Issued by NWS Mt. Holly, NJ
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-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --000 FXUS61 KPHI 231456 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 956 AM EST MON NOV 23 2009 .SYNOPSIS...-- Changed Discussion --HIGH PRESSURE OVER EASTERN NOVA SCOTIA THIS MORNING WILL RECEDE EAST. FAIRLY WEAK LOW PRESSURE OFF THE SOUTHEAST COAST WILL LIFT NORTHEAST AND PASS WELL TO THE EAST OF DELAWARE AND NEW JERSEY TONIGHT. VERY WEAK HIGH PRESSURE WILL RESIDE OVER THE AREA LATE TUESDAY AND WEDNESDAY, THEN A COLD FRONT FROM THE WEST WILL ARRIVE ON THURSDAY. LOW PRESSURE IS FORECAST TO DEVELOP OFF THE SOUTHEAST COAST ON THURSDAY AND IT SHOULD MOVE UP INTO NEW ENGLAND ON FRIDAY. HIGH PRESSURE IS EXPECTED TO BUILD SLOWLY INTO OUR REGION FROM THE WEST DURING THE WEEKEND.-- End Changed Discussion --&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...-- Changed Discussion --BASED ON LATEST SATELLITE AND RADAR TRENDS...WE HAVE CONTINUED THE TREND OF SLOWING THE ADVANCE OF RAIN INTO OUR CWA. SUBSIDENCE BEHIND THE CLOSED LOW NEAR NYC HAS HELPED BREAK DOWN THE SC IN THE NORTHERN PART OF OUR CWA, SOME MID AND HIGH LEVEL CLOUDS SHOULD MOVE INTO THAT AREA AHEAD OF THE NEXT SHORT WAVE THIS AFTERNOON. MAX TEMPS LEFT AS IS FOR NOW, WILL MAKE ANOTHER RE-ASSESSMENT AROUND 11 AM. RAIN WAS ADVANCING SLOWLY TOWARD THE VIRGINIA NORTHERN NECK EARLY THIS MORNING, AND THAT WAS ABOUT IN LINE WITH I295 TO I300 LIFT OFF THE NAM AND ECMWF. UNFORTUNATELY, AFTER THAT THE MODELS REFUSE TO COME TOGETHER. PLACEMENT OF BEST DYNAMICS, ISENTROPIC LIFT AND LOWER LEVEL FRONTOGENESIS ARE IN FLUX BY END OF THIS PERIOD, AND SO WE HAVE GONE WITH A FORECAST THAT COMBINES INDICATIONS OFF THE 00Z ECMWF /WHICH SHOWS MORE RUN-TO-RUN CONTINUITY/, CONTINUITY WITH THE PREVIOUS FORECAST AND NOWCASTING. THIS HAS MADE US SLOW THE PROGRESS OF RAIN INTO THE CENTRAL AND NORTHERN PARTS OF THE FORECAST AREA AND BACK OFF ON THE POPS SOME IN THE NORTHWEST. STILL NOT SEEING INSTABILITY PROGGED FOR OUR AREA, SO NOT SEEING A REASON TO RAISE QPF VALUES MUCH. ON TEMPERATURES, WE START FROM A FAIRLY WARM PLACE, AND INDICATIONS FROM H925 TEMPERATURE PROGS ARE THAT COLDER AIR DOES NOT LOOK TO GET PULLED DOWN FROM THE NORTH TODAY. WE THEREFORE HAVE SIDED WITH WARMER GUIDANCE. THE GRADIENT BETWEEN THE FAIRLY WEAK SURFACE LOW ADVANCING FROM THE SOUTH AND THE FAIRLY STRONG HIGH RETREATING TO THE NORTHEAST WILL MAKE FOR A DECENT FLOW TODAY.-- End Changed Discussion --&& .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/... THE BEST COMBINATION OF SYNOPTIC AND MESOSCALE INGREDIENTS COMES TOGETHER TONIGHT AS THE MAIN SHORT WAVE APPROACHES WITH AN ATTENDANT UPPER LEVEL JET. WE SHIFT THE AXIS OF MAIN PRECIPITATION A LITTLE EAST OF THE 00Z ECMWF. THE ECMWF HAS BEEN OSCILLATING ITS FOCUS A BIT FROM OFFSHORE TO ONSHORE THE PAST FEW RUNS, AND IT HAS TAKEN MORE OF AN ONSHORE FLAVOR THIS RUN. WE STILL DON`T SEE ANY SIGNS OF INSTABILITY. WE CONTINUE THE TEMPERATURE FORECAST THAT MINIMIZES THE DIURNAL OSCILLATION FROM THE NEAR TERM, AND WE WEAKEN THE WINDS GRADUALLY AS WE EXPECT THE LOW TO PASS WELL OFF THE COAST AND SLOWLY TAKE THE GRADIENT BETWEEN IT AND THE NORTHEASTERN HIGH AWAY FROM US. ENERGY FROM THE MID LEVEL IMPULSE PASSES TUESDAY MORNING. WE THEREFORE CONTINUE RAMPING DOWN THE POPS ON TUESDAY. WE DO NOT DRY OUT MUCH, AS THE SURFACE HIGH THAT BUILDS IN LOOKS VERY WEAK, AND BY WEDNESDAY WE MAY BEGIN TO FEEL SOME AFFECT FROM THE NEXT ADVANCING SYSTEM. WE MAINTAIN CONTINUITY ON TEMPERATURES TUESDAY AND TUESDAY NIGHT, AND THEN IN RESPONSE TO BOTH MAV AND MET GUIDANCE WE RAISE TEMPERATURES A BIT ON WEDNESDAY. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... A PATTERN CHANGE WILL CONTINUE TO GET UNDERWAY AS WE START THIS PERIOD. THE COMPUTER MODELS ARE IN GOOD AGREEMENT THAT A TROUGH WILL AMPLIFY ACROSS THE NORTHERN PLAINS AND GREAT LAKES REGION AS STRONG ENERGY DIVES SOUTHEASTWARD. THE SHORT WAVE ENERGY, COUPLED WITH THE JET STREAM POSITIONING, WILL TEND TO LEAD TO A CLOSED LOW FROM THE GREAT LAKES REGION DOWN TO THE OHIO VALLEY. WHILE THIS SYNOPTIC EVOLUTION IS AGREED UPON FAIRLY WELL BY THE COMPUTER GUIDANCE, DETAILS ESPECIALLY FROM LATE THURSDAY INTO SATURDAY BECOMES MORE DIFFICULT ALONG WITH LOWER CONFIDENCE AS TO THE LOCATION AND TRACK OF A CLOSED MIDLEVEL CENTER /AS IT MOVES EAST AND NORTHEASTWARD THROUGH THE CENTRAL APPALACHIANS AND NORTHEAST/. GIVEN THE UNCERTAINTY, WE INITIALIZED THE DATABASE WITH HPC GUIDANCE /COMPRISED OF THE ECMWF FOR WEDNESDAY NIGHT THROUGH THURSDAY NIGHT, THEN THE ECMWF/GFS ENSEMBLE MEANS FOR FRIDAY THROUGH SUNDAY/. WE DID MAKE SOME ADJUSTMENTS THOUGH AFTER ADDITIONAL COLLABORATION WITH OUR SURROUNDING OFFICES. BASED ON THE ABOVE, AN INITIAL COLD FRONT WILL BE ARRIVING WEDNESDAY NIGHT AS THE UPPER-LEVEL TROUGH AMPLIFIES TO OUR WEST. AS THE SYSTEM CLOSES OFF AND SLIDES EASTWARD, ENERGY ROTATING AROUND THIS WILL TEND TO KEEP THE CHC OF AT LEAST SOME SHOWERS ON THURSDAY. THERE IS SOME HINTS IN SOME OF THE MODEL GUIDANCE THAT AN INVERTED TROUGH MAY EXTEND ACROSS PORTIONS OF OUR AREA LATE THURSDAY INTO FRIDAY AS A NEW SURFACE LOW FORMS TO OUR EAST. IF THIS IS PRESENT, THEN PRECIPITATION COULD BE ENHANCED SOME ESPECIALLY AS THE MIDLEVEL LOW APPROACHES. FOR FRIDAY, THE SURFACE LOW IS FORECAST TO BE PULLING UP INTO THE VICINITY OF SOUTHERN NEW ENGLAND AND OUR AREA WILL BE UNDER A COLDER CYCLONIC FLOW. GIVEN THE COLDER AIR ARRIVING ALOFT, WE CANNOT RULE OUT SHOWERS /CONVECTIVE?/ WITH EVEN SOME SNOW POSSIBLE ESPECIALLY ACROSS THE NORTHERN AREAS. FOR NOW, WE JUST KEPT THE MENTION OF SNOW ACROSS THE FAR NORTHERN ZONES. IF ENOUGH MOISTURE AND INSTABILITY IS AROUND AS THE CLOSED LOW MOVES BY, WOULD NOT RULE OUT SOME SMALL HAIL/GRAUPEL WITH SOME SHOWERS. A BRISK NORTHWEST FLOW IS FORECAST TO SETUP AS WE GO THROUGH FRIDAY AND SATURDAY. THIS COULD KEEP SOME RAIN/SNOW SHOWERS GOING SATURDAY ESPECIALLY ACROSS THE FAR NORTHERN ZONES AS SOME LAKE ERIE/ONTARIO MOISTURE COULD GET PULLED SOUTHEASTWARD IN THE FORM OF STREAMERS. HIGH PRESSURE THEN BUILDS TO OUR SOUTH SUNDAY WITH THE NORTHWESTERLY FLOW GRADUALLY ON THE DECREASE. && .AVIATION /15Z MONDAY THROUGH FRIDAY/...-- Changed Discussion --THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. HIGH PRESSURE OVER THE CANADIAN MARITIME PROVINCES OF CANADA CONTINUES TO CAUSE AN EAST TO NORTHEAST FLOW OVER THE AREA EARLY TODAY. MOISTURE IS INCREASING ACROSS THE AREA RESULTING IN LOWERING CIGS TODAY. LIGHT RAINS AND FURTHER LOWERING CIGS WILL ARRIVE THIS AFTERNOON ACROSS THE TAF SITES. THE TIMING OF THE LOWERING CONDITIONS IS NOT CERTAIN...SO EXPECT AMDS THROUGH THE DAY. WINDS WILL BE MAINLY NE AROUND 10 TO 15 KTS TODAY. OUTLOOK... AS THE STORM SYSTEM TRACKS AWAY FROM OUR AREA TONIGHT, THE NERLY FLOW LOOKS TO CONTINUE. THIS WILL KEEP THE LOW-LEVEL MOISTURE IN PLACE, THEREFORE LOW CEILINGS AND/OR VISIBILITIES ALONG WITH SOME RAIN AND DRIZZLE WILL CONTINUE. WE MAY HAVE TO DEAL WITH A PROLONGED PERIOD OF LOWER CEILINGS TUESDAY AND WEDNESDAY AS MOISTURE GETS TRAPPED. A FRONTAL BOUNDARY IS FORECAST TO APPROACH LATE WEDNESDAY, THEN A STORM SYSTEM IS FORECAST TO DEVELOP TO OUR EAST LATER IN THE WEEK. THIS MAY BRING SOME WIND AND RAIN TO THE AREA.-- End Changed Discussion --&& .MARINE... STRONG HIGH PRESSURE IS WELL TO THE NORTH AND A WEAK LOW WILL BE MOVING OFFSHORE OF THE EAST COAST TODAY AND TUESDAY. THESE FEATURES WILL KEEP A DECENT NE FLOW OVER THE WATERS THROUGH TUESDAY. SCA FLAGS ARE ALREADY IN PLACE FOR THE COASTAL WATERS AND LOWER DEL BAY...AND WILL BE EXTENDED INTO UPPER DEL BAY TOO. THE SCA FLAG CONTINUE INTO TUESDAY FOR THE COASTAL WATERS. SEAS OUT AT THE BUOYS ARE 6 TO 8 FT EARLY THIS MORNING. CONDITIONS SHOULD DIMINISH TUE NGT AND SUB-SCA CONDITIONS WILL BE AROUND WED INTO THU. ANOTHER LOW WILL APPROACH FRI LIKELY CREATING MORE HAZARDOUS WINDS AND SEAS ON THE WATERS. && .TIDES/COASTAL FLOODING... TIDAL DEPARTURES ARE BEGINNING TO INCREASE NOW THAT THE NE FLOW HAS DEVELOPED. DURING THE PREVIOUS HIGH TIDE...THE GREATER DEPARTURES WERE LOCATED ACROSS THE SRN COASTAL WATERS AND LOWER DELAWARE BAY. THE NEXT HIGH TIDE WILL BE THE HIGHER OF THE TWO HIGH TIDES...AND SINCE THE NE WIND IS EXPECTED TO CONTINUE TODAY...THE LEVELS WILL PROBABLY COME CLOSE TO MINOR TIDAL FLOODING LEVELS. A COASTAL FLOOD ADVISORY WILL BE ISSUED FOR THE NEXT HIGH TIDE. I WILL NOT ISSUE IT FOR MONMOUTH COUNTY (AND NORTHWARD) SINCE GREATER DEPARTURES ARE NEEDED THERE...AND THE WIND DIRECTION MAY NOT FAVOR HIGHER DEPARTURES THERE. WE WILL CONTINUE TO MONITOR THROUGH TODAY. && .PHI WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --PA...NONE. NJ...COASTAL FLOOD ADVISORY UNTIL 3 PM EST THIS AFTERNOON FOR NJZ020>027. DE...COASTAL FLOOD ADVISORY UNTIL 3 PM EST THIS AFTERNOON FOR DEZ002>004. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EST WEDNESDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR ANZ430- 431.-- End Changed Discussion --&& $$ SYNOPSIS...DELISI NEAR TERM...DELISI/GIGI SHORT TERM...DELISI LONG TERM...GORSE AVIATION...O`HARA MARINE...O`HARA TIDES/COASTAL FLOODING...O`HARA
