Area Forecast Discussion
Issued by NWS Wilmington, NC

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000
FXUS62 KILM 160242
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
1042 PM EDT WED APR 15 2015

.SYNOPSIS...
LOW PRESSURE WILL DEVELOP ALONG A FRONT STALLED ALONG THE GEORGIA
COAST TONIGHT...SLOWLY WEAKENING LATE THURSDAY AND FRIDAY. HIGH
PRESSURE OVER NEW ENGLAND WILL SHIFT EAST AND OFFSHORE THURSDAY. A
WARM FRONT WILL MOVE NORTH THROUGH THE CAROLINAS ON SUNDAY WITH A
COLD FRONT TO FOLLOW MONDAY NIGHT INTO TUESDAY.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
AS OF 1030 PM WEDNESDAY...THE WEATHER SITUATION IS UNFOLDING
PRETTY MUCH AS EXPECTED. THE SOLID MASS OF RAIN HAS CLEARED THE
PEE DEE COUNTIES BUT RAIN CONTINUES TO FALL ACROSS
WHITEVILLE...SOUTHPORT AND WILMINGTON. THIS AREA SHOULD MOVE OFF
THE COAST IN THE NEXT 2 HOURS...LEAVING MUCH WEAKER FORCING FOR
THE OVERNIGHT NIGHT. LATEST HRRR AND HRRRX MODELS STILL SUGGEST
THE BEST POTENTIAL FOR OVERNIGHT RAIN WILL BE NORTH OF A LINE FROM
FLORENCE TO DILLON...TO ELIZABETHTOWN AND BURGAW...COINCIDENT
WITH THE BETTER 700 MB MOISTURE AND RESIDUAL ISENTROPIC LIFT ON
THE SYNOPTIC MODELS. THERE IS ALSO SMALL POSITIVE ELEVATED
INSTABILITY ON THE ORDER OF 100 J/KG WHICH COULD HELP SUPPORT
SHOWERS GIVEN SUFFICIENT SYNOPTIC TRIGGERING. FEW CHANGES ARE
NEEDED TO LOW TEMPERATURE FORECASTS OR WINDS. DISCUSSION FROM 730
PM FOLLOWS...

A STALLED FRONT JUST SOUTH OF SAVANNAH WILL DEVELOP AN AREA OF LOW
PRESSURE IN THE NEXT FEW HOURS. THIS LOW WILL NOT STRAY TOO FAR
OFFSHORE OVER THE NEXT 24 HOURS...BUT WILL MAINTAIN A STEADY
NORTHEAST WIND. SURFACE HIGH PRESSURE OVER SOUTHEASTERN CANADA
WILL SLIDE SOUTHEAST INTO NEW ENGLAND TONIGHT. THIS HIGH WILL
EXTEND A RIDGE AXIS SOUTHWARD INTO THE CAROLINAS...COMPRESSING THE
PRESSURE GRADIENT UP AGAINST THE LOW DEVELOPING OFF THE GEORGIA
COAST.

A COMPLEX UPPER LEVEL PATTERN ACROSS THE WESTERN U.S. HAS THE JET
STREAM SPLIT INTO TWO SEGMENTS. THE SOUTHERN STREAM WILL BRING
SEVERAL DISTURBANCES ACROSS THE CAROLINAS OVER THE NEXT 36-48
HOURS. ONE OF THESE DISTURBANCES IS MOVING ACROSS INTERSTATE 95
NOW PRODUCING THE LARGE SWATH OF RAIN NOW SEEN ON RADAR. THIS
FEATURE SHOULD WORK ITS WAY TO THE COAST AROUND MIDNIGHT...AND I
HAVE RAISED FORECAST POPS TO 100 PERCENT AREA-WIDE WITH 0.2 TO 0.4
INCHES OF RAIN EXPECTED OVER THE NEXT 12 HOURS. PLENTY OF MID-
LEVEL MOISTURE SHOULD HANG AROUND AFTER MIDNIGHT WITH JUST ENOUGH
WEAK ISENTROPIC LIFT PLUS ELEVATED INSTABILITY TO MAINTAIN SHOWERS
AFTER MIDNIGHT...ESPECIALLY NORTH OF FLORENCE AND MYRTLE BEACH.

LOW-LEVEL NORTHEAST WINDS WILL DRAG COOLER AIR SOUTHWARD
TONIGHT...WITH LOWS AWAY FROM THE COAST FALLING TO NEAR 50.
VARYING DEGREES OF MARINE INFLUENCE WILL KEEP THE IMMEDIATE COAST
WARMER WITH LOWS IN THE MID 50S POSSIBLE.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
AS OF 300 PM WEDNESDAY...THE FORECAST HAS BECOME NO LESS COMPLICATED
AND IN FACT...IN SOME RESPECTS...MODELS HAVE DIVERGED EVEN FURTHER
IN THE LAST 24 HOURS. THE GFS SOLUTION LOOKS VERY DIFFERENT FROM
PREVIOUS RUNS. THE NAM SOLUTION LOOKS SIMILAR TO PREVIOUS
THINKING...BUT THE PROGRESSION OF OFFSHORE LOW PRESSURE IS SLOWER
AND FURTHER EASTWARD THAN 24 HOURS AGO AND CERTAINLY MUCH STRONGER.
THE CANADIAN IS CONSIDERABLY SLOWER AND WEAKER THAN THE NAM AS IS
THE EUROPEAN...BUT BOTH DO CLOSE OFF LOW PRESSURE ALONG THE COAST OF
SOUTH CAROLINA. SLOWER SEEMS REASONABLE GIVEN THE STRENGTH OF HIGH
PRESSURE TO THE NORTH AND RESULTING WEDGE...THUS THE BEST WE CAN DO
AT THIS POINT IS TO GO ALONG WITH PERSISTENCE...BUT SLOW PROGRESSION.

WILL INCLUDE HIGHEST POPS THU ALONG THE COAST AND UP TO CATEGORICAL
THU MORNING ALONG THE CAPE FEAR COAST DUE TO STRENGTH OF ISENTROPIC
LIFT COUPLED WITH THE LIFT ASSOCIATED WITH LOW PRESSURE/TROUGH. WILL
THEN TREND POPS LOWER THU AFTERNOON AND NIGHT FROM SW TO NE WITH A
LINGERING RISK ALONG THE CAPE FEAR COAST FRI MORNING. GIVEN
PROXIMITY OF COASTAL TROUGH AND ELEVATED INSTABILITY...WILL INCLUDE
MENTION OF THUNDER FOR PORTIONS OF THE FORECAST AREA.

THE MOISTURE PROFILES DRY OUT CONSIDERABLY AS A RIDGE OF HIGH
PRESSURE ALOFT BUILDS TO THE COAST FROM THE WEST TOWARD THE END OF
THE PERIOD. WILL FINALLY DROP POPS BELOW THRESHOLD FRI AFTERNOON AND
NIGHT...EVEN ALONG THE SEABREEZE BOUNDARY.

BELOW NORMAL HIGH TEMPS ARE EXPECTED AGAIN ON THU AS WEDGE KEEPS LOW-
LEVEL MOISTURE TRAPPED BENEATH INVERSION. HIGHS WILL ONLY BE IN THE
LOWER TO MID 60S. DEVELOPING SUNSHINE ON FRI SHOULD ALLOW TEMPS TO
RETURN TO MORE SEASONABLE LEVELS...LOW AND MID 70S. LOWS THIS PERIOD
WILL BE MAINLY IN THE 50S.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AS OF 300 PM WEDNESDAY...GUIDANCE HAS SHIFTED PRETTY DRAMATICALLY
FROM JUST YESTERDAY...LEADING TO ENHANCED UNCERTAINTY DURING THE
EXTENDED. LARGE CLOSED LOW ACROSS THE SOUTHWEST WILL ONLY VERY
SLOWLY FILL AND EJECT TO THE NORTHEAST THROUGH THE WEEKEND...PHASING
WITH A DEEPENING NORTHERN STREAM CUTOFF LOW ACROSS THE GREAT LAKES
LATE MONDAY. THIS FEATURE WILL THEN AMPLIFY AND STALL ACROSS THE
GREAT LAKES THROUGH THE MIDDLE OF NEXT WEEK...PRODUCING 500MB
HEIGHTS OF -2 TO -3 SD`S BELOW CLIMO ACROSS THE NORTHEAST AND INTO
THE MID-ATLANTIC.

INITIALLY THE EXTENDED WILL BE WARM AND PLEASANT. SATURDAY IS
SHAPING UP TO BE A GORGEOUS DAY LOCALLY...WITH HIGHS ABOVE CLIMO AND
A LOT OF SUNSHINE. MOISTURE RETURNS SUNDAY IN A PRE-FRONTAL AIR MASS
WHICH WILL CONTINUE INTO MONDAY AHEAD OF A COLD FRONT. SUNDAY AND
MONDAY WILL BOTH FEATURE ABOVE CLIMO TEMPS...BUT WITH INCREASING
RAIN CHANCES AHEAD OF THE COLD FRONT. ATTM THE FRONT DOES NOT LOOK
TO BE STRONGLY FORCED SO WIDESPREAD CONVECTION IS NOT ANTICIPATED
MONDAY EVENING WITH THE FROPA. COOLER HIGH PRESSURE WILL BUILD IN
BEHIND THE FRONT FOR TUE/WED OF NEXT WEEK WITH TEMPS RETURNING TO
SEASONABLE LEVELS.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
AS OF 00Z...MOST TERMINALS IN VFR OR MVFR CATEGORY ATTM WITH A
BAND OF LIGHT TO MDT RAIN MOVING THROUGH THE AREA. EXPECT TO SEE
CONDITIONS DETERIORATE TO IFR AGAIN OVERNIGHT AFTER MAIN BAND OF
RAIN MOVES THROUGH AND PRECIP BECOMES MORE ISOLATED TO SCATTERED
IN NATURE. AN AREA OF LOW PRESSURE WILL BRING ADDITIONAL RAINFALL
AFTER DAY BREAK THURSDAY WHICH SHOULD ALLOW IFR TO MVFR CONDITIONS
TO PERSIST FOR MUCH OF THE REMAINDER OF THE FORECAST PERIOD.

EXTENDED OUTLOOK...PREDOMINATELY IFR CONDITIONS ARE EXPECTED INTO
EARLY FRIDAY MORNING WITH THE WEDGE. IMPROVING CONDITIONS DURING THE
DAY FRI. DETERIORATING CONDITIONS AGAIN SATURDAY NIGHT THROUGH
SUNDAY WITH A SLOW MOVING FRONT. SLIGHT CHANCE FOR SHOWERS MONDAY.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 1030 PM WEDNESDAY...STRONG NE WINDS HAVE QUICKLY DEVELOPED
THIS EVENING. RECENT WIND GUSTS INCLUDE 31 KNOTS AT SPRINGMAID
PIER IN MYRTLE BEACH...24 KNOTS ON BALD HEAD ISLAND...AND 23
KNOTS AT WRIGHTSVILLE BEACH. SEAS OUT AT THE FRYING PAN SHOALS
BUOY HAVE ALREADY REACHED 8 FEET...WITH SEAS NOW PASSING 5 FEET AT
BOTH NEARSHORE BUOYS NEAR CAPE FEAR. THIS UPDATE BACKED WINDS
AROUND MORE NORTHERLY NEARSHORE AND INCREASE SEA HEIGHTS
SLIGHTLY...ALL BASED ON CURRENT OBSERVATIONS. DISCUSSION FROM 730
PM FOLLOWS...

A FRONT STALLED JUST SOUTH OF SAVANNAH EXTENDS EAST WELL OFF THE
COAST. WEAK LOW PRESSURE WILL DEVELOP ALONG THE FRONT
TONIGHT...WHILE HIGH PRESSURE OVER NEW ENGLAND RIDGES SOUTHWARD
DOWN THE COAST. THE CAROLINAS WILL BE CAUGHT IN BETWEEN THESE TWO
SYSTEMS...WITH INCREASING EAST-NORTHEAST WINDS THE RESULT.

THE 18Z GFS APPEARS TO BE THE BEST INITIALIZED OF OUR MODELS THIS
EVENING...AND ITS FORECAST WINDS HAPPEN TO BE THE STRONGEST
TONIGHT...INDICATING WINDS NEARSHORE INCREASING TO 20-25 KT AND
25-30 KT AWAY FROM SHORE. THIS IS SLIGHTLY HIGHER THAN THE
PREVIOUS FORECAST HAD. LATEST CHECK OF BUOYS INDICATES SEAS ARE
INCREASING A BIT FASTER THAN EARLIER THOUGHT. I HAVE ADDED ABOUT
ONE FOOT TO THE PREVIOUS FORECAST...WITH SEAS NOW EXPECTED TO
BUILD TO 6-8 FEET OUT AT 20 MILES DISTANCE FROM SHORE...WITH 4-7
FEET EXPECTED CLOSER TO SHORE.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
AS OF 300 PM WEDNESDAY...ONGOING SMALL CRAFT ADVISORY CONDITIONS ARE
EXPECTED AT THE BEGINNING OF THE PERIOD AS LOW PRESSURE MOVES UP THE
SOUTHEAST COAST. THE PRESSURE GRADIENT BETWEEN DEVELOPING LOW
PRESSURE AND THE STRONG HIGH TO THE NORTH WILL ALLOW A TIGHT
PRESSURE GRADIENT TO PERSIST INTO THU AND THIS IS WHEN WE EXPECT THE
STRONGEST WINDS AND HIGHEST SEAS...UP TO 20 TO 30 KT...HIGHEST
NORTHERN WATERS AND SEAS UP TO 5 TO 8 FT THROUGHOUT. AS THE PRESSURE
GRADIENT SLACKENS AND LOW PRESSURE MOVES TO OUR N...WINDS AND SEAS
WILL SUBSIDE THU NIGHT AND FRI WITH THIS TREND PERSISTING INTO FRI
NIGHT. ENE WINDS THU WILL BACK TO NE THU NIGHT WITH NNE TO NE
WINDS THEN PERSISTING THROUGH THE END OF THE PERIOD.

LONG TERM /SATURDAY THROUGH MONDAY/...
AS OF 300 PM WEDNESDAY...HIGH PRESSURE WILL BUILD DOWN THE COAST AND
THEN MOVE OFFSHORE SATURDAY...CREATING A WEAK PRESSURE GRADIENT AND
WINDS SHIFTING FROM NE EARLY...TO E/SE LATE. WINDS SPEEDS THEN
STEADILY INCREASE SUNDAY AS THE GRADIENT STARTS TO PINCH AHEAD OF AN
APPROACHING COLD FRONT...BECOMING S/SW AT AROUND 15 KTS MOST OF
SUNDAY...AND THEN SW AT 15-20 KTS ON MONDAY DIRECTLY AHEAD OF THE
FROPA. COLD FRONT WILL CROSS THE WATERS AT THE VERY END OF THE
PERIOD WITH A WIND SHIFT TO THE NW AT 10-15 KTS. ALTHOUGH A WEAK SE
GROUND SWELL WILL BE PRESENT IN THE SPECTRUM DURING THE
EXTENDED...MUCH OF THE WAVE AMPLITUDE WILL BE FORMED VIA WIND
WAVES...AND SEAS WILL BE 2-3 FT SATURDAY...BUILDING TO 3-5 FT SUNDAY
AND MONDAY AHEAD OF THE COLD FRONT.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT FRIDAY FOR AMZ250-252-254-
     256.

&&

$$

SYNOPSIS...TRA
NEAR TERM...TRA
SHORT TERM...RJD
LONG TERM...JDW
AVIATION...RAN


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