Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 290752 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 352 AM EDT SUN MAR 29 2015 .SYNOPSIS...
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A HIGH PRESSURE SYSTEM CROSSING THE CENTRAL APPALACHIANS WILL SINK SOUTHEAST AND PASS OFF THE CAROLINA COASTAL WATERS THIS AFTERNOON. A COLD FRONT WILL MOVE THROUGH THE REGION ON MONDAY. ON ITS HEALS WILL BE A FAST MOVING LOW PRESSURE SYSTEM WHICH SHOULD SWEEP THROUGH THE AREA LATE TUESDAY. HIGH PRESSURE WILL BUILD INTO THE REGION FOR WEDNESDAY AND MOVE OFFSHORE ON THURSDAY. ANOTHER COLD FRONT IS FORECAST TO MOVE THROUGH THE FORECAST AREA EARLY ON SATURDAY.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A STRONG UPPER-LEVEL TROUGH WILL CONTINUE TO SHIFT TO OUR EAST THIS MORNING. AS THIS OCCURS, ADDITIONAL DRYING AND INCREASING SUBSIDENCE WILL OVERTAKE THE REGION /ANY LINGERING FLURRIES ACROSS THE NORTHEAST ZONES ENDING EARLY/. HIGH PRESSURE AT THE SURFACE WILL GRADUALLY BUILD INTO OUR AREA, ALTHOUGH ITS CENTER SHOULD TEND TO SETTLE TO OUR SOUTH THIS AFTERNOON. THIS HIGH IS WHAT IS RESPONSIBLE FOR THE VERY COLD AIRMASS IN PLACE, ALTHOUGH SOME MODERATION IS EXPECTED THIS AFTERNOON. AFTER A VERY COLD START, SOME WARMING ALOFT ALONG WITH SUNSHINE WILL HELP TO REBOUND THE TEMPERATURES THIS AFTERNOON. THE SURFACE FLOW WILL ALSO START TO SHIFT TO THE WEST AND SOUTHWEST THIS AFTERNOON, HOWEVER TURNING MUCH LIGHTER THAN YESTERDAY. OVERALL, A DRY DAY IS EXPECTED AND EVEN THOUGH AFTERNOON TEMPERATURES WILL BE HIGHER THAN YESTERDAY IT WILL STILL BE SEVERAL DEGREES BELOW WHERE WE SHOULD BE FOR THIS TIME OF THE YEAR. WE USED A NAM/GFS MOS BLEND FOR THE HIGH TEMPERATURES, ALTHOUGH LEANED CLOSEST TO THE WARMER GFS MOS.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
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A FAST FLOW REGIME WILL PLACE OUR NEXT STORM SYSTEM ON OUR DOORSTEP TOWARD DAYBREAK MONDAY. THE EVENING WILL START WITH SURFACE HIGH PRESSURE SLIDING TO OUR SOUTH AND SOUTHEAST, AS AN UPPER-LEVEL RIDGE ALSO SHIFTS OFFSHORE. THIS WILL ALLOW THE FLOW TO BACK SOME MORE AND BECOME SOUTH-SOUTHWEST. A SHORT WAVE TROUGH MOVING ACROSS THE GREAT LAKES SHOULD QUICKLY BE APPROACHING OUR AREA LATE. THE MODEL GUIDANCE SHOWS AN INCREASING LOW-LEVEL JET ARRIVING OVERNIGHT FROM THE SOUTHWEST. THIS WILL HELP TO DRIVE WAA ALOFT AND BRING IN SOME DEEPENING MOISTURE. THE FORECAST SOUNDINGS INDICATE AN INCREASE IN MID TO HIGH LEVEL CLOUDS WILL THEN THICKEN AND LOWER LATE. WHILE THE COLD FRONT REMAINS TO OUR WEST LATE, THE ASSOCIATED WAA AND LOW-LEVEL JET SHOULD PROVIDE ENOUGH LOW TO MID LEVEL ASCENT TO PRODUCE SOME SHOWERS. THESE SHOULD BE ARRIVING TOWARD DAYBREAK. THE OVERALL AIRMASS IN THE LOWER LEVELS MAY STILL BE A BIT TO DRY, THUS ANY PRECIPITATION LOOKS TO BE LIGHT. IN ADDITION, SOME ADDED EVAPORATIVE COOLING MAY ALSO ALLOW FOR SOME SNOW SHOWERS ESPECIALLY ACROSS THE NORTH. WE ARE EXPECTING THE TEMPERATURES TO BOTTOM OUT DURING THE FIRST HALF OF THE NIGHT, THEN BE STEADY OR EVEN RISE SOME TOWARD MORNING DUE TO THE SOUTHERLY FLOW, INCREASED CLOUDS AND WAA. THE POPS INCREASE INTO SLIGHT CHC TO THE LOWER RANGE OF CHC WELL AFTER MIDNIGHT FROM WEST TO EAST. AS FOR THE LOW TEMPERATURES, WE USED A NAM/GFS MOS BLEND WITH SOME DOWNWARD ADJUSTMENTS FOR THE TYPICALLY COLDER SPOTS. WE SHOULD BE ABLE TO DROP FAIRLY QUICKLY TO START THE EVENING GIVEN LIGHT WINDS, NOT MUCH CLOUDS AND LOW DEW POINTS. WE DID SHOW A GRADUAL INCREASE THEN WELL AFTER MIDNIGHT.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/...
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GFS HAD A VERY GOOD INITIALIZATION AT 500MB AND 850 VS THE WRF- NMMB. BOTH MODELS INITIALIZED EQUALLY WELL AT 925MB. LOOKS LIKE THEY CAUGHT UP TO THE AIR MASS, NOT AS MUCH COLD BIAS. THE DP/DT TREND AGAIN, JUST LIKE YESTERDAY WAS SLOWER AND MORE AMPLIFIED. THUS THIS LEANS AWAY FROM THE FASTER ENVELOPE OF SOLUTIONS IN THE LONG TERM. THE MIDWEEK CLIPPER STILL SHOWING ABOUT A 120 MILE WIDE WIDTH IN TRACK DIFFERENCES WITH FAIRLY LARGE THERMAL AND PTYPE IMPLICATIONS ACROSS OUR CWA. WHILE WE WILL CALL ON AN OLDIE BUT GOODIE THAT THE NAM/WRF HAS THE TRACK OF THE CLIPPER TOO DEEP INTO THE COLD AIR, BOTH THE SREF AND GEFS LEAN ITS WAY AND DEFINITELY DO NOT SUPPORT THE OP ECMWF OR UKMET. MODEL DIAGS ON THE ECMWF SHOW JUST AS MUCH FGEN FORCING, ADEQUATE JET AND MID LEVEL QVEC CONVERGENCE AS THE GFS SO NOT FEELING WARM AND CUDDLY ABOUT ITS SHREDDED SOLUTION. WITH THE ATTENDANT SHORT WAVE COMING INTO DEEPER RAOB COVERAGE IN CANADA WITH THE NEXT SOUNDING RUN, WE DID NOT MAKE TOO MANY CHANGES FROM OUR PREVIOUS SOLUTION. FURTHER DOWN THE ROAD, THE GFS IS SLOWLY WORKING ITS WAY TOWARD THE ECMWF SOLUTION OF A SLOWER CFP AT THE END OF THE WEEK. THE GEFS IS SLOWER THAN THE OP AND HERE WE HAVE GONE ALONG WITH CONTINUITY OF A SOLUTION CLOSER TO THE ECMWF. ON MONDAY MORNING, WE KEPT LOW POPS THRUT FOR A COUPLE OF HOURS AS THE CDFNT APPROACHES OUR AREA. GIVEN THAT THE WAA PUSH IS DONE AND THE BOUNDARY LAYER IS CONTINUING TO WARM, PTYPE BECOMES RAINIER. WE DID KEEP LOW CHANCE OF RAIN SHOWERS INTO THE AFTERNOON NORTH AS A PAIR OF SHORT WAVES HAVE YET TO MOVE THROUGH. THE FCST SOUNDINGS WOULD SUPPORT DEEPER MIXTURE FOR SHOWERS. GOING ALONG WITH THE THEME OF A SLOWER EVOLUTION, WE MAINTAINED PREDICTED MAX TEMPS. STAT GUIDANCE LOOKS REASONABLE (UNLESS THE CAA IS EVEN SLOWER). IT WILL BECOME WINDIER AS THE DAY PROGRESSES, GUSTS MIGHT EXCEED 30 MPH. WITH A GENERAL FAST PACE, WINDS SHOULD DECREASE OVERNIGHT ON MONDAY AND SHOULD PERMIT SOME RADIATIONAL COOLING IN OUTLYING AREAS PARTICULARLY. WE DO NOT BELIEVE CLOUDINESS WILL INCREASE IN TIME TO STOP THIS. MIN TEMPS ARE A STAT GUIDANCE BLEND. THEN ON TUESDAY AND TUESDAY NIGHT. ITS PRETTY UNIVERSAL THAT THE MODELS ARE THERMALLY COLD FOR MAINLY SNOW OVER THE HIGHER TERRAIN LOCATIONS OF OUR CWA. THE DIFFERENCES THOUGH REMAIN THAT SOME OP MODELS DO NOT BRING MEASURABLE PCPN INTO THIS AREA. ON THE OTHER END OF THE SPECTRUM, THE WRF-NMMB IS QUITE VIGOROUS WITH THE NORTHERN SOLUTION QPF, BUT WAY HIGHER THAN THE SREF MEAN. GIVEN THE FCST PWAT IS ONLY AROUND .5 SUSPECT THAT WHEN THE 03Z SREF IS RUN THAT THE OP WRF-NMM IS GOING TO BE EITHER THE WETTEST OR ONE OF THE WETTEST OF THE MEMBERS. AT THE OTHER END OF THE SPECTRUM, THE ECMWF IS WAY SUPPRESSED AND DRY NORTH. WHERE THERE IS MODELING CONSENSUS (CENTRAL) WE INCREASED POPS TO LIKELY. ELSEWHERE WE KEPT CHANCE POPS. ONCE WE GET AWAY FROM THE HIGHER TERRAIN, WITH A STRONG, WARMING WRLY FLOW IT LOOKS DIFFICULT TO MAINTAIN MUCH SNOW EXCEPT FOR POSSIBLY AT THE START OR TAIL END OF THE EVENT. NOT CONFIDENT ABOUT MAX TEMPS AT ALL AT THIS JUNCTURE GIVEN TRACK DIFFERENCES. THIS HAS THE LOOK OF LARGE FORECAST ERRORS. IN SPITE OF IMPACT DIFFERENCES, ALL THE MODELS AGREE THAT THIS EVENT SHOULD BE DONE OVERNIGHT TUESDAY WITH MOST FAVORING AN EXIT DURING THE EVENING. THEN SUNSHINE SHOULD RETURN ON WEDNESDAY AS CONVECTIVE TEMPS ARE PREDICTED TO BE OUT OF REACH. THERE WAS A THERMAL DOWNTICK FOR WEDNESDAY, BUT AIR MASS MODIFICATION BY AFTERNOON WOULD GET US CLOSE TO CONTINUITY FOR MAX TEMPS. SO ONLY A SLIGHT DOWNWARD TWEAK. LAST WEEK WE HAD A ONE DAY WONDER OF WARMER WEATHER. THIS WEEK LOOKS LIKE WE ARE GOING TO HAVE A TWO DAY WONDER OF WARMER WEATHER. (MAYBE NEXT WEEK WE CAN TRY FOR THE HAT TRICK?). MAX TEMPS ON BOTH THU AND FRI ARE PREDICTED TO BE WARMER THAN NORMAL. THURSDAY SHOULD BE THE DRIER OF THE TWO DAYS WITH JUST LOW CHANCES OF SHOWERS AS A WEAK WARM FRONT MOVES THROUGH. FRIDAY, ESPECIALLY THE AFTERNOON AND EVENING, HAVE THE GREATER CHANCE OF SHOWERS OCCURRING. AS OUR PREDECESSORS NOTED, IT IS UNSTABLE ALOFT AND SINCE BOTH THE GFS AND ECMWF AGREE ON THIS, WE ADDED ISOLATED THUNDER. THEN COOLER AND BREEZIER WEATHER SHOULD RETURN FOR THE WEEKEND.
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&& .AVIATION /08Z SUNDAY THROUGH THURSDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY, AND SURROUNDING AREAS. TODAY...VFR. NORTHWEST WINDS 10-15 KNOTS WITH LOCAL GUSTS TO 20 KNOTS EARLY, BECOMING WEST 5-10 KNOTS BY LATE AFTERNOON. THE WINDS SHOULD THEN GO MORE SOUTHWESTERLY NEAR EARLY EVENING. TONIGHT...VFR OVERALL, HOWEVER CLOUDS INCREASE AND LOWER AHEAD OF THE NEXT SYSTEM. A FEW SNOW OR RAIN SHOWERS MAY BE NEARING AREAS WEST OF KPHL TOWARD DAYBREAK. SOUTHWEST WINDS LESS THAN 10 KNOTS. OUTLOOK... MONDAY...MVFR CEILINGS AND VISIBILITIES POSSIBLE IN SHRA AND SHSN PRIMARILY IN THE MORNING, OTHERWISE VFR EXPECTED. COLD FRONT WILL BRING AN ABRUPT SHIFT OF GUSTY NORTHWESTERLY WINDS. MONDAY NIGHT...VFR WITH DIMINISHING WINDS. TUESDAY...MVFR CEILINGS AND VISIBILITIES WITH MAINLY RAIN POSSIBLE CENTERED ON THE AFTERNOON AND EVENING. SNOW POSSIBLE HIGHER TERRAIN AIRPORTS. WEDNESDAY THROUGH THURSDAY...MOSTLY VFR CONDITIONS. SOUTHWEST WINDS ON THURSDAY SHOULD BECOME GUSTY.
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&& .MARINE...
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HIGH PRESSURE BUILDS IN ACROSS THE AREA TODAY BEFORE SETTLING TO OUR SOUTH AND EAST TONIGHT. THIS WILL RESULT IN THE WINDS DIMINISHING THROUGH THE DAY. AS THE FLOW LESSENS, A SHIFT TO THE WEST AND THEN SOUTHWEST IS EXPECTED BY LATE AFTERNOON. THE SEAS ARE STILL NEAR 5 FEET ON PORTIONS OF THE COASTAL WATERS AND THE GUSTS ARE MARGINAL. THEREFORE, WE WILL CANCEL THE ADVISORY FOR OUR NORTHERN ZONES. THE ADVISORY WILL REMAIN IN EFFECT FOR OUR SOUTHERN WATERS FOR NOW AS SEAS ARE RIGHT AROUND 5 FEET STILL. THE ADVISORY FOR THE UPPER DELAWARE BAY WILL ALSO BE CANCELLED. FOR TONIGHT, A LIGHT SOUTHERLY FLOW WILL THEN INCREASE LATE AS A LOW-LEVEL JET ARRIVES AHEAD OF OUR NEXT SYSTEM. THE FORECAST SOUNDINGS SHOW THAT ENOUGH MIXING IS MAINTAINED TO ALLOW 25-30 KNOTS TO REACH THE SURFACE. THERE IS WAA OCCURRING, HOWEVER IT MAY NOT BE STRONG ENOUGH TO AFFECT THE MIXING. THEREFORE, A NEW SMALL CRAFT ADVISORY MAY BE NEEDED STARTING LATE TONIGHT. THE SOUTHERLY FLOW WILL ALSO BUILD THE SEAS ONCE AGAIN LATER TONIGHT. OUTLOOK... MONDAY AND MONDAY NIGHT...THE COLD FRONT SHOULD SWEEP THROUGH MONDAY, BRINGING AN ABRUPT SHIFT OF WESTERLY AND NORTHWESTERLY WINDS. GUSTS NEAR OR ABOVE 25 KT WILL BE POSSIBLE DURING THE DAY. SEAS WILL BE SLOW TO SUBSIDE ON THE OCEAN, PROBABLY TAKING UNTIL MONDAY EVENING. TUESDAY THROUGH WEDNESDAY...WINDS ARE EXPECTED TO STAY BELOW SCA CRITERIA THROUGH THIS PERIOD. HOWEVER, IF THE PASSING LOW PRESSURE SYSTEM IS STRONGER THAN FORECAST, WINDS ABOVE 25 KT ARE POSSIBLE PRIMARILY TUESDAY NIGHT. SEAS NEAR OR ABOVE 5 FT ARE POSSIBLE ON THE COASTAL WATERS THROUGH THIS TIME, BUT THERE IS STILL CONSIDERABLE UNCERTAINTY. WEDNESDAY NIGHT AND THURSDAY...INCREASING SOUTHERLY AND SOUTHWESTERLY FLOW WILL LIKELY RESULT IN ANOTHER ROUND OF SCA CONDITIONS ON THURSDAY.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT TODAY FOR ANZ431-452>455.
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&& $$ SYNOPSIS...GIGI/JOHNSON NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...GIGI AVIATION...GIGI/GORSE/JOHNSON MARINE...GIGI/GORSE/JOHNSON

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