Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 291446 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 946 AM EST MON DEC 29 2014 .SYNOPSIS... A WEAK AREA OF LOW PRESSURE OVER NORTH CAROLINA WILL MOVE EAST AND OFFSHORE LATER TODAY AND TONIGHT. A CANADIAN HIGH PRESSURE SYSTEM WILL ENTER THE NORTHERN PLAINS ON TUESDAY AND SLOWLY BUILD TO THE SOUTHEAST REACHING THE SOUTHERN MID ATLANTIC COASTAL WATERS ON FRIDAY. A LOW PRESSURE SYSTEM AND WARM FRONT SHOULD ADVANCE TOWARD OUR AREA ON SATURDAY. A NEW WAVE OF LOW PRESSURE ALONG ITS COLD FRONT MIGHT DEVELOP AND PASS SOUTHEAST OF THE REGION ON SUNDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... LIGHT RAIN CONTINUES ACROSS OUR SOUTHERN ZONES THIS MORNING BUT IS STARTING TO WEAKEN AND PUSH MORE TO THE SOUTH AS SOME MID LEVEL ENERGY ROTATES THROUGH THE REGION. THE CHANCE FOR SOME LIGHT RAIN WILL GRADUALLY TAPER OFF TOWARD THIS AFTERNOON WITH THE LOW CLOUDS DRIFTING TO THE EAST AS WELL. THE WEST TO SOUTHWEST FLOW IN THE MID LEVELS WILL USHER IN SOME CLOUDS ACROSS THE REGION TODAY AND WE SHOULD MAINLY SEE SOME MID AND HIGH LEVEL CLOUDS BUILDING THROUGH THIS AFTERNOON. TEMPERATURES LOOK TO BE ON TRACK WITH HIGHS REACHING INTO THE 40S ACROSS MUCH OF THE AREA, WITH 30S ACROSS THE NORTHERN MOST ZONES. THE NORTH TO NORTHWEST FLOW AT THE SURFACE WILL ALLOW FOR SOME COOLER AIR TO TRICKLE INTO THE REGION AND THIS WILL KEEP TEMPERATURES LOWER THAN WHAT WE SAW ON SUNDAY. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... AS A WEAK SHORT WAVE TROUGH ARRIVES LATE TONIGHT, A STRONGER SHORT WAVE IS FORECAST TO ARRIVE MAINLY ACROSS THE CENTRAL AND SOUTHERN ZONES. THE VORTICITY ASSOCIATED WITH THIS SHORT WAVE THOUGH IS MORE CHANNELIZED AND THE MOISTURE IS NOT ALL THAT DEEP. IT WAS GENERALLY THIS FEATURE DAYS AGO THAT SOME MODELS WERE SHOWING A DECENT OVERRUNNING TYPE EVENT, HOWEVER IT APPEARS TO BE FARTHER SOUTH AND WEAKER NOW. WHILE THERE IS SOME MID LEVEL LIFT ASSOCIATED WITH IT, MUCH OF THIS MAY END UP IN THE PRODUCTION OF A MID LEVEL CLOUD DECK. IF SOME LIGHT PRECIPITATION WERE TO DEVELOP LATE, IT WOULD BE ACROSS THE DELMARVA AND POSSIBLY INTO FAR SOUTHERN NEW JERSEY. THE FORECAST SOUNDINGS IN GENERAL HAVE A DRY LOOK TO THEM WITH PERHAPS SOME VIRGA/SNIRGA MOVING THROUGH. SINCE THERE IS NOT MUCH TO LATCH ONTO WITH THIS SHORT WAVE MOVING THROUGH LATE, WE MAINTAINED SOME SLIGHT CHC POPS ACROSS THE FAR SOUTH. GIVEN THE CAA CONTINUING, IT DOES BECOME COLD ENOUGH FOR THE PRECIPITATION TYPE TO BE SNOW. OTHERWISE, A FAIR AMOUNT OF CLOUDS ACROSS THE CWA ALTHOUGH THE FAR NORTH MAY END UP HAVING LESS CLOUDS FOR AWHILE BEING NORTH OF THE CHANNELIZED SHORT WAVE. IF THERE IS LESS CLOUD COVER LONGER, THEN TEMPERATURES WILL TEND TO BE COLDER GIVEN LIGHT ENOUGH WINDS AND LOWERING DEW POINTS. AS FOR LOW TEMPERATURES, WE USED A NAM/GFS MOS BLEND THEN MADE A FEW TWEAKS FOR LOCAL AFFECTS. && .LONG TERM /TUESDAY THROUGH SUNDAY/... A COLD START AND UNSETTLED END TO THE LONG TERM IN MORE WAYS THAN ONE. A HIGH PRESSURE SYSTEM ORIGINATING IN SIBERIA WILL ENTER THE CONUS ON TUESDAY. THIS WILL SOLIDIFY COLDER WEATHER ENTERING THE NEW YEAR. AS THIS MOVES OFFSHORE, A STORM SYSTEM FROM THE SOUTHWEST IS PREDICTED TO AFFECT OUR AREA OVER THE WEEKEND. THE GEFS MEAN IS PREDICTING A DUAL TELECONNECTION SWITCH WHICH IS A FAIRLY CONFIDENT SIGNAL A PCPN EVENT. AS FOR THE DETAILS, THE MODELS HAVE HAD A DIFFICULT TIME ON KEYING ON THE CORRECT 500MB PATTERN MUCH MORE THAN 4 TO 5 DAYS IN ADVANCE SINCE AUTUMN. GETTING DOWN TO THE SURFACE, THESE DIFFERENCES HAVE NOT BEEN SOLIDIFIED MUCH BEFORE 72 HOURS. AS A RECENT EXAMPLE THE NON-ECMWF MODELS DID NOT LOSE THEIR SNOWIER TUESDAY SOLUTION FOR OUR CWA UNTIL THE 12Z RUN SATURDAY AND IN THE NAM`S CASE NOT UNTIL YESTERDAY. SO IN ONE CORNER WE HAVE THE GFS, NOGAPS AND (INFERRING) UKMET TAKE A VERY STRONG LOW THROUGH THE SAINT LAWRENCE VALLEY. THERE IS A PLETHORA OF COLD AIR IN EASTERN CANADA AND HAVE LOW CONFIDENCE THAT THIS WILL BE EASILY DONE. IN THE OTHER CORNER WE HAVE THE ECMWF, PGFS AND CAN GGEM THAT TAKE A MUCH WEAKER LOW INTO THE SAINT LAWRENCE VALLEY, HANG BACK ENERGY IN THE DESERT SW AND THEN DO ANOTHER SHEARING VERSION OF OUR PRESENT SCENARIO OVER THE WEEKEND. WHILE WE LIKE THE WEAKER SAINT LAWRENCE VALLEY TRACK FORECAST, THE HANGING BACK OF ENERGY, ESPECIALLY WITH THE ECMWF, OPENS UP A WHOLE NEW BOWL OF UNCERTAINTY. SO GIVEN THE DIVERGENT SOLUTION WITH THIS PACKAGE, WE LEANED HEAVILY ON THE LATEST WPC SOLUTION FOR ANY ADJUSTMENTS, WHICH FOR RIGHT NOW PAINTS A VERY CLIMATOLOGICAL PICTURE OF SNOW TO RAIN TO SNOW FOR THE WEEKEND. THE MODEL INITIALIZATION LOOKED PRETTY GOOD AND A WRF-NMMB AND GFS BLEND WAS USED FOR THE START OF THE LONG TERM. AS FOR SOME DAY TO DAY DETAILS... ON TUESDAY A CHANNELIZED VORT MAX IS STILL EXPECTED TO PASS ACROSS THE FAR SOUTHERN PART OF OUR CWA. MID LEVEL MOISTURE IS STILL SUFFICIENT AS IS PREDICTED MID LEVEL QVEC CONVERGENCE TO GENERATE PCPN. THE LOWER LEVEL SOUNDINGS ARE DRY AND NOT SURE HOW MUCH OF THAT PCPN WOULD BE ABLE TO MAKE IT TO THE GROUND. POPS WERE KEPT AS CHANCE OR LOWER. BECAUSE OF THE LIGHT PCPN INTENSITY, PTYPE MACROS SUGGEST RAIN OR SNOW COULD OCCUR BECAUSE OF THE WARM BOUNDARY LAYER. AS TUESDAY DAY CONTINUES, MOISTURE IS PREDICTED TO BECOME MORE LIMITED AND WE ENDED THE CHANCES DURING THE AFTERNOON. STAT GUIDANCE LOOKED DECENT AND WAS SUPPORTED BY MODEL SOUNDINGS AND WAS FOLLOWED. THE DOWNWARD PROGRESSION OF TEMPERATURES WILL CONTINUE ON TUESDAY NIGHT. THE PREDICTED GRADIENT IS BORDERLINE FOR DECOUPLING SO IN OUTLYING AREAS WE MET MIN TEMPERATURE POTENTIALS HALFWAY. ON WEDNESDAY, A SECONDARY SURGE OF ARCTIC AIR WILL OCCUR. FCST 1000-850MB THICKNESSES ARE IN THE 1250M RANGE. THERE IS ANOTHER VORT MAX PREDICTED TO PASS THROUGH AND CONVECTIVE TEMPS PREDICTED TO BE REACHED NORTHWEST, MODEL DIFFERENCES CENTRAL AND NOT THERE DELMARVA/SOUTHEAST. GRANTED THAT THE SHORT WAVE TIMING COULD BE OFF, BUT ARCTIC THICKNESSES HAVE A WAY OF GENERATING FLURRIES AND MAYBE EVEN SNOW SHOWERS. WE ADDED THE CHANCE OF FLURRIES AS A STARTER. LOOKS LIKE LESS DECOUPLING CHANCES ON NEW YEARS EVE. NO PCPN RELATED ISSUES, BUT IT WILL BE OVERALL COLDER. A SUNNY, BUT BRISK AND COLD DAY FOR NEW YEARS DAY. THE LAKE EFFECT TRAJECTORY IS PREDICTED TO REMAIN NORTH OF OUR CWA. A BETTER RADIATING NIGHT IS POSSIBLE ON THURSDAY NIGHT WITH A SLIGHT AIR MASS RECOVERY ON FRIDAY. BECAUSE OF THE OVERALL SLOWER TIMING, WE REMOVED POPS FROM FRIDAY NIGHT. WE ARE KEEPING THE FORECAST OF A ONE-TWO PUNCH OF THE INITIAL LOW AND COLD FRONT PCPN ON SATURDAY WITH THE SECONDARY SHEARING LOW PCPN POSSIBLE ON SUNDAY. THE GEFS MEMBERS ARE PRETTY MUCH ALL CLUSTERED SIMILARLY TO THE OP GFS. THE CAN GEPS HAS ABOUT THREE QUARTERS OF ITS MEMBERS SIMILAR TO THE GEFS AND A QUARTER SIMILAR TO ITS OPERATIONAL AND ECMWF SOLUTION. THE ECMWF ENSEMBLE MEAN DOES NOT HAVE MUCH OF A SECONDARY LOW SUNDAY AS IT OPENS UP THE CLOSED SW CONUS LOW MUCH FASTER THAN THE OP. THERE IS A SWATH OF DEEP PURPLE UNCERTAINTY ABOUT SFC PRESSURE OVER NEW ENGLAND SUN EVE, NOT EXACTLY SMOKING ON THE WATER. OPERATIONALLY SEVEN DAYS AWAY, THIS HAS BEEN MORE THE RULE THAN THE EXCEPTION THIS COLD SEASON FOR ALL OF THE MODELS. && .AVIATION /15Z MONDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...VFR CEILINGS. NORTH-NORTHWEST WINDS BECOMING NORTH-NORTHEAST AT 5-10 KNOTS. SOME LIGHT RAIN EARLY THIS MORNING SOUTH OF KILG. TONIGHT...VFR CEILINGS MAINLY AROUND 10000 FEET. NORTH-NORTHEAST WINDS GENERALLY 4-8 KNOTS. OUTLOOK... TUESDAY...VFR CONDITIONS EXPECTED. GUSTY NORTH WINDS 20 TO 25 KNOTS. AIRPORTS IN DELMARVA SOUTH OF KILG AND IN NEW JERSEY SOUTH OF KACY AND KMIV THERE IS A RISK OF MVFR CEILINGS AT TIMES. TUESDAY NIGHT THROUGH FRIDAY...MOSTLY VFR CONDITIONS EXPECTED. GUSTY WEST WINDS EXCEEDING 20 KNOTS POSSIBLE DURING THE DAY ON BOTH WEDNESDAY AND THURSDAY. && .MARINE... OUR AREA WILL BE NORTH OF A STALLED FRONTAL BOUNDARY TODAY AND TONIGHT. A WEAK SYSTEM IS TRACKING ALONG IT EARLY THIS MORNING AND WILL SHIFT OFF THE DELMARVA COAST THROUGH THIS MORNING. THERE IS CAA OCCURRING TODAY AND THAT WILL STRENGTHEN SOME BY LATE TODAY AND TONIGHT. AS ANOTHER WEAK SYSTEM SLIDES BY TO OUR SOUTH LATER TONIGHT AND HIGH PRESSURE BUILDS INTO THE GREAT LAKES, THE PRESSURE GRADIENT WILL TIGHTEN ACROSS OUR AREA. THIS COMBINED WITH CAA WILL ALLOW FOR BETTER MIXING. THIS WILL RESULT IN A NORTH-NORTHEAST WIND INCREASING TONIGHT ESPECIALLY ACROSS THE SOUTHERN WATERS. IT DOES APPEAR TO GENERALLY BE MARGINAL, HOWEVER WIND GUSTS LOOK TO NEAR ADVISORY CRITERIA ACROSS THE SOUTHERN WATERS TOWARD 12Z TUESDAY. THEREFORE, A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE LOWER DELAWARE BAY AND THE COASTAL WATERS SOUTH OF LITTLE EGG INLET STARTING AT 10Z TUESDAY. OUTLOOK... TUESDAY...WE HAVE THE SMALL CRAFT ADVISORY ONGOING FOR LOWER DELAWARE BAY AND THE SOUTHERN ATLANTIC WATERS FOR A SURGE OF AROUND 25 KT GUSTS OCCURRING AS THE LOW PRESSURE SYSTEM MOVES FARTHER OFFSHORE AND INTENSIFIES. PEAK GUSTS SHOULD OCCUR MAINLY DURING TUESDAY MORNING. UPPER DELAWARE BAY AND NORTHERN COASTAL WATERS CONDITIONS ARE EXPECTED TO STAY BELOW SCA THRESHOLDS. TUESDAY NIGHT AND WEDNESDAY...SUB SCA CONDITIONS EXPECTED. MAY COME CLOSE LATE IN THE AFTERNOON WEDNESDAY. WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...WESTERLY WINDS WITH GUSTS NEAR SMALL CRAFT ADVISORY CRITERIA ARE POSSIBLE, PRIMARILY ON THE ATLANTIC COASTAL WATERS. FRIDAY...SUB SCA CONDITIONS EXPECTED. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY FROM 5 AM TO 4 PM EST TUESDAY FOR ANZ431- 452>455. && $$ SYNOPSIS...GIGI/JOHNSON NEAR TERM...MEOLA SHORT TERM...GORSE LONG TERM...GIGI AVIATION...GIGI/GORSE/JOHNSON MARINE...GIGI/GORSE/JOHNSON

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