Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 251607 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1107 AM EST TUE NOV 25 2014 .SYNOPSIS... HIGH PRESSURE OVER THE OHIO VALLEY WILL BUILD INTO OUR REGION LATE TODAY. THEN, A STORM WILL DEVELOP NEAR THE SOUTHEASTERN UNITED STATES COAST TONIGHT AND STRENGTHEN AS IT MOVES NORTHEAST...PASSING EAST OF CAPE COD EARLY THANKSGIVING MORNING. A LARGE AREA OF HIGH PRESSURE WILL THEN BUILD IN FROM THE CENTRAL PART OF THE NATION FOR FRIDAY THROUGH SATURDAY BEFORE IT MOVES OFFSHORE ON SUNDAY. A COLD FRONT ASSOCIATED WITH AN AREA OF LOW PRESSURE IN EASTERN CANADA WILL CROSS THE REGION SUNDAY OR MONDAY. && .NEAR TERM /THROUGH TONIGHT/... QUIET WEATHER... FOR THOSE IN THE WARNING AREA...GET YOUR WORK/ERRANDS DONE TODAY. REMAINDER OF TODAY...LOTS OF CLOUDS WITH WEAK HIGH PRESSURE CENTRAL APPS. CIRRUS GENERATED BY THE RRQ OF 250 MB JET AXISED NE-SW TO THE WEST OF THE APPALACHIANS WITH 210KT SPEED MAX`S MODELED ST LAWRENCE VALLEY. WET BULBS START LOWERING IN CAA WITH WESTERLY WIND GUST TO 20 KT. NO SIGNIFICANT CHANGE TO THE FORECAST AT THIS TIME. TONIGHT...RAIN DEVELOPS FROM SOUTH SOUTHWEST TO NORTH NORTHEAST AFTER MIDNIGHT AS LOW PRESSURE HEADS NEWD FOR THE NC COAST. NORTHERN FRINGE MAY REACH I80 AT 12Z AS START AS SNOW THERE AT SUNRISE (WALL OF RH). NO CHANGE AT THIS TIME TO ANY GRIDS. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... **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** 930 AM ESTF: FIRST WARNING ISSUANCE AND SOON STERLING JOINS US. LOW PRESSURE SYSTEM HAS BEEN TRENDING FASTER ONSET/DEPARTURE SINCE FIRST DISCUSSED IN DETAILS THIS PAST WEEKEND. WE WONT CHANGE ANY SNOW TOTAL GRIDS AT THIS TIME. WE CONTINUE MORE UNCERTAINTY SOUTHEAST OF THE WARNING AREA BUT 12Z/25 NAM PROFILE IS COLDER AT PHL WHICH COULD MEAN 3 TO 6 INCHES THERE EVEN DURING THE DAY. POCKETS OF POWER OUTAGES A CONCERN...ESPECIALLY NEAR 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. BARRING THE OFF LINE CHATTER OF AN IGW WHICH I DONT THINK WILL OCCUR IN THIS SITUATION BECAUSE I THINK WE`RE LACKING A COUPLE OF ELEMENTS INCLUDING A DRAMATIC SHORTENING 500 MB WAVE LENGTH, THE SREF AND ECMWF MIX I THINK HAVE BEEN STEADFAST ON ADVERTISING THIS EVENT. IF A GRAVITY WAVE WERE TO OCCUR I DONT THINK TODAYS SCIENCE CAN BE SURE HOW IT MODULATES THE PCPN THIS FAR IN ADVANCE, BUT PLEASE CORRECT ME. SO...THE BASICS: AN INTENSIFYING 500MB 12HR 190 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. PIVA AND COMMA HEAD SUGGEST SOME BANDING POTENTIAL VCNTY KRDG TO KMPO DURING THE DAY. 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. FROM THE MID SHIFT BELOW... MODEL GUIDANCE HAS COME INTO MUCH BETTER AGREEMENT OVERALL ON THE EVOLUTION OF A STORM WHICH WILL DEVELOP OFF THE SERN CONUS CST ON WED THEN TRACK NEWD DURG THE DAY ON WED. HOWEVER, WHILE THERE IS GOOD AGREEMENT ON THE SYNOPTIC FEATURES, THERE REMAINS SOME DISAGREEMENT ON THE THERMAL PROFILES AND SOME THE FINER DETAILS, WHICH COULD PROVE IMPORTANT AS THE EVENT PLAYS OUT. IT CONTINUES TO APPEAR AS THE AREAS N AND W OF PHILADELPHIA HAVE THE BEST SHOT OF SEEING SUBSTANTIAL ELEVATION RELATED SNOW, WHICH WILL IMPACT TRAVEL SIGNIFICANTLY. SRN AND ERN AREAS SE OF THE I95 CORRIDOR WILL LIKELY STAY ALL OR MOSTLY RAIN, SOME OF WHICH COULD BE HEAVY AT TIMES. THE POTENTIAL FOR SOME PONDING OF RAIN ON ROADWAYS AND POOR DRAINAGE AREAS IS POSSIBLE IN THESE LOCATIONS. ADDITIONALLY, IT WAS QUITE WARM ON MONDAY AND WILL BE FAIRLY WARM TODAY SO THE GROUND HAS IS WARM WHICH MAY NEGATE SOME ACCUMS, ESPECIALLY AT THE ONSET ON ROADWAYS ETC, UNLESS THE SNOW COMES DOWN HEAVY. SO, ULTIMATELY IT REMAINS TO BE SEEN WHAT WILL WIN OUT IN THIS AREA. THERE IS ALSO THE POTENTIAL FROM THE I-95 CORRIDOR N AND W FOR SOME MESOSCALE BANDING WHICH COULD INCREASE ANY SNOWFALL RATES, BUT THIS IS OFTEN DIFFICULT TO PREDICT MORE THAN A FEW HOURS IN ADVANCE, AND AMOUNTS CAN VARY WIDELY BETWEEN THOSE AREAS UNDER A BAND AND THOSE WHICH ARE NOT. THE MOST LIKELY PLACES TO REACH HEADLINE CRITERIA WOULD BE FROM BERKS COUNTY NEWD THROUGH THE LEHIGH VALLEY INTO NW NJ. && .LONG TERM /THURSDAY THROUGH MONDAY/... LOW PRES WILL MOVE ACRS ERN CANADA ON SUN AND ITS ASSOCD CDFNT WILL CROSS THE REGION SUN NIGHT OR ERLY MON, BRINGING ANOTHER SHOT OF PRECIP, MAINLY IN THE FORM OF RAIN. GUID IS NOW SUGGESTING THAT A WAVE COULD FORM ON THIS FRONT ON MON, WHICH WOULD LINGER PRECIP CHCS. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. REMAINDER OF TODAY...A PERIOD OF CIGS 4000-5000 FT IS DEVELOPING ENEWD FROM NEAR INTERSTATE 95 EASTWARD (SEE NAM 900-800MB LAYER RH) AND WILL CLEAR AWAY BY 21Z. OTRW CIRRUS CIGS THIS AFTN MAY BRIEFLY THIN A BIT THIS EVENING. WNW WIND WILL GUST NEAR 20 KT FOR A TIME TODAY. 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 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 AND 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. WE`LL RE-REVIEW THIS AFTERNOON. 12Z/25 NAM CHANGES BY 15Z BUT THE 12Z/25 GFS THERMAL PROFILES DO NOT! NO CONFIDENT ANSWER AT THIS TIME. OUTLOOK.... THU...CONDS RETURN TO VFR AND WINDS SHIFT TO WESTERLY OR NORTHWEST. THERE COULD BE BRIEF MVFR CONDITIONS IN SCATTERED SNOW SHOWERS LATER THURSDAY MAINLY JUST N OF KRDG AND KABE. WINDS MAY GUST TO 25 KT. FRI THRU SAT...VFR CONDITIONS EXPECTED. && .MARINE... SCA SEAS ON THE ATLC WATERS WILL BRIEFLY SUBSIDE THIS EVENING BELOW CRITERIA. QUIET ON THE DE BAY WATERS TODAY. EARLY TOMORROW MORNING, GALE CONDITIONS ARE LIKELY ON THE LOWER DELAWARE BAY AND THE ATLANTIC COASTAL WATERS. WED...A FULL BLOWN GALE WARNING IS IN EFFECT FOR THE COASTAL WATERS AND LOWER DELAWARE BAY PER AN INTENSIFYING STORM MOVING NEWD FROM THE NC COAST. SCA CONDITIONS EXPECTED ON THE UPPER DELAWARE BAY. BOTH THE 06Z AND 12Z NAM ARE ADVERTISING A PERIOD OF STORM FORCE WINDS VCNTY 44009 AROUND MIDDAY WEDNESDAY (NEAR 50 KT). WE WILL NOT KNOW FOR SURE SINCE NO 44009 WIND DATA. WED NIGHT...GALE CONDITIONS WILL CONTINUE EARLY, THEN SEAS AND WIND WILL DECREASE AND AND SCA WILL BE LIKELY NEEDED AS THE STORM MOVES NORTHEAST OF CAPE COD. OUTLOOK... THU...WIND AND SEAS CONTINUE TO DIMINISH BUT SCA WILL BE NEEDED PROBABLY THU AFTN OR EVE. FRI THROUGH SAT..WIND AND SEAS ARE EXPECTED TO REMAIN BELOW SCA CRITERIA. && .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 WEDNESDAY TO 1 AM EST THURSDAY FOR PAZ054-055. WINTER STORM WARNING FROM 7 AM TO 10 PM EST WEDNESDAY FOR PAZ060>062-101-103-105. WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY NIGHT FOR PAZ070-071-102-104-106. NJ...WINTER STORM WARNING FROM 7 AM WEDNESDAY TO 1 AM EST THURSDAY FOR NJZ001-007-008. WINTER STORM WARNING FROM 7 AM TO 10 PM EST WEDNESDAY FOR NJZ009. WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY NIGHT FOR NJZ010-015. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ450>455. 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...NIERENBERG 1105 NEAR TERM...DRAG 1105 SHORT TERM...DRAG/NIERENBERG 1105 LONG TERM...NIERENBERG AVIATION...DRAG/JOHNSON/NIERENBERG 1105 MARINE...DRAG/JOHNSON/NIERENBERG 1105 CLIMATE...

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