Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 211228
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
728 AM EST SUN DEC 21 2014

.SYNOPSIS...
UNSETTLED WEATHER IS EXPECTED TODAY THROUGH TUESDAY NIGHT AS SEVERAL
DISTURBANCES MOVE OVER THE REGION. A STRONG COLD FRONT WILL THEN APPROACH
FROM THE WEST ON WEDNESDAY...THEN SHIFT THROUGH THE AREA WEDNESDAY
AFTERNOON INTO EARLY WEDNESDAY NIGHT. DRY HIGH PRESSURE WILL THEN SETTLE
OVER THE SOUTHEAST INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
OUR DAMP AND COOL FORECAST IS ON TRACK THROUGH TONIGHT...THE CHANGES
WE MADE THIS MORNING WERE TO MAKE IT A BIT COOLER AND EVEN DAMPER
IN SOME LOCATIONS. ISENTROPIC ASCENT WILL CONTINUE TO STEEPEN AND
EXPAND OVER GEORGIA AND SOUTH CAROLINA TODAY. ANOTHER SHORT WAVE
TROUGH WILL LIFT FROM NORTH GEORGIA THIS MORNING...THROUGH THE
CAROLINAS TODAY WHILE THE AXIS OF THE BAROCLINIC ZONE REMAINS
ENTRENCHED FROM NORTH CENTRAL FLORIDA TO THE GULF STREAM TO OUR
EAST. OUR FORECAST AREA WILL BE IN THE GRIPS OF AN ANCHORED
SURFACE WEDGE PATTERN WHICH WILL REMAIN LOCKED IN UNDER PERIODS OF
LIGHT RAINS AND A NOSE OF WARMING TEMPS AT 925 MB. WE LOWERED
TEMPS TODAY ACROSS THE BOARD GIVEN OVERNIGHT SURFACE ANALYSIS AND
AN EMPHATICALLY COOLER SURFACE TEMP TREND PROGGED BY MANY OF THE
00Z MODELS. SOME AREAS MAY STRUGGLE TO HIT 50 DEGREES TODAY TO THE
NORTH OF I-16...WHILE RAINS HOLD TEMPS DOWN IN THE LOWER TO MID
50S IN AREAS SUCH AS DARIEN AND LUDOWICI GEORGIA.

FORECAST SOUNDINGS AND MODEL PROJECTIONS INDICATE MANY AREAS WILL SEE
MEASURABLE LIGHT RAINS TODAY WITH HIGHEST CONFIDENCE ACROSS THE SE HALF
OF THE FORECAST AREA GIVEN THE PROXIMITY TO LOWER CONDENSATION PRES
DEFICITS AND DEEPER MOISTURE FIELDS. POPS AVERAGE OUT IN THE LIKELY
CATEGORY TODAY...BUT RAINFALL AMOUNTS ON THE LIGHT SIDE ONCE AGAIN.

TONIGHT...RAINFALL COVERAGE WILL EXPAND AS ANOTHER ROUND OF UPPER SHORT
WAVES RIDE NE ALONG THE COOL SIDE OF THE BAROCLINIC ZONE. MODELS INDICATE
A SIGNIFICANT PUNCH OF LOW LEVEL WARM ADVECTION WILL LIFT THROUGH THE
REGION OVERNIGHT AND THIS SHOULD NUDGE THE COASTAL FRONT WELL OFFSHORE
JUST A BIT CLOSER IN...BUT THE WEDGE WILL REMAIN STRONG AND INTACT
ALL AREAS. 1/2 INCH OR LOCALLY HIGHER RAINFALL AMOUNTS ARE POSSIBLE
ALONG COASTAL SE GEORGIA... OTHERWISE AMOUNTS MAINLY 1/4 INCH OR LESS
TONIGHT. WE LOWERED LOW TEMPS A BIT WITH THE COOL AIR TRAPPED BELOW
THE WARM ADVECTION. THERE IS QUITE A BIT OF CONCERN FOR FOG TONIGHT
AS STRATUS COULD BUILD DOWN AND TANK LOCAL VSBYS. THE AREA OF MOST
CONCERN IS INLAND SE GEORGIA AND LATER FORECASTS MAY NEED SOME
STRONGER FOG MENTIONS.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
MONDAY...LIGHT SHOWERS SHOULD BE ONGOING TO START THE MORNING AS AN
AREA OF LOW PRESSURE CONTINUES TO LIFT NORTHEAST ALONG THE COAST. A
SOMEWHAT LULL IN PRECIP ACTIVITY IS POSSIBLE DURING THE AFTERNOON
WHILE GREATEST LIFTING SHIFTS TO THE NORTHEAST TEMPORARILY AND A
WEDGE OF HIGH PRESSURE MAINTAINS HOLD INLAND. HOWEVER...GIVEN THE
AMOUNT OF MOISTURE AVAILABLE DURING THE PERIOD...HAVE MAINTAINED
CHANCES OF RAIN THROUGH MONDAY NIGHT. TEMPS WILL BE DEPENDENT ON THE
STRENGTH OF THE WEDGE...BUT SHOULD PEAK INTO THE LOW/MID 50S INLAND
TO UPPER 50S/LOWER 60S IN SOUTHEAST GEORGIA AND ALONG THE COAST IN
SOUTH CAROLINA.

MONDAY NIGHT INTO TUESDAY NIGHT...HAVE BACKED OFF CONSIDERABLY ON
POPS TO START OFF MONDAY NIGHT...BUT SHOW AND INCREASING TREND
THROUGH TUESDAY WHILE ANOTHER PLUME OF MOISTURE ADVECTS TO THE AREA
AHEAD OF A COLD FRONT POSITIONED WELL THE OUR WEST. HAVE INTRODUCED
CATEGORICAL POPS TUESDAY AFTERNOON AS A WEAK COASTAL FRONT STRUGGLES
TO LIFT NORTH AGAINST THE PERSISTENT WEDGE INLAND. FOR THIS
REASON...DID NOT EXPAND A SLIGHT CHANCE OF THUNDERSTORMS OVER OUR
INTERIOR COUNTIES. HOWEVER...SBCAPES NEAR 800 J/KG ALONG WITH MODEST
MID LVL LAPSE RATES SHOULD RESULT IN SOME ENHANCEMENT OF SHOWERS AND
PERHAPS A FEW THUNDERSTORMS AS SEVERAL H5 SHORTWAVES SHIFT OVER THE
REGION AHEAD OF THE MAIN TROUGH AXIS DIGGING OVER THE CENTRAL UNITED
STATES. TEMPS WILL ONCE AGAIN BE DEPENDENT ON THE POSITION OF THE
COASTAL FRONT LIFTING NORTH. AT THIS TIME HAVE STAYED SLIGHTLY BELOW
GUIDANCE...WITH OVERALL HIGH TEMPS IN THE LOW 60S INLAND TO MID AND
UPPER 60S SOUTH OF INTERSTATE 16 IN SOUTHEAST GEORGIA.

AS DIURNAL HEATING IS LOST TUESDAY NIGHT...THUNDERSTORM CHANCES
SHOULD MAINLY OCCUR OFFSHORE...BUT DEEP MOISTURE CHARACTERIZED BY
PWATS NEAR 1.8 TO 1.9 INCHES SHOULD MAINTAIN WIDESPREAD SHOWERS INTO
WEDNESDAY MORNING WHILE FORCING INCREASES FROM THE WEST. TUESDAY
NIGHT TEMPS WILL BE MILD WITHIN A SOUTH/SOUTHEAST FLOW AHEAD OF THE
APPROACHING COLD FRONT...WITH LOWS ONLY DIPPING INTO THE MID 50S
INLAND TO LOWER 60S ALONG THE COAST.

WEDNESDAY...WIDESPREAD SHOWERS ALONG WITH A FEW EMBEDDED
THUNDERSTORMS ARE ANTICIPATED AHEAD/ALONG A COLD FRONT THAT IS NOW
EXPECTED TO SHIFT THROUGH THE AREA DURING THE AFTERNOON AND EVENING.
THE DAY SHOULD BRING ABOUT AN INCH OF PRECIP ACCUMULATION OVER MOST
AREAS WITH LOCALLY HIGHER AMOUNTS. STRONG LOW LVL WINDS ALSO SUGGEST
THAT WINDS COULD BE GUSTY WITH SOME MIXING. MODELS INSIST ON WARMING
TEMPS INTO THE LOWER 70S AHEAD OF THE FRONT...BUT WIDESPREAD CLOUD
COVER AND SHOWERS/THUNDERSTORMS SHOULD LIMIT OVERALL HEATING
POTENTIAL. HAVE THEREFORE KEPT HIGH TEMPS A FEW DEGREES BELOW
GUIDANCE...IN THE UPPER 60S TO AROUND 70.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
WIDESPREAD SHOWERS ALONG WITH A FEW THUNDERSTORMS WILL BE POSSIBLE
EARLY WEDNESDAY NIGHT BEFORE A COLD FRONT SHIFTS OFFSHORE. STRONG
COLD AIR ADVECTION BEHIND THE FRONT SHOULD RESULT IN SOME GUSTY WIND
CONDITIONS FOR PART OF THE NIGHT BEFORE ENHANCED WIND FIELDS SLIDE
OFFSHORE. CONDITIONS WILL THEN QUICKLY DRY OUT LATE WEDNESDAY NIGHT
INTO EARLY THURSDAY AS HIGH PRESSURE SETTLES OVER THE REGION BEHIND
THE DEPARTING FRONT AND PERSISTS INTO MUCH OF THE WEEKEND. OVERALL
HIGH TEMPS WILL BE COOLER ON THURSDAY...IN THE MID AND UPPER
50S...BEFORE SLIGHTLY WARMING INTO THE LOWER 60S UNDER A SOMEWHAT
ZONAL FLOW ALOFT. OVERNIGHT LOWS SHOULD RANGE IN THE MID/UPPER 30S
THURSDAY NIGHT...BEFORE WARMING INTO THE LOW/MID 40S INTO THE
WEEKEND.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
KCHS...WE MAINTAINED CONTINUITY WITH IFR CIGS UNTIL MIDDAY THEN
CIGS WILL BE CLOSE TO 1 KFT THIS AFTERNOON. STRATUS MAY BRIEFLY
SCATTER OUT AT TIMES THROUGH MID MORNING AND CONFIDENCE ON IFR
VERSUS MVFR THIS AFTERNOON IS LOW. THE PATTERN SUGGESTS IT COULD
REMAIN IFR WITH OCCASIONAL RAIN ANTICIPATED. TONIGHT...THE STRATUS
SHOULD BUILD DOWN OVERNIGHT WITH RAIN AND FOG AT TIMES LIKELY.
LIFR CIGS ARE POSSIBLE OVERNIGHT AND ESPECIALLY LATE AS THE LOW
LEVEL WIND FIELDS DIMINISH.

KSAV...MODELS FAIRLY CONSISTENT ON LOCKING IN IFR CIGS ALL DAY AND
AGAIN TONIGHT. THE SYNOPTIC PATTERN IS CERTAINLY FAVORABLE FOR THIS
TO OCCUR WITH A STRENGTHENING WEDGE INVERSION AND WARM AIR ADVECTION
PATTERN ATOP A COOL AND STABLE AIR MASS. WE FOLLOWED THIS GUIDANCE
AND PREVAILED LIGHT RAINS THIS MORNING. IT COULD RAIN LONGER INTO
THE DAY OR AT LEAST DRIZZLE. TONIGHT...CONDITIONS LOOK TO DETERIORATE
EVEN FURTHER WITH CIGS AT OR BELOW 500 FT WITH OCCASIONAL RAINS AND
A CHANCE FOR SOME FOG IF CIGS SETTLE RIGHT OFF THE SURFACE.

EXTENDED AVIATION OUTLOOK...PERIODS OF MVFR OR LOWER CONDITIONS ARE
LIKELY WITH RAIN/SHOWERS AND LOW STRATUS THROUGH TUESDAY WHILE A
WEDGE OF HIGH PRESSURE PERSISTS INLAND AND WAVES OF LOW PRESSURE
LIFT NORTHEAST ACROSS THE NEARBY ATLANTIC. ADDITIONAL FLIGHT
RESTRICTIONS APPEAR LIKELY TUESDAY NIGHT INTO WEDNESDAY AFTERNOON AS
A STRONG COLD FRONT APPROACHES FROM THE WEST WITH SHOWERS AND
THUNDERSTORMS. LLWS WILL BE A POSSIBILITY TUESDAY NIGHT AS STRONGER
WIND FIELDS SHIFT OVER THE AREA IN ADVANCE OF THE FRONT. WINDY
CONDITIONS SHOULD ALSO OCCUR NEAR THE TIME OF FRONTAL PASSAGE ON
WEDNESDAY. VFR CONDITIONS SHOULD THEN RETURN ON THURSDAY.

&&

.MARINE...
THE NAM AND IT/S LOCAL VARIATION WERE USED TO HANDLE A VERY TRICKY
MARINE FORECAST THIS MORNING AS PINCHING GRADIENT INITIALLY EXTENDING
ALONG THE OUTER FRINGES OF OUR NEAR SHORE SOUTH CAROLINA WATERS
SOUTH INTO THE OUTER GEORGIA WATERS. OVERNIGHT WE RAISED A SMALL
CRAFT ADVISORY FOR GEORGIA WATERS 20-60 NM AS GRAYS REEF HAS BEEN
REPORTING A SOLID 19-20 KT WITH HIGHER GUSTS AND SEAS UP TO 5 FT.

AT SOME POINT TODAY WE MAY NEED TO CONSIDER AN ADVISORY WITHIN 20
NM OF THE COAST BUT IT LOOKS FAIRLY MARGINAL WITH 15-20 KT NE WINDS
AND 4-5 FT COVERING THE SITUATION FOR THE MOST PART. TONIGHT AS
THE COASTAL FRONT TILTS NORTH WHILE A LOW PRES WAVE RIDES THE GULF
STREAM...THE GRADIENT MAY TIGHTEN THIS EVENING ALONG THE CHARLESTON
COAST BUT EVENTUALLY WEAKEN ALL WATERS LATE TONIGHT. MODEL PROGS
SUGGEST IF SMALL CRAFT ADVISORY CONDITIONS HAVE NOT DEVELOPED BY
THIS EVENING....CHANCES ARE DECENT FOR SLIGHTLY DIMINISHED WINDS
AND SEAS AFTER MIDNIGHT. THERE MAY BE SOME LOWER VSBYS AT TIMES
TONIGHT IN RAIN AND FOG OVER THE WATERS.

MONDAY AND TUESDAY...CONDITIONS SHOULD REMAIN BELOW SMALL CRAFT
ADVISORY LEVELS AS A WEDGE OF HIGH PRESSURE PERSISTS INLAND WHILE
LOW PRESSURE SLOWLY LIFTS NORTHEAST ALONG THE COAST. PERIODS OF
RAIN/SHOWERS ARE ANTICIPATED OVER THE WATERS THROUGH TUESDAY WHILE A
COASTAL FRONT REMAINS OVER THE COASTAL WATERS. IN GENERAL...WINDS
SHOULD BE NO HIGHER THAN 15-20 KT WITH SEAS RANGING BETWEEN
1-3 FT...HIGHEST IN OUTER GEORGIA WATER.

TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...CONDITIONS SHOULD BEGIN TO
DETERIORATE AS A COASTAL FRONT LIFTS NORTH WELL AHEAD OF A COLD FRONT
THAT EVENTUALLY SHIFTS OVER THE WATERS WEDNESDAY EVENING/NIGHT. SHOWERS
AND THUNDERSTORMS WILL BE POSSIBLE OVER MOST WATERS AHEAD OF THE
FRONT...WHILE WINDS AND SEAS INCREASE/BUILD WITHIN A SOUTHERLY FLOW.
AT THIS TIME...CONDITIONS SHOULD REACH SMALL CRAFT ADVISORY LEVELS
NEAR DAYBREAK WEDNESDAY AS THE PRESSURE GRADIENT TIGHTENS AHEAD OF
THE APPROACHING FRONT. GALE FORCE WIND GUSTS REMAIN POSSIBLE AS
THE COLD FRONT SHIFTS OFFSHORE WITH STRONG COLD AIR ADVECTION
BEHIND IT WEDNESDAY NIGHT. A GALE WATCH/WARNING COULD EVENTUALLY
BE NEEDED FOR A PORTION OF THE WATERS WEDNESDAY NIGHT AS WINDS
GUST TO 30-35 KT AWAY FROM THE COAST. SEAS WILL ALSO BUILD UPWARDS
TO 5-8 FT WEDNESDAY AFTERNOON INTO EARLY WEDNESDAY NIGHT BEFORE
IMPROVING LATE.

THURSDAY AND FRIDAY...CONDITIONS WILL IMPROVE QUICKLY OVER ALL WATERS
AS HIGH PRESSURE BECOMES CENTERED JUST SOUTH OF THE WATERS. WINDS/SEAS
SHOULD LOWER BELOW SMALL CRAFT ADVISORY LEVELS FOR ALL WATERS AROUND
DAYBREAK THURSDAY...THEN CONTINUE TO IMPROVE THROUGH LATE WEEK.

SEA FOG...MARINERS ARE ADVISED THAT LOW STRATUS DECKS AND PERIODS OF
RAIN OR DRIZZLE COULD EQUATE TO REDUCED VISIBILITIES MONDAY...BUT
THE BEST CHANCE OF SEA FOG COULD DEVELOP AS WARMER AIR ARRIVES ATOP
MID/UPPER 50 SHELF WATER TEMPS EARLY TUESDAY PRIOR TO WINDS
INCREASING ENOUGH TO SCOUR IT OUT LATER TUESDAY AND TUESDAY NIGHT.

&&

.TIDES/COASTAL FLOODING...
THIS MORNING/S HIGH TIDE AROUND 7 AM AT DOWNTOWN CHARLESTON MAY
APPROACH 7 FT MLLW BUT AN ADVISORY IS UNLIKELY AND ANY RAINFALL
AROUND AT THAT TIME WILL BE LIGHT OR JUST SPRINKLES.

GIVEN THE PERIGEAN SPRING TIDES EARLY THIS WEEK...THERE IS AN
INCREASING RISK FOR SHALLOW COASTAL FLOODING MONDAY AND TUESDAY
AROUND THE TIME OF THE MORNING HIGH TIDE. THIS SITUATION MIGHT BE
FURTHER EXACERBATED DUE TO STEADY RAINS PRIOR TO AND DURING THE
HIGH TIDAL CYCLE.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR AMZ374.

&&

$$

NEAR TERM...
SHORT TERM...DPB
LONG TERM...DPB
AVIATION...
MARINE...DPB
TIDES/COASTAL FLOODING...






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