969
FXUS62 KCHS 252025
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
425 PM EDT Sat May 25 2024

.SYNOPSIS...
A weak disturbance will move through the area this evening. Hot
conditions expected for Sunday and Memorial Day. A cold front
could bring impacts to the region Monday night into Tuesday.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Recent SPC mesoanalysis indicated that the environment across the
forecast area this afternoon featured MLCAPE around 2000 J/kg or
normalized CAPE of 0.15-0.2. DCAPE values may range between 1000-
1200 J/kg, especially across SE GA. The thermal profile combined
with effective bulk shear of 30-35 kts may support strong to severe
thunderstorms across SE GA/SC this afternoon and evening.

Pulse thunderstorms should remain along the sea breeze into late
afternoon. Another area of thunderstorms are forecast to increase
across SE GA with the arrival of an outflow associated with a MCS.
The convection along the MCS outflow should develop into loosely
organized thunderstorm clusters, tracking towards the coast. Recent
runs of the HRRR indicates that the greatest coverage of storms may
occur as the MCS outflow nears the sea breeze/coastal outflows later
this afternoon and evening, especially over the SC Lowcountry. Once
this convection develops, steering flow should result in these
storms tracking slowly east. The stronger storms may produced
localized damaging wind gusts. In addition, the environment will
also feature deep moisture, PW values between 1.5-1.7 inches. HREF
indicates that some thunderstorm clusters will have the potential of
producing 1.5-2 inches in a 3-hr period this PM. Showers and
thunderstorms should either dissipate or push over the coastal
waters this evening.

Conditions will remain mild and humid across the region tonight. Low
temperatures are forecast to range from the upper 60s inland to the
low to mid 70s along the coast.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
Sunday: Weak mid-level ridging will move overhead in the morning
hours with no precipitation initially expected. By the late
morning hours/ early afternoon a decaying MCV heading east out
of Texas and the Great Plains will be approaching the Carolinas
and Georgia. Taking a look at forecast soundings, shows an ever
increasing dry profile (especially looking at the GFS). The NAM
still does advertise enough boundary layer moisture though to
support deep moist convection. Usually in these circumstances a
decaying MCV (working in combination with an inland moving sea
breeze) is enough lift to at least support scattered
convection. This low level support will likely be greatest
across South Carolina with weaker forcing towards Georgia. As
such, the highest chance of precipitation will be across the
TriCounty of South Carolina with lower chances of rain towards
coastal Georgia. The other item of interest for Sunday will be
high temperatures in the low to mid 90s across the region. 850
MB temperatures are forecast to stay around 19 degrees C with
1000/ 850 mb thicknesses rising to 1425 m. Low temperatures
Sunday night will also be rather warm and likely bottom out only
in the lower to mid 70s.

Monday: A potent mid-level wave will be ejecting northeast
towards the Great Lakes with mid-level ridging across central
South Carolina. At 250 MB, an impressive split jet structure
(along with a LFQ of a subtropical jet) will be initially
centered over eastern Tennessee. Monday afternoon, the mid-level
wave will eject northeast and take on a negative tilt over the
Ohio River Valley. As this occurs, numerous showers and
thunderstorms will likely develop along the Appalachians. As
the PVA approaches the lee side of the mountains pressure falls
will start to commence (e.g., a Lee side through). The main
questions for us here locally though are how quickly will the
mid-level ridge depart and whether the vorticity gets sheared
out as it heads northeast. Bulk shear values are around 30 to 40
kt across the region Monday evening with net storm motion
orthogonal (or off of the lee side trough) which would support
discrete cells. Forecast soundings though show a rather hostile
thermodynamic environment in place Monday afternoon with
impressive capping noted on both the GFS and NAM (for CHS) at
850 MB. The capping does finally start to erode by Monday
evening though. Given this, early Monday afternoon currently
looks dry with an increasing chance of showers and thunderstorms
by the evening hours. Expect high temperatures in the lower
90s. Low temperatures Monday will be in the lower 70s.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
A rather anomalous pattern looks to setup in the extended portion of
the forecast as a potent upper level low dives south out of Ontario
and Quebec. This pattern is well advertised on the latest runs of
the GEFS, GEPS, and EPS with the NBM guidance following suite. This
pattern would favor a cold front swinging south through the area
Tuesday into Wednesday with dry conditions Wednesday and Thursday.

The wave pattern responsible for this, looks to be a double-
barreled shortwave with wave amplification occurring mostly on
Wednesday. As such, guidance does have the cold front initially
working its way south Tuesday afternoon towards the SC/ GA state
line before stalling. Then as the next shortwave dives south
Wednesday, the cold front is pushed off the coast and clears all
zones. This type of pattern usually favors an active sea breeze
with showers and thunderstorms along the coast (thanks to the
sea breeze being pinned along the coast).

Wednesday and Thursday: Surface high pressure will center across
the Ohio Valley with mostly dry conditions. The latest NBM
guidance shows a skewed temperature distribution (with the mean
being less than the mode) and think this makes sense given the
synoptic pattern. Highs on Thursday will likely be only in the
mid 80s.

Friday and Saturday: Ensemble guidance starts to diverge at the
end of the extended with a general trend to warming temperatures
(esp by Saturday) as the surface high pressure retreats east.
The latest run of the GFS shows impressive wave breaking by next
Saturday, but it should be noted that there is very little in
the way of ensemble support for this solution. Therefore, have
kept the forecast to advertise a recovery in temperatures (and
dewpoints) by next weekend. This also means a return of
afternoon showers and thunderstorms for next weekend.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
18Z TAF Discussion:
KCHS/KJZI/KSAV: Prior to the 18Z TAFs, KCLX was detecting an
increasing number of showers across SE GA and SC. A couple of
updrafts were located within the KCHS terminal. Showers and
thunderstorms should develop at least in the vicinity of the
terminals at the onset or an hour into the 18Z TAF period.
Thunderstorm coverage should peak late this afternoon into early
this evening, each TAF will feature a TEMPO for TSRA, generally
between 20-01Z. Convection should gradually dissipate or track
over the Atlantic waters this evening. The rest of the night
should remain VFR with light SW winds.

Extended Aviation Outlook:

Sunday: Mostly VFR conditions. A slight chance of showers and
thunderstorms are possible along an inland moving sea breeze.

Monday and Tuesday: An upper level disturbance will approach from
the west Monday morning and move across the region Monday night into
early Tuesday. This system will bring a chance of showers and
thunderstorms to all of the terminals along with episodic ceiling
and visibility restrictions. A cold front will then ooze south and
cross the terminals.

Wednesday and Thursday: VFR conditions with winds out of the north/
northwest. No precipitation forecast.

&&

.MARINE...
Tonight: The pattern will support southwest winds generally
around 10 kts with seas between 1-2 ft. Thunderstorms could move
off the Georgia and South Carolina coast later this evening
which could produce convective winds >34 kt.

Sunday through Thursday: Southwest winds will persist across the
waters through Monday with seas 2 to 3 feet on average. On Tuesday,
a cold front will hang up along the coast of SC/ GA with winds
remaining out of the southwest. By Wednesday, the cold front will
sweep off the SC/ GA coast with winds turning from the north. Expect
winds generally 15 kt or less with seas 2 to 3 ft.

&&

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

&&

$$

NEAR TERM...NED
SHORT TERM...Haines
LONG TERM...Haines
AVIATION...Haines/NED
MARINE...Haines/NED