098
FXUS62 KCHS 162242
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
542 PM EST Tue Dec 16 2025

.SYNOPSIS...
High pressure will prevail through Thursday before a cold front
pushes offshore Friday morning.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
For tonight, the mid-level ridge axis slides across the region,
with flow aloft becoming southwesterly. Skies will initially be
clear and with weak winds at the surface, radiational cooling
will bring temperatures back down into the lower 30s inland to
mid 40s along the coast. With dewpoints rising up into the mid
30s to lower 40s along the coast, some patchy fog can`t be ruled
out. The HREF and NBM both show low probabilities (<15%) for
visibilities below 1 mile, though the REFS is more convinced
with a narrow corridor for probabilities near 50% for 1 mile
visibility up along the southeast Georgia coast and up to
Beaufort, SC. Did adjust the forecast to be closer to what the
REFS is showing given the low dewpoint depression and light
winds, so be on the lookout for patchy fog Wednesday morning
along the southeast Georgia coast and up towards Beaufort, SC.
However, mid-upper level cloud coverage does increase overnight,
so it`s possible that may act against fog formation.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Wednesday: Weak ridging aloft will begin to break down as the mid-
level ridge axis propagates to the east and well offshore as a
broad, southern stream shortwave ejects east across the Southern
Plains and Northern Mexico. A fast, southwest flow will generally
prevail aloft with ongoing warm air advection helping to keep
temperatures moderating. High pressure over the Atlantic will
gradually push east with what appears to be a weak coastal trough
developing just offshore. A few showers could develop over the
Atlantic in the vicinity of the trough Wednesday night, primarily
near the west wall of the Gulf Stream, but dry conditions should
generally prevail both Wednesday and Wednesday night as cloud
steadily thicken. Highs will warm into the lower-mid 60s (a bit
cooler at the beaches) with overnight lows ranging from the lower-
mid 40s inland to the mid 50s at the beaches.

Thursday: Rain chances will quickly increase Thursday as the storm
stream shortwave propagates across the region and PWATs surge to
around 1.50". Models cross sections suggest forcing for ascent/UVVs
ahead of the shortwave will be modest owing to increased DPVA and
ongoing warm air advection/isentropic ascent within a column of deep
moisture with some secondary contributions from a passing
subtropical jet streak. Rain chances look the greatest from late
morning into the afternoon hours as the coastal trough offshore
works inland and gradually dissipates with the increasing southerly
flow ahead of an approaching cold front. Pops were increased into
the likely to categorical range with the greatest coverage occurring
along the lower South Carolina coast. Highs will warm into the upper
60s/lower 70s. Similar to yesterday, a rumble or two of thunder can
not be completely ruled out anywhere given the degree of forcing
aloft, but the risk looks highest along parts of the lower South
Carolina coast where some very marginal instability could work
inland from off the Gulf Stream. A slight chance for tstms was
introduced along the lower South Carolina coast to address this
potential. Probabilities still look too low to justify a mention of
tstms elsewhere at this time.

Thursday Night and Friday: The initial surge of shower activity
could tapper off during the evening hours Thursday, only to increase
again overnight as the cold front to the west begins to move into
the local area. There remains some uncertainty on how quickly the
front clears the coast late Thursday night with some guidance
members still keeping some degree of measurable rainfall risk until
mid-late morning Friday with a slightly delayed FROPA. The drier
16/13z NBM solution which keeps conditions rain-free during the day
Friday was still used as the basis for the forecast, but trends are
being watched closely. Breezy conditions could develop across the
coast Thursday night into Friday morning with a 45-50 kt pre-frontal
925 hPa low-level jet passing through. Winds on Lake Moultrie could
also surge a bit, but poor mixing profiles over the cold lake waters
should keep winds just below Lake Wind Advisory criteria. Lows
Thursday night will range from the upper 40s/lower 50s well inland
to the upper 50s at the beaches. Friday will feature clearing
conditions with highs peaking in the upper 50s/mid 60s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
High pressure will prevail for the weekend with signals that another
stronger area of high pressure could wedge into the region early
next week as a coastal trough/coastal front develops offshore.
Temperatures will be near normal with a brief period of above normal
temperatures possible Sunday.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
00Z TAFs: Dewpoints have begun to recover across the terminals
this evening. High resolution guidance indicates that dewpoints
may narrow towards dawn to yield a period or two of fog,
primarily near KCHS and KJZI. However, mid and high clouds will
stream across the region late tonight, possibly pushing over
KCHS and KJZI prior to sunrise. The TAFs at KCHS and KJZI will
limit fog mention to ground fog during a TEMPO from 8-12Z.
Otherwise, conditions will remain VFR with light winds.

Extended Aviation Outlook: There is an increased risk for MVFR or
lower ceilings and visibilities in showers Thursday into Thursday
night. A risk for low-level wind shear could develop Thursday night
as a strong, pre-frontal low-level jet (45-50 kt) pushes east
through the area.

&&

.MARINE...
Through tonight: No marine concerns as surface high pressure
continues across the region.

Wednesday through Sunday: The main forecast concern still centers on
the Thursday night to Friday morning time period where both winds
and seas could push Small Craft Advisory thresholds ahead of an
approaching cold front. Winds do tend to struggle a bit in warm air
advection regimes with cold sea surface temperatures helping to
temper mixing a bit, but LREF probabilities for winds >25 kt
continue to increase with each cycle and are still highest over the
South Santee-Edisto Beach nearshore and Georgia offshore leg.
Probabilities range from 40-80% in these areas, highest in the
eastern portions of the Georgia offshore waters closer to the west
wall of the Gulf Stream. Seas could get as high as 4-7 ft Friday
morning, again, highest in the areas noted above.

&&

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

&&

$$

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