Area Forecast Discussion
Issued by NWS Wilmington, NC

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000
FXUS62 KILM 180521
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
121 AM EDT THU SEP 18 2014

.SYNOPSIS...
HIGH PRESSURE WILL EXTEND DOWN INTO THE CAROLINAS FROM THE NORTH
PROVIDING FALL-LIKE WEATHER FOR THE REMAINDER OF THE WEEK. THE NEXT
COLD FRONT WILL MOVE THROUGH ON TUESDAY FOLLOWED BY COOL AND DRY
HIGH PRESSURE THROUGH THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1:30 AM THURSDAY...NO CHANGES TO THE FORECAST WITH THE
LATEST UPDATE. PREVIOUS DISCUSSION FOLLOWS:

ISOLATED CONVECTION HAS CONTINUED ACROSS ROBESON COUNTY AND ALSO
JUST OFF THE NEW HANOVER COUNTY BEACHES THIS EVENING. WITH SURFACE
TEMPERATURES NOW 70-74 DEGREES IN MOST LOCATIONS SURFACE-BASED
CAPE IS BELOW 1000 J/KG WITH 20-40 J/KG OF CONVECTIVE INHIBITION
TO DEAL WITH. HOWEVER LIFTING PARCELS FROM 925 MB GIVES ABOUT THE
SAME INSTABILITY WITH NO SIGNIFICANT CAPPING. THIS IS LIKELY THE
SOURCE REGION FOR THE ONGOING SHOWERS AND THUNDERSTORMS. ACTIVITY
APPEARS TO BE FOCUSED ALONG AN INVERTED TROUGH THAT IS THE LEADING
EDGE OF A MODEST NORTHEASTERLY SURGE OVER EASTERN NORTH CAROLINA.
GIVEN THE VERY MOIST AIRMASS UP THROUGH 850 MB THERE IS NO REASON
THIS INVERTED TROUGH/SURGE LINE CANNOT SERVE AS THE FOCUS FOR
ADDITIONAL SHOWERS OR THUNDERSTORMS ALL THE WAY THROUGH THE NIGHT
AS IT MOVES SOUTHWESTWARD THROUGH EASTERN SOUTH CAROLINA. IN
AGREEMENT WITH THE LATEST HRRR (NCEP PARALLEL VERSION) WILL
MAINTAIN 20-30 POPS ACROSS MOST OF EASTERN SOUTH CAROLINA THROUGH
THE NIGHT. THIS MAY HAVE SOME NEGATIVE IMPACT ON THE DEVELOPMENT
OF FOG AND LOW STRATUS LATE TONIGHT...BUT NO SIGNIFICANT CHANGES
WERE MADE TO THAT PORTION OF THE FORECAST. PREVIOUS DISCUSSION
FROM 730 PM FOLLOWS...

CHANGES TO THE FORECAST EARLY THIS EVENING CENTER ON OBSERVED RADAR
TRENDS. CONVECTION IS FINALLY DIMINISHING IN INTENSITY AND COVERAGE
ACROSS THE CAPE FEAR AREA...BUT A RENEWED CLUSTER OF STORMS IS
CROSSING THE SANTEE RIVER WITH ITS SIGHTS SET ON GEORGETOWN IN THE
NEXT HOUR. STORM MOTION IS BEING DRIVEN PRIMARILY BY BOUNDARIES AND
COLD POOL INTERACTIONS...ALTHOUGH A TREND NOTED WITH THE TALLER MORE
SIGNIFICANT THUNDERSTORMS HAS BEEN TO ACCELERATE EASTWARD DUE TO
STRONG WEST WINDS UP ABOVE 600 MB THAT THE SHALLOWER LESS
SIGNIFICANT CONVECTION ISN`T BEING AFFECTED BY. THE SPC MESOANALYSIS
PAGE SHOWS SURFACE-BASED CAPE IS AROUND 1500 J/KG WITH FAVORABLE
MID-LEVEL LAPSE RATES AROUND 6 DEG C/KM.

CONVECTIVE TRENDS THIS EVENING SHOULD BE TOWARD A SLOW DECREASE IN
ACTIVITY AS THE SURFACE COOLS. PLENTY OF DRY AIR ABOVE 700 MB HAS
BEEN HELPING PRODUCE CONVECTIVE OUTFLOW BOUNDARIES DUE TO
ENTRAINMENT INTO DOWNDRAFTS. THE LATEST FEW HRRR RUNS SHOW THERE MAY
BE A FEW LINGERING SHOWERS ACROSS NE SOUTH CAROLINA ROOTED IN A
LAYER OF UNSTABLE AIR AT 950-925 MB PERSISTING AFTER MIDNIGHT. I`LL
KEEP SOME 20 POPS GOING FROM MYRTLE BEACH AND MARION SOUTHWARD
BETWEEN 03-06Z TO ACCOUNT FOR THIS POTENTIAL.

NO SIGNIFICANT CHANGES HAVE BEEN MADE TO OTHER FORECAST ELEMENTS.
LOWS SHOULD STILL FALL INTO THE LOWER TO MID 60S FOR MOST AREAS AS
WEAK COOL ADVECTION DEVELOPS OVERNIGHT ON LIGHT NE WINDS BELOW 850
MB. LINGERING LOW-LEVEL MOISTURE WILL ALMOST CERTAINLY CREATE LOW
STRATUS AND FOG LATE TONIGHT...ESPECIALLY INLAND FROM THE COAST.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
AS OF 300 PM WEDNESDAY...HIGH PRESSURE BUILDING DOWN INTO THE
CAROLINAS FROM THE GREAT LAKES ON THURS WILL SHIFT EAST PRODUCING
A VERY PRONOUNCED WEDGE PATTERN BY FRI AFTN. AT THE SAME TIME THE
MID TO UPPER TROUGH OVER THE EAST COAST WILL LIFT OFF TO THE
NORTHEAST. BEFORE THE TROUGH LIFTS OFF...A COUPLE OF MINOR
PERTURBATIONS RIDING AROUND THE BASE MAY ENHANCE CLOUDS AND LOW
END PCP ON THURS...BUT NOT COUNTING ON MUCH. AS TROUGH LIFTS OFF
THROUGH FRI...IT MAY PROVIDE ENOUGH OF A WEAKNESS TO ALLOW
DEVELOPING LOW PRESSURE OFF THE SOUTHEAST COAST TO RETROGRADE
BACK TO THE W-NW THROUGH FRI NIGHT. OVERALL EXPECT DECENT
NORTHEAST FLOW AS GRADIENT BECOMES MORE PINCHED AS TROUGH OF LOW
PRESSURE SHIFTS NORTH TOWARD THE SOUTHEAST COAST THROUGH LATE FRI
INTO FRI NIGHT. THE NAM HAS THE LOW MOVING FARTHER WEST WITH A
GREATER ON SHORE FLOW OF MOISTURE THROUGH FRI AND A MUCH WETTER
FORECAST...WHILE THE GFS/ECMWF CONFINE THE GREATEST MOISTURE OFF
SHORE AND JUST ALONG THE COAST. FOR NOW WILL GO WITH BRUNT OF CLOUDS
AND POPS OFF SHORE AND JUST ALONG THE COAST IN NE FLOW THROUGH
FRI NIGHT.

NORTHEAST FLOW WILL HELP KEEP HIGH TEMPERATURES ALONG THE COAST A
LITTLE BELOW CLIMO THROUGH THE PERIOD. FARTHER INLAND HIGHS WILL BE
NEAR CLIMO WITH A LITTLE MORE SUN. LOW TEMPERATURES WILL END UP A
LITTLE ABOVE CLIMO DUE TO CLOUDS AND BOUNDARY LAYER MIXING.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AS OF 300 PM WEDNESDAY...POTENTIALLY UNSETTLED TO START THE
PERIOD...BUT EVEN BY D4 THERE IS CONSIDERABLE MODEL SPREAD. STALLED
BOUNDARY OFFSHORE WILL BE A FOCUS FOR LOW PRESSURE DEVELOPMENT...BUT
THE QUESTION REMAINS HOW CLOSE TO THE COAST THIS LOW WILL FORM. THE
NAM/CMC ARE IN ONE CAMP WITH DEEP EASTERLY FLOW AHEAD OF A LOW
PRESSURE MOVING RIGHT ALONG THE COAST...CAUSING WIDESPREAD AND
POSSIBLY HEAVY...RAINFALL. THE GFS/ECMWF ARE FURTHER OFFSHORE...WITH
NE FLOW THROUGH THE WEEKEND AS THE LOW PRESSURE STAYS WELL OFF THE
COAST. WPC FAVORING THE ECMWF AND ITS ENSEMBLES...WHICH HAVE
FLUCTUATED LITTLE FROM LAST WEEK...AND THUS WILL CONTINUE WITH THE
INHERITED FORECAST LEANING SIGNIFICANTLY ON THE ECMWF WITH SOME
BLENDING WITH THE WETTER SOLUTIONS. THIS SUGGESTS AT LEAST
WIDESPREAD CLOUD COVER SATURDAY AS THE LOW PRESSURE MAKES ITS
CLOSEST APPROACH...WITH SHOWERS MOST LIKELY ACROSS THE EASTERN
ZONES. IMPROVEMENT WILL OCCUR ON SUNDAY AS THE LOW PRESSURE PULLS
OFF TO THE NORTHEAST...AND TEMPS WILL BE AROUND SEASONABLE THROUGH
THE WKND...ALTHOUGH SUNDAY WILL LIKELY BE A BIT WARMER.

A BRIEF PERIOD OF RETURN FLOW DEVELOPS AHEAD OF A STRONG COLD FRONT
WHICH IS SLATED TO CROSS TUESDAY AFTN. THIS BRINGS A DAY OR TWO OF
WARMER TEMPERATURES...BEFORE CANADIAN HIGH PRESSURE ENVELOPS THE
REGION FOR MID-WEEK. CONVECTION LOOKS LIKELY ON TUESDAY WITH THE
COLD FRONT...AND WILL BUMP POP TO CHC FOR TUESDAY AS SURFACE
CONVERGENCE...PVA...AND SOME JET-LEVEL DIFFLUENCE COMBINE IN A RICH
THETA-E AIR MASS.

&&

.AVIATION /05Z THURSDAY THROUGH MONDAY/...
AS OF 06Z...EXPECT IFR/LIFR BR/STRATUS TO DEVELOP AT KFLO AND KLBT
AFTER 09Z WITH LIGHT/CALM WINDS AND DECREASING CLOUD COVER. ALONG
THE COAST...SLIGHTLY STRONGER NORTHEAST FLOW WILL LIKELY KEEP VSBYS
FROM DROPPING BELOW MVFR LEVELS BEFORE 12Z. THERE IS A CHANCE THAT
SOME TEMPO IFR CIGS COULD DEVELOP AT KCRE/KMYR BETWEEN 10-12Z...BUT
CONFIDENCE IS LOW SO WILL KEEP IFR STRATUS SCT ATTM. MVFR CIGS SEEM
MORE LIKELY FOR KILM/KCRE/KMYR JUST AFTER DAYBREAK. PATCHES OF MVFR
CIGS MAY LINGER THROUGH THE LATE MORNING...BUT EXPECT VFR AT ALL TAF
SITES BY MIDDAY. THEN VFR SHOULD PREVAIL THROUGH THE REST OF THE
PERIOD. NORTHEAST WINDS AOB 10 KT WILL BECOME MORE EASTERLY AFTER
18Z. DO NOT ANTICIPATE MUCH...IF ANY...PCPN DURING THE DAY GIVEN THE
DRY AIR ALOFT SEEN IN THE FCST SOUNDINGS.

EXTENDED OUTLOOK...GUSTY NORTHEAST WINDS EXPECTED FRI/SAT AS COOL
HIGH PRESSURE EXTENDS SOUTHWARD INTO THE CAROLINAS. EARLY MORNING
MVFR/IFR STRATUS POSSIBLE SAT/SUN MORNING. OTHERWISE VFR.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 1:30 AM THURSDAY...NO CHANGES TO THE FORECAST WITH THE
LATEST UPDATE. PREVIOUS DISCUSSION FOLLOWS:

WINDS ACROSS THE COASTAL WATERS NORTH OF CAPE FEAR ARE A LITTLE
STRONGER THAN ANTICIPATED EARLIER. THIS IS LIKELY DUE TO A
TIGHTENING PRESSURE GRADIENT BEHIND A MODEST SURGE LINE/INVERTED
TROUGH THAT IS DROPPING SLOWLY SOUTHWESTWARD ALONG THE COAST. WIND
GUSTS UP TO 21 KNOTS HAVE BEEN MEASURED AT CAPE LOOKOUT AND
WRIGHTSVILLE BEACH WITHIN THE PAST HOUR. NO MODEL HAS WINDS THIS
STRONG CURRENTLY...BUT I HAVE BUMPED WIND SPEED FORECASTS UP TO A
SOLID 15 KNOTS NORTH OF CAPE FEAR...AND 10-15 KNOTS SOUTH OF CAPE
FEAR TO NEAR MYRTLE BEACH. SEAS ARE UP TO A SOLID 4 FEET NORTH OF
CAPE FEAR IN A COMBINATION OF SWELL AND WIND WAVES. PREVIOUS
DISCUSSION FROM 730 PM FOLLOWS...

WEAK LOW PRESSURE WELL OFF THE SC COAST WILL MAINTAIN A LIGHT NE
WIND OVERNIGHT. HIGH PRESSURE NORTH OF THE GREAT LAKES WILL BEGIN TO
RIDGE SOUTHWARD LATE TONIGHT. A SLIGHT NE SURGE TONIGHT WILL
INCREASE WIND SPEEDS UP TO 10 TO 15 KT. EASTERLY SWELL FROM DISTANT
HURRICANE EDOUARD WILL ALLOW SEAS TO BE CONSIDERABLY HIGHER THAN THE
WIND SPEEDS WOULD OTHERWISE INDICATE... 3 TO 4 FT OUTSIDE OF
SHOALING/NEARSHORE INFLUENCES...WITH DOMINANT PERIODS OF 12 TO 13
SECONDS.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
AS OF 300 PM WEDNESDAY...HIGH PRESSURE RIDGING DOWN FROM THE NORTH
WILL PRODUCE LIGHT NORTHEAST FLOW ON THU AROUND 10 KTS OR LESS. WINDS
WILL WILL INCREASE SIGNIFICANTLY THROUGH FRI AS DISTINCT HIGH
PRESSURE WEDGE SETS UP AND LOW PRESSURE DEVELOPS OFF THE SOUTHEAST
COAST. NE WINDS WILL INCREASE UP TO 20 KT WITH HIGHER GUSTS THROUGH
FRI INTO FRI NIGHT AND MAY BECOME MORE EASTERLY DEPENDING ON
POSITION AND STRENGTH OF DEVELOPING LOW OFF THE SOUTHEAST COAST.
SEAS 2 TO 4 FT ON THURS WILL DIMINISH SLIGHTLY THROUGH THE DAY AS
LONG PERIOD SWELLS DECREASE. AS NE WINDS INCREASE THROUGH FRI...SEAS
MAY REACH SCA THRESHOLDS INTO FRI EVE...ESPECIALLY NORTH OF CAPE
FEAR...BUILDING TO 4 TO 5 FT WITH POTENTIAL FOR 6 FT. MAINLY IN
OUTER WATERS.

LONG TERM /SATURDAY THROUGH MONDAY/...
AS OF 300 PM WEDNESDAY...CONCERN THROUGH THE EXTENDED INVOLVES A LOW
PRESSURE SYSTEM PROGGED TO DEVELOP ALONG A STALLED COLD FRONT OFF
THE COAST. STILL SIGNIFICANT UNCERTAINTY INTO THE STRENGTH AND EXACT
PLACEMENT OF THIS FEATURE...BUT AT LEAST SOME IMPACTS ARE EXPECTED
LOCALLY. THIS LOW PRESSURE WILL MAKES ITS CLOSEST APPROACH TO THE
WATERS ON SATURDAY...PRODUCING ENHANCED NE WINDS  OF 15-20
KTS...POSSIBLY HIGHER IF THE LOW IS CLOSER/STRONGER THAN CURRENTLY
FORECAST. WINDS THEN BECOME VARIABLE ON SUNDAY AS A WEAK RIDGE OF
HIGH PRESSURE BUILDS TOWARDS THE AREA...BEFORE TURNING TO THE SW
WIND SW ON MONDAY...WITH SPEEDS RISING BACK TO 10-15 KTS. WAVES WILL
BE PRIMARILY NE-WIND-WAVE DRIVEN ON SATURDAY WITH HEIGHTS 4-5
FT...BUT AGAIN...IF THE SYSTEM IS STRONGER OR CLOSER AN SCA MAY BE
NEEDED. THEREAFTER...WAVE HEIGHTS FALL TO 2-4 FT ON SUNDAY...AND
THEN 1-3 ON MONDAY WITH A SW WIND WAVE AND WEAK SE SWELL FORMING IN
THE SPECTRUM.

&&

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

&&

$$

SYNOPSIS...RGZ
NEAR TERM...REK/RJD
SHORT TERM...RGZ
LONG TERM...JDW
AVIATION...BJR
MARINE...REK/RJD/JDW/RGZ



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