Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 040052 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 852 PM EDT SUN MAY 3 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD FARTHER OFFSHORE OF THE EAST COAST THROUGH MONDAY, BEFORE A COLD FRONT MOVES ACROSS THE AREA ON TUESDAY INTO TUESDAY NIGHT. THE COLD FRONT IS FORECAST TO STALL SOUTH OF THE AREA THROUGH THE END OF THE WEEK WITH HIGH PRESSURE NOSING ITS WAY SOUTHWARD ACROSS THE AREA THROUGH FRIDAY. THE HIGH BUILDS OFFSHORE OVER THE WEEKEND, WITH RETURN FLOW DEVELOPING ACROSS THE AREA. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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ANOTHER QUIET EVENING ACROSS THE AREA. THE DAYTIME CU HAS DISSIPATED ACROSS THE AREA. A FEW PATCHES OF AC WILL MOVE ACROSS THE REGION OVERNIGHT. WINDS ACROSS THE DEL VALLEY HAVE TURNED SE BEHIND THE SEA BREEZE...BUT THAT SHOULD DIMINISH SHORTLY. FEW CHANGES NEEDED TO THE GRIDS FOR THE OVERNIGHT.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... A WARM DAY IS IN STORE FOR OUR CWA WITH MANY PLACES POSSIBLY HAVING THE WARMEST DAY OF 2015 SO FAR. LAST COUPLE OF DAYS AS INDICATION, BIG DIURNAL SWINGS AS SFC TEMPS ARE DOING 12-13C ABOVE PREDICTED 925S AND AROUND 18C ABOVE ABOVE PREDICTED 850S. LOOKS LIKE STAT GUIDANCE IS PICKING UP ON THIS TREND. UNDER MORE NORMAL ANTECEDENT CONDITIONS PHILLY MIGHT JUST MAKE 80F. THE SLOW CANOPY DEVELOPING OF THE TREES IS LIKELY ALSO ASSISTING. FORECAST SOUNDINGS ARE SHOWING SLIGHTLY MORE CU BASED MOISTURE THAN TODAY, SO MAYBE MORE FLATTISH APPEARING CU AROUND BY MONDAY AFTERNOON. THEIR BASES MAY VERY WELL BE 7-8K, WE DONT SEE THAT TOO OFTEN AROUND HERE. THE GRADIENT BETWEEN THE APPROACHING FRONT AND THE DEPARTING HIGH IS PREDICTED TO START TIGHTENING DURING THE AFTERNOON. GFS 925MB WINDS LIKELY TOO HIGH AGAIN, REGARDLESS EVEN GOING WITH THE MORE CONSERVATIVE WRF-NMM MIXING TO A HIGHER LEVEL WILL LIKELY GENERATE WIND GUSTS 20 TO 25 MPH BY AFTERNOON. THE SOUTHWEST GRADIENT WILL ALSO FIGHT THE ADVANCEMENT OF ANY SEA BREEZE FRONT MORE THAN THE LAST TWO DAYS IN SPITE OF EVEN HIGHER TEMPS. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... A COLD FRONT IS FORECAST TO MOVE ACROSS THE AREA TUESDAY INTO TUESDAY NIGHT, AND SLOWLY SAG SOUTHWARD INTO WEDNESDAY. PW VALUES WILL INCREASE TO AROUND 1.0-1.5 INCHES AS THE FRONT SAGS ACROSS THE AREA, AND WITH AN INCREASE IN MOISTURE AND WARM TEMPERATURES, THERE IS SOME INSTABILITY FORECAST. CAPE VALUES APPROACHING 500-1000 J/KG, SLIGHTLY NEGATIVE LI VALUES, AND TOTAL TOTAL VALUES NEAR 50. SO AS THE FRONT MOVES THROUGH THE AREA, SCATTERED SHOWERS ARE EXPECTED, ALONG WITH ISOLATED THUNDERSTORMS. THE FRONT SHOULD SLOWLY MOVE ACROSS THE AREA INTO TUESDAY NIGHT, BUT MAY HAVE A HARD TIME PUSHING SOUTH OF THE AREA THROUGH THE EARLY PART OF WEDNESDAY. WHILE SHOWERS MAY LINGER INTO AT LEAST EARLY WEDNESDAY, THUNDERSTORM ACTIVITY WILL LIKELY DIMINISH WITH THE LOSS OF DAYTIME HEATING/INSTABILITY TUESDAY EVENING. AS THE FRONT SLOWLY PASSES SOUTH OF THE AREA WEDNESDAY, IT IS FORECAST TO STALL OUT TO OUR SOUTH THROUGH THE REMAINDER OF THE WEEK, AND MAY END UP WASHING OUT TO OUR SOUTH. WITH THE FRONT TO OUR SOUTH, HIGH PRESSURE FROM THE NORTH WILL NOSE ITS WAY INTO THE AREA THROUGH THE END OF THE WEEK. THIS SHOULD KEEP THE WEATHER DRY THROUGH FRIDAY, AND WITH SLIGHT RIDGING BUILDING ALOFT, TEMPERATURES ARE FORECAST TO REMAIN ABOVE NORMAL THROUGH THE END OF THE WEEK. WEDNESDAY MAY BE THE COOLEST DAY WITH A NORTH/NORTHEAST FLOW ACROSS THE AREA WHICH MAY BRING IN COOLER AIR AND KEEP CLOUD COVER IN AS WELL. THE DRY WEATHER SHOULD REMAIN THROUGH FRIDAY NIGHT, BUT ISOLATED SHOWERS MAY RETURN FOR SATURDAY AND SUNDAY AS RETURN FLOW DEVELOPS AS HIGH PRESSURE BUILDS OFFSHORE AND THE FRONT TO OUR SOUTH MAY LIFT BACK NORTH OF THE AREA. ACROSS THE AREA, INCREASING MOISTURE AND DAYTIME INSTABILITY ACROSS THE AREA WHICH COULD LEAD TO A SLIGHT CHANCE OF SHOWERS, ESPECIALLY ACROSS THE WESTERN HALF OF THE AREA. && .AVIATION /01Z MONDAY THROUGH FRIDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. 00Z TAFS WERE VFR. TONIGHT...CLEAR SKIES AND WINDS BECOMING LIGHT AND VARIABLE. AIR MASS AGAIN IS QUITE CLEAN AND WE ARE NOT ANTICIPATING ANY FOG AT THE TERMINALS. MONDAY...A SOUTHWEST WIND WILL DEVELOP IN THE MORNING AND SHOULD AVERAGE CLOSE TO 10 KNOTS. SOME GUSTINESS IS LIKELY AS THE DAY PROGRESS, MORE LIKELY IN THE AFTERNOON. THE PREDICTED MOISTURE AT THE CUMULUS LEVEL IS SLIGHTLY MORE THAN TODAY, SO MAYBE A FEW MORE HIGH BASED (LOOKS AROUND 7K AGAIN) CUMULUS CLOUDS AGAIN. OUTLOOK... MONDAY NIGHT...VFR. TUESDAY-TUESDAY NIGHT...GENERALLY VFR WITH SHOWERS/THUNDERSTORMS POSSIBLE. TEMPORARY LOWER CONDITIONS POSSIBLE WITH SHOWERS/THUNDERSTORMS. SOUTHWEST WIND GUSTS AROUND 20 KNOTS TUESDAY. WEDNESDAY...MVFR CIGS POSSIBLY DEVELOPING WITH SHOWERS. WEDNESDAY NIGHT-FRIDAY...IMPROVING CONDITIONS TO VFR OVERNIGHT WEDNESDAY AND CONTINUING THROUGH FRIDAY.
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&& .MARINE... SUB SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED THROUGH MONDAY DAY. LONGER PERIOD SWELLS CONTINUE TO SLOWLY SUBSIDE THIS AFTERNOON. WE SHOULD GET ANOTHER UP THE DELAWARE BAY WIND INCREASE LATER THIS AFTERNOON AND EVENING BUT PEAK BELOW SMALL CRAFT ADVISORY CRITERIA. ON MONDAY, A GENERAL SOUTHWEST GRADIENT WILL PREVAIL WITH OVERALL LIGHTER WINDS FARTHER OFFSHORE DUE TO LESS EFFICIENT MIXING. IN DELAWARE BAY AND ALONG THE IMMEDIATE COAST, THERE SHOULD BE MORE GUSTINESS, BUT WE ARE EXPECTING GUSTS TO PEAK AROUND 20 KNOTS. OVERALL GUSTIER IN THE AFTERNOON THAN MORNING. OUTLOOK... MONDAY NIGHT-FRIDAY...SUB SMALL CRAFT ADVISORY CONDITIONS EXPECTED. HOWEVER, WINDS MAY GUST AROUND 20 KNOTS AND SEAS APPROACH 4 FEET THROUGH THE PERIOD. FRONTAL BOUNDARY IS EXPECTED TO MOVE SOUTH OF THE WATERS LATE TUESDAY AND REMAIN SOUTH OF THE AREA THROUGH THE END OF THE WEEK. && .FIRE WEATHER...
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AFTER COORDINATING WITH THE STATE FORESTRY SERVICES AND COLLABORATING WITH NEIGHBORING OFFICES, WE HAVE ISSUED A FIRE WEATHER WATCH FOR PENNSYLVANIA AND NEW JERSEY FOR MONDAY AFTERNOON AND EVENING. DEW POINTS HAVE MIXED DOWNWARD MORE THAN STAT GUIDANCE HAS BEEN INDICATING TODAY. WE WERE RATHER CONSERVATIVE WITH AFTN DEW POINTS MONDAY AND PREDICTED RH(S) REACH 25 TO 30 PERCENT. WOULDN`T BE SURPRISED IF SOME LOWER 20 RH(S) OCCUR. IT HAS BEEN OBVIOUSLY DRY. THE LEAST CERTAIN ELEMENT IS THE WIND. THE GRADIENT IS PREDICTED TO INCREASE DURING THE AFTERNOON WITH A GENERAL GREATER CHANCE ACROSS NORTHERN PARTS OF THE WATCH AREA. BECAUSE OF LIGHTER WINDS AND GENERALLY HIGHER WIND CRITERIA, DELMARVA WAS NOT INCLUDED IN THIS WATCH.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...FIRE WEATHER WATCH FROM MONDAY AFTERNOON THROUGH MONDAY EVENING FOR PAZ054-055-060>062-070-071-101>106. NJ...FIRE WEATHER WATCH FROM MONDAY AFTERNOON THROUGH MONDAY EVENING FOR NJZ001-007>010-012-013-015>023-027. DE...NONE. MD...NONE. MARINE...NONE.
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&& $$ SYNOPSIS...ROBERTSON NEAR TERM...PO SHORT TERM...GIGI LONG TERM...ROBERTSON AVIATION...GIGI/ROBERTSON MARINE...GIGI/ROBERTSON FIRE WEATHER...

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