Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 301527
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1127 AM EDT WED JUL 30 2014

.SYNOPSIS...
A STATIONARY FRONT WILL REMAIN OFFSHORE THIS AFTERNOON THROUGH
THURSDAY. THE FRONT WILL THEN WEAKEN AND MOVE BACK TOWARD THE
COAST AS A SURFACE TROUGH FRIDAY. THIS TROUGH WILL PERSIST OVER
OR CLOSE TO THE REGION THROUGH EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
WEDNESDAY MORNING SOUNDINGS CONTINUE TO DEPICT A MARKED SUBSIDENCE
INVERSION WITHIN THE 800-700 MB LAYER. HOWEVER...MOISTURE/LAPSE
RATES WITHIN THE SUB-INVERSION LAYER HAVE BEEN SUFFICIENT TO
SUPPORT ISOLATED/SCATTERED SHOWERS WHERE SURFACE-850 MB CYCLONIC
FLOW AND MASS/MOISTURE CONVERGENCE HAS BEEN FOCUSED ROUGHLY ALONG/EAST
OF I-95. OF PARTICULAR INTEREST...A FAIRLY WELL-DEFINED TROUGH
AXIS HAD PERSISTED ACROSS SE GA JUST S/W OF THE SAVANNAH RIVER
WEDNESDAY MORNING. CONTINUED LOW-LEVEL CYCLONIC FLOW/CONVERGENCE
AND THE INLAND PROGRESS OF THE SEA BREEZE WILL CONTINUE TO
SUPPORT ISOLATED/SCATTERED SHOWERS...WITH DEVELOPMENT SPREADING
INLAND AS THE AFTERNOON PROGRESSES. PER LATEST TRENDS DEPICTED BY
HIGH RESOLUTION GUIDANCE BUMPED POPS UP MOST AREAS THIS AFTERNOON.

GIVEN THE SUBSIDENCE INVERSION...THE POTENTIAL FOR LIGHTNING WILL
REMAIN LIMITED. HOWEVER...A FEW STRONGER UPDRAFTS WEDNESDAY
MORNING HAD LOFTED 50 DBZ RETURNS WELL ABOVE THE FREEZING LEVEL
OF AROUND 14 KFT AGL...AND ISOLATED CLOUD TO WATER LIGHTNING
STRIKES HAD OCCURRED OVER COASTAL WATERS. THIS SCENARIO WILL
LIKELY PLAY OUT AS DIURNAL CONVECTION SPREADS INLAND...THUS A
MENTION OF THUNDER IS JUSTIFIED.

THE POTENTIAL FOR SEVERE WEATHER REMAINS VERY LOW. HOWEVER...
DOWNDRAFT CAPES EXCEEDING 1000 J/KG SUGGEST THE POTENTIAL FOR
GUSTY WINDS WHERE HEAVIEST RAIN OCCURS. ALSO OF NOTE...UNDER A
SYNOPTIC SCALE MID/UPPER LEVEL TROUGH AN UNSEASONABLY STRONG BAND
OF 0-6 KM SHEAR AS HIGH AS 40-50 KT REMAINED DRAPED OVER THE
REGION. HOWEVER...STRONGEST WINDS SHOULD REMAIN ABOVE MOIST
UPDRAFTS CAPPED BY THE SUBSIDENCE INVERSION...THUS LATEST THINKING
IS THAT DEEP LAYER SHEAR WILL NOT PLAY A SIGNIFICANT ROLE IN
CONVECTION EVOLUTION/MODE THIS AFTERNOON.

FINALLY...MOISTURE SPREADING OUT BENEATH THE ELEVATED INVERSION
COULD TRANSLATE TO MOSTLY CLOUDY SKIES AND COULD LIMIT TEMPERATURE
RECOVERY THIS AFTERNOON. MAINTAINED HIGHS AROUND 90S MOST AREAS AS
EVEN BRIEF BREAKS OF SUNSHINE WILL PUSH TEMPS UP...BUT SOME
LOCATIONS COULD REMAIN IN THE 80S THIS AFTERNOON.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
THURSDAY AND THURSDAY NIGHT...THE DEEP AND BROAD TROUGH WILL REMAIN
ACROSS THE EASTERN CONUS AS THE OFFSHORE STATIONARY FRONT BEGINS TO
DRIFT BACK TOWARDS SHORE THURSDAY NIGHT. THURSDAY WILL BE A DAY
WHERE DEEP MOISTURE BEGINS TO INCREASE ACROSS THE AREA WITH PWATS
STARTING THE DAY AROUND 1.5 INCHES AND INCREASING TO AROUND 1.8
INCHES BY THE OVERNIGHT. LOW LEVEL FLOW WILL BE NORTHEAST TO
EASTERLY THROUGH THE DAY AND MODEL SOUNDINGS SHOW A CAPPED
ATMOSPHERE EVENTUALLY YIELDING WEAK INSTABILITY LATE IN THE DAY. WE
WILL LIKELY SEE A SLIGHT INCREASE IN SHOWER/THUNDERSTORM ACTIVITY
COMPARED TO WEDNESDAY AND SLIGHT CHANCE POPS SEEM REASONABLE. CLOUD
COVER WILL BE ON THE INCREASE AS WELL WHICH WILL KEEP TEMPERATURES
DOWN A BIT. LOOK FOR HIGHS IN THE UPPER 80S TO AROUND 90 WHICH IS A
COUPLE OF DEGREES BELOW NORMAL. OVERNIGHT...THE OFFSHORE STATIONARY
FRONT WILL WEAKEN AND BECOME AN OPEN TROUGH AS IT BEGINS TO MOVE
BACK CLOSER TO SHORE. RAIN CHANCES WILL BE CONFINED TO THE ADJACENT
COASTAL WATERS WHICH WILL BE CLOSER TO THE TROUGH AXIS AND ANY
CONVERGENCE WITHIN IT.

FRIDAY THROUGH SATURDAY...THE END OF THE WEEK AND START OF THE
WEEKEND WILL FEATURE INCREASING DEEP MOISTURE AND INCREASING RAIN
CHANCES ESPECIALLY BY SATURDAY. THE SURFACE TROUGH WILL BE ALIGNED
RIGHT ALONG THE SOUTHEAST COAST...COINCIDENT WITH THE SOUTHWEST FLOW
ALOFT ON THE EAST SIDE OF THE MID/UPPER LEVEL TROUGH AXIS. THERE
WILL EVEN BE A BIT OF INCREASING UPPER DIVERGENCE IN THE ENTRANCE
REGION OF A SUBTLE JET CENTERED WELL TO THE NORTHEAST. POPS FOR THIS
PERIOD HAVE BEEN HELD TO BE NO HIGHER THAN HIGH CHANCE. CONFIDENCE
IS INCREASING THAT LIKELY POPS...OR EVEN HIGHER WILL BE NEEDED AT
SOME POINT BUT THESE ROUNDS OF HIGHER RAIN CHANCES WILL BE TIED TO
SUBTLE EMBEDDED SHORTWAVE ENERGY THAT IS DIFFICULT TO PEG DOWN AT
THIS TIME. BY SATURDAY...PWATS SURGE TO AROUND 2.1 INCHES AND THE
POTENTIAL FOR LOCALLY HEAVY RAINFALL INCREASES. IN FACT...QPF PROGS
FROM WPC ARE QUITE WET FOR THIS PERIOD AND FEATURE THE POTENTIAL FOR
WIDESPREAD AMOUNTS IN EXCESS OF 1 INCH. WIDESPREAD CLOUD COVER AND
ROUND OF PRECIPITATION WILL KEEP HIGHS IN THE UPPER 80S WITH LOWS IN
THE LOW 70S.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
THE UNSETTLED PATTERN WILL CONTINUE FOR THE LATTER HALF OF THE
WEEKEND AND AT LEAST INTO EARLY NEXT WEEK. THE TROUGH WILL REMAIN IN
THE VICINITY OF THE FORECAST AREA WITH A TROUGH ALOFT AND PWATS IN
EXCESS OF 2 INCHES. ALL THESE FACTORS ADD UP TO AN ACTIVE PERIOD
WITH RELATIVELY HIGH RAIN CHANCES. GIVEN THE TIME RANGE POPS HAVE
BEEN KEPT IN THE HIGH CHANCE RANGE...BUT IF THE MODELS CONTINUE
THEIR CURRENT TRENDS IT IS LIKELY THAT HIGHER POPS WILL EVENTUALLY
BE WARRANTED. LOCALLY HEAVY RAINFALL WILL REMAIN A CONCERN THROUGH
EARLY NEXT WEEK WITH ROUNDS OF CONVECTION ANTICIPATED. TEMPERATURES
WILL BE BELOW NORMAL...RUNNING ABOUT 3-5 DEGREES BELOW NORMAL FOR
HIGHS INTO THE MID WEEK TIME PERIOD.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
PROBABILITY FOR SHOWERS IN THE VICINITY OF THE TERMINALS HAS
INCREASED THROUGH THIS AFTERNOON. THUNDER/BRIEF FLIGHT
RESTRICTIONS CANNOT BE RULED OUT...BUT TAF UPDATE INDICATE ONLY
VCSH WITH PREVAILING VFR CONDITIONS. WILL AMEND AS DICTATED BY NEAR
TERM CONVECTIVE TRENDS.

EXTENDED AVIATION...
A SURFACE TROUGH WILL DRIFT INTO THE AREA LATE THIS WEEK AND THROUGH
THE WEEKEND. AN ACTIVE PERIOD IS EXPECTED AND OCCASIONAL FLIGHT
RESTRICTIONS ARE POSSIBLE DURING THIS TIME.

&&

.MARINE...
SURFACE WINDS LESS THAN 15 KT AND SUBTLE BOUNDARIES EMBEDDED
WITHIN THE OVERALL CYCLONIC/ONSHORE FLOW REGION SUGGEST A LOW
CHANCE FOR ISOLATED WATERSPOUTS THROUGH THIS AFTERNOON.

OTHERWISE...A CYCLONIC/WEAK PRES GRADIENT WILL PERSIST THIS AFTERNOON
THROUGH TONIGHT. A WEAK SURFACE LOW DEVELOPING OVER FLORIDA MAY
ALLOW FOR A BIT MORE OF A PRONOUNCED GRADIENT TONIGHT. FLOW MAINLY
ONSHORE THE NEXT 24 HOURS WITH SEAS 1-3 FT THIS AFTERNOON THROUGH
TONIGHT.

THURSDAY THROUGH SUNDAY...THE OFFSHORE STATIONARY FRONT WILL
DISSIPATE INTO A SURFACE TROUGH AND DRIFT BACK TOWARD THE
SOUTHEAST COAST. AS THE TROUGH MOVES INTO THE COASTAL
WATERS...WINDS WILL VARY AT TIMES BUT WILL MAINLY BE EAST TO
SOUTHEASTERLY. THE GRADIENT MAY TIGHTEN UP AT TIMES AND SUPPORT
SOME MODESTLY STRONGER WINDS...BUT OVERALL WINDS WILL BE 15 KT OR
LESS WITH SEAS GENERALLY 2-4 FT. SMALL CRAFT ADVISORIES ARE NOT
ANTICIPATED AT THIS TIME.

&&

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

&&

$$

NEAR TERM...SPR
SHORT TERM...BSH
LONG TERM...BSH
AVIATION...SPR
MARINE...BSH/SPR





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