Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 240030 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 830 PM EDT TUE SEP 23 2014 .SYNOPSIS... HIGH PRESSURE SYSTEM OVER OUR FORECAST AREA WILL STRENGTHEN AS IT MOVES NORTHEAST...REACHING THE CANADIAN MARITIMES ON WEDNESDAY. A LOW PRESSURE SYSTEM WILL DEVELOP OFF THE CAROLINA COAST AND LIFT NORTHEAST INTO DELMARVA ON THURSDAY BEFORE MOVING OFFSHORE ON FRIDAY. ANOTHER HIGH PRESSURE FROM THE GREAT LAKES WILL BUILD INTO THE REGION FOR THE WEEKEND. A COLD FRONT IS EXPECTED TO MOVE THROUGH THE AREA MONDAY NIGHT FOLLOWED BY A HIGH PRESSURE SYSTEM BUILDING INTO NORTHERN NEW ENGLAND ON TUESDAY. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 630 PM ESTF: HAVE LOWERED TEMPS A BIT OVER THE DELMARVA AS THE FIRST BATCH OF THICK CIRRUS PEELS AWAY TO THE EAST LEAVING A SLOT OF MOSTLY CLEAR SKY...EXCEPT THE SE CORNER OF DELAWARE WHERE THICK HIGH CLOUD COVER SHOULD HOLD FIRM. WINDS WERE DECREASED SLIGHTLY EARLY THIS EVENING PERMITTING IDEAL EVENING RADIATIONAL COOLING OVER MOST OF OUR FORECAST AREA. THE DEWPOINTS WERE RAISED SLIGHTLY PER REALITY AGAINST MODEL OUTPUT STATISTICS. RAN THE UPS CROSSOVER FOG TOOL AND ONLY FOUND SOME ISOLATED SPOTTY FOG POTENTIAL IN SUSSEX COUNTY OF FAR NW NJ EARLY WEDNESDAY MORNING. SO FROM THE 330 PM DISCUSSION... FAIR WEATHER IS EXPECTED TONIGHT AS HIGH PRESSURE WILL BE ACROSS THE REGION. SKIES WILL BE MOSTLY CLR ACROSS THE NORTH...AND PARTLY CLOUDY ACROSS THE SOUTH WHERE SOME HIGH CI/CS CLOUDS WILL BE OBSERVED. A SLOW INCREASE IN HIGH CLOUDS WILL BE SEEN OVERNIGHT. LOW TEMPERATURES WILL AGAIN BE COOL WITH DECENT RADIATIONAL COOLING EXPECTED. I WENT BELOW MAV MOS IN MOST AREAS. LOWS WILL RANGE FROM THE LOW/MID 40S NORTH...TO THE LOW/MID 50S OVER THE DELMARVA AND METRO PHILADELPHIA. WINDS WILL BE LIGHT AND VARIABLE...THEN BECOME E/NE AT 5 TO 10 MPH BY DAWN. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... THE 630 PM ESTF RAISED POPS IN SOUTHERN TALBOT AND CAROLINE COUNTIES AS WELL AS SOUTHERN SUSSEX COUNTY DE WHERE IT SHOULD BE RAINING AT A PRETTY HEAVY CLIP VERY LATE IN THE DAY WEDNESDAY. THAT WITHIN THE 850 EASTERLY FLOW OF 35-40 KT. THE SFC HIGH WILL BE EAST OF THE AREA WED MORNING. LOW PRESSURE WILL BE DEEPENING OFF THE CAROLINA COASTAL AREAS AND BEGINNING TO TRACK N. CLOUDS WILL INCREASE ACROSS THE REGION DURING THE DAY...BUT THE ONLY CHC FOR RAIN WILL ONLY BE ACROSS SRN DELAWARE AND THE SOUTHERN COASTAL AREAS OF NJ. THESE RAIN CHCS WOULD BE DURING THE AFTERNOON ONLY. WINDS WILL INCREASE FROM THE E AT 10 TO 20 MPH DURING THE DAY WITH GUSTS AROUND 25 MPH...POSSIBLY 30 ALONG THE COAST BY DAYS END. HIGH TEMPERATURES WILL MOSTLY BE IN THE LOW 70S REGION- WIDE. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... THE LONG TERM HAS BECOME MUCH MORE COMPLICATED WITH A GREATER IMPACT OVER OUR CWA THAN WAS THE CASE A COUPLE OF DAYS AGO. ALL OF THE MODELS ARE TRANSITIONING TO WHAT THE ECMWF AND CAN GGEM ORIGINALLY HAD. THE PROBLEM REMAINS IN THE DETAILS AS GULF STREAM CONVECTION WITH THIS DEVELOPING SYSTEM HAS RESULTED IN VERY LITTLE RUN TO RUN CONTINUITY AS TO THE LOCATIONS OF HEAVY RAIN. THAT BEING SAID, THE DP/DT ON THE SYSTEM HAS BEEN TOWARD A FASTER CLOSING OFF OF THE LOW (WHICH HAS ALREADY OCCURRED) AND THUS A MORE WESTWARD TUG BY IT ON THE SURFACE LOW. THE SPLIT OFF THE 12Z RUN IS WHETHER OR NOT THE LOW ALOFT WILL CLOSE AGAIN OVER PA. THIS MAKES ENDING OF PCPN CHANCES DIFFERENT. THE CAN GGEM QPF VERIFIED THE BEST THRU 12Z THIS MORNING, WHILE THE GFS LOOKED OFF TO THE BEST START OF THE 12Z MODELS IN THE SOUTHEAST. SINCE THE OP NAM LOOKED FAST GIVEN THE LOW HAS CLOSED FARTHER WEST THAN EARLIER PROJECTIONS, WE WENT CLOSER TO THE GFS TIMING. THE UKMET REMAINS THE MOST BENIGN MODEL WITH THIS EVENT, BUT GIVEN ITS BY ITSELF NOW WAS GIVEN LITTLE WEIGHT. WEDNESDAY NIGHT, RAIN, HEAVY AT TIMES WILL BE OVERSPREADING OUR CWA. POPS WERE INCREASED TO CAT EAST WHERE ALL THE MODELS HAVE DECENT MEASURABLE RAIN. HEAVY RAIN MENTION WAS KEPT EAST BASED ON MODELING CONSENSUS AND LOCATION OF THEIR 250MB DIVERGENCE ALOFT AND BETTER MID LEVEL FGEN FEATURES. WHILE SOME MODELS ARE SHOWING A SECONDARY PCPN MAX IN PA, THE PREDICTED PWATS ARE ABOUT HALF OF LOCALES CLOSER TO THE COAST. SFC BASED INSTABILITY IS NOT THERE, BUT SOME INSTABILITY IS BEING PREDICTED ALOFT. FOR NOW THE INSTABILITY IS TRAILING THE OMEGA VS BEING COINCIDENTAL IN OUR CWA, SO NO MENTION OF THUNDER. THAT BEING SAID THE PREDICTED CONVECTION TO OUR SOUTH IS NOT DOING WELL FOR MODEL QPF VERIFICATION. THERE HAS NOT BEEN MUCH RUN TO RUN CONTINUITY WITH REGARDS TO PLACEMENT OF HEAVY RAIN. THIS MODEL RUN SUITE DID NOT SEEM TO SUFFER FROM WHAT LOOKED LIKE FEEDBACK PBLMS THAT OCCURRED WITH SOME OF THE 00Z AND 06Z RUNS. WE ARE ENTERING THIS EVENT EXTREMELY DRY, EVEN FOR SEPTEMBER AND WOULD NEED MORE THAN THE 1 TO 3" PREDICTED FOR THIS EVENT FOR STREAMS AND RIVERS TO START HAVING PROBLEMS. SOME HEADWATER GUIDANCE IS NEAR 6 INCHES/12 HOURS. BIGGEST FLOODING ISSUES MAY BE ALONG THE IMMEDIATE COAST IF HEAVY RAIN COINCIDES WITH THE HIGH TIDE CYCLES. THERE SHOULD ALSO BE A RAIN IMPACT ON THE MORNING COMMUTE THURSDAY, ESPECIALLY IN THE NORTHERN TWO THIRDS OF OUR CWA. ON THURSDAY, THE SYNOPTIC SCALE PUSH OF HEAVIER RAIN IS EXPECTED TO MOVE THROUGH OUR CWA BY NOON. SECONDARY PCPN MAXES ARE NOW EITHER OFFSHORE OR NON GENERATED. NOW THAT THE MODELS HAVE KEYED IN FOR TWO SUCCESSIVE SOUNDING RUNS ON THE CLOSED LOW IN THE SE, THERE HAS BEEN A SLIGHTLY FASTER EVOLUTION OF THIS EVENT GOING FORWARD AND EVEN VS THE NIGHT RUN. DIFFERENCES ARISE AS TO HOW QUICKLY WILL THE TROF OR CLOSED LOW EXIT THE REGION. GIVEN THE DRIER AND FASTER TREND ON THE LATEST WRF AND ECMWF (ALTHOUGH THE LATTER IS STILL AMONG THE SLOWEST), WE DECREASED POPS FASTER ON THURSDAY AFTERNOON AND NIGHT AND HAVE FRIDAY DRY. ANOTHER WELL TIMED WEEKEND AS ALL OF THE MODELS HAVE US DRY AND UNSEASONABLY WARM IN THE WAKE OF THE DEPARTING LOW. THE NEXT BACKDOOR COLD FRONT SHOULD COME THROUGH LATER MONDAY OR TUESDAY. POPS WERE KEPT IN FOR MONDAY NIGHT AND ADDED FOR TUESDAY. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TONIGHT...VFR MOSTLY CLEAR NORTH AND VFR SCT-BKN CIRRUS SOUTH AOA 20000 FT. LIGHT N-NE WIND. WEDNESDAY...VFR BKN-OVC CIRRUS AOA 20000 FT TO START THE DAY WITH A SCT-BKN DECK NEAR 3000 FT DEVELOPING NORTHWARD LATE MORNING AND AFTERNOON. E-NE WIND GUST 20 KT INTERIOR AND NEAR 25 KT COAST...ESPECIALLY AFTERNOON. OUTLOOK... WEDNESDAY NIGHT AND THURSDAY...MVFR TO IFR CEILINGS ARE LIKELY WITH MVFR VSBYS OVER MUCH OF THE REGION AS A LOW PASSES JUST EAST OF THE REGION. SOME GUSTY EAST WINDS ARE ALSO POSSIBLE FOR COASTAL AIRPORTS. THE TERMINALS EXPECTED TO HAVE THE LONGEST AND MOST SIGNIFICANT IMPACTS ARE KMIV AND KACY WITH AIRPORTS IN NJ AND DE OVERALL MOST AFFECTED. THURSDAY NIGHT AND FRIDAY...BECOMING VFR. GREATEST IMPACT ON THURSDAY NIGHT AND EARLY FRIDAY SHOULD BE FOG. FRIDAY NIGHT THROUGH SUNDAY. PRIMARILY VFR CONDITIONS EXPECTED. SOME EARLY MORNING FOG POSSIBLE AT MORE RURAL AIRPORTS AND TERMINALS.
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&& .MARINE...
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NO HEADLINE OVERNIGHT. LAST GOOD NIGHT TO BE METEOROLOGICALLY SAFE ON THE ATLANTIC WATERS...POSSIBLY THROUGH SATURDAY. WEDNESDAY...SCA WIND GUSTS TO 25 KT SPREAD NORTHWARD DURING THE MORNING WITH 30 KT GUSTS BY LATE AFTERNOON. SEAS BUILD TO 5 FEET NNJ WATERS DURING THE AFTERNOON AND TO NEAR 8 OR 9 FT LATE DAY SOUTHERN NJ AND DE ATLANTIC WATERS. LIGHT RAIN WILL ARRIVE OVER THE SRN WATERS DURING WEDNESDAY AFTERNOON...THEN SPREAD N/W DURING THE EVENING. OUTLOOK... WEDNESDAY NIGHT AND THURSDAY...A GALE WATCH WAS ISSUED FOR MOST OF OUR COASTAL WATERS AS THERE SHOULD BE A PERIOD WHEN THE GRADIENT TIGHTENS TO THE POINT THAT GALES ARE POSSIBLE. LOWEST CONFIDENCE IN UPPER DELAWARE BAY AND OUR NORTHERN WATERS WHERE A SMALL CRAFT ADVISORY REMAINS IN EFFECT THROUGH WEDNESDAY NIGHT. SLOW IMPROVEMENT WITH THE WINDS ON THURSDAY, DECREASING SOUTH FIRST. DELAWARE BAY MOST LIKELY TO GO BELOW SCA CONDITIONS ON THURSDAY. THURSDAY NIGHT THROUGH FRIDAY NIGHT...WINDS ON THE OCEAN SHOULD BE BELOW SCA CRITERIA BY FRIDAY MORNING WITH DELAWARE BAY REMAINING BELOW SCA CRITERIA. SEAS MAY BE ANOTHER PROBLEM AS THEY ARE PREDICTED TO BE SLOW TO SUBSIDE. SCA CONDITIONS FOR SEAS ARE POSSIBLE THRU FRIDAY NIGHT. SATURDAY AND SUNDAY...SUB SMALL CRAFT ADVISORY CONDITIONS ON DELAWARE BAY. SEAS SHOULD SUBSIDE BELOW SMALL CRAFT ADVISORY CRITERIA ON THE OCEAN ON SATURDAY AND REMAIN BELOW FOR THE REST OF THE WEEKEND.
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&& .TIDES/COASTAL FLOODING...
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A 6 TO 18 HOUR PERIOD OF INTERMITTENT GALE FORCE EAST TO NORTHEAST WIND GUSTS (35KT) IS EXPECTED LATE WEDNESDAY INTO THURSDAY AND WILL PROBABLY CAUSE MINOR COASTAL FLOODING DURING ONE OR TWO OF THE 3 HIGH TIDE CYCLES BEGINNING WEDNESDAY EVENING. THE TIDAL INUNDATION FLOOD RISK WILL LINGER THROUGH THE THURSDAY NIGHT HIGH TIDE CYCLE. NORMAL ASTRONOMICAL PREDICTIONS WITHOUT ANY METEOROLOGICAL INFLUENCE DO NOT INDICATE ANY UNUSUALLY HIGH TIDES. TIDES VERSUS PREDICTED LATE EARLY THIS TUESDAY EVENING (812 PM EDT) ARE GENERALLY NEAR OR SLIGHTLY BELOW THE FORECAST VALUES. HOWEVER...POSITIVE SURGE DEPARTURES ARE EXPECTED TO GROW RAPIDLY WEDNESDAY EVENING AND SUSTAIN THAT 1 TO 2 FOOT WEDNESDAY EVENING HIGH TIDE POSITIVE DEPARTURE THROUGH THE THURSDAY NIGHT HIGH TIDE CYCLE. IF THE SURGE IS 1.8 TO 2 FEET AND COINCIDES WITH THE HIGH TIDE... MINOR FLOODING WOULD OCCUR. THERE IS A SMALL CHANCE THAT THE SURGE AT THE TIME OF THURSDAY MORNING-MIDDAY HIGH TIDE WILL BE 2.3 FEET IN WHICH CASE MODERATE COASTAL FLOODING WOULD OCCUR. TIMING IS EVERYTHING IN THIS SITUATION. THIS IS NO SLAM DUNK FOR A MODERATE EVENT ...EVEN FOR MINOR THE GFS/NAM MODEL GUIDANCE IS RESISTANT TO FORECASTING EXCEEDANCE OF MINOR THRESHOLD. GFS/NAM CONTINUE CONSERVATIVE ON THEIR 18Z RUNS AND THE ONLY THE STEVENS INSTITUTE SSWS CHECKS IN WITH MINOR AT LEWES AND JUST BARELY. NO COASTAL FLOOD WATCH SINCE THE MODERATE COASTAL FLOOD THREAT APPEARS TO BE MARGINAL LOWER END AT WORST, AND ITS POSSIBILITY AS OF THIS WRITING APPEARS TO BE LESS THAN 25 PERCENT ALONG ANY STRETCH OF THE COAST. IF MODEL GUIDANCE AND FORECASTER CONFIDENCE FOR MODERATE COASTAL FLOODING INCREASES IN FUTURE FORECASTS...A COASTAL FLOOD WATCH WILL BE ISSUED. IN THE MEANTIME...MINOR COASTAL FLOODING APPEARS TO BE A GOOD BET FOR THE THURSDAY MORNING HIGH TIDE CYCLE, IF NOT ALREADY FOR THE DELAWARE ATLANTIC COAST WEDNESDAY EVENING. DEPENDING ON THE POSITION OF THE SURFACE LOW... THE COASTAL FLOOD THREAT MAY LINGER THURSDAY NIGHT OR EVEN FRIDAY MORNING AS THE STRONG ONSHORE WIND FIELD INITIALLY MOVES NORTH ALONG THE MID ATLANTIC COAST TOWARD LONG ISLAND ON THURSDAY AND THEN SLIDES SEWD WITH THE EASTWARD TURNING SURFACE LOW ON FRIDAY. SINCE THE WIND EVENT HAS YET TO BEGIN AND WE`RE NOT SEEING THE REALITY OF EASTERLY FLOW ON THE COASTAL TIDE GAGES AND EVEN MINOR FLOODING IS NOT YET A GUARANTEE ...WE ARE NOT YET POSTING AN ADVISORY AND THIS WAS CHECKED AGAINST THE 18Z MODELS. ONE ADDITIONAL NOTE...SOME BEACH EROSION IS LIKELY AND WAVES OF 10 TO 12 FEET MAY ADD TO SPLASHOVER ONTO THE TYPICALLY VULNERABLE COASTAL BEACH PROPERTIES WEDNESDAY NIGHT AND THURSDAY. REVIEWING: THE PRIMARY GUIDANCE FOR THIS ANALYSIS DISCUSSION WAS THE 18Z GFS ESTOFS AND ETSS WHICH SHOWS A 1-2 FOOT SURGE. THE NAM VIA DBOFS IS LESS THREATENING...WITH ONLY AROUND A HALF FOOT SURGE! THE STEVENS INSTITUTE SSWS WAS CHECKED AND LOOKS REASONABLE AND PREDICTS ABOUT A 6.4 TO 6.5 FOOT TIDE FOR LEWES DELAWARE WEDNESDAY EVENING AT 936 PM.
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&& .RIP CURRENTS...
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WE ISSUED A HIGH RISK FOR THE FORMATION OF DANGEROUS RIP CURRENTS IN OUR 8 PM FORECAST FOR SURF ZONE FORECAST FOR WEDNESDAY OVER DELAWARE AND HELD OFF FOR NJ PENDING ONE MORE MODEL LOOK. IT APPEARS NJ WILL BE MODERATE DURING THE MORNING TRANSITIONING TO A HIGH RISK DURING MID AFTERNOON. A MODERATE OR HIGH RISK FOR THE FORMATION OF THE DANGEROUS RIP CURRENTS WILL LINGER THURSDAY. THE ENHANCED RISK FOR RIP CURRENTS MIGHT PERSIST INTO FRIDAY EVEN AS WINDS DIMINISH AND SEAS SLOWLY SUBSIDE.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...HIGH RIP CURRENT RISK FROM 8 AM EDT WEDNESDAY THROUGH WEDNESDAY EVENING FOR DEZ004. MD...NONE. MARINE...GALE WATCH FROM WEDNESDAY EVENING THROUGH LATE WEDNESDAY NIGHT FOR ANZ431-451>455. SMALL CRAFT ADVISORY FROM 6 AM TO 8 PM EDT WEDNESDAY FOR ANZ431-451>455. SMALL CRAFT ADVISORY FROM 6 AM WEDNESDAY TO 6 AM EDT THURSDAY FOR ANZ430-450.
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&& $$ SYNOPSIS...GIGI/JOHNSON NEAR TERM...DRAG/O`HARA 830 SHORT TERM...DRAG/O`HARA LONG TERM...GIGI AVIATION...DRAG/GIGI/JOHNSON/O`HARA 830 MARINE...DRAG/GIGI/JOHNSON/O`HARA 830 TIDES/COASTAL FLOODING...830 RIP CURRENTS...830

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