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Area Forecast Discussion

613
FXUS62 KCHS 241741
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
141 PM EDT THU APR 24 2014

.SYNOPSIS...
HIGH PRESSURE WILL SHIFT OFF THE COAST TODAY THROUGH FRIDAY.
A WEAK COLD FRONT COULD DRIFT IN FROM THE NORTH THIS WEEKEND
BEFORE HIGH PRESSURE BUILDS OVER THE AREA THROUGH EARLY NEXT WEEK.
A STRONGER COLD FRONT WILL CROSS THE REGION NEXT TUESDAY OR
WEDNESDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
EARLY THIS AFTERNOON...THE OVERALL FORECAST IS IN GOOD SHAPE. THE
ONLY ADJUSTMENT WAS TO BUMP WINDS UP THROUGH THE
AFTERNOON...ESPECIALLY ALONG THE LAND/SEA INTERFACE. OBSERVATIONS
AT FORT PULASKI...FOLLY BEACH...AND THE CHARLESTON HARBOR HAVE
ROUTINELY BEEN IN THE 15-20 KT RANGE OVER THE LAST FEW HOURS.
OTHERWISE...NO NOTABLE CHANGES.

LATE THIS MORNING...NO SIGNIFICANT CHANGES WERE MADE TO THE
INHERITED FORECAST. THE SOUTHERN EXTENT OF THE DEEP UPPER RIDGE
AXIS WILL MOVE ACROSS THE REGION TODAY AS HIGH PRESSURE SLIDES
OFFSHORE AND EAST OF THE AREA. NORTHEAST FLOW CURRENTLY OCCURRING
WILL GRADUALLY VEER TO A MORE SOUTHEASTERLY DIRECTION WITH A
PROGRESSIVE EMBEDDED SEA BREEZE THIS AFTERNOON. THE ONSHORE FLOW
WILL KEEP TEMPERATURES A BIT COOLER TODAY...ESPECIALLY ALONG AND
JUST INLAND OF THE COAST. GUIDANCE STILL SUPPORTS SOME HIGHS
APPROACHING THE MID 80S FOR INLAND SOUTHEAST GEORGIA. THERE
CONTINUE TO BE VERY LOW CHANCES OF AN ISOLATED SHOWER ALONG THE
ALTAMAHA THIS AFTERNOON...BUT I HAVE KEPT THE FORECAST DRY AS
MODEL SOUNDINGS DEPICT A PROMINENT MID LEVEL SUBSIDENCE INVERSION.
WE SHOULD SEE A BIT MORE IN THE WAY OF DIURNAL CUMULUS IN THE
AFTERNOON WITH AN INCREASE IN LOW LEVEL MOISTURE.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
TONIGHT...RETURN FLOW WILL BE IN FULL SWING AS A COLD FRONT
APPROACHES FROM THE WEST AND HIGH PRESSURE SLIPS FARTHER OFFSHORE.
MODELS SHOW SOME WEAK ISENTROPIC ASSENT DEVELOPING FROM SOUTH-
NORTH AS THE NIGHT PROGRESSES...BUT NONE OF THE VARIOUS MEMBERS
ARE OVERLY AGGRESSIVE IN THE DEVELOPMENT OF NOCTURNAL SHOWER
ACTIVITY AS MOST OF THE LIFT WILL GO TOWARDS CLOUD FORMATION GIVEN
THE HIGH CONDENSATION PRESSURE DEFICITS. WILL KEEP THE FORECAST
DRY WITH THE EXCEPTION OF THE CHARLESTON COUNTY COAST WHERE SOME
MARINE BASED CONVECTION COULD BRUSH AREAS FROM ROUGHLY FOLLY BEACH
TO MCCLELLANVILLE VERY EARLY THURSDAY. IT WILL BE A WARM NIGHT
WITH NOCTURNAL JETTING LIKELY KEEPING THE BOUNDARY LAYER FROM
FULLY DECOUPLING. LOWS WILL RANGE FROM THE UPPER 50S FAR INTERIOR
SOUTHEAST SOUTH CAROLINA TO THE LOWER-MID 60S ELSEWHERE. THIS IS
SLIGHTLY ABOVE THE 00Z GUIDANCE CONSENSUS.

FRIDAY...WE SHOULD SEE A FAIR AMOUNT OF CLOUDS TO START OFF THE DAY
AS MODEST ISENTROPIC ASCENT OCCURS AHEAD OF AN EASTWARD ADVANCING H5
SHORTWAVE JUST TO OUR NORTH. WE COULD SEE A FEW SHOWERS DURING
MORNING HOURS AS A RESULT...MAINLY ALONG THE COAST IN SOUTHEAST
SOUTH CAROLINA. A SLIGHT CHANCE OF SHOWERS AND/OR THUNDERSTORMS WILL
THEN BE POSSIBLE BY FRIDAY AFTERNOON AS INSTABILITY INCREASES DURING
PEAK HEATING WITH SBCAPES APPROACHING 700-1200 J/KG AND LIFTED INDEX
VALUES BETWEEN -1 TO -3C. THUNDERSTORM CHANCES APPEAR HIGHEST OVER
INLAND AREAS IN SOUTHEAST SOUTH CAROLINA WHERE FORCING FROM THE H5
SHORTWAVE AND A ARRIVING COLD FRONT ARE GREATEST. ALTHOUGH A CAPPING
INVERSION WILL SUPPRESS MOST DEEP CONVECTION...WE CAN NOT RULE OUT A
STRONGER THUNDERSTORM OR TWO BY FRIDAY EVENING. ACTIVITY WILL LIKELY
DIMINISH WITH COLD FROPA AND DIURNAL HEAT LOSS EARLY FRIDAY NIGHT.
1000-850 MB THICKNESS VALUES ALONG WITH SOME COMPRESSIONAL HEATING
SUPPORT OVERALL HIGH TEMPS IN THE LOW/MID 80S AWAY FROM THE COAST.
OVERNIGHT LOWS WILL RANGE IN UPPER 50S INLAND TO LOWER 60S ALONG THE
COAST BEHIND THE FRONT.

SATURDAY...HIGH PRESSURE WILL HOLD OVER THE AREA UNDER A BUILDING
RIDGE ALOFT. A DOWNSLOPING WIND COMPONENT WILL LIKELY SUPPORT ANOTHER
DAY OF WARM TEMPS WITH AFTERNOON HIGHS IN THE MID 80S OVER MOST
LOCATIONS AWAY FROM THE IMMEDIATE COAST. A WEAK AND DRY COLD FRONT
SHOULD STALL OR DISSIPATE NORTH OF THE FORECAST AREA SATURDAY
NIGHT...WITH LITTLE TO NO INFLUENCE OVER THE SOUTHEAST. THUS A
RAIN-FREE DAY IS EXPECTED. STRONG RADIATIONAL COOLING WILL ALLOW
OVERNIGHT TEMPS TO REACH THE UPPER 50S INLAND TO LOWER 60S ALONG THE
COAST.

SUNDAY...CONDITIONS LOOK FAIRLY DRY TO START OFF THE WEEK AS
ATLANTIC HIGH PRESSURE LINGERS OVER THE AREA WELL AHEAD OF A STRONG
LOW PRESSURE SYSTEM TRACKING EAST OVER THE CENTRAL UNITED STATES.
LIGHT SOUTHERLY FLOW ALONG WITH MID LVL RIDGING SHOULD RESULT IN
EVEN WARMER TEMPS THAN THE PREVIOUS DAY. LATEST 1000-850 MB
THICKNESSES FAVOR OVERALL HIGH TEMPS IN THE MID/UPPER 80S AWAY FROM
THE COAST...WARMEST IN SOUTHEAST GEORGIA.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
LIGHT SOUTHERLY FLOW ALONG WITH MID LVL RIDGING OVER THE SOUTHEAST
WILL LIKELY KEEP WARMER TEMPS OVER THE SOUTHEAST INTO EARLY NEXT
WEEK AHEAD OF THE APPROACHING LOW PRESSURE SYSTEM. IN GENERAL...HIGH
TEMPS WILL BE IN THE LOW/MID 80S MONDAY AND TUESDAY BEFORE COOLING A
FEW DEGREES ON WEDNESDAY AS CLOUD COVER INCREASES WITH THE LOW
PRESSURE SYSTEM SHIFTING OVER THE EASTERN CONUS. A SLIGHT CHANCE OF
SHOWERS AND THUNDERSTORMS WILL REMAIN IN THE FORECAST ON MONDAY AS
SOUTHERLY FLOW DEEPENS MOISTURE OVER THE AREA WHILE AN H5 SHORTWAVE
PASSES OVERHEAD. PRECIP CHANCES SHOULD THEN INCREASE TUESDAY AND
WEDNESDAY AHEAD OF AN EASTWARD MOVING COLD FRONT ASSOCIATED WITH THE
LOW PRESSURE SYSTEM. THERE ARE INDICATIONS THAT WE COULD SEE AN
ENHANCED PERIOD OF SHOWERS AND/OR THUNDERSTORMS LATE TUESDAY INTO
WEDNESDAY AS STRONGER INSTABILITY AND WIND FIELDS SET UP OVER THE
SOUTHEAST AHEAD OF THE FRONT. A FEW THUNDERSTORMS COULD BE
STRONG...ESPECIALLY ON WEDNESDAY DURING PEAK HEATING. SHOWERS AND/OR
THUNDERSTORMS COULD PERSIST INTO MUCH OF THURSDAY AS THE COLD FRONT
SHIFTS OFFSHORE EARLY WHILE THE LARGE MID/UPPER LVL TROUGH REMAINS
POSITIONED OVER THE EASTERN CONUS. OVERALL TEMPS SHOULD COOL OFF
POST FROPA...WITH HIGHS ONLY IN THE MID/UPPER 70S ON THURSDAY.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
VFR CONDITIONS WILL PREVAIL THROUGH THE EVENING WITH JUST MODERATE
SOUTHEAST FLOW IN THE AFTERNOON SEA BREEZE. OVERNIGHT...LOW LEVEL
MOISTURE WILL INCREASE IN THE ONSHORE FLOW AND THERE ARE
INDICATIONS OF INCREASING CLOUD COVER LATE...WITH SOME POTENTIAL
FOR MVFR CEILINGS TO DEVELOP. I HAVE KEPT THE FORECAST VFR FOR NOW
AS I THINK THE GUIDANCE IS A BIT TOO AGGRESSIVE AS IT USUALLY IS
IN SUCH ONSHORE REGIMES. WE MAY SEE AN ISOLATED SHOWER AND
POSSIBLY A THUNDERSTORM LATE TONIGHT AS A WEAK SURFACE TROUGH
LIFTS THROUGH THE AREA AHEAD OF A COLD FRONT TO THE WEST. KCHS HAS
THE BEST CHANCE TO SEE A SHOWER/THUNDERSTORM IN THE VICINITY...BUT
THE OVERALL PROBABILITY IS TOO LOW TO INCLUDE IN THE FORECAST AT
THIS POINT.

EXTENDED AVIATION OUTLOOK...LOW CHANCES OF MVFR CIGS/VSBYS LATE
MONDAY AND TUESDAY WITH SHOWERS AND/OR THUNDERSTORMS.

&&

.MARINE...
TODAY...EAST TO NORTHEAST WINDS WILL GRADUALLY VEER MORE SOUTHERLY
THIS AFTERNOON AS HIGH PRESSURE SHIFTS OFF THE COAST AND A ROBUST
SEA BREEZE CIRCULATION TAKES HOLD. WINDS WILL GENERALLY BE 10-15
KT WITH SEAS 1-3 FT...EXCEPT 15-20 KT ALONG THE LAND/SEA INTERFACE
AND IN THE CHARLESTON HARBOR.

TONIGHT...SOUTHERLY WINDS WILL DOMINATE AS HIGH PRESSURE SHIFTS
EVEN FARTHER OFFSHORE WINDS. WINDS WILL BE 10-15 KT WITH SEAS 2-3
FT.

FRIDAY THROUGH TUESDAY...A WEAK COLD FRONT WILL QUICKLY ADVANCE OVER
THE WATERS FRIDAY NIGHT...LEADING TO A MARGINAL SURGE OF WINDS
BETWEEN 15-20 KTS LATE. HIGH PRESSURE WILL THEN BUILD OVER THE
WATERS SATURDAY AND PERSIST INTO EARLY NEXT WEEK AHEAD OF A LOW
PRESSURE SYSTEM ADVANCING TO THE EASTERN CONUS. WINDS/SEAS ARE
EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS THROUGH EARLY
TUESDAY...BUT SHOULD APPROACH SMALL CRAFT ADVISORY LEVELS BY TUESDAY
NIGHT AS THE PRESSURE GRADIENT ENHANCES AHEAD OF A COLD FRONT
ADVANCING TO THE SOUTHEASTERN UNITED STATES BY MIDWEEK. IN
GENERAL...SOUTH/SOUTHEAST WINDS WILL REMAIN AT OR BELOW 15 KTS
THROUGH EARLY TUESDAY WHILE SEAS ARE NO HIGHER THAN 3-4 FT. BY
TUESDAY NIGHT...WINDS/SEAS SHOULD INCREASE/BUILD TO 20-25 KTS AND
4-6 FT...HIGHEST BEYOND 10 NM FROM THE COAST.

&&

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

&&

$$

SYNOPSIS...
NEAR TERM...BSH
SHORT TERM...DPB
LONG TERM...DPB
AVIATION...BSH
MARINE...DPB/ST




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