359
FXUS62 KCHS 181802
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
102 PM EST THU DEC 18 2025
SYNOPSIS
A COASTAL TROUGH WILL CONTINUE TO MOVE INLAND TODAY BEFORE A
COLD FRONT ARRIVES FRIDAY MORNING. HIGH PRESSURE WILL THEN
PREVAIL SATURDAY INTO SUNDAY. ANOTHER COLD FRONT WILL THEN MOVE
ACROSS THE AREA MONDAY, WITH HIGH PRESSURE THEN PREVAILING INTO
THE MIDDLE OF NEXT WEEK.
NEAR TERM /THROUGH TONIGHT/
REST OF TODAY: ALOFT, THE FORECAST AREA CONTINUES TO SIT WITHIN
SOUTHWEST FLOW AHEAD OF A SOUTHERN STREAM SHORTWAVE THAT
STRETCHES JUST EAST OF THE LOWER MS VALLEY AND INTO THE NORTHERN
GULF. THIS SHORTWAVE WILL CONTINUE TO TRACK EASTWARD THROUGH
THE DAY WHILE IT BEGINS TO DAMPEN AND INTERACT WITH THE MORE
SIGNIFICANT TROUGH THAT STRETCHES ACROSS THE UPPER MIDWEST. AT
THE SURFACE, ANALYSIS REVEALS THAT THE COASTAL TROUGH IS ALIGNED
RIGHT ALONG THE COAST JUST OFFSHORE. THE COASTAL TROUGH WILL
EVENTUALLY PUSH INLAND THIS MORNING AS A WARM FRONT AND SHOULD
CLEAR INTO THE SC MIDLANDS BY THE AFTERNOON. WE EXPECT TO SEE A
STEADY STREAM OF SHOWERS INLAND FROM THE COASTAL WATERS THANKS
TO ISENTROPIC ASCENT THROUGH THE MORNING WITH THE MAIN FEED OF
THIS ACTIVITY ALONG THE GA COAST INTO AN AREA FROM SAVANNAH TO
BEAUFORT. MODEL GUIDANCE THEN FAVORS HAVING THIS FEED OF SHOWERS
GRADUALLY SHIFT UP THE COAST THROUGH THE AFTERNOON, FOCUSING IN
ON THE CHARLESTON AREA IN THE MID TO LATE AFTERNOON HOURS.
THROUGH SUNSET, RAINFALL AMOUNTS ARE EXPECTED TO MOSTLY BE IN
THE 0.1-0.3" RANGE. BEHIND THE WARM FRONT, TEMPERATURES SHOULD
WARM INTO THE UPPER 60S WITH EVEN AN ISOLATED LOCATION REACHING
70.
THIS EVENING THROUGH TONIGHT: THE AFOREMENTIONED SOUTHERN
STREAM SHORTWAVE WILL CONTINUE TO PHASE AND ABSORB INTO THE MORE
SIGNIFICANT TROUGH EXTENDING ACROSS THE GREAT LAKES AND TOWARD
THE SOUTHERN APPALACHIANS. LARGER SCALE FORCING WITH THE TROUGH
AND JET ALOFT WITH COINCIDE WITH PRECIPITABLE WATER VALUES
SURGING INTO THE 1.4-1.6" RANGE DURING THE FIRST PART OF THE
EVENING. AT THE SURFACE, THE MAIN COLD FRONT WILL STILL BE
DISPLACED TO THE WEST ACROSS MS/AL IN THE EARLY PART OF THE
EVENING. THIS COMBINATION OF INCREASING MOISTURE AND DEEP LAYER
FORCING IS EXPECTED TO ALLOW FOR THE GREATEST COVERAGE OF
PRECIPITATION IN THE TIME PERIOD GENERALLY COVERING 6PM-
MIDNIGHT. THERE REMAINS THE POTENTIAL FOR SEEING SOME EMBEDDED
THUNDERSTORMS AS WELL. MODEL SOUNDINGS SHOW A RELATIVELY SHALLOW
LAYER OF WEAK INSTABILITY (CAPE 100-300 J/KG), THOUGH NOT
NECESSARILY SURFACE-BASED. ALSO OF NOTE IS THE STRENGTHENING
LOW-LEVEL WIND FIELD WITH 40-45 KNOTS AT 850 MB AND A NICELY
VEERING PROFILE YIELDING 0-1 AND 0-3 KM SRH AS HIGH AS 250-300.
CURRENT THINKING IS THAT THE LACK OF SURFACE-BASED INSTABILITY
WILL PREVENT ANY REAL SEVERE WEATHER THREAT. BUT, GIVEN THE
AMBIENT WIND FIELD, WE CAN'T COMPLETELY RULE OUT AN ISOLATED
THUNDERSTORM DISPLAYING SOME INTERESTING RADAR PRESENTATION AND
NEEDING TO BE WATCHED.
AFTER MIDNIGHT, THE BULK OF THE RAINFALL WILL SHIFT OFF TO THE
NORTHEAST AND WE WILL BE LEFT WITH JUST ISOLATED TO SCATTERED
SHOWERS AHEAD OF THE APPROACHING FRONT. ADDITIONAL RAINFALL
AMOUNTS FOR THE EVENING AND OVERNIGHT ARE FORECAST TO BE MOSTLY
IN THE 0.25-0.50" RANGE WITH A LOWER END POTENTIAL FOR SOME
AREAS TO SEE UP TO 0.75". THIS COULD BRING THE MAX STORM TOTAL
RAINFALL FOR THE EVENT UP TO AS MUCH AS AN INCH, PRIMARILY WHERE
DEVELOPING CONVECTION TRACKS AND PRODUCES SOME LOCALLY HIGHER
RAINFALL RATES. THERE COULD BE A FINAL LINE OF SHOWERS
IMMEDIATELY ALONG THE FRONT AS IT MOVES THROUGH AROUND OR JUST
AFTER SUNRISE FRIDAY, BUT THIS SHOULD BE DISSIPATING AND NOT
AMOUNT TO MUCH. TEMPERATURES WILL HOVER IN THE LOW 60S FOR MOST
OF THE NIGHT WITH THE MIN NOT OCCURRING UNTIL THE FRONT ARRIVES
AROUND OR JUST AFTER SUNRISE. INLAND AREAS WILL LIKELY STILL
COOL INTO THE LOW TO MID 50S, WHILE THE COAST LIKELY DOESN'T
DROP OUT OF THE UPPER 50S.
SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/
FRIDAY: A SURFACE COLD FRONT WILL BE EXITING THE REGION TO THE
EAST WITH WINDS TURNING FROM THE NORTHWEST. IN THE MID-LEVELS OF
THE ATMOSPHERE, A POTENT MID-LEVEL TROUGH AXIS WILL BE DIRECTLY
OVERHEAD FRIDAY MORNING WITH A TRAILING SHORTWAVE ADVECTING
NORTHEAST. MUCH DRIER AIR IS FORECAST TO MOVE IN BEHIND THE COLD
FRONT (WITH PWATS FALLING TO LESS THAN 0.2"), BUT GIVEN THE
SHORTWAVE SOME OF THE PRECIP COULD FALL JUST BEHIND THE COLD
FRONT OR ANNA FRONTAL. BY THE AFTERNOON THOUGH, ALL
PRECIPITATION WILL HAVE EXITED THE REGION. THE LLJ ON THE
BACKSIDE OF THE COLD FRONT IS FORECAST TO BE ~40 KT, HOWEVER THE
MEAN PBL WINDS ARE NEAR 25 KT. CURRENT TEMPERATURES ON LAKE
MOULTRIE ARE IN THE UPPER 40S WHICH WILL FURTHER WEAKEN LAPSE
RATES/ MIXING EFFICIENCY. AS SUCH, WILL HOLD OFF ON THE LAKE
WIND DURING THE DAY FRIDAY. EXPECT HIGH TEMPERATURES IN THE MID
TO UPPER 60S.
SATURDAY: THE MID-LEVEL TROUGH AXIS WILL EXIT THE REGION TO THE
EAST WITH STRONG DAVA SETTING UP OVERHEAD. THE MEANS SURFACE
HIGH PRESSURE WILL CENTER JUST EAST OF THE APPALACHIANS WITH
WINDS QUICKLY DECOUPLING SATURDAY MORNING. EXPECT LOW
TEMPERATURES NEAR FREEZING INLAND (SATURDAY MORNING) AND NEAR
THE LOWER 40S AT THE COAST. DURING THE AFTERNOON, SURFACE HIGH
PRESSURE WILL QUICKLY SLIDE EAST OFF OF THE MID-ATLANTIC COAST
WITH A QUASI COASTAL TROUGH/ SEA BREEZE PUSHING INLAND. THE MAIN
CHANGE WILL BE THE RISING DEWPOINTS AND INCREASING RELATIVE
HUMIDITY VALUES. NO PRECIPITATION IS FORECAST. EXPECT HIGH
TEMPERATURES IN THE LOWER 60S.
SUNDAY: ANOTHER POTENT SHORTWAVE WILL HEAD EAST JUST SOUTH OF
THE JAMES BAY. PARENT SURFACE HIGH PRESSURE WILL BE LOCATED
ACROSS THE MIDWESTERN UNITED STATES AND QUICKLY PULL EAST SUNDAY
MORNING. LOCALLY, SUNDAY LOOKS LIKE ANOTHER DAY WITH ABOVE
NORMAL TEMPERATURES WITH HIGHS IN THE MID TO UPPER 60S (MAYBE
70S ACROSS INTERIOR GEORGIA). LATE SUNDAY AFTERNOON INTO
EVENING, SURFACE HIGH PRESSURE THAT WAS OVER THE MIDWESTERN
UNITED STATES WILL START TO CROSSOVER THE APPALACHIAN MOUNTAINS.
AS THIS OCCURS, COLD DENSE AIR WILL START TO OOZE SOUTHWEST
WITH WINDS TURNING FROM THE NORTHEAST. THE BACK DOOR COLD FRONT
LOOKS TO CROSS THE REGION VERY EARLY MONDAY MORNING. NO
PRECIPITATION IS EXPECTED.
LONG TERM /MONDAY THROUGH THURSDAY/
MONDAY: SURFACE HIGH PRESSURE OVER THE MID-ATLANTIC WILL FILTER
COLDER AIR INTO THE REGION MONDAY WITH HIGH TEMPERATURES IN THE
MID 50S OR BELOW NORMAL FOR THIS TIME OF YEAR. ANOTHER ROUND OF
FREEZING TEMPERATURES ARE POSSIBLE (~50% CHANCE) TUESDAY
MORNING. IT SHOULD BE NOTED THAT ENSEMBLE GUIDANCE IS ACTUALLY
IN FAIRLY GOOD AGREEMENT FOR THE THE FORECAST WITH THE IQR ONLY
BEING 6 DEGREES ON HIGH TEMPERATURES FOR MONDAY (OR DAY 5)!
TUESDAY: HIGH PRESSURE QUICKLY DISINTEGRATES WITH TEMPERATURES
WARMING INTO THE MID TO UPPER 60S. MODEL SPREAD IS THE LARGEST
HERE AS THE EXACT TIMING OF WHEN THE SURFACE HIGH LOSES COHESION
IS UNKNOWN AND WILL IMPACT THE RESULTANT HIGH TEMPERATURES.
WEDNESDAY (AND INTO CHRISTMAS): EXTREMELY GOOD AGREEMENT WITH
GLOBAL ENSEMBLES ADVERTISING ABOVE NORMAL TEMPERATURES WITH LOWS
IN THE MID TO UPPER 40S AND HIGHS NEAR 70 DEGREES. NO
PRECIPITATION IS EXPECTED.
AVIATION /18Z THURSDAY THROUGH TUESDAY/
THE 18Z TAF PERIOD IS QUITE COMPLEX THANKS TO AN APPROACHING
COLD FRONT THAT IS EXPECTED TO PUSH OFFSHORE BY MID MORNING
FRIDAY. FOR THE AFTERNOON, SHOWERS WILL STREAM ONSHORE AND COULD
IMPACT THE TERMINALS FOR PERIODS OF TIME WITH BRIEF MVFR
CEILINGS AND VISIBILITIES. THIS WILL OCCUR FIRST AT KSAV, AND
THEN GRADUALLY SHIFT TO KCHS AND KJZI THROUGH MID TO LATE
AFTERNOON. THE MOST WIDESPREAD PRECIPITATION IS EXPECTED THIS
EVENING. WE ALSO CAN'T COMPLETELY RULE OUT A RUMBLE OR TWO OF
THUNDER FOR THE EVENING HOURS, BUT CURRENT CONFIDENCE IS TOO LOW
IN THE DIRECT IMPACT OF THUNDERSTORMS. RAINFALL WILL COME TO AN
END BY AROUND OR JUST AFTER MIDNIGHT AND THE FORECAST THEN
BECOMES MAINLY CEILINGS AND WIND CHANGES. GUIDANCE FAVORS IFR
CEILINGS SPREADING IN ACROSS THE AREA FOR A TIME FROM ROUGHLY
00-10Z. WINDS WILL TURN MORE SOUTHERLY AND THEN SOUTHWESTERLY,
BECOMING GUSTY AFTER MIDNIGHT. BEFORE SURFACE WINDS STRENGTHEN
WE WILL LIKELY SEE A PERIOD OF LLWS AT ALL 3 TAF SITES FROM THE
EVENING THROUGH THE EARLY MORNING HOURS. THE FRONT IS EXPECTED
TO PASS THROUGH THE TERMINALS AROUND 12Z, AND GUSTY WESTERLY
WINDS WILL CONTINUE THROUGH THE END OF THE TAF PERIOD. ALSO,
CEILINGS WILL LIFT AND THEN SKIES WILL CLEAR OUT BY THE LAST FEW
HOURS OF THE PERIOD AS WELL.
EXTENDED AVIATION OUTLOOK:
FRIDAY AFTERNOON AND SATURDAY: VFR. WINDS WILL BE GUSTY AT
TIMES FRIDAY BEHIND A COLD FRONT. SURFACE HIGH PRESSURE WILL BE
IN CONTROL FOR THE START OF SATURDAY WITH WINDS OUT OF THE
NORTHWEST. HIGH PRESSURE WILL THEN QUICKLY MOVE OFFSHORE WITH
WINDS AT THE TERMINALS TURNING FROM THE SOUTHEAST BY SATURDAY
AFTERNOON. EARLY SUNDAY MORNING WINDS WILL THEN TURN BACK FROM
THE WEST AS A COLD FRONT APPROACHES.
SUNDAY: WEST WINDS WITH A COLD FRONT APPROACHING FROM THE
NORTHWEST. VFR. WINDS VEERING FROM THE NORTHEAST AS A COLD FRONT
APPROACHES FROM NC.
MONDAY: MVFR/VFR. AVIATION USERS SHOULD BE PREPARED FOR SOME
MVFR CONDITIONS BEHIND A COLD FRONT THAT IS FORECAST TO CROSS
THE TERMINALS MONDAY MORNING. ANY MVFR CIGS WILL THEN SLOWLY
RISE TO VFR MONDAY AFTERNOON.
TUESDAY: VFR WITH SURFACE HIGH PRESSURE LOCATED OVER NC/ SC/
GA.
MARINE
TODAY: WINDS WILL GRADUALLY START TO INCREASE THROUGH THE
AFTERNOON WHILE TURNING MORE SOUTH-SOUTHEASTERLY AHEAD OF AN
APPROACHING FRONT. SPEEDS SHOULD MOSTLY TOP OUT AROUND 15 KNOTS
THROUGH SUNSET, HIGHEST IN THE OUTER WATERS WHERE WARMER SST'S
RESIDE. SEAS WILL STEADILY RISE, BECOMING 3-5 FEET AND PERHAPS
UP TO 6 FEET IN THE OUTER GA WATERS BY THE LATE AFTERNOON. AS
SUCH, A SMALL CRAFT ADVISORY (SCA) GOES INTO EFFECT FOR THE
OUTER WATERS.
THIS EVENING AND OVERNIGHT: AS A COLD FRONT APPROACHES FROM THE
WEST AND LOW-LEVEL WIND FIELDS STRENGTHEN, CONDITIONS WILL
STEADILY DETERIORATE ACROSS THE LOCAL WATERS. WINDS WILL TURN
MORE SOUTHERLY AND THEN SOUTHWESTERLY WITH SUSTAINED SPEEDS UP
TO AROUND 20 KNOTS AND GUSTS AS HIGH AS 25-30 KNOTS. SEAS WILL
INCREASE ACCORDINGLY, BUILDING AS HIGH AS 6-8 FEET IN THE
CHARLESTON COUNTY WATERS AND THE OUTER GA WATERS. SCA'S WILL BE
NEEDED FOR ALL WATERS INCLUDING CHARLESTON HARBOR.
MARINE FOG: AS SOUTHERLY FLOW AND SHOWERS SPREAD ACROSS THE
COASTAL WATERS THIS EVENING AND INTO THE OVERNIGHT, THERE
CONTINUES TO BE A LOW END CHANCE FOR AT LEAST SOME PATCHY FOG.
AS OF NOW IT LOOKS LIKE LOW-LEVEL WIND FIELDS WILL BE TOO
STRONG, BUT IT IS POSSIBLE THERE COULD BE SOME DEVELOPMENT
BEFORE WINDS INCREASE. WE ARE NOT EXPLICITLY ADVERTISING FOG IN
THE FORECAST RIGHT NOW, BUT IT CERTAINLY WILL NEED TO BE
WATCHED.
FRIDAY: A COLD FRONT WILL HAVE CROSSED THE MARINE ZONES FRIDAY
WITH WINDS GUSTING 25 TO 30 KT. EVEN OVER CHARLESTON HARBOR SOME
GUSTS 25 KT OR SLIGHTLY HIGHER ARE POSSIBLE. THE ONE EXCEPTION
TO THIS ARE THE NEARSHORE GEORGIA WATERS. SHELF WATER
TEMPERATURES ARE IN THE MID 50S WHICH SHOULD LIMIT MIXING. GIVEN
THAT, ONLY A 25% - 40% CHANCE EXISTS FOR WINDS TO REACH SMALL
CRAFT ADVISORY CRITERIA FOR THE NEARSHORE GEORGIA WATERS. SEAS
UP TO 6 FT ARE LIKELY THOUGH AND THEREFORE SMALL CRAFT
ADVISORIES ARE IN EFFECT FOR ALL WATERS. WINDS AND SEAS WILL
FALL BELOW SMALL CRAFT ADVISORY CRITERIA ACROSS ALL WATERS BY
FRIDAY EVENING.
SATURDAY AND SUNDAY: SEAS 2 TO 4 FT WITH WINDS GUSTING UP TO 15
KT AT TIMES. NO ADVISORIES OR WARNINGS ARE EXPECTED.
MONDAY: A COLD FRONT WILL CROSS THE WATERS IN THE EARLY MORNING
HOURS FROM THE NORTHEAST WITH WINDS GUSTING 25 TO 30 KT AT
TIMES. SMALL CRAFT ADVISORIES WILL LIKELY BE NEEDED FOR ALL
ZONES (THE ONE EXCEPTION BEING THE HARBOR).
TUESDAY: NORTHEAST WINDS TURNING FROM THE SOUTHEAST AROUND 10
KT WITH SEAS 4 TO 7 FT RELAXING TO 3 TO 6 FT.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EST FRIDAY
FOR AMZ330.
SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 7 PM EST FRIDAY
FOR AMZ350.
SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 1 PM EST
FRIDAY FOR AMZ352.
SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 1 PM EST FRIDAY
FOR AMZ354.
SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 7 PM EST
FRIDAY FOR AMZ374.
NEAR TERM...BSH
SHORT TERM...HAINES
LONG TERM...HAINES
AVIATION...BSH/HAINES
MARINE...BSH/HAINES
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