Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 281952
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
352 PM EDT TUE JUL 28 2015

.SYNOPSIS...
A SERIES OF WEAK AREAS OF LOW PRESSURE WILL DRIFT ACROSS THE REGION
THROUGH THURSDAY BEFORE A COLD FRONT APPROACHES FROM THE WEST LATE
THIS WEEK AND INTO THE WEEKEND. THE FRONT WILL THEN LINGER ALONG OR
NEAR THE COAST INTO EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
THIS EVENING AND TONIGHT...A FEW SHOWERS OR ISOLATED THUNDERSTORMS
COULD PERSIST FOR AN HOUR OR TWO AFTER SUNSET...BUT ARE EXPECTED TO
DIMINISH OR DISSIPATE DUE THE LOSS OF DAYTIME HEATING AND THE LACK
OF SIGNIFICANT FORCING. A LARGE MID LVL RIDGE OF HIGH PRESSURE
WILL PERSIST OVER THE CENTRAL UNITED STATES WHILE A MID LVL TROUGH
OF LOW PRESSURE REMAINS POSITIONED DOWNSTREAM OFF THE NORTHEAST
COAST FOR THE REST OF TONIGHT. AT THE SFC...WEAK AREAS OF LOW
PRESSURE ALONG/NEAR A BOUNDARY POSITIONED OVER FLORIDA AND OFF THE
SOUTHEAST COAST WILL SLOWLY DRIFT NORTH/NORTHEAST OFFSHORE. THE
PATTERN WILL FAVOR A LIGHT ONSHORE WIND...WHICH WILL HELP BUILD
MOISTURE OVER THE AREA THROUGH TONIGHT. BY LATE TONIGHT...STRATUS
AND FOG WILL LIKELY FORM...WITH LATEST GUIDANCE SUGGESTING GREATER
COVERAGE OF FOG OVER SOUTHEAST GEORGIA. FOR THIS REASON...HAVE
MAINTAINED PATCHY FOG OVER ALL LAND ZONES...AND INTRODUCED AREAS
OF FOG OVER MUCH OF SOUTHEAST GEORGIA. LOW TEMPS WILL RANGE FROM
THE LOW TO MID 70S...WITH SOME UPPER 70S ALONG THE IMMEDIATE
COAST.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
WEDNESDAY AND WEDNESDAY NIGHT...ALOFT THE FORECAST AREA WILL REMAIN
POSITIONED BETWEEN THE CENTRAL CONUS RIDGE AND A BROAD TUTT-LIKE
FEATURE OFF THE SOUTHEAST COAST. AT THE SURFACE...A WEAK LOW WILL
SIT OFF THE SOUTHEAST COAST AND MAY EVEN EXTEND BACK INLAND ACROSS
SOUTH GEORGIA AT TIMES. OVERALL...THE MODELS HAVE A RATHER
LACKLUSTER PRECIPITATION AND CONVECTIVE RESPONSE IN THE AFTERNOON
AND EVENING THANKS TO THE PRESENCE OF AN INVERSION AND LOW LEVEL CAP
AROUND 800 MB. THE FURTHER INLAND AND WEST YOU GO...THE CAP IS
WEAKER WHICH SHOULD RESULT IN MORE COVERAGE ACROSS INTERIOR
SOUTHEAST GEORGIA. NO SIGNIFICANT CHANGES HAVE BEEN MADE TO POPS
WITH CHANCES WEST OF I-95 AND SLIGHT CHANCES ELSEWHERE. THE
THERMODYNAMIC ENVIRONMENT IS VERY UNIMPRESSIVE SO THE SEVERE WEATHER
THREAT IS QUITE MINIMAL. OVERNIGHT...THE MAIN CONCERN WILL BE FOR
POTENTIAL DEVELOPMENT OF FOG/STRATUS LATE. HIGHS WILL RANGE IN THE
LOW TO MID 90S...LOWS IN THE MID TO UPPER 70S.

THURSDAY THROUGH FRIDAY...THE UPPER PATTERN WILL TRANSITION AS THE
CENTRAL CONUS RIDGE PUSHES BACK TO THE WEST AND THE OFFSHORE
TROUGH/TUTT WILL DRIFT BACK TOWARD THE COAST. DEEP MOISTURE WILL
INCREASE...ESPECIALLY THURSDAY NIGHT THROUGH FRIDAY...AS EVIDENCED
BY PWATS RISING TO AROUND 2.25 INCHES BY FRIDAY AFTERNOON WHICH
WOULD BE AROUND THE 90TH PERCENTILE. FRIDAY WILL CERTAINLY BE THE
MORE ACTIVE DAY AS A COLD FRONT PUSHES INTO THE REGION FROM THE
WEST/NORTHWEST. LIKELY POPS ARE IN PLACE JUST ABOUT EVERYWHERE
FRIDAY AFTERNOON/EVENING...AND ADDITIONAL CONCERN WILL BE FOCUSED ON
THE POTENTIAL FOR LOCALLY HEAVY/EXCESSIVE RAINFALL. 1000-500 MB MEAN
FLOW WILL BE LESS THAN 10 KNOTS SO SLOW AND MINIMAL STORM MOVEMENT
COULD RESULT IN AREAS OF HEAVY RAIN ESPECIALLY IN THE PRESENCE OF
INCREASING DEEP LAYER MOISTURE. TEMPERATURES WILL BE ON A SLIGHT
COOLING TREND...WITH HIGHS IN THE LOW 90S BY FRIDAY.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AN UNSETTLED REGIME FEATURING ABOVE NORMAL POPS AND BELOW NORMAL
HIGH TEMPERATURES WILL PREVAIL THROUGH THIS PERIOD AS A DEEP TROUGH
OF LOW PRESSURE/AN ASSOCIATED PLUME OF ENHANCED MOISTURE/HIGH PWATS
RESIDES OVER THE REGION. SEVERAL FACTORS REDUCE CONFIDENCE REGARDING
FORECAST DETAILS...MAINLY RELATED TO THE STRENGTH OF THE BERMUDA
HIGH AND THE INTERACTION OF THE ATLANTIC RIDGE WITH THE TROUGH OVER
THE SOUTHEAST. IF THE ATLANTIC RIDGE DOES NOT STRENGTHEN...THE
TROUGH AND DEEPEST MOISTURE REMAIN OVER THE REGION OR EVEN PUSH
SLIGHTLY OFFSHORE AS DEPICTED BY THE 28/00Z OPERATIONAL EUROPEAN. ON
THE OTHER HAND...IF THE BERMUDA HIGH EXPANDS...THE TROUGH AND DEEPER
MOISTURE COULD BE SHUNTED INLAND...SUPPORTING A SUBTLE WARMING/DRYING
TREND ESPECIALLY EARLY NEXT WEEK. DUE TO UNCERTAINTY REGARDING THE
SYNOPTIC SCENARIO AND THE USUAL MESOSCALE UNCERTAINTY REGARDING
CONVECTION EVOLUTION...CONTINUED TO CAP MAXIMUM POPS AROUND 50
PERCENT THIS WEEKEND INTO EARLY NEXT WEEK. EVENTUALLY... PERIODS
OF HIGHER POPS WILL LIKELY BE REQUIRED FOR SOME OR ALL OF THE
FORECAST AREA.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
VFR CONDITIONS WILL PREVAIL AT THE CHS AND SAV TERMINALS THROUGH
EARLY TONIGHT. MVFR CONDITIONS ARE LIKELY AT BOTH TERMINALS LATE
TONIGHT INTO EARLY WEDNESDAY MORNING...MAINLY DUE TO FOG. HAVE
MAINTAINED 4SM BR BETWEEN 08Z- 13Z AT BOTH TERMINALS. THERE IS
ALSO A LOW TO MODERATE CHANCE OF TEMPO IFR CONDITIONS OCCURRING
BETWEEN 09Z-13Z...WITH THE GREATEST CHANCE OCCURRING AT THE SAV
TERMINAL. VFR CONDITIONS SHOULD QUICKLY RETURN AT BOTH TERMINALS
BETWEEN 13-14Z WEDNESDAY AND PERSIST INTO THE AFTERNOON.

EXTENDED AVIATION OUTLOOK...FOG/STRATUS WILL BE POSSIBLE EACH MORNING
THROUGH THE END OF THE WEEK. LOW CHANCE FOR DIRECT IMPACTS FROM
THUNDERSTORMS WEDNESDAY AND THURSDAY...THEN INCREASING THUNDERSTORM
CHANCES FRIDAY THROUGH THE WEEKEND.

&&

.MARINE...
TONIGHT...WINDS/SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY LEVELS
AS WEAK LOW PRESSURE PERSISTS OFFSHORE. IN GENERAL...EAST WINDS WILL
BECOME NORTHEAST OVERNIGHT AND REMAIN AT OR BELOW 10 KTS. SEAS WILL
RANGE BETWEEN 1-3 FT...HIGHEST IN NORTHERN SC WATERS AND OFFSHORE
GEORGIA WATERS.

WEDNESDAY THROUGH SUNDAY...ONSHORE WINDS WILL PERSIST WEDNESDAY
THROUGH THURSDAY WITH SOME ENHANCEMENT OCCURRING WITH THE AFTERNOON
SEABREEZE. WINDS WILL THEN GRADUALLY BECOME MORE SOUTH/SOUTHWEST
THROUGH THE WEEKEND AS A COLD FRONT APPROACHES FROM THE WEST. SPEEDS
WILL GENERALLY BE LESS THAN 15 KNOTS...WITH PERIODIC INCREASES INTO
THE 15-20 KNOT RANGE WITHIN NOCTURNAL SURGES AND ALONG THE LAND/SEA
INTERFACE WITH THE SEA BREEZE. SEAS WILL BE 3 FEET OR LESS THROUGH
THE REST OF THE WEEK...THEN 2-4 FEET OVER THE WEEKEND.

&&

.TIDES/COASTAL FLOODING...
CURRENT EXTRATROPICAL SURGE GUIDANCE TAKES TIDE LEVELS NEAR 7.0 FT
MLLW IN THE CHARLESTON HARBOR FOR HIGH TIDE THIS EVENING...WHICH
OCCURS AT 628 PM. A COASTAL FLOOD ADVISORY COULD BE NEEDED FOR PARTS
OF THE SOUTHEAST SOUTH CAROLINA COAST IF THIS TREND CONTINUES...BUT
THE EVENT LOOKS VERY MARGINAL AT BEST. IF TIDE LEVELS DO NOT REACH
7.0 FT MLLW IN THE CHARLESTON HARBOR...THERE COULD STILL BE SOME
VERY MINOR SALT WATER INUNDATION FOR SOME OF THE NORMALLY FLOOD
PRONE AREAS OF DOWNTOWN CHARLESTON.

ELEVATED HIGH TIDE LEVELS ARE EXPECTED THROUGH THE REST OF THE WEEK
AND THE 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 WITH THE EVENING HIGH TIDE CYCLE. WILL MAINTAIN
THE MENTION IN THE HAZARDOUS WEATHER OUTLOOK.

&&

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

&&

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


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