000
FXUS62 KCHS 172336
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
736 PM EDT SAT MAY 17 2008
.SYNOPSIS...
WEAK HIGH PRES WILL SHIFT SE AND AWAY FROM THE AREA TONIGHT AND
SUNDAY...GIVING WAY TO A COOL FRONT SUNDAY NIGHT. A LOW PRES TROUGH
WILL DEVELOP ACROSS THE REGION MONDAY...WITH ANOTHER COOL FRONT TO
APPROACH BY MID WEEK...PERHAPS LINGERING NEARBY THROUGH LATE IN THE
WEEK.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
A MESO HIGH OFF THE COAST THIS EVENING WILL SHIFT SE AND AWAY FROM
THE REGION TONIGHT AS A CLIPPER TYPE SYSTEM MOVES THROUGH THE
UPPER MIDWEST AND INTO THE OHIO VALLEY BY MORNING. SLOW PRES FALLS
WILL DEVELOP ACROSS THE AREA AS A RESULT...WITH EVENTUALLY WEAK
CYCLONIC FLOW DEVELOPING. HOWEVER...PWATS ARE NO MORE THAN 3/4 TO
1 INCH BY LATE TONIGHT...SO A DRY FORECAST WILL CONTINUE DESPITE
THE APPROACH OF A SHORT WAVE AND THE UPPER LEVEL JET.
SHORT WAVE WILL MOVE OUT OF THE NE GULF OF MEXICO TONIGHT...AND
THAT ALONG WITH 110-120 KT UPPER LEVEL JET MOVING INTO THE SE
STATES LATE WILL CAUSE AN INCREASE IN MID AND HIGH LEVEL
CLOUDINESS THROUGH THE NIGHT. BEST RADIATIONAL COOLING WILL OCCUR
EARLY ON AS WINDS BECOME LIGHT AND BEFORE CLOUD COVER STARTS TO
MOVE IN. HOWEVER...WITH INCREASING CLOUDINESS OVERNIGHT AND S-SW
WINDS ALONG THE COAST INCREASING TO 10 OR 15 MPH...TEMPS WILL BEGIN
TO RISE A COUPLE OF DEGREES BY MORNING. OVERALL WE ARE LOOKING AT
MINIMUM TEMPS TONIGHT IN THE UPPER 50S AND LOWER 60S.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
THE FORECAST AREA IS SITUATED BETWEEN THE NEXT APPROACHING COLD
FRONT TO THE NW ON SUNDAY...WHILE A BAROCLINIC ZONE IS FOUND ACROSS
NRN FL. THE SHORT WAVE FROM TONIGHT WILL PASS INTO THE ATLC WITH
NVA IN ITS WAKE...WHILE A SECOND SHORT WAVE WHICH IS NOW IN TX
WILL MOVE TOWARD THE AREA BY LATE SUNDAY OR EARLY SUNDAY NIGHT.
MEANWHILE...THE CLIPPER LOW WILL MOVE INTO THE NE ON SUNDAY AND
THROUGH NEW ENGLAND SUNDAY NIGHT. TRAILING COLD FRONT WILL THEN
PUSH INTO THE LOCAL AREA OVERNIGHT SUNDAY.
AT THIS POINT IN TIME WE FEEL THAT ANY CONVECTION SUNDAY WILL
REMAIN JUST OUTSIDE THE FORECAST AREA TO THE NW WITH THE COLD
FRONT AND NEXT SHORT WAVE...AND TO THE S WHICH IS CLOSER TO THE
OLD FRONTAL BOUNDARY. WE NEED TO KEEP WATCH FOR POSSIBLE ISOLATED
CONVECTION TRYING TO SNEAK IN ALONG THE RESULTANT SEA BREEZE IN SE
GA DURING THE AFTN...BUT WILL CAP POPS AT LESS THAN 15 PERCENT AND
THUS NO REASON TO MENTION PRECIP IN THE FORECAST FOR SUNDAY.
FOR SUNDAY NIGHT...REMNANTS OF THE FRONTAL BOUNDARY TO THE S WILL
SHIFT E AND AWAY FROM THE AREA...WHILE NEXT UPSTREAM COLD FRONT
PUSHES SE AND INTO THE REGION. MOISTURE DOES INCREASE WITH THIS
SYSTEM AS PWATS INCREASE UP TO 1.4 TO 1.5 INCHES...AND THERE IS A
LITTLE INSTABILITY /LI/S -1/-2 AND CAPES AROUND 500 J/KG/...BUT
THIS OCCURS MAINLY OVER THE ATLC. THIS CERTAINLY COULD RESULT IN
SOME SHOWERS OR POSSIBLE TSTMS...BUT WITH FRONT MOVING IN AFTER
DARK AND BEST PVA INTO THE ATLC AS FRONT MOVES IN...WE WILL NOT
YET ADD ANY SMALL POPS TO THE FORECAST EXCEPT OVER THE NRN COASTAL
WATERS.
MID AND HIGH LEVEL CLOUDINESS TO START THE DAY SUNDAY SHOULD
SLOWLY THIN OUT THROUGHOUT THE DAY AS FIRST SHORT WAVE AND UPPER
LEVEL 120 KT JET SHIFTS INTO THE ATLC DURING THE AFTN. COULD BE
ENOUGH LOW LEVEL MOISTURE FOR A LITTLE CUMULUS
DEVELOPMENT...ESPECIALLY OVER ERN AREAS NEAR THE RESULTANT SEA BREEZE.
TEMPS WILL BE DEPENDENT UPON HOW QUICKLY CLOUDINESS BEGINS TO
DISSIPATE...BUT WITH W-SW FLOW WE SHOULD WARM AT LEAST INTO THE
LOWER AND MIDDLE 80S EXCEPT RIGHT AT THE BEACHES. MIN TEMPS SUNDAY
NIGHT LOOK TO BE A SIMILAR TO OR A COUPLE OF DEGREES HIGHER THAN
TONIGHT...DEPENDING UPON EXACT TIMING OF COLD FRONT WHICH PUSHES
INTO AT LEAST NRN AND CENTRAL AREAS OVERNIGHT.
BREEZY CONDITIONS TO OCCUR LATE SUNDAY MORNING INTO SUNDAY AFTN AS
MIXING HEIGHTS INCREASE TO AT LEAST 5K FT...AND WINDS WITHIN THIS
MIXED LAYER ARE 20-30 KT. WITH DECREASING CLOUDINESS DURING PEAK
HEATING WE SHOULD BE ABLE TO ACHIEVE A GOOD PORTION OF THESE
WINDS. THUS WILL HAVE BREEZY WORDING ACROSS ALL OF SC EXCEPT
INLAND JASPER...HAMPTON AND ALLENDALE COUNTIES FOR 15-25 MPH AND
GUSTY.
LAKE WINDS...ALTHOUGH MID AND HIGH LEVEL CLOUDINESS AND WARM
ADVECTION MAY LIMIT MIXING ACROSS LAKE MOULTRIE SUNDAY
AFTN/EVENING...BOUNDARY LAYER WINDS ARE 30 KT OR GREATER. THUS WE
WILL AT LEAST BE ABLE TO ACHIEVE WIND GUSTS OF 25 KT OR GREATER
WHILE SUSTAINED WINDS AT LEAST APPROACH 20 KT. THEREFORE WE WILL
RAISE A LAKE WIND ADVISORY FOR SUNDAY ACROSS LAKE MOULTRIE.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
FOR MONDAY...A SFC LOW WILL CONTINUE TO SHIFT EAST OVER THE
ATLANTIC OFF THE NORTHEASTERN COAST EARLY NEXT WEEK. A PERSISTENT
WEST FLOW ON THE SOUTHERN PERIPHERY OF A LONGWAVE TROUGH WILL
WEAKEN ON MONDAY AS THE PRESSURE GRADIENT BECOMES LESS PACKED.
CONDITIONS WILL REMAIN DRY AS A DOWNSLOPING WIND CONTINUES THROUGH
TUESDAY MORNING. HIGH TEMPS FOR MONDAY WILL REACH THE MID 80S
UNDER MOSTLY SUNNY SKIES.
TUESDAY AND WEDNESDAY...A CLIPPER TYPE SYSTEM IS EXPECTED TO
EJECT QUICKLY EAST OVER THE MID ATLANTIC STATES TUESDAY AND
WEDNESDAY. A WEAK FRONT ASSOCIATED WITH THIS SYSTEM WILL BRING THE
POSSIBILITY OF A FEW SHOWERS AND THUNDERSTORMS TUESDAY AFTERNOON
THROUGH EARLY WEDNESDAY MORNING... WITH A BETTER CHANCE OF PRECIP
BEING OBSERVED OVER SOUTHEAST SOUTH CAROLINA. HIGH TEMPS ARE
EXPECTED TO REACH THE UPPER 80S WITH A FEW 90S OVER INLAND
PORTIONS OF SOUTHEAST GA ON TUESDAY.
THURSDAY THROUGH SATURDAY...A RIDGE OF HIGH PRESSURE WILL DEVELOP
OVER THE REGION BEGINNING THURSDAY AND PERSIST THROUGH THE REST OF
THE EXTENDED. ALTHOUGH DYNAMIC FORCING WILL REMAIN LIMITED...HIGH
TEMPS IN THE UPPER 80S TO AROUND 90 IN MANY AREAS WILL PROMOTE
PULSE TYPE CONVECTION DURING AFTERNOON HOURS. A SLIGHT CHANCE OF
AFTERNOON SHOWERS AND THUNDERSTORMS ARE FORECASTED AS A RESULT
FROM THURSDAY THROUGH SATURDAY.
&&
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
BOTH KSAV AND KCHS SHOULD SEE A CONTINUATION OF VFR CONDITIONS
THROUGH SUNDAY. 18Z NAM GUIDANCE STILL INDICATES CONVECTIVE PCPN
SHOULD REMAIN S OF SAVANNAH DURING THE DAY AND WELL TO THE NW OF
CHARLESTON BY LATE AFTERNOON.
THE MAIN CONCERN AT BOTH TERMS DURING PEAK MIXING TIME ON SUNDAY
AFTERNOON WILL BE GUSTY SW SURFACE WINDS. THICKER MID LEVEL CLOUDS
IN THE MORNING SHOULD THIN DURING THE AFTERNOON. AN INCREASING MIXED
LAYER WITH 30 PLUS KT OF LOW LEVEL JET LIKELY TO INCITE GUSTS TO AT
LEAST THE MID 20 KT RANGE AT KCHS AND MAYBE NEAR 20 KT AT TIMES AT
KSAV.
EXTENDED AVIATION OUTLOOK...THERE WILL BE A POSSIBILITY OF MVFR
CONDITIONS WITH A WEAK FRONT DURING MID WEEK...OTHERWISE A FAIRLY
DRY PATTERN WILL ALLOW VFR WEATHER TO PREVAIL THROUGH THURSDAY.
&&
.MARINE...
HIGH PRES SHIFTS SE AWAY FROM THE AREA TONIGHT AND SMALL PRES FALLS
DEVELOP IN RESPONSE TO THIS AND THE CLIPPER TYPE SYSTEM MOVING INTO
OH VALLEY LATE. AS A RESULT...WIND FIELDS WILL GRADUALLY INCREASE
ACROSS THE COASTAL WATERS TONIGHT...WITH SUBTLE NOCTURNAL INCREASE
TO NEAR 15 KT. SEAS WILL BUILD ACCORDINGLY...BUT NO HIGHER THAN
ABOUT 3 OR 4 FT.
A MORE NOTICEABLE INCREASE IN WIND FIELDS DEVELOPS SUNDAY INTO
SUNDAY NIGHT...AS CLIPPER SYSTEM MOVES INTO THE NE STATES AND
ASSOCIATED PRES FALLS PERSIST ACROSS THE AREA DURING SUNDAY. LOW
LEVEL JET AND 1000 MB GEOSTROPHIC WINDS OF 30 OR 35 KT MOVES ACROSS
THE WATERS SUNDAY AFTN INTO THE FIRST PART OF SUNDAY NIGHT. THE
RESULT WILL BE A FURTHER INCREASE IN WINDS AND SEAS DURING THIS TIME
AND SCA/S ARE CERTAINLY POSSIBLE. AFTER COORDINATION WITH WFO ILM
AND WFO JAX WE WILL HOLD OFF ON ANY HEADLINES OVER THE ATLC WATERS
GIVEN THAT IT IS THE THIRD PERIOD OF THE FORECAST. BUT THE WFO CHS
EARLY MORNING FORECASTING STAFF WILL LIKELY NEED TO RAISE THE SCA
FLAGS FOR AT LEAST THE OUTER GA WATERS AND THE NRN SC FOR SUNDAY
NIGHT. SWLY WINDS WILL INCREASE TO AT LEAST 20 KT IF NOT
HIGHER...AND THE FAVORABLE FETCH WILL ALLOW SEAS TO BUILD TO AT
LEAST 5 OR 6 FT WITHIN 20 NM OF THE COAST...AND UP TO AT LEAST 6 OR
7 FT FURTHER OFFSHORE.
REGARDING CHARLESTON HARBOR...GIVEN THE ABOVE MENTIONED
SCENARIO...FURTHER ENHANCED BY RESULTANT SEA BREEZE SUNDAY
AFTN/EVENING AND BETTER MIXING PROFILES THAN OVER THE ATLC...WE
WILL GO AHEAD AND RAISE AN SCA FOR AMZ330 FROM 15Z SUNDAY THROUGH
02Z MONDAY.
WINDS AND SEAS WILL REMAIN QUIET OVER A MAJORITY OF THE EXTENDED
FORECAST...ESPECIALLY BY MID WEEK. A BRIEF PERIOD OF 3 TO 5 FEET
SEAS WILL OCCUR TUESDAY AFTERNOON INTO EARLY WEDNESDAY AS A WEAK
FRONT ENCOUNTERS THE SC AND GA WATERS. SOUTHWEST WINDS BETWEEN 15
TO 20 KNOTS ARE EXPECTED DURING WEAK FROPA. CONDITIONS MAY APPROACH
SCA CRITERIA IN THE OUTER GA WATERS FOR A SHORT PERIOD OF TIME
BEFORE QUICKLY IMPROVING WEDNESDAY MORNING.
CONDITIONS WILL BECOME RATHER TRANQUIL BY WEDNESDAY AS HIGH PRESSURE
SETTLES IN THEREAFTER. IN GENERAL...SOUTH WINDS OF 10 TO 15 KNOTS
WITH WAVES BETWEEN 1 TO 3 FEET WILL OCCUR THROUGH THE WEEKEND.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...LAKE WIND ADVISORY FROM 11 AM TO 10 PM EDT SUNDAY FOR SCZ045.
MARINE...SMALL CRAFT ADVISORY FROM 11 AM TO 10 PM EDT SUNDAY FOR AMZ330.
&&
$$
