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Area Forecast Discussion

269
FXUS62 KCHS 021142
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
742 AM EDT WED SEP 2 2015

.SYNOPSIS...
A WEAK TROUGH OF LOW PRESSURE WILL PERSIST OVER THE SOUTHEAST
THROUGH LATE WEEK. THIS WEEKEND...HIGH PRESSURE WILL PUSH A COLD
FRONT SOUTH OF THE REGION AND WILL BUILD INTO THE AREA FROM THE
NORTH...AND LOW PRESSURE COULD DEVELOP OFF THE SOUTHEAST COAST.
THE REGION WILL THEN REMAIN SITUATED BETWEEN INLAND HIGH PRESSURE
AND OFFSHORE LOW PRESSURE INTO THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
TODAY THE SMALL KNOT OF VORTICITY AND DEEP LAYERED MOISTURE POOL
MAXIMA ACROSS THE FLORIDA PANHANDLE IS FORECAST TO LIFT N TO NE
INTO SOUTH GEORGIA. SCATTERED SHOWERS AND PERHAPS ISOLATED TSTMS
ARE EXPECTED TO EXPAND IN COVERAGE ACROSS SOUTH GEORGIA LATER THIS
MORNING ONCE WE BEGIN TO SEE SOME DIFFERENTIAL HEATING BOUNDARIES
SET UP ACROSS SOUTH CENTRAL AND EAST CENTRAL GEORGIA. THIS WEAK
DISTURBANCE IS FORECAST TO STRETCH MORE WEST TO EAST THROUGH
TONIGHT NUDGED ALONG A BIT BY THE SHORT WAVE MOVING SE FROM THE
OHIO VALLEY TO THE MID ATLC COAST BY LATE TONIGHT. WITH DRIER AIR
TO THE NORTH AND TROPICAL AIR TO THE SOUTH THE MOISTURE GRADIENTS
ACROSS THE REGION MAKE POPS AND RAINFALL COVERAGE THE MOST
DEMANDING CHALLENGE THROUGH TONIGHT. MODEL CONSENSUS INDICATES
MORE WIDESPREAD RAINS SHOULD FALL OVER/NEAR THE OKEFENOKEE OR
SOMEWHERE BETWEEN LUDOWICI AND VALDOSTA. CHANCE POPS REMAIN IN
ORDER ALONG AND S OF I-16 TODAY WITH SOME DOWNPOURS POSSIBLE THIS
AFTERNOON ALONG THE ALTAMAHA AREA. DEPENDING ON HOW THE REMNANT OF
ERIKA BEHAVES...WE COULD SEE RAIN COVERAGE TRENDS GO EITHER WAY IN
OUR FAR SOUTHERN ZONES. WE LOWERED HIGH TEMPS A DEGREE OR TWO IN
THIS REGION GIVEN FAIRLY EXTENSIVE LAYERED CLOUDS PER CMC/NAM
CLOUD FORECAST PROGS.

ACROSS SOUTH CAROLINA...DIMINISHING RETURNS FOR RAIN CHANCES FROM
S TO N. ISOLATED AFTERNOON SHOWERS AND PERHAPS A FEW TSTMS MAY
DEVELOP ALONG THE SEA BREEZE BUT CURRENT THINKING IS THAT POPS
BELOW 20 PERCENT ARE BEST SERVED AROUND THE CHARLESTON AREA. WARM
AND HUMID WEATHER WITH A MIX OF SUN AND MAINLY HIGHER CLOUDS...
TEMPS IN THE LOWER 90S NW ZONES...CLOSE TO THE MID 90S BORDERING
THE SE MIDLANDS.

TONIGHT...CONTINUE TO HANG ONTO CHANCE POPS TO THE SOUTH OF I-16 AS
THE POCKET OF DEEP MOISTURE MOVES THROUGH. SIMILAR TO TODAY...THERE
IS NOT MUCH LOW LEVEL CONVERGENCE OR UPPER DIFLUENCE TO HANG OUR
HATS ON THUS THE MORE CONSERVATIVE POP SCHEME. IT CERTAINLY COULD
BE WET AROUND THE DARIEN AREA BUT IT SHOULD REMAIN MAINLY DRY
ACROSS MOST AREAS NORTH OF I-16.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
THURSDAY AND FRIDAY...AN UPPER LEVEL TROUGH OF LOW PRESSURE WILL
SETTLE OVER THE REGION. BENEATH THIS FEATURE...LOCALIZED CONVERGENCE
WITHIN A WEAK SURFACE TROUGH/ALONG THE SEA BREEZE SHOULD SUPPORT
SCATTERED MAINLY DIURNAL CONVECTION. CHANCE POPS ARE JUSTIFIED EACH
AFTERNOON/EARLY EVENING. 02/00Z NAM/EURO DEPICTION OF INSTABILITY
DEPICTS AT LEAST SOME POTENTIAL FOR BRIEF/ISOLATED PULSE SEVERE
THUNDERSTORMS WITH DAMAGING WIND GUSTS AROUND THE TIME OF MAXIMUM
HEATING...ALTHOUGH A SIGNIFICANT SEVERE WEATHER EVENT IS NOT
EXPECTED. ALSO...WEAK LOW/MID LEVEL WINDS COULD SUPPORT LOCALLY
HEAVY RAINFALL. ABOVE NORMAL HIGH TEMPS IN THE LOWER TO MID 90S AWAY
FROM THE BEACHES AND LOWS IN THE 70S ARE EXPECTED. ALSO OF
NOTE...HEAT INDEX VALUES 100-105F COULD BECOME COMMON OUTSIDE ANY
THUNDERSTORMS THURSDAY AFTERNOON...AND HEAT INDEX VALUES COULD TOP
OUT IN THE UPPER 90S/LOWER 100S AT MANY LOCATIONS FRIDAY AFTERNOON.

SATURDAY...A COMPLEX BLOCKING PATTERN WILL EVOLVE OVER THE EASTERN
CONUS/WESTERN ATLANTIC. AT THE SURFACE...EXPANDING HIGH PRESSURE TO
THE NORTH WILL PUSH A COLD FRONT THROUGH THE REGION...WHILE AN UPPER
LEVEL LOW WILL CLOSE OFF OVER THE SOUTHEAST. THIS REGIME SHOULD
SUPPORT AN ACTIVE CONVECTIVE REGIME...ALTHOUGH LATEST GUIDANCE
DEPICTS LESS THAN EXPECTED QPF DUE IN PART TO DRIER AIR WEDGING INTO
THE REGION FROM THE NORTHEAST. THUS...CAPPED MAXIMUM/AFTERNOON POPS
AT 40 TO 50 PERCENT. MEANWHILE...EXPECT HIGH TEMPS AROUND A CATEGORY
LOWER THAN THOSE OF FRIDAY...CLOSER TO NORMAL IN THE MID/UPPER 80S.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
A BLOCKING PATTERN WILL PREVAIL OVER THE EASTERN CONUS/WESTERN
ATLANTIC THROUGH THIS PERIOD. ONSHORE FLOW PROVIDED BY THE SPRAWLING
SURFACE HIGH PRESSURE TO THE NORTH...MOISTURE CONVERGENCE ENHANCED
BY A SURFACE TROUGH/LOW PRESSURE JUST OFF THE SOUTHEAST COAST AND
LOW PRESSURE ALOFT SHOULD TRANSLATE TO ABOVE NORMAL POPS AND
SLIGHTLY BELOW NORMAL HIGH TEMPERATURES. HOWEVER...POCKETS OF DRY
AIR CIRCULATING INTO THE REGION FROM THE NORTHEAST WILL COMPLICATE
POPS FORECASTS. THUS...HIGHEST POPS ARE PLACED SOUTH SOUTHERN
COUNTIES AND OVER ADJACENT COASTAL WATERS THROUGH THE PERIOD.
TOWARD THE MIDDLE OF NEXT WEEK...THE UPPER LOW COULD RETROGRADE
WEST OF THE REGION...AND PERHAPS THIS WILL SUPPORT SLIGHTLY LOWER
POPS AND A WARMING TREND.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
KSAV...AFTER A BOUT OF SHALLOW CLOUDS AND FOG EARLY THIS MORNING
CONDITIONS WERE ALREADY IMPROVING AT THE TERMINAL AROUND DAWN AND
WHILE THERE IS A SMALL CHANCE FOR LOWER CIGS THROUGH 13Z...WE
THINK VFR CONDITIONS WILL PREVAIL TODAY. RAINS WILL NOT BE TOO
FAR OFF TO THE SOUTH AND A FEW SHOWERS ARE POSSIBLE FROM LATE
MORNING INTO THE AFTERNOON HOURS. TONIGHT...CANNOT RULE OUT MORE
LATE NIGHT LOW CLOUDS BUT TOO EARLY FOR ANY INTRODUCTIONS ON THE
12Z CYCLE.

KCHS...VFR CONDITIONS SHOULD CONTINUE TO PREVAIL.

EXTENDED AVIATION OUTLOOK THROUGH MONDAY...MAINLY VFR. THE
PROBABILITY FOR FLIGHT RESTRICTIONS WILL INCREASE THIS WEEKEND.

&&

.MARINE...
THROUGH TONIGHT THE WATERS WILL BE RELATIVELY TRANQUIL WITH WINDS
MAINLY SW TO S LESS THAN 10 KT AND SEAS 2 FT OR LESS. CHANCES FOR
SHOWERS AND A FEW TSTMS INCREASE AS A WEAK MID LEVEL DISTURBANCE
DRIFTS EASTWARD ACROSS SOUTH GEORGIA.

THURSDAY THROUGH MONDAY...A WEAK PRESSURE PATTERN WILL PERSIST
THROUGH LATE WEEK...SUPPORTING WINDS LESS THAN 15 KT DOMINATED BY
THE PM SEA BREEZE AND AM LAND BREEZE. A COLD FRONT WILL CROSS THE
WATERS SATURDAY...AND STRONG HIGH PRESSURE WILL BUILD FROM THE
NORTH. THUS...NE WINDS WILL INCREASE AND SEAS WILL BUILD THIS
WEEKEND THROUGH EARLY NEXT WEEK. LATEST GUIDANCE HOLDS WINDS/SEAS
BELOW SMALL CRAFT ADVISORY LEVELS...AND WINDS/SEAS ARE CAPPED AT 15
TO 20 KT/3 TO 4 FT. HOWEVER...THE SYNOPTIC PATTERN SUGGESTS THE
POTENTIAL FOR STRONGER WINDS AND HIGHER SEAS. WILL ADJUST FORECASTS
AS NEEDED WITHIN SUBSEQUENT FORECAST PACKAGES.

RIP CURRENTS...AN ELEVATED RISK FOR RIP CURRENTS COULD DEVELOP AGAIN
NEXT WEEKEND INTO EARLY NEXT WEEK.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...SPR
LONG TERM...SPR
AVIATION...
MARINE...SPR



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