Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 121818
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
218 PM EDT SAT JUL 12 2014

.SYNOPSIS...
A WEAK TROUGH OF LOW PRESSURE OVER THE AREA TODAY WILL DISSIPATE
TONIGHT. ATLANTIC HIGH PRESSURE WILL PREVAIL SUNDAY INTO
MONDAY...THEN A COLD FRONT WILL SLOWLY DROP SOUTHEAST AND STALL
ACROSS THE AREA MID TO LATE NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
EARLY THIS AFTERNOON...POPS HAVE BEEN REORIENTED TO MATCH ONGOING
RADAR TRENDS. SOUTHEAST GEORGIA REMAINS QUIET FOLLOWING ALL THE
MORNING ACTIVITY WHILE SOUTHEAST SOUTH CAROLINA HAS BECOME QUITE
ACTIVE WITH HEAVY RAINFALL PRODUCING THUNDERSTORMS. THE SEVERE
THREAT REMAINS LOW...WITH LOCALLY HEAVY RAIN BEING THE MAIN
CONCERN FOR THE REST OF THE AFTERNOON. PREVIOUS DISCUSSION FOLLOWS
BELOW.

LATE THIS MORNING...AN INTERESTING SETUP THIS MORNING HAS RESULTED
IN A FAIRLY ACTIVE RADAR. SCATTERED TO WIDESPREAD SHOWERS AND
THUNDERSTORMS HAVE BEEN DEVELOPING AND EVOLVING AS THE FORECAST
AREA FINDS ITSELF RIGHT ALONG THE GRADIENT OF DEEP MOISTURE. WATER
VAPOR IMAGERY SHOWS A PROMINENT DRY MID/UPPER LEVEL PUNCH WORKING
SOUTH WITH A DEEP PLUME OF TROPICAL MOISTURE TO THE SOUTH THAT
STRETCHES FROM THE NORTHERN GULF OF MEXICO...UP THE SOUTH
CAROLINA/GEORGIA COAST AND OFF TO THE NORTH ATLANTIC. THIS SHARP
GRADIENT OF MOISTURE SHOWS UP WELL WHEN INVESTIGATING REGIONAL
SOUNDINGS. KJAX CAME IN WITH A 2.19 INCH PWAT...KCHS IS 1.81
INCHES...AND OFF TO THE NORTH KGSO IS JUST BARELY OVER AN INCH.
WATER VAPOR IMAGERY SHOWS THE LEADING EDGE OF THE DRIER AIR
ORIENTED WEST/EAST AND STRETCHING ROUGHLY FROM WALTERBORO TO
MONCKS CORNER AND JAMESTOWN. THE DEGREE OF SOUTHWARD MOVEMENT FROM
THIS DRY FEATURE AND THE IMPACT OF NOCTURNAL AND MORNING
CONVECTION TURNING THE ATMOSPHERE OVER WILL PLAY HEAVILY INTO THE
FORECAST TODAY. I HAVE MADE SOME ADJUSTMENTS TO HOURLY POPS BASED
ON THE HI-RES MODELS RUNS...BUT STILL GENERALLY FAVOR THE
SOUTHEAST GEORGIA COAST FOR THE HIGHEST POPS WHERE THE BETTER
MOISTURE WILL RESIDE. THE OVERALL SEVERE WEATHER THREAT IS LOW
GIVEN THE NEAR ABSENCE OF ANY SHEAR...THANKS TO FLOW IN THE 2-5KM
LAYER THAT IS AROUND 1 KT...AND THE DIMINISHED INSTABILITY DUE TO
PLENTIFUL CLOUDS LINGERING THROUGH THE AFTERNOON. OF MORE CONCERN
WOULD BE THE POTENTIAL FOR LOCALLY HEAVY RAIN THANKS TO THE NEAR
STATIONARY STORM MOTION AND THE TROPICAL-LIKE ATMOSPHERE ACROSS
THE SOUTHERN HALF OF THE FORECAST AREA. TEMPERATURES ARE VERY
TRICKY FOR TODAY WITH LOTS OF CLOUDS AND THE COVERAGE OF SHOWERS
AND STORMS. THE FORECAST STILL FEATURES LOW 90S INLAND AND NEAR 90
CLOSER TO THE COAST...WITH THE COOL SPOT BEING THE SOUTHEAST
GEORGIA COAST.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
MOST SHOWERS/THUNDERSTORMS SHOULD DISSIPATE THIS EVENING.
HOWEVER...IF THE UPPER LOW REMAINS NEARLY STATIONARY AS DEPICTED BY
MOST GUIDANCE...SHOWERS/THUNDERSTORMS WILL CONTINUE TO DEVELOP OVER
COASTAL COUNTIES...ESPECIALLY CENTRAL/SOUTH...AND ADJACENT COASTAL
WATERS THROUGH THE NIGHT. MAINTAINED CHANCE POPS IN THESE AREAS.
MEANWHILE...PATCHY STRATUS/FOG COULD ONCE AGAIN DEVELOP OVERNIGHT
ESPECIALLY WHERE RAIN FALLS INLAND.

A BROAD UPPER RIDGE WILL PREVAIL SUNDAY THOUGH IN THE LOWER LEVELS
THE FLOW WILL BE MOIST SOUTHERLY. MODEL SOUNDINGS SHOW A MODERATE
MID LEVEL CAP DURING THE DAY WHICH SHOULD LIMIT CONVECTIVE COVERAGE.
DEEPER MOISTURE COMBINED WITH WARMER TEMPS IN SOUTHEAST GA WILL
YIELD THE GREATEST SURFACE-BASED CAPES IN THAT AREA...THUS WE SHOW
SLIGHTLY HIGHER POPS ACROSS FAR SOUTHWESTERN ZONES. HIGH TEMPS WILL
BE IN THE LOW TO MID 90S.

ON MONDAY THE STRONG UPPER TROUGH OVER THE GREAT LAKES REGION WILL
SUPPRESS THE SUBTROPICAL RIDGE ACROSS THE DEEP SOUTH. THE RESULT
WILL BE A ZONAL FLOW REGIME...WITH LOW-LEVEL THICKNESS ADVECTION AND
SOME DOWNSLOPE COMPRESSION. THIS WILL PUSH TEMPS WELL INTO THE MID
90S IN MOST AREAS AND PIN THE SEA BREEZE NEAR THE COAST UNTIL LATE
IN THE AFTERNOON. A RATHER PROMINENT SURFACE TROUGH IN THE LEE OF
THE APPALACHIANS SHOULD ALLOW FOR DECENT CONVECTIVE DEVELOPMENT
INLAND. THE PREVAILING WSW FLOW MAY PUSH THIS ACTIVITY INTO OUR AREA
LATE IN THE DAY...WHICH COULD INTERACT WITH ONGOING AIRMASS TSTMS.
WE SHOW SLIGHTLY BETTER POPS ON MONDAY THAN SUNDAY BUT STILL NOTHING
HIGHER THAN 30 PERCENT.

ON TUESDAY THE POWERFUL UPPER TROUGH BEGINS TO CARVE OUT THE EASTERN
UNITED STATES WITH SOME SHORTWAVE ENERGY MOVING INTO THE FORECAST
AREA LATE IN THE DAY. MEANWHILE A COLD FRONT WILL DROP INTO THE SC
MIDLANDS AND PEE DEE REGION DURING THE AFTERNOON...POSSIBLY MAKING
IT INTO OUR WESTERN ZONES BY SUNSET. PWATS WILL EXCEED 2.1 INCHES ON
TUESDAY...PROVIDING AMPLE MOISTURE FOR NUMEROUS SHOWERS AND
THUNDERSTORMS. ALL INDICATIONS ARE THAT TUESDAY WILL BE RATHER WET
GIVEN THE SYNOPTIC FORCING...IMPROVING LAPSE RATES AND LOW-LEVEL
THETA-E ADVECTION. WE ARE SHOWING 50 POPS ALL AREAS ON TUESDAY WITH
INCREASING CLOUDINESS. HEAVY RAINFALL WITH LOCALIZED FLOODING COULD
BE AN ISSUE IF CELLS MERGE AND/OR MOVE OVER THE SAME AREAS.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
MUCH OF THE PERIOD WILL FEATURE ABOVE NORMAL RAIN CHANCES AND NEAR
TO SLIGHTLY BELOW NORMAL TEMPERATURES. AN UNSEASONABLY STRONG AND
DEEP LONGWAVE TROUGH WILL REMAIN ACROSS THE CENTRAL AND EASTERN
UNITED STATES TUESDAY NIGHT THROUGH THURSDAY BEFORE EVENTUALLY
FLATTENING OUT. A COLD FRONT WILL BE STALLED OVER THE AREA THROUGH
THURSDAY MORNING...POSSIBLY MOVING OFF THE COAST THURSDAY AFTERNOON.
THERE REMAIN CONSIDERABLE DIFFERENCES BETWEEN THE GFS AND ECMWF
REGARDING PRECIPITATION POTENTIAL THURSDAY AND BEYOND...THOUGH
TUESDAY NIGHT INTO WEDNESDAY WILL LIKELY FEATURE NUMEROUS SHOWERS
AND TSTMS.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
THE BIGGEST NEAR TERM CONCERN IS WHETHER OR NOT ADDITIONAL SHOWERS
AND THUNDERSTORMS WILL IMPACT THE TERMINALS. KCHS IS LIKELY GOING
TO BE QUIET SINCE THE PREVIOUS THUNDERSTORM MOVED THROUGH. KSAV
HAS A HIGHER PROBABILITY...BUT PERHAPS NOT UNTIL THE MID/LATE
AFTERNOON HOURS. FOR NOW I HAVE NOT INTRODUCED ANYTHING IN THE
AFTERNOON/EVENING TIME PERIOD. OVERNIGHT...CONDITIONS SHOULD
GENERALLY BE QUIET BUT THERE ARE CONCERNS ABOUT FOG/STRATUS
DEVELOPMENT FOLLOWING THE HEAVY RAIN THAT HAS FALLEN AT THE
TERMINALS TODAY. NUMERICAL GUIDANCE ISN/T HINTING AT ANYTHING
YET...BUT I HAVE KEPT SCATTERED MVFR CLOUDS IN THE FORECAST AS
WELL AS A MENTION OF GROUND FOG AT KSAV. MORE SHOWERS AND STORMS
ARE EXPECTED OVER THE COASTAL WATERS LATE TONIGHT...AND MAY BEGIN
MOVING ONSHORE TOWARD THE TERMINALS AROUND SUNRISE AND THEREAFTER.

EXTENDED AVIATION OUTLOOK...MAINLY VFR. BRIEF FLIGHT RESTRICTIONS
POSSIBLE DUE MAINLY TO AFTERNOON SHOWERS/THUNDERSTORMS WITH THE
GREATEST COVERAGE TUESDAY INTO WEDNESDAY.

&&

.MARINE...
LIGHT WINDS...DEEP MOISTURE AND SCATTERED/NUMEROUS
SHOWERS/THUNDERSTORMS WILL MAINTAIN AN ENVIRONMENT FAVORABLE FOR
ISOLATED WATERSPOUTS OVER COASTAL WATERS AT LEAST THROUGH THE
EARLY AFTERNOON.

OUTSIDE THUNDERSTORMS...LIGHT/VARIABLE WINDS THIS MORNING WILL
GIVE WAY TO THE SEA BREEZE CIRCULATION/ONSHORE WINDS LESS THAN 15
KT THIS AFTERNOON/EARLY EVENING. SE WINDS 10 KT OR LESS SHOULD
PREVAIL TONIGHT. SEAS WILL REMAIN AROUND 2 FT.

ATLANTIC HIGH PRESSURE WILL PREVAIL OVER THE WATERS SUNDAY THROUGH
FRIDAY. A COLD FRONT APPROACHING FROM THE NORTHWEST TUESDAY AND
WEDNESDAY WILL TIGHTEN THE PRESSURE GRADIENT...PUSHING WINDS INTO
THE 15-20 KT RANGE AT TIMES. BY THURSDAY THE FRONT WILL BE WEAKENING
OVER INLAND AREAS...ALLOWING WINDS TO DROP BACK TO MORE TYPICAL JULY
VALUES OF 10-15 KTS. THE DAYTIME SEA BREEZE WILL BE PRETTY STRONG
MONDAY THROUGH WEDNESDAY...AND WE CANNOT RULE OUT A SMALL CRAFT
ADVISORY FOR THE CHARLESTON HARBOR TO ADDRESS 25 KT GUSTS.

&&

.TIDES/COASTAL FLOODING...
THE SATURDAY EVENING HIGH TIDE CLOSE TO 9 PM WILL LIKELY EDGE JUST
ABOVE SHALLOW SALT WATER FLOODING LEVELS...ESPECIALLY ALONG THE SC
COAST...DUE TO ASTRONOMICAL FACTORS AND ONSHORE WINDS. A COASTAL
FLOOD ADVISORY COULD BE ISSUED LATER TODAY.

ASTRONOMICAL HIGH TIDES DUE TO THE FULL MOON/PERIGEE AND LIGHT TO
MODERATE ONSHORE WINDS COULD RESULT IN MINOR COASTAL FLOODING NEAR
THE TIMES OF HIGH TIDE DURING THE EVENING HOURS SATURDAY THROUGH
EARLY NEXT WEEK.

&&

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

&&

$$

NEAR TERM...BSH
SHORT TERM...SPR/JRL
LONG TERM...JRL
AVIATION...BSH
MARINE...SPR/JRL
TIDES/COASTAL FLOODING...



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