509
FXUS62 KCHS 041750
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1250 PM EST Thu Dec 4 2025

.SYNOPSIS...
High pressure will prevail across the region before a frontal
system impacts the area Friday into the weekend. High pressure
will then return next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Under a broad trough aloft, an inverted surface trough will be
building into the region throughout the rest of the afternoon and
into the evening hours. Moisture transport in combination with
isentropic lift will saturate the atmospheric column from top-down,
resulting in increasing coverage of rain showers building in from
the west. High temperatures remain seasonably cooler as a
result, with highs ranging from the lower 50s to lower 60s,
warmest along the coast. Will likely see two rounds of more
focused rainfall this afternoon into tonight, each associated
with a period of increased frontogenesis at varying levels. The
first is building in this afternoon at around the 700mb level,
as evident by the band of rain showers on radar, and will be
focused further south near/along the I- 16 corridor. However,
given the dry air near the surface layer, not expecting more
than a tenth of an inch before this band dissipates.

As a weak surface low begins to form and move up the inverted trough
into southern Georgia overnight, a second band of frontogenesis is
expected to form near the 850mb layer. This band is expected to
pivot more from the southwest to northeast, and remain across
interior southeast Georgia into the midlands of South Carolina. As
the surface low continues to approach the region, the 850mb band
will be sagging southwards increasing rainfall chances to include
coastal southeast South Carolina and coastal southeast Georgia.
Overall, the various ensembles would suggest probabilities for a
quarter of an inch are highest (40-60%) across interior southeast
Georgia and into interior southeast South Carolina, dropping to 10%
for those along the coast. Overnight lows are a touch warmer than
previous, in the lower to upper 40s.
&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
Multiple rounds of rain are expected Friday through the weekend.
Synoptically, the forecast area will remain ahead of mid level
trough axis, with a series of shortwaves expected to pass overhead.
At the surface, Friday will begin with a ridge of high pressure
extending into the Carolinas and an area of low pressure over the
northern Gulf. A front will extend from the low across southeast
Georgia, and then off the Southeast coast. Through the day, the low
will lift northeast along the front. An axis of deeper moisture will
become oriented across the region, with PWats expected to surge to
over 1.5 inches at times, which is well above normal for this time
of year per SPC sounding climatology. Increasing isentropic ascent
and larger scale forcing will lead to rain spreading across the
area. The highest coverage is expected to be in the daylight hours.
Friday rainfall totals are largely 0.75-1.25", except lesser
south of I-16, in the 0.25-0.75" range.

Additional waves of rainfall are expected Saturday and Sunday.
Saturday rainfall totals are forecast to fall in the 0.75-1.25" inch
range. Sunday rainfall coverage is a bit more uncertain with larger
model spread. Regardless, southeast Georgia should see the higher
rainfall totals on that day. NBM indicates the probability for
seeing greater than an inch in 24 hours ending Monday morning is
only around 10-20%.

All in all, the current forecast indicates a widespread 2-3 inches
of rain through the event (tonight/Thursday night through Sunday
night). No thunder is expected at this time. Luckily, rain rates
will not be particularly high and given almost half of the area is
classified in severe drought, flooding is not anticipated at this
time.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
The storm system that impacted the area over the weekend will exit,
allowing high pressure and drier weather to return. The main weather
concern during this time period is the chance for freezing
temperatures both Tuesday and Wednesday mornings. The probability
for reaching 32F or colder is highest over inland counties, with
only a 20-50% chance closer to the coast, roughly along and east of
Highway 17 (away from the beaches).

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
18Z TAF - Increased mid-level cloud deck will continue to build into
the region this afternoon, with clouds lowering into MVFR/IFR
territory this evening and into the overnight hours as rain showers
similarly build into the region. By the early morning hours,
showers will likely become more widespread, thus bringing higher
chances for IFR/LIFR cigs and MVFR/IFR visbys. Low ceilings
will likely remain across the area on Friday. It is possible
that LLWS conditions may develop over KSAV around dawn Friday,
but currently looks to be below critical thresholds so have left
it out with this cycle.

Extended Aviation Outlook: Flight restrictions, likely to IFR
or lower, are expected in low clouds and rain Friday into the
weekend.

&&

.MARINE...
No concerns across the marine zones for the rest of today into
tonight. The pressure pattern will support wind speeds between
10 to 15 kts. Seas will remain between 2 to 3 ft.

Friday through Tuesday: Low pressure is expected to pass across the
region Friday, with another wave passing through later in the
weekend. Rounds of rainfall are expected, but otherwise no marine
concerns with winds averaging 15 knots or less and seas 2-4 feet.
The storm system should finally pull away on Monday with increasing
winds and seas in its wake. Wind gusts and seas could approach Small
Craft Advisory criteria Monday into Monday night. No additional
concerns anticipated for Tuesday.

&&

.TIDES/COASTAL FLOODING...
Astronomical tides will 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 Sunday morning.

Friday, astronomical high tides peak (6.8 ft MLLW at Charleston
Harbor and 8.86 ft MLLW at Fort Pulaski) and this is when winds are
forecast to turn from the northeast. Overall, this type of setup can
overperform given the building anomalies from the northeast winds.
There is potential for tides to reach moderate flooding criteria
(7.5 ft MLLW), but current forecast keeps levels just shy.

Further south, from Beaufort county through the southeast Georgia
coast, the main tide of concern is Friday morning. There is
potential for tides to reach minor flooding criteria (9.5 ft MLLW),
but current forecast keeps levels just shy.

&&

.CLIMATE...
Record Precipitation:

December 7:
KCHS: 1.14/1976
KCXM: 0.82/1976
KSAV: 0.79/2017

&&

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

&&

$$

NEAR TERM...APT
SHORT TERM...ETM
LONG TERM...ETM
AVIATION...APT/ETM
MARINE...APT/ETM