809
FXUS62 KCHS 252344
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
744 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/...
Early this evening: Radar imagery shows that the main area of
thunderstorms from the afternoon has pushed off the Georgia
coast and dissipated while isolate to scattered convection is
flaring up across the Charleston Tri-County region. This make
sense as this area did not get worked over this afternoon and
the SPC Mesoanalysis page shows an area of 1,500 J/kg of MLCAPE
centered on Dorchester and Berkeley counties. As such, there are
a couple of thunderstorms ongoing. One is between Saint George
and Ridgeville, and the other is moving across Lake Marion. A
few other weaker showers and storms are popping up further east,
but these are the main storms at the time. The mesoscale is
quite messy, with plentiful subtle boundaries floating around
following earlier convection and this new convection starting to
throw out its own outflow. Through the next 3 hours or so, the
Tri-County will be the focus for new convection though we
anticipate the coverage will remain isolated to scattered at
best. Elsewhere, no convection is expected. The severe threat
certainly isn`t zero, but is quite low with the loss of diurnal
heating and ambient DCAPE values only in the 500-600 J/kg range.
Storm motions will continue to be to the southeast and this
activity should finally push off the coast by around 10-11pm.
The rest of the overnight is expected to be dry, with warm and
humid conditions. While there could be some patchy shallow
ground fog late tonight (especially in areas where it rained
today), we don`t expect any significant fog issues. So, fog has
not been added to the forecast at this time.

&&

.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 /00Z SUNDAY THROUGH THURSDAY/...
The main concern for the next few hours will be the potential
for showers and thunderstorms near KCHS and KJZI. Radar imagery
shows isolated to scattered showers and storms across the
Charleston Tri-County region, and this activity could pass
through KCHS in the next 1-2 hours. Chances are lower at KJZI,
but it is certainly still possible. We did not include any
mention of anything at KCHS with the 00z TAF issuance, but will
monitor for possible amendments.

Otherwise, VFR conditions should prevail at KCHS, KJZI, and KSAV
overnight. There could be some shallow ground fog, but no flight
restrictions are expected. Another round of isolated to
scattered thunderstorms will be possible Sunday afternoon,
primarily at KCHS and KJZI. However, for now, there is no
mention in the TAF`s.

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