Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 211430
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
930 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/...
I MADE THE MORNING UPDATE A LITTLE EARLIER THAN USUAL AS THERE IS
A CLEAR BREAK IN THE RAIN IN THE SOUTHWESTERN AREAS THAT SHOULD
MOVE ITS WAY UP THE COAST THROUGH THE REMINDER OF THE MORNING.
THIS IS DUE TO A COMBINATION OF A PUNCH OF MODESTLY DRIER IN THE
MID LEVELS...WHICH CAN BE SEEN IN THE 11Z POES SOUNDINGS IN
SOUTHEAST GEORGIA AND EXTREME SOUTHERN SC AS WELL AS INFERRED FROM
THE 7.4UM GOES SOUNDER CHANNEL...AND A SMALL AREA OF SUBSIDENCE BETWEEN
THE WAVE DEPARTING OFF THE SC COAST AND THE NEXT WAVE CURRENTLY IN
THE WESTERN GOMEX. THE RESULT IS A LOWERING OF POPS FOR THE NEXT
FEW HOURS BEFORE THINGS BEGIN TO FILL IN AGAIN LATER THIS
AFTERNOON WHEN THE STRONGER DIFFLUENCE AHEAD OF THE NEXT WAVE
BEGINS TO TAKE PLACE.

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 /14Z SUNDAY THROUGH THURSDAY/...
KCHS...WITH THE DRIER AIR STARTING TO MOVE IN FOR A WHILE...I
BACKED OFF ON THE IFR CONDITIONS FOR THE NEXT SEVERAL HOURS...AND
MAY NEED TO BACK OFF ON THE REDEVELOPMENT TIME OF SUCH CONDITIONS
UNTIL LATER IN THE DAY WITH SUBSEQUENT UPDATES. IFR CONDITIONS ARE
STILL EXPECTED TO REDEVELOP LATE TODAY AND REMAIN IN PLACE TONIGHT.

KSAV...CURRENT THINKING IS THAT THE IFR CIGS WILL HAVE A HARD TIME
BREAKING OUT TODAY WITH THE WEDGE SOLIDLY IN PLACE...ALTHOUGH I
COULD NOT RULE OUT A PERIODIC BUT SHORT LIVED IMPROVEMENT OVER THE
NEXT FEW HOURS IF SOME OF THE DRIER AIR TRIES TO SNEAK INTO THE
AREA. IFR CONDITIONS LOOK PRETTY CERTAIN TONIGHT.

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...
CURRENT FORECAST LOOKS GOOD FOR WINDS AND SEAS...SO I MADE NO
CHANGES WITH THE MORNING UPDATE. BUOY 41008 STILL HASNT REACHED
SUSTAINED SCA CRITERIA...BUT I EXPECT IT IS OCCURRING IN Z374
CLOSER TO THE GULF STREAM. THE REMAINDER OF THE COASTAL WATERS
WILL LIKELY STAY JUST BELOW THE NEED FOR HEADLINES...BUT IT WILL
BE BREEZY AND CHOPPY NONETHELESS FOR MARINERS TODAY.

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






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