323
FXUS62 KCHS 271739
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
139 PM 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/...
Isolated to scattered showers have moved into our far inland
Georgia zones in association in response to slightly higher
theta-E air, a bit greater MLCAPE and Normalized CAPE than there
is elsewhere, and along a differential heating boundary along
an old outflow or differential heating boundary. It is also
ahead of another small cluster of t-storms in central Georgia.
That activity is likely the focus for convection late afternoon
or evening into tonight. There remains a risk for severe weather
after 5 or 6 pm, and that risk does continue for at least
several hours given favorable thermodynamics and kinematics. We
did alter the hourly temperature curve to account for the cloud
cover, which in turn trimmed about 1-2F off many places for
highs this afternoon.

The forecast for this afternoon and evening is certainly a
challenge, but we`ll do our best to attempt to figure it out.

The MCS to our west over parts of Georgia and South Carolina
looks to weaken as it draws closer, as there is a theta-E
minimum, K-Indices of only about 10-15, and still quite a bit of
CINH. The morning sounding from KCHS shows a 3.1C cap, which
will hold into at least the afternoon. The most recent data
from the 12Z HRRR, RAP, and NAMNest keeps the vast majority of
the day and the forecast/warning area free of any deep
convection. Debris clouds from the MCS could also factor into
play, as should they persist longer, then that too would suggest
a late start to convection. Maybe some of the activity to the
west could brush the northwest tier late morning/early
afternoon, but it doesn`t look severe at this stage.

The convective parameters for any severe weather, which looks to
occur after 5 or 6 pm, are quite impressive. Most notably: mid
level lapse rates are around 7C/km; SBCAPE is greater than 2500
J/kg; TTI is near 50; LI is -7; 0-6 km shear is 40 kt.DCAPE is
around 1200-1400 J/kg and WINDEX from the modified sounding is
65 mph. These imply that damaging wind gusts are possible. Wet
Bulb Zero is between 10 and 11 thousand feet, and the Hail CAPE
is 600-900 J/kg. Both would imply the potential for large hail.
Given the shear, there is a low end risk for an isolated
tornado where boundaries interact.

Low level thickness looks too hot for max temperatures, but
given 850 mb temperatures of 18-19C, and the sea breeze only
slowly progressing inland, will yield highs in the lower 90s
inland from the Intra-Coastal. Breezy south-southwest winds
that develop along the beaches will hold those temperatures down
in the 80s.

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 /18Z MONDAY THROUGH SATURDAY/...
27/12z TAF Discussion:
KCHS/KJZI/KSAV: Upstream showers will likely fizzle before
reaching KSAV this afternoon. But we included VCSH just in case
they do survive this far east. Otherwise, SW winds are expected
to become a little gusty ahead of pre-frontal trough and cold
front, peaking at least as high as 15 or 20 kt.

As the pre-frontal trough and front draw closer, a better
chance of SHRA/TSRA exists during tonight at all terminals. The
most favorable timing is from 00Z to 07-08Z, which is covered
by VCTS. However, direct impacts currently look to occur between
01Z to 05Z, when we show gusty winds, TSRA and flight
restrictions. Adjustments certainly could be refined pending
latest trends.

VFR will return late tonight and Tuesday in wake of the cold
front.

Extended Aviation Outlook: Predominantly VFR.

&&

.MARINE...
This afternoon: S-SW winds will increase as a cold front
approaches and a modest sea breeze takes shape along the
beaches. Winds are expected to surge to 15 or 20 kt with higher
gusts in all legs, including the Charleston Harbor. Conditions
should remain below Small Craft Advisory thresholds, although
the Charleston Harbor will be close to the advisory threshold.
This will result from the counterflow created by onshore winds
and the outgoing tide, along with the warmer surrounding land
mass. 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.

&&

$$

NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...