Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 130127 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 927 PM EDT FRI SEP 12 2014 .SYNOPSIS... HIGH PRESSURE WILL SLIDE TO OUR NORTH AND NORTHEAST THROUGH TONIGHT. A LOW PRESSURE SYSTEM AND ITS ASSOCIATED FRONTAL BOUNDARIES WILL THEN AFFECT OUR AREA SATURDAY AND SATURDAY EVENING. HIGH PRESSURE ARRIVES FOR SUNDAY AND MONDAY. THE NEXT COLD FRONT IS SCHEDULED TO ARRIVE MONDAY NIGHT AND TUESDAY, WITH HIGH PRESSURE ONCE AGAIN BUILDING IN FOR WEDNESDAY AND THURSDAY. A WEAK COLD FRONT MAY SETTLE SOUTHEASTWARD ACROSS OUR AREA LATE THURSDAY, THEN HIGH PRESSURE BUILDS BACK IN FOR FRIDAY. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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THE GFS AND WRF-NMMB INITIALIZATION LOOKED PRETTY CLOSE WITH NO GLARING ERRORS OR WINNERS. THE GENERAL DP/DT IS A SLIGHTLY STRONGER TROFFING WITH TIME. OVERALL THE MODELS TIMING IS VERY SIMILAR, THE BIGGEST DIFFERENCE IS THE PLACEMENT OF THE QPF MAX(ES). WHILE MORE MODELS HAVE THEIR HIGHEST QPF NORTH (WHICH WE USED), THE INCREASINGLY SHARPER TROF MAKES US GIVE A SECONDARY THERMODYNAMIC QPF MAX SOUTH FAR SOUTH. SHARPER TROF, SLIGHTLY SLOWER TIMING, SO NO POPS WERE INCLUDED FOR TONIGHT. CLOUDINESS WILL INCREASE AND THE OVERALL TIMING WILL IMPACT THE PREDICTED LOW TEMPERATURES. WE TRIED TO BOTTOM THEM SLIGHTLY EARLIER AND LEVELED THEM TOWARD MORNING. BECAUSE OF THIS WE WERE GENERALLY CLOSER TO THE WARMER STAT GUIDANCE. WINDS WILL BE LIGHT. WITH THE EVENING UPDATE WE DID INCORPORATE THE LATEST LAV GUIDANCE WITH REGARDS TO TEMPERATURES OVER THE NEXT FEW HOURS.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... THIS HAS BEEN A TOUGH WEEK OF FORECASTING IN OUR CWA AS THE CONVECTION (REALLY THE LACK THEREOF) HAS RESULTED IN EXTREMELY NOISY AND NOT MUCH RUN TO RUN CONTINUITY IN SOLUTIONS. OUR FORECASTS HAVE BEEN TOO WET. THE PRECIPITATION CHANCE SATURDAY OUTSIDE OF MAYBE FAR SE IS VOID OF CONVECTIVE INITIATION/PROPAGATION. THUS A SYNOPTIC SCALE SYSTEM NEARLY ALWAYS HAS GREATER MODEL SKILL AND WE HAVE MORE CONFIDENCE ABOUT THE OUTCOME. THE TRENDING STRONGER, NEGATIVE TILT TROF SHOULD DEVELOP TWO LOW PRESSURE SYSTEMS. ONE ALONG A NEW BOUNDARY TO OUR WEST AND A SECOND OFF THE OLD FRONTAL BOUNDARY EAST OF DELMARVA. GFS DIAGS SUPPORT THE HEAVIER PCPN IN THE NORTHERN PART OF OUR CWA AS ITS THE LOCALE OF THE STRONGER ISENTROPIC TRANSPORT AT 305K, EQUIVALENT PTNL TEMP ADVECTION AS WELL AS THE ENTRANCE REGION OF THE 250MB JET. WHILE THE CONSENSUS FOR THE MODELING IS FOR THUNDER OR THUNDER POTENTIAL TO BE SOUTH OF OUR CWA, ANY FURTHER BACKING OF THE TROF SHOULD BRING THAT INTO OUR CWA. PWATS EXCEEDING 2" SOUTH OF OUR CWA IS NOT A BAD REASON EITHER. THE WRF-NMMB STANDS ALONG AT THIS POINT AT BEING FAIRLY NORTH WITH THE INSTAB ALF. WITH YDA`S NON-EVENT, THE OP-WRF WAS NEAR THE WETTEST IF NOT THE WETTEST SOLUTION OF THE 21 SREF ENSEMBLE MEMBERS. IT IS AGAIN WITH THIS EVENT. OUR QPF WILL SHOW A DOUBLE BARREL MAX, ONE IN THE NORTHERN PART OF OUR CWA WITH THE BETTER SYNOPTIC SCALE SUPPORT AND A SECOND OVER FAR SOUTHERN DELMARVA FOR THE POSSIBILITY OF CONVECTIVE ENHANCEMENT. POPS WERE INCREASED TO CAT FROM AROUND PHL NORTH WHERE THE BEST MODEL CONSENSUS EXISTS. THE CYCLOGEN OFF THE SOUTHERN DELMARVA MIGHT SHUNT SOME OF THE MOISTURE OFSHR (AND END ANY THUNDER PTNL ALSO). THIS (WHERE THE SECONDARY FORMS) IS ALSO ONE OF THE REASONS FOR THE WIDER QPF SPREAD SOUTH VS NORTH. TEMPS WE WENT TOWARD THE LOWER END OF STAT GUIDANCE AND ALSO HAD AN EARLIER IN THE DAY HIGH BEFORE THE HIGHER CONFIDENCE RAIN TIMING (AFTN) OCCURS. EAST WINDS SHOULD INCREASE, BUT ASIDE FROM THE IMMEDIATE SHORE (WHERE GUSTS SHOULD GET INTO THE 20S), THEY WILL NOT BE THAT STRONG. THIS IS A QUICK HITTER AND WE START LOWERING POPS LATE IN THE AFTERNOON. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... THE OVERALL SYNOPTIC SETUP IS COMPRISED OF AN INITIAL ROBUST SHORT WAVE TROUGH THAT THEN WEAKENS AS IT LIFTS NORTHEASTWARD ACROSS NORTHERN NEW ENGLAND SATURDAY NIGHT. AN UPPER-LEVEL TROUGH LOOKS TO LINGER ACROSS SOUTH-CENTRAL CANADA, AND THIS IS FORECAST TO AMPLIFY SOME AS IT MIGRATES FROM THE MIDWEST AND GREAT LAKES REGIONS MONDAY THEN TO THE NORTHEAST TUESDAY. AS RIDGING HOLDS INTO THE ROCKIES, A GENERAL UPPER-LEVEL TROUGH LOOKS TO REMAIN FROM THE GREAT LAKES TO THE NORTHEAST THROUGH THURSDAY. THIS MAY THEN START TO WEAKEN FRIDAY AS A TROUGH TOWARD THE NORTHERN PLAINS TRIES TO BUILD A DOWNSTREAM RIDGE. A MODEL BLEND WAS USED FOR SATURDAY NIGHT THROUGH MONDAY, THEN WENT WITH THE 12Z WPC GUIDANCE THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE FOLLOWING ADDITIONAL COLLABORATION WITH OUR SURROUNDING OFFICES. FOR SATURDAY NIGHT...A POTENT UPPER-LEVEL TROUGH SHOULD TEND TO START WEAKENING AS IT LIFTS TOWARD NORTHERN NEW ENGLAND. OVERALL THOUGH THIS FEATURE LOOKS TO BE A QUICK MOVER, THEREFORE ANY AREAS OF LINGERING RAIN ARE EXPECTED TO END DURING THE EVENING. THE LOW-LEVEL FLOW WILL BE BACKING TO THE NORTHWEST WITH DRIER AIR ADVECTING IN. THIS IS EXPECTED TO ALLOW FOR THE CLOUDS TO START CLEARING THROUGH THE NIGHT. FOR SUNDAY AND MONDAY...LOW PRESSURE SUNDAY IS FORECAST TO BE TRACKING INTO THE CANADIAN MARITIMES, WITH AN ASSOCIATED FRONTAL BOUNDARY DRAPED TO OUR SOUTH AND EAST. AS THE MAIN SHORT WAVE TROUGH QUICKLY LIFTS OUT, AN EXPANSIVE SURFACE HIGH IS FORECAST TO BUILD ACROSS THE GREAT LAKES AND INTO OUR REGION SUNDAY, THEN SHIFT OFFSHORE THROUGH MONDAY. THIS SURFACE HIGH IS CHARACTERIZED BY A COOL AIRMASS, THEREFORE A DRY AND COOL DAY IS ANTICIPATED SUNDAY BEFORE SOME SLIGHT MODERATION OCCURS ON MONDAY. A SHORT WAVE LOOKS TO DIVE ACROSS THE MIDWEST AND GREAT LAKES MONDAY AND AN ASSOCIATED WEAK SURFACE LOW SHOULD ACCOMPANY IT. THIS FEATURE WILL TAKE AIM ON OUR AREA LATE MONDAY, THEREFORE AN INCREASE IN THE CLOUDS WILL OCCUR ESPECIALLY AT NIGHT. THE ARRIVAL OF LARGER SCALE LIFT COMBINED WITH SOME DEEPER MOISTURE SHOULD ALLOW SOME SHOWERS TO DEVELOP AT NIGHT. THE QUESTION IS HOW ORGANIZED WILL THE SHOWERS BE WITH THIS GENERALLY QUICK MOVING SYSTEM, THEREFORE CARRIED POPS NO HIGHER THAN HIGH CHC ATTM. FOR TUESDAY...AN AMPLIFYING UPPER-LEVEL TROUGH WILL SWING ACROSS THE NORTHEAST AND MID ATLANTIC REGION TUESDAY, TAKING LOW PRESSURE WITH IT. THIS FEATURE LOOKS TO BE PROGRESSIVE, THEREFORE UNSETTLED AT TIMES TUESDAY MAINLY IN THE MORNING THEN IMPROVING CONDITIONS SHOULD SET IN DURING THE AFTERNOON AND AT NIGHT. THE INFLUX OF DRIER AND COOLER AIR ALONG WITH INCREASING SUBSIDENCE SHOULD ALLOW FOR CLEARING TO TAKE PLACE ESPECIALLY TUESDAY NIGHT. FOR WEDNESDAY THROUGH FRIDAY...WHILE A BROAD UPPER-LEVEL TROUGH IS FORECAST TO BE IN PLACE WEDNESDAY, SURFACE HIGH PRESSURE WILL ARRIVE FROM THE WEST. THIS WILL DELIVER ANOTHER ROUND OF MUCH DRIER AIR ALONG WITH A COOL AIRMASS FOR WEDNESDAY AND THURSDAY. A WEAK COLD FRONT HOWEVER MAY TRY AND SETTLE SOUTHEASTWARD ACROSS OUR AREA LATE THURSDAY, WITH A NEW AIRMASS AND ASSOCIATED SURFACE HIGH PRESSURE BUILDING BACK IN FOR FRIDAY. THE FRONT LOOKS TO HAVE LIMITED MOISTURE THIS FAR OUT IN TIME, THEREFORE KEPT THE FORECAST DRY. MOST OF THE WEATHER ELEMENTS WERE FAIRLY CLOSE TO THE 12Z WPC GUIDANCE. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. 00Z TAFS CONTINUING VFR CONDITIONS THIS EVENING AND BECOME MVFR BY NOONTIME SATURDAY. A SEABREEZE BOUNDARY WHICH PUSHED THROUGH MIV AND ACY DECAYED BEFORE REACHING PHL. SO WINDS THIS EVENING WILL BE A PREVAILING LIGHT EASTERLY TO NORTHEASTERLY FLOW EXCEPT FOR MIV AND ACY WHERE THE WINDS WILL COME AROUND TO THIS DIRECTION BY 05Z. THIS WILL HELP START REFORMING SOME LOWER CLOUDS. MOST OF THE EVENING/OVERNIGHT THOUGH THE PREVAILING CIGS WILL BE VFR MID AND HIGH LEVEL. TOWARD MORNING THE LIKELIHOOD OF A MVFR CIG RETURNING INCREASES. BY SATURDAY AFTERNOON MVFR CIG CONDITIONS ARE PREDICTED TO PERSIST WITH RAIN MOVING INTO THE TERMINALS BY THIS TIME. THIS MIGHT GENERATE A LOWER MVFR CIG (MAYBE IFR?) ALONG WITH THE POSSIBILITY OF SOME MVFR VSBYS ALSO. WINDS SHOULD REMAIN GENERALLY LIGHT FROM THE EAST. OUTLOOK... SATURDAY NIGHT...A PERIOD OF SUB-VFR CONDITIONS DUE TO RAIN EARLY, THEN IMPROVEMENT IS EXPECTED. NORTH TO NORTHWEST WINDS NEAR 10 KNOTS. SUNDAY...VFR WITH A NORTHERLY WIND GENERALLY 5-10 KNOTS. MONDAY AND TUESDAY...SOME SHOWERS SHOULD OCCUR MONDAY NIGHT AND TUESDAY MORNING AS A COLD FRONT MOVES THROUGH WITH TIMES OF SUB-VFR CONDITIONS, OTHERWISE VFR. WEDNESDAY...VFR OVERALL AS HIGH PRESSURE BUILDS IN.
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&& .MARINE... NO SMALL CRAFT ADVISORY WILL BE ISSUED WITH THIS PACKAGE, ALTHOUGH THERE IS SOME UNCERTAINTY ABOUT SATURDAY. SEAS AT BUOY9 ARE CURRENTLY SUBSIDING AS THE NORTHERLY PUSH WEAKENS. OTHERWISE A PREVAILING EASTERLY FLOW (A BRIEFLY STRONGER SE FLOW EARLY THIS EVENING IN DELAWARE BAY) WILL BE DEVELOPING. A LOW PRESSURE SYSTEM IS PREDICTED TO FORM OFF THE OLD FRONT AND MOVE FARTHER OFFSHORE ON SATURDAY. THIS MIGHT TIGHTEN THE GRADIENT ENOUGH TO REQUIRE A SMALL CRAFT ADVISORY. WE WILL CONTINUE TO MONITOR. REGARDLESS NEAR SMALL CRAFT ADVISORY WINDS AND SEAS ARE PREDICTED ALONG WITH RAIN ARRIVING. OUTLOOK... SATURDAY NIGHT...AS A FRONTAL BOUNDARY AND WEAK LOW PRESSURE SYSTEM SHIFTS TO OUR NORTHEAST, A NORTH-NORTHEAST SURFACE WIND WILL QUICKLY BECOME NORTHWESTERLY. WHILE THERE SHOULD BE A NORTHERLY WIND SURGE, IT APPEARS TO BE SHORT IN DURATION AND MOSTLY BELOW ADVISORY CRITERIA. SUNDAY THROUGH TUESDAY...HIGH PRESSURE BUILDS IN SUNDAY BEFORE SHIFTING OFFSHORE MONDAY. A STRONGER NORTHERLY WIND EARLY SUNDAY SHOULD DIMINISH AND BECOME NORTHEAST OR EAST LATER SUNDAY, THEN GRADUALLY SETTLE TO SOUTHEASTERLY MONDAY. A FRONTAL SYSTEM MOVING THROUGH MONDAY NIGHT AND TUESDAY WILL RESULT IN A WIND SHIFT TO THE NORTHWEST. OVERALL, THE FLOW LOOKS LIGHT ENOUGH THEREFORE CONDITIONS ARE ANTICIPATED TO BE BELOW ADVISORY CRITERIA. WEDNESDAY...HIGH PRESSURE BUILDS IN FROM THE NORTHWEST, HOWEVER A NORTHERLY SURFACE WIND MAY ALLOW FOR OFFSHORE SEAS TO APPROACH 5 FEET AT TIMES. && .RIP CURRENTS...
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A MODERATE RISK OF RIP CURRENTS THROUGH TONIGHT FOR THE NEW JERSEY AND DELAWARE COASTLINES.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GORSE NEAR TERM...GAINES/GIGI SHORT TERM...GIGI LONG TERM...GORSE AVIATION...GAINES/GIGI/GORSE MARINE...GIGI/GORSE RIP CURRENTS...GAINES/GIGI

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