Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 281450 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 950 AM EST SUN DEC 28 2014 .SYNOPSIS... LOW PRESSURE MOVING ACROSS QUEBEC TODAY WILL CAUSE A COLD FRONT TO CROSS OUR AREA. THE FRONT WILL MOVE WELL TO THE SOUTH TONIGHT AND MONDAY...WHILE A WEAK AREA OF LOW PRESSURE MOVES ALONG IT MONDAY AND MONDAY NIGHT. HIGH PRESSURE WILL RIDGE ACROSS THE REGION TUESDAY AND REMAIN IN CONTROL OF THE WEATHER THROUGH FRIDAY. A LOW PRESSURE SYSTEM AND FRONT MAY ADVANCE TOWARD OUR AREA NEXT WEEKEND. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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THE SHOWERS ARE MOVING IN/OUT FASTER THAN PREVIOUSLY EXPECTED SO WE HAVE ADJUSTED POPS ACCORDINGLY. THE LAST OF THE FIRST SURGE IS MOVING THROUGH CENTRAL AND SOUTHERN JERSEY WITH DRYING BEHIND IT...WE CARRY CATEGORICAL FOR A COUPLE MORE HOURS IN EASTERN NEW JERSEY AND TAPER THEM TO SLIGHT CHANCE ACROSS OUR WESTERN ZONES. THERE SHOULD BE A DECENT BREAK IN THE ACTION LATER THIS MORNING INTO THE MID-AFTERNOON HOURS BEFORE A WEAK WAVE OF LOW PRESSURE SLIDES JUST TO THE SOUTH OF THE REGION TOUCHING OFF MORE SHOWERS. THIS SECOND ROUND OF RAIN SHOULD STAY MOSTLY SOUTH OF THE PHILLY METRO AREA, WITH A FEW STRAY SHOWERS NORTH OF THE CITY. OTHERWISE, THE WRF-NMMB INITIALIZATION LOOKED BETTER THAN THE GFS AT 500MB WHILE AT 850MB AND 925MB BOTH MODELS WERE SIMILAR. WITH THE LATTER PAIR THERE WAS A COLD INITIALIZATION BIAS WHICH WAS TAKEN INTO CONSIDERATION FOR TONIGHT. WRF-NMMB ALREADY HAD SOME NORTHWEST BIASES. BECAUSE OF THE MONDAY NIGHT INTO TUESDAY FLIPS THAT THE GFS AND WRF-NMMB HAVE HAD, THIS PACKAGE DOES LEAN MORE HEAVILY THE ECMWF`S WAY WHICH HAS BEEN THE MOST CONSISTENT MODEL. THE BRIEF RUN OF SUNNY WEATHER HAS ENDED FOR OUR AREA. FOR TODAY, WE SEE TWO IMPULSES REFLECTED IN THE MODEL FIELDS THAT WILL AFFECT OUR AREA. THE FIRST IS PULLING THROUGH THE REGION AS WE TYPE WHILE THE SECOND ONE IS CURRENTLY IN SOUTHWEST VIRGINIA. THIS SECOND IMPULSE IS SLATED TO ARRIVE IN THE SERN HALF OF OUR CWA THIS AFTERNOON AS THE CDFNT COMPLETES ITS PASS THROUGH OUR CWA. HIGHEST POPS SLIDE SOUTHEASTWARD AS THE DAY PROGRESSES AND WE END SHOWER CHANCES NORTHWEST DURING THE EARLY AFTERNOON. IN REALITY PCPN STARTS HAVING AN UNDER-RUNNING LOOK TO IT DURING THE AFTERNOON, BUT WE WAITED UNTIL TONIGHT TO CONVERT THE SHOWERS TO RAIN TO KEEP FORMATTED PRODUCTS A LITTLE LESS CLUTTERED. MAX TEMPS ARE A STAT GUIDANCE BLEND. GIVEN TIMING OF PCPN WE MAY BE TOO WARM NORTHWEST AND TOO COLD SOUTHEAST. WINDS OVERALL SHOULD BE ON THE LIGHT SIDE, EVEN IN THE POST CDFNTL AIR MASS.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... THE NEXT IMPULSE TO BRING PCPN CHANCES INTO OUR AREA IS EMANATING FROM THE WESTERN GULF OF MEXICO. GIVEN ITS LONG TREK TO GET HERE AND TO FACTOR IN A BIT OF UNCERTAINTY, WE COMPROMISED BETWEEN THE GFS AND ECMWF DURING THIS TIME PERIOD. SO ONCE PCPN ASSOCIATED WITH IMPULSE NUMBER TWO EXITS, A STEADY RAIN IS MOST LIKELY TO OCCUR LATER AT NIGHT IN DELMARVA FROM IMPULSE NUMBER THREE. GIVEN THE COLD BIAS INITIALIZATION (ALSO LOCATION/MOVEMENT OF THE JET), WE SIDED WITH WARMER THERMAL FIELDS OVERNIGHT. PTYPE IS ALL LIQUID AND WE THINK THE GFS HINT OF SOME SLEET (ADVECTING IN SUB ZERO 925MB AIR) HAD TOO FAST OF A HEAD START TO OCCUR. SKIES SHOULD BECOME CLEARER (OR AT THE LEAST CLOUDS HIGHER) IN THE NORTHERN PART OF OUR CWA. MIN TEMPERATURES ARE GENERALLY AT OR ABOVE STAT GUIDANCE. LOWEST CONFIDENCE NORTHWEST WHERE SOME SKIES MIGHT CLEAR. && .LONG TERM /MONDAY THROUGH SATURDAY/... THE FRONT FROM THE NEAR/SHORT TERM PARTS OF THE FCST WILL HAVE SETTLED WELL SOUTH OF THE AREA MONDAY. MOST OF THE MODELS SHOW SOME WEAK WAVE DEVELOPING ALONG IT AND CRUISING BY TO THE SOUTH MONDAY. THE PREFERRED EC/GFS MODELS SOME SOME LIGHT QPF ACROSS THE DELMARVA MONDAY MORNING...SO WE HAVE GONE ALONG WITH THAT...BUT REDUCED POPS/QPF FROM YESTERDAYS FCST. THE TREND IN MOST MODELS HAS BEEN TO SUPPRESS THE SYSTEM. THE 00Z NAM REMAINS NORTH WITH THE QPF/HIGHER POPS. THE WPC CONSIDERS THE NAM AN OUTLIER SOLUTION... SO WE ARE GOING TO DISREGARD THAT FOR NOW. TUE THRU FRI...HIGH PRESSURE OVER THE PLAINS AND MIDWEST BRINGS COLDER AND DRY AIR TO THE REGION. TEMPERATURES WILL FALL TO A FEW DEGREES BELOW NORMAL TUE AND REMAIN AT OR BELOW NORMAL THRU FRIDAY. A SLGT CHC FOR A SNOW SHOWER ACROSS THE DELMARVA EARLY TUE...BUT OTHER THAN THAT A DRY FCST FOR THE PERIOD. FRI NIGHT/SAT...THE OP MODELS SHOWING ANOTHER LOW DEEPENING AND MOVING WEST OF THE AREA. CLOUDS WILL INCREASE FRI AND PCPN WILL OVERSPREAD THE AREA FRI NIGHT AND REMAIN INTO SAT. TEMPS COULD BE COLD ENOUGH FOR SOME SNOW/MIXED PRECIP FRI NIGHT...BUT READINGS WILL PROBABLY WARM ENOUGH FOR MOSTLY RAIN SAT. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. 12Z TAFS CONTINUE TO CONTAIN MVFR CONDITIONS MAINLY DURING MORE FREQUENT SHOWERS. THIS MORNING AND AFTERNOON...NORTHERN AIRPORTS AND TERMINALS VFR SHOWERS ARE ONGOING TERMINALS WITH CIGS LOWERING TO MVFR LATER IN THE MORNING. VFR CIG IMPROVEMENT DURING THE AFTERNOON AS SHOWERS DECREASE AND END. KPHL AREA AIRPORTS AND TERMINALS/AIRPORTS TO THE SOUTH/SOUTHEAST EXPECTING A VFR CIG MORNING WITH SPOTTIER MORNING SHOWERS AND MORE WIDESPREAD SHOWERS DURING THE AFTERNOON. MVFR CIGS APPEAR LESS LIKELY THAN PREVIOUSLY THOUGHT SO WE REMOVED THE TEMPO GROUPS. ALL TERMINALS VSBY RESTRICTIONS TOO BRIEF TO INCLUDE, MAINLY VFR VSBYS. WINDS WILL BECOME WEST TO NORTHWEST DURING THE LATE MORNING TO EARLY AFTERNOON AS THE COLD FRONT MOVES THROUGH. SPEEDS SHOULD BE LESS THAN 10 KNOTS. TONIGHT, VFR MID LEVEL CIGS RISING TO CIRRUS LEVELS AT NORTHERN AIRPORTS. NORTHWEST TO NORTH WINDS AVERAGING 5 TO 10 KNOTS. SOUTHERN TERMINALS AND DELMARVA AIRPORTS MIGHT SEE A SECOND SURGE OF MAINLY VFR RAIN LATE AT EVENING AND OVERNIGHT. OUTLOOK... MONDAY THRU EARLY TUESDAY...VFR NORTH. LOWER CONDITIONS POSSIBLE IN PCPN AND LOWER CLOUDS SOUTH. TUESDAY AFTERNOON THRU THURSDAY...VFR EXPECTED.
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&& .MARINE... SUB SMALL CRAFT ADVISORY CONDITIONS ARE PREDICTED THROUGH TONIGHT. THE SURGE OF STRONGER SOUTHWEST WINDS ALOFT THIS MORNING IS NOT MIXING DOWN AS HIGHEST OBSERVED WINDS ARE AROUND 15 KT. THE AIR TEMPERATURE/WATER TEMPERATURE DIFFERENTIAL IS NOT GOING TO IMPROVE THIS MORNING FOR MIXING AND BY THIS AFTERNOON, THE WIND FIELDS ALOFT ARE LIGHTER. THUS A CDFNTL PASSAGE DURING THE AFTERNOON WILL BRING SHOWERS, BUT NOT STRONGER WINDS TO THE AREA WATERS. WINDS WILL VEER TO A NORTHERLY PUSH BEHIND THE COLD FRONT TONIGHT, BUT THE OVERALL PRESSURE GRADIENT WILL REMAIN RELATIVELY WEAK AND EVEN WITH A BETTER AIR/WATER TEMPERATURE DIFFERENTIAL, SUB SMALL CRAFT ADVISORY CONDITIONS ARE PREDICTED TO CONTINUE. OUTLOOK... MON...MOSTLY SUB-SCA CONDITIONS. MON NIGHT/TUE...SCA CONDITIONS POSSIBLE. TUE NIGHT THRU THU...MOSTLY SUB-SCA CONDITIONS EXPECTED. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...O`HARA NEAR TERM...GIGI/HEAVENER SHORT TERM...GIGI LONG TERM...O`HARA AVIATION...GIGI/O`HARA MARINE...GIGI/O`HARA

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