Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 251458 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 958 AM EST THU DEC 25 2014 .SYNOPSIS...
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THE COLD FRONT HAS MOVED OFF SHORE. A HIGH PRESSURE SYSTEM OVER THE GULF COAST STATES WILL BUILD NORTHEAST AND REACH THE VIRGINIA COASTAL WATERS ON FRIDAY BEFORE RECEDING FARTHER OFFSHORE ON SATURDAY. A COLD FRONT IS FORECAST TO MOVE THROUGH OUR AREA SUNDAY AND THEN SLOW ITS SOUTHWARD PROGRESS AS A WAVE OF LOW PRESSURE MOVES ALONG IT ON MONDAY AND MONDAY NIGHT. A STRONG HIGH PRESSURE SYSTEM FROM CANADA SHOULD REACH THE NORTHERN PLAINS ON TUESDAY AND THEN GRADUALLY BUILD TOWARD THE MID ATLANTIC STATES ON WEDNESDAY.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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THE COLD FRONT PUSHED OFF SHORE A FEW HOURS AGO AND WILL CONTINUE TO MOVE AWAY FROM THE REGION. THE CLEARING LINE IS JUST ABOUT TO THE DELAWARE RIVER VALLEY AND WILL CONTINUE TO SLIDE EAST. THERE IS ANOTHER CANOPY OF LOW CLOUDS OVER CENTRAL PA, BUT DID NOT MAKE ANY CHANGES TO THE FORECAST SKY COVER AS DRY AIR ADVECTION SHOULD HELP TO ERODE THESE CLOUDS AS THEY TRY TO PUSH EAST INTO OUR REGION. BREEZY WESTERLY WINDS ARE EXPECTED TO CONTINUE THROUGH THE DAY. HOWEVER, THE STRONGEST WINDS MAY BE IN THE NEXT 2 TO 3 HOURS AS AFTER 18Z, THE LOW LEVEL JET DISSIPATES AND THE PRESSURE GRADIENT RELAXES. WITH COLD AIR ADVECTION ALL DAY, DO NOT EXPECT MUCH WARMING EVEN WHEN WE CLEAR OUT, BUT STILL SHOULD SEE DAYTIME HIGHS IN THE 50S FOR MOST AREAS (HIGHER TERRAIN OF THE POCONOS ARE NOT LIKELY TO BREAK OUT OF THE 40S.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... HIGH PRESSURE WILL EXPAND ACROSS THE AREA TONIGHT. FAIR WEATHER AND SEASONABLY COOL TEMPERATURES ARE IN THE FCST. LOWS WILL FALL INTO THE 30 TO 35 DEGREE RANGE IN MOST AREAS. WINDS WILL BECOME LIGHT. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... THE WRF-NMMB INITIALIZATION LOOKED BETTER THAN THE GFS AT MOST LEVELS. OUT WEST THE GFS`S TROF APPEARED TOO STRONG, WHICH IS NOT NORMALLY THE MODELING BIAS ERROR. IN SPITE OF THE START, THE OP GFS RUN KIND OF FLOWED IN THE SAME DIRECTION AS THE OTHER MODELS. ALL OF THE MODELS RESPECTIVE TO THEIR OWN PREVIOUS SOUNDING RUNS TRENDED FLATTER WITH THE WEAVES ON THE FRONT EARLY NEXT WEEK. THE BIGGEST LEAP WAS BY THE UKMET WHICH HAD BEEN TAKING A VIGOROUS LOW NW OF OUR CWA AROUND MONDAY. EVEN THE CAN GGEM WHICH IS MOST BULLISH WITH PCPN AND SNOW TRENDED FLATTER (STILL BULLISH THOUGH). WHILE THE 00Z RUN WAS FLATTER GIVEN HOW SUBTLE DIFFERENCES WITH EACH MODEL SOUNDING RUN HAS BEEN CAUSING CWA SIZE DISPLACEMENT OF PCPN FIELDS, THIS FORECAST PACKAGE HAS STAYED CLOSE TO CONTINUITY UNTIL SUCCESSIVE SOUNDING RUNS START PRODUCING A TRENDING AND CONSISTENT OUTCOME. WHAT WE DO KNOW IS THAT THE LONG TERM WILL START UNSEASONABLY MILD AND BECOME COLDER THAN NORMAL BY WEDNESDAY AS THE PV SETTLES AROUND BAFFIN ISLAND AND THE UPPER HUDSON BAY. RELATIVE TO NORMAL WHAT WILL OCCUR ON FRIDAY AND SATURDAY IS MORE OFF KILTER THAN THE END OF THE LONG TERM, EVEN IF IT WILL FEEL COLDER THAN IT REALLY IS. ALSO DURING THIS TRANSITION PERIOD, THE CHANCES FOR SNOW AS A PTYPE WILL INCREASE THROUGHOUT OUR CWA. THE QUESTION REMAINS WHETHER OR NOT THERE WILL BE ENOUGH MOISTURE AND LIFT TO HAVE THAT PTYPE GENERATE AND REACH THE GROUND. ANYTIME A HIGH PRESSURE SYSTEM BUILDS IN FROM TEXAS, ITS NOT GOING TO BE COLD. COUPLED WITH THE CURRENT INTENSE LOW PRESSURE SYSTEM LIFTING MORE NORTH THAN EAST DOESNT MAKE FOR A COLD RECIPE. SKYWISE THIS HAS BEEN ONE DEPRESSINGLY CLOUDY MONTH. BUT FOR ONCE, THE FORECAST SOUNDINGS ARE NOT INDICATING ANY TRAPPED STRATOCU UNDERNEATH THE INVERSION AS WELL AS GIVING US CONVECTIVE TEMPS IN THE 90S AND LOW 100S. DARE WE PREDICT, A MOSTLY SUNNY DAY? GFS MOS MAX TEMPS SUPPORT THE OP NAM`S THERMAL FIELDS MORE SO THAN ITS OWN MOS GUIDANCE. MAX TEMPS LEANED STRONGLY THE FORMER`S WAY. FRIDAY NIGHT SHOULD BE A DECENT RADIATIONAL COOLING NIGHT. WE LEANED COLDER THAN STAT GUIDANCE IN OUTLYING AREAS BECAUSE OF THIS. AS CAUTIOUSLY OPTIMISTIC AS WE WERE ABOVE THE LACK OF CLOUD COVER ON FRIDAY, WE ARE NOT AS MUCH NORTH FOR SATURDAY. SOME MODELS ARE SHOWING A WEAK WARM FRONT NEAR THE NORTHERN PART OF OUR CWA AS WELL AS THE UBIQUITOUS TRAPPED LOW LEVEL MOISTURE. WE MET THIS HALFWAY FOR NOW GIVEN THAT THE PREDECESSOR AIR MASS SHOULD BE STARTING DRY. THERE IS BETTER MODEL FCST SOUNDING AGREEMENT ABOUT MAX TEMPS. HERE WE ARE CLOSEST TO THE STAT GUIDANCE THAT SUGGESTED THE SAME: AN ECMWF AND GFS MOS BLEND. CLOUDS SHOULD START INCREASING ON SATURDAY NIGHT, VERY LOW CHANCE OF A SHOWER SNEAKING INTO THE POCONOS BEFORE DAWN, TOO LOW FOR NOW TO INCLUDE. ON SUNDAY, THE PCPN ASSOCIATED WITH THE COLD FRONT HAS LESS OF AN ANAFRONT LOOK TO IT, SO WE OPTED TO CALL IT SHOWERS. FCST SOUNDINGS INDICATE THAT THE SUB 850MB LAYER IS WARM ENOUGH FOR RAIN AS A PTYPE. FROM HERE THE FORECAST STARTS LAPSING INTO GREATER UNCERTAINTY BECAUSE OF MODELING HANDLING OF THE TROFFING IN THE SOUTHWESTERN CONUS. THE UNCERTAINTY IS FURTHER COMPLICATED BY THE POSSIBILITY OF CONVECTION IN THE FAR NORTHWEST GULF AND MODELING HANDLING OF EACH IMPULSE CORRECTLY. SO WHILE THERE IS STILL DECENT CONSENSUS ABOUT AN UPPER AIR IMPULSE FOR SUNDAY NIGHT, GEOGRAPHICALLY IT WAS SAGGED FARTHER SOUTH. THE FLOW ALOFT OVER THE EASTERN CONUS IS CONFLUENT, SO ONE WOULD EXPECT THE SHEARING AND DAMPENING OF IMPULSES. ON THE OTHER HAND, MODELS OFTEN WEAKEN THEM TOO QUICKLY. HIGHEST POPS MONDAY NIGHT ARE SOUTH OF THE MASON AND DIXON LINE. FORECAST SOUNDINGS ARE INDICATING SNOW AS A POSSIBLE PTYPE ABOUT AS FAR SOUTH AS THE PA TURNPIKE/I195 CORRIDOR LATE. SOUNDINGS SO FAR ARE NOT INDICATING MUCH SLEET OR FREEZING RAIN AS THERE IS NO STRONG SOUTHERLY PUSH OF COLD AIR AT EITHER 925MB OR THE SFC. IT GETS EVEN MORE UNCERTAIN MONDAY INTO MONDAY NIGHT AS THE LATEST ECMWF AND GFS HAVE TRENDED MUCH MORE SUBDUED WITH THE WAVE ON THE FRONT. AS STATED ABOVE UNTIL WE SEE SUCCESSIVE SOUNDING RUNS INDICATE SIMILAR SOLUTIONS AND WITH SOME GEFS MEMBERS WETTER, WE KEPT THE CHANCE OR SLIGHT CHANCE FOR PCPN. WHILE THE CHANCES FOR SNOW INCREASE FARTHER NORTH IN OUR CWA, THE CHANCES FOR PCPN ARE LESS. ON TUESDAY DRY OR NOT, THE MODELS ARE PREDICTING A CHANNELIZED VORT MAX TO MOVE THROUGH. THIS WAS ENOUGH FOR THE PGFS TO GENERATE PCPN OVER OUR CWA. WE KEPT IN SLGT CHC POPS. THERMALLY WERE PCPN TO OCCUR IN OUR CWA TUESDAY, IT WOULD BE COLD ENOUGH FOR SNOW IN MOST AREAS. WE KEPT TUESDAY NIGHT AND WEDNESDAY DRY. WITH THE RETURN OF THE -EPO RIDGE, THE HIGH PRESSURE ENTERING THE CONUS IS ORIGINATING IN SIBERIA. ITS FIRST ENTERING THE CONUS IN THE NORTHERN PLAINS, SO IT WILL LOSE SOME OF ITS FEROCITY AS IT MOVES EAST. REGARDLESS BELOW NORMAL TEMPERATURES ARE EXPECTED AS IT COMES CLOSER AT THE END OF THE LONG TERM. && .AVIATION /15Z THURSDAY THROUGH MONDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. HERE`S SOMETHING WE HAVEN`T HAD MUCH OF A CHANCE TO SAY LATELY: VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. MOST PLACES SHOULD BE BREAKING OUT OF THE CLOUDS SOON. FEW TO SCT040 MAY MOVE IN FROM THE WEST, BUT DRY AIR SHOULD HELP TO ERODE THEM AS THEY DO. BREEZY WESTERLY WINDS IN THE WAKE OF THIS MORNING`S COLD FRONT SHOULD CONTINUE THROUGH MOST OF THE DAY, THOUGH THE STRONGEST WINDS MAY BE THROUGH 18Z. AFTER 18Z, THE PRESSURE GRADIENT RELAXES. BY THIS EVENING, WINDS SHOULD BE RELATIVELY LIGHT. OUTLOOK... FRIDAY AND SATURDAY...VFR. SATURDAY NIGHT...SOME MVFR CIGS POSSIBLE NORTHWEST AIRPORTS, VFR CIGS ELSEWHERE. SUNDAY INTO MONDAY...MVFR, POSSIBLY IFR, CONDITIONS POSSIBLE AT TIMES AS WAVES OF PRECIPITATION MOVE FROM NORTH TO SOUTH ACROSS THE AREA. THE NORTHERN PART OF THE PRECIPITATION SHIELD COULD BE SNOW.
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&& .MARINE...
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WESTERLY WINDS CONTINUE WITH A SLIGHT SHIFT TO NORTHWESTERLY POSSIBLE BY THIS AFTERNOON. WIND SPEEDS SHOULD REMAIN IN THE SCA GUST RANGE FOR THE DAYTIME HOURS AT LEAST, LINGERING INTO THE EVENING HOURS ON THE ATLANTIC COASTAL WATERS. OUTLOOK... FRIDAY THROUGH MONDAY...SUB SMALL CRAFT ADVISORY CONDITIONS EXPECTED. A WEAK COLD FRONTAL PASSAGE SHOULD OCCUR ON SUNDAY. LOWEST CONFIDENCE IS ON MONDAY AS A WAVE OF LOW PRESSURE IS PREDICTED TO FORM SOUTH OF THE AREA WATERS ON THE MENTIONED FRONT. ITS POSSIBLE THAT SMALL CRAFT ADVISORY CONDITIONS MIGHT OCCUR IF THIS LOW INTENSIFIES FASTER THAN WE ARE CURRENTLY FORECASTING.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EST THIS EVENING FOR ANZ431- 450>455. SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ430. && $$ SYNOPSIS...GIGI/GORSE NEAR TERM...JOHNSON/O`HARA SHORT TERM...O`HARA LONG TERM...GIGI AVIATION...GIGI/JOHNSON/O`HARA MARINE...GIGI/JOHNSON/O`HARA

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