Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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584 FXUS61 KPHI 041354 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 954 AM EDT WED MAY 4 2016 .SYNOPSIS...
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LOW PRESSURE WILL CONSOLIDATE OFFSHORE THROUGH THURSDAY BEFORE MOVING NORTHEASTWARD. MEANWHILE, ANOTHER LOW PRESSURE SYSTEM DEVELOPS OFF THE MID ATLANTIC COAST THURSDAY NIGHT AND FRIDAY AND THEN MOVES NORTHEASTWARD THROUGH SATURDAY. A COLD FRONT IS FORECAST TO MOVE THROUGH SUNDAY MORNING FOLLOWED BY HIGH PRESSURE BUILDING IN FOR MONDAY AND TUESDAY.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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WE HAVE MADE SOME MINOR ADJUSTMENTS TO THE PREVIOUS FORECAST. AN AREA OF SHOWERS DEVELOPING OVER OUR SOUTHERN COUNTIES AT MID MORNING WILL INCREASE IN COVERAGE AS IT ADVECTS TO THE NORTH. IT SHOULD IMPACT THE REMAINDER OF OUR FORECAST AREA DURING THE BALANCE OF THE MORNING AND INTO THE EARLY TO MID AFTERNOON. THE LATEST HRRR SEEMS TO BE HANDLING THE OVERALL TREND WELL. OTHERWISE, LOW CLOUDS WILL PERSIST THROUGH THE DAY ALONG WITH FOG IN THE ELEVATED TERRAIN. TEMPERATURES WILL REMAIN BELOW NORMAL IN THE NORTHEASTERLY FLOW.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
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PWAT DRIES TO 0.75 INCHES AND INSTABILITY ALOFT DECREASES BUT A CONTD MOIST CYCLONIC CIRCULATION WITH PROBABLY PERIODS OF MEASURABLE DRIZZLE AND MAYBE A FEW POCKETS OF SHOWERS. 50 50 BLENDED 00Z/4 GFS NAM GUIDANCE. WE SEE THE SPC WRF DRIES US OUT CONSIDERABLY TONIGHT SO POPS ARE GENERALLY 60 PCT N AND 30-40 PCT SOUTH. BEST CHANCE FOR MEASURABLE MAY BE PRIOR TO MIDNIGHT. NE WIND GUSTY NEAR 15 MPH... EXPECT 20-25 MPH MONMOUTH COUNTY COAST.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
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THE SYNOPTIC SETUP IS COMPRISED OF AN OMEGA BLOCK, THEN THIS PATTERN IS FORECAST TO BREAK DOWN SOME DURING THE SECOND HALF OF THE WEEKEND AND ESPECIALLY EARLY NEXT WEEK. A FEW WEEKS AGO THERE WAS AN OMEGA BLOCK IN PLACE, HOWEVER AT THAT TIME WE WERE UNDER THE RIDGE. THIS GO AROUND WE ARE UNDER THE TROUGH PART OF THE BLOCK, KEEPING OUR WEATHER COOLER AND UNSETTLED. THE REST OF THE WEEK WILL THEREFORE BE UNSETTLED WITH SOME IMPROVEMENT DURING THE WEEKEND, THEN A MORE NOTABLE IMPROVEMENT ANTICIPATED FOR EARLY NEXT WEEK. WE USED A MODEL BLEND APPROACH FOR THURSDAY INTO SATURDAY, THEN BLENDED IN THE 00Z WPC GUIDANCE THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE FOLLOWING ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES. FOR THURSDAY AND FRIDAY...THE OMEGA BLOCK CONTINUES WITH A STRONG SHORT WAVE CLOSING OFF THE TROUGH AS IT TRACKS FROM THE OHIO VALLEY AND ACROSS THE SOUTHEASTERN STATES THURSDAY. SOME SHORT WAVE ENERGY TRACKING NORTHWARD ON THE EAST SIDE OF THE LARGE TROUGH WILL TEAM UP WITH ISENTROPIC LIFT ABOVE A MARINE LAYER AND PRODUCE SOME SHOWERS. THURSDAY MORNING HOWEVER COULD ALSO START WITH SOME DRIZZLE. THE ENTIRE TROUGH AND CLOSED LOW ARE FORECAST TO BECOME CENTERED ALONG THE EAST COAST FRIDAY WITH THE CLOSED LOW ITSELF MOVING OVER OUR CWA DURING FRIDAY. THIS WILL DRIVE LOW PRESSURE OFF THE MID ATLANTIC COAST NORTHWARD ALTHOUGH IT LOOKS TO NOT DEEPEN CONSIDERABLY. AS THIS OCCURS, THE 500 MB TEMPERATURES ARE FORECAST TO COOL TO NEAR -24C ON FRIDAY. THIS WOULD PROMOTE SOME INSTABILITY AND PERHAPS SOME LOW-TOPPED CONVECTION, HOWEVER CLOUD COVER AND NUMEROUS SHOWERS MAY TEMPER THIS POTENTIAL. OTHERWISE, AN EASTERLY LOW-LEVEL JET DEVELOPS FRIDAY ACROSS OUR NORTHEASTERN ZONES THEN THIS PIVOTS NORTH-NORTHWESTWARD DURING THE AFTERNOON. SOME GUIDANCE IS STRONGER WITH THIS FEATURE WHICH ALSO DRIVES A BAND OF STRONGER 700-800 MB FRONTOGENETIC FORCING. OVERALL, THERE LOOKS LIKE DECENT LIFT ON THE NOSE OF THE EASTERLY JET TO PROMOTE AN AREA OF SHOWERS/RAIN THAT PIVOTS INLAND DURING FRIDAY. WE MAY NOT SEE ANY BREAKS IN THE CLOUDS, BUT IF THERE ARE THEN ANY LOW- TOPPED CONVECTION COULD PRODUCE SMALL HAIL GIVEN THE VERY COLD 500 MB TEMPERATURES. AS OF NOW HOWEVER, ANY INSTABILITY LOOKS MEAGER. THE SYSTEM THEM MEANDERS OVER OUR AREA FRIDAY NIGHT AND WHILE THERE SHOULD BE A DECREASE IN THE SHOWER COVERAGE SOME SHOULD LINGER THROUGH THE NIGHT. FOR SATURDAY AND SUNDAY...THERE HAS BEEN A GENERAL SLOWING TREND IN THE GUIDANCE WHEN COMPARING THE MANY MODELS AND ENSEMBLES. THIS TENDS TO HAPPEN WITH BLOCKING PATTERNS AS IT TAKES LONGER FOR THE CLOSED LOW TO OPEN UP AND LIFT OUT. THERE ARE CONSIDERABLE DIFFERENCES AT THE SURFACE ON SATURDAY WHICH LEADS TO PLENTY OF DETAIL UNCERTAINTIES INCLUDING THE AMOUNT OF RAIN. WE THEREFORE LEANED CLOSER TO THE WPC GUIDANCE BUT ALSO INCORPORATING SOME CONTINUITY. THIS MEANS THAT SATURDAY LOOKS TO BE STILL UNSETTLED WITH SOME SHOWERS STILL HANGING AROUND. THE AMOUNT OF SHOWER ACTIVITY WILL DEPEND ON THE SHORT WAVE FORCING AROUND THE CLOSED LOW, HOWEVER PLENTY OF COLD AIR REMAINS ALOFT WHICH WILL HELP WITH SOME INSTABILITY. THIS SYSTEM SHOULD OPEN UP AND START SHIFTING EAST SATURDAY NIGHT AS UPSTREAM ENERGY IN THE FORM OF A TROUGH SLIDES SOUTHEASTWARD FROM THE GREAT LAKES. THIS DRIVES A COLD FRONT ACROSS OUR AREA MOSTLY SUNDAY MORNING WITH PERHAPS SOME SHOWERS. THE AIR ALOFT MODIFIES SOME THROUGH THE WEEKEND, THEREFORE MODERATING DAYTIME TEMPERATURES SHOULD RESULT ESPECIALLY ON SUNDAY. FOR MONDAY AND TUESDAY...WE TRANSITION OUT OF AN OMEGA BLOCK DURING THIS TIME FRAME, RESULTING IN WARMER TEMPERATURES. SOME GUIDANCE HOWEVER HAS A SHORT WAVE AMPLIFYING A TROUGH ACROSS THE NORTHEAST MONDAY BEFORE SHIFTING EAST TUESDAY AS A RIDGE APPROACHES FROM THE WEST. IT APPEARS THAT HIGH PRESSURE BUILDS IN WITH TIME, HOWEVER ENERGY IN THE PLAINS WILL SEND A DEVELOPING WARM FRONT TO OUR SOUTH TOWARD OUR AREA TUESDAY. WE KEPT THE FORECAST DRY ATTM WITH MUCH WARMER AIR BUILDING INTO THE AREA.
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&& .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...GENERALLY IFR CIGS WITH PATCHY 2-5 MI IN PERIODS OF SHOWERS. TIMING OF THE RAIN MAINLY LATE MORNING TO MID AFTERNOON. ISOLATED THUNDER NOT IMPOSSIBLE PER NAM/GFS INSTABILITY ALOFT, MAINLY DELMARVA OR SE PA/S NJ. NE WIND WITH A FEW GUSTS 15-20 KT VCNTY KPHL/KACY. TONIGHT...GENERALLY IFR CIGS WITH PATCHY 2-5 MI IN SCT SHOWERS DIMINISHING OR ENDING-EXITING NEWD EARLY/PATCHY DRIZZLE-FOG IN THE WAKE OF THE NEWD SHOWER DEPARTURE. POSSIBLE LIFR CIGS. NE WIND G 15-20 KT POSSIBLE KPHL- KTTN- KACY. OUTLOOK... THURSDAY AND FRIDAY...MVFR/IFR CEILINGS PERSIST WITH AN ONSHORE FLOW AND WEAK LOW PRESSURE NEAR THE COAST. TIMES OF SHOWERS ARE EXPECTED AS WELL WITH THE MOST WIDESPREAD ACTIVITY OCCURRING ON FRIDAY. NORTHEAST WINDS MAINLY IN THE 10-15 KNOT RANGE /LESS AT NIGHT/ WITH THE HIGHER SPEEDS MAINLY CLOSER TO THE COAST. SATURDAY AND SUNDAY...MVFR/IFR CEILINGS POSSIBLE TO START SATURDAY, THEN IMPROVEMENTS TO VFR SHOULD OCCUR. SOME SHOWERS ARE POSSIBLE AS ONE SYSTEM DEPARTS ON SATURDAY, THEN A COLD FRONT MOVES THROUGH MAINLY SUNDAY MORNING. THE WINDS SHIFT TO THE NORTHWEST SATURDAY THEN LIGHT SOUTHWEST AT NIGHT, BEFORE SHIFTING TO THE NORTHWEST AND INCREASING TO 10-15 KNOTS DURING SUNDAY.
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&& .MARINE...
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SCA WITH WIND NNJ AND SCA SNJ. DID NOT ATTM ADD SCA FOR DE COAST SINCE 44009 ON THE OUTER EDGE OF 455 IS MARGINALLY 5 FT. HOWEVER, AM NOW ANTICIPATING WE`LL NEED AN SCA IN THE DE ATLC WATERS FOR LATER TONIGHT. SST`S ARE NEAR OR SLIGHTLY ABOVE NORMAL. OUTLOOK... THURSDAY AND FRIDAY...A PERSISTENT ONSHORE FLOW WILL INCREASE FOR A TIME THURSDAY AS ONE LOW PRESSURE SYSTEM TO OUR SOUTH TRACKS NORTHEASTWARD. THIS SHOULD RESULT IN WIND GUSTS TO AROUND 25 KNOTS MAINLY ACROSS THE NORTHERN ATLANTIC COASTAL WATERS THURSDAY. A SECONDARY LOW PRESSURE SYSTEM ARRIVES DURING FRIDAY WITH A POSSIBLE 25-30 KNOT NORTHEASTERLY SURGE ACROSS OUR NORTHERN ATLANTIC COASTAL WATERS. THIS WILL DEPEND ON THE STRENGTH OF AN EASTERLY LOW-LEVEL JET THAT LIFTS NORTHWARD FRIDAY. THE SEAS ARE FORECAST TO BE 4-6 FEET MOSTLY FOR THE NEW JERSEY ATLANTIC COASTAL WATERS, AND THE SMALL CRAFT ADVISORY WAS EXTENDED THROUGH 22Z THURSDAY. THIS WILL LIKELY NEED TO BE EXTENDED AGAIN, AND SEAS MAY BUILD TO 5 FEET FARTHER SOUTH THROUGH FRIDAY AND THEREFORE THE ADVISORY MAY NEED TO BE EXPANDED SOUTHWARD. SATURDAY AND SUNDAY...A COLD FRONT ARRIVES SUNDAY MORNING WITH THE WINDS TURNING SOUTHWEST AHEAD OF IT LATE SATURDAY THEN SHIFTING TO THE NORTHWEST ON SUNDAY. THE WINDS ARE FORECAST TO INCREASE SUNDAY BEHIND THE FRONTAL PASSAGE, HOWEVER IT APPEARS THAT SPEEDS ARE BELOW ADVISORY CRITERIA. THE SEAS SHOULD ALSO BE DROPPING BELOW 5 FEET WITH SOME HELP ON SUNDAY DUE TO THE FLOW INCREASING FROM OFFSHORE.
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&& .TIDES/COASTAL FLOODING...
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CF ADVISORY ISSUED. GUIDANCE SUGGESTIONS OF INCREASED POSITIVE DEPARTURES COMBINED WITH INCREASING ASTRONOMICAL EVENING TIDES, LOWERING PRESSURE AND AN INCREASING ONSHORE WIND FAVORED AN ADVISORY ISSUANCE. IT WILL BE MARGINAL...PROBABLY PLUS OR MINUS .2 FT FROM THRESHOLD. THIS MORNINGS HIGH TIDE, ESPECIALLY NEAR LEWES WAS .3FT HIGHER THAN LAST EVENINGS. THAT UPWARD DEPARTURE TREND SHOULD CONTINUE THE NEXT SEVERAL CYCLES. THE LONG DURATION NORTHEASTERLY FETCH COMBINED WITH A DAILY INCREASE IN ASTRONOMICAL TIDES AS WE APPROACH THE NEW MOON FRIDAY WILL RESULT IN PERIODS OF MINOR EVENING COASTAL FLOODING. ALL AVAILABLE GUIDANCE SUGGESTS THERE COULD/SHOULD BE SOME MINOR TIDAL FLOODING AROUND THE TIMES OF HIGH TIDE THIS EVENING, THURSDAY EVENING, AND MORE LIKELY FRIDAY EVENING. FOR NOW, ISSUED A COASTAL FLOOD ADVISORY FOR THE NJ/DE COASTS AND DELAWARE BAY FOR THIS EVENINGS HIGH TIDE. THERE IS ALSO A SLIGHT CHANCE OF REACHING A MODERATE THRESHOLD FRIDAY EVENING, BUT CONFIDENCE IS LOW.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...COASTAL FLOOD ADVISORY FROM 5 PM THIS AFTERNOON TO 11 PM EDT THIS EVENING FOR NJZ012>014-020>027. DE...COASTAL FLOOD ADVISORY FROM 5 PM THIS AFTERNOON TO 11 PM EDT THIS EVENING FOR DEZ002>004. MD...NONE. MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 PM EDT THURSDAY FOR ANZ452-453. SMALL CRAFT ADVISORY UNTIL 6 PM EDT THURSDAY FOR ANZ450-451.
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&& $$ SYNOPSIS...GORSE NEAR TERM...DRAG/IOVINO SHORT TERM...DRAG LONG TERM...GORSE AVIATION...DRAG/GORSE MARINE...DRAG/GORSE TIDES/COASTAL FLOODING...STAFF

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