Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 290628
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
128 AM EST MON DEC 29 2014

.SYNOPSIS...
A COLD FRONT WILL SLOWLY APPROACH FROM THE WEST TONIGHT AND MOVE
THROUGH THE REGION LATE MONDAY AND MONDAY NIGHT. HIGH PRESSURE
WILL THEN BUILD INTO THE AREA TUESDAY THROUGH THURSDAY...BEFORE
MOVING INTO THE ATLANTIC LATE IN THE WEEK. A COLD FRONT COULD
APPROACH EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
MESOSCALE UPDATE...REPORTS FROM BERKELEY COUNTY WARNING POINT
INDICATE VSBYS ARE NEAR ZERO THROUGHOUT MUCH OF THE COUNTY. HERE
AT THE WFO THE VISIBILITY IS NEAR ZERO OUT THE WINDOW AT THE
CHARLESTON AIRPORT. HAVE EXPANDED THE DENSE FOG ADVISORY TO
INCLUDE INLAND BERKELEY...DORCHESTER AND INLAND COLLETON COUNTIES.

THE COLD FRONT IS STILL WELL TO THE WEST EARLY THIS MORNING.
WARM AND MOIST CONDITIONS PERSIST ACROSS ALL OF SOUTHEAST SOUTH
CAROLINA AND SOUTHEAST GEORGIA WHICH WILL LINGER THROUGH SUNRISE.
RAIN CHANCES ARE LIMITED AT BEST AND MAINLY CONFINED TO THE FAR
WESTERN AREAS JUST BEFORE SUNRISE. ADJUSTED POPS TO MATCH THIS
THINKING.

WEBCAMS AND SURFACE OBSERVATIONS INDICATE THE LARGE AREA OF THICK
SEA FOG THAT HAS BEEN LINGERING OFFSHORE AND ALONG THE BEACHES
SINCE LATE AFTERNOON IS FINALLY MAKING ITS TREK INLAND. VSBYS ARE
NEAR ZERO IN THE SEA FOG AND THESE CONDITIONS WILL SPREAD INLAND
THROUGH AT LEAST THE SOUTH CAROLINA COASTAL COUNTIES THROUGH
SUNRISE...POSSIBLY EVEN FARTHER INLAND. ALONG AND WEST OF
I-95...LOCALLY DENSE RADIATION FOG HAS FORMED. MODELS SHOW A
POTENTIAL FOR DENSE FOG IN THIS AREA AS WELL AS HIGH CLOUDS REMAIN
FAIRLY THIN AHEAD OF THE FRONT. MEANWHILE...LOW STRATUS...FOG AND
SEA FOG WITH ORIGINS FROM THE NORTHEAST GULF WILL SPREAD INTO
INLAND AREAS AS WELL THROUGH SUNRISE. THE END RESULT WILL BE LOW
CLOUDS AND DENSE FOG WILL PLAGUE MUCH OF THE AREA THROUGH MONDAY
MORNING. WILL ISSUE A DENSE FOG ADVISORY FOR CHARLESTON AND TIDAL
BERKELEY UNTIL 10 AM MONDAY. ELSEWHERE...CONDITIONS HAVE NOT YET
REACHED DENSE FOG ADVISORY CRITERIA...ALTHOUGH AN ADVISORY WILL
LIKELY BE NEEDED FOR SOME OTHER AREAS VERY SOON.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY/...
MONDAY...THE STRONG SHORT WAVE THAT MOVES QUICKLY WITHIN THE WEST/SW
FLOW ALOFT WILL DE-AMPLIFY AS IT SKIRTS THE AREA EARLY IN THE DAY.
HOWEVER...AS THE REMAINS OF THE IMPULSE HEADS INTO THE MID-ATLANTIC
REGION AND OFFSHORE FOR THE AFTERNOON IT LEAVES BEHIND A TAIL OF
VORTICITY ACROSS THE LOCAL REGION. THIS WILL CAUSE A WAVE OF LOW
PRESSURE TO FORM ALONG THE APPROACHING THE COLD FRONT IN OUR SC
COUNTIES...AND THAT ALONG WITH THE FRONT BECOME SOMEWHAT ALIGNED TO
THE FLOW ALOFT SUGGESTS THAT THE FRONTAL PROGRESSION WILL BE
SLUGGISH. WHILE THERE IS A DEFINITIVE BAROCLINIC ZONE THAT WILL
PREVAIL ACROSS THE REGION FROM OUT OF THE GULF OF MEXICO...DUE TO
THE BEST DYNAMICS STAYING TO THE NORTH...A SLACKENING OF THE
PRESSURE FIELDS AND LIMITED LOW LEVEL CONVERGENCE INDICATES THAT THE
APPROACH OF THE FRONT WILL BE IN A WEAKENING STATE AS IT SHIFTS INTO
OUR ZONES. DESPITE THIS THERE IS A GOOD INFLUX OF DEEPER MOISTURE
WITH PWATS BETWEEN 1 AND 2 STANDARD DEVIATIONS ABOVE NORMAL...ALONG
WITH AN SURGE IN UPWARD OMEGA FIELDS DURING THE LATE MORNING AND
AFTERNOON. THESE CONDITIONS COMBINED WITH ADDITIONAL FORCING FOR
ASCENT FROM THE PROXIMITY TO THE NEARBY 95-105 KT OR GREATER UPPER
JET WILL CAUSE A HIGH-END CHANCE OF SHOWERS THAT MOVE IN FROM
WEST/SW TO EAST/NE. WITH POOR LAPSE RATES AND LITTLE IF ANY SURFACE
BASED INSTABILITY THE RISK OF T-STORMS IS ALMOST ZERO. BUT WITH
SHOWALTER INDICES TO FALL BETWEEN 0-1C THERE MIGHT A LITTLE THUNDER
OR LIGHTNING IN ISOLATED SPOTS. QPF LOOKS TO BE ABOUT 1/10 TO 1/3
INCH ON AVERAGE. AREAS TO WIDESPREAD FOG IS STILL FOUND IN THE
MORNING...SOME OF WHICH WILL BE DENSE...BUT THEN IT LINGERS MAINLY
IN THE NEARBY COASTAL WATERS FOR THE LATE MORNING AND AFTERNOON. A
FAIRLY LARGE THERMAL GRADIENT WILL PREVAIL FROM NW TO SE PENDING THE
PROGRESSION OF THE SHOWERS AND THE COLD FRONT. WE ANTICIPATE THE
DIURNAL CURVE TO BOUNCE AROUND ACCORDINGLY...BUT EVEN SO WE/RE STILL
FAR ABOVE NORMAL YET AGAIN.

MONDAY NIGHT...THE COLD FRONT FINALLY LIMPS THROUGH THE FORECAST
AREA...GETTING SOME IMPETUS FROM WEAK LOW PRESSURE FORMING OFF THE
MID-ATLANTIC COAST. THE FRONT WILL START THE EVENING NEAR THE US-17
CORRIDOR IN SC AND THEN THROUGH THE SAVANNAH AREA TO NEAR
LUDOWICI...BEFORE SHIFTING EAST/SE AND THROUGH ALL BUT MCINTOSH
COUNTY BY 03Z...AND FINALLY THROUGH THE LAST COUNTY BEFORE MIDNIGHT.
THERE REMAINS ENOUGH FORCING WITH THE FRONT COMBINED WITH ADEQUATE
MOISTURE TO YIELD 30-50 POPS IN THE EVENING...BEFORE COVERAGE DROPS
OFF DURING THE LATE EVENING AND OVERNIGHT. WET GROUNDS AND SOME
BUILD DOWN OF STRATUS WILL SUPPORT AT LEAST PATCHY FOG...SOME OF
WHICH WILL BE DENSE. COLD ADVECTION ISN/T THAT IMPRESSIVE...BUT
ENOUGH TO DROP TEMPS DOWN NEAR 50 NW...LOWER AND MIDDLE 50S MOST
ELSEWHERE.

TUESDAY...ALTHOUGH THE COLD FRONT IS WELL OFF THE SE COAST...A
POST-FRONTAL SE-NW ORIENTED TROUGH WILL PERSIST AS IT DROPS
SOUTHWARD AND THROUGH THE AREA. THIS PREVENTS THE BEST CLEARING FROM
OCCURRING UNTIL LATE IN THE DAY AND NIGHT AS THIS FEATURE PASSES TO
THE SOUTH. WHILE A FEW SHOWERS MAY STILL OCCUR NEAR THE COASTAL
CORRIDOR EARLY ON IF THE FRONT IS SLOWER IN PUSHING INTO THE
ATLANTIC...THE VAST MAJORITY OF THE DAY WILL BE RAINFREE WITH AT
LEAST PARTIAL SUNSHINE. A HUMONGOUS AND POWERFUL CONTINENTAL HIGH
BUILDING EAST/SE FROM THE NORTHERN ROCKIES WILL CONTINUE TO BUILD
INTO THE REGION...AND COLD ADVECTION WILL INCREASE LATE IN THE DAY
AND AT NIGHT. WHILE IT WON/T BE QUITE AS WARM AS RECENT DAYS...WE/RE
STILL WELL ABOVE NORMAL ON MAX TEMPS TUESDAY...WITH MUCH COLDER AIR
TO EVENTUALLY ARRIVE AT NIGHT.

WEDNESDAY...ZONAL FLOW ALOFT AND STRONG SUBSIDENCE ASSOCIATED WITH
HIGH PRESSURE AT THE SURFACE IN THE GREAT PLAINS AND STRETCHING ATOP
THE AREA WILL GIVE US A MOSTLY SUNNY BUT NOTICEABLY COOLER DAY. A
FEW MARINE-INDUCED SHOWERS WILL STAY OFFSHORE WITHIN THE NORTH-NE
SYNOPTIC FLOW. WE LEANED FAIRLY CLOSE TO THE LOW LEVEL THICKNESS
FORECAST ON HIGH TEMPS...WITH LOWER 50S NORTH AND UPPER 50S TO NEAR
60 SOUTH. IN ADDITION IT/LL BE BREEZY ALONG THE COAST WITH A
TIGHTER GRADIENT TO DEVELOP BETWEEN THE INLAND HIGH AND THE
BAROCLINIC ZONE OFFSHORE.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
THE EXPANSIVE SURFACE HIGH WILL STEADILY SHIFT OVER THE SOUTHERN
UNITED STATES BY THURSDAY...BEFORE SHIFTING INTO THE ATLANTIC
WATERS FRIDAY AND SATURDAY. A STRONG CUT OFF LOW OVER SOUTHERN
CALIFORNIA THURSDAY MORNING WILL WEAKEN WHILE TRACKING ACROSS THE
SOUTHWEST STATES FRIDAY...EVENTUALLY PROVIDING THE NECESSARY
ENERGY TO SPIN UP A SURFACE LOW PRESSURE SYSTEM THAT WILL LIFT
INTO THE OHIO VALLEY SATURDAY. THE TRAILING COLD FRONT FROM THIS
SYSTEM WILL CROSS THE EASTERN UNITED STATES OVER THE WEEKEND. WILL
MAINTAIN DRY WEATHER WEDNESDAY NIGHT THROUGH THURSDAY AS HIGH
PRESSURE REMAINS IN CONTROL...THEN REINTRODUCE RAIN CHANCES FRIDAY
INTO THE WEEKEND TO ACCOUNT FOR THE NEXT FRONTAL SYSTEM. LATEST
MODEL SOLUTIONS SUGGEST BEST RAIN POTENTIAL WILL BE
SATURDAY...WHEN THE COLD FRONT IS CURRENTLY FORECAST TO BE
CROSSING THE REGION. WILL ADVERTISE SEASONAL TEMPERATURES THURSDAY
AND FRIDAY...THEN INDICATE A WARMING TREND FRIDAY NIGHT INTO THE
WEEKEND AHEAD OF THE APPROACHING FRONT.

&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
KCHS..VSBYS ARE STEADILY LOWERING AS A COMBINATION OF RADIATION
FOG AND POSSIBLY SEA FOG AFFECTS THE TERMINAL. EXPECT CONDITIONS
TO DROP BELOW AIRPORT MINIMUMS SOON WITH VSBYS DROPPING TO 1/4SM
VV001 AND STAYING THERE THROUGH ABOUT 13-14Z. THERE MAY BE SOME
VARIABLE VSBYS THROUGH ABOUT 08Z...BUT SHOULD SETTLE WELL INTO
LIFR AFTER THAT. CONDITIONS WILL IMPROVE TO MVFR 14-16Z AND REMAIN
THERE THROUGH SUNSET. LIGHT RAIN WILL LIKELY IMPACT THE TERMINAL
21-02Z AS A COLD FRONT DROPS SOUTH. VSBYS WILL BE LIMITED TO MVFR
FOR NOW...ALTHOUGH PERIODS OF IFR ARE POSSIBLE IN POCKETS OF
HEAVIER RAINFALL. LOW CLOUDS WILL FILL BACK IN BEHIND THE FRONT
WITH IFR CIGS.

KSAV...DIFFICULT FOG FCST FOR THE TERMINAL WITH HIGH RESOLUTION
MODELS OFFERING A NUMBER OF POSSIBLE OUTCOMES. WILL CONTINUE TO
STAY SOMEWHAT CONSERVATIVE UNTIL MORE PESSIMISTIC TRENDS BECOME
APPARENT...BUT IT IS CERTAINLY POSSIBLE CONDITIONS COULD DROP BELOW
ALTERNATE MINIMUMS AND EVEN AIRPORT MINIMUMS PRIOR TO SUNRISE. FOR
NOW WILL LIMIT CONDITIONS TO 2SM BR OVC006...OR JUST ABOVE
AIRFIELD MINIMUMS. AMENDMENTS WILL BE ISSUED AS NEEDED. EXPECT MVFR
CONDITIONS TO RETURN BY 14Z. LIGHT RAIN WILL OVERSPREAD THE
TERMINAL BY 20Z AND LINGER THROUGH 03Z AS A COLD FRONT DROPS
SOUTH. EXPECT IFR CIGS TO FILL IN BEHIND THE FRONT.

EXTENDED AVIATION OUTLOOK...FLIGHT RESTRICTIONS LIKELY INTO EARLY
TUESDAY AS A COLD FRONT MOVES INTO AND ACROSS THE REGION.

&&

.MARINE...
OVERNIGHT...WIDESPREAD DENSE SEA FOG WILL LINGER WITHIN 20 NM.
REPORTS FROM THE CHARLESTON HARBOR PILOT CONTROL INDICATES VSBYS
HAVE DROPPED BELOW 1 NM AND COMING DOWN. WILL EXPAND THE MARINE
DENSE FOG ADVISORY TO INCLUDE THE CHARLESTON HARBOR.

SEAS WILL AVERAGE 2-3 FT NEARSHORE WATERS AND 3-4 FT OFFSHORE
WATERS WITH 10 TO 15 KT OF SOUTHERLY FLOW AT MOST.

MONDAY...THERE REMAINS ENOUGH OF A GRADIENT BETWEEN ATLANTIC RIDGING
TO THE SE AND THE APPROACH OF A COLD FRONT FROM THE WEST/NW TO KEEP
SW WINDS UP AS HIGH AS 10 OR 15 KT...HIGHEST IN THE MORNING...BEFORE
THE PRESSURE GRADIENT SLACKENS LATE. SEAS WILL BE A MIX OF LONG
PERIOD SWELLS AND SHORT PERIOD WIND DRIVEN WAVES...AVERAGING 2-4 FT
AND HIGHEST ACROSS AMZ374. SEA FOG WILL STILL BE A PROBLEM FOR
NAVIGATION WITHIN THE FAVORABLE SOUTH-SW TRAJECTORIES. IF CHARLESTON
HARBOR GETS SHUT DOWN IT SHOULD IMPROVE FOR THE AFTERNOON AS SHOWERS
ARRIVE AND THE SURROUNDING LAND AREAS WARM ENOUGH FOR IT TO
DISSIPATE. EVEN SO...MARINE DENSE FOG ADVISORIES ARE STILL LIKELY.

MONDAY NIGHT...THE COLD FRONT WILL BE IN A WEAK STATE AS IT FINALLY
ARRIVES DURING THE EVENING AND PASSES THROUGH ALL WATERS DURING THE
LATE EVENING AND OVERNIGHT PERIOD. WINDS WILL CLOCK AROUND TO THE NW
AND NORTH BEHIND THE FRONT...BUT COLD ADVECTION AND ONLY SMALL
PRESSURE RISES SUPPORTS NO MORE THAN 10 OR 15 KT AND SEAS 2-3 FT.
SEA FOG WILL LIKELY LINGER UNTIL AT LEAST AFTER THE FRONT MOVES
THROUGH...ALTHOUGH SOME FOG/LOW STRATUS COULD PERSIST FROM OFF THE
LAND THROUGH THE REST OF THE NIGHT.

TUESDAY THROUGH THURSDAY...A MONSTROUS CONTINENTAL HIGH...INITIALLY
WITH PRESSURE NEAR 1060 MB AND BUILDING OUT OF THE NORTHERN ROCKIES
WILL CONTINUE TO BUILD EAST/SE THROUGH THE MIDDLE OF THE WEEK AS
IT/S PRESSURE STEADILY DROP OFF THROUGH THE PERIOD. THE PRESSURE
GRADIENT WILL INCREASE BETWEEN THIS LARGE ANTICYCLONE AND THE
REMAINS OF THE COLD FRONT TO THE SE...AND THAT ALONG WITH VARYING
DEGREES OF COLD ADVECTION AND/OR ISALLOBARIC PRESSURE RISES WILL
SUPPORT HIGHER WINDS/SEAS. SMALL CRAFT ADVISORIES ARE POSSIBLE FOR
AT LEAST PARTS OF THE MARINE AREA...ESPECIALLY TUESDAY NIGHT THROUGH
WEDNESDAY NIGHT. THANKFULLY THE RISK FOR SEA FOG WILL HAVE COME TO
AN END.

FRIDAY...THE INLAND HIGH CONTINUES TO PUSH EAST AND HEAD INTO THE
ATLANTIC FRIDAY NIGHT. A WEAK NEARBY COASTAL TROUGH WILL ATTEMPT TO
FORM AS A RESULT. UNLESS THERE IS MORE PINCHING OF THE GRADIENT AS A
RESULT OF THE TROUGH...WE DO NOT CURRENTLY ANTICIPATE SMALL CRAFT
CONDITIONS.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...DENSE FOG ADVISORY UNTIL 10 AM EST THIS MORNING FOR SCZ043>045-
     050-052.
MARINE...DENSE FOG ADVISORY UNTIL 10 AM EST THIS MORNING FOR AMZ330-350-
     352-354.

&&

$$

ST




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