Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 202125 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 425 PM EST SAT DEC 20 2014 .SYNOPSIS...
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HIGH PRESSURE WILL SLOWLY BUILD SOUTHWESTWARD INTO THE REGION FROM ATLANTIC CANADA THROUGH MONDAY. LOW PRESSURE WILL ORGANIZE OFF THE CAROLINAS MONDAY NIGHT AND MOVE NORTHEASTWARD OFFSHORE ON TUESDAY. MEANWHILE...ANOTHER AREA OF LOW PRESSURE WILL DEVELOP OVER THE OHIO VALLEY AND MOVE NORTHWARD INTO QUEBEC...LEADING TO A STRONG COLD FRONTAL PASSAGE ON THURSDAY NIGHT. HIGH PRESSURE WILL BUILD IN ON FRIDAY AND A WEAKER COLD FRONT MAY APPROACH THE REGION NEXT WEEKEND.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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WEAK HIGH PRESSURE WILL REMAIN ACROSS THE AREA TONIGHT. THERE IS PLENTY OF MOISTURE TRAPPED BELOW THE INVERSION WHICH IS AROUND 4K-5K FT ALOFT. THE CLOUDS ARE BREAKING UP SOMEWHAT JUST TO THE WEST AS OF MID-AFTERNOON...SO SOME BREAKS CAN BE EXPECTED THIS EVENING...MOSTLY ACROSS THE DELMARVA AND SRN NJ. ANOTHER SEASONABLY COLD NIGHT EXPECTED WITH LOWS IN THE LOW 20S NORTH AND MID OR UPPER 20S SOUTH. WINDS WILL BE LIGHT FROM THE NORTH.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
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AFTER A WEAK SHORTWAVE CROSSES THE AREA SUN MORNING...UPPER RIDGING WILL TAKE PLACE. THIS WILL HOPEFULLY ALLOW MORE SUNSHINE ACROSS THE AREA. WE HAVE WRITTEN A PARTLY TO MOSTLY SUNNY FCST FOR NOW. WE HELD ONTO SOME EXTRA CLOUD COVER ACROSS THE SRN POCONOS HOWEVER. HIGH TEMPERATURES SUNDAY WILL RISE INTO THE LOW 40S ACROSS SRN NJ AND THE DELMARVA...WHILE READINGS HOLD IN THE MID/UPPER 30S ACROSS THE NORTH/WEST AREAS. WINDS WILL REMAIN LIGHT...MOSTLY FROM THE NORTH.
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&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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HIGHLIGHTS... * FREEZING RAIN POSSIBLE MONDAY NIGHT OVER THE NORTHWEST. * INCREASING POTENTIAL FOR HEAVY RAIN CHRISTMAS EVE WITH TEMPERATURES WELL ABOVE NORMAL. * BRISK WESTERLY WIND CHRISTMAS DAY W/FLURRIES POSSIBLE. OVERVIEW... VIGOROUS MID-LEVEL DISTURBANCE AND ACCOMPANYING 160 KNOT UPPER-LEVEL JET MAX COMING ASHORE OVER THE PACIFIC NORTHWEST LATE THIS WEEKEND WILL LEAD TO A DEEP TROUGH OVER THE MISSISSIPPI VALLEY BY MID-WEEK. INITIAL PIECE OF ENERGY AHEAD OF THIS TROUGH IS EJECTED NORTHEAST AND WILL LEAD TO THE DEVELOPMENT OF AN AREA OF LOW-PRESSURE OFF THE CAROLINAS ON MONDAY. THIS WEAK FEATURE SHOULD TRACK OFFSHORE WELL SOUTHEAST OF THE REGION ON TUESDAY PER TODAYS 12Z UKMET AND GFS... FEEL THE NAM AND ECMWF ARE TOO FAR NORTH, SLOW, AND DEEP W/THIS FEATURE...THUS THEY ALSO CRANK OUT TOO MUCH QPF. NEVERTHELESS... QPF COMBINED WITH MARGINAL TEMPERATURE PROFILES OVER THE NORTHWEST COULD SUPPORT SOME LIGHT FREEZING RAIN MONDAY NIGHT. MID-LEVEL FLOW THEN BECOMES INCREASINGLY MERIDIONAL...PUMPING ANOMALOUSLY WARM AND MOIST AIR UP THE EAST COAST...SETTING THE STAGE FOR HEAVY RAIN ON CHRISTMAS EVE DAY. THE TROUGH LOOKS TO BECOME NEGATIVELY TILTED AS IT CROSSES THE REGION...LEADING TO A STRONG FRONTAL PASSAGE LATE WEDNESDAY INTO EARLY THURSDAY...WITH SOME FLURRIES POSSIBLE ON THE BACK-SIDE OF THE STORM SYSTEM. DETAILS... MONDAY... MID-LEVEL RIDGE CRESTS OVER THE REGION EARLY IN THE DAY...W/SURFACE HIGH ANCHORED ALONG THE EAST COAST IN A COLD-AIR DAMMING SIGNATURE. PRECIPITATION WILL BE LARGELY DRIVEN BY INSENTROPIC ASCENT OVER THE COLDER LOW-LEVEL AIRMASS AND WILL BEGIN LATE IN THE DAY AS MOISTURE STREAMS IN ALOFT AND LOW-LEVELS GRADUALLY SATURATE. THERE MAY BE A PERIOD OF LIGHT FREEZING RAIN OVER THE NORTHWEST AS A COLD AIR IS REINFORCED W/NORTHERLY SURFACE WINDS AND PRECIP LEADS TO EVAPORATIONAL COOLING. TUESDAY... ANY LIGHT FREEZING RAIN SHOULD END EARLY IN THE MORNING WITH STRONG WARM AIR ADVECTION ALOFT. ALTHOUGH THE BEST FORCING REMAINS WELL TO THE WEST...BROAD ISENTROPIC ASCENT AND INCREASING MOISTURE SHOULD LEAD TO SCATTERED RAIN SHOWERS THRU THE DAY. QPF SHOULD BE GENERALLY LIGHT. WEDNESDAY... A VIGOROUS TROUGH APPROACHES FROM THE WEST W/STILL SOME SPREAD NOTED FROM THE MEAN IN BOTH THE ECENS AND GEFS 500 HPA HEIGHT FIELDS... INDICATING SOME DISAGREEMENT WITH REGARD TO WHAT DEGREE IT GOES NEGATIVELY TILTED. NEVERTHELESS...A VERY DYNAMIC SYSTEM WITH SEVERAL INGREDIENTS COMING TOGETHER FOR UP TO 1-2 INCHES OF QPF...ESPECIALLY OVER THE HIGHER TERRAIN. NOTING A STRONG MID-LEVEL VORT MAX AND THE LEFT-FRONT QUADRANT OF A 160 KNOT UPPER-LEVEL JET TRAVERSING THE APPALACHIANS. ALSO NOTING STRONG WARM AIR ADVECTION AND ANOMALOUSLY HIGH /2-3 STANDARD DEVIATION/ PRECIPITABLE WATER VALUES STREAMING UP THE EASTERN SEABOARD. THUS THERE IS PLENTY OF MOISTURE AND ASCENT FOR HEAVY RAINFALL...W/THE MODELS KEYING IN ON WEDNESDAY AFTERNOON AND WEDNESDAY NIGHT FOR THE BULK OF THE PRECIP...AND THIS WILL NEED TO BE MONITORED FOR FLOODING POTENTIAL PARTICULARLY DUE TO THE HOLIDAY TRAVEL CHRISTMAS EVE. LATER SHIFTS WILL ALSO NEED TO FURTHER EVALUATE THE POTENTIAL FOR GUSTY SURFACE WINDS AND CONVECTION. THURSDAY AND FRIDAY... LOW-PRESSURE MOVES NORTHWARD INTO QUEBEC AND HIGH-PRESSURE BEGINS TO BUILD IN. TEMPERATURES WILL REMAIN ABOVE SEASONABLE LEVELS AND THERE COULD BE SNOW SHOWERS IN THE BLUSTERY NORTHWEST FLOW ON THURSDAY... PARTICULARLY NORTHWEST. SATURDAY...ANOTHER COLD FRONT MAY APPROACH THE REGION...BUT IT/S TOO EARLY TO SPECULATE...ESPECIALLY GIVEN THE UNCERTAINTY THAT THE STORM SYSTEM MOVING THROUGH THE NORTHEAST CONUS MID-WEEK COULD ADD TO THE FORECAST.
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&& .AVIATION /21Z SATURDAY THROUGH THURSDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THERE HAS BEEN PLENTY OF LOW LEVEL MOISTURE TRAPPED BELOW THE INVERSION AGAIN TODAY. CIGS HAVE BEEN MOSTLY 025-035 ACROSS THE AREA. WINDS HAVE BEEN LIGHT...MOSTLY IN THE NORTH QUADRANT. CONDITIONS WILL NOT CHANGE MUCH THIS AFTERNOON...BUT SATELLITE PICS DO SHOW SOME BREAKS IN THE DECK ACROSS NRN MD AND THE SUSQ VALLEY WHICH MAY ARRIVE ACROSS THE DEL VALLEY AROUND EVENING. MUCH OF THE GUIDANCE INDICATES MORE CLEARING (OF THE LOW CLOUDS) OVERNIGHT WITH SOME CI/CS ABOVE. WE HAVE GONE ALONG WITH THAT FOR THE TAFS...BUT A FEW SITES HOLDING ON TO LOW CLOUDS LONGER...WOULDN`T SURPRISE ME. SUNDAY...VFR EXPECTED WITH JUST SOME FEW-SCT LOW CLOUDS AND MOSTLY N OR NE WINDS. OUTLOOK... SUNDAY NIGHT AND MONDAY MORNING...VFR. MONDAY AFTERNOON...POTENTIAL FOR MVFR CIGS AS MARINE LAYER BECOMES ESTABLISHED AND STRATUS ADVECTS INLAND. MONDAY NIGHT THROUGH TUESDAY NIGHT...THE COMBINATION OF STRENGTHENING ONSHORE FLOW AND IN-SITU CAD FROM LIGHT RAIN OVERSPREADING THE TERMINALS COULD YIELD AN EXTENDED PERIOD OF MVFR/IFR CONDITIONS (CIGS WOULD BE THE MORE LIKELY CONTRIBUTOR TO IFR THAN VSBYS) MONDAY NIGHT INTO TUESDAY. WEDNESDAY...WINDS VEER MORE OUT OF THE SOUTH AS A WARM FRONT SLOWLY LIFTS NORTHWARD. RAIN IS EXPECTED TO BE THE MOST WIDESPREAD AND HEAVIEST DURING THIS PART OF THE FORECAST PERIOD. PREDOMINATELY MVFR AND IFR CONDITIONS. SOUTHERLY WINDS WILL BECOME BREEZY FOLLOWING WARM FROPA. WEDNESDAY NIGHT...COLD FRONT IS FORECAST TO MOVE THRU SOMETIME AT NIGHT. LOW CLOUDS AND RAIN WILL END FROM WEST TO EAST IN WAKE OF FROPA. THURSDAY...WESTERLY WINDS COULD BECOME STRONG BEHIND THE FRONT THURSDAY WITH BUFKIT FORECAST SOUNDINGS FROM THE 12Z GFS SHOWING THE POTENTIAL FOR 30-40 KT GUSTS.
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&& .MARINE...
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WEAK HIGH PRESSURE WILL REMAIN ACROSS THE WATERS TONIGHT AND SUNDAY. WINDS AND SEAS WILL REMAIN BELOW SCA FLAG CRITERIA. WINDS WILL MOSTLY BE NORTHERLY THROUGH THE PERIOD. OUTLOOK... SUNDAY NIGHT THROUGH MONDAY NIGHT...WINDS AND SEAS BELOW SCA CRITERIA. TUESDAY AND TUESDAY NIGHT...ONSHORE FLOW STRENGTHENS ON TUESDAY. WINDS 15-20 KT FORECAST ON TUESDAY. SEAS ARE FORECAST TO BUILD TO 5-6 FEET TUESDAY AND TUESDAY NIGHT, WARRANTING THE NEED FOR A SCA. WEDNESDAY AND WEDNESDAY NIGHT...SOUTHERLY WINDS STRENGTHEN AFTER WARM FROPA. DESPITE WINDS OF 40-50 KT FORECAST 1000 FT ABOVE THE SURFACE, THERMAL PROFILES NOT FAVORABLE FOR MIXING WITH THE SETUP OF WARM AIR MOVING ATOP THE COOLER WATERS. EXPECTING MORE OF A HIGH END SCA WITH 25-30 KT WINDS. WINDS FORECAST TO BECOME WESTERLY LATE WEDNESDAY NIGHT BEHIND A COLD FRONT BUT THE CORE OF THE COLD AIR WILL STILL REMAIN UPSTREAM OF THE WATERS. SEAS FORECAST TO INCREASE TO 6-8 FEET. THURSDAY...GUSTY WESTERLY WINDS EXPECTED. GALES CERTAINLY A POSSIBILITY.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...FRANCK NEAR TERM...O`HARA SHORT TERM...O`HARA LONG TERM...FRANCK AVIATION...KLEIN/O`HARA MARINE...KLEIN/O`HARA

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