Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 270827
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
427 AM EDT MON APR 27 2015

.SYNOPSIS...
HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE NORTHWEST
TODAY...SETTLE JUST NORTH OF THE AREA ON TUESDAY...THEN SHIFT INTO
THE ATLANTIC TUESDAY NIGHT. A STORM SYSTEM LIFTING OUT OF THE GULF
COAST REGION WILL AFFECT THE AREA WEDNESDAY AND WEDNESDAY
NIGHT...THEN DEPART TO THE NORTHEAST ON THURSDAY. HIGH PRESSURE WILL
THEN PREVAIL INTO EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
TODAY...HIGH PRESSURE WILL BUILD FROM THE NORTHWEST PUSHING A COLD
FRONT SOUTH OF THE AREA TOWARD THE FLORIDA PANHANDLE WHERE IT WILL
STALL OUT. DRIER AIR WILL MOVE IN BEHIND THE FRONT OVER THE LOCAL
AREA AND THUS EXPECT NO RAIN CHANCES DESPITE SOME WEAK SHORTWAVE
ENERGY ALOFT IN THE MAINLY ZONAL FLOW. AFTER MORNING CLOUDS
SHOULD SEE MORE IN THE WAY OF SUNSHINE WITH TEMPS REACHING THE MID
70S FOR MOST PLACES. COULD SEE SOME UPPER 70S NEAR DARIEN.

TONIGHT...EXPECT INCREASING CLOUDS AS DEEPER MOISTURE MOVES BACK
NORTHWARD FROM ALONG THE GULF COAST AHEAD OF A DEVELOPING AREA OF
LOW PRESSURE ALONG THE WESTERN/CENTRAL GULF COAST. CAN/T RULE OUT
A FEW LIGHT SHOWERS MAKING IT NORTHWARD AROUND THE ALTAMAHA RIVER
LATE BUT CONFIDENCE IS LOW IN MEASURABLE AMOUNTS SO WE MAINTAINED
A RAIN-FREE FORECAST. TEMPS WILL BE GREATLY DEPENDENT ON HOW
QUICK THE CLOUDS ARRIVE BUT WE COULD SEE SOME UPPER 40S AROUND
NORTHERN BERKELEY/CHARLESTON COUNTIES AS WELL AS WESTERN
DORCHESTER/COLLETON/ALLENDALE COUNTIES. ELSEWHERE LOWS SHOULD BE
IN THE 50S...WARMEST ALONG THE GA COAST WHERE TEMPS MAY NOT DROP
BELOW 60 GIVEN THE DEVELOPING/STRENGTHENING NORTHEAST WINDS.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
TUESDAY AND TUESDAY NIGHT...WEAK MID AND UPPER LEVEL RIDGING WILL
PREVAIL OVER THE REGION AHEAD OF A POSITIVELY TILTED TROUGH SHIFTING
ACROSS THE PLAINS STATES AND INTO THE MIDDLE MISSISSIPPI VALLEY. AT
THE SURFACE...HIGH PRESSURE WILL SETTLE JUST NORTH OF THE AREA
DURING THE DAY TUESDAY THEN SHIFT INTO THE WESTERN ATLANTIC TUESDAY
NIGHT. MEANWHILE AS THIS OCCURS...A LOW PRESSURE SYSTEM WILL TRACK
ALONG THE NORTHERN GULF COAST REGION AHEAD OF THE UPPER
TROUGH...WITH ITS ASSOCIATED WARM FRONT LIFTING TOWARD THE AREA
TUESDAY NIGHT. ISENTROPIC ASCENT AND MOISTURE DEPTH WILL GRADUALLY
RAMP UP FROM THE SOUTH TUESDAY AND TUESDAY NIGHT AS THE WARM FRONT
NEARS...ALL WHILE UPPER LEVEL DIFLUENCE STRENGTHENS. THE RESULT WILL
BE AN INCREASING PROBABILITY FOR RAINFALL THROUGH THE PERIOD. THE
FORECAST INDICATES A CHANCE OF SHOWERS MAINLY ACROSS SOUTHEAST
GEORGIA AND THE SOUTHERN TIP OF SOUTH CAROLINA BY THE END OF THE DAY
TUESDAY...AND SHOWERS BECOMING LIKELY SOUTH OF COLLETON COUNTY
TUESDAY NIGHT WITH A CHANCE OF SHOWERS FARTHER NORTH. SOME
THUNDERSTORMS WILL ALSO BE POSSIBLE TUESDAY NIGHT MAINLY SOUTH OF I-
16. TEMPERATURES WILL BE UNSEASONABLY COOL TUESDAY WITH A NORTHERLY
FLOW IN PLACE FOR MUCH OF THE DAY...WITH HIGHS IN THE LOWER 70S.
LOWS TUESDAY NIGHT WILL BE IN THE MID TO UPPER 50S...EXCEPT IN THE
LOWER 60S CLOSER TO THE GEORGIA COAST.

WEDNESDAY AND WEDNESDAY NIGHT...THE INITIAL UPPER LEVEL TROUGH WILL
WEAKEN AS IT CROSSES THE CENTRAL APPALACHIANS AND A MUCH STRONGER
CLOSED LOW DROPS SOUTHWARD ACROSS THE GREAT LAKES REGION AND INTO
THE OHIO VALLEY ALONG THE EASTERN PERIPHERY OF A STRONG RIDGE
CENTERED OVER THE FOUR CORNERS REGION. MEANWHILE...THE SURFACE LOW
OVER THE NORTHEAST GULF COAST REGION WILL EJECT NORTHEAST SOMEWHERE
IN THE VICINITY OF SOUTHEAST GEORGIA AND SOUTHERN SOUTH CAROLINA
DURING THE DAY WEDNESDAY...WITH ITS ASSOCIATED WARM FRONT LIKELY
LIFTING THROUGH SOUTHERN AND COASTAL PORTIONS OF THE FORECAST AREA
AHEAD OF THE LOW. THE LOW WILL THEN BEGIN DEPARTING TO THE NORTHEAST
WEDNESDAY NIGHT. WHILE THERE IS SOME MODEL DISCREPANCY WITH RESPECT
TO THE EXACT TRACK OF THE LOW...IT SEEMS THAT WEDNESDAY IS SHAPING
UP TO BE RATHER WET WITH THE FORECAST SHOWING SHOWERS LIKELY ACROSS
THE AREA. THE SHOWER POTENTIAL WILL THEN BEGIN TO TAPER OFF FROM THE
SOUTHWEST WEDNESDAY NIGHT AS THE LOW STARTS TO PULL AWAY. IT DOES
APPEAR THAT AT LEAST SOUTHERN AND COASTAL PORTIONS OF THE FORECAST
AREA MAY BECOME WARM SECTORED ON WEDNESDAY...WITH TEMPERATURES IN
THIS AREA POTENTIALLY WARMING INTO THE MID AND UPPER 70S...IF NOT
WARMER...WHILE CLOSER TO THE MIDLANDS HIGHS SHOULD ONLY BE IN THE
UPPER 60S WITH NORTHERLY FLOW STILL IN PLACE. IT MUST BE NOTED THAT
THIS IS A HIGHLY ANOMALOUS/AMPLIFIED PATTERN FOR THIS TIME OF
YEAR...AND THERE IS A POTENTIAL FOR SEVERE WEATHER TO DEVELOP IN THE
WARM SECTOR...WITH STRONG DEEP LAYER SHEAR INITIALLY WITH THE WARM
FRONT...THEN INCREASING SURFACE BASED INSTABILITY THROUGHOUT THE
DAY.

THURSDAY...THE POTENT CLOSED UPPER LOW WILL SWING INTO THE CENTRAL
APPALACHIANS ...CAUSING THE SURFACE LOW TO INTENSIFY SIGNIFICANTLY AS
IT LIFTS UP JUST OFF THE MID-ATLANTIC COAST. WHILE A DEEP/DRIER
WESTERLY FLOW WILL PREVAIL ACROSS THE REGION...SOME ISOLATED OR
SCATTERED INSTABILITY SHOWERS WILL BE POSSIBLE ALONG THE SOUTHERN
PERIPHERY OF THE UPPER LOW...ESPECIALLY ACROSS THE CHARLESTON TRI-
COUNTY AREA. HIGHS WILL BE UNSEASONABLY COOL IN THE LOWER 70S.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT WITH THE OVERALL SYNOPTIC
PATTERN IN THE LONG TERM PERIOD. IN THE MID AND UPPER LEVELS...A
LONG WAVE TROUGH WILL LINGER OVER THE EASTERN U.S. FRIDAY AND
SATURDAY BEFORE RIDGING GRADUALLY BUILDS FROM THE WEST INTO EARLY
NEXT WEEK. MEANWHILE AT THE SURFACE...THE REGION WILL BE POSITIONED
BETWEEN A STRONG LOW OFF THE MID-ATLANTIC/NORTHEAST COAST AND STRONG
HIGH PRESSURE CENTERED OVER THE MISSISSIPPI VALLEY FRIDAY AND
SATURDAY. THE HIGH WILL THEN BUILD OVER THE REGION THROUGH THE
WEEKEND...BEFORE SHIFTING INTO THE ATLANTIC ON MONDAY.
OVERALL...THIS PATTERN WILL FAVOR RAIN-FREE CONDITIONS WITH STRONG
SUBSIDENCE AND LIMITED MOISTURE...ALTHOUGH SOME ISOLATED CONVECTION
IS POSSIBLE MONDAY ONCE AN ONSHORE FLOW DEVELOPS AND THE SEA BREEZE
BECOMES MORE PRONOUNCED. TEMPERATURES WILL MODERATE ON FRIDAY...THEN
RETURN TO NEAR NORMAL OVER THE WEEKEND AND INTO EARLY NEXT WEEK.

&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
MVFR CEILINGS SHOULD PREVAIL THE REST OF THE OVERNIGHT ALTHOUGH
COULD SEE IFR OR EVEN VFR AT TIMES. ANY SUB-VFR CIGS SHOULD
BECOME VFR BY 15Z...PROBABLY A BIT SOONER AT KCHS.

EXTENDED AVIATION OUTLOOK...MVFR OR LOWER CONDITIONS ARE PROBABLE
LATE TUESDAY NIGHT AS A WARM FRONT LIFTS TOWARD THE AREA AND
WEDNESDAY INTO WEDNESDAY NIGHT AS LOW PRESSURE PASSES NEARBY AND
SHOWERS/THUNDERSTORMS BECOME LIKELY. OTHERWISE...VFR CONDITIONS ARE
EXPECTED TO PREVAIL.

&&

.MARINE...
TODAY AND TONIGHT...MORNING SURGE WILL DIMINISH AS HIGH PRESSURE
BUILDS FROM THE NORTHWEST...THEN RETURN LATE TONIGHT AS THE
PRESSURE GRADIENT STRENGTHENS AS THE HIGH BUILDS CLOSER AND LOW
PRESSURE STRENGTHENS ALONG THE GULF COAST. NO HEADLINES EXPECTED HOWEVER.

TUESDAY THROUGH SATURDAY...HIGH PRESSURE WILL BECOME CENTERED JUST
NORTH OF THE AREA ON TUESDAY...LEADING TO A WEAKENING PRESSURE
GRADIENT FROM THE NORTH AND SOMEWHAT IMPROVED WINDS/SEAS. CONDITIONS
SHOULD THEN DETERIORATE ON WEDNESDAY AS A LOW PRESSURE SYSTEM
APPROACHES FROM THE SOUTHWEST AND PASSES OVER THE COASTAL WATERS
LATE WEDNESDAY AND WEDNESDAY NIGHT. A PERIOD OF SMALL CRAFT ADVISORY
CONDITIONS ARE POSSIBLE FOR ALL WATERS WEDNESDAY NIGHT BEHIND THE
DEPARTING LOW PRESSURE SYSTEM...WITH BEST CHANCES OCCURRING IN
NORTHERN SC WATERS OFF THE CHARLESTON COUNTY COAST AND IN OFFSHORE
GEORGIA WATERS. WINDS/SEAS SHOULD THEN SLOWLY IMPROVE ON THURSDAY AS
THE LOW PRESSURE SYSTEM SHIFTS NORTH/NORTHEAST AND AWAY FROM THE
AREA...BEFORE IMPROVING FURTHER AS WEAK HIGH PRESSURE SETTLES OVER
THE WATERS ON FRIDAY AND SATURDAY.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...RJB
SHORT TERM...JAQ
LONG TERM...JAQ
AVIATION...JAQ/RJB
MARINE...JAQ/RJB


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