Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 162002 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 402 PM EDT SAT AUG 16 2014 .SYNOPSIS...
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A COLD FRONT WILL APPROACH FROM THE GREAT LAKES TONIGHT AND MOVE THROUGH THE AREA ON SUNDAY. THE FRONT WILL STALL OVER THE LOWER DELMARVA ON MONDAY. A WAVE OF LOW PRESSURE WILL TRACK ALONG THE FRONTAL BOUNDARY AND ACROSS THE MID-ATLANTIC REGION MONDAY NIGHT AND TUESDAY. HIGH PRESSURE BRIEFLY RETURNS TO THE AREA ON WEDNESDAY BEFORE RETREATING TO THE NORTHEAST. THE AFOREMENTIONED FRONTAL BOUNDARY IS EXPECTED TO REMAIN JUST SOUTH OF THE AREA THURSDAY INTO SATURDAY AS MORE WAVES OF LOW PRESSURE RIDE ALONG IT.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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A COLD FRONTAL BOUNDARY LOCATED OVER THE GREAT LAKES WILL MOVE SOUTHEAST TOWARD OUR REGION TONIGHT. SOME SCATTERED MID TO HIGH LEVEL CLOUDS WILL BE ON THE INCREASE AFTER MIDNIGHT. ISOLATED TO SCATTERED SHOWERS ARE ALSO POSSIBLE ACROSS NORTHERN NJ AND THE POCONOS. COVERAGE LOOKS RATHER LIMITED DUE TO MODEST DEWPOINT DEPRESSION SPREADS AT THE SURFACE AND LOW PW VALUES. THE BEST LIFT AND MAXIMUM VORTICITY WILL BE MORE FOCUSED TO OUR NORTH AS WELL. THE MODEL CONSENSUS BRINGS THE SLIGHT SHOWER CHANCE IN AFTER 06Z TONIGHT AND THEN POPS INCREASE FROM SLIGHT CHANCE TO LOW CHANCE BY MORNING FROM NORTH TO SOUTH. THINK THE IDEA OF A VERY LIGHT QPF EVENT IS SOUND MORE IN WITH THE 09Z SREF WHEN COMPARED TO THE WPC QPF. PRETTY TIGHT SPREAD WITHIN THE MET/MAV TODAY AND DID NOT DEVIATE FROM THOSE GUIDANCE SETS ON TEMPERATURES AND DEWPOINTS. WINDS WILL GENERALLY BE OUT OF THE SOUTHWEST AHEAD OF THE COLD FRONT.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
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THE COLD FRONT WILL CONTINUE TO MOVE SOUTHEAST THROUGH THE REGION. THIS PERIOD FEATURES A CHANCE OF SHOWERS AND PERHAPS A RUMBLE OF THUNDER MOVING FROM NORTH TO SOUTH ACROSS THE REGION WITH CAPE OF ONLY A FEW HUNDRED G/KG AT BEST. MOST OF THE DAY WILL BE DRY WITH SOME PLACES STAYING COMPLETELY DRY, PREFERRED SREF ONCE AGAIN FOR QPF. STAYED CLOSE TO THE MAV AND MET GUIDANCE SETS ON TEMPERATURES AND DEWPOINTS. WINDS WILL SHIFT TO NORTHWEST WITH THE FRONTAL PASSAGE. STEEPING LAPSE RATES SHOULD ALLOW FOR THE POTENTIAL OF SOME 15-20 MPH WIND GUSTS TO BE TRANSFERRED TO THE SURFACE IN THE AFTERNOON.
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&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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THE MEDIUM RANGE MODELS CONTINUE TO SHOW RUN TO RUN AND INTERNAL INCONSISTENCIES AT RESOLVING THE BLOCKY -NAO PATTERN AND MUCH LATER ON TRYING TO GIVE THE HEAT RIDGE ONE LAST CHANCE TO MOVE EAST. THERE IS UNCERTAINTY WITH REGARD TO THE AMPLITUDE AND PLACEMENT OF A TROUGH OVER THE NORTHEAST CONUS DURING THIS TIMEFRAME...WITH THE GFS ADVERTISING A DEEPER AND LESS PROGRESSIVE SOLUTION COMPARED TO THE EURO. IN ADDITION...THE GFS/EURO OPERATIONAL SOLUTIONS HAVE SUPPORT FROM THEIR RESPECTIVE ENS MEMBERS...BUT THERE IS STILL CONSIDERABLE SPREAD IN THE 500 HPA HEIGHTS...WHICH IS INDICATIVE OF THE UNCERTAINTY AT THIS POINT IN THE FCST. ALTHOUGH THERE HAS BEEN LITTLE RUN-TO-RUN MODEL CONSISTENCY...THERE HAS BEEN A TREND TO DEVELOP A REX-BLOCK OVER THE NORTHEAST CONUS AND ATLANTIC CANADA...ESPECIALLY GIVEN THE PERSISTENT POSITIVE HEIGHT ANOMALY CENTERED NEAR THE DAVIS STRAIGHT...WHICH WOULD FURTHER COMPLICATE THE FORECAST. IN THE START OF THE LONG TERM ODDLY THE DP/DT ON THE CLOSED LOW OVER IOWA IS FASTER, WEAKER AND FARTHER SOUTHEAST. BUT THEN THE NAM/GFS AND CAN GGEM GO STRONGER AND FARTHER NORTH ON THE DAY RUN VS THEIR 00Z/06Z RUNS. THE GFS DEVELOPS A FEEDBACK BULLSEYE IN SERN PA LATE TUESDAY WHICH PRETTY MUCH STARTS SETTING THE REST OF THIS RUN APART FROM ITS NIGHT RUN AND SOMEWHAT ITS ENSEMBLE MEAN. WHILE THE UKMET AND ECMWF HAVE THEIR OWN RUN TO RUN ISSUES, THEIR RUBBER BAND HAS NOT STRETCHED AS MUCH. SO FOR THIS PART OF THE FORECAST PACKAGE WE START WITH A GFS TIMING AND CAN GGEM/EURO COMPROMISE ON THE DETAILS AND THEN MOVE MORE TOWARD A GFS/UKMET COMPROMISE IN ESSENCE PRESERVING AT LEAST 2/3RDS OF CONTINUITY. THIS DOES NOT NEGATE THE HEAVY RAIN THREAT, BUT FOR NOW KEEPS IT MAINLY IN DELMARVA AND EXTREME SOUTHERN NEW JERSEY. SUNDAY NIGHT WE ARE EXPECTING PCPN CHANCES TO BE DONE BY THE START. LOWEST CONFIDENCE SOUTH. DECENT RADIATIONAL COOLING EXPECTED WITH LIGHT WINDS AND CLEAR SKIES. MONDAY LOOKS TO BE A MOSTLY SUNNY DAY WITH POSSIBLY SOME HIGH CLOUDINESS OF NOTICE DURING THE AFTERNOON. THE FCST AVAILABLE MOISTURE AT THE CUMULUS LEVEL DOES NOT LOOK OVERLY IMPRESSIVE. MAX TEMPS TOWARD THE WARM SIDE OF STAT GUIDANCE. MONDAY NIGHT, THE GENERAL MODEL TREND WITH A SLIGHTLY WEAKER CLOSE LOW IS FASTER. WHAT WILL ALSO BE THE DRIVER WITH IT WILL BE HOW QUICKLY THE CLOSED LOW OVER THE CANADIAN MARITIMES LEAVES. THE LONGER IT LINGERS, THE FARTHER SOUTH THE SYSTEM GOES. AS WAS THE CASE LAST WEEK, THE OLD RULE OF THUMB THAT ONE CAN NEVER GO FAR ENOUGH SOUTH WITH HEAVY RAIN WAS ALSO INCLUDED. THERE IS MUCH CONTINUITY IN OUR PRESENT FORECAST WITH THE HIGHEST POPS SOUTH AS WELL AS THE INCLUSION OF THUNDER AND HEAVY RAIN. LIKE LAST WEEK, THE MENTION OF HEAVY RAIN WAS TIED TO THE INCLUSION OF THUNDER. THE AIR MASS NORTH IS NOT PREDICTED TO SUPPORT UPRIGHT CONVECTION, WILL THIS BE THE SIGNAL TO KEEP HEAVY RAIN AT BAY AGAIN? OVERALL OUR MENTION OF HEAVY RAIN IS BEST DEPICTED TOWARD A CAN GGEM AND ECMWF COMPROMISE. TUESDAY, GENERAL IMPROVING CONDITIONS AFTER MORNING SHOWERS, HEAVY RAIN EARLY SOUTHEAST. THE DEVELOPING CAP MAY ARRIVE IN TIME TO MAKE THE AFTERNOON DRY. THIS IS ALSO BASED ON MODEL TIMING NOT SLOWING. MAX TEMPS WILL NEED THE SUN TO ARRIVE DURING THE AFTERNOON, OTHERWISE WE ARE WOEFULLY TOO HIGH. TUESDAY NIGHT AND WEDNESDAY, A BREAK BETWEEN SYSTEMS AS THE FIRST LOW MOVES OFFSHORE. HIGHER INSTABILITY WEST TRIGGERING THUNDERSTORMS MIGHT ARRIVE WEST BEFORE WEDNESDAY CONCLUDES. NEAR NORMAL TEMPS EXPECTED. A BETTER CHANCE FOR SHOWERS AND THUNDERSTORMS ON WEDNESDAY NIGHT AND THURSDAY AS THE WARM FRONTAL BOUNDARY MOVES CLOSER. THIS MIGHT BECOME A SECONDARY CHANCE FOR HEAVIER RAIN, THIS ONE THROUGHOUT OUR CWA. THEN AS LOW PRESSURE DEVELOPS ON THE FRONT AND HIGH PRESSURE ONCE AGAIN TRIES TO NOSE DOWN FROM NEW ENGLAND, LOWER CHANCES WERE CARRIED FOR THURSDAY NIGHT INTO FRIDAY NIGHT. WITH HIGHER DEW POINTS, IT FEEL MORE LIKE AUGUST AGAIN AND TEMPS SHOULD REMAIN CLOSER TO NORMAL. FOR SENSIBLE WEATHER ON SATURDAY...THE GFS/EURO GENERALLY SHOW A COASTAL LOW MOVING OFFSHORE WITH HIGH PRESSURE BUILDING IN... INDICATIVE OF A DRYING TREND WITH TEMPERATURES SLIGHTLY BELOW NORMAL. BUT GIVEN MODEL INCONSISTENCY AND UNCERTAINTY...CONFIDENCE IS VERY LOW AT THIS POINT /DAY 7/.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDITIONS CONTINUE TODAY WITH A WIND GUST OR TO NOT OUT OF THE QUESTION OVER 15KT. GIVEN MOST LOCATIONS ARE UNLIKELY TO EXPERIENCE STRONG WIND GUSTS TODAY, LEFT OUT OF TAFS. WE WILL SEE MID AND LEVEL HIGH CLOUDS CONTINUE TO MOVE IN FROM THE NORTHWEST AHEAD OF A COLD FRONT THROUGH TONIGHT. CLOUDS SHOULD MAINLY BE FROM 5-10,000 FEET UP WITH MOSTLY CLOUDY CONDITIONS IN THE MORNING AS THE FRONT PASSES THROUGH. A SHOWER OR RUMBLE OF THUNDER CAN NOT BE RULED OUT LATE TONIGHT AND SUNDAY. HOWEVER, COVERAGE LOOKS TO BE ISOLATED AND LEFT PRECIPITATION OUT OF TAFS AT ALL SITES. A BETTER CHANCE FOR WIND GUSTS IS PRESENT SUNDAY AFTERNOON AND PLACED GUSTS INTO THE TAF FOR PHL TOMORROW WITH TIMING FOCUSED AFTER 18Z. OUTLOOK... SUNDAY NIGHT AND MONDAY...VFR. MONDAY NIGHT THROUGH TUESDAY...SHOWERS AND THUNDERSTORMS MOVING ACROSS THE AREA WITH A MORE LIKELY MVFR/IFR IMPACT AT SOUTHERN AIRPORTS AND TERMINALS. ONSHORE FLOW SHOULD CONTRIBUTE TO SUB VFR CIGS. TUESDAY NIGHT THROUGH WEDNESDAY MORNING...PREDOMINATELY VFR. WEDNESDAY AFTERNOON THROUGH THURSDAY...VFR, BUT TIMES OF MVFR AND BRIEFLY IFR IN SCATTERED SHOWERS AND OR THUNDERSTORMS.
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&& .MARINE...
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SEAS WILL BE PRIMARILY BE BUILDING FROM 2 TO 3 FEET IN THIS PERIOD. A SOUTHWEST WIND WILL SHIFT TO NORTHWEST DURING THE DAY SUNDAY. SOME WIND GUSTS FROM 15-20 KNOTS ARE POSSIBLE IN THE AFTERNOON SUNDAY. OUTLOOK... SUNDAY NIGHT THROUGH MONDAY EVENING...SUB SMALL CRAFT ADVISORY CONDITIONS EXPECTED. MONDAY OVERNIGHT THROUGH TUESDAY NIGHT...THERE IS A CHANCE FOR SMALL CRAFT ADVISORY CONDITIONS DUE TO THE ONSHORE FLOW NORTH OF THE LOW PRESSURE SYSTEM INCREASING WINDS AND RAISING SEAS. HIGHEST CHANCE ON ON THE NJ OCEANIC WATERS. WEDNESDAY THROUGH THURSDAY...SUB SMALL CRAFT ADVISORY CONDITIONS RETURN AS THE PRESSURE PATTERN REMAINS WEAK OVER THE AREA.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GIGI/KLEIN NEAR TERM...GAINES/O`HARA SHORT TERM...GAINES/O`HARA LONG TERM...GIGI/FRANCK AVIATION...GAINES/GIGI/KLEIN/O`HARA MARINE...GAINES/GIGI/KLEIN/O`HARA

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