Area Forecast Discussion
Issued by NWS Wilmington, NC

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000
FXUS62 KILM 231456
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
1056 AM EDT TUE SEP 23 2014

.SYNOPSIS...
A COASTAL TROUGH JUST OFFSHORE WILL BRING INCREASING RAINFALL TO THE
AREA TODAY THROUGH WEDNESDAY...ALONG WITH WELL BELOW NORMAL
TEMPERATURES. RAINFALL CHANCES WILL DIMINISH LATE IN THE WEEK. A
WARMING AND DRYING TREND IS EXPECTED OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1000 AM TUESDAY...UPPER LOW TAKING SHAPE OVER THE SE STATES
...AND HAS BASICALLY BROKE OFF FROM THE MAIN BELT OF POLAR
WESTERLIES...VIA WATER VAPOR IMAGERY TRENDS. ATLANTIC AND GULF OF
MEXICO MOISTURE WILL GET ENTRAINED INTO THIS LOW. DYNAMICS FROM
THIS UPPER LOW INCLUDING MID-LEVEL VORTS/IMPULSES ROTATING THRU
IT...WILL PROVIDE ADDITIONAL MEANS OF SYNOPTIC/MESOSCALE LIFT.
OVERALL...HAVE KEPT CATEGORICAL POPS AT THE COAST....WITH A SLOW
DECLINE AS 1 PROGRESSES INLAND. USING THE I-95 CORRIDOR AS A
DIVIDING LINE BETWEEN THE BEST/HIER POP CHANCES EAST TO THE
COAST...WITH CHANCE ALONG AND WEST OF THE I-95 CORRIDOR. THE
COASTAL TROF/FRONT TO REMAIN JUST OFFSHORE AND WILL BE A FOCUS FOR
THUNDERSTORM ACTIVITY DUE TO THE INCREASING INSTABILITY.
HOWEVER...ELSWHERE AND OVER LAND AREAS HAVE INDICATED STRATIFORM
TYPE LIGHT RAINS TO DOMINATE. HAVE LOWERED AFTN MAXES ALREADY AND
MAY NEED TO LOWER AGAIN GIVEN THE LACK OF INCREASE TREND TO THE
LOCAL TEMPS.

PREVIOUS DISCUSSION...........................................
AS OF 630 AM TUESDAY...IF THERE WAS ANY DOUBT IN YOUR MIND THAT
SUMMER IS OVER...TODAY SHOULD ERASE IT. CANADIAN HIGH PRESSURE
OVER OH-PA WILL SHOVE A COOL DRY AIRMASS SOUTHWARD INTO THE
CAROLINAS. THE COLD FRONT AT THE LEADING EDGE OF THIS NEW AIRMASS
IS STALLING OUT OVER THE GULF STREAM. AN UPPER LEVEL LOW HAS CUT
OFF ACROSS FAR-WESTERN SOUTH CAROLINA...AND THE CIRCULATION AROUND
THIS FEATURE WILL DRAW A STREAM OF MID-LEVEL MOISTURE BACK OVER
THE FRONT AND ACROSS THE AREA TODAY. WEAK LOW PRESSURE WILL
ATTEMPT TO CLOSE OFF A CENTER ALONG THE FRONT ALONG THE GA/SC
COAST TONIGHT...BUT MODEL CONSENSUS SAYS IT SHOULD REMAIN AN OPEN
WAVE. HOWEVER THE LOWERING PRESSURES HERE WILL CONTRAST QUITE
STRONGLY WITH THE HIGH OFF TO THE NORTH...CREATING HEALTHY
NORTHEAST WINDS THAT WILL INCREASE TONIGHT TO 15-20 MPH INLAND
WITH GUSTS APPROACHING 30 MPH ON THE BEACHES.

A LARGE AREA OF RAIN WITH EMBEDDED CONVECTIVE SHOWERS HAS DEVELOPED
OVER THE COASTAL WATERS AND SHOULD SPREAD INLAND THIS MORNING.
POPS FOR THE COASTAL CITIES OF WILMINGTON...SOUTHPORT AND MYRTLE
BEACH HAVE BEEN INCREASED TO 80-90 PERCENT. FARTHER INLAND WHERE DRY
AIR IS QUITE A BIT BETTER ENTRENCHED MUCH OF THE PRECIPITATION
SHOULD EVAPORATE AND POPS ARE ONLY IN THE 30-50 PERCENT RANGE. THERE
SHOULD BE A FAIRLY TIGHT GRADIENT IN ACTUAL RAINFALL AMOUNTS JUST
OFF THE COAST WITH NO MORE THAN 0.50 INCHES EXPECTED TO FALL ON THE
BEACHES...BUT BETTER THAN ONE INCH PREDICTED JUST 15 OR 20 MILES OFF
CAPE FEAR. FARTHER INLAND FORECAST RAINFALL AMOUNTS ARE MUCH
LOWER...A TENTH OF AN INCH OR LESS ALONG AND WEST OF I-95.

ALL THIS CLOUD COVER AND RAIN SHOULD REALLY KEEP TEMPERATURES DOWN.
THE PATTERN LOOKS LIKE A CLASSIC MID-WINTER WEDGE DESPITE
TEMPERATURES A GOOD 25-30 DEGREES WARMER. STILL...HIGHS IN THE UPPER
60S TO LOWER 70S IN SEPTEMBER ARE NOTHING TO SNEEZE AT. THE 00Z AND
06Z GFS MOS LOOKS MUCH CLOSER TO REALITY THAN THE NAM...BUT EVEN IT
IS PROBABLY A LITTLE TOO WARM IN MOST AREAS.

AFTER A RELATIVE LULL IN PRECIPITATION COVERAGE LATE THIS AFTERNOON
AND THIS EVENING...SUBSTANTIAL RAINFALL MAY AGAIN SURGE ONTO THE
COAST OVERNIGHT AS STRONGER LOW-LEVEL WIND FIELDS DEVELOP AND
ISENTROPIC LIFT INCREASES. PRECIP SHOULDN`T PENETRATE QUITE AS FAR
INLAND HOWEVER DUE TO A MORE BACKED/NORTHERLY LOW-LEVEL WIND
DIRECTION...AND MY FORECAST POPS RANGE FROM 60-80 PERCENT ON THE
COAST TO 20-30 PERCENT ALONG THE I-95 CORRIDOR. UNDER CLOUDS AND A
STIFF NORTHEAST WIND LOWS SHOULD FALL INTO THE UPPER 50S INLAND AND
LOWER 60S NEAR THE COAST.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 300 AM TUESDAY...VERY UNSETTLED DURING THE SHORT TERM AS A
STAGNANT PATTERN CONTINUES ACROSS THE CONUS. ALOFT...AN UPPER LEVEL
LOW CLOSED OFF ACROSS SC WILL ONLY SLOWLY FILL AND LIFT...LIKELY
MAINTAINING AT LEAST SOME SEMBLANCE OF AN UPPER TROUGH THROUGH
THURSDAY NIGHT. THIS IS DUE TO A HIGHLY AMPLIFIED RIDGE ACROSS THE
ATLANTIC...AS WELL AS GROWING RIDGING ACROSS THE CENTER PART OF THE
COUNTRY FORCING SYSTEMS TO GRIND TO A HALT. AT THE SURFACE...A VERY
STRONG 1035+ MB SURFACE HIGH WILL WEDGE DOWN FROM NEW ENGLAND WHILE
A COASTAL TROUGH SHARPENS AND LURKS OFFSHORE...ALONG WITH VERY
STRONG MOIST ADVECTION.

THESE FEATURES TOGETHER WILL CREATE AN EXTENDED PERIOD OF COOL TEMPS
WITH WIDESPREAD SHOWERS AND CLOUDS...AS WELL AS GUSTY NE WINDS.
WHILE THERE IS STILL CONSIDERABLE SPREAD AMONG THE VARIOUS GUIDANCE
INTO HOW FAR WESTWARD THE COASTAL TROUGH WILL LIFT...AND THUS HOW
HEAVY THE RAIN WILL BE...IT SEEMS ALMOST CERTAIN THAT THE COAST WILL
SEE RAIN DURING THIS PERIOD...WITH A SHARP GRADIENT TOWARDS I-95.
THE INTERACTION OF THE UPPER LOW WITH THE COASTAL TROUGH WILL
SHARPEN THE TROUGH ON WEDNESDAY...AND MAY EVEN SPAWN A WEAK LOW
MOVING JUST ALONG THE COAST INTO THURSDAY. THIS COMBINED WITH DEEP
MOIST ADVECTION ON EASTERLY FLOW...DRIVING INCREASING ISENTROPIC
LIFT ATOP THE COASTAL BOUNDARY...SUGGESTS AT LEAST PERIODS OF HEAVY
RAIN POSSIBLE ALONG THE IMMEDIATE COAST WEDNESDAY...DECREASING
SOMEWHAT INTO THURSDAY. AGAIN...HOW FAR INLAND THE RAIN WILL
PENETRATE IS STILL UNCERTAIN...BUT THE HEAVIEST RAIN AND HIGHEST POP
WILL CERTAINLY BE RIGHT ALONG THE IMMEDIATE COAST.

TEMPS BOTH WED AND THU WILL STAY WELL BELOW CLIMO WITH HIGHS ONLY IN
THE LOW/MID 70S...MADE TO FEEL EVEN MORE RAW BY NE WINDS AND RAIN.
LOWS AT NIGHT HOWEVER WILL BE SOMEWHAT HELD IN CHECK BY THE SAME
CLOUDS AND RAIN...SO EVEN WITH COOL NE WINDS PERSISTING
OVERNIGHT...MINS WILL BE JUST ABOVE CLIMO IN THE LOW/MID 60S.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 300 AM TUESDAY...THE EXTENDED BEGINS COOL AND
UNSETTLED...MAYBE UNSURPRISINGLY BY THIS POINT...AS THE PERSISTENT
COASTAL TROUGH REMAINS JUST OFFSHORE WHILE HIGH PRESSURE REORGANIZES
ACROSS THE GREAT LAKES. LOW PRESSURE ALONG THE OFFSHORE BOUNDARY
MOVING NEAR NEW ENGLAND WILL PUSH NORTHEAST AWAY FROM THE AREA BY
SATURDAY...WHICH IN CONJUNCTION WITH THE EXPANSION OF THE MIDWEST
HIGH WILL DRIVE THE OFFSHORE BOUNDARY WELL EAST BY THE WKND.
ALOFT...THE QUASI-STATIONARY TROUGH WILL FILL AS RIDGING BLOSSOMS
ACROSS THE MIDDLE OF THE COUNTRY...BEFORE PUSHING OVERHEAD DURING
THE WKND. THESE FEATURES COMBINED SUGGEST A DRYING
TREND...ESPECIALLY FROM SATURDAY INTO MONDAY...ALONG WITH TEMPS
WARMING TO SEASONABLE OR ABOVE...AND THE FIRST WKND OF FALL WILL
FEATURE PLEASANT WEATHER ACROSS THE AREA.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
AS OF 12Z...EXPECT PERIODS OF -RA/RA THROUGH THE DAY AS AN UPPER LOW
TO OUR WEST DRAWS MOISTURE OVER A STALLED FRONT OFFSHORE. RADAR
IMAGERY THIS MORNING SHOWS SHRA OFF THE COAST WITH -RA/DZ MOVING
OVER OUR SOUTHERN TERMINALS. PCPN COVERAGE WILL INCREASE THROUGH THE
LATE MORNING/EARLY AFTN HOURS...WITH CIGS LIKELY LOWERING TO MVFR AT
THE COASTAL SITES WHERE RAIN WILL BE MORE PERSISTENT. THE INLAND
TERMINALS COULD SEE TEMPO MVFR LATER TODAY...BUT VFR WILL PREVAIL AT
KFLO/KLBT. BRIEF VSBY RESTRICTIONS ARE POSSIBLE ALONG THE COAST IF
CONVECTIVE SHOWERS MOVE ONSHORE...BUT HAVE ONLY INCLUDED VCSH ATTM
AS THIS ACTIVITY WILL MOSTLY REMAIN OFFSHORE. NORTHEAST WINDS WILL
BE 10-12 KT TODAY WITH HIGHER GUSTS POSSIBLE IN THE AFTN. THE MODELS
INDICATE A BRIEF LULL IN PCPN THIS EVENING...BUT EXPECT MORE -RA AT
KILM/KCRE/KMYR AFTER 06Z. LOWEST CIGS OVERNIGHT WILL BE AT THE
COAST...MVFR AND PERHAPS IFR NEAR THE END OF THE PERIOD. NORTHEAST
WINDS STRENGTHEN TONIGHT AS THE COASTAL TROUGH SHARPENS...BECOMING
AROUND 15 KT WITH 20+ KT GUSTS EARLY WED MORNING.

EXTENDED OUTLOOK...PERIODS OF RAIN AND MVFR/IFR CONDITIONS EXPECTED
THROUGH THURSDAY. CHANCE OF SHOWERS FRIDAY...MAINLY ALONG THE COAST.
VFR ON SATURDAY.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 1000 AM TUESDAY...THE COASTAL WATERS WILL REMAIN WEST OF THE
INVERTED COASTAL TROF/FRONT DURING THIS EVENT. A PINCHED GRADIENT
WILL DEVELOP BETWEEN THE STRONG RIDGING DOWN THE EAST COAST
AND THE INVERTED TROF/FRONT. THIS HAS ALREADY RESULTED WITH NE
WINDS HAVING INCREASED TO SCA VALUES...AND BUILDING SIGNIFICANT
SEAS. SEAS COULD PEAK AROUND 8 FT OUTER WATERS OFF CAPE FEAR...AND
OFF THE MOUTH OF WINYAH BAY. DOMINANT PERIODS WILL HOVER AROUND 6
SECONDS INDICATIVE OF WIND DRIVEN WAVES THE DOMINANT WAVE TYPE.

PREVIOUS DISCUSSION............................................
AS OF 630 AM TUESDAY...THIS MORNING`S SUITE OF MODEL RUNS HAVE
UNFORTUNATELY ALL TRENDED TOWARD STRONGER WIND SPEEDS AND HIGHER
SEAS DEVELOPING OVER THE NEXT 24 HOURS. A STALLED FRONT OUT OVER
THE GULF STREAM WILL DEVELOP A WAVE OF LOW PRESSURE ALONG IT
TONIGHT ALONG THE GEORGIA AND SOUTH CAROLINA COAST. CANADIAN HIGH
PRESSURE WILL ALSO TRY TO RIDGE SOUTHWARD FROM NEW ENGLAND. THIS
WILL PINCH THE PRESSURE GRADIENT RATHER SIGNIFICANTLY ALONG THE
CAROLINA COAST...WITH DETERIORATING WEATHER CONDITIONS THE RESULT.

WINDS CURRENTLY ARE NORTHERLY AT 10-15 KNOTS ACROSS THE SC WATERS
BUT HAVE VEERED NORTHEASTERLY NEAR 20 KNOTS ACROSS THE NC WATERS.
THIS SURGE OF NORTHEASTERLY WINDS SHOULD MOVE DOWN THE COAST OVER
THE NEXT FEW HOURS...WITH 25 KNOT WINDS DEVELOPING THIS AFTERNOON.
THE WORST CONDITIONS ARE EXPECTED TO OCCUR TONIGHT WHEN WINDS COULD
REACH 30 KNOTS. ONE CONCERN IS THE NORMALLY QUITE RELIABLE GFS MODEL
IS SHOWING WINDS JUST 1000 FEET ALOFT ACCELERATING TO 35 KNOTS
OVERNIGHT ALONG THE SOUTH CAROLINA COAST. DEPENDING ON HOW MUCH HEAT
FROM THE WARM OCEAN SURFACE CAN WARM THE AIRMASS...WE COULD
CONCEIVABLY SEE THESE GALE-FORCE WINDS COME DOWN TO THE SURFACE AT
LEAST IN GUSTS. SEAS CURRENTLY ONLY 2-4 FEET SHOULD BUILD STEADILY
IN RESPONSE TO THE WINDS...REACHING AS HIGH AS 6-8 FEET TONIGHT.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 300 AM TUESDAY...HIGH PRESSURE WILL WEDGE DOWN THE COAST
THROUGH THE SHORT TERM...WHILE A COASTAL TROUGH REMAINS JUST
OFFSHORE THE CAROLINAS. THIS WILL PRODUCE CONSISTENT NE WINDS
THROUGH THE PERIOD...WITH THE HIGHEST SPEEDS OCCURRING ON WEDNESDAY
AS A WAVE OF LOW PRESSURE MOVES ALONG THE TROUGH...PINCHING THE
GRADIENT. NE WINDS MAY EXCEED 25 KTS THE FIRST HALF OF
WEDNESDAY...WITH GUSTS APPROACHING GALE FORCE. THESE WINDS WILL EASE
SLOWLY WED NIGHT AND THE FIRST PART OF THURSDAY...BECOMING 15-20
KTS...BEFORE SLOWLY RAMPING UPWARD AGAIN THURSDAY NIGHT. THESE WINDS
WILL KEEP WAVE AMPLITUDES ELEVATED...4-7 FT EXPECTED WED AND THU.
THERE MAY BE A BRIEF PERIOD WED NIGHT INTO THURSDAY WHEN WAVE
HEIGHTS DROP BELOW SCA THRESHOLDS...BUT EVEN SO...EXPECT HEADLINES
TO BE IN EFFECT THE ENTIRETY OF THE PERIOD.

LONG TERM /FRIDAY THROUGH SATURDAY/...
AS OF 300 AM TUESDAY..HIGH PRESSURE WILL SOMEWHAT RE-ORIENT ITSELF
INTO THE WKND...BECOMING CENTERED ACROSS THE GREAT LAKES INSTEAD
OF NEW ENGLAND. WHILE THIS LEAVES A WEDGE IN PLACE LOCALLY...IT
WILL BE OF DECREASED STRENGTH...AND THUS NE WINDS WILL BE SOMEWHAT
LOWER THAN EARLIER IN THE WEEK...15-20 KTS INTO THE WKND. A SMALL
CRAFT ADVISORY WILL LIKELY BE NEEDED FOR AT LEAST A PORTION OF THE
EXTENDED...LIKELY MOST OF FRIDAY...FOR 4-6 FT SEAS...BEFORE
AMPLITUDES WANE ON SATURDAY.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT WEDNESDAY FOR AMZ250-252-
     254-256.

&&

$$
SYNOPSIS...JDW
NEAR TERM...DCH/TRA
SHORT TERM...JDW
LONG TERM...JDW
AVIATION...TRA







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