Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 291950
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
350 PM EDT WED JUL 29 2015

.SYNOPSIS...
A WEAK PRESSURE PATTERN WILL PERSIST OVER THE REGION UNTIL A WEAK
COLD FRONT APPROACHES FRIDAY. THE FRONT WILL THEN STALL THROUGH
EARLY NEXT WEEK WITH ATLANTIC HIGH PRESSURE GRADUALLY RETURNING BY
THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
REST OF THE AFTERNOON...BASED ON CURRENT VISIBLE SATELLITE IMAGERY
AND RADAR TRENDS IT APPEARS THAT SHOWERS AND STORMS ARE LINING UP
ACROSS AN AREA WELL WEST OF I-95 AS ANTICIPATED. THE CUMULUS FIELD
TO THE EAST IS QUITE MUTED AND THIS IS WELL SUPPORTED BY LI FIELDS
ON THE SPC MESOANALYSIS WHICH RANGE FROM AROUND -7 C ACROSS SOUTH
GEORGIA TO ONLY -2 OR -3 C ACROSS THE TRI-COUNTY REGION. MID-LEVEL
LAPSE RATES ARE QUITE WEAK AND DCAPE VALUES ARE MARGINAL AT BEST.
THE OVERALL SEVERE THREAT IS QUITE LOW FOR EVEN THE FAR WESTERN
ZONES THROUGH THE EVENING.

TONIGHT...ISOLATED SHOWERS AND THUNDERSTORMS MAY LINGER TILL JUST
AFTER SUNSET BUT THE BULK OF THE OVERNIGHT WILL BE DRY AND POP-FREE.
THE PRESSURE PATTERN WILL BE QUITE WEAK ON THE WEST AND NORTHWEST
PERIPHERY OF THE OFFSHORE LOW RESULTING IN A TRANQUIL NIGHT. THERE
ARE SOME INDICATIONS THAT SHALLOW GROUND FOG COULD DEVELOP...BUT THE
COVERAGE AND INTENSITY ISN/T EXPECTED TO BE ENOUGH TO CARRY IN THE
FORECAST. LOWS WILL RANGE IN THE MID TO UPPER 70S IN MOST
LOCATIONS.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
THURSDAY...WEAK LOW PRESSURE WELL OFFSHORE WILL DRIFT NORTHEAST
WHILE A WEAK COLD FRONT APPROACHES FROM THE NORTHWEST. BEST RAIN
CHANCES LOOK TO BE INLAND CLOSER TO THE FRONT/PRE-FRONTAL TROUGH.
CAN/T RULE OUT A FEW SEVERE STORMS...MAINLY OF THE PULSE
VARIETY...WITH DAMAGING WINDS AND HEAVY RAIN THE MAIN HAZARDS. HIGHS
SHOULD BE SLIGHTLY ABOVE NORMAL IN THE MID 90S INLAND AWAY FROM THE
COOLER COASTAL AREAS. SHOWERS AND A FEW THUNDERSTORMS SHOULD LINGER
DURING THE EVENING AND OVERNIGHT AS THE WEAK FRONT PUSHES EASTWARD
INTO SOUTHEAST SC/GA.

FRIDAY...A WEAK COLD FRONT WILL LIKELY BE NEAR INTERIOR PORTIONS OF
SOUTHEAST SC/GA TO START THE DAY BEFORE DISSIPATING AS DAYTIME
HEATING COMMENCES. THIS BOUNDARY ALONG WITH DEEP MOISTURE AND THE
AFTERNOON SEA BREEZE WILL SUPPORT AT LEAST SCATTERED SHOWERS AND
THUNDERSTORMS INTO EARLY EVENING. LIGHT LOW-MID LEVEL WINDS AND DEEP
MOISTURE COULD YIELD A SLIGHTLY ENHANCED RISK FOR HEAVY
RAINFALL/LOCALIZED FLOODING. HIGHS LOOK TO BE HELD DOWN A BIT GIVEN
THE INCREASED CLOUD/RAIN COVERAGE BUT SHOULD STILL BE NEAR NORMAL IN
THE LOWER 90S AWAY FROM THE COAST. SHOWERS AND THUNDERSTORMS WILL
DIMINISH FRIDAY NIGHT BUT POSSIBLY NOT COMPLETELY AS THE WEAK
FRONT/TROUGH LINGERS OVER THE AREA.

SATURDAY...THE FORECAST IS A BIT LESS CONFIDENT THIS DAY AS THERE
ARE SOME MODEL DIFFERENCES REGARDING THE POSITION OF THE UPPER
TROUGH AND DEEPER MOISTURE. THE 12Z/29 NAM12/GFS DO NOT SHOW MUCH
RAIN ALTHOUGH THE ECMWF STILL DOES. FOR NOW WE PREFER TO MAINTAIN
CONTINUITY UNTIL CONFIDENCE INCREASES.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
THE STATIONARY FRONT...ASSOCIATED DEEP LAYERED TROUGH...WEAK
STEERING WINDS AND RESERVOIR OF ABOVE-NORMAL PWATS WILL PERSIST OVER
THE REGION THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK. THIS
ENVIRONMENT WILL SUPPORT ELEVATED POPS AND A CONTINUING THREAT FOR
LOCALLY HEAVY RAINFALL/SHORT FUSE FLOODING. LIKELY POPS APPEAR
REASONABLE FOR SATURDAY. THEN...MODEL DISAGREEMENT ARISES REGARDING
THE POSITION OF THE TROUGH AND ASSOCIATED AXIS OF DEEPEST MOISTURE
SUNDAY-MONDAY. IF THE ATLANTIC RIDGE ALLOWS THE TROUGH AXIS TO PUSH
OFF THE COAST...THE FOCUS FOR HEAVIEST RAIN WILL SHIFT OVER THE
ATLANTIC WATERS. HOWEVER...IF THE ATLANTIC RIDGE REMAINS STRONGER
AND HOLDS THE TROUGH AXIS AND RICH MOISTURE OVER THE REGION AS
DEPICTED BY THE 29/00Z EUROPEAN...ELEVATED POPS/THE ASSOCIATED
POTENTIAL FOR LOCALLY HEAVY RAIN WILL PERSIST. DUE TO
UNCERTAINTY...CAPPED MAXIMUM POPS AT AROUND 50 PERCENT SUNDAY AND
MONDAY. EVENTUALLY...THE TROUGH WILL EVENTUALLY WEAKEN OR WILL SHIFT
OFFSHORE...ALLOWING HIGH PRESSURE TO GRADUALLY BUILD INTO THE REGION
WITH MORE TYPICAL TEMPERATURES/POPS TUESDAY THROUGH WEDNESDAY.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 18Z THURSDAY. FOR
THIS AFTERNOON...SHOWERS AND THUNDERSTORMS ARE EXPECTED TO REMAIN
AWAY FROM THE TERMINALS. IF THERE IS A CHANCE FOR A SITE TO BE
IMPACTED...IT WOULD BE MORE LIKELY AT KSAV. THEN OVERNIGHT...SOME
LOW END POTENTIAL FOR SHALLOW GROUND FOG BUT WE ARE NOT EXPECTING
ANY PREVAILING CEILING/VISIBILITY RESTRICTIONS.

EXTENDED AVIATION OUTLOOK...LOW CHANCE FOR DIRECT IMPACTS FROM
THUNDERSTORMS THURSDAY...ALBEIT A BIT MORESO AT KSAV. INCREASING
THUNDERSTORM CHANCES FRIDAY...POSSIBLY PERSISTING INTO EARLY NEXT
WEEK...AS A FRONT STALLS OUT OVER THE AREA.

&&

.MARINE...
TONIGHT...VERY QUIET CONDITIONS ARE EXPECTED UNDER THE INFLUENCE OF
A WEAK PRESSURE PATTERN OVER THE LOCAL WATERS. WINDS WILL REMAIN
ONSHORE BUT DIMINISH TO LESS THAN 10 KNOTS AFTER MIDNIGHT BEFORE
BECOMING MORE NORTHEAST LATE TONIGHT. SEAS WILL BE 1-2 FEET...EXCEPT
UP TO 3 FEET OVER THE OUTER WATERS.

THURSDAY THROUGH MONDAY...AS A COLD FRONT APPROACHES THEN STALL OVER
THE REGION...WINDS WILL GRADUALLY VEER TOWARD THE SOUTH/SOUTHWEST
LATE WEEK INTO EARLY NEXT WEEK. WHILE WIND SPEEDS WILL GENERALLY BE
LESS THAN 15 KNOTS... THE SEA BREEZE CIRCULATION AND PERIODIC
NOCTURNAL SURGES COULD PUSH WINDS TO 15-20 KNOTS. SEAS OF 2 TO 3
FEET WILL REMAIN COMMON... ALTHOUGH PERIODS OF 4 FT SEAS COULD OCCUR
ESPECIALLY AT 20 NM AND BEYOND. ALSO...THUNDERSTORMS ARE EXPECTED AT
ANY TIME LATE WEEK INTO EARLY NEXT WEEK. THUNDERSTORMS COULD GREATLY
ALTER SYNOPTIC WINDS AND WILL CREATE LOCALIZED HAZARDS...PERHAPS
INCLUDING WATERSPOUTS PARTICULARLY THU/FRI/SAT MORNINGS.

&&

.TIDES/COASTAL FLOODING...
A COASTAL FLOOD ADVISORY HAS BEEN ISSUED FOR THE EVENING HIGH TIDE
FOR THE SOUTHEAST SOUTH CAROLINA COAST. THE PREDICTED TIDE IN THE
CHARLESTON HARBOR IS 6.3 FEET AND TIDAL DEPARTURES HAVE BEEN
RUNNING SOLIDLY AROUND 1 FOOT TODAY. THIS SHOULD RESULT IN A HIGH
TIDE IN THE 7.1-7.3 FEET MLLW RANGE. AT FORT PULASKI...THE
PREDICTED TIDE IS 8.0 FEET AND TIDAL DEPARTURES HAVE BEEN LESS
THAN 1 FOOT FOR MOST OF THE DAY. HIGH TIDE AT FORT PULASKI WILL
LIKELY PEAK AT OR JUST ABOVE 9 FEET...JUST BELOW THE 9.2 FEET MLLW
THRESHOLD FOR SHALLOW COASTAL FLOODING. ONSHORE WINDS HAVE ALSO
BEEN STRONGER...IN THE 10-15 KNOT RANGE...ALONG THE CHARLESTON
COUNTY COAST THIS AFTERNOON.

ELEVATED HIGH TIDE LEVELS ARE EXPECTED THROUGH THE UPCOMING
WEEKEND THANKS TO THE UPCOMING PERIGEAN SPRING TIDE AND FULL MOON
CYCLE. ONSHORE WINDS WILL ALSO PROVIDE ADDITIONAL ENHANCEMENT AT
TIMES...AND SHALLOW COASTAL FLOODING WILL BE POSSIBLE THROUGH THE
WEEKEND ESPECIALLY DURING THE EVENING HIGH TIDE CYCLES.
THUS...WILL MAINTAIN MENTION IN THE HAZARDOUS WEATHER OUTLOOK.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...COASTAL FLOOD ADVISORY UNTIL 10 PM EDT THIS EVENING FOR
     SCZ048>051.
MARINE...NONE.

&&

$$

NEAR TERM...BSH
SHORT TERM...RJB
LONG TERM...SPR
AVIATION...BSH
MARINE...BSH/RJB
TIDES/COASTAL FLOODING...BSH/RJB



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