AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
135 AM EDT FRI JUL 8 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 THIS MORNING/...
SATELLITE AND SHORT TERM MODEL DATA SHOW A SLUG OF DEEP TROPICAL
MOISTURE IS POISED TO MOVE ONSHORE OVERNIGHT AS WEAK LOW PRESSURE
ORGANIZES OVER THE EASTERN GULF OF MEXICO. INCREASING LOW-LEVEL
CONVERGENCE ALONG THE COAST AND THE ADJACENT COASTAL WATERS
COUPLED WITH A MOIST ATMOSPHERE /NOTED PWATS OF 1.88 INCHES OF THE
00Z CHS RAOB/ WILL SUPPORT ISOLATED TO SCATTERED SHOWERS TOWARD
SUNRISE. LOW- LEVEL TRAJECTORY FORECASTS TEND TO FAVOR THE
CHARLESTON COUNTY COAST FOR ANY SHOWERS THAT FORM...BUT WE CAN NOT
RULE OUT SHOWER ACTIVITY AFFECTING ANYWHERE ALONG AND EAST OF THE
I-95 CORRIDOR. WILL FORECAST 20 PERCENT POPS ALONG I-95 WITH POPS
UP TO 30 PERCENT ACROSS MUCH OF CHARLESTON COUNTY LATE.

INCREASING CLOUD COVER AND A MODEST 20 KT 925 MB LOW-LEVEL JET
SUGGESTS FULL DECOUPLING IS UNLIKELY. THIS WILL HELP KEEP
TEMPERATURES UP. FURTHER INCREASED LOWS BY 1-2 DEGREES FOR MANY
LOCATIONS. LOWS WILL RANGE FROM THE MID 70S INLAND WITH UPPER
70S COAST.

SMOKE...FIRE WEATHER OFFICIALS INDICATE SMOKE IS STILL RATHER
THICK NEAR AND DOWNWIND OF THE TERRELL MILL POND WILDFIRE BURNING
SOUTH OF HINESVILLE. WILL SHOW AREAS OF SMOKE ACROSS PARTS OF
LIBERTY AND BRYAN COUNTIES AS WELL AS A SMALL PART OF LONG...
MCINTOSH AND CHATHAM COUNTIES. ATTM IT DOES NOT APPEAR THAT SMOKE
WILL IMPACT THE SAVANNAH METRO AREA.

&&

.SHORT TERM /6 AM THIS 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 /06Z FRIDAY THROUGH TUESDAY/...
THERE ARE SOME PATCHY MVFR CIGS ALONG THE EXTREME SOUTHERN COAST
OF SOUTH CAROLINA JUST PRIOR TO 06Z AND WE SUSPECT AREAS OF MVFR
CIGS MAY IMPACT KCHS LATER TONIGHT INTO MID MORNING AS DEEPER
MOISTURE BUILDS AND PATCHY IFR CIGS CANNOT BE RULED OUT. A BIT
LESSER CHANCE AT KSAV BUT WITH DEBRIS CLOUDS THINNING AND ALREADY
THE OBSERVATION REPORTING FEW 600 FT STRATUS...MVFR/IFR MAY BE
POSSIBLE OVERNIGHT...AT LEAST IN A PATCHY MODE.

TODAY INTO THIS EVENING...WE THINK VFR CONDITIONS WILL PREVAIL
WITH THE BEST CHANCES OF SHOWERS AND TSTMS AT KCHS DURING THE
MORNING HOURS...AND POSSIBLY AROUND KSAV THIS AFTERNOON. OUR
CONFIDENCE IS NOT HIGH ENOUGH TO GO WITH ANYTHING BUT CB
MENTIONS AT THIS TIME. SURFACE WINDS WILL BE A BIT STRONGER
THIS AFTERNOON AND EVENING THAN PREVIOUS DAYS...ESPECIALLY AT
KCHS WHERE PERHAPS A FEW GUSTS NEAR 20 KT AT TIMES LATE DAY.

EXTENDED AVIATION OUTLOOK...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.

&&

$$