128
FXUS62 KCHS 202341
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
641 PM EST SAT DEC 20 2025
SYNOPSIS
HIGH PRESSURE WILL PREVAIL OVER THE WEEKEND, WITH ANOTHER COLD
FRONT FORECAST TO IMPACT THE AREA MONDAY.
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/
EARLY THIS EVENING: ALOFT, NEARLY ZONAL FLOW WILL PREVAIL WITH A
BROADLY CYCLONIC FLOW REGIME. AT THE SURFACE, HIGH PRESSURE WILL
PREVAIL WITH A VERY WEAK GRADIENT ALLOWING FOR FULL DECOUPLING
AND CALM WINDS BY THE EARLY MORNING HOURS. THE ONLY FORECAST
CHALLENGE FOR THE OVERNIGHT IS THE FOG AND LOW STRATUS POTENTIAL
MODEL GUIDANCE SEEMS QUITE BULLISH ABOUT ALONG THE SOUTHEAST GA
COAST, POTENTIALLY EXTENDING UP INTO THE LOWER SOUTHEAST SC
COAST AS WELL. VIRTUALLY EVERY SOURCE OF HI-RES MODEL GUIDANCE
INCLUDING PROBABILISTIC GUIDANCE FROM THE NBM AND HREF SUGGESTS
THAT FOG WILL BEGIN DEVELOPING IN THE EARLY MORNING HOURS ACROSS
MCINTOSH COUNTY AND WILL THEN STEADILY EXPAND UP THE COAST AND
ACROSS SOUTHEAST GA THROUGH SUNRISE. FURTHERMORE, MUCH OF THE
GUIDANCE ACTUALLY GIVES RELATIVELY HIGH CHANCES (30-50%) OF
DENSE FOG ACROSS AN AREA THAT INCLUDES DARIEN, HINESVILLE,
SAVANNAH, RIDGELAND, AND POTENTIALLY EVEN UP TO BEAUFORT. THE
FOG POTENTIAL SEEMS REASONABLE GIVEN THE CALM WINDS, CLEAR
SKIES, AND SOME MOISTURE POOLING IN THIS AREA WHERE DEWPOINTS
ARE IN THE MID TO UPPER 40S THIS EVENING, SUGGESTING WE WILL
FALL BELOW CROSSOVER TEMPERATURES WITH LOWS. AS SUCH, WE HAVE
TRENDED THE FORECAST TO INCLUDE PATCHY FOG ALONG THE ENTIRE
SOUTHEAST GA COAST UP THROUGH COASTAL COLLETON COUNTY. ALSO, WE
HAVE ADDED A TIER OF AREAS OF FOG ALONG THE GA COAST UP THROUGH
WESTERN BEAUFORT COUNTY. WE COULD EVENTUALLY NEED TO INCLUDE
SOME DENSE FOG, BUT WILL WAIT UNTIL WE CAN SEE FOG DEVELOPMENT
BEGIN AND MAKE SURE IT IS TRACKING WITH MODEL GUIDANCE. LOWS
SHOULDN'T BE QUITE AS CHILLY AS LAST NIGHT, BUT STILL SHOULD SEE
WIDESPREAD UPPER 30S INLAND RANGING TO THE LOW 40S ALONG THE
COAST.
SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/
QUASI-ZONAL UPPER LEVEL FLOW AND A WEAK SURFACE HIGH PRESSURE
WILL CONTINUE THE QUIET CONDITIONS, WITH AFTERNOON HIGHS IN THE
MID 60S TO LOWER 70S ACROSS THE AREA. A WEAK COLD FRONT PUSHES
THROUGH DURING THE AFTERNOON HOURS, THOUGH THE COLDER AIR LAGS
BEHIND OVERNIGHT INTO MONDAY. OVERNIGHT LOWS IN THE UPPER 30S TO
MID 40S EXPECTED.
UPPER LEVEL RIDGING PUSHES A SURFACE HIGH PRESSURE ONTO THE
EAST COAST NORTH OF THE AREA, INCREASING THE SURFACE PRESSURE
GRADIENT. THIS WILL RESULT IN BREEZY CONDITIONS BUILDING
OVERNIGHT INTO MONDAY, WITH GUSTS INTO THE TEENS TO LOWER 20S
THROUGHOUT THE DAY. WITH THE FRESH INFLUX OF COOLER AIR,
AFTERNOON TEMPERATURES WILL BE BELOW NORMAL IN THE UPPER 50S TO
LOWER 60S.
WINDS DECREASE OVERNIGHT INTO TUESDAY AS THE SURFACE HIGH
PRESSURE WEAKENS AND MOVES INTO THE ATLANTIC. AS THEY SWING
AROUND TO BECOME OUT OF THE SOUTH-SOUTHWEST, WARMER TEMPERATURES
WILL BE ADVECTED BACK ACROSS THE REGION WITH AFTERNOON HIGHS IN
THE UPPER 60S TO MID 70S EXPECTED.
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
THE AFOREMENTIONED UPPER LEVEL RIDGE CONTINUES INTO THE
EXTENDED, WITH ANOTHER SURFACE HIGH PRESSURE EXPECTED TO MOVE
DOWN INTO THE REGION END OF THIS HOLIDAY WEEK. THIS WILL RESULT
IN ABOVE NORMAL TEMPERATURES AND DRY CONDITIONS. AFTERNOON HIGHS
LOOK TO BE IN THE UPPER 60S TO MID 70S RANGE.
AVIATION /00Z SUNDAY THROUGH THURSDAY/
THE 00Z TAF PERIOD BEGINS WITH VFR CONDITIONS AT KCHS, KJZI, AND
KSAV. THE MAIN FORECAST CHALLENGE IS THE POTENTIAL FOR FOG AND
LOW STRATUS PRIMARILY AT KSAV. MODEL GUIDANCE CONTINUES TO TREND
TOWARD A MORE FOGGY SOLUTION AND WE HAVE ALSO INTRODUCED IT INTO
THE KSAV TAF. WE HAVE INCLUDED A TEMPO GROUP FROM 10-14Z FOR 3SM
FOG AND AN IFR CEILING. THERE CERTAINLY IS THE POTENTIAL FOR THE
FOG TO BECOME DENSE AND THIS WILL NEED TO BE A CONSIDERATION FOR
THE 06Z TAF'S. IF THE FOG DEVELOPMENT IS REALLY AGGRESSIVE IT
COULD EXPAND UP TO KJZI, BUT FOR NOW WE HAVE JUST INCLUDED
SHALLOW GROUND FOG THERE. FOG AND LOW STRATUS AT KSAV SHOULD MIX
OUT BY MID MORNING AND VFR CONDITIONS WILL THEN PREVAIL AT ALL 3
SITES THROUGH THE REST OF THE PERIOD.
EXTENDED AVIATION OUTLOOK: VFR EXPECTED TO PREVAIL THROUGH
SUNDAY, WITH A PERIOD OF MVFR CIGS POSSIBLE MONDAY MORNING IN
THE WAKE OF A FRONTAL PASSAGE. NORTHEASTERLY WINDS ARE EXPECTED
TO BE BREEZY ON MONDAY, WITH GUSTS IN THE 14-18 KT RANGE.
MARINE
TONIGHT: PREVAILING HIGH PRESSURE WILL YIELD NORTHEAST WINDS 5
TO 10 KT WITH TRANSIENT GUSTS UP TO 15 KT ACROSS ALL WATERS.
SEAS 2 TO 4 FT. ALSO OF NOTE, MODEL GUIDANCE IS SUGGESTING THAT
FOG AND VERY LOW CEILINGS COULD DEVELOP ALONG THE SOUTHEAST GA
COAST LATE TONIGHT AND POTENTIALLY SPREAD OUT INTO THE COASTAL
WATERS. FOG COULD IMPACT THE WATERS, PRIMARILY THE NEARSHORE GA
WATERS AND THE LOWER SC WATERS. AS SUCH, WE HAVE ADDED PATCHY
FOG TO THE FORECAST. IT IS POSSIBLE THAT FOG COULD BECOME DENSE,
BUT CONFIDENCE IS LOW RIGHT NOW.
SUNDAY - MONDAY: TRANQUIL CONDITIONS CONTINUE INTO SUNDAY.
OVERNIGHT INTO MONDAY, NORTH-NORTHEASTERLY WINDS STRENGTHEN WITH
WAVE HEIGHTS SIMILARLY BUILDING. CONFIDENCE FOR WIND GUSTS
GREATER THAN 25 KNOTS IS HIGH FOR ALL NEAR AND OFFSHORE WATERS,
WITH BOTH THE HREF AND REFS SHOWING 90%+ PROBABILITIES FOR WIND
GUSTS GREATER THAN 25 KNOTS, THOUGH BOTH ENSEMBLES SHOW VERY LOW
PROBABILITIES (<10%) FOR GALE FORCE WINDS. FOR THE CHARLESTON
HARBOR, PROBABILITIES FOR THESE WINDS IS IN THE 60-80% RANGE,
HIGHEST NEAR THE ENTRANCE AND DECREASING INTO THE HARBOR. WAVE
HEIGHTS OF 6-8 FEET ARE ALSO EXPECTED TO BUILD INTO THE REGION
OVERNIGHT INTO MONDAY. THUS, A SMALL CRAFT ADVISORY WILL BE
NEEDED FOR THE EARLY OVERNIGHT HOURS INTO MONDAY, THOUGH UNSURE
IF THE CHARLESTON HABOR WILL NEED TO BE INCLUDED, WITH ADVISORY
LEVEL WINDS AND SEAS TAPERING OFF OVERNIGHT INTO TUESDAY. SOME
INDICATIONS THAT THE SAVANNAH TO ALTAMAHA SOUND WATER FROM
20-60NM OUT MAY HANG ONTO THE SCA CONDITIONS UNTIL LATE TUESDAY
AFTERNOON OR EVENING.
TUESDAY - WEDNESDAY: NO HIGH CONFIDENCE MARINE CONCERNS AT THIS
TIME.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...NONE.
NEAR TERM...BSH
SHORT TERM...APT
LONG TERM...APT
AVIATION...BSH/APT
MARINE...CPM/BSH/APT
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