Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 290248
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1048 PM EDT THU APR 28 2016

.SYNOPSIS...
A WEAKENING COLD FRONT WILL APPROACH THE AREA LATE TONIGHT...WILL
CROSS THE REGION FRIDAY...THEN WILL SHIFT OFFSHORE AND DISSIPATE
OVER THE WEEKEND. LOW PRESSURE WILL TRACK TO OUR NORTH
SUNDAY...BRINGING UNSETTLED CONDITIONS TO THE AREA. ATLANTIC HIGH
PRESSURE WILL THEN PREVAIL EARLY NEXT WEEK BEFORE A COLD FRONT
APPROACHES THE AREA MID WEEK.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
LATE THURSDAY EVENING...SHOWERS HAD DISSIPATED OVER/UPSTREAM OF
THE REGION. WHILE AN ISOLATED SHOWER/THUNDERSTORM OR TWO CANNOT
BE COMPLETELY RULED OUT AS A SURFACE COLD FRONT APPROACHES THE
REGION OVERNIGHT...ONGOING RADAR TRENDS AND RECENT GUIDANCE
INCLUDING THE 00Z NAM SUGGEST THAT PRECIPITATION HAS ENDED FOR
TONIGHT. THUS...LOWERED POPS BELOW 15 PERCENT WITH NO MENTION OF
SHOWERS FOR THE BALANCE OF THE NIGHT.

MEANWHILE...GROUND FOG WILL ATTEMPT TO DEVELOP OVERNIGHT...BUT
A PERSISTENT SURFACE PRESSURE GRADIENT AND ELEVATED W/SW WINDS
JUST OFF THE SURFACE SHOULD MITIGATE THE COVERAGE/IMPACT OF ANY
FOG. HOWEVER...IF THE SURFACE PRESSURE GRADIENT WEAKENS AND/OR
LOW-LEVEL WINDS SLACKEN LATER ON...MORE SIGNIFICANT FOG COULD
DEVELOP TOWARD DAYBREAK...ESPECIALLY WHERE HEAVIER RAIN FELL
THURSDAY AFTERNOON. OTHERWISE...TEMPERATURES SHOULD BOTTOM OUT IN
THE MID/UPPER 60S AT MANY LOCATIONS...PERHAPS HOLDING AROUND 70F
ON THE BEACHES....ALTHOUGH A FEW LOCATIONS WHERE HEAVIEST RAIN
OCCURRED COULD BOTTOM OUT IN THE LOWER 60S.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
FRIDAY...A DEEP LAYER RIDGING AND DRIER MID AND UPPER LEVELS WILL
MOVE IN WITH NO PRECIPITATION MOST OF THE PERIOD. EXPECTED. A WEAK
FRONT IS EXPECTED TO STALL AND DISSIPATE JUST SOUTH OF THE AREA.
VERY WARM AGAIN WITH HIGHS IN THE UPPER 80S TO AROUND 90...EXCEPT
SLIGHTLY COOLER NEAR THE COAST AS LIGHT WINDS TURN TO ONSHORE BY
AFTERNOON. MOSTLY CLEAR FRIDAY NIGHT WITH LOWS IN THE 60S.

SATURDAY...THE DEEP LAYER RIDGE SHIFTS EASTWARD THROUGH THE DAY AS
THE NEXT UPPER TROUGH MOVES INTO THE CENTRAL PORTION OF THE COUNTRY.
BY LATE IN THE DAY THERE COULD BE ENOUGH MOISTURE AND SOME WEAK
UPPER FORCING ON THE EAST OF THE ADVANCING TROUGH TO PRODUCE
ISOLATED CONVECTION OVER THE WESTERN PORTION. THUS HAVE KEPT SLIGHT
CHANCE POPS OVER THAT REGION. HIGHS AGAIN VERY WARM IN THE UPPER 80S
TO NEAR 90...EXCEPT COOLER AT THE COAST DUE TO SOUTHERLY FLOW
VEERING TO A RESULTANT SEA BREEZE DURING THE AFTERNOON. INCREASING
MOISTURE/CLOUDS SATURDAY NIGHT AS THE UPPER TROUGH MOVES
EASTWARD...BUT REMAINING WELL NORTH OF THE AREA. THERE WILL BE SOME
WEAK UPPER IMPULSES MOVING ACROSS THE REGION IN THE DEEP SOUTHWEST
FLOW...BUT WITH LACK OF STRONG FORCING AND LOSS OF
HEATING/INSTABILITY...HAVE KEPT ONLY SLIGHT CHANCE POPS. LOWS AGAIN
MILD IN THE MID TO UPPER 60S.

SUNDAY...LOOKS TO BE THE MOST UNSETTLED DAY OF THE PERIOD.
SUFFICIENT DEEP LAYER MOISTURE AND CAPE VALUES 1000-1500 J/KG ON THE
SOUTHEAST SIDE OF THE UPPER TROUGH OVER THE OH RIVER VALLEY...SHOULD
TRANSLATE TO SCATTERED SHOWERS AND THUNDERSTORMS. AGAIN...NO STRONG
UPPER FORCING...THUS FEEL BEST CHANCES WILL BE MAINLY AFTERNOON
COINCIDENT WITH MAXIMUM HEATING/INSTABILITY. HIGHS A TAD COOLER
THAN PREVIOUS DAYS DUE TO CLOUD COVER...IN THE MID 80S MOST AREAS.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
CHANCES OF SHOWERS AND THUNDERSTORMS WILL PERSIST SUNDAY NIGHT INTO
MONDAY AHEAD OF A COLD FRONT EXPECTED TO SHIFT THROUGH THE AREA
MONDAY AFTERNOON/EVENING. DRYER HIGH PRESSURE WILL THEN FILTER INTO
THE REGION MONDAY NIGHT INTO EARLY TUESDAY...BEFORE SFC LOW PRESSURE
DEVELOPS TO THE SOUTH OR SOUTHWEST AND TRACKS OVER THE AREA TUESDAY
AFTERNOON THROUGH WEDNESDAY. CHANCES OF SHOWERS AND THUNDERSTORMS
WILL REMAIN IN THE FORECAST MID WEEK UNTIL SFC LOW PRESSURE SHIFTS
OFFSHORE WEDNESDAY NIGHT. DRY CONDITIONS AND BELOW NORMAL TEMPS ARE
THEN EXPECTED HEADING INTO LATE WEEK WHILE A LARGE TROUGH OF LOW
PRESSURE DOMINATES THE EASTERN CONUS.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
LOW PROBABILITY FOR BRIEF FLIGHT RESTRICTIONS MAINLY IN GROUND
FOG LATE TONIGHT...ESPECIALLY AT KCHS. OTHERWISE...VFR THROUGH
FRIDAY.

EXTENDED AVIATION OUTLOOK...VFR EXPECT TO PREVAIL.
SATURDAY NIGHT THROUGH EARLY NEXT WEEK...BETTER DEEP LAYER MOISTURE
RETURNS WITH SCATTERED MAINLY AFTERNOON SHOWERS AND THUNDERSTORMS
POSSIBLE...WHICH COULD PRODUCE BRIEF FLIGHT RESTRICTIONS.

&&

.MARINE...
OVERNIGHT...A PERSISTENT SURFACE PRESSURE GRADIENT BETWEEN
A LOW PRESSURE/A COLD FRONT APPROACHING FROM THE N/NW AND OFFSHORE
HIGH PRESSURE WILL MAINTAIN SW WINDS 10-15 KT MUCH OF THE
NIGHT...AND A FEW GUSTS TO 20 KT WILL BE POSSIBLE. WINDS SHOULD
VEER TOWARD THE W LATE AND COULD BEGIN TO DIMINISH. SEAS WILL
AVERAGE 2-4 FT...HIGHEST BEYOND 20 NM.

FRIDAY THROUGH TUESDAY...NO HIGHLIGHTS. EXPECT WIND SPEEDS
ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY
CRITERIA...GENERALLY IN THE 10-15 KT RANGE/HIGHEST ACROSS
CHARLESTON COUNTY AND OUTER GA WATERS. THROUGH THE PERIOD...
WINDS GENERALLY 15 KNOTS OR LESS AND SEAS 3 FEET OR LESS.
ATLANTIC HIGH PRESSURE WILL DOMINATE FRIDAY THROUGH SATURDAY. BY
SUNDAY AND LIKELY INTO MONDAY...BECOMING A BIT MORE UNSETTLED AS
AN UPPER TROUGH MOVES WELL NORTH OF THE WATERS. EXPECT ISOLATED TO
SCATTERED SHOWERS AND THUNDERSTORMS THROUGH THIS PERIOD. THERE IS
MODEL UNCERTAINTY BY LATER MONDAY AND TUESDAY. THE GFS AND
CANADIAN MODELS SHOW A COLD FRONT MOVING SOUTH OF THE AREA LATER
MONDAY AND TUESDAY WITH HIGH PRESSURE BUILDING FROM THE
NORTH...WHILE THE ECMWF KEEPS UNSETTLED CONDITIONS WITH AN
ELONGATED AREA OF LOW PRESSURE OVER THE MID ATLANTIC STATES. DUE
TO UNCERTAINTY...HAVE KEPT PREVIOUS FORECAST OF SLIGHT CHANCE POPS
THROUGH THIS PERIOD...AND WILL LET THE MIDNIGHT SHIFT RE-EVALUATE.

&&

.EQUIPMENT...
DATA FROM THE CHARLESTON HARBOR TIDE STATION REMAINS UNAVAILABLE
THURSDAY EVENING. THE NATIONAL OCEAN SERVICE IS WORKING TO
RESTORE SERVICE. AN ESTIMATED TIME FOR RESTORATION OF DATA IS
UNKNOWN.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...ECT/SPR
SHORT TERM...RFM
LONG TERM...
AVIATION...ECT/SPR
MARINE...ECT/RFM/SPR



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