Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 221620 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1220 PM EDT SUN MAR 22 2015 .SYNOPSIS... STRONG HIGH PRESSURE CENTERED NEAR THE UPPER GREAT LAKES TODAY WILL GRADUALLY BUILD SOUTHEASTWARD AND OVER OUR AREA TONIGHT THROUGH TUESDAY. A WARM FRONT ARRIVES ON WEDNESDAY, FOLLOWED BY A COLD FRONT ON THURSDAY. HIGH PRESSURE THEN GRADUALLY BUILDS TOWARD OUR AREA ALONG WITH COLDER AIR FOR FRIDAY AND SATURDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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THE WATER VAPOR IMAGERY AT MIDDAY SHOWS AN ACTIVE PATTERN. A TROUGH IS IN EASTERN CANADA AND ACROSS THE NORTHEASTERN U.S. A STRETCHED OUT SYSTEM IS ACROSS THE SOUTHERN STATES. AN INTENSE SURFACE LOW IS MOVING ACROSS THE CANADIAN MARITIMES, AND THE CYCLONIC FLOW ENHANCED AROUND THIS FEATURE IS MAINTAINING THE TROUGH IN THE EAST. THIS IS DRIVING COLDER AIR DOWN ACROSS THE NORTHEAST AND MID ATLANTIC REGIONS. STRONG HIGH PRESSURE CENTERED NEAR THE UPPER GREAT LAKES WILL SLOWLY BUILD SOUTHEASTWARD THROUGH THIS AFTERNOON. A TIGHT PRESSURE GRADIENT HOWEVER WILL BE ACROSS OUR AREA, AND WITH DEEPER MIXING THE SURFACE WINDS WILL BE GUSTY AT TIMES. THE EARLIER LAKE EFFECT STREAMER THAT WAS DROPPING SOUTHWARD INTO FAR NORTHEASTERN PENNSYLVANIA HAS WEAKENED CONSIDERABLY, THEREFORE WE WILL MAINTAIN A DRY FORECAST ATTM. OTHERWISE, SOME STRATOCUMULUS WILL MOVE ACROSS PORTIONS OF MAINLY OUR NORTHERN ZONES. MEANWHILE, SOME HIGH LEVEL CLOUDS WILL BE ACROSS THE AREA AT TIMES DUE TO THE STRETCHED OUT SOUTHERN STATES ENERGY. THE HIGH TEMPERATURES WERE RAISED SOME ESPECIALLY FROM THE INTERSTATE 95 CORRIDOR ON SOUTH AND EAST BASED ON TRENDS AND MIXING. THE HOURLY GRIDS WERE ADJUSTED TO ACCOUNT FOR THIS AND ALSO BASED ON THE LATEST OBSERVATIONS.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... DRY WEATHER WILL CONTINUE THROUGH TONIGHT AS HIGH PRESSURE CONTINUES TO BUILD TOWARD THE REGION. WE SHOULD LOSE THE WIND GUSTS BY SUNSET, BUT THERE MAY REMAIN A SLIGHT BREEZE THROUGH THE NIGHT FOR MANY AREAS AS THE HIGH WON`T BE FULLY OVER THE AREA JUST YET. TEMPERATURES CONTINUE TO BE FORECAST WELL BELOW NORMAL. A BLEND OF MAV/MET MOS AND MOSGUIDE WERE USED FOR OVERNIGHT LOWS. && .LONG TERM /MONDAY THROUGH SATURDAY/... AS WITH THE SHORT TERM, COOLER WEATHER WILL RULE THE LONG TERM, WITH A BRIEF EXCEPTION WEDNESDAY INTO EARLY THURSDAY. MONDAY AND TUESDAY...POLAR HIGH CONTINUES TO BUILD OVER THE REGION RESULTING IN HIGHS 10 TO 15 DEGREES BELOW NORMAL. WITH THE HIGH NEARER THE REGION, AND A MINIMAL PRESSURE GRADIENT ACROSS THE REGION, WINDS WILL BE RATHER LIGHT THROUGH THIS PERIOD. WEDNESDAY INTO THURSDAY...COMPARED TO MODEL RUNS YESTERDAY, TIMING OF BOTH THE WARM FRONT AND THE COLD FRONT HAS TRENDED EARLIER. LIKELY RELATED TO THE FACT THAT THE UPPER LEVEL TROUGH ISN/T AS NEGATIVELY TILTED, INDICATING A SLIGHTLY MORE PROGRESSIVE PATTERN. THE WARM FRONT, AND THUS BEGINNING OF THE PRECIP, SHOULD NOW MOVE IN DURING THE DAY WEDNESDAY. IMMEDIATELY BEHIND THE FRONT, LOOKS TO BE A STRATIFORM LIGHT RAIN EVENT WITH QPF AMOUNTS GENERALLY LESS THAN A TENTH OF AN INCH DURING THE DAY WEDNESDAY. HOWEVER, WEDNESDAY NIGHT INTO THURSDAY, AS THE LOW LEVELS WARM, INSTABILITY INCREASES. AS SUCH, EXPECT THE RAIN TO TRANSITION TO MORE CONVECTIVE DRIVEN, WITH SOME THUNDERSTORMS POSSIBLE ESPECIALLY DURING THE DAY THURSDAY. COLD FRONT IS NOW EXPECTED TO ARRIVE THURSDAY AFTERNOON OR EVENING. THURSDAY NIGHT INTO SATURDAY...A SECONDARY TRAILING UPPER LEVEL TROUGH MAY PROVIDE A FEW MORE CHANCES FOR PRECIPITATION THROUGH THIS PERIOD, THIS TIME MORE PROBABLE TO BE IN THE FORM OF A MIX OF RAIN AND WINTRY PRECIPITATION. HOWEVER, THERE IS CONSIDERABLE DRY AIR ADVECTION BEHIND THE COLD FRONT, AND AT LEAST ONE MODEL, THE GFS HAS TRENDED ALMOST COMPLETELY DRY THROUGH THIS PERIOD. FOR NOW THOUGH, KEPT LOWER END CHANCES IN AS SOME WEAK LOW LEVEL ON SHORE FLOW COULD PROVIDE ENOUGH MOISTURE FOR LIGHT PRECIP. SUNDAY...SURFACE RIDGE BUILDS IN BRINGING TRANQUIL, ALTHOUGH LIKELY STILL COOL, WEATHER. && .AVIATION /16Z SUNDAY THROUGH THURSDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THIS AFTERNOON...VFR. NORTHWEST WINDS 10-15 KNOTS WITH GUSTS TO 20-25 KNOTS. TONIGHT...VFR. NORTHWEST TO NORTH WINDS DIMINISHING TO 10 KNOTS OR LESS. OUTLOOK... MONDAY AND TUESDAY...VFR CONDITIONS EXPECTED. WEDNESDAY AND THURSDAY...CEILINGS LOWERING TO MVFR THEN IFR AS RAIN MOVES IN. MVFR VISIBILITY RESTRICTIONS POSSIBLE TOO. CONDITIONS MAY IMPROVE TO VFR THURSDAY NIGHT.
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&& .MARINE...
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WINDS AND SEAS REMAIN BELOW ADVISORY LEVELS ACROSS THE SOUTHERN HALF OF THE ATLANTIC WATERS AND DELAWARE BAY, THEREFORE NO SMALL CRAFT ADVISORY. FORECAST SOUNDINGS INDICATE GUSTS TO 25 KNOTS ON THE NORTHERN HALF OF THE ATLANTIC WATERS THROUGH TODAY, SO WE WILL KEEP THE SMALL CRAFT ADVISORY HERE. WE SHOULD LOSE THE WIND GUSTS BY SUNSET, BUT THERE SHOULD REMAIN A STEADY BREEZE THROUGH THE NIGHT FOR MANY AREAS. OUTLOOK... MONDAY THROUGH WEDNESDAY...WINDS AND SEAS SHOULD REMAIN BELOW SCA CRITERIA. WEDNESDAY NIGHT INTO THURSDAY...WINDS AND SEAS WILL INCREASE ABOVE SCA THRESHOLDS BY WEDNESDAY NIGHT. GUSTS ABOVE 30 KT WILL BE POSSIBLE ON THURSDAY IN THE WAKE OF A COLD FRONT.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ450- 451. && $$ SYNOPSIS...GORSE/JOHNSON NEAR TERM...GORSE SHORT TERM...ROBERTSON LONG TERM...JOHNSON AVIATION...GORSE/JOHNSON MARINE...JOHNSON/ROBERTSON

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