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855
FXUS62 KCHS 280205
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1005 PM EDT Thu Jun 27 2024

.SYNOPSIS...
High pressure will remain over the western Atlantic while weak
fronts linger near the area through the end of the week.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
-- Changed Discussion --
Tonight: Upper level trough lingers nearby through the night, as
a stationary front oscillates in the vicinity. Lingering
showers early on will taper off due to the lack of forcing and
best moisture convergence pulling offshore. Many places have
already fallen to near the low temperatures based on the rained
cooled air mass. Those actual lows will be down in the lower and
middle 70s all locations. There is enough evidence that fog and
stratus will form due to the light or calm winds and the soaked
grounds. We added mention of patchy fog after midnight to the
forecast.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Friday: A rather fragmented mid-level pattern will be overhead as a
weak mid-level ridge centers across Texas. Toward the Carolinas,
vorticity will be elongated from the Atlantic southwest to the
southeastern United States. The vorticity will start to get torn
apart as it exists on the periphery of the aforementioned ridge.
Looking down at 700/ 850 MB actually has the vorticity retrograding
back west underneath the  mid-level ridge and being picked up in the
next wave. Towards the SC coast, the secondary weakness will remain
though with forecast soundings advertising widespread instability
(MLCAPE around ~1500 J/kg). Given this, have PoPs at likely for
Friday with most of the convection being favored in the afternoon to
evening hours. Expect high temperatures again in the low 90s as 850
MB temperatures remain around 19 degrees C. The other concern over
the last couple of days has been the chance for another Heat
Advisory Friday. Current thinking is that dewpoints will be a few
degrees lower Friday compared to Thursday as enough convective
overturning occurs for slightly more mixing. So the widespread 78/
80 dewpoints of Thursday will be a degree or two less Friday. This
coupled with high temperatures a degree or two lower will keep max
heat index values around 105 degrees (or just shy of 108 degrees/
Heat Advisory criteria).

Saturday and Sunday: This weekend looks rather active with multiple
rounds of afternoon into evening showers and thunderstorms likely.
In the mid-levels of the atmosphere, weak PV will continue to decay
with mid-level ridging retreating west as a trough axis begins to
amplify across the Eastern United States. Simultaneously, PWATs are
forecast to climb to between 2.25" and 2.4". Instability will also
be impressive, with MLCAPE values around 1800 J/kg Saturday and
around 2000 + (J/kg) by Sunday. Likely PoPs are advertised for both
Saturday and Sunday afternoon. High temperatures for both days are
currently advertised to be in the low to mid 90s (thanks to 850 MB
temperatures warming to 21 degrees C), but this could be moderated
due to ongoing afternoon convection. Max Heat Index values are
currently advertised to reach Heat Advisory criteria in places both
Saturday and Sunday. A Heat Advisory might be required for the
coastal zones this weekend.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Ensemble guidance is in fairly good agreement for the extended with
a rather active period forecast Monday as a weak cold front
approaches from the northwest. Tuesday into Wednesday the GEFS/
GEPS/ and EPS all indicate that mid-level ridging will slide east
slowly building over the southeastern United States. WPC Cluster
Analysis shows good agreement of this, with only slight differences
in the strength and expanse of the 594 dam ridge.

Sunday night into Monday: A cold front will approach the area from
the northwest on Monday with showers and thunderstorms initiating
across the Midlands of SC and Piedmont of NC. High temperatures
Monday will be only around 90 degrees in most places given the
likely coverage of storms.

Tuesday: There is uncertainty on Tuesday with a weak backdoor cold
front that is forecast to slide down the east side of the
Appalachians. Guidance is indicating that the front makes it through
the coastal plain of SC, before washing out and heading north by
Wednesday. Synoptically, a mid-level ridge over the Southern Plains
of the United States will nudge east Tuesday with a mid-level trough
quickly exiting the east coast. This type of setup generally does
allow a weak cold front to temporarily push south before retreating
north. Most of the time though, convective enhancement to the front
(via a reinforcing cold pool) is needed to really get the front
through. Either way, this will bring a chance of showers and
thunderstorm to the region Tuesday afternoon (less coverage compared
to Monday) with highs only in the upper 80s.

Wednesday: Mid-level ridging will nudge east and center across MS/
AL/ GA with air rapidly drying in the 500 - 750 MB level. This will
really start to limit convective development with temperatures again
warming back into the low to mid 90s.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
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KCHS/KJZI/KSAV: Lingering rains, mainly at KCHS and KJZI will
taper off before midnight. Some low stratus and/or light fog
could impacts the terminals late at night into Friday morning
due to light or calm winds and the wet grounds. Flight
restrictions are likely at all sites in the convection and again
in the stratus/fog.

The potential for convection Friday afternoon and evening will
be reevaluated in later TAFs, but additional flight
restrictions can occur.

Extended Aviation Outlook: Prevailing VFR conditions through the
period. Brief flight restrictions are possible each afternoon due to
showers and thunderstorms. The highest chances of thunder will
be  Saturday, Sunday, and Monday afternoons thanks to the
proximity of an upper level disturbance. By Tuesday, a weak cold
front will wash north with mid-level high pressure taking
control of the region. This will likely limit shower and
thunderstorm development Tuesday and Wednesday.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
Tonight: Earlier convection has altered the synoptic pattern,
but as we go through the night a southwesterly flow is expected
to reestablish itself, mainly no more than 10 or 15 kt. Seas
will average 2-3 feet throughout, mainly in swell. The risk for
any strong t-storms has ended for the night. Low end chance that
some fog/stratus over land late at night will impact the Port
of Savannah and the Charleston Harbor.

Extended Marine: Surface high pressure will remain anchored across
the western Atlantic with southerly flow generally expected through
the period. Each afternoon, a gradual backing of the winds to
southeast is expected as a sea breeze forms, with winds strongest
along the land/sea interface. A weak cold front will ooze southwest
over the waters Monday into Tuesday, but the wind shift will be
transient with a quick return of southerly winds forecast. Seas will
be 2 to 4 ft.

Rip Currents: A lingering 2 ft, 9 second swell coupled with some
astronomical influences and typical sea breeze enhancements along
the beaches support a moderate risk for rip currents for all beaches
Friday and Saturday.
-- End Changed Discussion --

&&

.FIRE WEATHER...
The South Carolina forestry commission reported low fuel moistures
across portions of the area today. Widespread coverage of showers
and thunderstorms Saturday and Sunday will help to alleviate some of
the low fuel moisture values.

&&

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

&&

$$

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