Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 280202 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1002 PM EDT MON APR 27 2015 .SYNOPSIS... A LARGE AND COMPLEX LOW PRESSURE SYSTEM OVER THE WESTERN NORTH ATLANTIC WILL CONTINUE TO MOVE SLOWLY OUT TO SEA. MEANWHILE, HIGH PRESSURE WILL TRY TO BUILD INTO OUR REGION GRADUALLY FROM THE NORTHWEST AND WEST THROUGH WEDNESDAY. ANOTHER AREA OF LOW PRESSURE IS FORECAST TO PASS OFF THE NORTH CAROLINA COAST ON THURSDAY AFTERNOON. THE LOW IS EXPECTED TO STRENGTHEN AS IT MOVES OUT TO SEA ON THURSDAY NIGHT AND FRIDAY. HIGH PRESSURE IS ANTICIPATED TO BUILD INTO OUR REGION FROM THE WEST FOR THE COMING WEEKEND. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... NOT MUCH CHANGE TO THE SHORT TERM GRIDS WITH THE LATE EVENING UPDATE. HAVE PULLED THE SLIGHT CHANCE POPS ACROSS THE REGION AS THE BETTER INSTABILITY/ENERGY REMAINS TO OUR WEST, THOUGH A BRIEF SPRINKLE MAY OCCUR IN OUR EXTREME NORTHWESTERN ZONES THROUGH MIDNIGHT...OTHERWISE WE WILL REMAIN DRY. MID LEVELS REMAIN MOIST ENOUGH TO SUPPORT EXTENSIVE CLOUDS UNTIL SUBSIDENCE BEGINS IN THE WAKE OF THE MID LEVEL TROUGH THROUGH THE OVERNIGHT HOURS. TEMPERATURES WILL CONTINUE TO SLOWLY FALL TONIGHT. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... BY TOMORROW, THE LOW OVER THE NORTHWEST ATLANTIC WILL BE NEARLY VERTICALLY STACKED. OUR REGION WILL STAY UNDER THE INFLUENCE OF NORTHWESTERLY AND NORTHERLY FLOW AS THIS LOW SLOWLY SLIDES EAST AWAY FROM THE REGION. THICKNESSES WILL INCREASE SLIGHTLY, THUS EXPECT A MODEST WARMING TREND WITH HIGHS GENERALLY IN THE UPPER 50S TO UPPER 60S. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... WE SHOULD REMAIN UNDER THE OUTER INFLUENCE OF A MID LEVEL LOW OFF NOVA SCOTIA ON TUESDAY NIGHT. A WEAK MID LEVEL RIDGE IS FORECAST TO APPROACH FROM THE WEST AND NORTHWEST AND IT IS FORECAST TO BE OVERHEAD ON WEDNESDAY AND WEDNESDAY NIGHT. DRY WEATHER IS EXPECTED FROM TUESDAY NIGHT THROUGH WEDNESDAY NIGHT ALTHOUGH THERE SHOULD BE AN INCREASE IN HIGH LEVEL CLOUDS DURING THE PERIOD. A LONG WAVE MID LEVEL TROUGH IS ANTICIPATED TO BE OVER THE EASTERN STATES FOR THURSDAY INTO FRIDAY. A CLOSED LOW IS FORECAST TO DROP FROM THE GREAT LAKES TO THE MIDDLE ATLANTIC STATES FROM WEDNESDAY NIGHT THROUGH THURSDAY NIGHT BEFORE MOVING EASTWARD AND OFF THE COAST ON FRIDAY. SURFACE LOW PRESSURE IS EXPECTED TO MOVE FROM GEORGIA AND SOUTH CAROLINA ON WEDNESDAY TO THE WATERS OFF CAPE HATTERAS ON THURSDAY AFTERNOON. THERE REMAINS SOME DISAGREEMENT AMONG THE MODEL GUIDANCE REGARDING THE STRENGTH AND TRACK OF THE LOW AS IT MOVES OUT TO SEA ON THURSDAY NIGHT AND FRIDAY. WHILE A FAIR AMOUNT OF CLOUD COVER SEEMS LIKELY, THE NORTHWESTERN EXTENT OF THE MAIN PRECIPITATION SHIELD WITH THE SYSTEM REMAINS A LOW CONFIDENCE FORECAST. ALSO, AN AREA OF CONVECTIVE PRECIPITATION IS EXPECTED TO DEVELOP OVER THE OHIO RIVER VALLEY ON WEDNESDAY NIGHT INTO THURSDAY IN RESPONSE TO THE MID LEVEL LOW. SOME REMNANT OF THAT ACTIVITY MAY DRIFT TOWARD OUR REGION, AS WELL. THE MODEL GUIDANCE SEEMS TO BE SUGGESTING A DRY WEDGE POKING DOWN INTO OUR REGION FROM THE NORTHEAST FOR THURSDAY INTO THURSDAY NIGHT DUE TO THE CIRCULATION AROUND THE LOW. ALSO, SUBSIDENCE AROUND THE SYSTEM MAY CONTRIBUTE TO THE DEVELOPMENT OF AN AREA OF LESSENING PRECIPITATION AROUND ITS OUTER EDGE. AS A RESULT, WE WILL KEEP OUR PRECIPITATION PROBABILITIES MAINLY IN THE CHANCE RANGE. THE WIND FORECAST ASSOCIATED WITH THE SYSTEM REMAINS A BIT UNCERTAIN, AS WELL. WHILE THE BACKING FROM AN EAST TO A NORTH WIND FROM THURSDAY INTO FRIDAY APPEARS LIKELY, THE SPEED FORECAST IS DEPENDENT UPON THE EVENTUAL TRACK OF THE SYSTEM. WE HAVE GONE WITH A MIDDLE OF THE ROAD SOLUTION FOR THE TIME BEING. THE LONG WAVE TROUGH IS FORECAST TO MOVE OUT OVER THE WESTERN NORTH ATLANTIC FOR THE WEEKEND. A MID LEVEL SHORT WAVE MAY DROP DOWN FROM THE NORTHWEST AROUND SUNDAY. THE FEATURE IS ANTICIPATED TO HAVE LIMITED MOISTURE ASSOCIATED WITH IT. A RIDGE FROM THE WEST IS FORECAST TO BUILD OVER THE EASTERN STATES ON MONDAY. DAYTIME TEMPERATURES SHOULD BE ABOVE NORMAL ON WEDNESDAY, THEN THEY ARE FORECAST TO FALL BELOW NORMAL FOR THURSDAY AND FRIDAY DUE TO THE CLOUD COVER, EAST TO NORTH WIND AND POSSIBLE RAIN. TEMPERATURES ARE EXPECTED TO RETURN ABOVE NORMAL OVER THE WEEKEND. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. NOT MUCH TO ADD TO THE PREVIOUS 18Z TAFS SO WE KEEP THE FORECAST STATUS QUO FOR THE TIME BEING. VFR CONDITIONS SHOULD CONTINUE THROUGH THE TAF PERIOD, WITH MOSTLY MID LEVEL CLOUDS BETWEEN 6000 AND 8000 FT AGL. THERE IS A SMALL CHANCE OF LOW LEVEL CLOUDS (AROUND 2000 FT AGL) DEVELOPING PRIMARILY WEST OF THE FALL LINE, INCLUDING KRDG AND KABE, BETWEEN 09 AND 15Z. HOWEVER, GIVEN HOW DRY THE AIR MASS IS IN THE BOUNDARY LAYER, THINK THIS IS VERY UNLIKELY. MORE GUSTY NORTHERLY WINDS EXPECTED STARTING TOMORROW LATE MORNING. OUTLOOK... TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...MAINLY VFR. THURSDAY AND THURSDAY NIGHT...MAINLY VFR WITH A CHANCE OF RAIN. CONDITIONS MAY DROP INTO THE MVFR RANGE AT TIMES. AN EAST TO NORTHEAST WIND AROUND 10 TO 15 KNOTS IS EXPECTED ALONG WITH ITS POTENTIAL IMPACT ON OPERATIONS AT KPHL. FRIDAY...MAINLY VFR WITH A CHANCE OF SHOWERS. FRIDAY NIGHT AND SATURDAY...MAINLY VFR. && .MARINE... SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED TO DEVELOP LATE THIS EVENING, WITH WIND GUSTS AT OR JUST ABOVE 25KT. WIND GUSTS SHOULD BEGIN TO DIMINISH BY MID TUESDAY MORNING. ONCE WIND SPEEDS DECREASE, SUB SCA CONDITIONS ARE EXPECTED FOR THE REMAINDER OF THE DAY. SEAS WILL LIKELY REMAIN BELOW 5 FT THROUGH THE ENTIRE PERIOD. OUTLOOK... TUESDAY NIGHT THROUGH THURSDAY MORNING...NO MARINE HEADLINES ARE ANTICIPATED. THURSDAY AFTERNOON THROUGH FRIDAY...A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED FOR WIND GUSTS OF 25 TO 30 KNOTS AND FOR WAVES ON OUR OCEAN WATERS IN EXCESS OF 5 FEET. THE WIND DIRECTION IS ANTICIPATED TO BACK GRADUALLY FROM THE EAST TO THE NORTH. THERE IS THE POTENTIAL FOR GALE FORCE GUSTS IF LOW PRESSURE OVER THE OCEAN TRACKS CLOSER TO THE COAST THAN CURRENTLY EXPECTED. FRIDAY NIGHT AND SATURDAY...WIND SPEEDS ARE FORECAST TO REMAIN BELOW THE SMALL CRAFT ADVISORY CRITERION. HOWEVER, WAVE HEIGHTS ON OUR OCEAN WATERS MAY REMAIN AROUND OR ABOVE 5 FEET. && .FIRE WEATHER... NORTH NORTHWESTERLY WINDS GUSTING ABOVE 20 MPH WILL BE POSSIBLE ACROSS THE REGION ON TUESDAY. RELATIVE HUMIDITY VALUES AROUND 30 PERCENT ARE POSSIBLE PRIMARILY OVER NJ, SOUTHEASTERN PA (SOUTHEAST OF THE POCONOS), AND EXTREME NORTHERN DELMARVA. SINCE CONDITIONS WILL BE MARGINAL AT WORST, WILL WAIT FOR AT LEAST ONE MORE FULL SUITE OF MODEL RUNS BEFORE MAKING A DECISION IF TO ISSUE AN SPS OR RFW. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT TUESDAY FOR ANZ430-431- 450>455. && $$ SYNOPSIS...IOVINO NEAR TERM...HEAVENER/JOHNSON SHORT TERM...JOHNSON LONG TERM...IOVINO AVIATION...IOVINO/JOHNSON MARINE...IOVINO/JOHNSON FIRE WEATHER...JOHNSON

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