Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 151946 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 346 PM EDT MON SEP 15 2014 .SYNOPSIS...
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HIGH PRESSURE WILL SHIFT OFFSHORE EARLY TONIGHT. A FAST MOVING AREA OF LOW-PRESSURE WILL MOVE THROUGH THE REGION EARLY TUESDAY. HIGH PRESSURE WILL SLIDE IN FROM THE WEST DURING MID WEEK. ANOTHER COLD FRONTAL PASSAGE PROBABLY OCCURS LATE THURSDAY. CANADIAN HIGH PRESSURE FOLLOWS TO NEW ENGLAND FRIDAY AND LINGERS INTO NEXT WEEKEND. A COLD FRONT FROM THE WEST MAY REACH THE EASTERN SEABOARD NEXT MONDAY.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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HIGH PRESSURE OVER THE AREA LATE THIS AFTERNOON WILL CONTINUE TO PUSH OFFSHORE THIS EVENING, WHICH WILL LEAD TO RETURN FLOW AHEAD OF AN APPROACHING COLD FRONT. THE FRONTAL BOUNDARY IS EXPECTED TO BEGIN MOVING INTO OUR WESTERN AREAS A FEW HOURS BEFORE DAYBREAK, BEFORE PROGRESSING EASTWARD THROUGH THE MORNING. PRETTY MUCH ALL GUIDANCE HAS THE BEST PROBABILITIES AND MOST QPF ACROSS THE NORTHERN HALF/THIRD OF THE AREA WHERE THE STRONGEST PART OF THE SHORT WAVE/VORT MAX ALOFT PASSES. SO WE WILL HAVE LIKELY POPS UP NORTH, AND CHANCES SOUTH. THERE DOES NOT LOOK TO BE ANY INSTABILITY, SO WE KEEP THUNDERSTORMS OUT OF THE FORECAST. OVERNIGHT LOWS ARE A BLEND OF MAV/MET MOS AND MOSGUIDE WHICH BRINGS EVERYONE PRETTY CLOSE TO NORMAL.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
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THE COLD FRONT WILL BE PROGRESSING TROUGH THE AREA AND OFFSHORE DURING THE MORNING HOURS TUESDAY. ANY REMAINING SHOWERS ACROSS OUR EASTERN HALF OF THE AREA WILL PULL AWAY DURING THE MORNING AS THE SHORT WAVE QUICKLY LIFTS TO THE NORTHEAST. THIS WILL LEAD TO A DRY FORECAST FOR THE AFTERNOON WITH PARTLY-MOSTLY CLOUDY SKIES. DAYTIME HIGHS ARE A BLEND OF MIXED ECMWF 925 MB TEMPS, MAV/MET MOS, AND MOSGUIDE WHICH KEEPS EVERYONE PRETTY CLOSE TO NORMAL.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
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500 MB: TROUGH IN EASTERN NORTH AMERICA FLATTENS AND WARMS NEXT WEEKEND IN ADVANCE OF A STRONG SHORT WAVE MOVING SEWD INTO THE UPPER MIDWEST AND GREAT LAKES NEXT SUNDAY AND MONDAY. TEMPERATURES: SEVERAL DEGREES BELOW NORMAL WEDNESDAY-FRIDAY; NEARLY NORMAL SATURDAY AND POSSIBLY SEVERAL DEGREES ABOVE NORMAL NEXT SUNDAY AND MONDAY. FORECAST BASIS: UNLESS OTHERWISE NOTED THE LONG TERM PERIOD OF THIS FORECAST IS GENERALLY BASED ON A 50 50 BLEND OF THE 12Z/15 NAM/GFS MOS FOR THE PERIOD TUESDAY NIGHT - WEDNESDAY NIGHT...THE 12Z/15 GFS MOS THURSDAY...THEN THEREAFTER (FRIDAY ONWARD) THE 1522Z/15 WPC GRIDDED GUIDANCE WHICH AT TIMES IS BLENDED 50 50 WITH THE 12Z/15 MEXMOS. ALL THIS WAS EVENTUALLY CHECKED AGAINST THE 12Z/15 ECMWF TO SEE IF WE`RE IN THE BALLPARK WITH ECMWF CYCLICALLY PERSISTENT 18Z 2 METER TEMPERATURES. PRECIPITATION PROBABILITY GUIDANCE IS CHECKED AGAINST THE 09Z/15 SREF 3HRLY POPS FOR .01 THROUGH 00Z FRIDAY AND THEREAFTER THE 12Z/15 GEFS 6HR POPS FOR 0.05 THE DAILIES BELOW... ESSENTIALLY DRY TUESDAY NIGHT THROUGH SUNDAY WITH MAYBE THE BEST CHANCE OF SHOWERS NEXT MONDAY. OVERALL THIS LOOKS LIKE AN EXTENDED PERIOD OF DECENT LATE SUMMER/EARLY FALL WEATHER FOR OUR AREA. TUESDAY NIGHT-WEDNESDAY...FAIR AND COOL AS WEAK HIGH PRESSURE ARRIVES. LIGHT WIND. WEDNESDAY NIGHT - THURSDAY...PARTLY CLOUDY. LIGHT WIND BECOMING NORTH LATE THURSDAY. FRIDAY...THERE MAY BE MORE CLOUDINESS THAN CURRENTLY FORECAST WITH A COMBINATION OF GUSTY ONSHORE FLOW AND THE COOL POOL ASSOCIATED WITH THE HIGH PRESSURE SYSTEM. NORTHEAST FLOW GUSTY AT TIMES 15 TO 20 MPH. MAYBE SOME SPRINKLES? NEXT WEEKEND...PARTLY CLOUDY. STILL AN EASTERLY FLOW SATURDAY PROBABLY TURNING LIGHT SOUTHERLY SUNDAY. NEXT MONDAY: A COLD FRONTAL PASSAGE OR APPROACH WITH POSSIBLE SHOWERS. FALL BEGINS AT NIGHT.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS WE EXPECT VFR CONDITIONS TO REMAIN ACROSS THE AREA THROUGH THE TAF PERIOD, ALTHOUGH CLOUDS WILL THICKEN AND LOWER THROUGH THE NIGHT INTO TUESDAY MORNING AS A COLD FRONT APPROACHES AND MOVES THROUGH THE AREA. THERE REMAINS A CHANCE FOR SHOWERS TO ACCOMPANY THE FRONT, ESPECIALLY FOR OUR NORTHERN TAFS, SO A SHOWER GROUP REMAINS IN THE TAFS AT THIS TIME, CENTERED AROUND THE DAYBREAK HOURS. THERE IS A POSSIBILITY WE MAY GET CLOSE TO 2,000-3,000 FOOT CIGS WITH THE FRONTAL PASSAGE AND SHOWERS, BUT HAVE KEPT THEM OUT OF THE TAFS AT THIS TIME. VARIABLE WINDS THIS AFTERNOON WILL BECOME MORE SOUTH TO SOUTHWESTERLY THIS EVENING AND OVERNIGHT, GENERALLY LESS THAN 5 KNOTS. ONCE THE FRONT PASSES THROUGH TOMORROW MORNING, WINDS WILL SWITCH TO A NORTHWEST DIRECTION, PICKING UP TO AROUND 10 KNOTS. OUTLOOK... TUESDAY NIGHT - SATURDAY...VFR WITH INTERMITTENT PATCHY CIGS AOA 3500 FT AT TIMES. LIGHT WIND MAY BECOME GUSTY NORTHERLY 15 KT LATE THURSDAY ESPECIALLY ALONG THE COAST...THEN GUSTY NORTHEAST 20 KT FRIDAY AND WIND TURNING EASTERLY SATURDAY WITH GUSTS TO 15 KT.
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&& .MARINE...
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SUB-ADVISORY CONDITIONS WILL REMAIN ACROSS THE WATERS AS HIGH PRESSURE MOVES OFFSHORE TONIGHT. A COLD FRONT WILL MOVE ACROSS THE WATERS TUESDAY MORNING, WHICH WILL ALLOW WINDS TO GUST UP TO 20 KNOTS, BUT REMAIN BELOW ADVISORY LEVELS. OUTLOOK... TUESDAY NIGHT...LIGHT WIND AND SEAS AOB 3 FT. NO MARINE HEADLINES. WEDNESDAY AND THURSDAY...SCA MAY BE NEEDED FOR PORTIONS OF THE ATLANTIC WATERS EITHER FOR HAZARDOUS SEAS WEDNESDAY INTO THURSDAY OR POSSIBLY INCREASING NORTHERLY WIND LATE THURSDAY...SUBSEQUENT TO THE NEXT CFP. CONFIDENCE ON ANY SCA FOR WEDNESDAY IS WELL BELOW AVERAGE DESPITE THE GFS WW3 GUIDANCE. SUSPICION IS THAT THIS GUIDANCE WILL BE 1-2 FEET TOO HIGH FOR WEDNESDAY...AND PREFER A CLOSER FIT TO THE LOWER HURRICANE WW GUIDANCE. EDOUARDS NORTHWARD TRACK WELL TO THE EAST OF 70W IS THE REASONING FOR HESITATING ON BUYING INTO THE GFS WW3 GUIDANCE. RECENT HISTORY WITH CRISTOBALS HIGH SWELL BIAS FOR OUR PORTION OF THE MID ATLANTIC COAST LINGERS IN THE MEMORY BANK. FRIDAY-SATURDAY...STRONGER ONSHORE NORTHEAST FLOW IS EXPECTED TO DEVELOP AND SCA LEVEL WIND GUSTS AND/OR SEAS SHOULD BE REALIZED, MOST LIKELY FOR THE CENTRAL TO SOUTHERN ATLANTIC COASTAL WATERS AND LOWER DELAWARE BAY. WINDS GUSTS AROUND 25 KNOTS AND SEAS OF 5 TO 7 FEET ARE POSSIBLE.
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&& .RIP CURRENTS...
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WEDNESDAY AND THURSDAY: THERE MAY BE AN ENHANCED RISK FOR THE FORMATION OF DANGEROUS RIP CURRENTS...ESPECIALLY ALONG THE NJ COAST...IN RESPONSE TO THE ARRIVAL OF 12 TO 15 SECOND PERIOD SWELLS FROM EDOUARD. EDOUARDS NORTHWARD PASSAGE FAR TO THE EAST OF 70W PROBABLY WILL MEAN THE GFS WW SWELL GUIDANCE IS TOO HIGH AND SO HAVE FAVORED THE LESSER HURRICANE MODEL GUIDANCE (OSBH07). AT THIS TIME THE CONFIDENCE FOR MODERATE RISK POTENTIAL FOR WED/THU IS CONSIDERED BELOW AVERAGE AND WE`LL NEED A 3 FOOT ESE SWELL OF 13 TO 15 SECONDS TO RAISE THAT RISK POTENTIAL.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...DRAG/FRANCK 345 NEAR TERM...ROBERTSON 345 SHORT TERM...ROBERTSON 345 LONG TERM...DRAG 345 AVIATION...DRAG/ROBERTSON 345 MARINE...DRAG/ROBERTSON 345 RIP CURRENTS...345

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