426
FXUS62 KCHS 301731
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
131 PM EDT Sun Jun 30 2024

.SYNOPSIS...
Atlantic high pressure will prevail today, while a trough of
low pressure resides inland. A cold front will impact the area
Monday into Tuesday before dissipating offshore. High pressure
will return for the latter half of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Early this afternoon: No change to the forecast thinking
regarding afternoon convection coverage and strength. Previous
discussion continues below.

Late this morning: Aloft, we begin with west-east oriented
ridging that stretches from near the Four Corners region to the
Southeast coast. However, there is a weakness in the ridge
across the Southern Appalachians and late in the day a mid-level
shortwave is progged to approach the forecast area from the
northwest. At the surface, analysis shows the forecast area
sitting in a weakly forced area ahead of an upstream front. A
lee trough is expected to take shape this afternoon, and this
should serve as the initiation for upstream convection late in
the day. Overall, we don`t anticipate much convective coverage
today other than isolated to maybe scattered diurnal development
along the coast or along differential heating boundaries further
inland. Better convective coverage will be possible more into
the evening hours as upstream clusters develop and track into
the area, mostly closer to sunset and after. Model soundings
today show very warm profiles and even some capping for portions
of the area. This should keep the coverage rather minimal
through the afternoon. However, we can`t rule out a stronger
storm or two thanks substantial instability and DCAPE values
well over 1,000 J/kg. Wind profiles are also very weak so storm
motion will be minimal and largely driven by boundary
interactions. With slow moving storms and precipitable water
values great than 2 inches, locally heavy rainfall is expected.

With temperatures peaking in the mid 90s for much of the area
and dew points in the mid to upper 70s, another hot and humid
day is on tap. Heat index values are forecast to reach or exceed
108 everywhere and as a result the Heat Advisory has been
expanded to include all of southeast Georgia and southeast South
Carolina. The advisory is in effect through 7 pm, and we could
see a few isolated locations rise into the 110-112 degree range.


Tonight: The h5 shortwave will continue to advance across the
local area overnight, likely promoting few to scattered showers
and thunderstorms through about midnight, potentially longer
across southeast South Carolina. However, activity will likely
show signs of weakening by mid evening due to the loss of
diurnal heating and mostly weak shear in place. Conditions will
remain mild and humid once again. In general, low temps should
range between the mid 70s inland to upper 70s/around 80 closer
to the coast.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
Monday will be the most active day of the set. A cold front
will sink into the area and eventually stall in the vicinity
later in the day and Monday night. The airmass will be quite
juicy ahead of the front with anomalously high precipitable
water values exceeding 2.25 inches in many spots. Numerous to
widespread showers and thunderstorms are expected to impact the
area late morning into the evening, generally over the northern
zones first and then moving further south with time. Current
forecast rainfall totals Monday through Monday night average 1-2
inches across the eastern half of the forecast area, with some
pockets of 2-3 inches. It is worth noting that latest HREF
guidance does show probabilities for 3 inches or greater in
spots. This could produce localized flooding especially in urban
and poor drainage areas. Elsewhere, further inland, totals are
less than an inch. Organized severe weather is not anticipated,
however isolated instances of damaging wind gusts will be
possible in strongest storms. SPC maintains the area within a
Marginal risk of severe weather. With anticipated cloud cover
and convection, temperatures will not be as hot as previous
days. Highs will range from the upper 80s to lower 90s, warmest
near the Altamaha. Convection could still percolate Monday
night, but highest rain chances eventually become more focused
over the coastal waters.

High pressure will ridge south into the area on Tuesday, while
a stalled front lingers near the coast and across far southern
Georgia. Scattered to numerous showers and thunderstorms will be
possible, with best coverage across southeast Georgia where
deepest moisture of PWats >2 inches still resides. It will be
notably cooler with highs largely in the mid 80s. Lows Tuesday
night will range from the upper 60s inland to mid/upper 70s
closer to the coast.

The front will largely wash out on Wednesday, with high
pressure returning as the primary feature. Shower/thunderstorm
chances remain in the forecast with again the highest coverage
appearing to be over southeast Georgia. Highs will mainly be in
the upper 80s to low 90s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Strong mid level ridge will build over the Southeast for late
week into the weekend. At the surface, high pressure will reside
offshore with a trough of low pressure inland. Isolated to
scattered showers and thunderstorms will be possible each day,
mainly in the afternoon and evenings, driven primarily by
mesoscale boundaries such as the sea breeze. Perhaps the bigger
story will be the heat. The synoptic pattern favors increasing
temperatures and humidity. Current forecast indicates a
potential need for excessive heat headlines for Friday and
Saturday.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
The first issue for the terminals will be the potential for an
hour or two of thunderstorms nearby through about 20z. The best
chances will be at KCHS and KSAV, and any development should be
inland of KJZI. This activity should be short-lived but could
produce a brief period MVFR conditions if a shower or storm
develops right on top of the terminal.

The second issue will be later this evening for showers and
thunderstorms to track into the Charleston Tri-County region and
impact KCHS and KJZI. The main window of time for this would be
roughly from around 01-05z. These thunderstorms should be
weakening as they arrive, but could still produce a brief period
of flight restrictions late this evening. Can`t rule this out at
KSAV as well, but the chances appear to be lower.

Finally, the more confident concern for thunderstorms comes near
the end of the 18z TAF period. Model guidance is quite
consistent with thunderstorms along the coastal corridor, with
high chances for flight restrictions at KCHS, KJZI, and KSAV. We
have introduced TSRA starting at 16z at KCHS and KJZI, and at
17z at KSAV. This highlights the beginning of the time window
when thunderstorms could impact the terminals, and the highest
chances will be near the end and just beyond the 18z TAF window.

Extended Aviation Outlook: Widespread shower and thunderstorm
impacts are likely possible Monday afternoon and evening at all
terminals. Otherwise, brief flight restrictions are possible in
showers and thunderstorms, mainly in the afternoon and evenings
through the period.

&&

.MARINE...
Today and Tonight: Local waters will remain nestled between
high pressure across the Atlantic and an inland trough. The
pressure gradient between these two features should favor a
slight uptick in south-southwest winds through the period,
around 15 kt at times, highest near the coast when a sea breeze
takes shape during the afternoon and perhaps into late evening
hours with some nocturnal surging. Seas will be no higher than
2-3 ft.

Monday through Friday: Southerly flow initially will turn
northeast and easterly as a cold front sinks into the area later
Monday into Tuesday. Speeds increase a bit, but conditions
still stay below Small Craft Advisory criteria. Winds will
eventually turn southerly again late week as Atlantic high
pressure returns. Seas through the period average 2-3 feet,
except they could build as high as 4-5 ft Tuesday behind the
front. Widespread showers/tstms will impact the waters Monday,
possibly reducing vsbys to 1 NM or less at times.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 7 PM EDT this evening for GAZ087-088-
     099>101-114>119-137>141.
SC...Heat Advisory until 7 PM EDT this evening for SCZ040-042>045-
     047>052.
MARINE...None.

&&

$$

NEAR TERM...BSH/DPB
SHORT TERM...ETM
LONG TERM...ETM
AVIATION...BSH/ETM
MARINE...DPB/ETM