Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 292224 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 624 PM EDT SUN MAR 29 2015 .SYNOPSIS... A COLD FRONT IS EXPECTED TOMORROW. ON ITS HEALS WILL BE A FAST MOVING LOW PRESSURE SYSTEM WHICH SHOULD SWEEP THROUGH THE AREA LATE TUESDAY. HIGH PRESSURE WILL BUILD INTO THE REGION FOR WEDNESDAY AND MOVE OFFSHORE ON THURSDAY. THE NEXT COLD FRONT WILL COME LATE IN THE WEEK. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... SURFACE RIDGING CRESTS TO OUR SOUTH AND EAST LATER THIS EVENING AS THE WINDS ACROSS OUR REGION BACK FURTHER TOWARDS THE SOUTH- SOUTHWEST. AN POSITIVE FLUX IN MOISTURE IS EXPECTED TO OCCUR TONIGHT AS THE RETURN FLOW AND 40 KNOT LOW-LEVEL JET MOVES IN OVERHEAD, THOUGH WE DO HAVE A RELATIVE MINIMUM STARTING POINT WITH OUR SURFACE DEWPOINTS. A WEAK COLD FRONT WILL PUSH TOWARD THE REGION LATE TONIGHT AND CROSS MOST OF THE AREA BY LATER MONDAY MORNING. NOT MUCH MOISTURE WITH THIS FRONT AND DEWPOINTS WERE STILL IN THE SINGLE DIGITS IN MOST AREAS THROUGH LATE SUNDAY AFTERNOON. HOWEVER...MODELS ARE INDICATING UP TO A TENTH OF AN INCH OF PRECIPITATION OVER OUR SOUTHERN FLANK...AND A FEW HUNDREDS IN THE NORTH. NORMALLY THIS WOULD NOT BE NEWSWORTHY, BUT WITH CLEAR SKIES AND LIGHTER WINDS INTO THE OVERNIGHT HOURS...TEMPERATURES ARE EXPECTED TO DROP BELOW FREEZING NORTH AND WEST OF PHILADELPHIA. ANY PRECIPITATION THAT FALLS DURING THE LATE OVERNIGHT HOURS (4 AM TO 7 AM)COULD BE IN THE FROM OF MAINLY LIGHT SNOW SHOWERS...ESPECIALLY NORTH OF I-78. THE SNOW GRIDS HAVE BEEN ADJUSTED ACCORDINGLY. NO IMPACT IS EXPECTED...AND ANY ACCUMULATION WOULD BE ON GRASSY SURFACES IN THE HIGHER ELEVATIONS. THE CHANGEOVER BACK TO LIGHT RAIN SHOULD OCCUR WITHIN AN HOUR OR SO AFTER SUNRISE MONDAY MORNING...ASSUMING ENOUGH MOISTURE IS AVAILABLE AT THE POINT IN TIME. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... THE FRONT WILL CLEAR THE REGION BY LATE MORNING HELPING TO PULL ANY LINGERING MOISTURE OFF TO OUR EAST...RATHER QUICKLY. DRYING AND WARMING TREND IS EXPECTED FOR MONDAY AS WE MAINTAIN THE SOUTHWEST- WEST SURFACE FLOW. TEMPERATURES SHOULD BE ABLE TO CLIMB BACK TO AVERAGE, IF NOT ABOVE ONCE WE START TO CLEAR SOME OF THE STRATOCU OUT OF THE REGION. WENT WITH THE WARMER MAV GUIDANCE. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... STILL CONSIDERABLE UNCERTAINTY WITH THIS FORECAST ESPECIALLY AS THE SPLIT FLOW PATTERN CONTINUES FOR MUCH OF THE WEEK. TUESDAY AND WEDNESDAY...THE BIG QUESTION THROUGH THIS PERIOD WILL BE THE TRACK OF THE FAST MOVING CLIPPER SYSTEM TUESDAY INTO TUESDAY NIGHT. MOST MODELS BRING THE CENTER OF THE SURFACE LOW ACROSS DELMARVA AND SOUTHERN NJ, WITH THE EXCEPTION OF THE NAM, WHICH TAKES A NORTHERN TRACK, BRINGING THE CENTER OF THE LOW ACROSS NORTHERN NJ. WITH MORE MODEL AGREEMENT ON THE SOUTHERN TRACK, FORECAST FAVORS THE SOUTHERN TRACK, KEEPING HIGHER POPS ACROSS THE SOUTH AND FAVORING THE COLDER GUIDANCE FOR HIGHS ON TUESDAY. BY WEDNESDAY, A SURFACE HIGH MOVES IN FOR A BRIEF APPEARANCE. THURSDAY THROUGH SATURDAY...THIS CONTINUES TO BE THE MOST UNCERTAIN PERIOD OF THE FORECAST. THE GFS AND ECMWF CONTINUE TO SHOW VAST DIFFERENCES IN THE TIMING AND TRACK OF A PAIR OF LOWS. THE FIRST LOW OVER THE HUDSON BAY REGION LATE IN THE WORK WEEK. THE QUESTION WILL BE IF AND WHEN THE ASSOCIATED COLD FRONT WILL TRACK AS FAR SOUTH AS OUR REGION. THE SECOND LOW THE GFS SHOWS DEVELOPING OVER THE SOUTHERN HIGH PLAINS BY THURSDAY NIGHT AND SLIDING EAST JUST SOUTH OF REGION THROUGH SATURDAY, KEEPING A STATIONARY FRONT SOUTH OF US THROUGH THIS TIME. THE ECMWF ON THE OTHER HAND...SHOWS THE LOW FILLING AND ESSENTIALLY DISAPPEARING BY FRIDAY. GIVEN THE UNCERTAINTY, STAYED CLOSE TO THE PREVIOUS FORECAST. HOWEVER, AT THIS POINT, AM CONCERNED THAT THE ECMWF MAY BE UNDERESTIMATING LEE SIDE CYCLOGENESIS. WITH BOTH SOLUTIONS THOUGH, THE END RESULT IS THAT IT WILL BE COOLER (40S AND 50S) FOR THE WEEKEND. && .AVIATION /22Z SUNDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY, AND SURROUNDING AREAS. TONIGHT...VFR. CLEAR SKIES PREVAIL THROUGH THE EVENING HOURS AS HIGH PRESSURE CRESTS OVER THE REGION. THE WINDS WILL CONTINUE TO BACK TOWARDS THE WEST-SOUTHWEST THIS EVENING BEFORE BECOMING SOUTHERLY LATE TONIGHT. THIS IS AHEAD OF A COLD FRONT PASSAGE MONDAY MORNING. MONDAY...MOSTLY VFR. THE COLD FRONT WILL CROSS THE REGION MONDAY MORNING AND COULD PRODUCE A BRIEF PERIOD OF RAIN/SNOW AT THE TERMINALS. COVERAGE LOOKS SPOTTY AND WAS NOT CONFIDENT ENOUGH TO ADD PRECIPITATION TO THE TAFS, THOUGH FARTHER SOUTH INTO THE DELMARVA HAS THE BETTER CHANCES. RIGHT BEHIND THE FRONT THE WINDS VEER TOWARDS THE SOUTHWEST A BIT AND INCREASE WITH SOME GUSTS INTO THE LOW-20S. BRIEF MVFR CIGS ARE POSSIBLE RIGHT BEHIND THE FRONT, OTHERWISE BKN-OVC 5000FT DECK SHOULD PERSIST THROUGH MUCH OF THE AFTERNOON BEFORE SCATTERING OUT. OUTLOOK... TUESDAY...CEILINGS AND VISIBILITIES DECREASING TO MVFR, POSSIBLY IFR, WITH INCOMING RAIN. SNOW POSSIBLE IN HIGHER TERRAIN. WEDNESDAY...MOSTLY VFR CONDITIONS. THURSDAY AND FRIDAY...MOSTLY VFR, CHANCE FOR RA AND SLIGHT CHANCE FOR TSRA. WITH PRECIPITATION, MVFR CONDITIONS POSSIBLE. && .MARINE... TONIGHT - MONDAY...SUB-SCA EXPECTED ACROSS THE WATERS THROUGH THE LATE EVENING HOURS. THEN WINDS BACK TOWARDS THE SOUTH-SOUTHWEST AND THE SEAS BEGIN TO INCREASE AGAIN. THE PRESSURE GRADIENT TIGHTENS WITH SOME ENHANCED MIXING AND GUSTS CLOSE TO 30 KNOTS RIGHT AROUND A COLD FRONT PASSAGE. WINDS VEER TOWARDS THE WEST-SOUTHWEST BEHIND THE FRONT AND CONTINUE TO GUST FOR A PERIOD. THE GUSTS ON THE BAY AND OCEAN SHOULD DROP BY MONDAY EVENING WHILE THE SEAS REMAIN SOMEWHAT ELEVATED ALONG THE OCEANFRONT. SCA IS GOOD FROM 6Z TONIGHT TO 6Z TUESDAY NIGHT. OUTLOOK... TUESDAY...ONCE WAVES DECREASE BELOW 5 FT EARLY TUESDAY MORNING, WINDS AND SEAS SHOULD REMAIN BELOW SCA CRITERIA FOR THE REST OF THE DAY. TUESDAY NIGHT AND WEDNESDAY...WINDS SHOULD REMAIN BELOW SCA CRITERIA UNLESS THE LOW IS STRONGER THAN FORECAST. SEAS WILL BE DEPENDENT ON THE WIND FORECAST BUT AT THIS POINT ARE GENERALLY EXPECTED TO REMAIN NEAR OR BELOW 5 FT. THURSDAY AND FRIDAY...SOUTHERLY AND SOUTHWESTERLY WINDS WILL LIKELY INCREASE ABOVE 25 KT FOR AT LEAST PART OF THIS PERIOD. SEAS WILL LIKELY INCREASE ABOVE SCA CRITERIA AS WELL. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY FROM 2 AM MONDAY TO 2 AM EDT TUESDAY FOR ANZ450>455. SMALL CRAFT ADVISORY FROM 2 AM TO 6 PM EDT MONDAY FOR ANZ430- 431. && $$ SYNOPSIS...JOHNSON NEAR TERM...MIKETTA SHORT TERM...HEAVENER/MIKETTA LONG TERM...JOHNSON AVIATION...HEAVENER/JOHNSON MARINE...HEAVENER/JOHNSON

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