Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 252059 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 359 PM EST TUE NOV 25 2014 .SYNOPSIS...
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LOW PRESSURE NEAR FLORIDA THIS EVENING WILL STRENGTHEN AS IT PASSES NEAR THE MID ATLANTIC COAST WEDNESDAY, BEFORE RACING TO THE NORTHEAST WEDNESDAY NIGHT. HIGH PRESSURE IS FORECAST TO BUILD ACROSS THE EAST COAST FRIDAY INTO EARLY SATURDAY, BEFORE SQUEEZING TO THE SOUTH SATURDAY NIGHT. A COLD FRONT IS EXPECTED TO SAG DOWN ACROSS THE AREA SUNDAY NIGHT, BEFORE SLOWLY MOVING THROUGH THE AREA MONDAY INTO MONDAY NIGHT.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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TONIGHT...TEMPORARY CLEARING LATE THIS AFTERNOON IN E PA SOON SEALS UP WITH THICKENING AND LOWERING CLOUDS AS DYNAMICS WITH THE FLORIDA LOW AND GULF COAST SHORT WAVE FLOOD NORTHWARD. RAIN DEVELOPS RAPIDLY FROM SOUTH SOUTHWEST TO NORTH NORTHEAST AFTER MIDNIGHT AS LOW PRESSURE HEADS NEWD FOR THE NC COAST. NORTHERN FRINGE REACHING KRDG/KABE AT 11Z MAY BEGIN AS RAIN/SNOW MIX PER MARGINAL WARM BOUNDARY LAYER TEMPS (A WALL OF DEEP RH MOVING NORTHWARD IN OUR CWA AFTER MIDNIGHT). 50 50 BLENDED 12Z/25 NCEP MOS GUIDANCE.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
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UPDATE TO THIS SECTION COMING BY 330 PM. **HIGH VISIBILITY HIGH IMPACT SNOW EVENT FOR ELEVATIONS OF E PA AND NW NJ 9A-9P AND LIKELY A DEVELOPING IMPACT EVENT TO NEAR SEA LEVEL JUST NW OF I-95 WEDNESDAY AFTERNOON/EVENING** THIS FORECAST WAS A 50 50 BLEND OF THE 12Z/25 WARMER GFS AND COLDER ECMWF PARTIAL THICKNESSES AND THEN ADJUSTING THE WET BULBING 12Z/25 BLENDED MOS TEMPS COLDER, ESPECIALLY WITH THE COLUMN ALL SNOW DOWN TO 5000 FT AND ICE NUCLEI SEEDED FOR CRYSTALS BY CIRRUS. LOW PRESSURE SYSTEM HAS BEEN TRENDING FASTER ONSET/DEPARTURE SINCE FIRST DISCUSSED IN DETAILS THIS PAST WEEKEND. SNOW GRIDS ARE POSTED. WE SAW THE WARMER 18Z NAM (700MB ABOVE ZERO DOWN HERE NEAR PHL). THE SNOW AMOUNTS NEAR I-95 FROM CECIL COUNTY MARYLAND THROUGH WILMINGTON DELAWARE AND THEN NORTHEAST THROUGH PHILADELPHIA UP TO NEW BRUNSWICK ARE HIGHLY UNCERTAIN. THE ADVISORY AREA SNOW AMOUNTS ARE SHAKY AND WE MAY NOT MUCH MORE UNTIL NOON TOMORROW? THE ADVISORY MAY NEED TO BE EXPANDED SOUTHWEST INTO NE MD IN FUTURE FORECASTS. POCKETS OF POWER OUTAGES A CONCERN...ESPECIALLY JUST NORTHWEST OF INTERSTATE 95. SUGGEST TRAVEL INTO EASTERN PENNSYLVANIA AND NORTHWEST NEW JERSEY BE COMPLETED NO LATER THAN 7 AM WEDNESDAY, OR WAIT TIL AFTER 7 PM WEDNESDAY NIGHT (IE...AFTER ROADS ARE CLEANED UP/CLEARED OF SLUSHY SNOW). ITS THAT 12 HOUR WINDOW DURING THE DAY WEDNESDAY THAT IS GOING TO BECOME A SIGNIFICANT TRAVEL PROBLEM, ESPECIALLY THE HILLY AREAS. ITS UNUSUAL TO FORECAST HEAVY WET SNOW IN A 1000-500MB 543-546 THICKNESS WITHOUT A BIG (1030MB) SURFACE HIGH TO THE NORTH BUT THIS IS A SITUATION THAT I THINK HEAVY SNOW WILL OCCUR, ESPECIALLY ELEVATIONS FOR REASONS BELOW. THERMAL PROFILES AND PCPN MICROPHYSICS WITH CIRRUS SEEDING MARGINAL -2 TO -8C BELOW 15,000 FEET!! THIS IS ANOTHER TEST OF THAT PRECIPITATION MICROPHYSICS WHICH HAS WORKED SO WELL IN THE PAST. AN INTENSIFYING 500MB 12HR 180 M HFC MOVING NEWD COMBINES WITH ISALLOBARIC GRADIENT TO PULL 0-6KM 1C OR LESS WBZ AIR PROGRESSIVELY SEWD TO NEAR I95 BY 18Z AND TO THE ATLANTIC COAST BY 00Z/27 (WEDNESDAY EVENING-TOO LATE FOR ANY SNOW SNJ AND DE COASTS). ELEVATIONS CHANGE TO SNOW FIRST FROM NORTHWEST TO SOUTHEAST WEDNESDAY MORNING. PIVA AND COMMA HEAD SUGGEST SOME BANDING POTENTIAL VCNTY KRDG TO KMPO DURING THE DAY. ALSO SUPPORT FROM CSI PRODUCT OF THE NAM BUT AGAIN ITS THE NAM. THE MAX UVM RIGHT NOW IS TENDING TO SHOW UP BELOW THE IDEAL DENDRITIC GROWTH ZONE IN THE MULTI MODEL PROFILES BUT THAT CAN CHANGE. A RECORD DAILY SNOWFALL FOR ALLENTOWN PA IS LIKELY TO OCCUR (A VULNERABLE RECORD). SNOW WATER RATIOS PER INTERNAL COLLABORATION 6 TO 1 I-95 MAYBE 8 TO 1 KRDG TO KABE AND 10 OR 12 TO 1 FOR THE POCONOS. SMALL CHANCE OF MINOR TIDAL FLOODING ALONG THE DE COAST FOR TOMORROW MORNINGS HIGH TIDE. SMALL CHANCE WE`LL NEED A WIND ADVISORY FOR THE DELAWARE COAST TOMORROW MORNING. SNOW/PRECIPITATION ENDS FROM SW TO NE WEDNESDAY EVENING WITH SOME REMAINING BANDING SNOW OVER NE PA AND NW NJ. FLURRIES MAY OCCUR LATE AT NIGHT?
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/... ON THANKSGIVING, THERE WILL REMAIN A CHANCE FOR ISOLATED SHOWERS FOR PORTIONS OF THE AREA, ALTHOUGH WE EXPECT MOST AREAS TO REMAIN DRY. THERE COULD REMAIN SOME SNOW SHOWERS IN THE NORTHERLY FLOW ACROSS OUR NORTHERN AREAS, AND AS A SHORT WAVE ROUNDS THE BASE OF THE TROUGH ALOFT, IT MAY HELP CREATE AN AREA OF SHOWERS ACROSS THE SOUTHERN PORTIONS OF THE AREA AS WELL. MOST AREAS SHOULD STAY PRECIP FREE, BUT IF IT DOES SNOW ACROSS THE NORTHERN ELEVATIONS, A LIGHT ACCUMULATION COULD OCCUR WITH SOME SHOWERS. BY THURSDAY NIGHT, ANY PRECIPITATION IS EXPECTED TO END AS WE BEGIN TO LOSE GOOD MOISTURE ALOFT. FRIDAY INTO EARLY SATURDAY, HIGH PRESSURE BEGINS TO BUILD ACROSS THE EAST COAST, WHICH IS EXPECTED TO KEEP THE WEATHER MOSTLY PRECIPITATION FREE. THE MODELS DO PUSH A WEAK SHORT WAVE/VORTICITY IMPULSE ACROSS THE AREA FRIDAY NIGHT, WITH THE GFS SHOWING MORE MOISTURE TO WORK WITH THAN THE ECMWF. FOR NOW WE WILL KEEP THE WEATHER DRY UNTIL WE GET BETTER COLLABORATION BETWEEN THE TWO. THE HIGH PRESSURE PUSHES TO OUR SOUTH LATER SATURDAY INTO EARLY SUNDAY, BEFORE A FRONTAL BOUNDARY APPROACHES THE AREA SUNDAY NIGHT INTO MONDAY. MODELS ARE HINTING AT A SLIGHT CHANCE OF SHOWERS SATURDAY NIGHT INTO SUNDAY AS A COUPLE OF WEAK SHORT WAVE/VORTICITY IMPULSES SLIDE ACROSS THE AREA. HOWEVER, THE GREATER THREAT IS EXPECTED TO BE SUNDAY NIGHT INTO MONDAY NIGHT AS THE FRONTAL BOUNDARY SAGS ACROSS THE AREA. MODELS INDICATE THAT SOME MOISTURE IS LOST AS THE FRONT SAGS ACROSS THE AREA, BUT THERE WILL REMAIN A CHANCE IN THE FORECAST FOR NOW. AS HIGH PRESSURE BUILDS BACK ACROSS THE NORTHEAST ON TUESDAY, DRY WEATHER SHOULD RETURN TO THE AREA THROUGH TUESDAY. AFTER BELOW NORMAL TEMPERATURES FOR THE FIRST HALF OF THE EXTENDED THROUGH SATURDAY, A WARMING TREND IS EXPECTED FOR THE LATTER HALF OF OF THE WEEKEND INTO EARLY NEXT WEEK WITH TEMPERATURES RETURNING ABOVE NORMAL. && .AVIATION /21Z TUESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TONIGHT...VFR WITH CIGS LOWERING TO 4000 FT FROM SOUTH TO NORTH AFTER 06Z THEN RAIN BEGINS AS PER THE TAFS. LIGHT NORTHWEST WINDS TURN NORTH NORTHEAST AFTER 06Z AND GUST 15-20 KT BY DAYBREAK. WED AND WED EVENING... WIDESPREAD MVFR AND IFR CONDITIONS IN RAIN CHANGING TO SNOW EXCEPT MAINLY SNOW AT KRDG/KABE. PRECIPITATION WILL BE HEAVY AT TIMES AND IFR CONDITIONS IN ALL SNOW SHOULD OCCUR FOR A TIME WEDNESDAY IN THE I-95 TAF CORRIDOR FROM KTTN THROUGH KPNE KPHL KILG. PAVEMENT ACCUMULATIONS OF SEVERAL INCHES ARE EXPECTED AT KRDG AND KABE WHERE A SHORT PERIOD OF ONE QUARTER MILE HEAVY SNOW IS FORECAST. EVEN SLOPPY WET SNOW ACCUMULATION IS POSSIBLE AT KPHL. THIS IS A WET SNOW WHERE IT OCCURS EXCEPT MORE CRYSTALLINE VCNTY THE POCONOS WHERE IT WILL BE SLIGHTLY COLDER! CONFIDENCE IS HIGH ABOUT THE EVENT, BUT IMPERFECT REGARDING PRECIPITATION PHASE CHANGE FROM RAIN TO SNOW IN THE PHILADELPHIA AREA. OUTLOOK... THURSDAY-THURSDAY NIGHT...MOSTLY VFR. ISOLATED RAIN OR SNOW SHOWERS POSSIBLE DURING THE DAY WHICH MAY TEMPORARILY LOWER CONDITIONS. FRIDAY-SUNDAY...MOSTLY VFR. WIND GUSTS 15-20 KNOTS EACH DAY; NW FRIDAY, SW SATURDAY & SUNDAY.
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&& .MARINE...
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&& .CLIMATE... REGARDING THE MIDWEEK COASTAL STORM BRINGING SNOW TO A LARGE PORTION OF OUR REGION, WE HAVE INCLUDED DAILY SNOWFALL RECORDS BELOW FOR OUR FOUR PRIMARY CLIMATE SITES THAT HAVE A LONG-STANDING UNBROKEN PERIOD OF RECORD (POR) WITH RESPECT TO HISTORICAL SNOWFALL DATA. DAILY SNOWFALL RECORDS: NOVEMBER 26TH: NOVEMBER 27TH: PERIOD OF RECORD: ACY: TRACE 1977,1957,1955 1.2 INCHES 1978 1874 PHL: 6.0 INCHES 1898 6.9 INCHES 1949,1938 1872 ILG: 0.1 INCHES 1950 4.5 INCHES 1978 1894 ABE: 1.7 INCHES 1925 7.0 INCHES 1938 1922 OTHER COOPERATIVE SITE SHORTER HISTORICAL RECORD CAN BE FOUND AT THE NWS MOUNT HOLLY WEBSITE UNDER NOW DATA. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...WINTER STORM WARNING FROM 7 AM TO 10 PM EST WEDNESDAY FOR PAZ054-055-060>062-101-103-105. WINTER WEATHER ADVISORY FROM 9 AM TO 10 PM EST WEDNESDAY FOR PAZ070-071-102-104-106. NJ...WINTER STORM WARNING FROM 7 AM TO 10 PM EST WEDNESDAY FOR NJZ001-007>010. WINTER WEATHER ADVISORY FROM 9 AM TO 10 PM EST WEDNESDAY FOR NJZ012-015. DE...NONE. MD...NONE. MARINE...GALE WARNING FROM 4 AM TO 10 PM EST WEDNESDAY FOR ANZ431- 450>455. SMALL CRAFT ADVISORY FROM 4 AM TO 10 PM EST WEDNESDAY FOR ANZ430. && $$ SYNOPSIS...ROBERTSON NEAR TERM...DRAG 4P SHORT TERM...DRAG 4P LONG TERM...ROBERTSON AVIATION...DRAG/ROBERTSON 4P MARINE...DRAG/ROBERTSON 4P CLIMATE...

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