Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 282104
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
404 PM EST SUN DEC 28 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 MONDAY MORNING/...
A COLD FRONT NEAR THE APPALACHIANS WILL SLOWLY APPROACH FROM THE
WEST. A VERY WARM AND HUMID AIR MASS IS IN PLACE AHEAD OF THE
FRONT WITH HIGHS NEAR RECORD LEVELS THIS AFTERNOON. THE DEEPER
MOISTURE WILL MOVE INTO WESTERN PORTIONS OF THE AREA LATE AND THIS
IS WHEN WE THINK THE BEST CHANCE OF SOME SHOWERS WILL BE ALTHOUGH
CAN/T RULE OUT ISOLATED LIGHT SHOWERS PRIOR TO THAT. IT WILL BE
ANOTHER WARM NIGHT WITH LOW TEMPS WELL ABOVE NORMAL MAINLY IN THE
MID TO UPPER 50S...POSSIBLY NOT GETTING BELOW 60 NEAR THE COAST.

THE BIGGEST ISSUE OVERNIGHT WILL BE THE POTENTIAL FOR SEA FOG TO
SPREAD INLAND. CURRENTLY THERE IS LITTLE...IF ANY...SEA FOG.
HOWEVER...MUCH MODEL GUIDANCE CONTINUES TO INDICATE THERE WILL BE
MORE DEVELOPING THIS EVENING AND WITH A SLIGHT ONSHORE WIND
COMPONENT SOME OF THE FOG SHOULD SPREAD INLAND. IN
ADDITION...SEA FOG FROM THE GULF OF MEXICO COULD ADVECT INTO THE AREA
FROM THE SOUTHWEST. SOME OF THE FOG COULD BECOME DENSE WITH
VISIBILITIES OF ONE QUARTER MILE OR LESS...ESPECIALLY NEAR THE
COAST. THUS...A DENSE FOG ADVISORY MAY EVENTUALLY BE ISSUED.

&&

.SHORT TERM /6 AM MONDAY 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 /21Z SUNDAY THROUGH FRIDAY/...
EXPECT VFR CONDS AT BOTH KCHS AND KSAV TO PREVAIL UNTIL THIS
EVENING WHEN CIGS WILL LOWER AGAIN AHEAD OF AN APPROACHING COLD
FRONT AND SEA FOG WILL LIKELY PUSH INLAND...AT LEAST ACROSS
SOUTHERN SOUTH CAROLINA. STILL SHOW LIFR CONDS AT KCHS FROM ABOUT
06Z THROUGH DAYBREAK BEFORE FOG SHOULD DISSIPATE AND/OR SHIFT BACK
CLOSER TO THE COAST DUE TO THE WEST TO SOUTHWEST WINDS.
HOWEVER...LOW CIGS...AT LEAST IN THE MVFR RANGE...COULD LINGER
LONGER. AT KSAV...IT LOOKS LIKE A MUCH TOUGHER FORECAST AS THEY
WILL LIKELY BE ON THE EDGE OF THE SEA FOG MOVING INLAND. TOWARD
DAYBREAK THOUGH THERE SHOULD AT LEAST BE IFR CONDS. COULD ALSO SEE
SOME SHOWERS...THOUGH MOSTLY LIGHT...TOWARD THE END OF THE TAF
PERIOD AS THE COLD FRONT NEARS AND DEEPER MOISTURE MOVES INTO THE
AREA.

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

&&

.MARINE...
TONIGHT...CONDITIONS LOOK TO FAVOR WIDESPREAD SEA FOG ACROSS THE
NEARSHORE WATERS AND INTO WESTERN PORTIONS OF THE OUTER GA WATERS
AS A VERY WARM AND HUMID AIR MASS CONTINUE TO MOVE INTO THE AREA
AHEAD OF AN APPROACHING COLD FRONT. DESPITE 10-15 KT SOUTHWEST
WINDS SOME OF THE FOG COULD BE DENSE AND A DENSE FOG ADVISORY MAY
EVENTUALLY BE ISSUED FOR ALL OR PART OF THE AREA. THIS WILL LIKELY
IMPACT CHARLESTON HARBOR AND COULD ALSO IMPACT SAVANNAH HARBOR. SEAS
WILL AVERAGE 2-3 FT NEARSHORE WATERS AND 3-4 FT OFFSHORE
WATERS.

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...NONE.
MARINE...NONE.

&&

$$

NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...





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