Area Forecast Discussion
Issued by NWS Wilmington, NC

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000
FXUS62 KILM 280259
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
1059 PM EDT SAT SEP 27 2014

.SYNOPSIS...
HIGH PRESSURE BUILDING FROM THE NORTH WILL BRING A DRYING TREND
THROUGH THE WEEKEND AS A COASTAL TROUGH WEAKENS OFFSHORE. A WET
FORECAST IS SHAPING UP FOR EARLY NEXT WEEK AS LOW PRESSURE MOVES
ACROSS THE SOUTHEAST. HIGH PRESSURE WILL RE-BUILD FROM THE NORTH
THROUGH MID WEEK...WITH A COLD FRONT MOVING IN AT THE END OF THE
WEEK.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
AS OF 1045 PM SATURDAY...SOME TWEAKING OF SKY CONDITIONS FOR THIS
UPDATE. BASED ON LATEST SAT IMAGERY TRENDS...LOOKING AT MAINLY
HIGH AND SOME MID LEVEL CLOUDS FOR THE NC PORTION OVERNITE...
AND...ALL 3 DECKS FOR THE ILM SC PORTION OF THE CWA. WILL CONTINUE
WITH THE LOW CHANCE FOR -RA OR DRIZZLE FOR THE SC COUNTIES.
TWEAKED MINS A DEGREE OR 2 LOWER FOR THE ILM NC PORTIONS DUE TO
LESS CLOUDS...OTHERWISE NO EDITS NEEDED.

PREVIOUS DISCUSSION..............................................
AS OF 730 PM SATURDAY...LATEST LOCAL KLTX AND 88D MOSAIC KEEPS THE
MAIN PCPN SHIELD SOUTH OF CAPE FEAR. LATEST HRRR MODEL KEEPS ANY
ONSHORE MOVEMENT OF THE PCPN ACROSS THE ILM SC COUNTIES. AS A
RESULT...HAVE ADJUSTED POPS KEEPING THEM AT LOW CHANCE TO AFFECT
MAINLY THOSE SC COUNTIES OVERNIGHT. CLOUDINESS HAS BEEN ADJUSTED
UPWARDS DUE TO ONGOING VARIABLY SKY CONDITIONS AND THE TRAPPED
MOISTURE BELOW 700 MB AS ADVERTISED BY VARIOUS MODEL TIME HEIGHT
DISPLAYS ACROSS THE FA. MIN TEMPS SLIGHTLY TWEAKED...TOWARDS THE
UPWARD SIDE DUE TO MORE CLOUDINESS AND THREAT OF PCPN.

PREVIOUS DISCUSSION....................................
AS OF 3 PM SATURDAY...HIGH PRESSURE CONTINUES TO WEDGE DOWN THE
COAST THIS AFTN...INTERACTING WITH A COASTAL TROUGH THAT SEEMS TO
BE EVER-PRESENT JUST OFFSHORE. WEAK LOW PRESSURE OFF THE
CHARLESTON, SC COAST WILL CONTINUE TO DROP WEAKLY TO THE SOUTH
TONIGHT AS HIGH PRESSURE BECOMES MORE DOMINANT.

AREAS OF SHOWERS ALONG THE COASTAL TROUGH HAVE BEEN TRYING TO PUSH
ONSHORE TODAY...DRIVEN BY THE E/NE FLOW BETWEEN THE SURFACE WEDGE
AND COASTAL TROUGH. THE MID-LEVELS OF THE COLUMN...THOSE ABOVE
750MB...ARE VERY DRY...AND THE CONTINENTAL AIR MASS IS DRIER THAN
THAT OFFSHORE. THIS IS PRECLUDING MOST OF THE SHOWER ACTIVITY FROM
MAKING IT ONSHORE...BUT CANNOT RULE OUT SOME ISOLATED LIGHT
SHOWERS THROUGH TONIGHT...FOCUSED ALONG THE COAST...WITH BEST
CHANCE ALONG THE GRAND STRAND AND DOWN TOWARDS THE SOUTH SANTEE
RIVER. THE NAM FORECAST PROFILES ARE HANDLING THE CLOUD COVER BEST
TODAY...SO USING THIS AS A GUIDE EXPECT LOW LEVEL CLOUDINESS TO
PERSIST INTO TONIGHT. AS THE HIGH BECOMES MORE STRONGLY ENTRENCHED
LOCALLY CLOUD COVER WILL WANE...BUT EXPECT ONCE AGAIN QUITE A BIT
OF STRATUS AROUND TONIGHT. THIS WILL LIMIT OVERALL COOLING AND
HAVE AGAIN SIDED WITH THE LAV NUMBERS...AND AM FORECASTING LOWS
AROUND 60 IN THE FAR WESTERN ZONES...TO NEAR 70 ALONG THE GRAND
STRAND.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
AS OF 3 PM SATURDAY...UPPER RIDGE OVER EASTERN CONUS BREAKS DOWN
THROUGH THE SHORT TERM AS A SERIES OF STRONG SHORT WAVES DROP
ACROSS NEW ENGLAND AND THE GREAT LAKES REGION. THE SURFACE PICTURE
IS A LITTLE MUDDLED DUE TO A WEAK PRESSURE PATTERN AND A
DIVERGENCE OF MODEL SOLUTIONS. HOWEVER...A CONSENSUS OF GUIDANCE
HAS A FRONTAL SYSTEM DRAPED ACROSS THE DEEP SOUTH ON SUNDAY
LIFTING NORTH ON MONDAY INTO COASTAL GEORGIA AND SOUTH CAROLINA.
INCREASING MOISTURE ADVECTION WILL MAKE FOR A CLOUDY MONDAY WITH
POPS STEADILY INCREASING FROM SLIGHT CHANCE IN THE MORNING TO
LIKELY OVERNIGHT. SUNDAY HOWEVER LOOKS TO BE A DECENT DAY WITH
MINIMAL CHANCES OF PRECIP AND A GOOD BIT OF SUN...ESPECIALLY EARLY
ON. DAYTIME HEATING WILL LIKELY POP A CU FIELD IN THE
AFTERNOON...AND THE CIRRUS SHIELD WILL STEADILY INCREASE IN
ADVANCE OF MONDAYS FRONTAL SYSTEM. TEMPERATURES WILL BE QUITE
SEASONAL THROUGH THE PERIOD.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
AS OF 3 PM SATURDAY...FORECAST MODELS FOR THE MEDIUM RANGE ARE IN
DECENT AGREEMENT ON THE SYSTEM MOVING ACROSS THE SOUTHEAST DURING
THE FIRST COUPLE OF DAYS. BOTH THE GFS AND ECMWF OPERATIONAL
MODELS SHOW A RATHER LETHARGIC SHORTWAVE THAT WAVERS BETWEEN AN
OPEN WAVE AND CLOSED LOW. I HAVE MAINTAINED THE GOOD CHANCE OF
SHOWERS FOR THE FIRST PART OF TUESDAY TRENDING DOWN THEREAFTER.

THE AFOREMENTIONED OPERATIONAL MODELS DIVERGE WITH REGARDS TO THE
MID LEVEL PATTERN FOR THE REMAINDER OF THE PERIOD. THE GFS KEEPS A
WEAKNESS AROUND THE AREA...MUCH LIKE WE HAVE SEEN THIS WEEK WHILE
THE ECMWF HAS A MORE PROGRESSIVE SOLUTION. WPC FAVORS MORE
BLENDING WITH ECMWF SOLUTIONS SO I HAVE BACKED OFF THE SLIGHT
CHANCE POPS LINGERING INTO WEDNESDAY AND THURSDAY. BEYOND THIS...A
STRONG SHORTWAVE MOVING THROUGH THE OHIO VALLEY AND ATTENDANT COLD
FRONT MOVE ACROSS LATE FRIDAY AND SATURDAY. AT THIS POINT THE
FRONT LOOKS TO BE MOISTURE STARVED AND INTRODUCED LOWER CHANCE
POPS FOR THE NEW DAY OF THE FORECAST PERIOD...SATURDAY.

REGARDING TEMPERATURES...I GENERALLY ADDED A DEGREE OR TWO ACROSS
THE BOARD TO WPC GUIDANCE AS THE WESTERLY FLOW THAT IS FORECAST TO
DEVELOP SHOULD ALLOW A DOWNSLOPE COMPONENT TO WARRANT. HOWEVER
MOST VALUES ARE WITHIN A FEW DEGREES OF CLIMATOLOGY.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
AS OF 00Z...LINGERING MVFR CIGS AT KCRE/KMYR OVER THE NEXT FEW
HOURS...AND POSSIBLY AGAIN ALONG THE COAST JUST BEFORE DAYBREAK.
OTHERWISE EXPECT VFR AS HIGH PRESSURE CONTINUES TO BUILD ACROSS THE
AREA WITH A WEAKENING COASTAL TROUGH OFFSHORE.

LATEST RADAR DEPICTS LIGHT SHOWERS OFFSHORE BUT AS THEY CONTINUE TO
MOVE TOWARDS THE COAST...THEY CONTINUE TO WEAKEN AND ESSENTIALLY
DISSIPATE. LATEST OBS INDICATE VFR PREVAILS ACROSS THE AREA THIS
EVENING WITH THE EXCEPTION OF MVFR DUE TO LOW CIGS AT KMYR.
ANTICIPATE POSSIBILITY OF MVFR DUE TO LOW CIGS TO LINGER OVER THE
NEXT FEW HOURS AT KCRE/KMYR...AND THE POSSIBLY RE-OCCUR BEFORE
DAYBREAK ALONG THE COAST. OTHERWISE EXPECT VFR THROUGH THE OVERNIGHT
HOURS WITH NORTHEAST WINDS 5 TO 10 KTS. ON SUNDAY...ANY MVFR DUE TO
LOW CIGS COULD LINGER INTO THE LATE MORNING HOURS...BUT CONDITIONS
WILL GRADUALLY IMPROVE TO VFR WITH PERSISTENT NORTHEAST WINDS.

EXTENDED OUTLOOK...CHANCE OF SHOWERS/MVFR MONDAY AND TUESDAY AS LOW
PRESSURE MOVES ACROSS THE SOUTHEAST. MVFR/IFR CIGS ON WEDNESDAY/
POSSIBLY THURSDAY.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 1045 PM SATURDAY...SCEC ALL WATERS TO CONTINUE. TWEAKED
NE WINDS A KNOT OR 3 HIER BASED ON LATEST TRENDS AND 1ST LOOK AT
00Z GUIDANCE. SIG. SEAS TO RUN 3 TO 5 FT...EXCEPT A FOOT LOWER
SOUTH OF CAPE FEAR TO LITTLE RIVER INLET DUE TO THE SHADOW EFFECTS
FROM A NE WIND AND THE CONFIGURATION OF THE COASTLINE.

PREVIOUS DISCUSSION.............................................
AS OF 730 PM SATURDAY...SCA WILL BE LOWERED TO SCEC FOR THE ILM NC
WATERS...AND A SCEC WILL REMAIN IN EFFECT FOR THE ILM SC WATERS.
THE SCEC FOR ALL WATERS WILL REMAIN IN EFFECT THRU MIDDAY SUNDAY.

MODESTLY TIGHTENED SFC PG ACROSS THE WATERS WILL PRODUCE NE 15 TO
OCCASIONALLY 20 KT OF WINDS OVERNIGHT. SIGNIFICANT SEAS WILL RUN 3
TO 5 FT...EXCEPT 2 TO 4 FT SOUTH OF CAPE FEAR TO LITTLE RIVER
INLET. DOMINANT PERIODS WILL RUN 5 TO 6 SECONDS. NOT MUCH OF ANY
GROUND SWELL TO SPEAK OF.

PREVIOUS DISCUSSION...................................
AS OF 3 PM SATURDAY...HIGH PRESSURE WEDGING DOWN THE COAST AND A
COASTAL TROUGH POSITIONED ABOUT 50 MILES OFFSHORE...CONTINUE TO
KEEP THE COASTAL WATERS PINCHED IN BETWEEN. THIS IS CREATING GUSTY
NE WINDS OF 15-25 KTS...AND SEAS OF 3 TO 6 FT THIS AFTN. A SLOW
DECREASE IN WIND SPEEDS IS EXPECTED TONIGHT AS THE HIGH PRESSURE
PUSHES FURTHER SOUTH...WEAKENING THE GRADIENT...BUT SPEEDS OF
10-20 KTS WILL REMAIN INTO SUNDAY MORNING. HOWEVER...THE SLIGHTLY
LOWER SPEEDS WILL ALLOW WAVE HEIGHTS TO DROP TO BELOW 6 FT...AND
THE SCA SHOULD BE ABLE TO EXPIRE AT 8PM FOR THE NORTHERN WATERS.
THEREAFTER...A SCEC MAY BE NEEDED FOR THE MUCH OF THE REST OF THE
NEAR TERM AS SEAS ARE FORECAST TO REMAIN 3-5 FT.

SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 3 PM SATURDAY...NORTHEAST WINDS OF 10 TO 15 KTS ON SUNDAY
WILL DECREASE TO AROUND 10 KTS OR LESS ON MONDAY AS OVERALL
PRESSURE GRADIENT SLACKENS. SEAS OF AROUND 3 FT ON SUNDAY WILL
DECREASE TO AROUND 2 FT ON MONDAY.

LONG TERM /TUESDAY THROUGH THURSDAY/...
AS OF 3 PM SATURDAY...A MODEST NORTHEASTERLY FLOW WILL GREET
MARINERS TUESDAY MORNING ALONG WITH WIDESPREAD RAINFALL. WIND
SPEEDS WILL BE LIGHT INITIALLY...LESS THAN TEN KNOTS. AS WE
PROGRESS INTO EARLY WEDNESDAY...THE FLOW WILL BACK TO MORE OF A
DUE NORTHERLY DIRECTION AND INCREASE TO 10-15 KNOTS AS THE LOW
PRESSURE SYSTEM PULLS AWAY SLOWLY. BY THE END OF THE PERIOD WINDS
ARE BACK TO A NORTHEAST DIRECTION AS HIGH PRESSURE BUILDS DOWN
FROM THE CANADIAN MARITIMES. SIGNIFICANT SEAS SHOULD BE ON THE LOW
SIDE CITING THE LACK OF STRONG WINDS AND CHANGES IN THE
FETCH...GENERALLY 1-3 TO 2-4 FEET.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...REK
NEAR TERM...DCH/JDW
SHORT TERM...REK
LONG TERM...SHK
AVIATION...SGL



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