Area Forecast Discussion
Issued by NWS Charleston, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS62 KCHS 180542
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
142 AM EDT SAT APR 18 2015

.SYNOPSIS...
A WEAKENING WEDGE OF HIGH PRESSURE WILL PERSIST INLAND THROUGH
SATURDAY NIGHT. A WARM FRONT WILL LIFT NORTH OF THE REGION
SUNDAY...THEN A COLD FRONT WILL SWEEP THROUGH MONDAY EVENING. HIGH
PRESSURE WILL PREVAIL TUESDAY THROUGH THURSDAY. A WEAK COLD FRONT
COULD PUSH THE REGION LATE WEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
AN EXPANDING AREA OF SOAKING RAINS CONTINUES TO PUSH EAST-
NORTHEAST ACROSS EAST-CENTRAL AND SE GEORGIA THIS MORNING. THE
RAIN ALIGNS WELL WITH AN AREA OF ENHANCED 295-305K ISENTROPIC
ASSENT NOTED ON THE LATEST RAP/NAM ISENTROPIC 4-PANELS. THERE
ALSO SEEMS TO BE AN MCV EMBEDDED WITHIN THE PCPN AND RADARS HAVE
ESTIMATED OVER 2 INCHES OF RAIN TO THE WEST OF OUR ZONES. SOME
AREAS COULD PICK UP 1/2 TO 1 INCH OF RAIN AS THIS FEATURE MOVES
OVER THE FORECAST AREA OVERNIGHT...MAINLY TO THE WEST OF I-95.
WE MAINTAINED CATEGORICAL TO LIKELY POPS FROM W TO E OVERNIGHT.

LOWS IN THE LOWER-MID 60S WITH VERY LITTLE NOCTURNAL FLUCTUATIONS
WITH DEEP MOISTURE IN PLACE AND WIDESPREAD CLOUDS.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH MONDAY/...
SATURDAY...A SHORTWAVE TROUGH WILL BE SHIFTING OFF THE COAST DURING
THE MORNING FOLLOWED BY RIDGING ALOFT DURING THE AFTERNOON. POPS
START THE DAY GRADUATED FROM CHANCE NORTH TO SLIGHT CHANCE
SOUTH/WEST. THE RIDGING/DRYING TREND COULD MINIMIZE OR ELIMINATE THE
POTENTIAL FOR DIURNAL SHOWERS DURING THE AFTERNOON. HOWEVER...
LOCALIZED CONVERGENCE WILL DEVELOP ALONG VARIOUS BOUNDARIES
INCLUDING THE REMNANTS OF THE SURFACE WEDGE REGIME WHICH COULD
ACTUALLY SPREAD TOWARD THE S/SW AND THE SEA BREEZE. SINCE MODEL
SOUNDINGS DEPICT A SUBTLE DRYING TREND...A FEW SHOWERS CANNOT BE
RULED OUT ALONG/NEAR THESE BOUNDARIES...THUS SLIGHT CHANCE POPS
ARE CARRIED THROUGH THE AFTERNOON.

UNCERTAINTY REGARDING THE POSITION/STRENGTH OF THE PERSISTENT WEDGE
AND ASSOCIATED CLOUD COVER TRANSLATES TO AN UNCERTAIN TEMPERATURE
FORECAST SATURDAY. HIGHS RANGING FROM THE MID/UPPER 70S
NORTHERN...COASTAL AND INLAND COUNTIES TO THE LOWER 80S NEAR THE
ALTAMAHA RIVER APPEAR REASONABLE.

SATURDAY NIGHT AND SUNDAY...A LONGWAVE TROUGH ACROSS THE CENTRAL
UNITED STATES WILL SHIFT EAST WITH EMBEDDED SHORTWAVE ENERGY LIFTING
INTO THE SOUTHEAST STATES. FOCUSED LOW/MID-LEVEL MOISTURE TRANSPORT
WILL SURGE NORTH...INITIALLY INTO AREAS WEST OF THE REGION...THEN
THIS WARM CONVEYOR BELT MOISTURE WILL SHIFT EAST INTO THE
REGION...SUPPORTED BY DYNAMIC FORCING FOR ASCENT AS DEPICTED BY
UPPER DIVERGENCE/500 MB HEIGHT FALLS. THE WARM CONVEYOR BELT
FEATURING DEEP MOISTURE/PWATS NEARING 2 INCHES...OVERRUNNING ABOVE
THE SURFACE WEDGE REGIME...STRENGTHENING DYNAMIC FORCING FOR ASCENT
AND A DESTABILIZING ENVIRONMENT AS A SURFACE WARM FRONT PRESSES
NORTH INTO/THROUGH THE REGION WILL TRANSLATE EAST ACROSS THE REGION.
WHILE UNCERTAINTY REMAINS REGARDING IMPORTANT FORECAST
DETAILS...ESPECIALLY PRECIPITATION TIMING...THIS SCENARIO SUPPORTS
POPS RAMPING UP TO LIKELY AT LEAST ACROSS INLAND COUNTIES LATE
SATURDAY NIGHT...THEN LIKELY/CATEGORICAL POPS REMAIN IN ORDER
SUNDAY.

THE HIGH PWATS AND RELATIVELY LONG RESIDENCE TIME OF THE WARM
CONVEYOR BELT/PLUME OF HIGH PWATS SUGGEST THE POTENTIAL FOR LOCALLY
HEAVY RAINFALL...PERHAPS STARTING LATE SATURDAY NIGHT THEN
CONTINUING THROUGH SUNDAY. ALSO...DESTABILIZATION...0-6 KM BULK
SHEAR OF 30-40 KNOTS AND ENHANCED HELICITY SUGGESTS THAT POTENTIAL
FOR AT LEAST ISOLATED SEVERE THUNDERSTORMS ALONG AND SOUTH OF THE
WARM FRONT...PARTICULARLY SUNDAY AFTERNOON/EVENING.

THE WARM CONVEYOR BELT/ASSOCIATED STRONGEST FORCING AND DEEPEST
MOISTURE SHIFTS OFFSHORE SUNDAY NIGHT...THUS COVERAGE OF SHOWERS
SHOULD GRADUALLY DIMINISH FROM CHANCE/WITH TIME. MAINTAINED CHANCE
POPS EVEN OVERNIGHT...BUT STRONGER DRYING/SUBSIDENCE COULD TRANSLATE
TO LOWER POPS FOR A TIME LATE SUNDAY NIGHT INTO MONDAY.

MONDAY...THE LONGWAVE UPPER TROUGH UPSTREAM WILL DRIVE A SURFACE
COLD FRONT TOWARD THE REGION. WARM ADVECTION AND COMPRESSIONAL
HEATING AHEAD OF THE COLD FRONT WILL YIELD A WARM DAY WITH HIGHS IN
THE MIDDLE 80S COMMON. SURFACE DEWPOINTS ARE EXPECTED TO REMAIN IN
THE MIDDLE 60S...AND THERMODYNAMIC/KINEMATIC PARAMETERS ARE
SUFFICIENT TO SUPPORT THUNDERSTORMS AND PERHAPS EVEN AN ORGANIZED
SEVERE WEATHER EVENT AHEAD OF THE COLD FRONT MONDAY
AFTERNOON/EVENING. HOWEVER...MODEL SOUNDINGS DEPICT A TREND TOWARD
CAPPING/STRONGER DRYING ALOFT...AND THIS COULD IN TURN LIMIT THE
COVERAGE/PERSISTENCE OF DEEP MOIST CONVECTION. THUS...POPS ARE
CAPPED AT CHANCE MONDAY AFTERNOON.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
THE COLD FRONT AND ANY ASSOCIATED CONVECTION WILL SHIFT OFFSHORE
MONDAY NIGHT...FOLLOWED BY DRIER HIGH PRESSURE WHICH WILL THEN
PREVAIL FOR MOST OF THE LONG TERM PERIOD. EXPECT HIGHS IN THE UPPER
70S TO LOWER 80S AND LOWS IN THE MIDDLE 50S TO LOWER 60S. A WEAK
COLD FRONT MAY APPROACH OR MOVE THROUGH NEXT FRIDAY WITH ISOLATED
SHOWERS.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
KSAV...IT HAS TRENDED WET OVERNIGHT WITH RAINS SPREADING IN FROM
THE SW AND W. CONDITIONS SHOULD DETERIORATE WITH SOME LOWER CIGS
DEVELOPING AND MVFR/IFR VSBYS A GOOD BET WITH CIGS AND VSBYS AT
TIMES. THE BACK EDGE OF THE RAINS SHOULD BE PAST BY MID MORNING
AT THE LATEST AND CONDITIONS SHOULD BECOME VFR FOR THE AFTERNOON
AND EARLY EVENING. CANNOT RULE OUT SOME ADDITIONAL SHOWERS OR
SOME LOWER CIGS LATE IN THE TAF PERIOD.

KCHS...A SHORT WAVE TROUGH IN THE MID LEVELS WILL TAP DEEP
MOISTURE ADVECTION OVERNIGHT TO PRODUCE SOME RAINS. AT THIS TIME
WE THINK MOST OF THE RAINS WILL BE FAIRLY LIGHT BUT THEY COULD
BE STEADY. MVFR/IFR CIGS COULD DEVELOP ANYTIME AFTER 08Z AND
LINGER UNTIL MID MORNING. THE RAINS SHOULD DWINDLE LATER THIS
MORNING WITH VFR EXPECTED FOR THE AFTERNOON. SIMILAR TO KSAV...
CANNOT RULE OUT ADDITIONAL SHOWERS LATER TODAY OR SOME LOWER CIGS
LATE IN THE TAF PERIOD.

EXTENDED AVIATION OUTLOOK...A PERIOD OF VFR IS POSSIBLE SATURDAY
AFTERNOON INTO SATURDAY EVENING...THEN FLIGHT RESTRICTIONS SHOULD
PREVAIL LATER SATURDAY NIGHT THROUGH SUNDAY NIGHT. VFR COULD RETURN
MONDAY...ALTHOUGH A COLD FRONT COULD PRODUCE SHOWERS/THUNDERSTORMS
AND ASSOCIATED FLIGHT RESTRICTIONS MONDAY AFTERNOON AND/OR EVENING.
VFR SHOULD THEN PREVAIL LATER MONDAY NIGHT THROUGH MID WEEK.

&&

.MARINE...
OVERNIGHT...VARIABLE CONDITIONS OVERNIGHT WITH THE MARINE AREA
CAUGHT BETWEEN WEAK LOW PRESSURE OFFSHORE AND A DECAYING INLAND
WEDGE. SEAS WILL AVERAGE 2-4 FT THROUGH THE NIGHT.

SATURDAY THROUGH WEDNESDAY...EXPECT CHANGEABLE WINDS DURING THE
SATURDAY THROUGH TUESDAY PERIOD. WINDS/SEAS ARE EXPECTED TO REMAIN
BELOW SCA THRESHOLDS SATURDAY/SATURDAY NIGHT. A WEAK PRESSURE
PATTERN WILL ALLOW THE SEA BREEZE CIRCULATION TO DOMINATE SATURDAY
AFTERNOON./EVENING...THEN BUILDING HIGH PRESSURE FROM THE NORTH
WILL TURN SYNOPTIC WINDS TOWARD THE EAST/NORTHEAST SATURDAY NIGHT
INTO SUNDAY. A WARM FRONT WILL ADVANCE NORTH THROUGH THE WATERS
LATER SUNDAY OR SUNDAY NIGHT...AND A TIGHTER GRADIENT WILL SUPPORT
STRONGER WINDS WHICH WILL VEER FROM EAST/NORTHEAST TO THE SOUTH.
ELEVATED SOUTH/SOUTHWEST WILL THEN PREVAIL AHEAD OF AN APPROACHING
COLD FRONT MONDAY. SMALL CRAFT ADVISORY WINDS CANNOT BE RULED OUT
SUNDAY THROUGH MONDAY...BUT FOR NOW THE MOST LIKELY SCENARIO CAPS
WINDS AT 20 KNOTS AND SEAS AT 3-5 FT...HIGHEST BEYOND 20 NM.
IN THE WAKE OF COLD FROPA...OFFSHORE WINDS AND SEAS BELOW SCA
THRESHOLDS SHOULD PREVAIL MONDAY NIGHT THROUGH TUESDAY. AS THE
HIGH SHIFTS EAST...WINDS SHOULD VEER TOWARD THE NORTH/NORTHEAST
MIDWEEK.

&&

.TIDES/COASTAL FLOODING...
DUE TO ENHANCED ASTRONOMICAL HIGH TIDES WITH THE UPCOMING PERIGEE
AND NEW MOON...THE RISK FOR SHALLOW COASTAL FLOODING WILL CONTINUE
THROUGH THE WEEKEND. COASTAL FLOOD ADVISORIES MAY BE
NEEDED...MAINLY WITH THE EVENING HIGH TIDES.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
TIDES/COASTAL FLOODING...


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.