604
FXUS62 KCHS 050237
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1037 PM EDT Fri Apr 4 2025

.SYNOPSIS...
Strong high pressure centered over the Atlantic will prevail
into this weekend. A cold front will push offshore Monday with
high pressure prevailing for much of next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Mainly updated the forecast to include patchy fog across the
forecast area for a few hours prior to daybreak Saturday. Some
locations could see calm or very light winds, along with dew
point depressions near 0F.

Tonight: Any isolated shower activity will likely come to an
end with the loss of instability around sunset, just prior to 8
PM. The overall pattern remains unchanged with deep layered high
pressure centered just off the Southeast Coast. Some guidance
suggests stratus developing across the region overnight, but
low-lvl moisture is generally less than the previous night.
Light southerly winds during the night will help maintain mild
temps, with lows only dipping into the low-mid 60s across most
areas. Despite the mild temps, sfc dewpts approach air temps
late, suggesting the potential for patchy fog prior to daybreak.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
Saturday and Sunday: An anomalously strong upper high centered off the
Southeast U.S. coast will peak in intensity Saturday before
meandering a bit farther offshore Sunday. This will keep the
westward extension of the Bermuda High in place across the Carolinas
and Georgia. Model soundings depict this rather well with a
pronounced capping inversion noted both across the coastal corridor
and the interior. While the genesis of robust resultant sea breeze
circulations is likely both afternoons as highs warm into the mid
80s to around 90 away from the beaches, shower activity appears
highly unlikely given the broad subsidence in place aloft. Pops
around 0% were held for Saturday then rise to 0-10% during the day
Sunday as the cap begins to weaken and low-level theta-e begins to
increase out ahead of an approaching cold front. By Sunday night,
the cap is mostly gone as upper forcing begins to increase from the
west in response to a sharp southern stream upper trough moving
across the lower Mississippi Valley. While most of the shower
activity will remain to the west for much of the night, enough warm
air advection/isentropic lift should be in place to support some
degree of shower activity after midnight. Rain chances will
certainly ramp up closer to daybreak Monday as the primary line of
showers/tstms with the approaching cold front draws closer to far
interior areas. Lows both Saturday night and Sunday night will range
from the mid 60s inland to the upper 60s at the coast and barrier
islands.

Monday: The approaching southern stream upper trough looks a bit
more amplified in the various guidance compared to yesterday`s runs.
Although the trough`s orientation looks to maintain a positive slope
prior to phasing with the northern shortwave digging across the
Great Lakes, model cross section suggest DCVA induced forcing,
possibly with some contributions form the right entrance region of a
departing 130+kt jet streak, will be fairly strong with modest deep-
layered UVVs noted coincident with a nearly saturated column up
through 200 hPa. This should result in a maintenance of a large line
of showers/tstms with the approaching cold front. This activity is
targeted to reach western areas during the morning hours and push
east to the coast as the day progresses. Pops were increased
slightly to 90-100%. High temperatures are somewhat uncertain given
timing of the approaching line of convection will have an impact.
Highs look to peak in the lower 70s well inland to the upper
70s/near 80 just inland from the beaches.

Net mixed-layer instability will likely remain muted given the
fairly moist profiles in place, but enough forcing should be present
to support at least isolated to scattered tstms at times with
possibly a slightly greater tstm coverage occurring just inland from
the coast where warmer surface temperatures and higher dewpoints are
expected. Modified soundings at both KCHS and KNBC suggest a narrow
corridor of MLCAPE >800 J/kg impacting mainly the lower South
Carolina coast could materialize as temperatures rise into upper 70s
to around 80. Confidence on this level of instability remains low as
much will depend on the timing of the arrival of the main line of
convection and if enough breaks in the extensive cloud canopy can
occur. In terms of severe weather, the situation looks like a
typical early spring high shear/low CAPE scenario with 0-6km bulk
shear forecast to be >50 kt. As noted, the thermodynamic environment
is less than ideal so an organized severe event looks unlikely,
although one or two strong to severe tstms can not be completely
ruled out given the shear in place.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Rain will steadily end Monday evening as a cold front gradually
shifts offshore and Canadian high pressure begins to build in from
the northwest. A dry, reinforcing cold front will drop south through
the area Tuesday as the upper trough finally shifts offshore. Below
normal temperatures will dominate for much of the extended period.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
VFR at KCHS/KJZI/KSAV through 00Z Saturday. Some patchy fog
could develop for a few hours just before daybreak; however,
most likely should be non-impactful as probabilities for low
vsbys/cigs remain relatively low. South winds gusting around
20-25 kt are expected at the terminals beginning early
afternoon Saturday.

Extended Aviation Outlook: Gusty winds are expected on Sunday.
Flight restrictions are likely Monday as showers with a few tstms
impact the area ahead of a cold front.

&&

.MARINE...
This Afternoon and Tonight: Strong Atlantic high pressure will
encompass the local waters, leading to southeast/south winds
mainly around 10-15 kt or less. The exception will be in
Charleston Harbor prior to sunset, where post sea breeze
influences generate gusts around 20 kt for a few hours. Seas
are a mixture of swells and wind driven waves through the night,
equating to significant wave heights of 3-4 ft within 20 nm of
the coast and 4-5 ft across the outer Georgia waters.

Saturday through Wednesday: Winds will enhance once again along the
land/sea interface and Charleston Harbor Saturday afternoon as the
sea breeze moves inland. Gusts will reach as high as 20 kt, just sky
of Small Craft Advisory criteria in the Charleston Harbor. Southerly
winds will prevail across all waters through Monday morning as a
cold front approaches. The combination of a tightening pressure
gradient and increasing low-level wind fields will support winds
reaching 15-20 kt late Saturday night into the day Sunday. Gusts
could get close to advisory criteria for all waters. Speeds will
peak 20-25 kt Monday afternoon as the cold front gets closer to the
waters and Small Craft Advisories will be needed. Seas will build to
4-6 ft over the Georgia offshore leg Saturday evening and peaking 5-
7 ft Sunday night into Monday so a Small Craft Advisory has been
issued for those waters through late Monday evening. Seas will reach
4-6 ft over the remaining nearshore waters Sunday evening, peaking 4-
7 ft Monday morning. Winds and seas will diminish Monday night
through Wednesday.

Rip Currents: Lingering 3 ft swells every 8 to 10 seconds will
support a Moderate Risk for rip currents for all beaches through
this evening. Gusty south to southeast winds with the afternoon sea
breeze and lingering 8 second east/southeast swell will support
another moderate risk for rip currents at the beaches Saturday. The
moderate risk will persist into Sunday as the synoptic flow
strengthens ahead of an approaching cold front. East/southeast swells
are forecast to increase slightly with periods 8-9 seconds, which
may put parts of the Georgia coast close to the high risk category,
especially if seas builds a bit more or winds end up being slightly
higher than expected.

&&

.CLIMATE...
Record High Temperatures:

April 5:
KSAV: 90/1988

April 6:
KSAV: 90/1967


Record High Minimum Temperatures:

April 3:
KCHS: 67/2012
KCXM: 68/2012
KSAV: 68/2012

April 4:
KCHS: 70/1974
KCXM: 69/1974
KSAV: 69/1974

April 5:
KCHS: 65/2017
KCXM: 67/2023
KSAV: 66/1957

April 6:
KCHS: 68/2023 KSAV: 68/2023

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory from 10 PM Saturday to midnight EDT
     Monday night for AMZ374.

&&

$$

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