Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 011139
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
739 AM EDT FRI AUG 1 2014

.SYNOPSIS...
A TROUGH OF LOW PRESSURE WILL LINGER NEAR THE SOUTHEAST COAST THROUGH
THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
PRIOR TO MID MORNING...A VERY COMPLEX MESOSCALE FOR THIS TIME OF YEAR
OVER GEORGIA AND THE CAROLINAS. A LAYER OF DRIER AIR ATOP THE BOUNDARY
LAYER WAS MOVING THROUGH ALONG AND W OF I-95 PRODUCING BUILD-DOWN
STRATUS WHICH IS RESULTING IN FOG IN SE GEORGIA AND INLAND SOUTH
CAROLINA. A WEDGE PATTERN WAS LOCKED INTO NORTH GEORGIA AND UPSTATE
SOUTH CAROLINA WHILE THE COASTAL TROUGH HAD SHIFTED BACK OFFSHORE
SINCE 08Z. MOISTURE CONVERGENCE REMAINED SUBSTANTIAL ALONG COASTAL
ZONES. MOST OF THE CONVECTIVE RAINS OFFSHORE WITH ISOLATED ACTIVITY
DEVELOPING ALONG COASTAL GEORGIA SHORTLY AFTER DAYBREAK.

EXCESSIVE RAINS FELL ACROSS A CHUNK OF THE CHARLESTON AREA YESTERDAY
WITH FLOODING OCCURRING AROUND LOW TIDE WHICH WAS A FORTUNATE
OUTCOME FOR THE TIDE CYCLE. THE STALLED COASTAL TROUGH ALONG WITH
RICH LOW LEVEL MOISTURE FIELDS AND A SERIES OF SHORT WAVES THROUGH
GEORGIA AND THE CAROLINAS SHOULD CONTINUE TO PROVIDE A RISK OF
PERIODIC CONVECTIVE RAINS ACROSS THE FORECAST AREA THROUGH
TONIGHT. THIS MORNING...HIGH RESOLUTION MODELS SUGGEST THE COASTAL
CONVERGENCE WILL EVENTUALLY RESULT IN REPEATING CONVECTION ALONG
THE SOUTH CAROLINA COAST WHICH SHOULD PEAK BETWEEN MID MORNING AND
MID AFTERNOON BEFORE CONVERGENCE SHIFTS A BIT FURTHER INLAND. A
FLOOD WATCH ISSUED LAST EVENING WAS TRIMMED TO DROP COLLETON
COUNTY BUT RETAINED UNTIL 15Z GIVEN THE LATEST MODEL TRENDS AND
APPROACHING LATE MORNING HIGH TIDE. MORNING RADAR TRENDS AND 12Z
SOUNDING ANALYSIS WILL DICTATE WHETHER IT WILL NEED AN EXTENSION
INTO THE AFTERNOON HOURS.

AFTER LOW CLOUDS AND FOG DISSIPATE OVER SE GEORGIA...INSTABILITY
WILL INCREASE AND SCATTERED SHOWERS AND TSTMS SHOULD BREAK OUT
THIS AFTERNOON. NOT EVERY AREA INLAND FROM I-95 WILL SEE RAIN
TODAY...BUT THERE COULD BE SOME MULTI-CELL CLUSTERS PRODUCING
LOCALLY HEAVY RAIN. CLOUDS WILL TEMPER HIGH TEMPS AGAIN TODAY WITH
UPPER 80S MANY PLACES. A FEW 90S POSSIBLE INLAND GEORGIA.

TONIGHT...THE RISK FOR HEAVY RAINS MAY REDEVELOP ALONG COASTAL SOUTH
CAROLINA AS MOISTURE CONVERGENCE STRENGTHENS AND MOISTURE PROFILES
DEEPEN. SCATTERED TO PERHAPS NUMEROUS SHOWERS AND ISOLATED TSTMS
EXPECTED TO DEVELOP AFTER MIDNIGHT WITH MODELS IN GOOD CONSENSUS
THAT WE WILL NEED TO WATCH FOR ADDITIONAL LOCALIZED FLOODING.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
A VERY UNSETTLED AND WET PATTERN WILL DOMINATE THE SOUTHEAST U.S.
COAST THROUGH MONDAY WITH DEEP/TROPICAL MOISTURE FEATURING PWATS
IN EXCESS OF 2 INCHES ADVECTING NORTHEAST OUT OF THE GULF OF
MEXICO AND INTERACTING WITH A DECAYING COASTAL FRONT. A BROAD
LONG-WAVE TROUGH EXTENDING FROM A LARGE CYCLONE OVER CANADA
COUPLED WITH VARIOUS WAVES OF UPPER DIVERGENCE ASSOCIATED WITH THE
RIGHT ENTRANCE AGEOSTROPHIC CIRCULATION OF THE UPPER JET WILL
PROVIDE FAVORABLE PERIODS OF UPPER FORCING...WHILE AT THE SURFACE
LOW-LEVEL CONVERGENCE ALONG THE COASTAL FRONT AND EVENTUAL MESOSCALE
BOUNDARY INTERACTIONS WILL SUPPORT WELL ABOVE NORMAL RAIN CHANCES
THROUGH THE PERIOD. LIKELY POPS OF 60-70 PERCENT WILL BE SHOWN
EACH DAY WITH ACTIVITY TAPERING OFF DURING THE OVERNIGHT HOURS.
HOWEVER...A SOUTHERLY FLOW REGIME ATOP THE BOUNDARY LAYER WILL
SUPPORT NOCTURNAL SHOWER/TSTM ACTIVITY JUST ABOUT EACH NIGHT WITH
THE BEST RAIN CHANCES OCCURRING OVER THE COASTAL COUNTIES. THERE
WILL BE A CONTINUED RISK FOR LOCALLY HEAVY RAINFALL AND THE
POTENTIAL FOR FLOODING WITH THE 925-700 HPA FLOW REMAINING FAIRLY
LIGHT. HIGHS EACH DAY WILL WILL GENERALLY MAX OUT IN THE UPPER 80S
WITH OVERNIGHT LOWS IN THE LOWER-MID 70S.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
DRIER...MORE SEASONABLE WEATHER WILL RETURN BY MID WEEK AS THE FRONT
MEANDERS OFFSHORE AND DISSIPATES. ATLANTIC HIGH PRESSURE WILL
GRADUALLY REESTABLISH ITSELF ACROSS THE REGION WITH MORE A MORE
TYPICAL CONVECTIVE PATTERN EXPECTED. HIGHS WILL BE IN THE UPPER 80S
TO LOWER 90S WITH LOWS IN THE LOWER-MID 70S. TROPICAL STORM BERTHA
IS FORECAST TO REMAIN OFFSHORE AS IT CURVES WELL OFF THE SOUTHEAST
U.S. COAST.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
KCHS...MORNING SUNSHINE SHOULD ENHANCE CONVECTIVE COVERAGE ONCE THE
LAND MASS WARMS AFTER MID MORNING. HIGH RESOLUTION MODELS CONTINUE
TO SHOW SHOWERS AND STORMS LINING UP ALONG CHARLESTON COUNTY FROM
LATE MORNING THOUGH MID AFTERNOON. WE HAVE PERIODIC TSTMS 15Z-19Z.
CHANCE FOR HEAVY DOWNPOURS AND MVFR OR LOWER CONDITIONS UNDER
MULTICELL CLUSTERS. IF SHOWERS AND TSTMS MANAGE TO EVADE THE TERMINAL
TODAY...STILL A GOOD CHANCE FOR LATE NIGHT DEVELOPMENT TONIGHT AS
MOISTURE DEEPENS WITH AN UPPER DISTURBANCE NEARBY.

KSAV...A BUILD DOWN STRATUS/FOG EVENT OVERNIGHT WITH LIFR CONDITIONS
AT 1130Z. LAMP GUIDANCE INDICATES CONDITIONS IMPROVING BETWEEN 13Z
AND 15Z...WE SPLIT THE DIFFERENCE AND FORECAST VFR CONDITIONS BY 14Z.
SCATTERED SHOWERS AND TSTMS A GOOD BET FOR THE AFTERNOON HOURS AS
THE COASTAL FRONT INTERACTS WITH A DEVELOPING SEA BREEZE. TIMING
AND COVERAGE A BIT QUESTIONABLE AT THIS POINT BUT WE SHOW VCTS FOR
THE AFTERNOON HOURS AT THIS POINT. A REPEAT LOW CLOUD AND FOG SETUP
IS POSSIBLE LATE TONIGHT BUT MODELS NOT IN AGREEMENT AND THE AIR
MASS APPEARS TO BE MORE UNSTABLE...FAVORING LATE NIGHT SHOWERS
INSTEAD OF FOGGY CONDITIONS.

EXTENDED AVIATION OUTLOOK...PERIODS OF IFR/MVFR LIKELY THROUGH
TUESDAY AS NUMEROUS SHOWERS/TSTMS IMPACT THE REGION.

&&

.MARINE...
ONSHORE FLOW MORE SOUTHEASTERLY ON THE ATLC SIDE OF A SURFACE TROUGH
ALONG THE COAST THROUGH TONIGHT. SPEEDS MAINLY BELOW 15 KT WITH
SEAS 2 TO 4 FT ON AVERAGE...HIGHEST BEYOND 20 NM OFF THE COAST.
SHOWERS AND TSTMS WILL BE PERIODIC AND MAINLY NOCTURNAL...LOWERING
VSBYS AT TIMES.

SATURDAY THROUGH WEDNESDAY...PINNING DOWN WIND DIRECTION WILL BE
TRICKY OVER THE WEEKEND AS A STATIONARY FRONT MEANDERS VERY NEAR THE
COAST. SPEEDS LOOK TO REMAIN LIGHT HOWEVER AND SHOULD NOT POSE A
CHALLENGE TO MARINERS. WINDS WILL RETURN TO A MORE CLIMATOLOGICALLY
FAVORED SOUTHERLY REGIME BY MID WEEK AS ATLANTIC HIGH PRESSURE TAKES
HOLD. SWELLS GENERATED BY TROPICAL STORM BERTHA COULD IMPACT THE
WATERS MONDAY INTO WEDNESDAY AS IT CURVES WELL OFFSHORE OF THE
SOUTHEAST U.S. COAST. THERE IS A POSSIBILITY THAT COMBINED SEAS
COULD REACH SMALL CRAFT ADVISORY THRESHOLDS DURING THIS PERIOD...BUT
ITS A BIT TOO FAR TO REALLY PIN THAT DOWN THIS FAR OUT. SEAS WILL BE
CAPPED AT 4-5 FT FOR NOW.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...FLASH FLOOD WATCH UNTIL 11 AM EDT THIS MORNING FOR SCZ044-045-
     050-052.
MARINE...NONE.

&&

$$

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





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