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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KILM 221050
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
650 AM EDT WED MAY 22 2013

.SYNOPSIS...
WESTERN ATLANTIC HIGH PRESSURE WILL DOMINATE THE WEATHER ACROSS
THE EASTERN CAROLINAS THROUGH EARLY THURSDAY. SHOWERS AND
THUNDERSTORMS WILL INCREASE THURSDAY AND THURSDAY NIGHT AHEAD OF
AN APPROACHING COLD FRONT. THE FRONT WILL CROSS THE REGION FRIDAY
MORNING. A MUCH COOLER AND DRIER AIR MASS WILL FOLLOW...COMPLEMENTS
OF A CANADIAN HIGH PRESSURE...AND AFFECT THE AREA THIS WEEKEND.
THE HIGH WILL SLIDE OFF THE EAST COAST EARLY NEXT WEEK WITH
TEMPERATURES REBOUNDING TO NEAR NORMAL...ALONG WITH AN INCREASE IN
DIURNALLY DRIVEN CONVECTION.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 300 AM WEDNESDAY...THE WEAK UPPER LEVEL SHEAR AXIS THAT HAS
BEEN NEARLY STATIONARY ACROSS THE EASTERN CAROLINAS FOR THE PAST TWO
DAYS HAS DECAYED AS LIGHT SOUTHERLY FLOW HAS ESTABLISHED ITSELF
THROUGHOUT THE 500-700 MB LAYER. ALTHOUGH THE OVERALL AIRMASS
REMAINS THE SAME AS YESTERDAY...TRIGGERS FOR TODAY`S CONVECTION WILL
BE SURFACE BOUNDARIES ONLY. EARLY MORNING CONVECTION MOVING ONSHORE
ACROSS OAK ISLAND THROUGH WILMINGTON IS ASSOCIATED WITH A LOW-LEVEL
CONVERGENCE AXIS WHERE SOUTHWEST WINDS ACROSS THE SC COASTAL WATERS
CONVERGE WITH SOUTH WINDS CLOSER TO THE GULF STREAM. THIS CONVECTIVE
ACTIVITY SHOULD BECOME MORE ISOLATED IN NATURE TOWARD DAYBREAK...BUT
THE REMNANT CONVERGENCE AXIS MAY BECOME ACTIVE AGAIN BY LATE
MORNING AS THE DEVELOPING SEABREEZE CIRCULATION CREATES ADDITIONAL
CONVERGENCE IN THE LOW LEVELS.

BY EARLY AFTERNOON WE SHOULD HAVE A DEVELOPING FIELD OF SCATTERED
SHOWERS ACROSS MOST OF THE AREA EAST OF I-95 AND WEST OF THE
BEACHES. AS THE SEABREEZE MAKES GOOD PROGRESS INLAND THIS AFTERNOON
EXPECT CLEARING CONDITIONS WITHIN 20 MILES OF THE COAST...BUT
SHOWER AND T-STORM CHANCES WILL INCREASE TO 30-40 PERCENT WEST OF
THE SEABREEZE BOUNDARY IN A MODERATELY UNSTABLE AND COMPLETELY
UNCAPPED AIRMASS. 850 MB TEMPS IN THE +15C TO +17C RANGE WILL
SUPPORT TEMPERATURES IN THE MID 80S INLAND TODAY...WITH LOWER 80S
CLOSER TO THE COAST.

SOUTHWESTERLY WINDS WILL INCREASE ABOVE THE SURFACE TONIGHT AS A
MID-LATITUDE STORM SYSTEM SWEEPS EAST INTO THE GREAT LAKES. A WEAK
VORTICITY MAXIMUM LOCATED ACROSS GEORGIA THIS EVENING WILL MOVE
EASTWARD AND SHOULD SUSTAIN ISOLATED TO SCATTERED SHOWER AND T-STORM
POTENTIAL THROUGH THE NIGHT ACROSS THE EASTERN CAROLINAS. WHILE THE
SC PEE DEE REGION WILL BE THE CLOSEST GEOGRAPHICALLY TO THE INCOMING
VORT ALOFT...PRECIP CHANCES MAY ACTUALLY BECOME GREATEST IN THE
WILMINGTON AREA AS MODELS ARE INSISTENT THAT A BLOB OF GULF STREAM
CONVECTION WILL MOVE NORTH INTO THE CAPE FEAR REGION OVERNIGHT. LOWS
SHOULD FALL TO 66-70...WARMEST AT THE BEACHES.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
AS OF 300 AM WEDNESDAY...THIS PERIOD WILL BE HIGHLIGHTED BY THE
EVOLUTION OF A RATHER DEEP MID-LEVEL TROF THAT WILL DOMINATE THE
WEATHER ACROSS THE FA BY THE END OF THIS PERIOD. AT THE BEGINNING OF
THE SHORT TERM...THE AMPLIFYING UPPER TROF IS PROGGED TO BE JUST
EAST OF THE MISSISSIPPI RIVER...AND BY LATE FRIDAY NIGHT ITS NORTH
TO SOUTH TROF AXIS WILL HAVE MOVED JUST OFF THE NORTH AND SOUTH
CAROLINA COASTS...VIA NAM AND GFS MODELS. MODELS AT TIMES HAVE TRIED
TO MAKE THIS AN AMPLIFIED FULL LATITUDE TROF BUT INDIVIDUAL
VORTS/IMPULSES ROTATING THROUGH THIS UPPER FEATURE...ARE PROGGED TO
MOVE AT DIFFERENT SPEEDS AND THUS PREVENTING THE CARVING OF A TRUE
FULL LATITUDE TROF. ONE OF THE STRONGER VORTS IS PROGGED TO TRACK
ACROSS THE FA FRIDAY AFTERNOON/EVENING AS DYNAMICS FROM THIS FEATURE
AND COLDER TEMPS ALOFT PROVIDE ENOUGH INSTABILITY FOR ISOLATED
CONVECTION.

AT THE SURFACE...WESTERN ATLANTIC RIDGING WILL CONTINUE ACROSS THE
FA EARLY THURSDAY. A PRE-FRONTAL OR LEE SIDE TROF ORIENTED N-S WILL
DEVELOP ACROSS THE WEST-CENTRAL CAROLINAS AND BECOME THE FOCUS FOR
CONVECTION DEVELOPMENT AS IT SLOWLY PROGRESSES EASTWARD. IN ADDITION
...MID-DAY/AFTERNOON DIURNALLY INDUCED CONVECTION WILL BREAK OUT
ACROSS THE COASTAL PORTIONS OF THE ILM CWA. WILL INDICATE 50 POPS
INLAND...WITH 30-40 CLOSER TO THE COAST DURING THE DAY THURSDAY. FOR
THURSDAY NIGHT...THE APPROACHING COLD FRONT WILL BECOME THE PRIMARY
FORCE FOR INDUCING CONVECTION. HOWEVER...THE SUB-TROPICAL/TROPICAL
MOISTURE FEED WILL HAVE BEEN PUSHED OFFSHORE AND NO LONGER THE
PRIMARY SOURCE. THINKING IS THAT ENOUGH MOISTURE WILL REMAIN FOR
ADDITIONAL CONVECTION TO FIRE AHEAD OF THE COLD FRONT...DEPENDING
HOW MUCH THE ATM IS ABLE TO DE-STABILIZE FROM THE CONVECTION THAT
DEVELOPED EARLIER IN THE DAY. AS A RESULT...WILL HIGHLIGHT 40-50
POPS IN THE EVENING AND SLOWLY DROP THEM TO SLIGHT CHANCE OVERNIGHT.
MODELS AFTER MIDNIGHT FRIDAY...DIVERGE FROM ONE ANOTHER WITH RESPECT
TO THEIR SOLUTIONS RELATED TO THE TIMING AND PLACEMENT OF THE COLD
FRONT. FOR EXAMPLE THE NAM AND CANADIAN HAVE THE FRONT OFF THE
CAROLINA COASTS BY DAYBREAK FRI...WHEREAS THE GFS LAGS BEHIND AND
ONLY HAS IT PROGRESSING THROUGH THE COASTAL CAROLINAS BY DAYBREAK
FRI. WILL LEAN TOWARD THE SLIGHTLY SLOWER PROGRESSION OF THE CFP.
POST FRONTAL DRIER AIR FINALLY ADVECTS ACROSS THE FA DURING THE DAY
FRI. CANADIAN HIGH PRESSURE WILL FINALLY PROVIDE RELIEF FROM THE
HUMID SUBTROPICAL/TROPICAL AIR MASS THAT AFFECTED THE FA FOR MUCH OF
THIS WEEK.

AS FOR MAX/MIN TEMPS...A RANGE OF 80 TO 85 FOR HIGHS THU...SIMILAR
TO WHAT THE NAM/GFS MOS GUIDANCE SHOWS. THE COLD AIR ADVECTION
BEHIND THE CFP WILL LAG BEHIND...AND BE OFFSET BY A DOWNSLOPE
TRAJECTORY IN THE WIND FIELDS. AS A RESULT...HAVE GONE ABOVE
GUIDANCE FOR FRIDAYS HIGHS WITH THE COASTAL COUNTIES LIKELY TO BE
WARMER THAN INLAND. A COMPROMISED MOS GUIDANCE MIN FORECAST WAS
USED.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 300 AM WEDNESDAY...FOR SATURDAY THRU MONDAY MID LEVEL FEATURES
REMAIN RELATIVELY UNCHANGED WITH THE TROF AXIS ASSOCIATED WITH THE
UPPER TROF HAVING ONLY PROGRESSED JUST OFF THE EAST COAST. THE
CENTRAL U.S. WILL BE HIGHLIGHTED BY AN UPPER RIDGE WITH ITS AXIS
RUNNING N-S ALONG THE MISSISSIPPI RIVER. BY TUESDAY...THE EUROPEAN
FLATTENS THIS RIDGE WHEREAS THE GFS PROGRESSES IT EASTWARD AND
MAINTAINING ITS IDENTITY. PREFERRED THE GFS SOLUTION AT THIS POINT.
AT THE SFC...CANADIAN HIGH PRESSURE TO RIDGE ACROSS THE FA SATURDAY.
ITS CENTER IS PROGGED TO BREAK APART BY SUNDAY...WITH THE SOUTHERN
EXTENT OF ITS CENTER MOVING ACROSS AND OFFSHORE FROM THE CAROLINAS
MONDAY AND TUESDAY. SUBSIDENCE ALOFT WILL KEEP A LID ON THE
DIURNALLY DRIVEN CU FROM DEVELOPING IN THE VERTICAL. THEREFORE NO
POPS THROUGH SUNDAY. FOR LATE SUNDAY NIGHT THRU TUESDAY...MODELS ARE
HINTING AT A BACK-DOOR COLD FRONT DROPPING SOUTHWARD...AND BECOMING
STATIONARY JUST NORTH OF THE FA. THIS MAY BECOME AN AID TO POSSIBLE
MCS/MCC THAT DEVELOP WELL UPSTREAM MON AND TUE...WHICH WILL FOLLOW
THE NW-SE UPPER FLOW. TOO FAR OUT IN TIME TO PREDICT THEIR
TIMING...HOWEVER ENOUGH OF A POSSIBILITY TO PLACE A LOW CHANCE POP
IN THE GOING FORECAST.

FOR THIS UPCOMING MEMORIAL DAY WEEKEND...SATURDAY THROUGH MONDAY
MORNING TEMPS ACROSS THE FA WILL RUN 5 TO 10 DEGREES BELOW
NORMAL...ESPECIALLY WITH OVERNIGHT LOWS. FOR MONDAY THRU
TUESDAY...WILL BE LOOKING AT NEAR NORMAL TEMPS. IF THE BACK-DOOR
COLD FRONT DROPS FURTHER SOUTH THAN ANTICIPATED...THE NW FLOW AHEAD
OF IT COULD PUSH TEMPS WELL INTO THE 80S TO AROUND 90...MUCH HIGHER
THAN THE CURRENT MOS GUIDANCE.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
AS OF 12Z...A BIT LESS DEEP MOISTURE TODAY WITH MAINLY SOUTHERLY
FLOW. A LOW LCL INDICATES A MVFR CEILING COULD FORM AN HOUR OR SO
AFTER SUNRISE. HRRR MODEL INDICATES AN EARLY START TO CONVECTION
ALONG THE SEA BREEZE TODAY...WITH SHOWERS LIKELY NOT AS STRONG DUE
TO LACK OF MOISTURE. MOST OF THE ACTIVITY WILL ACTUALLY BE BETWEEN
THE INLAND AND COASTAL TERMINALS...NEARING THE INLAND TERMINALS BY
18Z. SOUTHERLY FLOW WILL BE A BIT GUSTY THIS AFTERNOON...DIMINISHING
DIURNALLY THIS EVENING. WILL REEVALUATE BACK END OF TAFS ON THE NEXT
MODEL RUN AS ANOTHER SLUG OF MOISTURE ADVECTS IN FROM THE SOUTH.

EXTENDED OUTLOOK...SHOWERS/T-STORMS POSSIBLE THURSDAY THROUGH EARLY
FRIDAY. OTHERWISE VFR.
-- End Changed Discussion --

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 300 AM WEDNESDAY...BERMUDA HIGH PRESSURE WILL MOVE LITTLE
THROUGH TONIGHT...CONTINUING TO PUMP AIR FROM THE CARIBBEAN
NORTHWARD ACROSS THE CAROLINA COASTAL WATERS. LOW PRESSURE WILL MOVE
EAST ACROSS THE GREAT LAKES...TOO FAR AWAY FOR ANY DIRECT AFFECTS
JUST YET. A TYPICAL SUMMER/TROPICAL WEATHER REGIME IS EXPECTED WITH
SCATTERED SHOWERS AND THUNDERSTORMS OVER THE COASTAL WATERS ENDING
THIS MORNING...THEN REDEVELOPING TONIGHT. MODELS ARE ACTUALLY QUITE
INSISTENT THAT AT LEAST ONE CONCENTRATED BATCH OF CONVECTION COULD
ROLL IN OFF THE GULF STREAM OVERNIGHT AND TOWARD COASTAL NORTH
CAROLINA.

OUTSIDE OF ANY SHOWER AND THUNDERSTORM ACTIVITY...SOUTH WINDS SHOULD
AVERAGE 10-15 KNOTS WITH 3-4 FT SEAS. DOMINANT WAVE PERIODS AT THE
FRYING PAN SHOALS BUOY ARE 6 SECONDS...WITH YESTERDAY`S 10 SECOND
EASTERLY SWELL HARDLY REGISTERING ANYMORE.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
AS OF 300 AM WEDNESDAY...WESTERN ATLANTIC RIDGING WILL PROVIDE A
RATHER SOLID 15 KT SOUTHERLY FLOW DURING THU...BECOMING SW LATE
THU AFTERNOON AND NIGHT. THE SFC PG WILL TIGHTEN BETWEEN THE
APPROACHING COLD FRONT AND THE WESTERN ATLANTIC HIGH CENTERED WELL
OFFSHORE FROM THE SE U.S.COAST. COULD SEE 15 TO 20 KT WITH SOME
HIGHER GUSTS. CFP SLATED FOR AFTER DAYBREAK FRI...WITH WINDS
VEERING TO W TO NW 10 TO 15 KT...INCREASING TO 15 TO 25 KT FRIDAY
NIGHT DUE TO COLD AIR ADVECTION COMBINED WITH A TIGHTENED SFC PG.
SIGNIFICANT SEAS WILL RANGE FROM 2 TO 4 FT THU...BUILDING TO 3 TO
5 FT LATE THU THROUGH EARLY FRI. TEMPORARILY DROPPING BACK TO 2 TO
4 FT DURING FRIDAY...THEN BUILDING BACK TO 3 TO 5 FT FRI NIGHT
WITH 6 FOOTERS POSSIBLE OUTER WATERS OFF CAPE FEAR. SIG. SEAS WILL
PRIMARILY BE DRIVEN BY AN ESE GROUND SWELL AT 8 TO 9 SECOND
PERIODS DURING EARLY THU...WITH 4 TO 6 SECOND PERIOD WIND DRIVEN
WAVES TO DOMINATE LATE THU THRU FRI NITE. SCEC CONDITIONS POSSIBLE
FOR ALL WATERS...WITH A BORDERLINE SCA FOR THE ILM NC WATERS
DURING THE INFLUX OF COLD AIR FRI NIGHT.

LONG TERM /SATURDAY THROUGH SUNDAY/...
AS OF 300 AM WEDNESDAY...POSSIBLE SCEC OR SCA CONDITIONS WILL
PEAK DURING EARLY SATURDAY...WITH A DIMINISHING AND SUBSIDING
TREND FOR WINDS AND SIGNIFICANT SEAS RESPECTIVELY DURING THE
LATTER 2/3RDS OF THIS PERIOD. ALL IN RESPONSE TO THE CENTER OF THE
MODERATING CANADIAN HIGH PUSHING ACROSS THE LOCAL WATERS SUNDAY
THROUGH SUNDAY NIGHT. WINDS ARE PROGGED TO BECOME VARIABLE IN
DIRECTION DURING SUNDAY AND SUNDAY NIGHT AT 10 KT OR LESS.
SIGNIFICANT SEAS WILL BE DRIVEN BY LOCALLY PRODUCED SHORT PERIOD
WIND DRIVEN WAVES ON SATURDAY...WITH AN 8 TO 9 SECOND PERIOD SMALL
EASTERLY SWELL DOMINATING ON SUNDAY.

&&

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

&&

$$
SYNOPSIS...DCH
NEAR TERM...TRA
SHORT TERM...DCH
LONG TERM...DCH
AVIATION...43