Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 171911 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 311 PM EDT THU APR 17 2014 .SYNOPSIS...
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A RIDGE OF HIGH PRESSURE WILL REMAIN ACROSS THE FORECAST AREA TONIGHT THROUGH FRIDAY NIGHT. A COLD FRONT WILL CROSS THE REGION FRIDAY NIGHT. MORE HIGH PRESSURE WILL BUILD DOWN FROM CANADA AND REMAIN ACROSS THE AREA THIS WEEKEND AND INTO MONDAY NIGHT. ANOTHER DISTURBANCE WILL AFFECT THE REGION TUESDAY INTO WEDNESDAY.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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FROST ADVISORIES ISSUED FOR SOME LOCATIONS AROUND THE I95 CORRIDOR FOR LATE TONIGHT WHERE THE GROWING SEASON HAS STARTED. A GFS/WRF-NMMB BLEND SEEMED TO WORK BEST OFF THE 12Z SOUNDINGS AND MODELING INITIALIZATION. OUR FORECAST IMPACT UNFORTUNATELY IS COMING FROM NON SOUNDING LOCATIONS AND THUS ADDS A LAYER OF UNCERTAINTY TO THE NEAR AND SHORT TERM FORECASTS. THE MOISTURE OFF THE OCEAN, THE RAP HAS HAD A BETTER HANDLE ON IT THAN THE PLAN FORECAST MOISTURE FIELDS OF THE GFS AND WRF-NMMB. IT WAS USED AS A BASIS FOR TONIGHT`S FORECAST. THE SPREADING UNCERTAINTY OF THE CLOUD COVER AND WIND COUPLED WITH BELOW NORMAL TEMPS DID NOT MAKE THE FROST/FREEZE DECISION AN EASY OR CONFIDENT ONE. PLEASE CHECK FOR FURTHER UPDATES LATER THIS AFTERNOON AND EVENING. BASED ON THE RAP`S PREMISE WE SEE THAT MIXING IS FINALLY STOPPING THE WESTWARD PROGRESSION OF THE STRATOCU CIG. BUT, WE EXPECT THIS PROCESS TO START ITSELF LATER THIS EVENING AND OVERNIGHT AS THE MOISTURE REMAINS TRAPPED UNDERNEATH THE INVERSION AND IS FORECAST TO SPREAD. EAST OF THE GFS AND WRF-NMMB RIDGE AXIS LINE IS A PROXY TO WHERE THE CIGS HAVE BEEN ABLE TO SUSTAIN THEMSELVES. THIS AXIS SHIFTS WEST TONIGHT AS WE ARE EXPECTING THE CLOUDS TO GO. BASED ON INCREASING DEW POINTS AND MORE MARGINAL TEMPERATURES WE HAVE OPTED TO CONVERT THE FREEZE WATCH TO A FROST ADVISORY. HIGHEST CONFIDENCE IS IN THE WESTERN PART OF THE HEADLINES WITH LOWER CONFIDENCE IN NJ. WE DID KEEP THE MENTION OF SOME PATCHY FROST (IN THE HWO TOO) IN LOCALES FARTHER TO THE SE (BUT NOT IN CENTRAL/LOWER DELMARVA). BEING CONSISTENT WITH THE CLOUD AND WIND IDEA, FOR MIN TEMPS WE ARE HIGHER THAN STAT GUIDANCE EAST AND CLOSER TO A STAT GUIDANCE BLEND WEST.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
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THE 925MB LEVEL DRY AIR SOUTH OF MAINE AND EAST OF MASSACHUSETTS IS DESTINED TO MOVE WESTWARD OVERNIGHT AND BE OVER OUR CWA ON FRIDAY. ALSO THE SFC HIGH IS FORECAST TO BE NESTLED PRETTY MUCH OVER OUR CWA. WE ARE EXPECTING THE LOW CLOUD CIG TO DISSIPATE DURING THE MORNING. THIS IN PART WILL BE REPLACED BY HIGH LEVEL CLOUDINESS ASSOCIATED WITH THE WEAKENING COLD FRONT APPROACHING FROM THE WEST. GIVEN THE LATEST RIDGE AXIS POSITION, WE REMOVED THE LOW CHC OF PCPN NEAR THE COAST. AWAY FROM THE COAST WE LEANED TOWARD THE HIGHER OF THE STAT GUIDANCE FOR MAX TEMPS AND MORE OF A BLEND CLOSER TO AND ALONG THE ATLANTIC.
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&& .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
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A FAIRLY BENIGN PATTERN FOR OUR REGION DURING THE LONG TERM. A WEAK UPPER TROUGH WILL MOVE THROUGH THE NORTHEAST AND MIDDLE ATLANTIC FRIDAY THRU SATURDAY. ANOTHER TROUGH WILL WILL MOVE FROM THE GREAT LAKES MONDAY NIGHT AND CROSS INTO THE ATLANTIC BY EARLY WEDNESDAY. THESE TWO SYSTEMS ARE FAIRLY WEAK AND SHOULD ONLY BRING SMALL CHC FOR SHOWERS TO THE AREA MON NIGHT INTO TUE NIGHT. PREVIOUS FCSTS HAD SOME SHOWERS IN FOR FRI NIGHT ALSO...BUT WE HAVE REMOVED THEM FROM THE FCST ATTM...SINCE THE CHC LOOKS LESS WITH THE MEAGER AMTS OF LIFT AND LIMITED MOISTURE. TEMPERATURES WILL START OUT COOL FOR FRI WITH HIGHS ONLY IN THE LOW/MID 50S ACROSS THE AREA. READINGS WILL THEN CLIMB TO NEAR NORMAL LEVELS FOR SAT THRU MONDAY. TEMPERATURES WILL THEN BE 5 TO 10 DEGREES ABOVE NORMAL NEXT TUESDAY...BEFORE SETTLING BACK TO NEAR NORMAL NEXT WED. NORMAL TEMPERATURES FOR THIS TIME OF YEAR ARE HIGHS IN THE MID 60S AND LOWS IN THE MID 40S FOR PHILADELPHIA. UP ACROSS THE NORTH IN THE POCONOS AN NRN NJ...THE NORMALS ARE CLOSE TO 10 DEGREES LESS THAN THOSE FOR PHILADELPHIA.
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&& .AVIATION /19Z THURSDAY THROUGH TUESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THE 18Z TAFS MVFR CONDITIONS ARE FORECAST TO OCCUR AT ALL OF THE TAF SITES TONIGHT AND FRIDAY MORNING, ALTHOUGH CONFIDENCE IS PROGRESSIVELY LOWER THE FARTHER WEST OUR TAF SITES ARE. FOR THE REST OF THIS AFTERNOON INTO EARLY THIS EVENING A VFR STRATOCU CIG IS EXPECTED TO CONTINUE TO MOVE WEST AND BE BATTLED BY SOME MIXING AND DRY AIR. FROM KPHL AREA TERMINALS EASTWARD WE ARE EXPECTING A VFR CIG AT TIMES, ALTHOUGH KACY MIGHT BECOME MVFR. FARTHER WEST NO CIG EXPECTED. EAST WINDS WILL AVERAGE AROUND 10 KTS WITH GUSTINESS UP TO AROUND 20 KTS FROM THE KPHL AREA TERMINALS EASTWARD. REST OF EVENING AND OVERNIGHT, PREDICTING A MVFR CIG TO OVERSPREAD ALL THE TERMINALS ARRIVING AT KABE AND KRDG AFTER MIDNIGHT. WINDS SHOULD BECOME LIGHTER FROM THE EAST. ON FRIDAY MORNING, THE MVFR CIG IS EXPECTED TO DISSIPATE WITH A CIRRUS DECK ABOVE IT. SYNOPTIC SCALE WINDS OVERALL SHOULD BE LIGHTER (GENERALLY AN EASTWARD COMPONENT) THAN TODAY AND A SEA BREEZE FRONT MAY FORM DURING THE AFTERNOON. OUTLOOK... FRI NIGHT THRU MON NIGHT...MOSTLY VFR. TUESDAY...MOSTLY VFR WITH SCT SHOWERS.
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&& .MARINE...
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NO CHANGES TO THE MARINE HEADLINES. SCA CONDITIONS IN THE LOWER DELAWARE BAY ARE EXPECTED TO END THIS EVENING. THE WIND PART OF THE SCA SHOULD ALSO END OVER THE OCEAN TONIGHT. BUT, SEAS WILL TAKE LONGER TO GET BELOW SCA CRITERIA ON THE OCEAN AS WE ARE EXPECTING THEM TO LINGER THROUGH THE DAY ON FRIDAY. OUTLOOK... FRI NIGHT AND SAT...SEAS ON THE OCEAN WILL REMAIN JUST BELOW SCA CONDITIONS. SAT NIGHT THRU SUN NIGHT...SCA CONDITIONS ON THE OCEAN. MON THRU TUESDAY...MOSTLY SUB-SCA CONDITIONS.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...FROST ADVISORY FROM 1 AM TO 8 AM EDT FRIDAY FOR PAZ060-101>104- 106. NJ...FROST ADVISORY FROM 1 AM TO 8 AM EDT FRIDAY FOR NJZ012-015-019. DE...NONE. MD...FROST ADVISORY FROM 1 AM TO 8 AM EDT FRIDAY FOR MDZ008. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT FRIDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ431.
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&& $$ SYNOPSIS...O`HARA NEAR TERM...GIGI SHORT TERM...GIGI LONG TERM...O`HARA AVIATION...GIGI/O`HARA MARINE...GIGI/O`HARA

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