Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 192051 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 351 PM EST FRI DEC 19 2014 .SYNOPSIS... HIGH PRESSURE JUST NORTH OF LAKE SUPERIOR WILL GRADUALLY MOVE EASTWARD INTO NORTHERN NEW ENGLAND THRU MONDAY. A WAVE OF LOW PRESSURE WILL FORM ALONG THE MID-ATLANTIC COASTLINE ON MONDAY AND MOVE NORTHEASTWARD JUST OFFSHORE ON TUESDAY. MEANWHILE... A STRONG AREA OF LOW-PRESSURE WILL FORM OVER THE MISSISSIPPI VALLEY AND MOVE THRU THE GREAT LAKES REGION DURING THE MIDDLE OF THE WEEK...BRINGING A STRONG COLD FRONT THRU THE REGION BY THURSDAY. HIGH PRESSURE IS PROJECTED TO BUILD IN ON FRIDAY. && .NEAR TERM /UNTIL 6 AM SATURDAY/... EXTENSIVE LOW CLOUD DECK THAT COVERED THE AREA THIS MORNING HAS ERODED CONSIDERABLY THIS AFTN. CLOUD COVER PERSISTS OVER DELMARVA AND OVER NWRN NJ AND ADJ PA. GIVEN THE NWLY LOW-LVL FLOW...THINK THE CLOUDS DOWN SOUTH WILL CONT TO ERODE WHILE THE NRN AREA WILL BE MORE PERSISTENT INTO THIS EVENING. TEMPS IN CLEARING AREAS HAVE RESPONDED ONLY SLIGHTLY DUE TO THE LOW DEC SUN ANGLE. FOR TONIGHT...NW WINDS WILL CONTINUE BUT WILL BECOME LIGHTER AS CANADIAN LOW PRES MOVES AWAY AND HIGH PRES MOVES CLOSED WITH RESULTING RELAXED PRES GRAD. MOSTLY CLEAR TO PARTLY CLOUDY SKIES TONIGHT SHOULD ALLOW FOR DECENT COOLING WITH OVERNIGHT MINS GENLY 5 TO 10 DEGS COOLER THAN LAST NIGHT. && .SHORT TERM /6 AM TO 6 PM SATURDAY/... FOR SATURDAY...HIGH PRES CENTERED OVER CANADA SHIFTS EWD FROM ONTARIO INTO QUEBEC. A RIDGE AXIS IS FCST TO EXTEND SWD THROUGH THE MID-ATLANTIC REGION RESULTING IN ONLY LIGHT NLY WINDS. SOME LOW-LVL MOISTURE SHOULD REMAIN TRAPPED BELOW THE LARGE-SCALE SUBSIDENCE INVERSION BUT HARD TO SAY HOW EXTENSIVE ANY LOW CLOUDS MAY BE. THE 12-KM NAM SHOWS A THIN LOW CLOUD LAYER DEVELOPING DURG THE DAY BUT HIGHER-RES ARW/NMM AND THE GFS DO NOT. THERE WILL BE SOME HIGHER CLOUDS ALSO ASSOCD WITH THE SHRTWV NOW MOVING ENEWD OUT OF THE SRN PLAINS...HWVR POPS REMAIN NEAR ZERO. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... HIGHLIGHTS... * SLIGHT CHANCE OF SNOW SHOWERS SUNDAY MORNING MAINLY NORTH. * SNOW POSSIBLE NORTHWEST OF THE I-95 CORRIDOR LATE MONDAY THRU EARLY TUESDAY. * POTENTIAL FOR HEAVY RAIN INCREASING ON CHRISTMAS EVE DAY. OVERVIEW... MID-LEVEL BLOCKING PATTERN OVER NOAM BEGINS TO DISLODGE IN RESPONSE JET ENERGY MOVING INTO THE PACIFIC NORTHWEST THIS WEEKEND...CARVING OUT A DEEP TROUGH OVER THE MS VALLEY EARLY EARLY NEXT WEEK...WHICH LEADS TO INCLEMENT WEATHER IN THE TUESDAY THRU WEDNESDAY TIME FRAME. DETAILS... SUNDAY... SHORTWAVE LIFTING THROUGH THE REGION EARLY IN THE DAY MAY GENERATE ENOUGH LIFT ALONG WITH MARGINAL MOISTURE IN THE COLUMN TO PRODUCE SOME LIGHT SNOW SHOWERS...MAINLY DURING THE PRE-DAWN HOURS. LITTLE IF ANY ACCUMULATION EXPECTED AS MOISTURE IS VERY LIMITED. RIDGING THEN BUILDS IN SO FAIR WEATHER IS EXPECTED THE REMAINDER OF THE DAY. MONDAY AND TUESDAY... HIGH PRESSURE ANCHORS ALONG THE LEE OF THE APPALACHIANS. A SOUTHERN STREAM SHORTWAVE WILL INDUCE LOW-PRESSURE OF THE MID-ATLANTIC COAST. MODELS BRING QPF NORTHWARD INTO THE AREA ON MONDAY NIGHT INTO EARLY TUESDAY. THERMAL PROFILES ARE COLD ENOUGH FOR SNOW TO THE NORTHWEST OF THE I-95 CORRIDOR...BUT THE BEST LIFT IS FOCUSED JUST SOUTHEAST OF THIS AREA...AND THE SYSTEM COULD TRACK FURTHER TO THE SOUTH PER 12Z UKMET MODEL. STILL A LOT OF UNCERTAINTY WITH ULTIMATE TRACK. WEDNESDAY... A MID-LEVEL RIDGE WILL MOVE THROUGH THE REGION TUESDAY NIGHT INTO EARLY WEDNESDAY LEADING TO A BRIEF RESPITE BETWEEN WEATHER SYSTEMS. THEN A MID-LEVEL TROUGH IS PROJECTED TO BECOME NEGATIVELY TILTED OVER THE OHIO VALLEY ON WED...LEADING TO A MERIDIONAL FLOW ALONG THE EAST COAST...WITH THE ENTIRE COLUMN EXPECTED TO BE WELL ABOVE FREEZING ACROSS THE CWA FAVORING A RAIN EVENT. THERE ARE SEVERAL INGREDIENTS COMING TOGETHER FOR HEAVY RAIN. IN PARTICULAR...DEEP GULF MOISTURE...LOW-LEVEL ISENTROPIC LIFT...MID-LEVEL PVA...AND THE RIGHT-REAR QUADRANT OF A 140 KNOT UPPER-LEVEL JET JUST NORTH. THE SYSTEM SHOULD BE FAIRLY PROGRESSIVE BUT WILL HAVE TO MONITOR POTENTIAL FOR FLOODING. THU AND FRI... LOW-PRESSURE MOVES NORTHWARD INTO QUEBEC AND HIGH-PRESSURE BEGINS TO BUILD IN. TEMPERATURES WILL RETURN TO SEASONABLE LEVELS AND THERE COULD BE SNOW SHOWERS IN THE BLUSTERY NORTHWEST FLOW. && .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/... SMWHAT GUSTY NW WINDS WILL CONTINUE FOR A COUPLE MORE HOURS BUT SHOULD DIE DOWN SOME BY SUNSET AS THE SFC COOLS/DECOUPLES AND THE LARGER SCALE PRES GRADIENT RELAXES. LIGHT NW WINDS WILL CONTINUE OVERNIGHT. THE EARLIER LOW CLOUDS HAVE MOSTLY DISSIPATED AND ATTM ARE NOT EXPECTED TO RETURN TONIGHT. SOME LOW CLOUDS ARE POSSIBLE ON SATURDAY BUT SHOULD NOT BE AS EXENSIVE AS THIS MORNING. WINDS ON SATURDAY WILL BE LIGHT NORTHERLY AS A HIGH PRESSURE RIDGE MOVES OVER HEAD. OUTLOOK... SUNDAY...VFR CONDITIONS EXPECTED. MONDAY AND TUESDAY...IFR POSSIBLE IN SHRA AND SHSN. WEDNESDAY...IFR POSSIBLE IN RA AND FG. && .MARINE... SUB-SCA CONDS ARE EXPECTED FOR THE NEXT 24 HOURS AT LEAST. SMWHT GUST NW WINDS THIS EVENING WILL GRADUALLY DIMINISH TONIGHT THROUGH SATURDAY AS A RIDGE OF HIGH PRES MOVES OVERHEAD. SEAS ARE CURRENTLY RUNNING 2 TO 3 FT BUT THEY SHOULD GRADUALLY DIMINISH ALSO. OUTLOOK... SUNDAY AND MONDAY...SUB-SCA CONDITIONS EXPECTED. TUESDAY...SCA MAY BE NEEDED FOR BUILDING SEAS. WEDNESDAY...GALE WARNING MAY BE NEEDED. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...FRANCK NEAR TERM...AMC SHORT TERM...AMC LONG TERM...FRANCK AVIATION...AMC/FRANCK MARINE...AMC/FRANCK

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