Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 291732 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 132 PM EDT MON SEP 29 2014 .SYNOPSIS... WEAK HIGH PRESSURE RESIDES OVER THE AREA TODAY. LOW PRESSURE OVER THE EASTERN GREAT LAKES TONIGHT WILL MOVE ACROSS PENNSYLVANIA TUESDAY WHILE A WEAK COLD FRONT SLIDES SOUTH ACROSS THE REGION. THAT LOW PRESSURE SYSTEM WILL DEVELOP OUT TO SEA WEDNESDAY WITH HIGH PRESSURE IN EASTERN CANADA RIDGING DOWN INTO THE MID ATLANTIC STATES THURSDAY. A STRONGER COLD FRONT WILL MOVE EAST ACROSS THE MID ATLANTIC STATES EARLY SATURDAY. WEAK HIGH PRESSURE FOLLOWS NEXT SUNDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... QUIET WEATHER CONTINUES ACROSS THE REGION TODAY. WEAK HIGH PRESSURE REMAIN OFFSHORE WHILE A WEAK LOW MOVES ACROSS THE GREAT LAKES AREA. AN UPPER TROUGH WILL MOVE TOWARD THE AREA ALSO...CREATING A BKN-OVC SKY OF HIGH CI/CS CLOUDS. EVENTHOUGH THE RADAR MAY APPEAR SOMEWHAT JUICY THE COLUMN IS VERY DRY AND WILL TAKE MOST OF THE DAY TO MOISTEN UP TO ALLOW FOR ANY CHANCE OF VERY LIGHT SHOWERS, CONTINUED DRY FORECAST ATTM. TEMPERATURES TODAY WILL BE A FEW DEGREES COOLER THAN SUNDAY...BUT STILL ABOVE NORMAL FOR THE CLOSING DAYS OF SEPTEMBER. READINGS WILL RANGE FROM THE MID 70`S TO 80 IN MOST AREAS AND A FEW LOW 70S ACROSS THE HIGHER ELEVATIONS ACROSS THE NORTH. TEMPERATURES/DEWPOINTS WERE ADJUSTED SLIGHTLY GIVEN RECENT METAR OBS FOR TODAY AND LAV GUIDANCE WAS ALSO INCORPORATED. WINDS WILL REMAIN LIGHT...MOSTLY WEST OR SOUTHWEST. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... THE UPPER TROUGH WILL CROSS THE AREA TONIGHT WHILE A WEAK SFC LOW MOVES INTO NY STATE. THERE WILL STILL BE PLENTY OF UPPER MOISTURE ACROSS THE AREA...BUT NO PCPN IS EXPECTED WITH THE LOWER PARTS OF THE ATMOSPHERE EXPECTED TO REMAIN DRY. LOW TEMPERATURES TONIGHT WILL CONTINUE 5 TO 7 DEGREES ABOVE NORMAL...WITH LOWS IN THE LOW 60S OVER METRO PHILADELPHIA...TO THE MID/UPPER 50S ELSEWHERE. WINDS WILL CONTINUE TO BE LIGHT. && .LONG TERM /TUESDAY THROUGH SUNDAY/...
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500 MB: A RATHER STRONG CLOSED LOW SHORT WAVE MOVING SOUTHEAST FROM THE EASTERN GREAT LAKES TUESDAY WILL CROSS SOUTHERN NEW ENGLAND WEDNESDAY THEN SLOWLY DEPART EAST OF NEW ENGLAND THURSDAY. A HIGH AMPLITUDE TROUGH OVER CENTRAL NORTH AMERICA FRIDAY WILL SEND ONE OF ITS SHORT WAVES ACROSS THE NORTHEAST SATURDAY THEN THE CYCLONIC FLOW PROBABLY FLATTENS OUT SUNDAY. TEMPERATURES: SEPTEMBER WILL PROBABLY AVERAGE CLOSE TO 1.5 DEGREES ABOVE NORMAL. CALENDAR DAY TEMPERATURES SHOULD AVERAGE 5 TO 8 DEGREES ABOVE NORMAL TUESDAY THROUGH FRIDAY THEN COOL TO SLIGHTLY BELOW NORMAL BY SUNDAY. FORECAST BASIS: UNLESS OTHERWISE NOTED THE LONG TERM PERIOD OF THIS FORECAST IS GENERALLY BASED ON A 50 50 BLEND OF THE 00Z/29 NAM/GFS MOS FOR THE PERIOD TUESDAY-WEDNESDAY...THE 00Z/29 GFS MOS WEDNESDAY NIGHT-THURSDAY...THEN THEREAFTER (THURSDAY NIGHT ONWARD) THE 0522Z/29 WPC GRIDDED GUIDANCE. ALL THIS IS EVENTUALLY CHECKED AGAINST THE 00Z/29 ECMWF TO SEE IF WE`RE IN THE BALLPARK WITH ECMWF CYCLICALLY PERSISTENT 18Z 2 METER TEMPERATURES. PRECIPITATION PROBABILITY GUIDANCE IS CHECKED AGAINST THE 21Z/28 SREF 3HRLY POPS FOR .01 THROUGH 00Z SATURDAY AND THEREAFTER THE 00Z/29 GEFS 6HR POPS FOR 0.05. THE DAILIES... MODEL AMPLITUDE AND TRACK STILL DIFFER ON THE MIDWEEK CLOSED LOW SHORT WAVE BUT OVERALL...ENOUGH AGREEMENT EXISTS TO EXPRESS AVERAGE CONFIDENCE IN THE FORECAST DETAILS FOR THIS LONG TERM PERIOD. WE`RE COUNTING ON PROGRESSIVE AND NOT COUNTING ON AN EXTENDED PERIOD OF INVERTED TROF HANG BACK ALA THE 00Z/29 NAM. TUESDAY-WEDNESDAY...MODEL GUIDANCE IS COMING AROUND TO FAVORING ENOUGH STRENGTH/POTENCY IN THE SHORT WAVE DRIVING SEWD FROM THE GREAT LAKES TO MAKE ITS OWN SFC LOW PRESSURE AND SEND IT FROM ROUGHLY TORONTO TOMORROW MORNING THROUGH PA TUESDAY AFTERNOON AND THEN EVENTUALLY OFFSHORE MIDWEEK. THE COMBINATION OF THE SOUTHWARD MOVING BACKDOOR COOL FRONT...DEEP AND LIGHT E-SE FLOW NORTH OF THE BOUNDARY (I78 REGION NORTHWARD)...PWAT OF 1.25 INCHES...ELEVATED INSTABILITY WITH SWI SUBZERO AND THE STRONG SHORT WAVE PASSAGE SHOULD PERMIT SLOW MOVING SHOWERY RAINS TO DEVELOP IN E PA AND THE NORTHERN HALF OF NJ TUESDAY AND TAPER OFF WEDNESDAY. WHILE SOME AREAS WILL MISS THE RAIN...OTHERS COULD EASILY SEE AN INCH. ITS BOTHERSOME THAT THE NAM AND ECMWF HAVE BEEN AT TIMES ADVERTISING 2-5 INCHES OF RAIN FROM NNJ TO S OF LI THE PAST 48 HOURS OF CYCLES. THE IMPLIED MESSAGE...SLOW MOVERS CAN BE DECENT RAIN PRODUCERS. THUNDER IS IN THE GRIDS NOW FROM NW NJ INTO E PA LATE TUE AFTN/EVENING. THE PRIMARY FAVORED WINDOW OF OPPORTUNITY FOR NEEDED RAINFALL N OF I78 IS 21Z TUE-18Z WED. S OF I78...ESPECIALLY THE DELMARVA AND FAR SE PA...VARIABLE CLOUDINESS THROUGH THE PERIOD WITH CHANCE OF A SHOWER BUT NOT NEARLY AS THREATENING AS FURTHER NORTH. PATCHY FOG POSSIBLE EARLY TUESDAY AND EARLY WEDNESDAY MORNINGS. THURSDAY...PROBABLY DRYING OUT IN DEVELOPING NNW FLOW ENTIRE REGION AS THE CLOSED LOW SHIFTS TO THE E OF NEW ENGLAND AND HEIGHTS WARM WITH THE RIDGE ARRIVING BEHIND THE DEPARTING CLOSED LOW ALOFT. PATCHY FOG POSSIBLE EARLY THU FRIDAY-EARLY SATURDAY...PATCHY FOG POSSIBLE EARLY FRIDAY THEN DRY PROBABLY MOST OF FRIDAY WITH A PERIOD OF SHOWERS PROBABLE AT NIGHT OR EARLY SATURDAY AS A COLD FRONT ARRIVES...ASSOCIATED WITH THE HIGH AMPLITUDE TROUGH AXIS SOUTHWARD FROM THE GREAT LAKES. LATER SATURDAY-SUNDAY...DRIES OUT WITH A GUSTY WESTERLY WIND. COOLER THAN NORMAL FOR A SHORT TIME BEFORE THE NEXT BRIEF WARMING CYCLE!
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&& .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. HIGH LEVEL VFR CLOUDS AOA 15,000 FEET CONTINUE TO ADVECT IN FROM THE SOUTHEAST IN ASSOCIATION WITH LOW PRESSURE TO SOUTH. THIS LOW PRESSURE WILL PASS OFFSHORE KEEPING ANY PRECIPITATION TO A ISOLATED LIGHT SHOWER OR SPRINKLE, WITH ACY/MIV HAVING THE BEST CHANCE. DRY TAFS. OVERNIGHT SOME SCATTERED LOWER VFR CLOUDS AROUND 4,000 FEET MAY DEVELOP. CURRENTLY IS IT MORE LIKELY THAT THE HIGHER LEVEL CLOUDS WILL PREVENT THE FORMATION OF LOWER CLOUDS OR FOG, EXCEPT AT RDG AND MIV WHICH TYPICALLY HAVE THE BEST CHANCE TO SEE FOG. ANY FOG SHOULD BURN OFF BY 14Z LEAVING SOME SCATTERED CLOUDS AOA 4,000 FEET, SO ANOTHER VFR DAY TUESDAY. THE NEXT FRONTAL BOUNDARY WILL APPROACH FROM THE NORTHWEST TUESDAY NIGHT. HOWEVER, NO PRECIPITATION THROUGH 00Z WED. OUTLOOK... WEDNESDAY...MAINLY VFR CIGS WITH POSSIBLE MVFR CONDS IN SHOWERS KABE/KRDG/KTTN DURING THE MORNING. E/NE WINDS GUST 15 KNOTS. THURSDAY...POSSIBLE MVFR FOG EARLY OTHERWISE VFR SCT-BKN CLOUDS AOA 4000 FT. N-NW WIND GUST 15 KT. FRIDAY...VFR CIGS EXCEPT POSSIBLE MVFR CONDS IN ST/FOG EARLY FRIDAY MORNING AND THEN AGAIN FRIDAY NIGHT IN SHOWERS NEAR A COLD FRONT. E-SE WIND BECOMING S OR SW LATE AT NIGHT.
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&& .MARINE... QUIET CONDITIONS CONTINUE ON THE WATERS. WEAK HIGH PRESSURE REMAIN OFFSHORE AND A WEAK LOW WILL DEVELOP ACROSS THE GREAT LAKES TONIGHT AND MOVE INTO NY STATE TUE. A LIGHT...MOSTLY SWRLY...FLOW WILL BE ACROSS THE WATERS. WINDS MAY TURN ERLY LATE TONIGHT. WIND SPEEDS UNDER 10 KNOTS EXPECTED. PARTLY/MOSTLY SUNNY TODAY AND PARTLY CLOUDY TONIGHT. SEAS AROUND 2 FT ON THE OCEAN AND 1 TO 2 FT OVER DEL BAY. OUTLOOK... TUESDAY: WINDS AND SEAS INCREASE WITH DEVELOPING EAST-NORTHEAST FLOW BUT SHOULD REMAIN BELOW SCA CRITERIA. TUESDAY NIGHT THROUGH WEDNESDAY NIGHT: NE FLOW TUESDAY NIGHT THROUGH WEDNESDAY NIGHT SHOULD INCREASE TO SCA CRITERIA ALONG THE NNJ COAST TUESDAY NIGHT AND THEN POSSIBLY SOUTHWARD TO THE ENTIRE ATLC COAST LATER WEDNESDAY OR WEDNESDAY NIGHT. DELAWARE BAY MAY NOT SEE WIND GUSTS ABOVE 22 KT WITH ANY SCA HEADLINE THERE NOT LIKELY AS OF THIS WRITING. THURSDAY...SMALL CHANCE OF SCA SEAS ON THE ATLANTIC WATERS FROM NE SWELLS GENERATED BY AN OFFSHORE LOW. FRIDAY...WIND BECOMING SOUTH BY NIGHT. SMALL CHANCE OF AN SCA AT NIGHT. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...DRAG NEAR TERM...GAINES/O`HARA SHORT TERM...O`HARA LONG TERM...DRAG AVIATION...DRAG/GAINES/O`HARA MARINE...DRAG/O`HARA

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