710
FXUS62 KCHS 271007
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
607 AM EDT Mon May 27 2024

.SYNOPSIS...
A cold front will move into the region tonight and stall into
mid week. High pressure will return for the second half of the
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
No major changes were made for the sunrise update. Still expect
the MCS moving into west and northwest Georgia to weaken once
it gets into central Georgia.

Today through This Evening: A potentially complex convective
scenario will unfold across the Southeast U.S. today as a cold
front approaches from the west. It is unknown how the convective
pattern will evolve this afternoon and evening with a number of
complex interactions expected to occur over the next 18 hours.
This is leading to below normal forecaster confidence.

Early this morning, a well organized mesoscale convective
system (MCS) is trekking across the Tennessee Valley and will
move into parts of the Deep South and Southeast U.S. through
daybreak. The MCS should slowly weaken with time as it gradually
encounters an increasingly unfavorable environment across
central and eastern portions of South Carolina and Georgia
featuring building convective inhibition (CINH) within an
increasingly drier lower troposphere. Guidance is similar is
keeping the bulk of any significant measurable rainfall well to
the west and northwest through early afternoon. There are
signals, however, that a few light remnant rain showers with
possibly a rumble or two of thunder could penetrate interior
Southeast Georgia into portions of Allendale, Hampton and
northern Colleton Counties by early afternoon as an increasingly
diffuse outflow boundary mixes out somewhere across the
interior. Slight chance pops were utilized to highlight this
possibility. Despite increasing 0-6 km bulk shear, no severe
weather should occur as convection should become increasingly
shallow within a relatively dry environment characterized by
meager 850 hPa theta-e and K-indices in the single digits.

Attention shifts to late this afternoon into this evening as a
cold front draws closer to the region and the thermodynamic
environment across Southeast South Carolina and Southeast
Georgia becomes increasingly more favorable for the development
and maintenance of deep convection. While the 27/00z CAMs are
similar in showing convection increasing across the area late,
it remains unclear exactly where convective initiation to the
west will occur, which will have downstream implications across
the forecast area due to possible complex mesoscale boundary
interactions. Despite these unknowns, the CAM consensus is
showing some degree of convection impacting much of Southeast
South Carolina and Southeast Georgia. Similar to the location of
convective initiation, timing is a bit uncertain, although a
number of the members point to 6 PM to 11 PM as the window for
best coverage of showers/tstms across the region. Pops were
increased to 50% percent for most areas during this time, but
were capped until near term guidance supports a better, more
consolidated signal. Corridors of higher pops will likely be
needed for some areas later today as convective trends become
more apparent.

The troposphere will quickly moisten with time as the cold front
gets closer. The advection of 850 theta-e will bring a ribbon of
higher quality moisture in from the west as convection steadily
builds. This coupled with strengthening 0-6km bulk shear and
building net mixed-layer instability owing to strong insolation
during the afternoon will support continued upscale growth
along one or multiple convective clusters as they move west-east
across Southeast South Carolina and Southeast Georgia. DCAPE of
1200-1500 J/kg will support a risk for damaging winds. If cold
pools can develop and mature, there is a risk that more organized
damaging wind threat could evolve as a few of the CAMs suggest.
In addition, WBZ heights around 11-12.0 kt and a sizable HCAPE
area noted on modified soundings will support large hail in the
most intense updrafts. Hail size may be limited somewhat by the
warm boundary layer conditions that are expected today as
temperatures in the lower 90s. Most of Southeast South Carolina
and Southeast Georgia has been outlooked in a slight risk with
the early morning day 1 WFO guidance convective outlook per
earlier coordination with the Storm Prediction Center (SPC). At
this time, the risk for severe weather looks greatest across the
interior as some data suggests some degree of mid-level capping
could hold across the coastal counties thus limiting the severe
potential somewhat there. Much will depend on how organized
activity to the west becomes.

Overnight: The risk for severe weather should end before
midnight with rain slowly ending from west-east as the night
progresses. The cold front is progged to push offshore shortly
after sunrise Tuesday. Overnight lows will range from the upper
60s well inland to the mid 70s at the beaches.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
A cold front will get hung up near the coast on Tuesday. This
could serve as a focus for a few showers and thunderstorms,
mainly along the South Carolina coast, but even then coverage
looks sparse with most places staying dry. Not much of an air
mass change with temperatures again peaking in the lower 90s.
Lows Tuesday night are mainly in the mid to upper 60s.

Surface trough redevelops over the region on Wednesday before
high pressure builds Wednesday night and Thursday. Aloft, broad
troughing remains over the eastern U.S. Potential for precip
looks too low for explicit mention so a dry forecast persists
both days. Highs in the upper 80s/near 90 Wednesday will be
notably cooler in the low/mid 80s for Thursday. Lows Wednesday
night will be in the 60s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
High pressure will be the dominant surface feature Friday
through the weekend. Aloft, the trough axis initially along the
East Coast will shift offshore, allowing a ridge to build over
the region. It looks to be a fairly quiet period with just low-
end (20%) diurnal rain chances and seasonable temperatures.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
27/12z TAF Discussion:
KCHS/KJZI/KSAV: VFR for much of the period. There remains some
uncertainty on how an area of showers/tstms ahead of a cold
front will evolve this afternoon/evening. There is general
consensus that the 00-04z time frame remains the primary impact
window for all three terminals. For now, TEMPO groups for MVFR
conditions in TSRA will be included for all terminals during
that period. Further adjustments will most certainly be needed
in later forecast cycles as convective trends become more
apparent.

Extended Aviation Outlook: Predominantly VFR.

&&

.MARINE...
Today: Southerly winds will increase this afternoon as a cold
front approaches and a modest sea breeze takes shape along the
beaches. Winds are expected to surge to 15 kt with gusts to 20
kt in all legs, including the Charleston Harbor. The only
exception will be the South Santee-Edisto Beach nearshore leg
where a solid 15-20 kt appears likely. Conditions should remain
below Small Craft Advisory thresholds, although locally rough
conditions could occur in the Charleston Harbor the counterflow
created by onshore winds and the outgoing tide. Seas will
average 2-3 ft.

Tonight: Winds will gradually subside to 10-15 kt with seas 2-3
ft. Convection will push offshore later this evening and
overnight as the cold front draws closer. These storms could
pose a risk to mariners with gusts in excess of 35 kt, hail and
frequent cloud-to-water lightning.

Tuesday through Saturday: No notable marine concerns are
expected through late week. A cold front will get hung up near
the coast into midweek before high pressure returns for the
latter half of the week. Wind speeds average 15 knots or less
and seas largely stay in the 1-3 foot range.

&&

.CLIMATE...
Record High Minimum Temperatures:

May 27:
KCHS: 76/1991
KCXM: 79/2019
KSAV: 77/1878

&&

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

&&

$$