild conditions across southeast South Carolina and
southeast Georgia, save for a band of thicker mid level cloud
cover moving off the coast. A persistent southwest wind has held
temperatures in the upper 70s to lower 80s all night.

Upper level trough will advance to the New England and mid
Atlantic Coast region through today and eventually off the coast
tonight. Surface trough will edge into the eastern Carolinas and
central Georgia region this afternoon before stalling tonight.

Today: Quiet conditions anticipated through the morning hours
albeit with temperatures quickly warming through the 80s and
into the 90s by noon. Southern end of the upper trough in tandem
with the incoming surface trough should kick off a thin line of
showers and thunderstorms upstream this afternoon that advance
through the forecast area and off the coast by this evening.
There may also be some secondary shower/thunderstorm development
along the sea breeze boundary...where higher low level
dewpoints/instability will be pooled. Latest forecast will
advertise mainly scattered shower/thunderstorm chances
essentially after 2 pm, although increase/decrease in precip
chances may be warranted when convective evolution becomes
clear.

Temperatures will easily reach the lower to middle 90s (93-97F)
across the region this afternoon...a little cooler along the
coast. Surface dewpoints will tend to mix out/lower across
inland areas, keeping heat index values in check under 105. But
pooling moisture/dewpoints along the coast could again lead to
elevated heat index values in excess of 105F. That said,
passing showers/storms will quickly knock temps/HI values back
down. So while a few locations along the coast could achieve
Heat Advisory criteria this afternoon (108F), given the more
isolated nature, no heat related headlines are planned at this
time.

Severe weather chances: SPC Day 1 outlook continues to delineate
a marginal risk for severe storms in the eastern Carolinas
owing to slightly enhanced flow aloft near the base of the
upper trough over top a warm/unstable air mass across the
region. A few strong storms producing damaging gusts are
possible.

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 /07Z MONDAY THROUGH FRIDAY/...
VFR conditions will prevail at CHS/JZI/SAV terminals through 06Z
Tuesday. However, tempo MVFR cigs/vsbys can not be ruled out Monday
afternoon through Monday evening as a trough pushes through the
region with showers and/or thunderstorms that potentially
impact the terminals. Confidence in timing/duration of the event
remains too low to include in the latest TAF issuance, but
flight restrictions could need to be included in later TAF
issuances.

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

&&

.MARINE...
Through tonight: An enhanced pressure gradient across southeast
coast is producing rather stout southwest flow across the
coastal waters early this morning, with winds running 15 to 20
knots and gusts 20 to 30 knots, including Charleston Harbor.
Thus, Small Craft Advisories have been expanded into all SC
nearshore zones including Charleston Harbor until 11 AM. Winds
appear to be a little weaker in the Georgia coastal waters with
a Small Craft Advisory for the outer waters still valid through
8 AM.

Winds and seas should diminish late morning and through the
afternoon, but later shifts will need to assess whether or not
headlines need to be extended.

Extended Marine: 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...None.
SC...None.
MARINE...Small Craft Advisory until 11 AM EDT this morning for AMZ330-
     350-352.
     Small Craft Advisory until 8 AM EDT this morning for AMZ374.

&&

$$