893
FXUS62 KCHS 171612
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1112 AM EST WED DEC 17 2025
SYNOPSIS
HIGH PRESSURE WILL WEAKEN AND SHIFT OUT OF THE AREA ON THURSDAY
AHEAD OF AN APPROACHING COLD FRONT. THE COLD FRONT IS EXPECTED
TO MOVE THROUGH THE AREA FRIDAY MORNING AND HIGH PRESSURE WILL
RETURN THROUGH THE WEEKEND. ANOTHER COLD FRONT WILL MOVE THROUGH
FROM THE NORTH ON MONDAY, FOLLOWED BY HIGH PRESSURE ACROSS THE
REGION INTO THE MIDDLE OF NEXT WEEK.
NEAR TERM /THROUGH TONIGHT/
SATELLITE AND MARINE OBSERVATIONS SHOW A WEAK COASTAL TROUGH IS
BECOMING BETTER DEFINED JUST OFFSHORE AS HIGH PRESSURE SHIFTS
FARTHER EAST OUT IN THE ATLANTIC. MODELS ARE SIMILAR IN SHOWING
ISENTROPIC ASCENT DEVELOPING THROUGH THE NIGHT AS THE COASTAL
TROUGH SHARPENS OFFSHORE. IMPULSES EJECTING OUT AHEAD OF THE
PRONOUNCED SHORTWAVE DIGGING ACROSS TEXAS INTO NORTHERN MEXICO
WILL BEGIN TO TRAVERSE THE REGION EARLY THURSDAY. THE COMBINATION
OF STRENGTHENING ISENTROPIC ASCENT AND INCREASING UVVS ALOFT
AHEAD OF THESE IMPULSES WILL SUPPORT A SLOW, BUT STEADY INCREASE
IN SHOWER COVERAGE AS NET MOISTURE VALUES CLIMB, LIKELY
STARTING OVER THE ATLANTIC NEAR THE COASTAL TROUGH ITSELF WITH
BANDS SLOWLY EXPANDING/DEVELOPING ONSHORE AS DAYBREAK
APPROACHES. THE STRONGEST 295-300K ISENTROPIC ASCENT WILL IMPACT
THE UPPER GEORGIA AND FAR SOUTHERN SOUTH CAROLINA COASTS,
DIRECTED INTO THE LOWER SAVANNAH RIVER VALLEY REGION THROUGH
DAYBREAK. THE HIGHEST POPS, 30-50%, WERE PLACED IN THIS REGION
CONSISTENT WITH THE MUCH OF THE NEAR TERM GUIDANCE AND THE
17/12Z HREF. LOWS TONIGHT WILL RANGE FROM THE MID-UPPER 40S
INLAND TO THE MID- UPPER 50S AT THE BEACHES, MUCH WARMER
COMPARED TO THE PAST SEVERAL NIGHTS.
SHORT TERM /THURSDAY THROUGH SATURDAY/
THURSDAY AND THURSDAY NIGHT: ALOFT, THE DAY WILL START WITH
SOUTHWEST FLOW AHEAD OF A SOUTHERN STREAM SHORTWAVE RIDING ALONG
THE GULF COAST. THIS SHORTWAVE WILL LIFT TOWARD THE FORECAST
AREA THROUGH THE DAY THEN SHOULD GRADUALLY PHASE WITH A STRONGER
NORTHERN STREAM TROUGH ACROSS THE MIDWEST AND THE GREAT LAKES
REGION. AT THE SURFACE, HIGH PRESSURE WILL START THE DAY JUST
OFF THE COAST OF NEW ENGLAND AND WILL SHIFT OFF TO THE NORTHEAST
THROUGH THE DAY. ACROSS OUR AREA, THE INLAND HIGH WILL STEADILY
WEAKEN AND A COASTAL TROUGH WILL SHIFT INLAND AND NORTHWARD
MUCH LIKE A WARM FRONT FEATURE. THE FORECAST AREA WILL THEN BE
PLACED SOLIDLY IN THE WARM SECTOR AHEAD OF AN ADVANCING COLD
FRONT THAT WILL BEGIN TO MOVE THROUGH FROM WEST TO EAST LATE
THURSDAY NIGHT. RAIN CHANCES WILL BE UNDERWAY STARTING THURSDAY
MORNING AS THE COASTAL TROUGH STARTS TO MOVE INLAND AND WE GET
INTO A FEED OF MOISTURE AND CONVERGENCE ALONG THE COAST
STRETCHING INLAND. AMONG THE HI-RES MODEL SOLUTIONS, THE
CONSENSUS FAVORS THE FEED OF SHOWERS TO BE SOMEWHERE IN THE
CORRIDOR BETWEEN SAVANNAH AND BEAUFORT ALONG THE GA COAST AND
THE LOWER SC COAST. THIS FEED OF SHOWERS IS THEN EXPECTED TO
MIGRATE UP THE COAST THROUGH THE AFTERNOON HOURS, IMPACTING THE
CHARLESTON COAST AND THE TRI-COUNTY REGION DURING THE AFTERNOON
AND INTO THE EARLY EVENING. PRECIPITATION ASSOCIATED WITH THE
TROUGH ALOFT AND THE ARRIVING COLD FRONT SHOULD THEN SPREAD IN
FROM THE WEST DURING THE EVENING AND SHOULD WRAP UP JUST BEFORE
SUNRISE FRIDAY MORNING. THERE REMAINS SOME UNCERTAINTY REGARDING
HOW WIDESPREAD THE RAINFALL WILL BECOME THURSDAY EVENING INTO
EARLY FRIDAY MORNING, PRIMARILY DUE TO SOME MODEL SOLUTIONS
HANDLING OF CONVECTION ACROSS NORTH FL AND THE POTENTIAL FOR IT
TO PASS JUST TO THE SOUTH AND REMAIN OFFSHORE. THE POTENTIAL FOR
ISOLATED THUNDER CONTINUES, BUT THE INSTABILITY IS EXPECTED TO
BE WEAK AND PRECLUDE ANY SEVERE WEATHER THREAT. RAINFALL AMOUNTS
ARE FORECAST TO GENERALLY BE IN THE 0.25-0.75" RANGE WITH THE
EVENT. TEMPERATURES SHOULD BE MILD, WITH HIGHS SURGING INTO THE
UPPER 60S ON THURSDAY FOLLOWED BY LOWS ONLY IN THE MID TO UPPER
50S BEFORE THE COLD FRONT PASSES LATER FRIDAY MORNING.
FRIDAY THROUGH SATURDAY: THE TROUGH AXIS WILL SHIFT OFFSHORE
FRIDAY MORNING FOLLOWED BY ZONAL FLOW THROUGH SATURDAY. CURRENT
MODEL CONSENSUS FAVORS THE COLD FRONT SHIFTING OFFSHORE BY MID
TO LATE FRIDAY MORNING AND THEN DRY HIGH PRESSURE WILL BUILD IN
THROUGH THE FIRST HALF OF THE WEEKEND. THERE COULD BE A BAND OF
WEAKENING SHOWERS ALONG THE COLD FRONT FRIDAY MORNING, BUT MOST
MODEL GUIDANCE SUGGESTS THIS SHOWER ACTIVITY WILL DISSIPATE AND
NOT PRODUCE ANY NOTABLE RAINFALL. LOOK FOR LOW TO MID 60S FOR
HIGHS EACH DAY, WITH CHILLY TEMPERATURES IN THE LOW TO MID 30S
INLAND FRIDAY NIGHT.
LAKE WINDS: SOUTHWEST WINDS ARE FORECAST TO SURGE AHEAD OF A
FRONT EARLY FRIDAY MORNING, BECOMING MORE WESTERLY BEHIND THE
FRONT THROUGH THE MID FRIDAY MORNING HOURS. THERE COULD BE A
SHORT WINDOW OF TIME WHERE GUSTS TO AROUND 25 KNOTS COULD OCCUR
ACROSS LAKE MOULTRIE, AND A LAKE WIND ADVISORY COULD BE NEEDED.
LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/
OVERALL, THE LONG TERM PERIOD IS EXPECTED TO FEATURE QUIET
WEATHER FOR THE LATTER HALF OF THE WEEKEND THROUGH EARLY NEXT
WEEK. ALOFT, ZONAL FLOW WILL PREVAIL ON THE NORTH SIDE OF A
LARGE BUILDING RIDGE THAT EXTENDS ACROSS THE CARIBBEAN, THE
GULF, AND ACROSS CENTRAL AMERICA. A BACKDOOR FRONT IS EXPECTED
TO PUSH THROUGH ON MONDAY, RESULTING IN BELOW NORMAL
TEMPERATURES. THEREAFTER, WE SHOULD SEE TEMPERATURES QUICKLY
REBOUND AND HEAD TOWARDS ABOVE NORMAL VALUES AS WE MOVE INTO THE
MIDDLE OF NEXT WEEK.
AVIATION /18Z WEDNESDAY THROUGH SUNDAY/
17/18Z TAF DISCUSSION:
KCHS/KJZI: VFR WILL PREVAIL THROUGH ABOUT 09Z WITH AN INCREASING
RISK FOR MVFR OR LOWER CONDITIONS THEREAFTER. BANDS OF SHOWERS
ARE EXPECTED TO DEVELOP OFFSHORE TONIGHT IN THE VICINITY OF A
COASTAL TROUGH THEN MEANDER/DEVELOP INLAND AS DAYBREAK
APPROACHES. CONFIDENCE WITH THE ONSET OF RAIN IS A BIT UNCERTAIN
AT BOTH TERMINALS WITH SIMULATED REFLECTIVITY PROGS SHOWING A
NUMBER OF POSSIBLE OUTCOMES IN A SLIGHT RAIN SCENARIO. THE RISK
FOR STEADIER RAINS ARRIVING IS MORE CERTAIN BY MID- MORNING
WHICH WILL CONTINUE BEYOND THE 18Z TAF PERIOD AT ALL THREE
TERMINALS. FOR NOW, VCSH WAS HIGHLIGHTED FROM 10Z ON, BUT
REFINEMENTS IN INTENSITY AND TIMING WILL MOST CERTAINLY BE
NEEDED AS CONFIDENCE BUILDS. THURSDAY THROUGH MONDAY: A COASTAL
TROUGH WILL LIFT NORTHWARD AND INLAND THURSDAY MORNING, FOLLOWED
BY INCREASING SOUTHERLY FLOW THURSDAY EVENING AND THURSDAY
NIGHT AHEAD OF AN APPROACHING COLD FRONT. WIND SPEEDS SHOULD
INCREASE INTO THE 20-25 KNOT RANGE WITH GUSTS UP TO 30 KNOTS
LATE THURSDAY NIGHT. SMALL CRAFT ADVISORIES WILL LIKELY BE
NEEDED FOR ALL OF THE WATERS, POTENTIALLY EVEN CHARLESTON
HARBOR. THE COLD FRONT WILL PASS THROUGH FRIDAY MORNING AND
WINDS WILL TURN WESTERLY. WINDS WILL REMAIN ELEVATED IN THE
WESTERLY FLOW. OVERALL, WINDS AND SEAS WILL THROUGH FRIDAY AND
SCA CONDITIONS SHOULD COME TO AN END. CONDITIONS SHOULD THEN BE
QUIET THROUGH THE WEEKEND. THE NEXT SURGE OF WINDS AND SEAS WILL
COME MONDAY AS A BACKDOOR FRONT PASSES THROUGH FROM NORTH TO
SOUTH. ANOTHER ROUND OF SCA'S COULD BE NEEDED FOR AT LEAST
PORTIONS OF THE WATERS ON MONDAY.
ONE OTHER THING TO KEEP AN EYE ON IS THAT THERE ARE SOME HINTS IN
MODEL GUIDANCE THAT A PERIOD OF MARINE FOG WILL BE POSSIBLE
THURSDAY EVENING. THE BEST CHANCES WILL BE ACROSS THE NEARSHORE
WATERS, BUT THE OVERALL DURATION SHOULD BE SHORT-LIVED AS A
COLD FRONT WILL PASS THROUGH FRIDAY MORNING.KSAV: VFR THROUGH
LATE EVENING WITH INCREASING RISK FOR MVFR OR LOWER CONDITIONS
THEREAFTER. A BAND OF SHOWERS IS EXPECTED TO FORM NEAR THE
TERMINAL BY 06Z, BUT ITS PLACEMENT AND TIMING IS A BIT UNCERTAIN
STILL. FOR NOW, A TEMPO GROUP FOR MVFR VSBYS IN SHOWERS WAS
HIGHLIGHTED 06-10Z. THIS BAND SHOULD MOVE EAST OF TERMINAL INTO
THE SOUTH CAROLINA LOWCOUNTRY BY DAYBREAK.
EXTENDED AVIATION OUTLOOK: PERIODS OF SUB-VFR CONDITIONS WILL
BE POSSIBLE THURSDAY AND THURSDAY NIGHT AHEAD OF AN APPROACHING
COLD FRONT. THE FRONT WILL MOVE THROUGH THE AREA BY MID TO LATE
FRIDAY MORNING AND PREVAILING VFR CONDITIONS WILL RETURN. THERE
REMAINS A LOW END CHANCE OF LLWS THURSDAY NIGHT AS A STRONG
WINDS JUST ABOVE THE SURFACE SURGE ACROSS THE REGION.
MARINE
THROUGH TONIGHT: THE LOCAL MARINE AREA WILL BECOME INCREASINGLY
INFLUENCED BY A SHARPENING COASTAL TROUGH JUST OFFSHORE.
NORTHEAST WINDS WILL GENERALLY PREVAIL, EXCEPT BECOMING EAST TO
SOUTHEAST OVER THE EASTERN PORTIONS OF THE GEORGIA OFFSHORE
WATERS OVERNIGHT. SPEEDS WILL AVERAGE 10 KT OR LESS, EXCEPT
INCREASE TO 10-15 KT IN THE FAR EASTERN PORTIONS OF THE GEORGIA
OFFSHORE WATERS. SEAS WILL REMAIN 4 FT OR LESS.
THURSDAY THROUGH MONDAY: A COASTAL TROUGH WILL LIFT NORTHWARD AND
INLAND THURSDAY MORNING, FOLLOWED BY INCREASING SOUTHERLY FLOW
THURSDAY EVENING AND THURSDAY NIGHT AHEAD OF AN APPROACHING
COLD FRONT. WIND SPEEDS SHOULD INCREASE INTO THE 20-25 KNOT
RANGE WITH GUSTS UP TO 30 KNOTS LATE THURSDAY NIGHT. SMALL CRAFT
ADVISORIES WILL LIKELY BE NEEDED FOR ALL OF THE WATERS,
POTENTIALLY EVEN CHARLESTON HARBOR. THE COLD FRONT WILL PASS
THROUGH FRIDAY MORNING AND WINDS WILL TURN WESTERLY. WINDS WILL
REMAIN ELEVATED IN THE WESTERLY FLOW. OVERALL, WINDS AND SEAS
WILL THROUGH FRIDAY AND SCA CONDITIONS SHOULD COME TO AN END.
CONDITIONS SHOULD THEN BE QUIET THROUGH THE WEEKEND. THE NEXT
SURGE OF WINDS AND SEAS WILL COME MONDAY AS A BACKDOOR FRONT
PASSES THROUGH FROM NORTH TO SOUTH. ANOTHER ROUND OF SCA'S COULD
BE NEEDED FOR AT LEAST PORTIONS OF THE WATERS ON MONDAY.
ONE OTHER THING TO KEEP AN EYE ON IS THAT THERE ARE SOME HINTS IN
MODEL GUIDANCE THAT A PERIOD OF MARINE FOG WILL BE POSSIBLE
THURSDAY EVENING. THE BEST CHANCES WILL BE ACROSS THE NEARSHORE
WATERS, BUT THE OVERALL DURATION SHOULD BE SHORT-LIVED AS A
COLD FRONT WILL PASS THROUGH FRIDAY MORNING.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...NONE.
--/BSH
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