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Area Forecast Discussion

889
FXUS62 KCHS 180839
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
439 AM EDT FRI APR 18 2014

.SYNOPSIS...
LOW PRESSURE WILL TRACK FROM THE GULF OF MEXICO TODAY TO A POSITION
OFF THE GEORGIA COAST LATE SATURDAY THEN WILL ADVANCE OFFSHORE SUNDAY.
THIS LOW WILL PRODUCE A SOAKING RAIN ACROSS THE REGION. HIGH PRESSURE
WILL BRIEFLY BUILD INTO THE REGION MONDAY. A WEAKENING COLD FRONT WILL
PUSH THROUGH THE AREA BY WEDNESDAY...FOLLOWED BY HIGH PRESSURE AND WARMER
TEMPERATURES THROUGH LATE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
PRE-DAWN...HIGH CLOUDS HAVE BEEN THICKENING OVERNIGHT. THE CLOUD
COVERAGE AND STEADY ONSHORE FLUX IN THE BOUNDARY LAYER HAS LEVELED
TEMPS OUT IN THE MID TO UPPER 50S MANY AREAS...QUITE A BIT MILDER
THAN 24 HOURS AGO. DEEP MOISTURE WAS INVADING FLORIDA AND SW GEORGIA
AS MID/UPPER FLOW STRENGTHENING AND BACKING IN RESPONSE TO A STRONG
AND ELONGATED SHORT WAVE DIGGING THROUGH THE ARKLATEX EARLY THIS
MORNING. WE CONTINUE TO ADVERTISE A CHANCE OF RAIN TO THE SOUTH OF
I-16 TOWARD DAYBREAK OTHERWISE MOST WILL SEE DRY WEATHER TO START
THE DAY.

THE SYNOPTIC PLAYERS IN PLACE THIS MORNING INCLUDE THE SURFACE
WEDGE SOLIDLY ANCHORED IN AND DEVELOPING LOW PRESSURE OVER THE
NORTHERN GULF OF MEXICO. DEEP CONVECTION HAD ERUPTED OVER THE GULF
OF MEXICO WITH IR SATELLITE TOPS COOLING ACROSS THE EASTERN GULF
COAST REGION AS DEEP MOISTURE AND INCREASING UPPER DYNAMICS MINGLE
TO THE SW OF OUR REGION. CYCLOGENESIS UNDERWAY ACROSS THE NORTHERN
GULF REGION WITH EXCELLENT MODEL CONSENSUS THAT MERGING MID LEVEL
SHORT WAVE ENERGY WILL CUT-OFF A MID LEVEL LOW OVER/NEAR THE
FLORIDA PANHANDLE BY THIS EVENING.

RAINS WILL INCREASE TODAY FROM SOUTHERN GEORGIA THIS MORNING INTO
SOUTHERN SOUTH CAROLINA AFTER MID AFTERNOON AND INTO THE CHARLESTON
AREA LATER IN THE AFTERNOON. THE GFS/ECMWF CONTINUE TO INDICATE
IMPRESSIVE UPPER DIFLUENCE...STRONG ISENTROPIC ASCENT AND DEEP
OMEGA TAKING SHAPE OVER THE FORECAST AREA WHILE PWATS RISE OVER
1.75 INCHES. THE FORECAST NEEDED ONLY SLIGHT TIMING ADJUSTMENTS
TO THE ONSET OF THE PCPN TODAY OTHERWISE...RAIN...HEAVY AT TIMES
SPREADING THROUGH THE FORECAST AREA WITH CATEGORICAL POPS.

THE DECISION TO ISSUE A FLOOD WATCH FOR PORTIONS OF OUR AREA WAS A
DIFFICULT ONE AND DRIVEN NOT SO MUCH ON CONCERNS FOR RAINS EXCEEDING
4 INCHES IN TOO MANY AREAS...BUT MORE-SO DUE TO THE COINCIDENCE OF
THE HEAVY RAINS WITH A HIGH ASTRONOMICAL TIDE CYCLE COMING UP
THIS EVENING. AREAS OF SOUTHEAST GEORGIA AROUND LUDOWICI ALSO
RECEIVED 2 TO 3 INCHES OF RAIN WITH THE LAST EVENT. THE GFS HAS
BEEN SHOWING SOME OF THE DEEPEST OMEGA IN RECENT MEMORY ON
TIME/HEIGHT CROSS-SECTIONS FOR SEVERAL DAYS AND THE FORCING AND
DEEP MOISTURE TANDEM REMAINS EXTREMELY IMPRESSIVE.

LATE TONIGHT...RAINS COULD BEGIN TO TAPER OFF FROM THE SOUTH LATE
TONIGHT AS THE UPPER LOW TAKES BETTER DEFINITION AND A DRY SLOT
BEGINS TO PUNCH IN FORM THE SW. THE COASTAL FRONT MAY NUDGE CLOSE
TO THE COAST LATE AND WE RAISED LOW TEMPS AT BIT ALONG AND EAST OF
I-95 TONIGHT.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
SATURDAY...THE DEEP UPPER LOW AND ASSOCIATED SURFACE LOW WILL
CONTINUE TO ADVANCE TOWARD THE EAST/NORTHEAST. WITH THE EXCEPTION OF
THE 18/00 UTC NAM...GUIDANCE DEPICTS A MARKED DRY SLOT PUNCHING INTO
THE FORECAST AREA IN THE MORNING FOLLOWED BY THE ONSET OF DEEP LAYER
WRAP-AROUND MOISTURE DURING THE AFTERNOON. THIS SCENARIO SUGGESTS A
TEMPORARY LULL IN PRECIPITATION COVERAGE DURING THE MORNING FOLLOWED
BY INCREASING PRECIPITATION COVERAGE DURING THE AFTERNOON. THE
EVENTUAL EXTENT OF WRAP-AROUND PRECIPITATION COVERAGE REMAINS
SOMEWHAT UNCERTAIN DEPENDING ON THE TRACK OF THE UPPER LOW. GIVEN
THE MOST LIKELY JUXTAPOSITION OF WRAP-AROUND MOISTURE AND
DEFORMATION ENHANCED BY THE UPPER LOW JUSTIFIES LIKELY POPS SATURDAY
AFTERNOON/EVENING ACROSS NORTHERN/EASTERN COUNTIES...TAPERED TO
HIGH-END CHANCE POPS SOUTH/WEST. ALSO OF NOTE...DUE TO STEEPENING
MID-LEVEL LAPSE RATES/ELEVATED INSTABILITY ASSOCIATED WITH THE UPPER
LOW ADDED A SLIGHT CHANCE OF THUNDER SATURDAY/SATURDAY EVENING.

HIGH TEMPERATURES SATURDAY REMAIN UNCERTAIN...IN THE 60S MOST
LOCATIONS BUT PERHAPS PUSHING INTO THE LOWER 70S SOUTH DEPENDING ON
THE TRACK OF THE SURFACE LOW AND PROGRESS OF THE ASSOCIATED WARM
FRONT.

SATURDAY NIGHT INTO SUNDAY...FORCING FOR ASCENT WITHIN COMMA FEATURE
OVER FORECAST AREA WILL GRADUALLY RELAX WITH TIME AS THE UPPER LOW
ADVANCES OFFSHORE. THUS...POPS SHOULD GRADUALLY DIMINISH ALTHOUGH
TIMING OF LOWERING POPS REMAINS UNCERTAIN. THE LATEST FORECAST
TRANSITIONS FROM CHANCE/LIKELY POPS SATURDAY EVENING TO SLIGHT
CHANCE/CHANCE POPS SUNDAY AFTERNOON. ALSO...SUNDAY WILL BE A
BREEZY/WINDY DAY AS THE N/NW GRADIENT TIGHTENS BETWEEN OFFSHORE LOW
PRESSURE AND INLAND HIGH PRESSURE. TEMPERATURES SUNDAY AFTERNOON
WILL TOP OUT IN THE UPPER 60S/LOWER 70S...STILL BELOW NORMAL FOR
MID-APRIL.

EXPECT MORE TRANQUIL CONDITIONS MONDAY...INCLUDING MORE SUNSHINE AND
DIMINISHING WIND. TEMPERATURES WILL TOP OUT IN THE 70S...CLOSE TO
NORMAL.

LAKE WINDS...GUSTY WINDS WILL LIKELY PROMPT A LAKE WIND ADVISORY
SATURDAY NIGHT/EARLY SUNDAY THROUGH SUNDAY NIGHT/EARLY MONDAY.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
A TROUGH AT THE SURFACE AND ALOFT AND AN ASSOCIATED BAND OF ENHANCED
MOISTURE WILL ADVANCE THROUGH THE REGION TUESDAY AFTERNOON INTO
TUESDAY NIGHT. MOISTURE IS NOT IMPRESSIVE...BUT AT LEAST SLIGHT
CHANCE POPS ARE JUSTIFIED. THEN...SURFACE HIGH PRESSURE WILL SUPPORT
RAIN-FREE CONDITIONS AND TEMPERATURES IN THE UPPER 70S/LOWER 80S
WEDNESDAY/THURSDAY.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
LOW CLOUDS WILL EXPAND AND SLOWLY MOVE NORTH LATE TONIGHT INTO
FRIDAY AS LOW PRESSURE APPROACHES FROM THE SOUTH. SUSPECT MODEL
GUIDANCE IS TOO QUICK IN BRINGING MVFR CIGS INTO BOTH TERMINALS
OVERNIGHT...ESPECIALLY AT KCHS. MAINTAINED A SLIGHTLY SLOWER
SOLUTION WITH MVFR CIGS REACHING KSAV PRIOR TO DAYBREAK. KEPT KCHS JUST
ABOVE MVFR FOR NOW. AN EXPANSIVE AREA OF RAIN WILL MOVE SOUTH-
NORTH DURING THE DAY FRIDAY. EXPECT PREVAILING RAINS TO REACH KSAV
BY MID AFTERNOON...ROUGHLY 18Z-19Z WITH PREVAILING RAINFALL NOT
REACHING KCHS UNTIL VERY LATE IN THE DAY. MVFR/IFR CONDITIONS
EXPECTED IN THE 00Z-06Z TIME FRAME SATURDAY...BOTH CIGS AND VSBYS
IN RAIN.

EXTENDED AVIATION OUTLOOK...FLIGHT RESTRICTIONS INTO SUNDAY. VFR
THEREAFTER. GUSTY WINDS POSSIBLE SUNDAY.

&&

.MARINE...
THE GRADIENT WILL REMAIN PINCHED THROUGH TONIGHT WITH SOME RELAXATION
OF THE GRADIENT LATER TONIGHT AS THE COASTAL FRONT NUDGES FURTHER
TOWARD THE COAST. A SOLID SMALL CRAFT ADVISORY REMAINS IN EFFECT
FOR ALL WATERS INCLUDING THE CHARLESTON HARBOR FOR NE FLOW 20 TO
25 KT WITH GUSTS TO 30 KT LOCALLY. SEAS 5-7 FT NEAR SHORE AND 7 TO
10 FT WELL OFF THE GEORGIA COAST TODAY.

SMALL CRAFT ADVISORY CONDITIONS WILL REMAIN COMMON SATURDAY...THEN
GALES ARE POSSIBLE SATURDAY NIGHT/EARLY SUNDAY INTO SUNDAY NIGHT AS
THE GRADIENT TIGHTENS BETWEEN OFFSHORE LOW PRESSURE AND INLAND HIGH
PRESSURE. CONDITIONS SHOULD THEN GRADUALLY IMPROVE MONDAY AND MONDAY
NIGHT...AND WIND/SEAS ARE THEN EXPECTED TO REMAIN BELOW SCA
THRESHOLDS TUESDAY THROUGH MIDWEEK.

RIP CURRENTS...MODERATE TO HIGH RISK TODAY...HIGHEST ALONG THE
GEORGIA COAST. AN ENHANCED RISK FOR RIP CURRENTS WILL PERSIST
THROUGH THE WEEKEND AND PERHAPS INTO EARLY NEXT WEEK.

&&

.HYDROLOGY...
PLENTY OF MOISTURE AND FORCING FOR WIDESPREAD MODERATE TO HEAVY
RAINFALL THIS AFTERNOON THROUGH TONIGHT. A FLOOD WATCH HAS BEEN
ISSUED FOR MAINLY COASTAL AREAS COINCIDENT WITH THE HIGH TIDE
THIS EVENING BUT LOCALIZED FLOODING FURTHER INLAND IS CERTAINLY
POSSIBLE AS STORM TOTAL RAINFALL LIKELY BETWEEN 2 AND 4 INCHES
MAINLY AREAS.

MAIN STEM RIVERS AND ASSOCIATED TRIBUTARIES WILL LIKELY SEE
SIGNIFICANT RISES WITH THE POTENTIAL FOR MINOR FLOODING DEPENDING
ON OBSERVED RAINFALL AMOUNTS.

&&

.TIDES/COASTAL FLOODING...
TIDES WILL CONTINUE TO RUN HIGH THROUGH THE WEEKEND AND COASTAL
FLOOD ADVISORIES COULD BE NEEDED DURING THE NIGHTTIME HIGH TIDE
CYCLES. GIVEN THE TIDE DEPARTURES THE PAST COUPLE OF NIGHTS AND
THE POOR PERFORMANCE OF THE GFS EXTRATROPICAL PREDICTIONS...IT IS
LOOKING MORE LIKELY THAT AN ADVISORY WILL BE ISSUED TONIGHT ALONG
THE SOUTH CAROLINA COAST AND PERHAPS AT FORT PULASKI.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...FLASH FLOOD WATCH FROM 2 PM EDT THIS AFTERNOON THROUGH LATE
     TONIGHT FOR GAZ114>119-137>141.
     HIGH RISK FOR RIP CURRENTS THROUGH THIS EVENING FOR GAZ117-119-
     139-141.
SC...FLASH FLOOD WATCH FROM 2 PM EDT THIS AFTERNOON THROUGH LATE
     TONIGHT FOR SCZ048>051.
     HIGH RISK FOR RIP CURRENTS THROUGH THIS EVENING FOR SCZ048-049-
     051.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 AM EDT MONDAY FOR AMZ350-352.
     SMALL CRAFT ADVISORY UNTIL 6 AM EDT MONDAY FOR AMZ330-354.
     SMALL CRAFT ADVISORY UNTIL 5 AM EDT TUESDAY FOR AMZ374.

&&

$$

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






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