425 
FXUS62 KCHS 021929
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
329 PM EDT SUN JUN 2 2013

.SYNOPSIS...
ATLANTIC HIGH PRESSURE WILL BEGIN TO RETREAT TONIGHT...AHEAD OF A
COLD FRONT SLOWLY ADVANCING INTO THE AREA MONDAY AND TUESDAY. HIGH
PRESSURE WILL THEN BUILD FROM THE NORTH BY MID WEEK. A STATIONARY
FRONT AND LOW PRESSURE COULD IMPACT THE SOUTHEAST COAST LATE WEEK
INTO NEXT WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
CONVECTIVE TRENDS THIS AFTERNOON ARE EVIDENCE OF BOTH INCREASED
LOW LEVEL MOISTURE LEVELS THAN PREVIOUS DAYS...AS WELL AS RESIDUAL
SUBSIDENCE FROM LINGERING DEEP LAYER RIDGING. SCATTERED CONVECTION
HAS INITIATED ALONG AND INLAND OF THE SEABREEZE...WITH ADDITIONAL
SHOWER ACTIVITY ADVECTING LOCALLY ONTO THE SOUTH CAROLINA
COASTLINE FROM ENHANCED CONVERGENCE OVER THE WATERS. ONLY A FEW
SHOWERS HAVE INTENSIFIED INTO THUNDERSTORMS...LIKELY A RESULT OF
RATHER UNIMPRESSIVE INSTABILITY AND LIMITED MID LEVEL LAPSE RATES.
LINGERING DRY MID LEVEL AIR HAS SUPPORTED DOWNDRAFT CAPE VALUES
ABOVE 1000 J/KG...SUGGESTING THAT AN ISOLATED STORM COULD PRODUCE
STRONG WIND GUSTS...ESPECIALLY WHERE BOUNDARY INTERACTIONS OCCUR.
HOWEVER...THE OVERALL SEVERE WEATHER THREAT REMAINS LOW.

AS THE SEABREEZE SLOWLY PROGRESSES INLAND LATE THIS AFTERNOON INTO
EARLY EVENING...EXPECT SHOWER/THUNDERSTORM COVERAGE TO ALSO SHIFT
WEST AND DIMINISH IN COVERAGE TOWARD SUNSET. CONSIDERING THE
STEADY BREAKDOWN OF DEEP RIDGING...ALONG WITH THE APPROACH OF AN
UPPER SHORTWAVE AND WEAK FRONT FROM THE WEST...UPSTREAM CONVECTIVE
ACTIVITY COULD PERSIST THROUGH THE NIGHT. THERE IS LESS CERTAINTY
AS TO THE EVOLUTION OF PRECIPITATION OVER THE MARINE ZONES THAT
HAS BEEN STREAMING ONSHORE. AT THIS POINT...HAVE DECREASED RAIN
CHANCES BELOW 15 PERCENT FOR COASTAL COUNTIES AND THE NEARSHORE
WATERS AROUND SUNSET. SUBSEQUENT FORECAST ISSUANCES MAY NEED TO
ACCOUNT FOR LATE AFTERNOON TRENDS AND REASSESS THE NEED TO
REINTRODUCE SLIGHT CHANCE POPS FOR THE NORTHERN COASTLINE IF
SHOWERS PERSIST.

DIURNAL CUMULUS AND CLOUD COVER ASSOCIATED WITH AFTERNOON
CONVECTION WILL ALSO DISSIPATE BY THE EVENING HOURS...YET WILL
LIKELY BE REPLACED BY A COMBINATION OF STRATOCUMULUS AND CIRRUS
AFTER MIDNIGHT. LOW TEMPERATURES WILL BE QUITE MILD TONIGHT UNDER
THE INSULATING EFFECTS OF THICKENING SKY COVER LATE...RANGING FROM
ABOUT 69 TO 73 DEGREES.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
MONDAY AND MONDAY NIGHT...NO SIGNIFICANT CHANGES FROM ONGOING 
FORECAST REASONING OF THE PAST FEW DAYS. A BROAD MID/UPPER LEVEL 
TROUGH AND ASSOCIATED SHORTWAVE ENERGY WILL SHIFT EAST OVER THE 
REGION AND WILL PUSH A DIFFUSE SURFACE COLD FRONT INTO THE REGION 
AND EVENTUALLY OFFSHORE BY EARLY TUESDAY. MEANWHILE...A PLUME OF 
DEEP MOISTURE WITH PWATS APPROACHING 2 INCHES...ABOUT 2 STANDARD 
DEVIATIONS ABOVE NORMAL FOR EARLY JUNE....WILL ADVANCE INTO THE 
FORECAST AREA. THE COMBINATION OF UPPER SUPPORT FROM THE 
TROUGH...CONVERGENCE ALONG THE FRONT...AND DEEP MOISTURE WILL RESULT 
IN NUMEROUS TO WIDESPREAD SHOWERS AND THUNDERSTORMS BEGINNING MONDAY 
MORNING. GIVEN DECENT PRECIPITATION COVERAGE WITHIN A DRIER AIR MASS 
SUNDAY AFTERNOON...MAINTAINED HIGH LIKELY TO CATEGORICAL POPS 
BEGINNING MONDAY MORNING...AND MOST/ALL LOCATIONS WILL RECEIVE 
MEASURABLE RAINFALL. DUE TO DEEPER MOISTURE/EXTENSIVE CLOUD COVER
AND PRECIPITATION COVERAGE...SURFACE BASED INSTABILITY AND THE 
ASSOCIATED POTENTIAL FOR SEVERE WEATHER WILL REMAIN QUITE 
LIMITED...WITH ONLY A LOW PROBABILITY FOR BRIEF/PULSE MODE DAMAGING 
WINDS WHERE MESOSCALE BOUNDARY INTERACTIONS OCCUR. OF MORE CONCERN 
DUE TO THE SIGNIFICANT AMBIENT MOISTURE IS THE POTENTIAL FOR LOCALLY 
EXCESSIVE RAINFALL. THE EXPECTATION IS FOR CONVECTIVE COVERAGE TO 
DIMINISH AND BECOME MORE CONFINED TO THE EASTERN HALF OF THE AREA 
OVERNIGHT...INCLUDING THE ADJACENT COASTAL WATERS WHERE THE BETTER 
INSTABILITY WILL RESIDE. OVERALL HIGHS WILL RUN A FEW DEGREES BELOW 
NORMAL BUT WILL BE LARGELY DEPENDENT ON WHERE AND WHEN PRECIPITATION 
STARTS TO DEVELOP IN THE MORNING. LOWS WILL BE QUITE MILD AND A 
COUPLE OF DEGREES ABOVE CLIMO.

TUESDAY THROUGH WEDNESDAY...THE UPPER PATTERN WILL FLATTEN OUT AND 
BECOME INCREASINGLY DIFFUSE AS THE TROUGH WEAKENS AND MOVES 
OFFSHORE. BEHIND THE SURFACE FRONT...A WEAK PRESSURE PATTERN WILL 
REIGN ON TUESDAY BEFORE HIGH PRESSURE BUILDS FROM THE NORTH  
WEDNESDAY. WILL MAINTAIN SLIGHT CHANCE/CHANCE POPS THROUGH THE 
PERIOD AS STRONG DRYING IS NOT INDICATED BY 02/12 GUIDANCE. 
MAX PRECIP CHANCES WILL BE LARGELY DRIVEN BY DIURNAL HEATING AND 
DESTABILIZATION LEADING TO ISOLATED/SCATTERED SHOWERS/THUNDERSTORMS. 
THE DEVELOPING ONSHORE FLOW ASSOCIATED WITH THE HIGH TO THE NORTH 
WILL LIKELY RESULT IN CONVECTION STARTING IN THE LATE MORNING TIME 
PERIOD WITH SOME RESIDUAL AT LEAST ISOLATED ACTIVITY CONTINUING 
THROUGH THE OVERNIGHT. TEMPS ARE CURRENTLY PROGGED TO BE AT OR A 
COUPLE OF DEGREES BELOW NORMAL.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
GENERAL AGREEMENT ON THE PATTERN FOR THE LONG TERM PERIOD IS 
RELATIVELY GOOD AMONGST THE MODELS. THE MAIN FEATURE OF INTEREST IS 
THE GULF OF MEXICO SURFACE LOW PROGGED TO DEVELOP OVER THE EASTERN 
GULF BY THURSDAY...LIFT NORTHEASTWARD ACROSS THE FLORIDA PENINSULA 
AND UP THE SOUTHEAST COAST. THOUGH THE MODELS AGREE IN 
PRINCIPAL...SIGNIFICANT DIFFERENCES IN TIMING...TRACK...AND STRENGTH 
REMAIN AND MUDDY THE FORECAST WATERS. FOR INSTANCE...THE 02/00Z GFS 
IS A BIT FURTHER OFF THE SC/GA COASTLINE AND THEREFORE PRODUCES VERY 
LITTLE INLAND PRECIPITATION. ON THE OTHER HAND...THE 02/00Z ECMWF 
MORE CLOSELY HUGS THE COAST AND DEPICTS SIGNIFICANT PRECIPITATION 
FOR THESE SAME COASTAL LOCATIONS. THE FORECAST CONTINUES TO 
ADVERTISE AN EXTENDED PERIOD OF CHANCE POPS DUE TO THE UNCERTAINTY.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
MAINLY ISOLATED SHOWERS/THUNDERSTORMS WILL BE IN THE VICINITY OF
BOTH KCHS AND KSAV THROUGH THE AFTERNOON. EXPECT PRECIPITATION TO
GRADUALLY SHIFT FARTHER INLAND OF THE TERMINALS AS THE AFTERNOON
PROGRESSES. DIURNAL CUMULUS AND OVERSPREADING CLOUDS FROM SCATTERED
CONVECTION WILL DIMINISH TOWARD THE EVENING HOURS...AND EXPECT A
LULL IN AVIATION IMPACTS UNTIL AROUND MIDNIGHT.

AN APPROACHING FRONT FROM THE WEST AND ASSOCIATED UPPER LEVEL
ENERGY WILL SUPPORT AN INCREASE IN CLOUDS AND RAIN POTENTIAL LATE
TONIGHT INTO MONDAY MORNING. CEILINGS WILL RETURN AT BOTH TAF
SITES AFTER MIDNIGHT...HOWEVER PREFER TO ONLY MENTION SCATTERED
MVFR CLOUDS DUE TO SOME UNCERTAINTY IN COVERAGE AND HEIGHTS.
CONFIDENCE IS FAIRLY HIGH THAT WIDESPREAD RAIN WILL BE IMPACTING
THE AREA BY MID TO LATE MONDAY MORNING...AND HAVE THUS INCLUDED
-SHRA AT BOTH KCHS AND KSAV AFTER 14Z.

GUSTY SOUTH/SOUTHEAST WINDS THIS AFTERNOON WILL DIMINISH BY
SUNSET...YET DO NOT EXPECT WINDS TO COMPLETELY DECOUPLE OVERNIGHT.

EXTENDED AVIATION...PRIMARILY VFR. LOW END CHANCES FOR OVERNIGHT
FOG/STRATUS EARLY IN THE WEEK. EXPECT PERIODIC IMPACTS FROM
NUMEROUS TO WIDESPREAD SHOWERS/THUNDERSTORMS ON MONDAY. MORE
SCATTERED SHOWERS/THUNDERSTORMS AND CORRESPONDINGLY LOWER CHANCES
OF IMPACTS WILL CONTINUE THROUGH MID WEEK.

&&

.MARINE...
TONIGHT...THE COASTAL WATERS WILL REMAIN ALONG THE PERIPHERY OF
THE RETREATING ATLANTIC RIDGE...SUPPORTING SOUTH/SOUTHEAST WINDS
AROUND 15 KT INTO EARLY MONDAY MORNING. SEAS WILL GENERALLY RANGE
FROM 2 TO 4 FT WITHIN 20 NM OF THE COAST AND 4 TO 5 FT IN THE
OUTER WATERS. COVERAGE OF SHOWERS AND THUNDERSTORMS WILL INCREASE
AFTER MIDNIGHT.

MONDAY THROUGH THURSDAY...A WEAKENING COLD FRONT WILL MOVE INTO THE 
LOCAL WATERS LATE MONDAY AND WILL SLOWLY ADVANCE SOUTH AND EAST OF 
THE REGION THROUGH TUESDAY. A WEAKENING PRESSURE PATTERN WILL 
PREVAIL THROUGH TUESDAY...WITH SOUTH/SOUTHEAST WINDS 15 KT OR LESS 
MONDAY WEAKER/MORE ERRATIC TUESDAY. THEN...HIGH PRESSURE WILL BUILD 
FROM THE NORTH WEDNESDAY AND THURSDAY RESULTING IN A STRONGEST 
EASTERLY FLOW AND HIGHER SEAS FOR THE LATTER HALF OF THE WEEK.
02/12Z GUIDANCE HAS BACKED OFF WITH REGARDS TO WIND SPEED AND 
ASSOCIATED SEAS MID TO LATE WEEK...SO THE PROBABILITY FOR 
SMALL CRAFT ADVISORY CONDITIONS WILL REMAIN ON THE LOW SIDE. 
HOWEVER...BY LATE WEEK FORECAST UNCERTAINTY INCREASES. A STATIONARY 
FRONT WILL BE POSITIONED CLOSE TO THE SOUTHEAST COAST...AND BROAD 
LOW PRESSURE COULD DEVELOP OVER THE EASTERN GULF...PERHAPS TRACKING
NORTHEAST ALONG THE STATIONARY FRONT OR REMAINING IN PLACE OVER THE 
GULF. IF A LOW PRESSURE DEVELOPS...A TIGHTER PRESSURE GRADIENT COULD 
DEVELOP WITH ELEVATED WINDS/SEAS LATE WEEK OR NEXT WEEKEND. 

&&

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

&&

$$

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