Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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662 FXUS61 KPHI 050436 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1136 PM EST THU FEB 4 2016 .SYNOPSIS... AN AREA OF LOW PRESSURE WILL TRACK ALONG AN OFFSHORE FRONT TONIGHT AND FRIDAY MORNING BEFORE MOVING NORTHEAST OF OUR AREA. HIGH PRESSURE GRADUALLY BUILDS INTO OUR REGION LATE FRIDAY AND SATURDAY, THEN A WEAK COLD FRONT MOVES THROUGH EARLY SUNDAY. A STRONG OCEAN STORM SHOULD TRACK WELL OFFSHORE LATER SUNDAY INTO MONDAY, THEN ANOTHER STORM LOOKS TO REDEVELOP OFF OF THE MID ATLANTIC COAST LATER MONDAY AND TUESDAY BEFORE MOVING OUT TO SEA WEDNESDAY INTO THURSDAY. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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1115 PM UPDATE...MADE SOME EDITS TO THE HOURLY POP AND WX GRIDS TO HOPEFULLY BETTER ACCOUNT FOR THE TIMING OF THE CHANGEOVER FROM RAIN TO SNOW OVERNIGHT. BASED ON THE LATEST OBSERVATIONS AND MODEL GUIDANCE, THE TREND WAS TO DELAY THE EASTWARD PROGRESSION OF RAIN-SNOW LINE BY 1-3 HOURS DEPENDING ON THE LOCATION AS THERE IS A SIGNIFICANT AMOUNT OF WARM AIR IN THE BOUNDARY LAYER TO OVERCOME INITIALLY. DESPITE THIS DELAY IN THE CHANGEOVER, SNOW AMOUNTS WERE NOT LOWERED AS STRONG DYNAMICAL COOLING AND HEAVIER PRECIP RATES HAVE THE POTENTIAL TO YIELD SNOWFALL RATES OF AROUND AN INCH AN HOUR DURING RUSH HOUR (ESPECIALLY IN EASTERN NJ) UNDER A MESOSCALE BAND FORMING TO THE NW OF THE DEEPENING COASTAL LOW. THE BULK OF THE ACCUMULATING SNOW IS EXPECTED TO FALL BETWEEN 4-9 AM FOR THE I-95 CORRIDOR AND BETWEEN 5 AND 10 AM FARTHER EAST TOWARD THE NJ AND DE COAST. THIS COINCIDES WITH RUSH HOUR, SO PLEASE GIVE YOURSELF CONSIDERABLY EXTRA TIME TO GET TO YOUR DESTINATION IN THE MORNING AND EVEN CONSIDER DELAYING YOUR TRAVEL (IF POSSIBLE) IF THE ROADS BECOME SNOW COVERED DURING RUSH HOUR. ARGUABLY THERE IS A SLIGHT BOOST OF CONFIDENCE THAT SNOWFALL FORECAST IS IN GOOD SHAPE WITH THE SIMULATED SNOWFALL FROM THE LATEST 00Z HRRRX USING A VARIABLE DENSITY JUST ABOUT MATCHES OURS. THIS FORECAST PARAMETER FROM THE HRRRX PERFORMED EXTREMELY WELL WITH THE BLIZZARD TWO WEEKS AGO THOUGH THE SETUPS FOR THESE TWO EVENTS ARE VASTLY DIFFERENT. NOTE THE PARAMETER FROM THE HRRR/HRRRX OR ANY OTHER MODELS THAT ASSUMES A 10:1 SNOW RATIO FOR THIS EVENT WILL BE OVERDONE AS IT DOESN`T TAKE INTO ACCOUNT THERMAL PROFILES THAT ALTER THE MICROPHYSICS, MIXING AND SURFACE MELTING (WHICH ALL ARE IMPORTANT FACTORS IN THIS EVENT). PREVIOUS DISCUSSION... A WINTER WEATHER ADVISORY IS IN EFFECT FOR MUCH OF OUR FORECAST AREA FOR LATE TONIGHT THROUGH FRIDAY MORNING. THE LOW HAS ALREADY BEGUN TO INTENSIFY ALONG THE NOW STATIONARY FRONT AND SHOULD CONTINUE TO LIFT NORTHEAST OVERNIGHT. FEW CHANGES TO THE FORECAST WITH THE EVENING UPDATE. HIGH RESOLUTION MODELS INCLUDING THE HRRR AND RAP HAVE TRENDED SNOWIER WITH THE LATEST RUNS. HOWEVER, I HESITATE TO CHANGE THE SNOW AMOUNTS AS MANY LOCATIONS STILL HAVE DEW POINT TEMPERATURES WELL ABOVE 32 DEGREES, MEANING WE`RE STILL SEVERAL HOURS AWAY FROM THE CHANGE OVER TO ALL SNOW. THUS FOR NOW, WILL CONTINUE WITH THE SNOW AMOUNTS AND WINTER WEATHER ADVISORY CONFIGURATION FROM THE 4 PM UPDATE, BUT WILL BE WATCHING THE TIMING OF THE CHANGE OVER VERY CLOSELY. TIMING...RAIN CONTINUES OVER THE COASTAL PLAINS AND HAS BEGUN TO MOVE INTO THE DELAWARE VALLEY. EXPECT THAT IT SHOULD MOVE WEST THROUGH THE OVER NIGHT HOURS REACHING THE LEHIGH VALLEY DURING THE EARLY MORNING HOURS. THE TIMING OF THE SNOW LOOKS LIKE IT WILL IMPACT PART, IF NOT ALL, OF THE MORNING COMMUTE AND THAT IS WHY WE HAVE INCLUDED AREAS TO THE WEST OF PHILADELPHIA. IT CERTAINLY LOOKS LIKE IT COULD BE A SLOPPY AND SLIPPERY MORNING COMMUTE ACROSS MUCH OF THE AREA. SNOW/RAIN...SNOW SEEMS LIKELY ACROSS THE REGION ALTHOUGH WITH TEMPERATURES STILL HANGING OUT IN THE 40S LATE THIS EVENING, PRECIPITATION WILL CONTINUE AS ALL RAIN THROUGH AT LEAST MIDNIGHT, AND THEN TRANSITION OVER TO A RAIN/SNOW MIX AND THEN ALL SNOW DURING THE VERY EARLY MORNING HOURS (AT THIS POINT EXPECT THE TRANSITION TO ALL SNOW TO BE BETWEEN 2 AND 6 AM DEPENDING ON HOW MUCH DEW POINTS FALL). AS THE PRECIPITATION FALLS, IT WILL START TO COOL THE COLUMN. THE BIG QUESTION WILL BE JUST HOW FAST THAT COLUMN COOLS. PRECIPITATION INTENSITY WILL DEFINITELY PLAY A ROLE AND AS WE SEE SOME HEAVIER PRECIPITATION FALL, THE COLUMN WILL COOL FASTER AND WE SHOULD SEE A QUICK CHANGEOVER FROM RAIN TO SNOW. THE BEST VERTICAL MOTION APPEARS TO OCCUR DURING THE OVERNIGHT/EARLY MORNING PERIOD AND THIS WOULD LEND TO HIGHER CONFIDENCE OF AN ACCUMULATING SNOW. WHILE THE GROUND TEMPS MAY BE FAIRLY WARM RIGHT NOW, INCREASED PRECIPITATION INTENSITY WILL ALLOW FOR ALL SURFACES TO ACCUMULATE, EVEN PAVED ROADS. AMOUNTS WILL VARY WITH LESSER AMOUNTS AS YOU MOVE FURTHER INLAND AND HIGHEST AMOUNTS MORE TOWARDS THE COAST. THERE STILL REMAINS SOME UNCERTAINTY WITH RESPECT TO SNOWFALL AMOUNTS AS SOME OF THE GUIDANCE HINTS AT HIGHER TOTALS (THAN CURRENTLY FORECAST) IN EASTERN NEW JERSEY. CONFIDENCE IS NOT HIGH ENOUGH AT THIS TIME TO ISSUE A WARNING BUT WILL NEED TO MONITOR AS THE SYSTEM DEVELOPS FURTHER.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... SNOW WILL GRADUALLY BE ENDING THROUGH FRIDAY MORNING FROM WEST TO EAST AS THE LOW PRESSURE PULLS FURTHER AWAY FROM OUR AREA. MOST AREAS SHOULD SEE SNOW ENDING BY 10AM WITH SOME OF THE COASTAL LOCATIONS POSSIBLY SEEING SOME FLAKES THROUGH AROUND NOON. HIGH PRESSURE WILL BUILD TOWARDS OUR AREA FROM THE SOUTHEAST AND WE EXPECT THE AREA TO DRY OUT AND REMAIN THAT WAY AS WE HEAD INTO THE WEEKEND. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... SUMMARY...AN ACTIVE PATTERN WITH AN OCEAN STORM LATE SUNDAY INTO MONDAY WHICH SHOULD SLIDE WELL OFFSHORE, THEN QUICKLY ON ITS HEELS IS THE POTENTIAL FOR LOW PRESSURE TO REDEVELOP OFF THE MID ATLANTIC COAST MONDAY NIGHT INTO WEDNESDAY AS COLDER AIR ARRIVES. THE OVERALL SYNOPTIC SETUP INVOLVES A TROUGH FRIDAY NIGHT THAT CONTINUES TO SHIFT TO OUR EAST. A MORE COMPLEX PATTERN THEN EVOLVES WITH A CLOSED LOW IN CANADA WITH ANOTHER PIECE OF ENERGY IN THE SOUTHERN STATES SATURDAY. THE LATTER SHOULD ALLOW A STORM TO DEVELOP OVER THE WEEKEND OFF THE SOUTHEAST COAST WHICH THEN DEEPENS RAPIDLY, HOWEVER THE ORIENTATION OF THE TROUGH LOOKS TO BE SUCH TO KEEP IT OFFSHORE AS IT TURNS NORTHEASTWARD. AN IMPRESSIVE TROUGH THEN IN THE PLAINS MOVES EASTWARD EARLY NEXT WEEK AND THIS SHOULD ALLOW FOR SOME SORT OF REDEVELOPMENT OF LOW PRESSURE OFF THE MID ATLANTIC COAST LATE MONDAY AND TUESDAY. THIS SYSTEM MAY BE ONE TO WATCH GIVEN SUCH A DEEP INCOMING TROUGH THAT COULD CLOSE OFF INTO THE MID ATLANTIC REGION. HOWEVER, THE INTERACTION WITH THE INITIAL OCEAN STORM COULD VERY WELL INFLUENCE THE DEVELOPMENT OF THIS SECOND STORM. WE USED A MODEL BLEND WITH CONTINUITY FOR FRIDAY NIGHT INTO SUNDAY, THEN BLENDED IN MOSTLY THE 12Z WPC GUIDANCE THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE FOLLOWING ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES. FOR FRIDAY NIGHT...THE UPPER-LEVEL FLOW BACKS MORE TO THE SOUTHWEST AHEAD OF THE NEXT UPPER-LEVEL TROUGH THAT BEGINS TO SLIDE NEAR THE GREAT LAKES. THIS ALLOWS HIGH PRESSURE TO BUILD INTO OUR AREA, WHICH WILL RELAX THE PRESSURE GRADIENT. THERE SHOULD BE DECENT RADIATIONAL COOLING COMBINED WITH LOW DEW POINTS, THEREFORE A COLD NIGHT IS ANTICIPATED. FOR SATURDAY AND SUNDAY...SURFACE HIGH PRESSURE BUILDS IN BRIEFLY SATURDAY BEFORE WEAKENING INTO SUNDAY. OUR REGION LOOKS TO END UP BETWEEN SYSTEMS DURING THE WEEKEND AS A MAIN TROUGH SWINGS ACROSS NEW ENGLAND AND ANOTHER ONE CLOSES OFF ACROSS THE SOUTHEAST STATES. THE LATTER SHOULD DRIVE SURFACE LOW DEVELOPMENT OFF OF THE SOUTHEAST COAST DURING SUNDAY WHICH THEN SHOULD GO OUT TO SEA AS IT RAPIDLY INTENSIFIES, ALTHOUGH IT MAY TOSS AT LEAST SOME CLOUDINESS OUR WAY. THE NORTHERN SYSTEM SHOULD SEND A COLD FRONT INTO OUR AREA LATER SUNDAY, HOWEVER THIS FEATURE LOOKS WEAK AND MOISTURE STARVED. AS A RESULT, WE KEPT THE FORECAST DRY ATTM. FOR MONDAY AND TUESDAY...THE PATTERN IS FORECAST TO UNDERGO SIGNIFICANT AMPLIFICATION AS A ROBUST TROUGH MOVES ACROSS THE PLAINS AND INTO THE EAST DURING THIS TIME FRAME. THIS LOOKS TO RESULT IN LOW PRESSURE INTO THE GREAT LAKES, HOWEVER THEN HANDING OFF ENERGY EASTWARD THAT REDEVELOPS LOW PRESSURE OFF OF THE MID ATLANTIC COAST LATE MONDAY AND TUESDAY. THE REDEVELOPMENT/TRACK OF THIS STORM MAY DEPEND ON THE ACTUAL TRACK AND INTENSITY OF THE PREVIOUS ONE WHICH IS MORE OFFSHORE. IN ADDITION, THERE COULD BE A SURFACE TROUGH THAT EXTENDS ACROSS PORTIONS OF OUR AREA TUESDAY WHERE LIFT IS ENHANCED, HOWEVER THIS WILL DEPEND ON THE LOCATION OF THE SURFACE LOW REDEVELOPMENT. THIS HAS THE POTENTIAL TO BECOME A DECENT COASTAL STORM WITH COLD AIR COMING INTO PLAY. WHILE THERE IS A SIGNAL IN THE GUIDANCE REGARDING A STORM, THE TRACK AND INTENSITY IS LESS CERTAIN AND THAT WILL DETERMINE THE ACTUAL DETAILS /IF ANY/ FOR OUR AREA WHICH INCLUDES RAIN, SNOW, WIND AND COASTAL IMPACTS. GIVEN THE VARIABILITY IN THE MODEL GUIDANCE, NO MAJOR CHANGES WERE MADE TO THIS TIME FRAME. FOR WEDNESDAY AND THURSDAY...A STRONG UPPER-LEVEL TROUGH IS FORECAST TO BE IN THE EAST, BASICALLY MOVING OVER OUR AREA. THIS WOULD TAKE ANY COASTAL STORM OFF TO OUR NORTHEAST WEDNESDAY ALLOWING FOR GENERALLY IMPROVING CONDITIONS. AN ARCTIC FRONT OF SORTS MAY SLIDE ACROSS OUR AREA DURING WEDNESDAY, HOWEVER CYCLONIC FLOW WILL RESULT IN SOME CLOUDS AND COLDER AIR WITH POSSIBLY EVEN SOME SNOW SHOWERS. HIGH PRESSURE BEGINS TO ARRIVE DURING THURSDAY FROM THE WEST. && .AVIATION /04Z FRIDAY THROUGH TUESDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. OCCASIONAL RAIN WILL CONTINUE AT THE DELAWARE VALLEY SITES (KPHL, KPNE, KTTN, AND KILG) AND THE COASTAL PLAIN SITES (KMIV AND KACY) THROUGH THE REST OF THE EVENING. PRECIPITATION SHOULD MOVE INTO KRDG AND KABE AFTER MIDNIGHT. TIMING OF THE CHANGE OVER TO A RAIN AND SNOW MIX AND EVENTUALLY ALL SNOW IS UNCERTAIN, BUT AT THIS POINT, EXPECT TO SEE THE MIX BEGIN BETWEEN 04 AND 06Z, AND THE CHANGE TO ALL SNOW HAPPEN BETWEEN 06 AND 10Z. GIVEN HOW LATE THE PRECIPITATION WILL BEGIN AT KRDG AND KABE, IT MAY BEGIN AND STAY ALL SNOW. GENERALLY EXPECTING THE LOWEST VISIBILITIES AND CEILINGS TO BE COINCIDENT WITH THE PERIOD OF ALL SNOW. FRIDAY...IMPROVEMENT TO VFR BY 15Z ACROSS THE TERMINALS, EXCEPT FOR KACY AND KMIV WHICH MAY REMAIN MVFR THROUGH 18Z. PRECIPITATION SHOULD END EARLY WITH SNOW MOVING TO THE EAST THROUGH MID-MORNING. EXPECT VFR CONDITIONS TO PREVAIL ACROSS THE REGION BY EARLY AFTERNOON. WINDS WILL STRENGTHEN OUT OF THE NORTHWEST AROUND 15 TO 20 KNOTS SUSTAINED WITH GUSTS UP NEAR 30 KNOTS POSSIBLE THROUGH THE AFTERNOON. OUTLOOK... FRIDAY NIGHT...VFR. LIGHT NORTHWEST TO WEST WINDS. SATURDAY AND SUNDAY...VFR OVERALL WITH SOME INCREASE IN CLOUDS POSSIBLE, WITH A WEAK COLD FRONT MOVING THROUGH LATER SUNDAY. SOUTHWEST WINDS SATURDAY LESS THAN 10 KNOTS, BECOMING NORTHERLY SUNDAY. MONDAY AND TUESDAY...THE CEILINGS SHOULD LOWER AS LOW PRESSURE REDEVELOPS OFF OF THE MID ATLANTIC COAST. THIS COULD BRING A PERIOD OF RAIN/SNOW TO THE AREA WHICH WOULD REDUCE THE VISIBILITY. THERE IS LESS CONFIDENCE THOUGH WITH THIS STORM AS ITS EFFECTS WILL BE DETERMINED BY THE TRACK AND INTENSITY. && .MARINE... A GALE WARNING HAS BEEN ISSUED FOR THE COASTAL WATERS AND A SCA HAS BEEN ISSUED FOR THE DELAWARE BAY. GALE GUSTS ARE LIKELY OVER THE OCEAN WATERS FROM THE PRE DAWN HOURS THROUGH EARLY AFTERNOON. GUSTS ABOVE 25 KT ARE EXPECTED ACROSS THE DELAWARE BAY. A FEW GUSTS NEAR GALE FORCE MAY BE POSSIBLE AT THE MOUTH OF THE BAY. WINDS ARE EXPECTED TO SLOWLY SUBSIDE THROUGH LATE AFTERNOON, THOUGH SCA CONDITIONS ON THE COASTAL WATERS ARE LIKELY THROUGH MUCH OF THE DAY TIME HOURS. OUTLOOK... FRIDAY NIGHT...THE CONDITIONS ARE ANTICIPATED TO LOWER BELOW SMALL CRAFT ADVISORY CRITERIA DURING THE EVENING AS HIGH PRESSURE BEGINS TO BUILD IN. SATURDAY AND SUNDAY...THE CONDITIONS SHOULD BE BELOW SMALL CRAFT ADVISORY CONDITIONS FOR MUCH OF THIS TIME AS HIGH PRESSURE WEAKENS IN PLACE. HOWEVER, A POTENTIALLY STRONG OCEAN STORM TO OUR SOUTHEAST LATER SUNDAY COULD BE CLOSE ENOUGH TO ALLOW SEAS TO BUILD AND WINDS TO INCREASE TO ADVISORY LEVELS SUNDAY NIGHT. MONDAY AND TUESDAY...AN OFFSHORE STORM TRACKS WELL EAST OF OUR WATERS INTO MONDAY, WHICH COULD ENHANCE SEAS AND WIND GUSTS. ANOTHER COASTAL STORM MONDAY NIGHT THROUGH TUESDAY COULD RESULT IN GALE FORCE WINDS GUSTS, HOWEVER THIS WILL DEPEND ON THE TRACK AND INTENSITY OF THE STORM WHICH CURRENTLY HAS LOWER CONFIDENCE. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...WINTER WEATHER ADVISORY UNTIL 10 AM EST FRIDAY FOR PAZ070-071- 101>106. NJ...WINTER WEATHER ADVISORY UNTIL 10 AM EST FRIDAY FOR NJZ008>010- 012-015>019. WINTER WEATHER ADVISORY UNTIL NOON EST FRIDAY FOR NJZ013-014- 020>027. DE...WINTER WEATHER ADVISORY UNTIL 10 AM EST FRIDAY FOR DEZ001. WINTER WEATHER ADVISORY UNTIL NOON EST FRIDAY FOR DEZ002>004. MD...WINTER WEATHER ADVISORY UNTIL 10 AM EST FRIDAY FOR MDZ008-012. WINTER WEATHER ADVISORY UNTIL NOON EST FRIDAY FOR MDZ015-019- 020. MARINE...GALE WARNING FROM 4 AM TO 1 PM EST FRIDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL 4 PM EST FRIDAY FOR ANZ430-431.
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&& $$ SYNOPSIS...GORSE NEAR TERM...JOHNSON/MEOLA/KLEIN SHORT TERM...MEOLA LONG TERM...GORSE AVIATION...GORSE/JOHNSON/MEOLA MARINE...GORSE/JOHNSON

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