Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 141931 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 331 PM EDT SUN SEP 14 2014 .SYNOPSIS... HIGH PRESSURE ACROSS THE REGION TONIGHT WILL MOVE OFFSHORE BY LATER MONDAY. A COLD FRONT IS THEN EXPECTED TO CROSS OUR REGION LATE MONDAY NIGHT AND EARLY TUESDAY. HIGH PRESSURE WILL BUILD ACROSS THE REGION TUESDAY AND WEDNESDAY, THEN A WEAK COLD FRONT MAY SETTLE THROUGH OUR AREA LATER WEDNESDAY OR EARLY THURSDAY. HIGH PRESSURE THEN BUILDS IN FOR THURSDAY AND FRIDAY BEFORE SHIFTING OFFSHORE SATURDAY, WITH ANOTHER COLD FRONT POSSIBLY APPROACHING LATER SUNDAY. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... REMAINDER OF THE AFTERNOON...CIRRUS NEAR 300MB SPREADS NEWD ACROSS THE AREA AND THICKENS A BIT. TONIGHT...BECOMING CLEAR THIS EVENING WITH LIGHT NORTHWEST OR CALM WIND AND RATHER COOL TEMPS...7 TO 12 DEGREES BELOW NORMAL. IDEAL RADIATIONAL COOLING CONDITIONS. LOWS IN THE 40 TO 45 DEGREE RANGE EXCEPT LOWER 50S URBAN CENTERS AND 45 TO 50 DELMARVA. . THE 12Z/14 50 50 BLENDED NAM/GFS GUIDANCE WAS ALREADY UPDATED INTO THE FCST GRIDS AND WORDING. THE LOW CLOUDINESS YOU SEE EDGING NEWD FROM WVA MAY START SHOWING A SCT-BKN DECK ALONG THE SW EDGE OF OUR FCST AREA NEAR KRDG TOWARD 10Z AS PER THE MORE AGGRESSIVE NAM 1000-850 MB RH BUT THE GFS AND ECMWF ARE SLOWER AND MORE EWD WITH ITS DEVELOPMENT. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... A SUNNY MORNING WITH SOME INCREASING CLOUDS DURING THE LATE AFTERNOON FROM CIRRUS THRU AC AND SC LAYERS. NEAR OR SLIGHTLY BELOW NORMAL TEMPS FOR MID SEPTEMBER. BLENDED 12Z/14 GFS/NAM MOS GUIDANCE WITH LIGHT WINDS TRENDING SW IN THE AFTN EXCEPT SEA BREEZES COAST. EXCEPTION COULD BE MD E SHORE AND SE PA WHERE A DECK OF CLOUDS FROM WVA MAY ARRIVE DURING THE MORNING. NEEDS REEVALUATION OVERNIGHT. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... THE OVERALL SYNOPTIC SETUP IS COMPRISED OF AN UPPER-LEVEL TROUGH FROM THE MIDWEST TO THE NORTHEAST THROUGH ABOUT THURSDAY. SOME SHORT WAVES EMBEDDED IN THE FLOW WILL AMPLIFY THE TROUGH SOME EASTWARD A FEW TIMES, ONE MOST NOTABLY SLIDING BY MONDAY NIGHT AND TUESDAY MORNING. AN UPPER-LEVEL RIDGE IS THEN FORECAST TO MIGRATE ACROSS THE MIDDLE OF THE NATION THURSDAY INTO FRIDAY, ALLOWING THE TROUGH TO LIFT OUT SOME OF THE NORTHEAST. A POTENTIAL RIDGE COULD THEN BUILD ACROSS PORTIONS OF THE EAST AND ALSO THE SOUTHERN STATES FRIDAY AND SATURDAY. AN ASSOCIATED SURFACE HIGH WILL BUILD ACROSS OUR AREA BUT THEN SHIFT OFFSHORE SATURDAY. AS THE HIGH GIVES WAY AND A TROUGH AMPLIFIES ACROSS THE MIDWEST TO GREAT LAKES, THE NEXT COLD FRONT IS SCHEDULED TO APPROACH OUR AREA LATER SUNDAY. A MODEL BLEND WAS USED FOR MONDAY NIGHT THROUGH WEDNESDAY, THEN UTILIZED THE 12Z WPC GUIDANCE THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE FOLLOWING ADDITIONAL COLLABORATION WITH OUR SURROUNDING OFFICES. FOR MONDAY NIGHT AND TUESDAY...A SHORT WAVE DIVING ACROSS THE GREAT LAKES MONDAY NIGHT WILL HELP DEVELOP A WEAK SURFACE LOW NEAR THE MID ATLANTIC. AS SOME WAA INCREASES AHEAD OF IT, AN INCREASE IN THE CLOUDS WILL OCCUR. THE ARRIVAL OF LARGE SCALE LIFT COMBINED WITH SOME DEEPER MOISTURE SHOULD ALLOW FOR A RIBBON OF SHOWERS TO DEVELOP LATER MONDAY NIGHT. WHILE THERE IS STILL SOME QUESTION ON HOW ORGANIZED THE SHOWERS WILL BE AS THE SYSTEM IS GENERALLY MOVING QUICKLY, ENOUGH MOISTURE AND LIFT SHOULD GENERATE A TIME OF FAIRLY WIDESPREAD SHOWERS. THIS APPEARS TO BE MORE FOCUSED ACROSS THE CENTRAL AND NORTHERN ZONES, WHICH ARE CLOSER TO THE SHORT WAVE PASSAGE. THEREFORE, POPS WERE MAINTAINED AS INCREASING FROM WEST TO EAST WITH LIKELY POPS INDICATED MAINLY LATE /HIGHEST ACROSS THE CENTRAL AND NORTHERN AREAS/. AN AMPLIFYING UPPER-LEVEL TROUGH WILL SWING ACROSS THE NORTHEAST AND MID ATLANTIC REGION TUESDAY, TAKING WEAK LOW PRESSURE WITH IT. THIS FEATURE LOOKS TO BE PROGRESSIVE, THEREFORE ANY SHOWERS WILL BE ENDING TUESDAY MORNING WITH IMPROVING CONDITIONS SETTING IN DURING THE AFTERNOON AND AT NIGHT. THE ARRIVAL OF DRIER AND COOLER AIR ALONG WITH INCREASING SUBSIDENCE SHOULD ALLOW FOR CLEARING TO TAKE PLACE ESPECIALLY AT NIGHT. THERE COULD BE SOME STRATOCUMULUS WITHIN THE WEAK CAA REGIME FOR A TIME ESPECIALLY TOWARD THE NORTHWEST ZONES, AND IT MAY BE A BIT BREEZY AT TIMES DURING THE DAY WITH SOME DEEPER MIXING. FOR WEDNESDAY THROUGH FRIDAY...WHILE AN UPPER-LEVEL TROUGH IS FORECAST TO BE IN PLACE WEDNESDAY AND THURSDAY, SURFACE HIGH PRESSURE WILL ARRIVE FROM THE WEST. THIS WILL DELIVER ANOTHER ROUND OF DRIER AIR ALONG WITH A COOL AIRMASS. A WEAK COLD FRONT HOWEVER MAY SETTLE SOUTHEASTWARD ACROSS OUR AREA LATE WEDNESDAY INTO THURSDAY, WITH A NEW AIRMASS AND ASSOCIATED SURFACE HIGH PRESSURE BUILDING BACK IN FOR FRIDAY. THE FRONT CONTINUES TO LOOK RATHER WEAK WITH LIMITED MOISTURE, THEREFORE KEPT THE FORECAST DRY. MOST OF THE WEATHER ELEMENTS WERE FAIRLY CLOSE TO THE 12Z WPC GUIDANCE. FOR SATURDAY AND SUNDAY...A BUILDING RIDGE TO OUR SOUTH AND EAST SHOULD SUPPORT AN EXPANSIVE SURFACE HIGH THAT WILL BE SHIFTING TO OUR EAST. THE PLACEMENT OF THIS HIGH WILL BE CRUCIAL IN DETERMINING OUR SENSIBLE WEATHER, AS AN ONSHORE FLOW MAY HANG ON FOR AWHILE AND CAUSE CLOUDINESS DUE TO THE OCEAN INFLUENCE. OVERALL, LESS CERTAINTY WITH THE DETAILS THIS FAR OUT HOWEVER THE SURFACE HIGH LOOKS TO DOMINATE OVERALL. AN AMPLIFYING TROUGH ACROSS THE MIDWEST AND GREAT LAKES IS SCHEDULED TO DRIVE A COLD FRONT TOWARD OUR AREA LATER SUNDAY, WITH THE FLOW TURNING MORE SOUTHERLY ALLOWING FOR WARMER AIR TO ADVECT INTO OUR CWA. OVERALL, WE STAYED CLOSE TO THE 12Z WPC GUIDANCE. && .AVIATION /20Z SUNDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THROUGH TONIGHT...VFR WITH ~30000 FT CIRRUS OF VARIABLE THICKNESS SWEEPING NEWD THRU THE AREA THIS EVENING THEN OFF TO THE EAST OF THE COAST BY 02Z/15. LIGHT NORTHWEST OR CALM WIND. SMALL CHANCE PATCHY FOG NEAR SUNRISE IN THE SHELTERED RIVER VALLEYS. ALSO A SMALL CHC OF A 3000 FT DECK OF SC EDGING INTO THE KRDG AREA AROUND 10-12Z BUT LOW PROBABILITY ATTM. MONDAY...VFR DURING THE MORNING WITH MULTI LAYERS AOA 4000 FT ARRIVING LATE IN THE DAY (SC, AC, CI). LIGHT WIND BECOMING SW DURING THE AFTN EXCEPT SE ALONG THE COASTS. ATTM THERE IS A LOW PROBABILITY OF A DECK OF 3000 FT SC DEVELOPING IN SE PA/NE MD SOONER THAN FCST BUT IT DEPENDS ON THE MOVEMENT OF THE CURRENT SC DECK EDGING NEWD FROM WVA. THIS POSSIBILITY WILL BE REEVALUATED OVERNIGHT. OUTLOOK... MONDAY NIGHT AND TUESDAY...MAINLY VFR. SOME SHOWERS SHOULD MOVE THROUGH LATE MONDAY NIGHT AND EARLY TUESDAY MORNING WITH BRIEF SUB-VFR CONDITIONS. SOUTH-SOUTHWEST WINDS 5-10 KNOTS BECOMING NORTHWESTERLY MONDAY NIGHT INTO TUESDAY, THEN INCREASING TO 10-15 KNOTS TUESDAY. WEDNESDAY THROUGH FRIDAY...VFR OVERALL AS HIGH PRESSURE DOMINATES OUR WEATHER. && .MARINE... QUIET THROUGH MONDAY WITH NO HEADLINES. ATLC SEAS GENERALLY AOB 3 FT. DE BAY WAVES MOSTLY 1 FT OR LESS. WINDS VARIABLE ONSHORE LATE THIS AFTERNOON LESS THAN 10 KT BECOMING LIGHT NORTHWEST TONIGHT AND MONDAY MORNING THEN ONSHORE SELY MON AFTN. OUTLOOK... MONDAY NIGHT AND TUESDAY...A QUICK MOVING SYSTEM CROSSES OUR AREA LATER MONDAY NIGHT AND EARLY TUESDAY MORNING ALLOWING FOR A WIND SHIFT TO OCCUR. DESPITE THE WINDS SHIFTING TO THE NORTHWEST OR NORTH TUESDAY AND INCREASING SOME, IT APPEARS THAT THE WINDS AND SEAS OVERALL REMAIN BELOW ADVISORY CRITERIA. WEDNESDAY THROUGH FRIDAY...A NORTH TO NORTHEAST FLOW COULD BE A BIT GUSTY AT TIMES ESPECIALLY FRIDAY AND THIS WILL BUILD THE SEAS SOME. THE WINDS MUCH OF THE TIME THOUGH SHOULD BE BELOW ADVISORY CRITERIA. HOWEVER, THE SEAS AS OF NOW MAY REACH 5 FEET ESPECIALLY ACROSS OUR CENTRAL AND SOUTHERN COASTAL WATERS DUE TO THE NORTHEASTERLY FLOW. OUR CONFIDENCE LOWERS THROUGH THIS PERIOD GIVEN LESS CERTAINTY WITH THE PRESSURE GRADIENT. && .RIP CURRENTS... THERE IS A MODERATE RISK FOR THE FORMATION OF DANGEROUS RIP CURRENTS FOR NJ WITH CONDITIONS IMPROVING LATE THIS AFTERNOON. LOW RISK FOR DE. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GORSE NEAR TERM...DRAG SHORT TERM...DRAG LONG TERM...GORSE AVIATION...DRAG/GORSE MARINE...DRAG/GORSE RIP CURRENTS...

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