Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 191955 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 355 PM EDT FRI SEP 19 2014 .SYNOPSIS...
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HIGH PRESSURE WILL SHIFT OFFSHORE TONIGHT. A WARM FRONT WILL LIFT TO OUR NORTHWEST SATURDAY, THEN A COLD FRONT IS EXPECTED TO AFFECT THE AREA LATE SUNDAY INTO SUNDAY NIGHT. THIS FRONT WILL MOVE TO OUR SOUTH, WHILE HIGH PRESSURE BEGINS TO BUILD IN FROM THE WEST ON MONDAY. A WEAKENING FRONT MAY BRIEFLY AFFECT THE AREA ON TUESDAY, BEFORE THE HIGH FULLY BUILDS ACROSS THE AREA FOR MUCH OF THE REMAINDER OF THE WEEK.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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A 1030 MB SURFACE HIGH WAS CENTERED OVER NEW ENGLAND THIS AFTERNOON. THE HIGH WILL SHIFT EASTWARD TOWARD THE GULF OF MAINE THROUGH THIS EVENING BEFORE MOVING FARTHER OFFSHORE LATE TONIGHT. EASTERLY FLOW AROUND THE HIGH THIS AFTERNOON HAS DRAWN RELATIVELY COOL/MOIST MARINE LAYER INLAND. STRATOCU HAS BEEN PERSISTENT SO FAR THIS AFTERNOON OVER THE SOUTHERN HALF OF NJ- WHERE MOISTURE REMAINS TRAPPED AT THE TOP OF THE BOUNDARY LAYER. THERE IS A BRIEF POTENTIAL FOR PARTIAL CLEARING TOWARD SUNSET BUT EXPECT CLOUDS TO REDEVELOP TONIGHT UNDER CONTINUED ONSHORE FLOW. FARTHER INLAND,MARINE LAYER NOT AS WELL ESTABLISHED AND STRATOCU HAS BEEN ABLE TO SCT OUT THIS AFTERNOON. HOWEVER, CLOUDS OVER VA WILL SPREAD INTO EASTERN PA THROUGH TONIGHT AS SOUTHERLY FLOW AND ISENTROPIC LIFT NEAR H8 STRENGTHENS AROUND THE WESTERN PERIPHERY OF THE HIGH. OFFICIAL MIN TEMP FORECAST FALLS ON THE WARMER ENVELOPE OF GUIDANCE AS RADIATIONAL COOLING SETUP NOT IDEAL OWING TO THE INCREASING CLOUD COVER THAT IS EXPECTED AND THE ONSHORE FLOW. THERE MAY BE A BETTER SETUP FOR RADIATIONAL COOLING THIS EVENING BEFORE THE CLOUDS ARRIVE ACROSS THE FAR NORTH. AREAS SUCH AS THE LEHIGH VALLEY, POCONOS AND NORTHWEST NJ HAVE A POTENTIAL TO SEE FOG DEVELOP OVERNIGHT.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
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HIGH PRESSURE WILL MOVE FARTHER OFFSHORE INTO THE NORTHERN ATLANTIC WATERS ON SATURDAY. AN AREA OF LOW PRESSURE IS FORECAST TO TRACK NORTH OF THE GREAT LAKES WHILE ANOTHER LOW PRESSURE SYSTEM DEVELOPS OFF THE SOUTHEAST COAST. THE PATTERN IN BETWEEN THESE TWO SYSTEMS WILL ALLOW THE ABOVE MENTIONED HIGH OVER THE ATLANTIC TO RIDGE BACK WESTWARD INTO THE MID-ATLANTIC STATES. SOUTHERLY FLOW AROUND THE PERIPHERY OF THE HIGH WILL PROMOTE WAA IN THE LOW LEVELS. THIS PATTERN WILL RESULT IN MAX TEMPS THAT ARE 5-10F WARMER ON SATURDAY THAN TODAY. SATURDAY MAY POTENTIALLY BE THE FIRST DAY WITH ABOVE NORMAL TEMPS SINCE SEP 11, ALBEIT NOT MUCH MORE THAN A COUPLE OF DEGREES ABOVE. MODEL BUFKIT SOUNDINGS DEPICT A SATURATED BOUNDARY LAYER INITIALLY SATURDAY MORNING AS A RESULT OF THE ONSHORE FLOW AT THE START OF THE PERIOD. THE 12Z NAM TRIES TO MIX OUT MOISTURE AND RESULTANT CLOUDS RATHER QUICKLY (BY 15Z) ACROSS THE ENTIRE CWA WHILE THE 12Z GFS INDICATES A MUCH CLOUDIER SOLUTION ALONG AND EAST OF THE FALL LINE THRU MUCH OF THE DAY AS MARINE AIR IS STUBBORN TO MIX OUT. DEEPER MOISTURE IN THE COLUMN AS FORECAST BY THE 12Z WOULD INDICATE THE POTENTIAL FOR SHOWERS TO DEVELOP NEAR THE COAST WITH THE ONLY DISCERNIBLE FORCING MECHANISM BEING LOW-LEVEL ISENTROPIC LIFT. KEPT POPS VERY LOW DUE TO THE UNCERTAINTY AND CONFINED SLIGHT CHANCE FOR SHOWERS TO COASTAL LOCALES SINCE MOISTURE FLUX IF FORECAST TO BE GREATEST OFFSHORE.
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&& .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
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SATURDAY NIGHT, HIGH PRESSURE PULLS AWAY TO OUR NORTHEAST AHEAD OF THE APPROACHING COLD FRONT. AT THE SAME TIME, AN AREA OF LOW PRESSURE WILL BE MOVING ALONG THE EAST COAST NEAR THE CAROLINA COASTS. THE LOW WILL MOVE NORTHWARD AND PASS EAST OF OUR AREA, BUT WILL LIKELY NOT PASS CLOSE ENOUGH TO OUR AREA TO BRING ANY SIGNIFICANT IMPACTS BEFORE THE FRONT APPROACHES AND PUSHES IT NORTHEASTWARD. WE MAY HAVE ANOTHER POSSIBILITY FOR LOW CLOUDS AND FOG AND/OR DRIZZLE AS THE LOW APPROACHES SATURDAY NIGHT AND THE LOW LEVELS MOISTEN. SO WE HAVE ADDED PATCHY FOG/DRIZZLE FOR SATURDAY NIGHT/SUNDAY MORNING. THE FRONTAL BOUNDARY SHOULD BE ENTERING OUR WESTERN AREAS DURING SUNDAY AFTERNOON, BEFORE SWEEPING ACROSS OUR AREA SUNDAY EVENING AND SUNDAY NIGHT. MODELS HAVE THE HIGHEST POPS AND QPF MOSTLY TO OUR WEST DURING THE DAY, BEFORE LOWERING AS THE FRONT MOVES THROUGH OUR AREA SUNDAY EVENING. SO WE WILL HAVE HIGHEST RAIN CHANCES SUNDAY AFTERNOON ACROSS THE NORTHWESTERN AREAS, DIMINISHING TO LOW END CHANCE SUNDAY EVENING. THERE IS SOME INSTABILITY ACROSS THE AREA AND ESPECIALLY TO THE WEST DURING THE DAY, BUT THE QUESTION IS WHETHER OR NOT WE LOSE THE INSTABILITY BEFORE THE ACTIVITY REACHES OUR AREA. WE WILL MAINTAIN THE SLIGHT CHANCE OF THUNDERSTORMS AS THERE IS THE POSSIBILITY FOR SOME ISOLATED CONVECTION. ON MONDAY, THE FRONT WILL BE MOVING OUT TO SEA, WHILE HIGH PRESSURE BEGINS BUILDING IN FROM THE WEST ACROSS THE AREA THROUGH MONDAY NIGHT. A WEAKENING FRONTAL BOUNDARY MAY BRIEFLY AFFECT THE AREA ON TUESDAY, BUT FOR NOW THE FRONT LOOKS LIKE IT SHOULD BE A MOSTLY DRY FRONTAL PASSAGE. THEN HIGH PRESSURE FULLY BUILDS BACK ACROSS THE AREA FOR MUCH OF THE REMAINDER OF THE WEEK, WHICH WILL PROVIDE DRY WEATHER ACROSS THE AREA. ACTUALLY, THE FRONTAL PASSAGE SUNDAY/SUNDAY NIGHT LOOKS LIKE OUR ONLY CHANCE OF RAIN FOR THE ENTIRE EXTENDED PERIOD, SO LETS HOPE WE GET SOMETHING FROM IT. TEMPERATURES ON SUNDAY WILL BE THE WARMEST OF THE EXTENDED WITH TEMPERATURES 5-10 ABOVE NORMAL. THEN TEMPERATURES RETURN CLOSER TO NORMAL OR FOR THE REMAINDER OF THE PERIOD.
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&& .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. CIGS HAVE LIFTED TO VFR AT ALL TERMINALS AS OF 19Z. THIS MARINE STRATOCU ARE FORECAST TO REMAIN BETWEEN 3-5 KFT THRU THIS EVE BEFORE CIGS LOWER OVERNIGHT. GUIDANCE IS IN GOOD AGREEMENT WITH MVFR CIGS DEVELOPING AFTER 06Z AND CONTINUING THRU DAYBREAK. THERE IS MORE UNCERTAINTY CONCERNING HOW QUICKLY LOW CLOUDS ERODE AND CIGS IMPROVE TO VFR. THE MARINE LAYER WILL GRADUALLY MIX OUT FROM WEST TO EAST DURING THE LATE MORNING AND AFTERNOON ONCE LOW-LEVELS WINDS VEER OUT OF THE SOUTH. CURRENT THINKING IS IMPROVEMENT TO VFR CIGS MAY NOT OCCUR UNTIL CLOSER TO MIDDAY FOR MOST TERMINALS, WHICH IS LATER THAN INDICATED BY THE 12Z NAM. OUTLOOK... SATURDAY NIGHT...LOWER CIGS AND/OR VSBYS POSSIBLE WITH STRATUS/FOG DEVELOPMENT OVERNIGHT SATURDAY/SUNDAY MORNING. SUNDAY-SUNDAY NIGHT...LOWER CONDITIONS POSSIBLE IN THE MORNING THE BECOMING VFR DURING THE DAY. A COLD FRONT APPROACHES LATE IN THE DAY INTO SUNDAY NIGHT WITH SCATTERED SHOWERS/THUNDERSTORMS AND LOWER CONDITIONS POSSIBLE. MONDAY-WEDNESDAY...MOSTLY VFR. GUSTY W-NW WINDS 15-20 KNOTS MONDAY. LESS GUSTY TUESDAY AND WEDNESDAY.
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&& .MARINE...
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NORTHEAST WINDS WILL CONTINUE BETWEEN 10-20 KT THRU THE REMAINDER OF THE AFTERNOON BEFORE WINDS SHIFT OUT OF THE EAST TONIGHT. BUOYS AROUND THE AREA SHOW SEAS HAVE INCREASED TO 5 FT AND THUS HAVE EXPANDED SCA TO INCLUDE ALL ATLANTIC MARINE ZONES THRU 2 AM. WINDS AND SEAS WILL GRADUALLY RELAX IN THE NORTHERN ZONES OVERNIGHT AS THE AXIS OF HIGH PRESSURE SHIFTS OVERHEAD. SCA REMAINS IN EFFECT THRU SATURDAY SOUTH OF MANASQUAN INLET WITH 5 FT SEAS EXPECTED. OUTLOOK... SATURDAY NIGHT-SUNDAY...SMALL CRAFT ADVISORY EXTENDED AS SEAS LOOK TO LINGER INTO EARLY SATURDAY NIGHT BEFORE SUBSIDING LATER IN THE NIGHT INTO SUNDAY. SUNDAY NIGHT...A COLD FRONT APPROACHES SUNDAY NIGHT WITH SHOWERS AND POSSIBLY THUNDERSTORMS WITH INCREASING WINDS. WINDS AND WAVES MAY APPROACH SMALL CRAFT ADVISORY LEVELS BEHIND THE COLD FRONT OVERNIGHT INTO EARLY MONDAY MORNING.. MONDAY-WEDNESDAY...CONDITIONS EXPECTED TO TO DROP BELOW ADVISORY LEVELS DURING THE DAY MONDAY AND STAY BELOW THROUGH WEDNESDAY.
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&& .RIP CURRENTS... WITH LONG PERIOD SWELLS STILL PRESENT TODAY, A TIGHTENING GRADIENT AND INCREASING WAVE HEIGHTS, IN HOUSE GUIDANCE CONTINUES TO SUGGEST A MODERATE RISK TODAY FOR NJ AND DE. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT SUNDAY FOR ANZ451>455. SMALL CRAFT ADVISORY UNTIL 2 AM EDT SATURDAY FOR ANZ450.
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&& $$ SYNOPSIS...ROBERTSON NEAR TERM...KLEIN SHORT TERM...KLEIN LONG TERM...ROBERTSON AVIATION...KLEIN/ROBERTSON MARINE...KLEIN/ROBERTSON RIP CURRENTS...KRUZDLO

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