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Area Forecast Discussion

150
FXUS62 KCHS 280719
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
319 AM EDT TUE JUL 28 2015

.SYNOPSIS...
THE REGION WILL REMAIN SITUATED BETWEEN WEAK HIGH PRESSURE TO THE
NORTH AND LOW PRESSURE TO THE SOUTH UNTIL LATE THIS WEEK.
THEN...BROAD LOW PRESSURE WILL DEVELOP AND WILL PERSIST OVER THE
REGION LATE THIS WEEK INTO EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
THROUGH SUNRISE...CONDITIONS APPEAR SIMILAR TO YESTERDAY MORNING
WHERE WIDESPREAD DENSE FOG AFFECTED MUCH OF SOUTHEAST SOUTH
CAROLINA. SATELLITE DATA SHOW HIGH CLOUDS POISED TO CLEAR
SOUTHEAST GEORGIA VERY SOON...WHILE DEBRIS CLOUDINESS ASSOCIATED
WITH ONGOING CONVECTION OVER THE SOUTHERN FOOTHILLS OF NORTH
CAROLINA IS BEGINNING TO PROPAGATE INTO THE CHARLESTON TRI-COUNTY
AREA. THE LATEST RAP AND NAM12 1000MB CONDENSATION PRESSURE
DEFICIT PROGS SUGGEST THE MOST LIKELY AREA FOR SIGNIFICANT FOG TO
FORM WILL BE OVER SOUTHEAST GEORGIA...ESPECIALLY SOUTH OF THE I-16
CORRIDOR. THIS SEEMS REASONABLE GIVEN THE LACK OF CLOUD COVER AND
THERE ARE ALREADY SIGNALS OF LOW STRATUS BEGINNING TO DEVELOP.
WHILE SOME FOG IS LIKELY ACROSS SOUTHEAST SOUTH CAROLINA...INCOMING
DEBRIS CLOUDINESS COULD TEMPER THE COVERAGE THERE SOMEWHAT. WILL
CONTINUE TO HIGHLIGHT AREAS OF FOG IN THE GRIDDED AND TEXT
FORECASTS THROUGH SUNRISE. A DENSE FOG ADVISORY MAY VERY WELL BE
NEEDED FOR PARTS OF THE AREA OVER THE COMING HOURS.

THE KCLX RADAR IS PINNING LIGHT RETURNS OFF THE SOUTHERN SOUTH
CAROLINA COAST. THIS ACTIVITY IS LIKELY MILITARY CHAFF AND NOT
HYDROMETEORS PER DUAL-POL MULTI-LAYER CORRELATION COEFFICIENT
PRODUCTS. ISOLATED SHOWERS CONTINUE TO PERCOLATE OFF THE GEORGIA
COAST NEAR WEAK LOW PRESSURE.

TODAY...THE REGION WILL REMAIN ALONG THE FAR EASTERN PERIPHERY OF
A LARGE ANTICYCLONE CENTERED OVER THE CENTRAL PLAINS WITH AN
ADJACENT MID-LEVEL TROUGH POSITIONED WELL OFFSHORE OVER THE
SOUTHWEST ATLANTIC. AS THE SURFACE...DUAL LOW PRESSURE AREAS ARE
NOTED ALONG A BROAD SURFACE TROUGH THAT EXTENDS FROM THE EASTERN
GULF OF MEXICO...THROUGH CENTRAL FLORIDA AND INTO THE GULF STREAM
OFF THE SOUTH CAROLINA/GEORGIA COASTS. THE LOW CENTERS WILL REMAIN
ILL-DEFINED TODAY AND LIKELY DISSIPATE AT SOME POINT DURING THE
NEXT 12 HOURS AS THE SURFACE TROUGH LINGERS. IT WILL BE ANOTHER
HOT AND MUGGY DAY FOR THE LOWCOUNTRY AND COASTAL EMPIRE WITH ONLY
ISOLATED SHOWERS/TSTMS EXPECTED TO DEVELOP THIS AFTERNOON. LOW-
LEVEL CONVERGENCE ALONG THE SEA BREEZE WILL BE RATHER WEAK SO ANY
CONVECTION SHOULD DEVELOP FARTHER INLAND COMPARED TO YESTERDAY
AFTERNOON. TWENTY PERCENT POPS LOOK REASONABLE IN THIS SYNOPTIC
REGIME AND MAINLY CONFINED TO AREAS WEST OF THE I-95 CORRIDOR.
HIGHS WILL RANGE FROM THE MID-UPPER 90S INLAND TO THE UPPER 80S-
LOWER 90S AT THE COAST WITH MID 80S AT THE BEACHES. HEAT INDICES
WILL APPROACH 103-106 IN A FEW LOCATIONS THIS AFTERNOON WHICH IS
BELOW THE HEAT ADVISORY CRITERIA OF 110.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
TONIGHT...CUMULUS WILL DISSIPATE QUICKLY AFTER SUNSET WITH ONLY
CIRRUS EXPECTED TO TRAVERSE THE SKY THROUGH THE NIGHT. SOME
STRATOCUMULUS WILL LIKELY LINGER OVER THE COAST WITH THE ONSHORE
FLOW. SOME FOG AND STRATUS IS LIKELY FORM AGAIN EARLY WEDNESDAY
MORNING...BUT ITS POTENTIAL SEVERITY IS A BIT UNKNOWN THIS FAR
OUT...ESPECIALLY GIVEN THE MODELS HAVE BEEN PERFORMING WELL BELOW
AVERAGE ON CAPTURE FOG TRENDS. LOWS WILL RANGE FROM THE LOWER 70S
INLAND TO THE MID 70S AT THE COAST WITH UPPER 70S/NEAR 80 AT THE
BEACHES AND DOWNTOWN CHARLESTON.

WEDNESDAY MORNING...ANY FOG/STRATUS WILL GIVE WAY TO PARTLY SUNNY
CONDITIONS. THEN...ISOLATED/SCATTERED DIURNAL THUNDERSTORMS ARE
EXPECTED TO DEVELOP DURING THE AFTERNOON AS A CHANNEL OF
VORTICITY/DEFORMATION ON THE EASTERN PERIPHERY OF AN INLAND UPPER
RIDGE INTERACTS WITH THE SEA BREEZE. POPS ARE GRADUATED FROM SLIGHT
CHANCE NEAR THE COAST TO CHANCE ALONG/WEST OF I-95 WHERE HIGHER
PWATS WILL RESIDE. OTHERWISE...EXPECT HIGH TEMPERATURES IN THE
LOWER/MID 90S INLAND AND 80S ALONG THE IMMEDIATE COAST.

WEDNESDAY NIGHT...DIURNAL CONVECTION SHOULD DISSIPATE OVER
LAND...ALTHOUGH THE GFS MAINTAINS CONVECTION NEAR THE COAST INTO THE
OVERNIGHT HOURS. MEANWHILE...MODEL SOUNDINGS AND THE 28/00Z NAM PROG
OF 1000 MB PRESSURE CONDENSATION DEFICITS SUGGESTS THAT FOG/STRATUS
COULD DEVELOP. TEMPERATURES SHOULD BOTTOM OUT IN THE LOWER TO MID
70S INLAND AND 75-80F CLOSE TO THE COAST.

EXPECT A SIMILAR REGIME THURSDAY. ANY MORNING FOG/STRATUS WILL GIVE
WAY TO PARTLY SUNNY SKIES...AND ISOLATED/SCATTERED DIURNAL
SHOWERS/THUNDERSTORMS SHOULD AGAIN DEVELOP ESPECIALLY DURING THE
AFTERNOON/EARLY EVENING. ACCOUNTING FOR THE EAST/WEST MOISTURE
GRADIENT WHICH SHOULD PERSIST ACROSS THE REGION...POPS ARE TAPERED
FROM SLIGHT CHANCE ALONG THE COAST TO CHANCE INLAND. OTHERWISE...
EXPECT HIGH TEMPS IN THE LOWER/MID 90S INLAND AND 80S ON THE
BEACHES.

THE POTENTIAL FOR STRATUS/FOG COULD DIMINISH THURSDAY NIGHT.
OTHERWISE...DIURNAL/EVENING CONVECTION SHOULD GRADUALLY DISSIPATE.
DESPITE THE 28/00Z GFS DEPICTION OF PERSISTENT CONVECTION
OVERNIGHT...LOWERED POPS BELOW 15 PERCENT WITH NO MENTION OF
PRECIPITATION OVER LAND AFTER MIDNIGHT.

PER LATEST MODEL TRENDS...FRIDAY SHOULD PROVE TO BE THE MOST
CONVECTIVELY ACTIVE DAY OF THIS FORECAST PERIOD. A TROUGH AT THE
SURFACE AND ALOFT WILL BEGIN TO TAKE SHAPE OVER THE REGION...AND A
PLUME OF DEEP MOISTURE FEATURING PWATS WELL OVER 2 INCHES/1 TO 2
STANDARD DEVIATIONS ABOVE NORMAL WILL SAG INTO THE REGION FROM THE
NORTH. THIS REGIME SHOULD READILY SUPPORT AT LEAST SCATTERED/
NUMEROUS SHOWERS/THUNDERSTORMS FRIDAY AFTERNOON. IN GENERAL...LATEST
GUIDANCE POINTS TO HIGHEST POPS ACROSS INTERIOR/NORTHERN
COUNTIES...THUS INTRODUCED LIKELY POPS THERE FRIDAY AFTERNOON.
HOWEVER...THIS SCENARIO WILL LIKELY CHANGE OVER THE NEXT FEW DAYS.
MEANWHILE...FRIDAY TEMPERATURES ARE TRICKY DUE TO UNCERTAINTY
REGARDING THE TIMING OF CONVECTION INITIATION. THUS...DID NOT MAKE
SIGNIFICANT CHANGES TO ONGOING TEMPERATURES IN THE LOWER/MID 90S
INLAND AND 80S ALONG THE COAST...BUT CONVECTION/ASSOCIATED CLOUD
COVER COULD GREATLY ALTER MIDDAY/AFTERNOON TEMPERATURES.

THE POTENTIAL FOR SEVERE WEATHER/LOCALLY HEAVY RAINFALL APPEARS
LIMITED WITHIN DIURNAL CONVECTION WEDNESDAY AND THURSDAY.
FRIDAY...THE POTENTIAL FOR SEVERE WEATHER SHOULD INCREASE...ALTHOUGH
FORECAST INSTABILITY IS NOT OVERLY IMPRESSIVE. OF GREATER
CONCERN...HIGH PWATS AND WEAK TROPOSPHERIC FLOW COULD PROMOTE
LOCALLY EXCESSIVE RAINFALL BEGINNING FRIDAY. IN PARTICULAR...
IF HEAVY RAIN FALLS ALONG THE COAST DURING ELEVATED HIGH TIDES...
THE POTENTIAL FOR LOCALIZED FLOODING COULD BE ENHANCED.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
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 /06Z TUESDAY THROUGH SATURDAY/...
THE PRIMARY CONCERN IS FOG/STRATUS THROUGH SUNRISE. CONDITIONS
APPEAR SIMILAR TO YESTERDAY MORNING WHERE DENSE FOG WAS FAIRLY
WIDESPREAD. LATEST HIGH RESOLUTION GUIDANCE FAVORS KSAV FOR THE
HIGHER PROBABILITIES FOR IFR OR LOWER CONDITIONS PRIOR TO
SUNRISE...ASSUMING A BATCH OF MID-LEVEL CLOUDS MOVES INTO THE KCHS
AREA AS EXPECTED. WILL GO AHEAD AND SHOW PREVAILING LOW-END MVFR
VSBYS 09-1330Z WITH TEMPO IFR FROM 10-12Z...BUT WILL NOT ESTABLISH
CIGS ATTM. AT KCHS...WILL KEEP CONDITIONS LOW-END MVFR. AMENDMENTS
WILL MOST CERTAINLY BE NEEDED THROUGHOUT THE EARLY MORNING AS
TRENDS BECOME MORE APPARENT. VFR WILL PREVAIL ONCE ANY FOG/STRATUS
MIXES OUT BY 13-14Z. ONLY ISOLATED SHOWERS AND TSTMS EXPECTED
TUESDAY AFTERNOON. COVERAGE TOO LOW TO JUSTIFY ANY MENTION IN THE
00Z TAFS.

EXTENDED AVIATION OUTLOOK...FLIGHT RESTRICTIONS WILL BE POSSIBLE IN
STRATUS/FOG WEDNESDAY MORNING. A LOW PROBABILITY FOR FLIGHT
RESTRICTIONS EXISTS WITHIN AFTERNOON THUNDERSTORMS WEDNESDAY AND
THURSDAY. THE PROBABILITY FOR THUNDERSTORMS/ASSOCIATED FLIGHT
RESTRICTIONS WILL INCREASE FRIDAY AND SATURDAY.

&&

.MARINE...
TODAY...PATCHY FOG IS POSSIBLE IN THE CHARLESTON HARBOR THIS
MORNING. APPROACHING DEBRIS CLOUDINESS SHOULD KEEP THE FOG IN
CHECK...BUT TRENDS WILL BE MONITORED. A MORE UNIFORM EAST FLOW
IS EXPECTED TO DEVELOP BY THIS AFTERNOON AS THE SEA BREEZE
DEVELOPS AND WEAK LOW PRESSURE PASSES OFF TO THE EAST. WINDS LOOK
TO REMAIN 10 KT OR LESS WITH SEAS AVERAGING 2-3 FT.

TONIGHT...EAST WINDS WILL TIP BACK TO THE NORTHEAST OVERNIGHT WITH
SPEEDS AROUND 5 KT. SEAS WILL AVERAGE 2-3 FT...EXCEPT 1-2 FT OVER
THE GEORGIA NEARSHORE WATERS.

WEDNESDAY THROUGH SUNDAY...ONSHORE WINDS WILL PERSIST WEDNESDAY
THROUGH THURSDAY...WITH SOME ENHANCEMENT OCCURRING DURING
AFTERNOON SEABREEZE CIRCULATIONS. IN GENERAL...WINDS WILL REMAIN
AT OR BELOW 15 KTS WITH SEAS NO HIGHER THAN 2-4 FT...HIGHEST
BEYOND 20 NM. AFTER A TRANSITION THROUGH A WEAK PRESSURE PATTERN
THURSDAY NIGHT AND FRIDAY...WINDS SHOULD BECOME SOUTH/SOUTHWEST BY
THIS WEEKEND...PERHAPS INCREASING TO 15-20 KT IN SOME AREAS WITH
THE AFTERNOON SEABREEZE AND WITH NOCTURNAL SURGES. SEAS SHOULD
REMAIN BETWEEN 2-4 FT NEARSHORE AND 4-5 FT BEYOND 20 NM THIS
WEEKEND. THUNDERSTORMS COULD PRODUCE LOCAL HAZARDS AND COULD
GREATLY ALTER SYNOPTIC WINDS ESPECIALLY LATE WEEK THROUGH THIS
WEEKEND.

&&

.TIDES/COASTAL FLOODING...
TIDAL DEPARTURES ARE EXPECTED TO HOLD FAIRLY STEADY FOR THE NEXT
12 HOURS OR SO. CURRENT EXTRATROPICAL SURGE GUIDANCE TAKE TIDE
LEVELS VERY NEAR 7.0 FT MLLW IN THE CHARLESTON HARBOR FOR HIGH
TIDE THIS EVENING...WHICH IS THE THRESHOLD FOR SHALLOW COASTAL
FLOODING FOR THE LOWER SOUTH CAROLINA COAST. A COASTAL FLOOD
ADVISORY MAY BE NEEDED FOR PARTS OF THE LOWER SOUTH CAROLINA COAST
IF THIS TREND CONTINUES...BUT THE EVENT LOOKS MARGINAL AT BEST.
EVEN IF TIDE LEVELS DO NOT REACH 7.0 FT MLLW IN THE CHARLESTON
HARBOR...SOME VERY MINOR SALT WATER INUNDATION IS LIKELY TO OCCUR
IN SOME OF THE NORMALLY FLOOD PRONE AREAS OF DOWNTOWN CHARLESTON...
ASSUMING LEVELS SURPASS 6.8 FT MLLW. THERE ARE NO CONCERNS FOR
SHALLOW COASTAL FLOODING ALONG THE GEORGIA COAST WITH THIS
EVENING/S HIGH TIDE CYCLE.

ELEVATED HIGH TIDE LEVELS WILL PREVAIL THROUGH THIS WEEKEND/INTO
EARLY NEXT WEEK DUE TO THE UPCOMING JULY 31 FULL MOON/AUGUST 2
PERIGEE AND PERSISTENT ONSHORE WINDS. EXTRATROPICAL SURGE GUIDANCE
CONTINUES TO FORECAST A SERIES OF SHALLOW SALT WATER FLOODING
EVENTS...ESPECIALLY AROUND THE TIMES OF THE EVENING HIGH TIDES.
EVENING HIGH TIDES COULD ATTAIN COASTAL FLOOD ADVISORY LEVELS ALONG
THE SOUTH CAROLINA COAST WEDNESDAY INTO EARLY NEXT WEEK AND ALONG
THE GEORGIA COAST WEDNESDAY OR THURSDAY THROUGH AT LEAST THIS
WEEKEND. WILL CONTINUE TO HIGHLIGHT THE POTENTIAL FOR SHALLOW SALT
WATER FLOODING/COASTAL FLOOD ADVISORIES WITHIN THE HAZARDOUS WEATHER
OUTLOOK.

&&

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

&&

$$

ST/SPR



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