Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 281616
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1116 AM EST SUN DEC 28 2014

.SYNOPSIS...
HIGH PRESSURE WILL PULL FURTHER OFFSHORE TODAY. A COLD FRONT WILL
SLOWLY 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 NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
HIGH PRESSURE WILL GIVE WAY TO AN APPROACHING COLD FRONT FROM THE
WEST. THE DEEPEST MOISTURE AND BETTER RAIN CHANCES WILL REMAIN
WEST OF THE AREA TOWARD CENTRAL GA/SC BUT COULD SEE SOME SHOWERS
NEAR MILLEN GEORGIA LATE. A WARM AIR MASS WILL BE ADVECTING IN AND
DESPITE PLENTY OF CLOUD COVER TEMPERATURES SHOULD PUSH WELL ABOVE
NORMAL INTO THE LOWER 70S NORTH AND WEST TO THE MID 70S SOUTH AND
EAST WHERE A BIT MORE SUN IS EXPECTED. A FEW UPPER 70S WILL BE
POSSIBLE CLOSE TO THE ALTAMAHA RIVER.

THERE IS A POTENTIAL FOR SIGNIFICANT SEA FOG DEVELOPMENT OVER THE
COASTAL WATERS TODAY AS WARM/MOIST AIR BEGINS TO FLOW OVER THE
CHILLY SHELF WATERS THAT ARE IN PLACE OFF THE COAST. ANY SEA FOG
THAT FORMS OFFSHORE COULD CERTAINLY BEGIN TO MOVE INLAND LATE THIS
AFTERNOON AS A SEA BREEZE CIRCULATION KICKS IN. DEPENDING ON HOW
STRONG THE THERMALLY DIRECT CIRCULATION BECOMES...FOG COULD BE
ADVECTED AS FAR INLAND AS THE INTRACOASTAL WATERWAY...CHARLESTON
HARBOR AND POSSIBLY THE SAVANNAH RIVER...AFFECTING DOWNTOWN
CHARLESTON AND PARTS OF DOWNTOWN SAVANNAH BY LATE AFTERNOON. SOME
OF THE FOG COULD BECOME DENSE AT TIMES WITH VISIBILITIES ONE
QUARTER MILE OR LESS...THUS A DENSE FOG ADVISORY MAY BE ISSUED
LATER TODAY.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/...
TONIGHT...MEAN RIDGING WILL LIKELY GIVE WAY ENOUGH OVERNIGHT THAT
ISOLATED TO PERHAPS LOW-END SCATTERED SHOWERS COULD IMPACT MAINLY
THE CENTRAL AND WESTERN PORTIONS OF THE FORECAST AREA LATE TONIGHT
AS A COLD FRONT AND WEAK FRONTAL WAVE APPROACHES. RAINFALL
AMOUNTS...IF ANY...WILL BE LIGHT AS MODELS STILL DEPICT A WELL-
DEFINED MID-LEVEL CLOUD POCKET HOLDING FIRM. WILL HIGHLIGHT 20-30
PERCENT POPS IN THESE AREAS...ALTHOUGH CONFIDENCE FOR ACTUALLY
SEEING MEASURABLE RAINFALL IS LOW. IT WILL BE ANOTHER WARM NIGHT
WITH LOWS RANGING FROM THE UPPER 50S INLAND TO THE LOWER 60S
COAST.

OUR BIGGEST CONCERN TONIGHT IS FOR THE POTENTIAL FOR A WIDESPREAD
DENSE SEA FOG EVENT UNFOLDING ACROSS THE AREA. AREAS OF SEA FOG
WILL LIKELY BE ONGOING ACROSS THE COASTAL WATERS AND POSSIBLY THE
COASTAL COUNTIES AT SUNSET...WHICH SHOULD SPREAD INLAND UNDERNEATH
THE NOCTURNAL INVERSION AS THE NIGHT PROGRESSES. IN ADDITION...
MODELS SUGGEST A SECONDARY AREA OF SEA FOG AND RADIATION FOG WILL
DEVELOP OVER THE NORTHEAST GULF AND FLORIDA PANHANDLE THIS
EVENING...THEN GRADUALLY SPREAD IN FROM THE SOUTH AND SOUTHWEST
AFTER MIDNIGHT. CONDITIONS CERTAINLY LOOK FAVORABLE FOR WIDESPREAD
FOG TO AFFECT MANY AREAS TONIGHT...BUT FORECASTING THE TIMING AND
EXTENT OF SEA FOG IS ALWAYS A CHALLENGE. CONFIDENCE IN SEA FOG
FORMING IS RATHER HIGH GIVEN EXTENSIVE SEA FOG HAS ALREADY
OCCURRED DURING PREVIOUS WARM SPELLS EXPERIENCED OVER THE PAST FEW
WEEKS...BUT IT REMAINS TO BE SEEN EXACTLY HOW THIS EVENT WILL PLAY
OUT. WILL HIGHLIGHT AREAS OF FOG AND WIDESPREAD FOG ALL AREAS
TONIGHT...GRADUALLY SPREADING INLAND AND FROM THE SOUTH OVERNIGHT.
THE INTRODUCTION OF DENSE AND VISIBILITY ATTRIBUTES MAY EVENTUALLY
BE NEEDED IN THE GRIDDED AND TEXT FORECASTS. A DENSE FOG ADVISORY
MAY VERY WELL BE NEEDED FOR SOME AREAS OVERNIGHT AND THIS
POTENTIAL WILL REMAIN HIGHLIGHTED IN THE HAZARDOUS WEATHER
OUTLOOK.

MONDAY...WEAKENING SHORTWAVE ENERGY WILL MOVE ACROSS THE MID
ATLANTIC AND CAROLINA COASTLINE DURING THE MORNING AND AFTERNOON
TIME FRAME. A COLD FRONT WILL SHIFT INTO THE FORECAST AREA AND
GRADUALLY SLIP OFF THE SOUTHEAST COAST THROUGH THE EVENING AND
OVERNIGHT. ALTHOUGH THE BEST CHANCE OF RAIN DURING THE SHORT TERM
PERIOD APPEARS TO OCCUR WITH FRONTAL PASSAGE MONDAY AFTERNOON...
PREFER TO CAP POPS BELOW THE LIKELY CATEGORY CONSIDERING SOME
UNCERTAINTIES REGARDING COVERAGE. WILL INDICATE RAIN CHANCES
PEAKING IN THE 40 PERCENT RANGE TO ACCOUNT FOR SOME FRONTAL
CONVERGENCE AND MOISTURE ACCESS...WHILE STILL REMAINING
CONSERVATIVE SINCE THE FRONT WILL BE NEARLY PARALLEL TO THE
DAMPENING FLOW ALOFT AND SHORTWAVE ENERGY WILL BE IN A WEAKENING
STATE. COMPRESSIONAL WARMING IN ADVANCE OF THE COLD
FRONT...COMBINED WITH A DOWNSLOPE FLOW COMPONENT...WILL SUPPORT
ANOTHER UNSEASONABLY WARM DAY. EXPECT TEMPERATURES TO PEAK IN THE
UPPER 60S TO LOW 70S...WHILE LOW TEMPERATURES ARE RELATIVELY MILD
IN THE LOW TO MID 50S.

TUESDAY...RAIN WILL STEADILY DIMINISH IN COVERAGE FROM NORTHWEST
TO SOUTHEAST THROUGH THE MORNING HOURS...AS THE COLD FRONT AND AN
ASSOCIATED WAVE OF LOW PRESSURE MOVE FARTHER AWAY FROM THE COAST.
RAIN CHANCES WILL FALL BELOW 15 PERCENT BY EARLY AFTERNOON...WITH
SKY COVER SLOWLY SCATTERING TOWARD THE EVENING HOURS. COLD
ADVECTION AND NORTH FLOW IN THE WAKE OF THE FRONT AND ALONG THE
PERIPHERY OF EXPANSIVE HIGH PRESSURE BUILDING FROM THE WEST WILL
SUPPORT COOLER AND DRIER CONDITIONS. HIGH TEMPERATURES WILL RANGE
FROM THE LOW 60S NORTH TO THE MID 60S SOUTH...WITH NIGHTTIME LOWS
FALLING INTO THE UPPER 30S TO LOWER 40S.

WEDNESDAY...AN IMPRESSIVELY STRONG AND EXPANSIVE SURFACE HIGH WILL
STRETCH ACROSS MUCH OF THE CENTRAL AND EASTERN UNITED STATES BY
MID WEEK. EXPECT RATHER QUIET CONDITIONS TO PREVAIL...WITH
TEMPERATURES A DEGREE OR TWO BELOW SEASONAL NORMALS. HIGH
TEMPERATURES WILL BE IN THE LOW 50S NORTH TO UPPER 50S SOUTH UNDER
MOSTLY CLEAR SKIES.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
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 /16Z SUNDAY THROUGH THURSDAY/...
LOW CLOUDS HAVE MOVED INTO KSAV FROM THE SOUTHWEST LEADING TO IFR
CONDS...ALTHOUGH CIGS SHOULD LIFT TO MVFR THIS AFTERNOON AND
POSSIBLY EVEN VFR. KCHS SHOULD SEE SOME MVFR CIGS TOO...POSSIBLY
EVEN MARGINAL IFR. SEA FOG IS EXPECTED TO DEVELOP OFF THE COAST
LATER TODAY...SOME OF WHICH WILL SPREAD INLAND LATE THIS
AFTERNOON WITH THE SEA BREEZE WITH A BIGGER PUSH EXPECTED
OVERNIGHT. AT THIS TIME...THE BEST CHANCES FOR SIGNIFICANT IMPACTS
LOOKS TO BE AT KCHS...ALTHOUGH PROBABILITIES ARE HIGH AT KSAV AS
WELL. WILL TAKE A SOMEWHAT CONSERVATIVE APPROACH WITH THE 12Z TAFS
SINCE THE TIMING AND EXTENT IS STILL A BIT UNCERTAIN. WILL SHOW
MVFR VSBYS/CIGS THIS EVENING...DROPPING TO LIFR AT KCHS BY 06Z
WITH HIGH-END IFR AT KSAV. BOTH SITES COULD VERY WELL DROP BELOW
AIRFIELD MINIMUMS AFTER 06Z...BUT WILL NOT INTRODUCE THOSE
CONDITIONS JUST YET.

EXTENDED AVIATION OUTLOOK...FLIGHT RESTRICTIONS LIKELY LATE
MONDAY INTO MONDAY NIGHT AS A COLD FRONT MOVES ACROSS THE REGION.

&&

.MARINE...
TODAY...SOUTH TO SOUTHWEST WINDS 10-15 KT TODAY AHEAD OF AN
APPROACHING COLD FRONT. A WARM AND MOIST AIR MASS WILL MOVE INTO
THE AREA LEADING TO FAVORABLE CONDITIONS FOR SEA FOG...LIKELY
DEVELOPING OFF SOUTHEAST GEORGIA AND THEN SPREADING NORTHWARD OFF
SOUTH CAROLINA. SOME OF THE FOG COULD BECOME DENSE AT TIMES AND
THUS A MARINE DENSE FOG ADVISORY MAY EVENTUALLY BE NEEDED. A
MARINE WEATHER STATEMENT HAS BEEN ISSUED TO ADDRESS THIS CONCERN.
SEAS WILL AVERAGE 2-3 FT NEARSHORE AND 3-4 FT OFFSHORE...MAINLY IN
LONG PERIOD EAST SWELLS WITH PERIODS AROUND 15 SECONDS.

TONIGHT...CONDITIONS LOOK TO FAVOR WIDESPREAD DENSE SEA FOG ACROSS
THE NEARSHORE WATERS AS SOUTHWEST WINDS DOMINATE WITH SPEEDS LESS
THAN 10 KT. IT IS STILL UNCLEAR EXACTLY HOW WIDESPREAD AND DENSE
THE SEA FOG WILL BECOME...BUT CONFIDENCE IS INCREASING THAT A
NASTY DENSE SEA FOG EVENT WILL OCCUR. WILL GO AHEAD AND INTRODUCE
WIDESPREAD FOG IN THE GRIDDED AND TEXT FORECASTS...BUT NO
INTRODUCE DENSE WORDING JUST YET. SEAS WILL AVERAGE 2-3 FT
NEARSHORE WATERS AND 3-4 FT OFFSHORE WATERS...MAINLY IN LONG
PERIOD EAST SWELL.

MONDAY...A COLD FRONT WILL SLIP INTO THE COASTAL WATERS DURING
THE EVENING/OVERNIGHT HOURS...ALLOWING SOUTHWEST FLOW EARLY IN THE
DAY TO VEER NORTH OVER THE SOUTH CAROLINA WATERS AND NORTHWEST
ACROSS GEORGIA MARINE ZONES. SEA FOG WILL PERSIST ACROSS THE
NEARSHORE WATERS DURING THIS TIME...MOST LIKELY JUST OUTSIDE OF
CHARLESTON AND SAVANNAH HARBORS. HOWEVER...IF WINDS BACK MORE TO
THE SOUTH DURING THE DAYTIME PERIOD...FOG COULD IMPACT ONE OR BOTH
OF THESE PORTS.

TUESDAY THROUGH THURSDAY...AN IMPRESSIVE AREA OF HIGH PRESSURE
WILL BUILD ACROSS THE CENTRAL AND EASTERN UNITED STATES EARLY IN
THE WEEK...EVENTUALLY SETTLING OVER THE SOUTHEAST COAST BY
THURSDAY. THE PRESSURE GRADIENT WILL TIGHTEN ON THE PERIPHERY OF
THE BUILDING SURFACE HIGH...AND CONSIDERING SOME COLD ADVECTION IN
THE WAKE OF THE DEPARTING COLD FRONT...MARGINAL SMALL CRAFT ADVISORY
CONDITIONS ARE POSSIBLE FOR PORTIONS OF THE WATERS TUESDAY INTO
EARLY WEDNESDAY. AS THE CENTER OF THE HIGH SHIFTS TOWARD THE
SOUTHEAST STATES THURSDAY...THE PRESSURE GRADIENT WILL WEAKEN
SUFFICIENTLY TO ALLOW WINDS/SEAS TO SUBSIDE.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.

&&

$$

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






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