Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 182004 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 404 PM EDT THU SEP 18 2014 .SYNOPSIS...
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A WEAK FRONTAL BOUNDARY WILL MOVE OFFSHORE TONIGHT. HIGH PRESSURE RETURNS TO THE NORTHEAST TONIGHT AND FRIDAY, THEN WILL SHIFT OFFSHORE FRIDAY NIGHT. A WARM FRONT WILL LIFT TO OUR NORTHWEST SATURDAY, THEN A COLD FRONT IS EXPECTED TO AFFECT THE AREA LATE SUNDAY INTO EARLY MONDAY. THIS FRONT WILL SLOWLY MOVE TO OUR SOUTH MONDAY, WHILE HIGH PRESSURE BEGINS TO BUILD IN FROM THE WEST. A WEAKENING FRONT MAY BRIEFLY AFFECT THE AREA ON TUESDAY, BEFORE THE HIGH FULLY BUILDS ACROSS THE AREA.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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AN UPPER LOW WAS LOCATED OVER EASTERN CANADA THIS AFTERNOON WHILE ATTENDANT LARGE-SCALE UPPER TROUGH EXTENDED SOUTHWARD DOWN THE EASTERN SEABOARD. DIFFUSE SFC COLD FRONT ASSOCIATED WITH THIS SYSTEM WAS POSITIONED NEAR THE NEW ENGLAND COAST, EXTENDING TO THE SOUTHEAST NEAR I-95 IN THE MID-ATLANTIC STATES. WEAK CONVERGENCE AND LOCALLY HIGHER MOISTURE NEAR THE SFC FRONT AND DPVA AHEAD OF A SHORTWAVE TROUGH ALOFT HAS ENHANCED COVERAGE OF STRATOCU IN SOUTHERN NJ AND DELMARVA AND HAS ALSO LED TO THE DEVELOPMENT OF A FEW SHOWERS IN NORTHEAST MD DURING THE EARLY AFTERNOON. HAVE HIGHLIGHTED THE DELMARVA AND EXTREME SOUTHWESTERN NJ WITH ISOLATED SHOWERS THRU THE REMAINDER OF THE AFTERNOON. THE COLD FRONT WILL MOVE SOUTH OF THE AREA TONIGHT AS SPRAWLING CANADIAN HIGH PRESSURE BUILDS SOUTHEAST INTO OUR REGION. CLOUDS WILL DISSIPATE ACROSS MOST OF THE AREA AFTER SUNSET AS DAYTIME MIXING WANES AND DRIER AIR ADVECTS INTO THE REGION. CLOUDS MAY LINGER OVERNIGHT ACROSS THE CENTRAL DELMARVA. MIN TEMPS RANGE FROM NEAR 40F AT MT POCONO (WHERE SKIES WILL CLEAR TONIGHT) TO NEAR 60F IN GEORGETOWN, DE (WHERE SKIES WILL REMAIN MOSTLY CLOUDY TONIGHT)
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
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THE CENTER OF HIGH PRESSURE WILL SHIFT SOUTHEASTWARD FROM SOUTHERN QUEBEC TO THE GULF OF MAINE ON FRIDAY. NORTH-NORTHEAST FLOW AROUND THE HIGH IN THE MORNING WILL VEER OUT OF THE EAST BY THE END OF THE DAY FRIDAY AS THE HIGH MOVES OFFSHORE. EXPECT MARINE LAYER TO ADVECT INLAND DURING THE LATE MORNING AND AFTERNOON. MARINE CLOUDS SHOULD BE MORE WIDESPREAD ACROSS THE DELMARVA AND SOUTHERN NJ WHERE BOTH ONSHORE WINDS AROUND THE HIGH AND ISENTROPIC LIFT ARE GREATEST. KEPT SHOWERS OUT OF THE FORECAST BUT THE 12Z NAM DOES DEPICT LIGHT PRECIP FOR OUR SOUTHERN ZONES. DO THINK THE NAM WAS TOO BULLISH REGARDING RETURN OF LOW-LEVEL MOISTURE. BELOW NORMAL TEMPS ARE EXPECTED AGAIN ON FRIDAY. FORECAST HIGHS RANGE FROM THE MID 60S IN THE POCONOS TO MID 70S IN THE CENTRAL DELMARVA.
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&& .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
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HIGH PRESSURE BUILDS OFFSHORE OF NEW ENGLAND FRIDAY NIGHT, WHICH WILL INCREASE AN EASTERLY/SOUTHEASTERLY FLOW ACROSS THE AREA. THIS COULD LEAD TO A PERIOD OF LOW CLOUDS AND IF THE MOISTURE IS DEEP ENOUGH, THERE IS POTENTIAL FOR FOG/DRIZZLE TO DEVELOP ACROSS AT LEAST THE NORTHWESTERN THIRD OF THE AREA. THEREFORE WE HAVE INTRODUCED PATCHY DRIZZLE AND FOG ACROSS THESE AREAS FRIDAY NIGHT INTO SATURDAY MORNING. WITH HIGH PRESSURE OFFSHORE SATURDAY/SATURDAY NIGHT, RETURN FLOW DEVELOPS WHICH WILL ALLOW DEWPOINTS TO CONTINUE TO INCREASE ACROSS THE AREA. A WARM FRONT WILL LIKELY LIFT TO OUR NORTHWEST, BUT MAY NOT PASS CLOSE ENOUGH TO OUR AREA TO BRING ANY EFFECTS. ALSO, THERE IS A WEAK SHORT WAVE/VORTICITY IMPULSE SATURDAY, BUT WITH LIMITED VERTICAL MOISTURE, WE DO NOT EXPECT MUCH IN THE WAY OF PRECIPITATION, SO FOR NOW WE KEEP IT DRY. ON SUNDAY, A FRONTAL BOUNDARY WILL BE APPROACHING FROM THE WEST. WE DO NOT EXPECT THE FRONT TO MOVE INTO OUR AREA UNTIL LATER IN THE DAY ON SUNDAY, BEFORE MOVING ACROSS THE AREA SUNDAY NIGHT INTO EARLY MONDAY. SO WE WILL HAVE HIGHEST RAIN CHANCES SUNDAY AFTERNOON INTO SUNDAY NIGHT. THERE IS SOME INSTABILITY ACROSS THE AREA AND TO THE WEST DURING THE DAY, BUT THE QUESTION IS WHETHER OR NOT WE LOSE THE INSTABILITY BEFORE THE ACTIVITY REACHES OUR AREA. FOR NOW WE WILL KEEP THUNDER OUT OF THE FORECAST UNTIL IT LOOKS LIKE WE HAVE A BETTER SHOT OF INSTABILITY AND PRECIPITATION COINCIDING WITH EACH OTHER. ON MONDAY, THE FRONT WILL BE MOVING OUT TO SEA, AND WHAT EVER SHOWERS ARE LEFT OVER ACROSS THE EASTERN PARTS OF THE AREA WILL MOVE AWAY WITH IT. HIGH PRESSURE WILL BEGIN BUILDING IN FROM THE WEST ACROSS THE AREA MONDAY INTO MONDAY NIGHT, BEFORE A WEAKENING FRONTAL BOUNDARY MOVES INTO THE AREA ON TUESDAY. FOR NOW THE FRONT LOOKS LIKE IT MAY BE A MOSTLY DRY FRONTAL PASSAGE. THEN HIGH PRESSURE FULLY BUILDS BACK ACROSS THE AREA FOR THE MIDDLE OF THE WEEK, WHICH WILL PROVIDE DRY WEATHER ACROSS THE AREA.
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&& .AVIATION /20Z THURSDAY THROUGH TUESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. REST OF TODAY AND THIS EVENING...VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. SCATTERED TO BROKEN STRATOCU WITH BASES AROUND 5 TO 6 KFT WILL BE PRESENT THROUGH THE REMAINDER OF THE DAY, BEFORE THINNING SOME THIS EVENING AND OVERNIGHT. MAINLY WESTERLY TO WEST-NORTHWEST WINDS WILL CONTINUE INTO THIS EVENING AND REMAIN UNDER 10 KNOTS. OVERNIGHT AND FRIDAY...CONTINUED VFR CONDITIONS. WEST-NORTHWEST WINDS WILL VEER AROUND TO THE NORTH AND THEN NORTHEAST INTO FRIDAY MORNING. SPEEDS WILL INCREASE TO AROUND 10 KNOTS. SOME GUSTS INTO THE 15 TO 18 KNOT RANGE ARE POSSIBLE THROUGH FRIDAY MORNING TO MIDDAY, MAINLY FROM ABOUT THE PHL METRO AND TO THE SOUTH AND EAST. WINDS WILL THEN BECOME MORE EAST-SOUTHEAST BY LATE-DAY FRIDAY. OUTLOOK... FRIDAY NIGHT...LOWER CIGS AND/OR VSBYS POSSIBLE WITH STRATUS/FOG DEVELOPMENT OVERNIGHT WITHIN A PERSISTENT EASTERLY FLOW. SATURDAY-SATURDAY NIGHT...MOSTLY VFR DURING THE DAY. LOWER CIGS AND/OR VSBYS POSSIBLE WITH STRATUS/FOG DEVELOPMENT OVERNIGHT SATURDAY/SUNDAY MORNING. SUNDAY-SUNDAY NIGHT...LOWER CONDITIONS POSSIBLE EARLY, THEN VFR DURING THE DAY. A COLD FRONT APPROACHES LATE IN THE DAY INTO SUNDAY NIGHT WITH RAIN AND LOWER CONDITIONS POSSIBLE. MONDAY-TUESDAY...MOSTLY VFR. GUSTY W-NW WINDS 15-20 KNOTS MONDAY AND TUESDAY AFTERNOON.
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&& .MARINE...
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LONG PERIOD SWELLS GENERATED BY EDOUARD CONTINUE TO REACH THE NJ AND DE COAST THIS AFTN (LATEST OBS SHOW 11-13 SEC WAVE PERIODS). SEAS AND WINDS EXPECTED TO REMAIN BELOW SCA LEVELS THROUGH FRIDAY MORNING. NE WINDS VEER OUT OF THE EAST ON FRIDAY. WINDS WILL INCREASE 15-20 KT WITH ISOLATED GUSTS NEAR 25 KT DURING THE AFTERNOON OVER THE ATLANTIC COASTAL ZONES. EXPECT SEAS TO BUILD TO 5 FT DURING THIS TIME OWING TO A LONG ONSHORE FETCH AROUND HIGH PRESSURE OVER THE GULF OF MAINE. SCA WAS ISSUED FOR THESE ZONES. OUTLOOK... FRIDAY NIGHT...SMALL CRAFT ADVISORY IN EFFECT AS WINDS AND SEAS EXPECTED TO REMAIN ELEVATED IN THE EASTERLY FLOW. SATURDAY...SEAS MAY REMAIN ELEVATED INTO SATURDAY, SO THE ADVISORY MAY NEED TO BE EXTENDED INTO SATURDAY. SATURDAY NIGHT-SUNDAY...CONDITIONS EXPECTED TO DROP BELOW ADVISORY LEVELS, BUT WINDS MAY GUST NEAR 20 KNOTS. SUNDAY NIGHT...A COLD FRONT APPROACHES SUNDAY NIGHT WITH RAIN AND INCREASING WINDS. WINDS MAY APPROACH SMALL CRAFT ADVISORY LEVELS BEHIND THE COLD FRONT. MONDAY-TUESDAY...CONDITIONS EXPECTED TO TO DROP BELOW ADVISORY LEVELS.
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&& .RIP CURRENTS... IN HOUSE GUIDANCE SUGGESTS A MODERATE RISK TODAY FOR NJ/DE BECAUSE OF LONG PERIOD SWELLS GENERATED BY EDOUARD. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY FROM 2 PM FRIDAY TO 6 AM EDT SATURDAY FOR ANZ451>455.
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&& $$ SYNOPSIS...ROBERTSON NEAR TERM...KLEIN SHORT TERM...KLEIN LONG TERM...ROBERTSON AVIATION...KLINE/ROBERTSON MARINE...KLEIN/ROBERTSON RIP CURRENTS...

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