Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 231629 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 1229 PM EDT SAT MAY 23 2015 .SYNOPSIS... HIGH PRESSURE CENTERED NEAR THE NATION`S CAPITOL WILL SHIFT OFFSHORE...REMAINING OFF THE EAST COAST FOR SEVERAL DAYS. HIGHER HUMIDITY LEVELS WILL RETURN NEXT WEEK ALONG WITH A SMALL RISK FOR SHOWERS AND THUNDERSTORMS BEGINNING WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1230 PM SATURDAY...1032 MB HIGH PRESSURE (QUITE STRONG FOR LATE MAY) CENTERED NEAR THE NATION`S CAPITOL WILL SHIFT OFFSHORE TONIGHT. THIS WILL MAINTAIN AN EASTERLY WIND ACROSS THE CAROLINAS TODAY...SHIFTING MORE DIRECTLY ONSHORE AT THE BEACHES WITH THE SEABREEZE. THE ATMOSPHERIC COLUMN REMAINS BONE DRY AND ASIDE FROM A A TINY BIT OF CIRRUS FROM TIME TO TIME...SKIES SHOULD REMAIN CLEAR. NO ADDITIONAL CHANGES HAVE BEEN MADE TO THE FORECAST. DEWPOINTS ARE FALLING INTO THE 40S INLAND FROM THE COAST AS WE TAP INTO THE LAYER OF VERY DRY AIR ALOFT SAMPLED BY THE 12Z MHX WEATHER BALLOON. DEWPOINTS AS LOW AS 17 DEGREES F (-8C) WERE MEASURED AS AN ALTITUDE OF 2600 FEET ABOVE GROUND LEVEL. WHILE DEWPOINTS DOWN HERE AT THE SURFACE WILL NOT PLUNGE THIS LOW... DEWPOINTS IN THE MID 40S AWAY FROM THE COAST SHOULD RESULT IN MINIMUM RELATIVE HUMIDITY DROPPING TO 26-31 PERCENT.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 330 AM SATURDAY...THIS PERIOD WILL BE HIGHLIGHTED AS NEARLY PICTURE PERFECT WX FOR THIS MEMORIAL HOLIDAY WEEKEND. NOT TOO HOT NOR COLD. NO PRECIPITATION...AND...MOSTLY SUNNY SKIES EACH DAY AND MOSTLY CLEAR SKIES EACH NIGHT. MID AND UPPER LEVEL RIDGING OVERHEAD TO AFFECT THE FORECAST AREA. IN FACT...THE MID-UPPER LEVEL HIGH WILL BE ANCHORED JUST OFF THE SOUTHEAST U.S. COAST...WITH ITS SOUTH TO NORTH RIDGE AXIS JUST WEST OF THE ILM CWA SUNDAY...WILL DRIFT TO A POSITION THATS NEARLY OVERHEAD BY MONDAY NIGHT. SFC HIGH PRESSURE CENTERED JUST OFF THE DELMARVA COAST ON SUNDAY...WILL DRIFT EASTWARD AND FURTHER OFFSHORE BY MONDAY NIGHT. ITS SFC RIDGE AXIS WILL EXTEND WSW INTO NC AND FOR THE MOST PART ITS AXIS TO REMAIN NORTH OF THE ILM CWA. THIS POSITION WILL RESULT WITH AN ONSHORE FLOW PATTERN THAT WILL EXTEND UPWARDS TO NEAR 850MB. THIS PATTERN WILL RESULT IN THE DAILY MAX AND MIN TEMPS RUNNING AT OR JUST BELOW CLIMO. THE MOISTURE IN THE LOWER LEVELS WILL INCREASE DUE TO THE ONSHORE FLOW...AND LIKELY BE USED TO PRODUCE DIURNALLY DRIVEN SCATTERED CU EACH DAY...ESPECIALLY ALONG THE DAILY RESULTANT WIND BOUNDARY AKA THE SEA BREEZE. IN ADDITION TO THE CU...CONVECTIVE DEBRIS CLOUDS IN THE FORM OF THIN TO OCCASIONALLY OPAQUE CIRRUS WILL OCCASIONALLY SPILL OVER THE UPPER RIDGE AXIS AND ACROSS THE ILM CWA. AS FOR TEMPS...STAYED WITH THE MODEL MOS GUIDANCE EXHIBITING THE LOWER MAX/MINS. WITH AN ONSHORE FLOW ACROSS A DECENT FETCH FOR BOTH DAYS...EXPECT AN E TO SE GROUND SWELL TO INCREASE IN SIZE...AND ALSO BECOME PERPENDICULAR TO THE AREA BEACHES. THIS WILL LIKELY INCREASE THE RIP CURRENT THREAT FOR AREA BEACHES THROUGHOUT THE ILM CWA. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 330 AM SATURDAY...THE MID TO UPPER LEVEL RIDGE AXIS TO BE NEARLY OVERHEAD ON TUESDAY...THEN SLIGHTLY DRIFT JUST OFF THE SOUTHEAST U.S. COAST TOWARD THE END OF THE WEEK. THIS A RESULT OF UPSTREAM FORCING TRYING TO PUSH/PROGRESS THIS FEATURE EASTWARD. HOWEVER...A FLY IN THE OINTMENT IN THE FORM OF A MID-UPPER LOW OVER THE MID-ATLANTIC OCEAN APPROACHING THE US MAINLAND FROM THE SOUTHEAST. IT LOOKS OMINOUS ALOFT...HOWEVER AT THE SFC...THERE IS NO ACCOMPANYING STRONG SFC LOW...JUST A TROF OF LOW PRESSURE. THIS UPPER LOW WILL SLOW THE PROGRESSION OF THE UPPER RIDGE EASTWARD...AND THUS ALLOW THE CONTINUANCE OF DECENT WX CONTINUING THRU THE END OF THE WORK WEEK OF NEXT WEEK. ENOUGH SUBSIDENCE ALOFT WILL PREVENT WIDESPREAD PCPN...HOWEVER THE FORCING FROM THE DAILY SEA BREEZE WILL LIKELY BE ENOUGH TO CARRY A LOW CHANCE FOR CONVECTION. MOISTURE IN THE FORM OF CLOUDS COULD REACH THE COASTAL CAROLINAS AS THE MID-ATLANTIC UPPER LOW REACHES ITS CLOSEST APPROACH ON FRI. FOR NOW HAVE KEPT ANY PCPN ASSOCIATED WITH IT WELL OFFSHORE FROM THE MAINLAND. HAVE ALSO PREVENTED THE PCPN WEST OF THE ILM CWA FROM MOVING EASTWARD INTO THE ILM CWA...AS THE FA REMAINS SANDWICHED BETWEEN THE ATLANTIC LOW AND THE MID-UPPER TROF ALONG THE SPINE OF THE APPALACHIANS. MAX/MIN TEMPS THRU THIS PERIOD WILL BE JUST ON EITHER SIDE OF CLIMO. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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AS OF 18Z...POTENTIAL FOR MVFR OVERNIGHT INTO THE EARLY MORNING HOURS ON SATURDAY DUE TO PATCHY FOG. OTHERWISE...HIGH PRESSURE WILL ALLOW FOR VFR TO PREVAIL THROUGH THE VALID TAF PERIOD. VFR PREVAILS THIS AFTERNOON WITH EASTERLY WINDS AOB 10 KTS...AND INTERMITTENT HIGHER GUSTS TO AROUND 20 KTS. LATEST VISIBLE IMAGERY DEPICTS FEW COVERAGE OF CU JUST DEVELOPING AND THIN CIRRUS...WHICH WILL DISSIPATE INTO THE EVENING HOURS. WINDS WILL BECOME LIGHT OVERNIGHT AND THIS WITH NEARLY CLEAR SKIES WILL ALLOW FOR IDEAL RADIATIONAL COOLING CONDITIONS. AS A RESULT...MAY SEE AREAS OF MVFR DUE TO FOG IN THE EARLY MORNING HOURS ON SATURDAY. HOWEVER CONFIDENCE IS LOW ATTM. OTHERWISE EXPECT VFR ON SATURDAY WITH EASTERLY WINDS INCREASING TO AOB 12 KTS. EXTENDED OUTLOOK...MORNING FOG POSSIBLE MONDAY AND WEDNESDAY. OTHERWISE EXPECT VFR.
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&& .MARINE...
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NEAR TERM /THROUGH TONIGHT/... AS OF 1230 PM SATURDAY...1032 MB HIGH PRESSURE CENTERED OVER MARYLAND WILL SHIFT OFF THE EAST COAST THIS EVENING. THIS WILL MAINTAIN AN EASTERLY WIND ACROSS THE WATERS TODAY...SHIFTING MORE DIRECTLY ONSHORE NEAR THE COAST WITH THE SEABREEZE. WIND SPEEDS SHOULD BE STRONGER WITH INCREASING DISTANCE FROM THE HIGH: AROUND 10 KNOTS NORTH OF CAPE FEAR BUT CLOSER TO 15 KT EAST OF WINYAH BAY AND GEORGETOWN. AN LENGTHENING EASTERLY FETCH SOUTH OF THE HIGH WILL LEAD TO GRADUALLY BUILDING SEAS. DOMINANT WAVE PERIODS OF 4-5 SECONDS THIS MORNING WILL BEGIN TO LENGTHEN AS A 9-10 SECOND EAST- SOUTHEAST SWELL DEVELOPS...WITH SEAS AVERAGING 2-3 FEET TODAY AND 3-4 FEET BY LATE TONIGHT. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 330 AM SATURDAY...THE SFC RIDGE AXIS FROM THE HIGH OFFSHORE FROM THE DELMARVA COAST...IS PROGGED TO EXTEND WSW INTO NC BUT REMAIN FOR THE MOST PART NORTH OF THE ILM WATERS. THIS WILL RESULT IN AN ONSHORE E-SE FLOW THRU THIS PERIOD. EXPECT A SEMI-TIGHTENED SFC PG SOUTH OF THE SFC RIDGE AXIS...THUS RESULTING IN SPEEDS AROUND 15 KT. WITH A DECENT FETCH...EXPECT SIGNIFICANT SEAS TO BUILD TO 3 TO 4 FT...POSSIBLY A FEW 5 FOOTERS LATE MON NIGHT. IN ADDITION...LOOK FOR INCREASING PERIODS THAT COULD RESULT IN WIND DRIVEN WAVES TRANSITIONING INTO A PSEUDO GROUND SWELL. LONG TERM /TUESDAY THROUGH WEDNESDAY/... AS OF 330 AM SATURDAY...WEAKENING UPPER RIDGING TO HOLD ON THRU WEDNESDAY AS IT BECOMES SANDWICHED ACROSS THE AREA WATERS. THIS DUE TO THE APPROACHING MID-UPPER MID-ATLANTIC LOW FROM THE SE...AND AN UPPER TROF TRYING TO PROGRESS EASTWARD ACROSS EASTERN U.S. AND GETS HUNG UP ALONG THE WINDWARD SIDE OF THE APPALACHIANS. THE SFC PRESSURE PATTERN ACROSS THE LOCAL WATERS WILL RESULT IN SE WINDS AT 10 TO 15 KT....LIKELY A SOLID 15 KT ACROSS THE SOUTHERNMOST WATERS DUE TO AN INCREASED SFC PG. NO REAL SFC ENTITY ACCOMPANYING THE MID-ATLANTIC UPPER LOW...JUST A SFC TROF EXHIBITED BY THE MODELS. BUT WITH A DECENT E-SE FETCH CONTINUING TO OCCUR...LOOK FOR A SOLID 3 TO 4 FT SEAS WITH 5 FOOTERS NOT OUT OF THE QUESTION AS WAVEWATCH3 ILLUSTRATES.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ NEAR TERM...TRA SHORT TERM...DCH LONG TERM...DCH AVIATION...SGL

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