Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 300948 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 548 AM EDT MON MAR 30 2015 .SYNOPSIS...
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A COLD FRONT WILL PASS THROUGH THE AREA EARLY THIS AFTERNOON. ON ITS HEALS WILL BE A FAST MOVING LOW PRESSURE SYSTEM WHICH SHOULD SWEEP THROUGH THE AREA LATE TUESDAY. A HIGH PRESSURE SYSTEM WILL BUILD INTO THE REGION FOR WEDNESDAY AND MOVE OFFSHORE ON THURSDAY. THE NEXT COLD FRONT SHOULD MOVE THROUGH THE REGION LATE FRIDAY. A SECONDARY COLD FRONT SHOULD MOVE THROUGH THE AREA LATE SATURDAY FOLLOWED BY A HIGH PRESSURE SYSTEM FOR THE START OF NEXT WEEK.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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DESPITE THE RATHER DRY LOWER LEVELS EARLIER THIS MORNING, IT MUST HAVE BEEN SHALLOW ENOUGH AS IT DID NOT TAKE LONG FOR THE SNOW TO REACH THE GROUND AS THE RADAR REFLECTIVITY MOVED OVERHEAD. A LEAD SHORT WAVE MOVING ACROSS THE DELMARVA AND SOUTHERN NEW JERSEY ATTM IS TEAMING UP WITH LOW-LEVEL WAA AND A LOW-LEVEL JET. THE ASSOCIATED ASCENT RESULTED IN A BURST OF SNOW FROM ABOUT PHILADELPHIA ON SOUTH AND EASTWARD. THERE WAS A COATING OF SNOW ASSOCIATED WITH A NARROWING BAND OF SNOW, WHICH IS NOW WEAKENING. THE HIGHER REFLECTIVITY SNOWING UP ON THE RADAR WITH THIS BAND APPEARS TO BE A PHASE CHANGE OCCURRING AS KACY WENT FROM SNOW TO RAIN. SOME ADDITIONAL PRECIPITATION IS DEVELOPING ACROSS THE WASHINGTON DC TO BALTIMORE AREAS AND IS MOVING NORTHEASTWARD. THIS LOOKS TO BE MAINLY LIGHT RAIN SHOWERS. THE MAIN FORCING LOOKS TO BE MAINLY ACROSS OUR SOUTHERN ZONES WHERE THE LOW-LEVEL WAA AND LOW-LEVEL JET RESIDE. WE WILL CONTINUE WITH CHC POPS FOR AT LEAST SCATTERED SHOWERS THIS MORNING. OTHERWISE, THE SYNOPTIC SETUP IS COMPRISED OF A FAST FLOW REGIME. THIS WILL ALLOW A FRONTAL BOUNDARY TO QUICKLY MOVE THROUGH OUR AREA BY MIDDAY. THIS IS ATTACHED TO LOW PRESSURE THAT WILL TRACK WELL TO OUR NORTH. THE ASSOCIATED UPPER-LEVEL TROUGH IS FAIRLY STRONG WITH EMBEDDED SHORT WAVE ENERGY, HOWEVER THERE IS NOT A LOT OF MOISTURE TO WORK WITH. THE CLOUDINESS SHOULD PERSIST THROUGH AT LEAST THE FIRST HALF OF THE DAY, THEN SOME THINNING SHOULD TAKE PLACE /ALTHOUGH STRATOCUMULUS MAY HANG ON LONGER ACROSS THE NORTHWEST ZONES/. ONCE THE FRONT SHIFTS EAST THE WINDS SWING AROUND TO THE WEST AND NORTHEAST FROM ABOUT MIDDAY ON. DESPITE A FRONT MOVING THROUGH, THE AIRMASS IS EXPECTED TO BE WARMER TODAY COMPARED TO YESTERDAY. THE FORECAST SOUNDINGS SHOW DECENT BOUNDARY LAYER MIXING DEVELOPING, AND THEREFORE IT WILL BECOME A BREEZY DAY. AS FOR THE HIGH TEMPERATURES, WE MAINLY USED AN EVEN GFS/NAM MOS BLEND.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... AN UPPER-LEVEL TROUGH IS FORECAST TO SWING ACROSS THE AREA THIS EVENING. THIS MAY MAINTAIN SOME CLOUDS ESPECIALLY ACROSS THE NORTHERN AREAS, HOWEVER ENOUGH DRYING SHOULD TAKE PLACE FOR THE SKY TO CLEAR OUT. THE FAST NORTHWEST FLOW WILL THEN DRIVE THE NEXT SHORT WAVE /CLIPPER SYSTEM/ ACROSS THE GREAT LAKES LATE. THIS WILL BE TRACKING ALONG A THERMAL GRADIENT ALOFT WITH SOME DOWNSTREAM WAA OCCURRING. AS A RESULT, SOME INCREASE IN CLOUDS MAY START TO TAKE PLACE TOWARD MORNING FROM WEST TO EAST. AS A LOW PRESSURE SYSTEM MOVES FARTHER AWAY TO OUR NORTHEAST, THE PRESSURE GRADIENT WILL RELAX AND SO WILL THE MIXING. THEREFORE, THE WINDS ARE EXPECTED TO DIMINISH FAIRLY QUICKLY IN THE EVENING. AS FOR THE LOW TEMPERATURES, WE USED MAINLY AN EVEN BLEND OF THE NAM/GFS MOS. && .LONG TERM /TUESDAY THROUGH SUNDAY/... THE GFS AND WRF-NMMB INITIALIZATION LOOKED CLOSER TONIGHT, STILL AN EDGE TO THE GFS AT 500MB. AT 850MB AND 925MB THERE ARE SOME 1-2C ERRORS WITH A SLIGHT EDGE TO THE GFS AGAIN. THE DP/DT VS LAST NIGHT OVERALL LOOKS SLIGHTLY MORE PROGRESSIVE, AS THE PENDULUM HAS SWUNG THE OTHER WAY. THE 00Z MODEL SUITE HAS MERGED SLIGHTLY WITH OUR CLIPPER LOW, STILL A FAIRLY WIDE SPREAD FOR SO CLOSE IN TIME EVENT. AS THE ECMWF AND NAM/WRF-NMMB HAVE RESPECTIVELY REPRESENTED THE DRIEST/SOUTHERNMOST AND WETTEST/NORTHERNMOST SOLUTIONS, WE ARE GOING TO REMAIN CLOSER TO THE ENSEMBLE MEAN UNTIL WE GET MORE CONTINUITY. IN REALITY THE OP GFS RUN IS CLOSE TO BOTH THE SREF AND GEFS ENSEMBLE MEAN. SLIGHTLY ON THE WET SIDE. ITS PBLY GOING TO BE TOUGH WITH PWAT VALUES PREDICTED TO GET TO 0.5 INCHES FOR SOME OF THOSE WETTER SOLUTIONS TO VERIFY. NOT SURE IF IT WILL HAPPEN AGAIN, BUT WOULDNT BE A SHOCKER IF THE 00Z OP WRF/NAM IS AMONG THE WETTEST OF THE SREF ENSEMBLE MEMBERS. LIKE LAST NIGHT, THE ECMWF MASS FIELDS (QVEC, FGEN AND JET LOCATION) ARE NOT THAT DIFFERENT FROM THE GFS. THERMALLY THE TRACK IS ALSO A CHALLENGE, BUT THERE IS MORE CONSENSUS WITH PRECIPITATION GETTING INTO THE NORTHERN PART OF OUR CWA AND BETTER CONSENSUS EXCEPT FOR THE NAM FOR HIGHER TERRAIN LOCATIONS NORTHWEST TO LEAN MOSTLY SNOW. AFTER THE SNOW TALK TO END MARCH, MILDER WEATHER WILL GREET US FOR THE START OF APRIL. THE BACK END OF THE LONG TERM HAS ITS ISSUES TOO WITH THE THE UKMET EXTREMELY PROGRESSIVE AND THE CAN GGEM AND GFS RIDING IN THE CABOOSE. THE 500MB PATTERN LOOKS PROGRESSIVE AND WITH THE INHERENT DEMISE OF THE +EPO RIDGE, BELIEVE THE WPC ROUTE OF A MORE PROGRESSIVE SOLUTION FOR THE COLD FRONT IS PREFERRED. TUESDAY AND TUESDAY NIGHT TIMING WE ARE GOING TO LEAN TOWARD THE GFS TIMING DUE TO THE MORE PROGRESSIVE DP/DT AND ALSO WAA PRECIP LIKES TO START EARLY (LOOK AT NOW). THE ANTECEDENT AIR MASS IN THE SOUTHERN HALF OF OUR CWA LOOKS TO BE WARM ENOUGH FOR MAINLY RAIN ON TUESDAY. COULD GET SOME SLEET AT THE ONSET, BUT PROBABILITY TOO LOW TO INCLUDE. UP NORTH, THE WAA IS EXPECTED TO ONLY GET TO ABOUT I80 BEFORE IT STARTS PIVOTING AS THE CLIPPER TRACKS FARTHER TO THE EAST. GIVEN THE NARROW FGEN BANDING PREDICTED WITH THIS SYSTEM, ITS TOUGH EVEN AT THIS POINT TO PICK THE AXIS OF HEAVIER PCPN. GFS DIAGS SUGGEST BETWEEN MASON DIXON AND THE I78 CORRIDOR AND WE HAVE SEEN THE ECMWF REMAIN EVEN FURTHER SOUTH. SO WHILE HIGHER TERRAIN LOCATIONS FAR NORTH WERE KEPT MAINLY SNOW, NOT CONFIDENT ENOUGH THAT THEY WOULD HAVE ADVISORY LEVEL ACCUMS AT THIS POINT TO ISSUE ONE. MENTION WILL CONTINUE IN THE HWO. TEMPERATURES ARE NEARLY A STRAIGHT GFS MOS PLAY GIVEN ITS COMPROMISE TRACK POSITION. CONFIDENCE THOUGH REMAINS LESS THAN AVERAGE. WE COULD BE TOO LOW IN DELMARVA WITH MAX TEMPS. AS THE CLIPPER PULLS OFFSHORE, COLDER AIR WILL START ADVECTING DEEPER INTO OUR CWA. MOST OF THE TIME AT THIS JUNCTURE OF THE SEASON THIS MEANS PRECIPITATION ENDS BEFORE OR RIGHT ABOUT THE TIME OF THE TRANSITION TO SNOW. WEDNESDAY HAS TRENDED COLDER. GIVEN THE OP GFS LOOKS SLIGHTLY AMPED VS ITS ENSEMBLE MEAN, OUR PREDICTED MAX TEMPS ARE WARMER THAN ITS STAT GUIDANCE. ALSO THE WRF/NAM NORMALLY DOES BETTER WITH STRATOCU/CU LEVEL CLOUDS AND ITS SOUNDINGS ARE NOT BRINGING US TO THE CONVECTIVE TEMPERATURE, EVEN IN THE POCONOS. YET ANOTHER CHILLY NIGHT ON WEDNESDAY NIGHT. THE HIGH PRESSURE SYSTEM FADES OVERNIGHT AND A GRADIENT MIGHT INCREASE OR DEVELOP TOWARD MORNING. WE SHOWED SOME OUTLYING AREA RADIATIONAL DIFFERENCES TO THE MINS, BUT NOT AS MUCH AS CLIMO. A WARMER DAY ON THURSDAY WITH THE INCREASING SOUTHWEST GRADIENT. MAX TEMPS ARE CLOSER TO THE PREDICTED SOUNDINGS MID AFTN SUGGESTIONS THAN OFF THE SUB 850 THERMALS WHICH LOOK TO HANG ONTO A COOL WEDGE TOO LONG FOR DECENT SOUTHWEST FLOW. GIVEN BETTER MODELING FRONT END CONSENSUS, WE LOWERED POPS FURTHER FOR THURSDAY AFTERNOON. TIMING UNCERTAINTIES ENOUGH TO KEEP CHANCE POPS IN FOR THURSDAY NIGHT. ALTHOUGH BETTER CHANCES FOR SHOWERS AND THUNDERSTORMS (STILL UNSTABLE AT THE SHOWALTER LEVEL) IS ON FRIDAY AND FRIDAY NIGHT. THERE ARE MODELING DIFFERENCES AS TO WHETHER OR NOT A WAVE WILL FORM ON THE COLD FRONT AND ALSO WHEN AND WHERE. GEFS MEAN IS VERY SUPPORTIVE OF THE CURRENT OP ECMWF, SO REASONING FOR HIGHEST POPS AND ALSO WHY WE HAVE SATURDAY AFTERNOON DRY. A SECOND COLD FRONT IS PREDICTED TO MOVE THROUGH EARLY ON EASTER SUNDAY. FOR NOW WE ARE PASSING IT THROUGH DRY. NET EFFECT IS TO KEEP SLIGHTLY COOLER THAN NORMAL TEMPS GOING THROUGH THE WEEKEND. && .AVIATION /10Z MONDAY THROUGH FRIDAY/...
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&& .MARINE... A FRONTAL BOUNDARY WILL MOVE THROUGH THE AREA AROUND MIDDAY. THIS FRONT IS WEAK AS A WARMER AIRMASS IS TO FOLLOW FOR TODAY. A LOW- LEVEL JET OF ABOUT 40 KNOTS IS MOVING ACROSS THE AREA THIS MORNING ESPECIALLY THE CENTRAL AND SOUTHERN ZONES. WHILE THE AIRMASS IS COOLER TO START, IT WILL BE WARMING TODAY. AS A RESULT, THE BETTER MIXING SHOULD BE THIS MORNING FOR A TIME THEN SHIFT TO ALONG THE COAST DURING THE COURSE OF THE DAY AS THE BOUNDARY LAYER WARMS. AS A RESULT, THE STRONGEST WIND GUSTS SHOULD BE MOSTLY THIS MORNING FOR A TIME FROM THE SOUTH AND SOUTHWEST. THERE IS SOME UNCERTAINTY THOUGH HOW MUCH MIXING IS ACTUALLY REALIZED, HOWEVER GIVEN THE POTENTIAL AND ALSO THAT SEAS ON THE OCEAN SHOULD BUILD TO ABOUT 5 FEET WE WILL KEEP THE SMALL CRAFT ADVISORY GOING. THE WINDS ARE EXPECTED TO DIMINISH THIS EVENING WITH THE SEAS ALSO SUBSIDING. AS A RESULT, THE CONDITIONS ARE EXPECTED TO RETURN TO SUB-ADVISORY LEVELS DURING TONIGHT. OUTLOOK... TUESDAY...SUB SMALL CRAFT ADVISORY CONDITIONS EXPECTED. TUESDAY NIGHT AND WEDNESDAY...WINDS SHOULD REMAIN BELOW SCA CRITERIA UNLESS THE LOW IS STRONGER THAN FORECAST. SEAS WILL BE DEPENDENT ON THE WIND FORECAST BUT AT THIS POINT ARE GENERALLY EXPECTED TO REACH CLOSE TO SMALL CRAFT ADVISORY CRITERIA ON THE OCEAN. WEDNESDAY NIGHT...SUB SMALL CRAFT ADVISORY CONDITIONS EXPECTED. THURSDAY THROUGH FRIDAY...SOUTHERLY AND SOUTHWESTERLY WINDS WILL LIKELY INCREASE ABOVE 25 KT FOR AT LEAST PART OF THIS PERIOD. SEAS ON THE OCEAN WILL LIKELY INCREASE TO SCA CRITERIA AS WELL. WE WENT BELOW WAVE WATCH GUIDANCE AS IT NORMALLY IS TOO BULLISH IN SOUTHWEST FLOW REGIMES ESPECIALLY IN THIS INSTANCE THAT THE AIR SHOULD BE MUCH WARMER THAN THE WATER TEMPS. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT TUESDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ430- 431. && $$ SYNOPSIS...GIGI/JOHNSON NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...GIGI AVIATION...GIGI/GORSE/JOHNSON MARINE...GIGI/GORSE/JOHNSON

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