123
FXUS62 KCHS 021127
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
627 AM EST Tue Dec 2 2025

.SYNOPSIS...
A storm system will pass through the region late today bringing
much needed rainfall to coastal South Carolina and Georgia.
High pressure then returns for the middle of this week before
the next frontal system impacts the area Friday into the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Early this morning, satellite water vapor showed a strong shortwave
advancing over the Mississippi River Valley, with a deep plume of
moisture across the Southeast U.S. Regional radar composite
indicated widespread rain extending from the coast of GA/SC west to
the AL/MS line. The widespread rain will slide northeast today,
supported by the shortwave, strong jet divergence, and deep
isentropic lift. In addition, PW values across the forecast area
will increase through early this morning, peaking during the mid to
late morning hours around 1.8 inches. Coverage of light rain will
increase across the CWA early this morning, temperatures should
remain generally steady in the low to mid 50s. Rainfall rates are
forecast to peak during the mid to late morning, yielding at least
moderate rainfall. NBM indicates isolated thunderstorms along and
east of the I-95 corridor this morning. However, given the coverage
of the rainfall, cold air damming should reach peak strength this
morning, limiting deep instability to less than 200 J/kg.

This afternoon, near term guidance times the sfc low to reach
eastern NC, sweeping the cold front across the CWA. Showers should
shift east with the front, allowing the forecast area to dry from
west to east by late this afternoon. Rainfall totals from today are
forecast to range from 1-1.75 across the far inland counties of GA
and SC to around .75 east of I-95. After a morning of steady
temperatures in the low to mid 50s, temperatures should peak in the
60s early this afternoon, then cooling through the rest of the
afternoon.

Tonight, a dry and cool air mass will spread across the forecast
area in the wake of the cold front. Linger low level moisture will
likely support some degree of stratocu across the region through
late tonight. Using a blend of guidance, low temperatures are
forecast to range from the mid to upper 30s inland to the low 40s
along the coast.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Wednesday: Surface high pressure will be centered over the Ohio
River Valley Wednesday, with cold dense air slowly making its way
over the Appalachian Mountains. As the dense air begins to spill
east, a reinforcing cold front will surge south and then southwest
down the east side of the Appalachians. The front looks to cross the
area Wednesday morning before washing out. No precipitation is
expected through the period as dry air remains entrenched with
temperatures below normal for this time of year.

Thursday: The high pressure from Wednesday will quickly collapse as
the ageostrophic convergence transitions neutral to divergence as a
potent mid-level wave moves east over the Hudson Bay. Low level
winds turn from the southwest with overrunning commencing. Looking
at the 300 or 295 K surface though shows a relatively dry air mass
remaining in place with condensation pressure deficits large. Even
where saturation is implied, moisture profiles below the 300 K
surface are extremely dry. As such, most of the area will likely
(>80%) remain dry Thursday.

Friday: Model consensus really starts to diverge Friday, with local
forecast spread widening rapidly on Saturday. Taking a look at the
upper level pattern, a long wave trough axis will center over the
central United States with wave breaking potentially occurring over
the Baja of California. The latest run of the WPC Ensemble
Sensitivity Analysis webpage, reveals that this is indeed what
causes the forecast spread. Some guidance has the wave completely
breaking off from the long wave trough, while other guidance has the
wave being more progressive. Either way for Friday, precipitation
will spread over the region as a coastal low forms in the northern
Gulf and heads northeast. Precipitation looks likely by Friday
afternoon (>55%). Given the widespread precipitation and cloud
cover, high temperatures will mostly be in the mid 50s, or well
below normal for this time of year.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
Saturday: Forecast confidence on when the precipitation comes to an
end is relatively low for Saturday. As mentioned above, this is
likely predicated on the evolution of the coastal low near the Baja
of California. As of current thinking, it appears that precipitation
will slowly come to an end Saturday evening. As mentioned above,
confidence is low though. About 55% of the guidance has most of
Saturday dry, while 25% of the guidance has precipitation coming to
an end by Saturday evening, with the final 20% of the guidance
shows precipitation continuing through Saturday.

Sunday and Monday: A cold front will then cross the area late
Saturday or early Sunday, with dry weather forecast. Expect
temperatures below normal.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Prior to the 12Z TAFs, KCLX detected widespread rain advancing
north across the terminals, accompanied by IFR ceilings. Cold
air damming will be reinforced by the widespread rain fall this
morning, supporting north-northeast winds and IFR conditions
through mid-day. In addition, strengthening llvl jet and
directional shear should yield LLWS at each terminal this
morning. A period of heavier rainfall rates should pass over the
terminals this morning after sunrise, reducing visibility down
to 2SM at times, highlighted with TEMPOs from 12-17Z. Rainfall
is timed to shift east of the terminals during the mid to late
afternoon hours as the front sweeps east. In the wake of the
front, winds will shift from the northwest and cloud bases will
gradually lift, improving to MVFR by this evening.

Extended Aviation Outlook:
Wednesday and Thursday: VFR.

Friday and Saturday: Cloud bases will lower on Friday and reach MVFR
by the late morning with eventual IFR conditions forecast.
Widespread precipitation forecast. At this time, no thunder is
forecast.

&&

.MARINE...
South winds should continue to strengthen through this morning, with
gusts reaching 25 kts or more across the outer GA and Charleston
County nearshore waters. Wave heights will increase today, with 6 ft
or greater seas developing with the SC nearshore and outer GA waters
today. The wind and sea conditions will be highlighted with Small
Craft Advisories today into this evening. A cold front should sweep
across the marine zones late this afternoon, resulting in winds
veering from the northwest from 10 to 15 kts, decreasing to 10 kts
during the pre-dawn hours Wednesday morning. Seas should gradually
subside during the night, ranging between 3-4ft after midnight.

Wednesday and Thursday: Northwest winds veering from the north
Wednesday morning 10 to 15 kt. Seas 2 to 4 ft. No precipitation is
expected.

Friday and Saturday: Winds will veer from the northeast 10 to 15 kt.
Widespread showers and possibly a thunderstorm expected Friday and
Saturday morning. Winds will then turn from the northwest behind a
cold front. Expect seas 2 to 4 ft.

&&

.TIDES/COASTAL FLOODING...
Upcoming 5 AM high tide cycle: Current tidal trends at the
Charleston Harbor tide gage indicate that the tide departure has
steadily increased since the afternoon high tide and has
remained around 1 ft following the ~10:30 pm low tide. This
morning`s high tide is at ~5 am and the astronomical tide is
6.23 ft MLLW, meaning we would need to see at least a 0.77 ft
departure to reach the minor coastal flooding threshold of 7 ft
MLLW. Over the next 2-3 hours, northeast flow along the coast
will continue but is expected to weaken slightly as an
elongated area of low pressure stretches along the coast and the
pressure gradient relaxes. Though wind speeds will come down,
we should see the ambient pressure decrease by 7-9 mb which
should counter the loss of wind force. All this to say, we think
a departure of a little less than 1 ft is likely around the
time of high tide and the forecast is for a peak tide value of
7.0-7.2 ft MLLW. A Coastal Flood Advisory has been issued for
Charleston and coastal Colleton counties.

Astronomical tides will then continue to rise with the morning
high tide cycles through Friday and remain elevated through the
weekend. Coastal Flood Advisories will likely be needed for
morning high tide cycles, primarily at Charleston Harbor
(Charleston and Coastal Colleton counties) through late week.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 1 AM EST Wednesday for AMZ350-374.
     Small Craft Advisory from 10 AM this morning to 7 PM EST this
     evening for AMZ352.

&&

$$

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