AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
418 PM EDT THU JUL 7 2011

.SYNOPSIS...
LOW PRESSURE STRETCHING FROM THE EASTERN GULF OF MEXICO NORTHEAST
OFF THE SOUTHEAST US COAST WILL PERSIST THROUGH FRIDAY...WHILE A
COLD FRONT APPROACHES FROM THE NORTHWEST DURING THE WEEKEND. THE
FRONT WILL DISSIPATE OVER THE AREA SUNDAY AND MONDAY...BEFORE
ANOTHER FRONT APPROACHES FROM THE NORTH BY THE MIDDLE OF NEXT
WEEK.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
LATE AFTERNOON CONVECTION TO DIMINISH THIS EVENING. THEN...A LOW
PRESSURE TROUGH WILL EXTEND FROM THE EASTERN GULF OF MEXICO
NORTHEAST OFF THE SOUTHEAST US COAST. A WEAK WAVE OF LOW PRESSURE
COULD DEVELOP OFF THE FLORIDA COAST AND MOVE NORTHEAST OFF THE
GA/SC COASTS. EITHER WAY...IT LOOKS LIKE INCREASING DEEP MOISTURE
WILL EXTEND UP THE COAST AND THERE SHOULD BE ENOUGH CONVERGENCE TO
LEAD TO SHOWERS AND TSTMS OVER THE COASTAL WATERS AND ALONG THE
COAST. LOWS IN THE LOWER TO MID 70S...EXCEPT UPPER 70S CLOSER TO
THE COAST.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
THE FORECAST FOR THE SHORT TERM PERIOD CONTINUES TO LOOK
DIFFICULT...AS MUCH OF THE SENSIBLE WEATHER IMPACTS WILL BE HIGHLY
DEPENDENT ON A LOW SYSTEM OVER THE EASTERN GULF OF MEXICO AND A
COLD FRONT APPROACHING FROM THE NORTHWEST. MOST NUMERICAL MODEL
SOLUTIONS INDICATE THE MAIN SURFACE LOW REMAINING OVER THE
GULF...WHILE A SUBTLE WAVE OF LOW PRESSURE TRACKS NORTHWARD ALONG
THE EAST COAST. PLENTIFUL DEEP MOISTURE WILL SHIFT UP THE COAST
WITHIN SOUTHERLY FLOW BETWEEN THE ATLANTIC RIDGE AND A BROAD UPPER
TROUGH OVER THE GULF. THE NAM AND GFS DISAGREE ON THE AMOUNT OF
DEEP MOISTURE PUSHING ONSHORE BY FRIDAY AFTERNOON...WITH THE NAM
SOLUTION SUGGESTING THE FORECAST AREA COULD BE CAUGHT IN THE DRY
SLOT ALONG THE WESTERN PERIPHERY OF THE SURFACE WAVE. THUS THERE
IS SOME RATHER SIGNIFICANT MODEL DISAGREEMENT REGARDING RAIN
COVERAGE FOR FRIDAY. SREF AND ECMWF RUNS LEAN TOWARD A WETTER
SOLUTION SIMILAR TO THE GFS...AND WILL INDICATE A SOLID CHANCE FOR
SHOWERS/THUNDERSTORMS IN THE 40 TO 50 PERCENT RANGE FRIDAY
AFTERNOON. HESITANT TO INDICATE ANY HIGHER PROBABILITIES UNTIL THE
NAM SOLUTION COMES INTO BETTER AGREEMENT WITH OTHER MODELS.

THE WAVE OF LOW PRESSURE WILL DISSIPATE NORTH OF THE AREA BY
SATURDAY...WITH THE REGION BECOMING LOCATED BETWEEN ATLANTIC HIGH
PRESSURE AND THE FRONTAL TROUGH TO THE WEST/NORTHWEST. ABUNDANT
DEEP MOISTURE AND PWAT VALUES ABOVE 2 INCHES LEND CONFIDENCE
TOWARD 50 PERCENT SHOWER/THUNDERSTORM CHANCES ON SATURDAY.
ALTHOUGH THE FRONT WILL REMAIN NORTH OF THE AREA ON
SATURDAY...THE SURFACE TROUGH WILL LIKELY SAG INTO THE AREA AND
PROVIDE ADDITIONAL SYNOPTIC SUPPORT FOR THUNDERSTORM FORMATION.

THE WEAKENING FRONT WILL DESCEND INTO THE FORECAST AREA ON
SUNDAY...AS SURFACE HIGH PRESSURE ATTEMPTS TO BUILD FROM THE
NORTH. THE BEST MOISTURE AND CONVERGENCE WILL BE ACROSS SOUTHERN
SECTIONS OF THE AREA BY SUNDAY AFTERNOON...AND WILL CONTINUE TO
INDICATE HIGHEST RAIN PROBABILITIES SOUTH OF THE CHARLESTON TRI
COUNTY AREA. MOISTURE PROFILE WILL STILL REMAIN FAVORABLE FOR
SCATTERED SHOWERS/THUNDERSTORMS ACROSS THE ENTIRE FORECAST AREA ON
SUNDAY...AND WILL THEREFORE INDICATE POPS FROM THE 30 PERCENT
RANGE NORTH TO THE 40 PERCENT RANGE SOUTH.

HIGH TEMPERATURES WILL GENERALLY REACH THE LOW TO MID 90S AWAY
FROM THE LOCALLY COOLER COASTLINE EACH AFTERNOON. SATURDAY WILL
LIKELY BE THE COOLEST DAY DUE TO THICKER CLOUD COVER...WHILE
TEMPERATURES ON SUNDAY COULD BE THE WARMEST WITHIN A BUILDING
UPPER RIDGE.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
THE ATMOSPHERE WILL DRY OUT SOME ON MONDAY AND TUESDAY AS UPPER
RIDGING BUILDS BACK IN AND PWATS DROP TO BELOW NORMAL LEVELS.
HOWEVER...DUE TO FEWER CLOUDS...TEMPS WILL BE A COUPLE OF DEGREES
HIGHER AWAY FROM THE COAST...MEANING THAT WE ARE STILL LIKELY TO AT
LEAST REACH THE CONVECTIVE TEMP EACH AFTERNOON. SLIGHT CHANCE OF
CONVECTION SHOULD COVER IT FOR NOW. THE NEXT FRONT STARTS TO
APPROACH FROM THE NORTH FOR WEDNESDAY AND THURSDAY...BUT IT IS VERY
HARD TO TELL THIS FOR OUT IN TIME IF THE FRONT WILL HAVE ENOUGH PUSH
TO MAKE IT INTO THE AREA...OR IF THE MID LEVEL RIDGE WILL HOLD ON
STRONG ENOUGH TO KEEP THE FRONT AT BAY TO OUR NORTH. I HAVE GONE
WITH CLIMO POPS AND TEMPS.

&&

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
KCHS...VFR TODAY WITH CB MENTIONS THIS AFTERNOON AS THE SEA BREEZE
DRIFTS INLAND. AFTER MIDNIGHT TONIGHT...MODELS INDICATE INCREASING
MOISTURE ADVECTION AND POTENTIAL FOR SOME SHOWERS AND TSTMS MOVING
IN OFF THE ATLC ALONG WITH POSSIBLE MVFR/IFR CIGS WITH THE STRONG
CONVERGENCE OF DEEP TROPICAL MOISTURE. WE HAVE SHOWN SOME LATE
NIGHT CB AND SCATTERED LOW CLOUDS AS AN INTRO TO THE IMPENDING
MOIST SURGE.

KSAV...VFR TODAY GIVEN THE ONSHORE SYNOPTIC FLOW KEEPING MOST OF
THE SMOKE FROM FIRES TO THE SW...MAINLY S OF THE TERMINAL. THERE
WILL LIKELY BE CB AROUND THIS AFTERNOON BUT OUR HUNCH IS THAT IT
WILL BE MORE ISOLATED THAN WHAT WAS SEEN ON WED. TONIGHT...LATE
NIGHT VSBY CONCERNS AGAIN AND AN OUTSIDE CHANCE OF SOME PATCHY
MVFR/IFR CIGS LATE. WE WILL CONTINUE WITH VFR UNTIL TRENDS BECOME
MORE EVIDENT.

EXTENDED AVIATION...MAINLY VFR CONDITIONS EXPECTED. VISIBILITIES AND
CEILINGS COULD BECOME BRIEFLY LOWER WITHIN ANY SHOWERS AND
THUNDERSTORMS THROUGH THE PERIOD. DIFFICULT TO KNOW WHETHER THERE
WILL STILL BE SMOKE AROUND...AS IT DEPENDS ON THE STATE OF THE
WILDFIRES AT THAT TIME.

&&

.MARINE...
TONIGHT...WINDS TO INCREASE TONIGHT AS A WEAK WAVE OF LOW PRES
APPROACHES FROM THE S CAUSING AN INCREASE IN THE PRES GRADIENT.
WINDS MAY DIMINISH TOWARD DAYBREAK...ESPECIALLY ACROSS THE GA
WATERS...AS THE LOW/WAVE PUSHES INTO THE SC WATERS. SEAS LOOK TO
BUILD AS WELL...MOSTLY DUE TO INCREASING SE SWELL. WILL KEEP CONDS
BELOW ADVISORY LEVELS FOR NOW BUT IT WILL BE CLOSE FOR THE WATERS
BEYOND 20 NM.

FRIDAY THROUGH TUESDAY...SOUTHERLY WINDS WILL SURGE FRIDAY NIGHT
INTO SATURDAY AS THE PRESSURE GRADIENT TIGHTENS BETWEEN ATLANTIC
HIGH PRESSURE AND A COLD FRONT APPROACHING FROM THE NORTHWEST.
LATEST THINKING IS THAT WIND SPEEDS WILL REMAIN JUST BELOW SMALL
CRAFT ADVISORY CRITERIA DURING THIS TIME...HOWEVER OCCASIONAL
GUSTS ABOVE 20 KT COULD OCCUR FOR PORTION OF THE WATERS. WINDS
WILL WEAKEN AND BECOME A BIT MORE VARIABLE IN DIRECTION AS THE
WEAKENING FRONT SLIPS SOUTHWARD INTO THE WATERS ON SUNDAY. THE
WINDS WILL COME DOWN A BIT ON MONDAY AND TUESDAY WITH WEAK HIGH
PRESSURE BUILDING INTO THE AREA. WINDS AND SEAS SHOULD STAY BELOW
ADVISORY CRITERIA THROUGH THE PERIOD.

RIP CURRENTS...SE SWELLS WILL INCREASE THROUGH MOST OF FRIDAY AND
THIS WILL CONTRIBUTE TO AN ENHANCED RISK FOR RIP CURRENTS THROUGH
THEN.

&&

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

&&

$$