-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KILM 200529
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
130 AM EDT MON MAY 20 2013

.SYNOPSIS...
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WESTERN ATLANTIC HIGH PRESSURE WILL RIDGE ACROSS THE FORECAST AREA
FOR THE MAJORITY OF THIS WEEK. A DISTURBANCE ALOFT MOVING ACROSS THE
AREA EARLY IN THE WEEK...WILL MAINTAIN THE THREAT FOR SHOWERS AND
THUNDERSTORMS THROUGH TUESDAY. A COLD FRONT WILL PUSH ACROSS THE
AREA LATE IN THE WEEK...FOLLOWED BY DRY CANADIAN HIGH PRESSURE FOR
THE WEEKEND.
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&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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AS OF 130 AM MONDAY...QUITE AN EXPLOSION OF SHOWER ACTIVITY ACROSS
THE AREA THIS MORNING FROM THE NC/SC SANDHILLS EXTENDING IN AN
ISOLATED FASHION DOWN TOWARD THE GRAND STRAND BEACHES. THE LATEST
HRRR MODEL SHOWS SOLID CHANCES FOR SHOWERS AND STORMS OVER THE NEXT
FEW HOURS ACROSS THE BENNETTSVILLE AND LUMBERTON AREA...WITH
ACTIVITY NEAR THE COAST REMAINING A FRAGMENTED/SCATTERED APPEARANCE
AS IT MOVES NORTH INTO COASTAL SE NORTH CAROLINA. NO SIGNIFICANT
CHANGES HAVE BEEN MADE TO FORECAST LOWS. PREVIOUS DISCUSSION FROM
1130 PM FOLLOWS...

VIA LATEST 88D TRENDS...EARLIER WIDESPREAD CONVECTIVE ACTIVITY
ACROSS THE FA HAS DISSIPATED TO ISOLATED IN AREAL COVERAGE AS OF
LATE THIS EVENING. IN GENERAL...THE ATM HAS BEEN WORKED OVER
INLAND...WHERE-AS CLOSER TO THE COAST THE ATM HAS HAD TIME TO
RECOVER SOME FROM THE ITS EARLIER ACTIVITY. THIS TREND WILL ALSO
OCCUR INLAND LATER TONIGHT. WITH A 1ST LOOK AT THE 00Z NAM...AID
FROM DYNAMICS ALOFT...PVA ASSOCIATED WITH THE MAIN 5H VORT
ASSOCIATED WITH THE WEAK S/W MID-LEVEL S/W TROF HAVING CRASHED INTO
THE UPPER RIDGE EARLIER THIS WEEKEND...CONVECTION SHOULD BEGIN TO
FIRE ACROSS THE CENTRAL CAROLINAS JUST OUTSIDE WEST OF THE ILM
CWA...AND DRIFT INTO THE FA DURING THE PRE-DAWN HRS. ACROSS THE
ADJACENT ATL WATERS...CONVECTION WILL FIRE UP ACROSS THE WARMER
WATERS JUST OUTSIDE OF THE ILM COASTAL WATERS...AND PUSH ACROSS THE
COASTAL WATERS AND ONSHORE DURING THE PRE-DAWN MON HRS. WITH THE
SLIGHTLY COOLER THEN NORMAL SHELF WATERS IN PLACE FOR THIS TIME OF
THE YEAR...THE QUESTION RESIDES OF JUST HOW MUCH OF A
NEGATIVE/WEAKENING INFLUENCE WILL IT HAVE ON THIS CONVECTION PRIOR
TO MOVING ONSHORE. POPS AGAIN HAVE BEEN RE-ADJUSTED/RE-STRUCTURED TO
ACCOUNT FOR CURRENT RADAR TRENDS...AND THE INCREASED CONVECTIVE
POTENTIAL LATER OVERNIGHT. 00Z RAOBS INDICATE PWS OF 1.4 MHX TO 1.8
CHS INCHES. HAVE INCLUDED A HEAVY RAIN SUFFIX TO THE PCPN WHICH ALSO
RESULTED IN A RE-TOOLING OF THE QPF ACROSS THE FA. OVERNIGHT MIN
TEMPS AND HOURLY DEWPOINTS REMAIN ON QUE.
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&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
AS OF 300 PM SUNDAY...MAIN FORECAST CHALLENGE WILL BE POPS AND THE
TIMING THEREOF AT LEAST THROUGH THE FIRST DAY...MONDAY. THE MID
LEVEL PATTERN WILL CONSIST OF A WEAK RIDGE EXTENDING INTO THE
TENNESSEE VALLEY/WESTERN NORTH CAROLINA REGION WITH A BROAD
WEAKNESS ALONG THE EAST COAST AT LEAST FROM FLORIDA NORTH TO THE
DELMARVA. PRECIPITABLE WATER VALUES REMAIN ELEVATED MONDAY INTO
MONDAY EVENING NEAR ONE AND THREE QUARTERS OF AN INCH. THE FORCING
WILL BASICALLY CONSIST OF THE WEAK MID LEVEL FORCING...A BROAD
DEFORMATION ZONE IN THE 700-300MB LAYER...AND DIFFERENTIAL HEATING
VIA THE SEA BREEZE AND INTERVALS OF CLOUDS.

INTERESTING TO LOOK AT THE CURRENT MESOSCALE CONVECTIVE SYSTEMS WEST
OF OUR AREA AND THE DEFORMATION. THESE APPEAR TO BE THE PRODUCT OF
THIS BROAD ZONE. HOWEVER THIS AREA OF FORCING...WHILE STILL PRESENT
IN A WEAKER STATE MONDAY AND OVER OUR AREA...MOVES LITTLE AND DO NOT
ANTICIPATE AS MUCH ORGANIZED CONFECTION...MORESO OF WHAT WE ARE
SEEING TODAY. MORE OF A SOUTHWEST FLOW DEVELOPS TUESDAY WITH PW
VALUES DROPPING SOMEWHAT AND THIS IS REFLECTED IN LOWER POP VALUES.

FOR TEMPERATURES...LOW CONFIDENCE FORECAST BUT I FOLLOWED A
CONSISTENT TREND OF LOWER VALUES MET NUMBERS MONDAY VIA HIGHER POPS
AND WARMER NUMBERS TUESDAY...MAV NUMBERS.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
AS OF 300 PM SUNDAY...WEDNESDAY SHOULD BE THE LAST DAY WITH THE
ABSENCE OF ANY SYNOPTIC SCALE ASCENT AS WEST ATLANTIC SURFACE AND
UPPER RIDGE HOLD ON. THE LATTER WILL BE WEAKENING HOWEVER AND LARGE
SCALE WEAK FORCING MAY KICK IN AS EARLY AS WEDNESDAY NIGHT. THE
AFTERNOON HOURS WILL STILL BE SUSCEPTIBLE TO ISOLATED COVERAGE OF
CONVECTION BORNE OF MESOSCALE BOUNDARIES ESPECIALLY WITH
TEMPERATURES ON THE WARM SIDE OF CLIMO...YIELDING EXTRA INSTABILITY.
THURSDAY AND FRIDAY MAY TURN ACTIVE WITH UPPER TROUGH AND SURFACE
COLD FRONT BOTH IMPINGING UPON THE REGION FROM THE NW. THE SPEED
AND AMPLITUDE OF THE TROUGH AND ENSUING COOLER/DRIER AIR IS NOT
AGREED UPON BY MODEL GUIDANCE. THE SLOWER AND LESS AMPLIFIED 00Z
EC SEEMS AT ODDS WITH THE MORE AGGRESSIVE GFS/GEM. THE QUICKER
SOLUTIONS OF CONTINUITY HAVE BEEN PRESERVED...IMPLYING THAT SOME
CONSIDERABLY DRIER AIR WILL WORKING OVER THE WEEKEND.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
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AS OF 06Z...NIGHTTIME SHOWERS ARE INCREASING IN COVERAGE OVER THE
EASTERN CAROLINAS AHEAD OF A WEAK UPPER LEVEL DISTURBANCE OVER THE
WESTERN CAROLINAS. MOISTURE FROM THESE SHOWERS SHOULD CREATE IFR
STRATUS IN FLO/LBT AFTER 08Z. ALONG THE COAST WARMER TEMPERATURES
DUE TO ONSHORE FLOW OFF THE ATLANTIC SHOULD MAINTAIN MVFR CIGS...
ALTHOUGH IT IS NOT IMPOSSIBLE THAT ISOLATED IFR CONDITIONS COULD
DEVELOP NEAR HEAVIER SHOWER ACTIVITY. AFTER DAYBREAK...CIGS WILL
GRADUALLY LIFT TO MVFR/VFR. SOUTHWEST WINDS WILL PREVAIL AOB 10 KTS
WITH GUSTS UP TO 18 KTS ALONG THE COAST LATER IN THE DAY. INCREASED
CHANCES FOR ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS
THROUGHOUT THE DAY....SLOWLY TAPERING OFF INTO THE EVENING HOURS.
FOR CURRENT FCST HAVE KEPT IN VCSH GIVEN UNCERTAINTY OF
TIMING/OCCURRENCE OF ANY CONVECTIVE ACTIVITY.

EXTENDED OUTLOOK...AFTN SHOWERS/TSTMS POSSIBLE MONDAY AND
TUESDAY. OTHERWISE PREVAILING VFR.
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&&

.MARINE...
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NEAR TERM /THROUGH TONIGHT/...
AS OF 130 AM MONDAY...NO SIGNIFICANT CHANGES NEEDED TO THE FORECAST
EARLY THIS MORNING. PREVIOUS DISCUSSION FROM 1130 PM FOLLOWS...

LATEST COASTAL AND MARITIME OBS INDICATE WINDS GENERALLY NEAR 10 KT
NEAR SHORE...AND UP TO 15 KT ACROSS THE OUTER WATERS. BASED ON THE
LATEST AND PROGGED SFC PRESSURE PATTERN...160-190 DEGREE WIND
DIRECTIONS TO OCCUR OVERNIGHT. THE PROGGED SFC PG HAS WIND SPEEDS
GENERALLY INCREASING TO 10-15 KT THRUOUT THE AREA WATERS.
SIGNIFICANT SEAS WILL GENERALLY BE 2 TO 3 FT...WITH 4 FOOTERS
POSSIBLE ACROSS THE OUTER WATERS 10-20 NM OUT. A 1 TO 2 FOOT
EASTERLY PSEUDO GROUND SWELL AT 8 TO 9 SECOND PERIODS...WILL MESH
WITH LOCALLY GENERATED WIND WAVES AT 4 TO 5 SECOND PERIODS. CURRENT
ISOLATED CONVECTIVE ACTIVITY...WILL INCREASE TO SCATTERED TO AREAS
IN COVERAGE DURING THE PRE-DAWN HRS AND INTO DAYLIGHT MONDAY
MORNING. COULD SEE WINDS GUSTING TO 20 TO 30 KT FROM THE STRONGER
TSTMS...ESPECIALLY THOSE TRAVERSING ACROSS SSTS OF 70 DEGREES OR
HIGHER...IE THE OUTER WATERS OFF CAPE FEAR.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 300 PM SUNDAY...SURFACE PATTERN CHANGES LITTLE THROUGH THE
PERIOD WITH IF ANYTHING...A SLIGHT TURN IN THE WINDS TOWARD THE
SOUTHWEST TUESDAY. DIRECTION SHOULD REMAIN STRAIGHT SOUTHERLY MONDAY.
OVERALL WINDS WILL CONTINUE TO DISPLAY SUMMERTIME SPEEDS IN A 10-15
KNOT RANGE. SEAS WILL ALSO DISPLAY LITTLE IN THE WAY OF VARIABILITY
WITH 2-4 FEET AS PERIODS REMAIN DOMINATED BY WIND WAVES.

LONG TERM /WEDNESDAY THROUGH FRIDAY/...
AS OF 300 PM SUNDAY...SOUTH TO SOUTHWESTERLY FLOW THROUGH THE
PERIOD WITH BERMUDA HIGH PRESSURE BEING THE MAIN PLAYER AT LEAST
INITIALLY. THE INCREASED DURATION OF FETCH WILL ALLOW FOR SOME
LONGER PERIOD SWELL ENERGY TO BEGIN MOVING INTO THE SOUTHEASTERN
U.S. AS A RESULT THERE SHOULD BE A DECREASE IN THE OVERALL WAVE
PERIOD WHILE SIGNIFICANT WAVE HEIGHT IS ON THE RISE. THERE COULD
EVEN BE SOME SCEC-WORTHY 5 FT SEAS ALONG THE OUTER EDGES OF THE
FCST ZONES BY THURSDAY. APPROACHING COLD FRONT ON FRIDAY COULD
VEER THE WIND SLIGHTLY. THIS BOUNDARY MAY BE COMING THROUGH AS
EARLY AS FRIDAY NIGHT BUT A SLOWER SOLUTION SEEMS LIKELY IN
FUTURE MODEL RUNS.
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&&

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

&&

$$

NEAR TERM...DCH/TRA
SHORT TERM...SHK
LONG TERM...MBB
AVIATION...SGL/TRA