Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 170531
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
131 AM EDT WED SEP 17 2014

.SYNOPSIS...
A TROUGH WILL MOVE THROUGH THE AREA THIS MORNING....FOLLOWED BY A
STRONG COLD FRONT APPROACHING FROM THE NORTHWEST LATE TONIGHT AND
PUSHING THROUGH THE REGION LATE WEDNESDAY. AN INLAND WEDGE OF HIGH
PRESSURE WILL THEN PREVAIL IN THE WAKE OF THE FRONT INTO THE
WEEKEND. ANOTHER COLD FRONT WILL APPROACH FROM THE WEST EARLY NEXT
WEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
UPSTREAM CONVECTION HAS WEAKENED OVER THE CSRA BUT REMAINING
ROBUST AND PERSISTENT ACROSS NORTHERN PARTS OF SOUTH CAROLINA.
MODELS CONTINUE TO KEEP THE BULK OF THIS CONVECTION NORTH AND
TREND TOWARD WEAKENING OVERNIGHT. AXIS OF DEEPEST MOISTURE WAS
SLIDING SE OVERNIGHT AND WHILE ADDITIONAL COASTAL RAINS ARE
POSSIBLE...THEY WILL TEND TO REMAIN OFFSHORE FOR THE MOST PART
AS A WEAK WAVE OF LOW PRES DEVELOPS ALONG THE GULF STREAM.

GIVEN SATURATED GROUNDS FROM SUBSTANTIAL RAINFALL EARLIER IN THE
DAY AND LIGHT/NEARLY CALM SURFACE WINDS...FOG/STRATUS WILL BE AN
ISSUE ONCE AGAIN LATE TONIGHT. THUS HAVE MAINTAINED AREAS OF FOG
MENTION IN THE GRIDS.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH FRIDAY/...
WEDNESDAY...A MID LVL TROUGH OF LOW PRESSURE WILL BEGIN SLIDING
OFF THE EASTERN SEABOARD BY DAYBREAK...SPAWNING AN AREA OF LOW
PRESSURE ALONG AN EAST-WEST EXTENDING SFC COLD FRONT THAT
GRADUALLY SHIFTS THROUGH THE ENTIRE AREA BY WEDNESDAY EVENING. THE
FRONT WILL LIKELY SLOW IN PROGRESSION WHILE ENCOUNTERING AN
AFTERNOON SEABREEZE IN SOUTHEAST GEORGIA...BEFORE SHIFTING FURTHER
SOUTH AND/OR OFFSHORE THROUGH WEDNESDAY EVENING. AMPLE MOISTURE
ALONG AND AHEAD OF THE FRONT SHOULD SUPPORT SCATTERED SHOWERS AND
THUNDERSTORMS THROUGH WEDNESDAY AFTERNOON...WITH BEST CHANCES
OCCURRING WHERE THE FRONT AND SEABREEZE COLLIDE. A FEW SHOWERS
AND/OR ISOLATED THUNDERSTORM WILL REMAIN POSSIBLE INTO LATE
EVENING AND EARLY OVERNIGHT HOURS AS SOME MOISTURE CONTINUES TO
LINGER BEHIND THE FRONT. ACTIVITY SHOULD THEN DIMINISH THEREAFTER
AS DRYER AIR ASSOCIATED WITH HIGH PRESSURE BUILDS FROM THE
NORTH/NORTHWEST.

LATEST 1000-850 THICKNESS VALUES SUPPORT ALONG WITH A DOWNSLOPING
WIND COMPONENT OFF THE SFC SUPPORT OVERALL HIGH TEMPS IN THE
MID/UPPER 80S WEDNESDAY AFTERNOON. OVERNIGHT LOW TEMPS SHOULD BE
SLIGHTLY COOLER THAN PREVIOUS DAYS AS HIGH PRESSURE BUILDS FROM THE
NORTH LATE...IN THE MID 60S AWAY FROM THE COAST.

THURSDAY AND FRIDAY...HIGH PRESSURE WILL BUILD FROM THE NORTH AND
NORTHWEST THROUGH EARLY THIS WEEKEND...RESULTING IN DRYER CONDITIONS
ON THURSDAY AS THE FLOW REMAINS MAINLY OFFSHORE. WE COULD SEE AN
ISOLATED SHOWER AND/OR THUNDERSTORMS DEVELOP ALONG THE COAST LATE AS
SFC FLOW BECOMES MORE NORTH/NORTHEAST IN RESPONSE TO THE CENTER OF
HIGH PRESSURE SHIFTING OVER THE NORTHEASTERN UNITED STATES.
HOWEVER...ACTIVITY WILL LIKELY REMAIN CONFINED TO COASTAL LOCATIONS.
BY FRIDAY...A STRONGER NORTHEAST FLOW WILL SET UP ALONG THE
SOUTHEAST COAST AS HIGH PRESSURE BECOMES CENTERED OFF THE NORTHEAST
COAST. THIS SHOULD SUPPORT SLIGHTLY HIGHER CHANCES OF PRECIP AS
MOISTURE BEGINS TO RETURN OFF THE ATLANTIC. EXPECT MOST ACTIVITY TO
REMAIN ALONG THE COAST INITIALLY BEFORE GRADUALLY SHIFTING INLAND
WITH AN AFTERNOON SEABREEZE. HAVE MAINTAINED LOW-END CHANCE POPS
FRIDAY ALONG THE COAST AND SLIGHT CHANCE POPS FURTHER INLAND WITH
THE AFTERNOON SEABREEZE.

OVERALL HIGH TEMPS WILL BE COOLER AS HIGH PRESSURE EXTENDS OVER THE
AREA FROM THE NORTH. EXPECT AFTERNOON HIGHS IN THE LOW/MID 80S ON
THURSDAY AND LOW 80S ON FRIDAY. THURSDAY NIGHT TEMPS WILL ALSO REFLECT
COOLER CONDITIONS...WITH LOWS IN THE LOW/MID 60S AWAY FROM THE
COAST.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
A WEDGE OF SURFACE HIGH PRESSURE INLAND AND A COASTAL TROUGH WILL
CONTROL THE PATTERN THROUGH SATURDAY...BEFORE BREAKING DOWN SUNDAY
AHEAD OF ANOTHER STRONG COLD FRONT APPROACHING EARLY NEXT WEEK.
EXPECT BEST RAIN CHANCES TO BE FOUND ALONG THE COAST AND OVER THE
MARINE ZONES THROUGH THE WEEKEND...AS THESE LOCATIONS WILL BE
CLOSEST TO MOISTURE AND CONVERGENCE ASSOCIATED WITH THE COASTAL
TROUGH. HIGH TEMPERATURES WILL ONCE AGAIN BE SUPPRESSED IN THE
LOWER 80S FOR SATURDAY AFTERNOON...BEFORE CONDITIONS BEGIN TO
MODERATE SUNDAY AS THE INLAND WEDGE PATTERN WEAKENS. MEDIUM RANGE
MODELS ARE SUGGESTING THAT THE NEXT COLD FRONT COULD MOVE THROUGH
THE REGION BY TUESDAY...YET ARE NOT INDICATING A SUBSTANTIAL
AMOUNT OF PRECIPITATION ASSOCIATED WITH ITS PROGRESSION. WILL THUS
REMAIN RATHER CONSERVATIVE WITH RAIN CHANCES TOWARD THE END OF THE
FORECAST PERIOD...CAPPING POPS IN THE SLIGHT CHANCE TO LOW CHANCE
RANGE FOR MONDAY AND TUESDAY.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
LOW STRATUS WAS DEVELOPING PRIOR TO 06Z W AND N OF KCHS AND WE
EXPECTED IFR CONDITIONS TO SET IN LATER TONIGHT AS THESE LOW
CLOUDS EXPAND. THERE COULD ALSO BE FOG WITH VSBYS BELOW 1 NM
BUT AT THIS TIME CONFIDENCE IS BETTER ON LOW CIGS. AT KSAV,,,WE
TRENDED A BIT MORE OPTIMISTIC LATER TONIGHT WITH MVFR VSBYS AND
SCATTERED LOW CLOUDS IN THE FIRST COUPLE HUNDRED FEET. IF COULD
BECOME IFR OR LOWER BUT FORECAST SOUNDINGS ARE FAR FROM CONCLUSIVE.

LOW CIGS AND ANY FOG AROUND AT DAYBREAK SHOULD GIVEN WAY TO VFR
CONDITIONS BY LATE MORNING INTO THE AFTERNOON HOURS. THERE ARE
ADDITIONAL CHANCES FOR SCATTERED SHOWERS AND TSTMS AGAIN THIS
AFTERNOON...WE HAVE VCSH AFTER MIDDAY TO TREND.

EXTENDED AVIATION OUTLOOK...OUTSIDE OF SHRA AND/OR TSRA...FLIGHT
RESTRICTIONS WILL BE POSSIBLE EACH MORNING WITH FOG AND/OR LOW
STRATUS SHIFTING ONSHORE.

&&

.MARINE...
OVERNIGHT...WE HAVE SEEN A LITTLE SWELL ENERGY FROM DISTANT MAJOR
HURRICANE EDOUARD TRICKLING INTO OUR COASTAL WATERS...AND
ADDITIONAL SWELL ENERGY IS TO ARRIVE AS TIME PROGRESSES. THE BULK
OF THE WAVE SPECTRUM WILL BE COMPRISED OF THESE CONDITIONS...WHICH
AVERAGES 2 FT ORE LESS ...BUILDING ANOTHER FOOT OR TWO LATE.
MEANWHILE...WITH A WEAK PRESSURE PATTERN OUR WIND FIELDS WILL BE
DRIVEN BY A WEAK SURFACE TROUGH DROPPING THROUGH FROM THE
NORTH/NW... AND THE LAND BREEZE CIRCULATION. THIS ALLOWS WINDS TO
VEER TO THE WEST BY MIDNIGHT...THEN AROUND TO THE NW OR NORTH
LATE. OUTSIDE OF THE CONVECTION WINDS WILL OBTAIN NO MORE THAN
ABOUT 10 KT. THERE IS ALSO A MODERATE TO HIGH PROBABILITY OF FOG
IMPACTING THE CHARLESTON HARBOR LATE IN THE OVERNIGHT PERIOD. BE
SAFE ON THE COASTAL WATERS.

WEDNESDAY THROUGH SUNDAY...LIGHT WINDS WILL INCREASE AND BECOME
NORTH/NORTHEAST BEHIND A COLD FRONT THAT SHIFTS OVER THE WATERS
WEDNESDAY THROUGH THURSDAY. SEAS WILL BE COMPRISED MAINLY OF LONG
PERIOD SWELLS FROM DISTANT TROPICAL CYCLONE EDOUARD...AROUND 2 TO
4 FT WITHIN 20 NM AND 3 TO 5 FT FARTHER OFFSHORE. A STRONGER
NORTHEAST FLOW WILL THEN DEVELOP OVER THE WATERS ON FRIDAY AND
PERSIST INTO SATURDAY AS THE PRESSURE GRADIENT BECOMES ENHANCED
ALONG THE SOUTHERN EDGE OF HIGH PRESSURE CENTERED ALONG THE
NORTHEAST COAST. HOWEVER...WINDS/SEAS ARE EXPECTED TO REMAIN JUST
BELOW SMALL CRAFT ADVISORY CRITERIA AT THIS TIME. CONDITIONS
SHOULD MODERATE OVER THE WATERS WITHIN A TRANSITIONING PATTERN BY
SUNDAY.

RIP CURRENTS...LONG PERIOD SWELL FROM HURRICANE EDOUARD WILL OCCUR
ALONG THE BEACHES WEDNESDAY INTO THURSDAY. DESPITE ONLY LIGHT
ONSHORE WINDS...2-3 FT SWELLS WITH PERIODS NEAR 14 SECONDS SUPPORT
AN ENHANCED PERIOD OF RIP CURRENTS ALONG THE SOUTH CAROLINA AND
GEORGIA BEACHES. A MODERATE RISK OF RIP CURRENTS IS THEREFORE
EXPECTED ALONG ALL BEACHES ON WEDNESDAY...AND POSSIBLY THURSDAY.

&&

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

&&

$$

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





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