Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 050810 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 410 AM EDT WED AUG 5 2015 .SYNOPSIS...
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THE COLD FRONT PUSHING SOUTH AND EAST OF THE AREA WILL STALL TO OUR SOUTH WHILE HIGH PRESSURE TRIES TO BUILD IN FROM THE WEST INTO THURSDAY. AN AREA OF LOW PRESSURE WILL DEVELOP ALONG THE BOUNDARY TO OUR SOUTH THURSDAY INTO THURSDAY NIGHT, THEN SLOWLY MOVE OFF THE NORTH CAROLINA COAST LATE FRIDAY INTO SATURDAY. THE LOW IS THEN FORECAST TO MOVE NORTHWARD OVER THE WESTERN ATLANTIC, WHILE HIGH PRESSURE TRIES TO NOSE DOWN INTO OUR AREA FROM THE NORTHEAST OVER THE WEEKEND. ANOTHER FRONTAL BOUNDARY IS EXPECTED IN THE EARLY TO MIDDLE PART OF NEXT WEEK.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A COLD FRONT HAS PUSHED JUST SOUTH AND EAST OF THE AREA EARLY THIS MORNING. CONVECTION ALONG AND AHEAD OF THE FRONT HAS ACCORDINGLY MOVED OFFSHORE. THE FRONT WAS RATHER DIFFUSE WITH THE TEMPERATURE AND DEWPOINT GRADIENT SEPARATED 50-100 MILES BEHIND (I.E., NORTH) OF THE PRESSURE TROUGH/WIND SHIFT. PATCHY FOG MAY DEVELOP TOWARD DAYBREAK IN SOUTHERN NJ AND THE DELMARVA, WHERE THE GROUND IS WET FROM LAST NIGHT`S STORMS AND DEWPOINTS ARE STILL IN THE UPPER 60S AND LOW 70S, BUT MID-LEVEL CLOUDS SHOULD HELP TO LIMIT THE EXTENT OF IT. THE FRONT WILL STALL JUST TO OUR SOUTH AND EAST TODAY WHILE HIGH PRESSURE BUILDS IN FROM THE GREAT LAKES/MIDWEST REGIONS. W-NW WINDS WILL INCREASE THIS AFTERNOON IN RESPONSE TO A TIGHTENING PRESSURE GRADIENT BETWEEN THESE TWO SYSTEMS. GUSTS TO 20 MPH SHOULD BE COMMON DURING THE MID AND LATE AFTERNOON. A VORT MAX ASSOCIATED WITH THE PASSAGE OF THE UPPER TROUGH IS FORECAST TO PASS THRU OUR NORTHERN ZONES LATE THIS AFTERNOON. THERE IS LIMITED MOISTURE WITH THIS SYSTEM, SO OPTED TO KEEP POPS BELOW 20 PERCENT BUT ADDED ISO/SCT SPRINKLES ALONG AND NORTH OF I-78. MAX TEMPS IN NORTHEAST PA AND NORTHWEST NJ SHOULD BE NEAR CLIMO (UPPER 70S IN THE POCONOS/MID 80S IN THE LEHIGH VALLEY AND NW NJ). HOWEVER, WITH THE COOLER AIR LAGGING BEHIND THE FRONT, EXPECT MAX TEMPS TO BE 3-6 DEGREES ABOVE NORMAL IN PHILA AND LOCATIONS TO THE SOUTH AND EAST (UPPER 80S AND LOW 90S). IF THE FORECAST HIGH OF 91F FOR PHL IS REALIZED TODAY, IT WOULD EXTEND THE STRETCH OF 90-DEGREE DAYS TO 9 CONSECUTIVE DAYS FOR THE CITY.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
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HIGH PRESSURE CONTINUES TO BUILD IN FROM THE GREAT LAKES TONIGHT. WINDS WILL VEER OUT OF THE N-NW IN ASSOCIATION WITH THE PRESSURE SURGE BUT SHOULD OVERALL BE LIGHT ENOUGH TO NOT IMPEDE RADIATIONAL COOLING MUCH. THEREFORE, WEIGHTED THE TEMP FORECAST ON THE COOLER SIDE OF GUIDANCE UNDER MAINLY CLEAR SKIES AND LIGHT WINDS. MIN TEMPS RANGE FROM THE LOW 50S IN THE POCONOS TO UPPER 60S IN PHILA AND ALONG THE COAST. FOG POTENTIAL WILL BE LOW DUE TO A DRY AIRMASS IN PLACE.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
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THURSDAY INTO THURSDAY NIGHT, AN AREA OF LOW PRESSURE WILL BE DEVELOPING ALONG THE STALLED FRONTAL BOUNDARY TO OUR SOUTH. MEANWHILE, A COUPLE OF SHORT WAVE/VORTICITY IMPULSES WILL BE MAKING THEIR WAY ACROSS THE AREA FROM LATE THURSDAY INTO LATE FRIDAY. THIS SHOULD LEAD TO SOME RAINFALL FOR AT LEAST THE SOUTHERN PORTIONS OF THE FORECAST AREA WHICH WILL BE CLOSER TO THE SURFACE LOW. AREAS FARTHER NORTH AWAY FROM THE LOW MAY NOT SEE ANY RAINFALL AS MODELS ARE KEEPING THE MAJORITY OF THE RAIN FURTHER SOUTH. SO WE`VE LOWERED POPS SOME ACROSS MUCH OF THE AREA. THE LOW IS FORECAST TO DRIFT INTO THE WESTERN ATLANTIC INTO THE WEEKEND WHILE HIGH PRESSURE TRIES TO NOSE DOWN INTO OUR AREA FROM THE NORTH. WITH DRIER AIR EXPECTED TO FILTER IN AND NO SIGNIFICANT SHORT WAVE/VORTICITY DISTURBANCES ALOFT, WE EXPECT A DRY FORECAST INTO THE WEEKEND. MODELS HAVE SLOWED DOWN THE ARRIVAL OF THE NEXT FRONTAL SYSTEM AND ASSOCIATED PRECIPITATION. BEFORE THEY WERE BRINGING IT IN AS EARLY AS MONDAY, BUT NOW THEY ARE BRINGING AN AREA OF LOW PRESSURE AND ASSOCIATED RAINFALL THROUGH THE OHIO RIVER VALLEY MONDAY INTO TUESDAY, AND INTO OUR AREA LATE TUESDAY INTO WEDNESDAY. DUE TO THE UNCERTAINTY, WE`VE KEPT A CHANCE OF RAINFALL FOR MONDAY INTO WEDNESDAY, ALTHOUGH IT WILL LIKELY NOT RAIN THE ENTIRE PERIOD.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. MAINLY MVFR VSBYS IN FOG AT MIV AND ACY THRU ABOUT 12Z, WHERE THE GROUND IS WET FROM EARLIER RAINFALL. ADDED A SHORT TEMPO GROUP AT MIV FOR IFR VSBYS IN DENSER FOG FOR A COUPLE OF HOURS JUST BEFORE SUNRISE. CONFIDENCE NOT PARTICULARLY HIGH THOUGH WITH MID-LEVEL CLOUDS AROUND. OTHERWISE, VFR TODAY AND TONIGHT FOR THE TERMINALS. W-NW WINDS WILL INCREASE THIS AFTERNOON WHEN GUSTS OF 15-20 KT ARE EXPECTED. WINDS WILL DIMINISH TOWARD SUNSET. OUTLOOK... THURSDAY...VFR. THURSDAY NIGHT-FRIDAY NIGHT...MVFR/IFR CONDITIONS POSSIBLE ACROSS SOUTHERN AREAS WITH RAIN POSSIBLE. GENERALLY VFR ACROSS THE NORTH. SATURDAY-SUNDAY...GENERALLY VFR. MVFR CONDITIONS POSSIBLE ALONG THE COASTAL AREAS. NORTHEAST WINDS WITH GUSTS 15-25 KNOTS, ESPECIALLY ALONG THE COAST DURING THE DAY SATURDAY AND SUNDAY.
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&& .MARINE...
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SCA CANCELLED FOR THE COASTAL ATLANTIC MARINE ZONES AS WINDS HAVE SUBSIDED TO UNDER 20 KT AND SEAS ARE BELOW 5 FT. NO MARINE HAZARDS EXPECTED TODAY AND TONIGHT. OUTLOOK... THURSDAY-THURSDAY NIGHT...SUB-SMALL CRAFT ADVISORY CONDITIONS EXPECTED. FRIDAY-FRIDAY NIGHT...WINDS AND SEAS INCREASE AND APPROACH SMALL CRAFT ADVISORY LEVELS, POSSIBLE EXCEEDED ADVISORY LEVELS LATE FRIDAY NIGHT. SATURDAY-SATURDAY NIGHT...WINDS AND SEAS EXPECTED TO REMAIN ABOVE SMALL CRAFT ADVISORY LEVELS THROUGH SATURDAY. WINDS EXPECTED TO DROP BELOW ADVISORY LEVELS SATURDAY NIGHT, BUT SEAS REMAIN ELEVATED. SUNDAY...WINDS REMAIN BELOW ADVISORY LEVELS, HOWEVER SEAS ARE FORECAST TO REMAIN ABOVE ADVISORY LEVELS.
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&& .CLIMATE...
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YESTERDAY WAS PHILADELPHIA`S 8TH CONSECUTIVE DAY OF 90 OR HIGHER (AS MEASURED AT PHILADELPHIA INTERNATIONAL AIRPORT). IT`S BEEN A RELATIVELY EASY GOING 8 DAY STREAK OF 90 DEGREE DISCOMFORT...THE MOST DIFFICULT BEING THE 29TH AND 30TH WHEN HEAT INDICES TOPPED OUT IN THE UPPER 90S. IF THE TEMPERATURE NUDGES 90 AT PHILADELPHIA TODAY, THE 9 DAY STREAK WOULD BE THE LONGEST HERE SINCE THE 12 CONSECUTIVE DAY STRETCH THAT ENDED JULY 9 2012. AS IT STANDS NOW, THE CURRENT 8 DAY STREAK RANKS 21ST TO 34TH LONGEST. IT BEGAN JULY 28TH. THE MEAN NUMBER OF 90 OR HIGHER DAYS IN A YEAR IN THE PERIOD OF RECORD DATING BACK TO 1874 IS 21. THIS YEAR WE`VE HAD 22 SO FAR (1 IN MAY, 7 IN JUNE, 10 IN JULY AND 4 SO FAR IN AUGUST). IF YOU RECALL THE SUMMER OF 2010, THERE WERE 55 DAYS OF 90 OR HIGHER IN PHILADELPHIA. THE LONGEST CONSECUTIVE DAY STREAK OF 90 OR HIGHER IN PHILADELPHIA WAS 18 DAYS ENDING AUGUST 15 1988. THEN 17 ENDING AUGUST 5 1995 13 ENDING SEPTEMBER 5 1953
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE.
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&& $$ SYNOPSIS...ROBERTSON NEAR TERM...KLEIN SHORT TERM...KLEIN LONG TERM...ROBERTSON AVIATION...KLEIN/ROBERTSON MARINE...KLEIN/ROBERTSON CLIMATE...DRAG

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