Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 262333
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
633 PM EST FRI DEC 26 2014

.SYNOPSIS...
HIGH PRESSURE WILL PERSIST TONIGHT...BEFORE SHIFTING OFF THE COAST
SATURDAY. A WEAK WARM FRONT WILL DEVELOP TO THE NORTH AND NORTHWEST
OF THE AREA SATURDAY NIGHT INTO SUNDAY...BEFORE A COLD FRONT MOVES
THROUGH LATE MONDAY OR MONDAY NIGHT. HIGH PRESSURE WILL BUILD INTO THE
REGION FOR MUCH OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
EARLY FRIDAY EVENING...ONGOING FORECASTS REMAINED IN GOOD SHAPE
AND REQUIRED ONLY MINOR ADJUSTMENTS TO HOURLY TRENDS...ESPECIALLY
TO ACCELERATE THE RATE OF COOLING THIS EVENING.

HIGH PRESSURE WILL PERSIST TO THE NORTH WHILE A COASTAL TROUGH OF
LOW PRESSURE DEVELOPS OFFSHORE. MOISTURE WILL BE ON A SLOW
INCREASING TREND...MAINLY IN THE FORM OF MID/HIGH CLOUDS BUT
SOME LOW-LEVEL MOISTURE AND ISENTROPIC ASCENT COULD YIELD SOME
STRATUS TOWARD DAYBREAK. ANY LIGHT SHOWERS SHOULD REMAIN
OFFSHORE. THERE COULD ALSO BE SOME LIGHT/SHALLOW FOG INLAND BUT DO
NOT ANTICIPATE SIGNIFICANT VISIBILITY REDUCTIONS. SHOULD SEE TEMPS
DROP OFF PRETTY QUICKLY AROUND SUNSET AND THEN A BIT MORE SLOWLY
LATE. LOW TEMPS MAINLY IN THE MID/UPPER 30S WELL INLAND...WITH
MID/UPPER 40S AT THE COAST WHERE A LITTLE NORTH/NORTHEAST BREEZE
WILL CONTINUE.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
SATURDAY...A MID/UPPER ANTICYCLONE CENTERED NEAR CUBA AND THE
BAHAMAS WILL REMAIN IN PLACE...WHILE SURFACE HIGH PRESSURE INITIALLY
OVER THE CAROLINAS WILL TRAVERSE INTO THE ATLANTIC DURING THE AFTERNOON
WITHIN THE WESTERLY FLOW ALOFT. ON THE SOUTH/SW EDGE OF THE SURFACE
HIGH A WEAK INVERTED COASTAL TROUGH WILL HOLD OVER THE ATLANTIC IN A
POSITION OUT NEAR THE WEST WALL OF THE GULF STREAM. WEAK ISENTROPIC
ASCENT ON THE 290K AND 295K SURFACES WILL ONLY HAVE MINIMAL MOISTURE
TO WORK WITH...SO THIS SHOULDN/T PRODUCE ANYTHING MORE THAN AN
INCREASE IN STRATOCUMULUS CLOUDS WITHIN A VERY SHALLOW EAST-SE
MARITIME FLOW. PROVIDED THE COASTAL TROUGH STAYS FAR ENOUGH
OFFSHORE...ANY LIGHT SHOWERS SHOULD ALSO REMAIN OVER THE ATLANTIC.
MEANWHILE...A MID LEVEL IMPULSE WILL HEAD IN OUR GENERAL DIRECTION
FROM OUT OF THE GULF AND WILL CAUSE AN INCREASE IN MID/HIGH
CLOUDINESS AS IT SKIRTS BY TO OUR NW LATE IN THE DAY. DESPITE AN
AVERAGE CLOUD COVER OF ABOUT 55-75 PERCENT AND HIGHEST SOUTH AND
WEST...CONSIDERABLE WARM ADVECTION WILL BOOST TEMPS INTO THE MID AND
UPPER 60S AWAY FROM THE NOTICEABLY COOLER SHORELINE.

SATURDAY NIGHT...WHILE THERE IS LITTLE CHANGE IN THE POSITION OF THE
MID/UPPER HIGH...HEIGHTS DO COME DOWN A TAD AS THE SHORT WAVE
BRUSHES THE AREA AS IT LIFTS INTO NC. WITH THE SURFACE HIGH TO MOVE
OUT NEAR 70W OR EVEN A LITTLE FURTHER EAST THE COASTAL TROUGH TRIES
TO TRAVEL CLOSER TO THE COAST...BUT APPEARS TO GET HUNG UP BY THE
COOLER SHELF WATER. SIMULTANEOUSLY A WARM FRONT WILL FORM NEAR THE
CENTRAL/SOUTHERN APPALACHIANS AND ANY OVER-RUNNING RAINS IN
ASSOCIATION WITH THIS FEATURE WILL LIKELY STAY OUTSIDE THE CWFA.
MAYBE A FEW COASTAL SHOWERS IN PROXIMITY THE ATLANTIC TROUGH WILL
ATTEMPT TO MOVE ONSHORE...BUT PROBABILITIES ARE LESS THAN 15
PERCENT. DEPENDENT UPON HOW MUCH MID/UPPER CLOUD COVER PERSISTS WE
SHOULD GET AT LEAST A LITTLE FOG TO FORM IN SYNC WITH A SINKING OF
THE PRE-EXISTING STRATOCUMULUS INTO LOWER STRATUS DECKS. WE HAVE
ADDED PATCHY FOG TO THE FORECAST AS A RESULT. MUCH WARMER THAN
RECENT NIGHTS DUE TO MORE CLOUD COVER AND CONTINUED WARM ADVECTION.

SUNDAY AND SUNDAY NIGHT...THE STAGNANT ANTICYCLONE ALOFT WILL
FINALLY GET SHUNTED SOME TO THE EAST/SE AS A DECENT SHORT WAVE
ARRIVES WITHIN THE WEST/SW FLOW AND REACHES OUR AREA AS IT DAMPENS
BY DAYBREAK MONDAY A LIGHT SOUTHERLY FLOW ON THE BACK SIDE OF THE
ATLANTIC SURFACE HIGH WILL SUPPLY A SMALL INCREASE IN MOISTURE...BUT
IT LOOKS TO TAKE UNTIL AFTER MIDNIGHT SUNDAY NIGHT FOR ANY SHOWERS
TO ARRIVE IN RESPONSE TO THE SHORT WAVE ALOFT. OF MORE IMPORTANCE
AND IN RESPONSE TO THE RELATIVELY WARMER/HUMID AIR MASS ATOP THE
COOLER NEARBY COASTAL WATERS...WE LOOK FOR THE DEVELOPMENT OF SEA
FOG WITHIN THE LIGHT SOUTHERLY FLOW BY LATE SUNDAY/SUNDAY NIGHT.
COVERAGE OF THE FOG WILL FAN OUT AND EXPAND INLAND DURING THE LATE
EVENING AND OVERNIGHT WITH EVEN SMALL CONDENSATION PRESSURE DEFICITS
AND HIGHER DEW POINTS ADVECTING IN. WE HAVE ADDED AREAS OF FOG TO
THE FORECAST...SOME OF WHICH CERTAINLY COULD BECOME DENSE ENOUGH FOR
ADVISORIES. WE HAVE ALSO INCLUDED THIS IN THE HAZARDOUS WEATHER
OUTLOOK. CONTINUED WARM ADVECTION WILL SUPPORT TEMPS FAR ABOVE
NORMAL.

MONDAY...AS THE WEAKENING SHORT WAVE PASSES INTO THE ATLANTIC EARLY
IN THE DAY IT LEAVES BEHIND A BROADLY CYCLONIC OR A QUASI-ZONAL FLOW
WEST-SW ALOFT...WHICH BECOMES SOMEWHAT ALIGNED TO THE NEXT COLD
FRONT WHICH INCHES ITS WAY IN FROM THE WEST/NW DURING THE AFTERNOON.
WHILE THERE IS AMPLE MOISTURE AND SOME FORCING FROM THE NEARBY RIGHT
ENTRANCE REGION OF THE UPPER JET...DEVELOPING NVA...RESTRICTED
INSTABILITY AND WEAK LOW LEVEL CONVERGENCE LOOKS TO SUPPORT NO MORE
THAN CHANCE POPS. WHILE THERE ARE HINTS OF A SMIDGEN OF ELEVATED
INSTABILITY...CERTAINLY IT INS/T ENOUGH TO INCLUDE THUNDER IN THE
FORECAST. DESPITE PLENTY OF CLOUD COVER THERE IS STILL ENOUGH WARM
ADVECTION AND COMPRESSIONAL HEATING IN ADVANCE OF THE COLD FRONT TO
PRODUCE HIGHS YET AGAIN WELL ABOVE SEASONAL NORMS. FOG COVERAGE WILL
SHRINK IN THE MORNING AND LOOKS TO BECOME CONFINED TO THE BARRIER
ISLANDS OR JUST OFFSHORE FOR THE REST OF THE DAY.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
THERE REMAINS CONTINUING DISCREPANCIES BETWEEN MODEL SOLUTIONS
REGARDING THE PROGRESSION OF A COLD FRONT AND THE
PLACEMENT/STRENGTH OF ASSOCIATED LOW PRESSURE OFF THE EAST COAST
FROM MONDAY NIGHT THROUGH MID WEEK. PREFER TO KEEP MENTION OF
ISOLATED RAIN IN THE FORECAST MONDAY NIGHT THROUGH
TUESDAY...ACCOUNTING FOR SOME WEAK PRECIPITATION GENERATED BY
BOTH GFS AND ECMWF SOLUTIONS ON THE BACK SIDE OF THE FRONT AND
ALONG THE PERIPHERY OF BUILDING HIGH PRESSURE. EXPECT DRY WEATHER
TO PREVAIL MID TO POSSIBLY LATE WEEK...AS THE EXPANSIVE SURFACE
HIGH BUILDS ACROSS THE SOUTHEAST UNITED STATES. LATEST MODEL
TRENDS HAVE SLOWED THE DEVELOPMENT OF A STORM SYSTEM OVER THE
WESTERN GULF OF MEXICO...THUS RAIN CHANCES CURRENTLY IN THE
FORECAST FOR THURSDAY NIGHT INTO FRIDAY COULD BE DECREASED IF
THESE TRENDS CONTINUE. EXPECT A COOLING TREND BACK TOWARD SEASONAL
NORMALS TUESDAY THROUGH LATE WEEK.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
VFR THROUGH SATURDAY. LOW PROBABILITY FOR BRIEF VSBY RESTRICTIONS
IN GROUND FOG AROUND DAYBREAK SATURDAY...AND A VERY LOW CHANCE FOR
OCCASIONAL MVFR CEILINGS SATURDAY AFTERNOON.

EXTENDED AVIATION OUTLOOK...THERE COULD BE SOME FLIGHT RESTRICTIONS
IN FOG/STRATUS LATE SATURDAY NIGHT/SUNDAY MORNING...BUT A BETTER
CHANCE OF IFR OF LOWER CONDITIONS SUNDAY NIGHT INTO MONDAY MORNING
WITH A CHANCE OF SEA FOG TO OCCUR.

&&

.MARINE...
TONIGHT...HIGH PRESSURE WILL PERSIST TO THE NORTH WHILE A COASTAL
TROUGH OF LOW PRESSURE TRIES TO DEVELOP OFFSHORE. THIS WILL KEEP A
SLIGHTLY ENHANCED PRESSURE GRADIENT OVER THE LOCAL WATERS WITH
NORTH/NORTHEAST WINDS 15 KT OR LESS. SEAS WILL REMAIN 3 FT OR
LESS...HIGHEST BEYOND 20 NM.

SATURDAY...SUBTLE PINCHING OF NE WINDS BETWEEN A TROUGH OUT NEAR THE
WEST WALL OF THE GULF STREAM AND HIGH PRESSURE INLAND BEFORE IT
PULLS OFFSHORE...AND WILL PRODUCE NE WINDS AS HIGH AS 10-15 KT IN
THE MORNING BEFORE THEY START TO DIMINISH IN THE AFTERNOON. SEAS
WILL HOLD AROUND 2 OR 3 FT THROUGHOUT THE DAY.

SATURDAY NIGHT...THE PRESSURE PATTERN BECOMES FAIRLY BENIGN WITH THE
REMNANTS OF A WEAK COASTAL TROUGH STILL OUT NEAR THE GULF STREAM
THAT DISSIPATES LATE. EAST OR SE WINDS AT LESS THAN 10 KT EARLY WILL
VEER AROUND OVERNIGHT AS THE TROUGH WEAKENS AND LAND BREEZE
CIRCULATIONS ATTEMPT TO DEVELOP. SEAS NOTHING MORE THAN 2 OR 3 FT.

SUNDAY THROUGH MONDAY...A LIGHT SOUTHERLY FLOW WILL DEVELOP ON THE
WEST/SW PERIPHERY OF ATLANTIC HIGH PRESSURE SUNDAY INTO SUNDAY
NIGHT...BEFORE VEERING A LITTLE FURTHER SW AND INCREASING IN ADVANCE
OF THE NEXT COLD FRONT THAT DROPS INTO THE SE STATES MONDAY. WINDS
AND SEAS WILL REMAIN BELOW ANY SMALL CRAFT ADVISORY CONDITIONS
THROUGH THE PERIOD. OF MORE IMPORTANCE WILL BE THE FORMATION OF SEA
FOG ACROSS THE COOLER SHELF WATERS BY LATE SUNDAY OR SUNDAY
NIGHT...WHICH THEN CONTINUES INTO MONDAY. WARMER AND MORE HUMID AIR
OVER-RIDING THE COOLER NEAR SHORE WATERS WITHIN FAVORABLE SOUTHERLY
TRAJECTORIES APPEARS HIGHLY FAVORABLE FOR THE DREADED SEA FOG TO
FORM. WE HAVE ADDED MENTION TO THE HAZARDOUS WEATHER OUTLOOK SINCE
DENSE FOG AND MARINE DENSE FOG ADVISORIES WILL LIKELY BE REQUIRED.

MONDAY NIGHT THROUGH WEDNESDAY...THE COLD FRONT FINALLY MOVES
THROUGH EARLY IN THE PERIOD...FOLLOWED BY CONTINENTAL HIGH PRESSURE
INTO MID WEEK. SOME COLD ADVECTION AND EVENTUALLY A TIGHTENING OF THE
PRESSURE GRADIENT WILL SUPPORT HIGHER WINDS AND SEAS...AND WE/LL
MAINTAIN A WEATHER WATCH FOR POSSIBLE SMALL CRAFT ADVISORIES.

&&

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

&&

$$

NEAR TERM...RJB/SPR
SHORT TERM...33
LONG TERM...
AVIATION...33/RJB/SPR
MARINE...33/RJB/SPR





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