Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 210141 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 941 PM EDT SAT SEP 20 2014 .SYNOPSIS... HIGH PRESSURE WILL MOVE FARTHER OFF THE NEW ENGLAND COAST TONIGHT. A WAVE OF LOW PRESSURE OFF THE SOUTHEAST COAST WILL MOVE NORTHWARD UP THE EASTERN SEABOARD TONIGHT AND SUNDAY WHILE A COLD FRONT APPROACHES FROM THE WEST. THE FRONT IS EXPECTED TO MOVE THROUGH THE MID-ATLANTIC STATES SUNDAY NIGHT. HIGH PRESSURE BUILDING IN FROM THE MIDWEST EARLY IN THE WEEK WILL PERSIST OVER THE AREA THROUGH THE END OF THE WEEK. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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BASED ON LATEST SATELLITE IMAGERY, HAVE DECREASED SKY COVER OVER ALL BUT THE EXTREME SE WHERE IT IS STILL CLEAR. STILL EXPECT LOW CLOUDS TO FORM LATER TONIGHT IN TE ONSHORE FLOW, BUT VERY LITTLE IS OUT THERE NOW. ALSO, LATEST RADAR SHOWED SOME PRECIP OFF THE CST BUT NOTHING INLAND SO HAVE MADE SOME MINOR DOWNWARD ADJUSTMENTS TO POPS ALONG THE WRN PERIPHERY OF WHERE WE HAD POPS TO ACCOUNT FOR THEM NOT MAKING IT VERY FAR INLAND. A WEAKENING RIDGE OF HIGH PRESSURE WILL MOVE OFFSHORE TONIGHT. THE ONSHORE FLOW WILL CONTINUE AND ALONG WITH THAT COMES THE HIGHER DEW POINTS AND MODERATE TEMPERATURES. ANY PRECIPITATION TONIGHT WILL BE LIMITED TO NJ AND ERN/SRN DELAWARE WHICH WILL BE ASSOCIATED WITH THE DEVELOPING LOW OFF THE CAROLINA COASTAL AREAS. THE LOW WILL CREATE AN ENHANCED WIND GRADIENT ACROSS THESE AREAS. POPS WILL BE A THE CHC RANGE ACROSS THESE AREAS...AND IT WOULD BE HIGHER...BUT THE LOW IS EXPECTED TO TRACK NE OFFSHORE. LOW TEMPERATURES TONIGHT WILL BE MILDER THAN RECENT NIGHTS WITH LOWS IN THE MID/UPPER 50S NORTH AND LOW/MID 60S ACROSS OTHER AREAS. PATCHY FOG MAY DEVELOP ACROSS NJ AND THE DELMARVA LATER TONIGHT.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... LOW PRESSURE IS SHOWN MOVING UP ALONG THE COAST SUNDAY WHILE A SECOND LOW MOVES ACROSS THE GREAT LAKES AND HEADS TOWARD THE ST. LAWRENCE VALLEY. A COLD FRONT ATTACHED TO THE SECOND LOW WILL APPROACH FROM THE WEST DURING THE AFTERNOON. SHOWERS WILL OCCUR WITH THE FIRST LOW...NEAR THE SHORE AREAS EARLY...THEN WITH THE COLD FRONT OVER THE NRN/WRN AREAS LATE. IT WILL LIKELY BE A MOSTLY CLOUDY START TO THE DAY AND SOME MORNING FOG MAY BE SLOW TO BURN OFF. LIMITED SUN WILL BE ENOUGH TO BRING TEMPERATURES INTO THE UPPER 70S TO LOW 80S IN MOST AREAS. WINDS WILL BE LIGHT EARLY...THEN FAVOR A SRLY/SWRLY DIRECTION AHEAD OF THE APPROACHING FRONT. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... A COLD FRONT IS FORECAST TO MOVE THROUGH THE AREA SUNDAY NIGHT. MODELS ARE IN GOOD AGREEMENT WITH TIMING OF FROPA OCCURRING DURING THE EVENING WEST OF I-95 AND OVERNIGHT FARTHER TO THE EAST. EXPECT TO SEE A BRIEF PERIOD OF SHOWERS WITH THE FROPA AS FORCING FOR ASCENT ASSOCIATED WITH THE UPPER TROUGH AND JET STREAK TRAVERSES THE AREA. THE TROUGH WILL BE DEEPENING AS IT APPROACHES THE EASTERN SEABOARD, BUT AMPLIFICATION IS FORECAST TO OCCUR TOO LATE FOR DEEPER MOISTURE FROM THE GULF OF MEXICO OR ATLANTIC TO REACH OUR AREA IN TIME. THE FORECAST PRE-FRONTAL ENVIRONMENT FROM 12Z GFS/NAM AND 09Z SREF BUFKIT SOUNDINGS IS CHARACTERIZED BY WEAK LAPSE RATES AND MEAGER INSTABILITY. DO NOT EXPECT PRECIP TO BE PARTICULARLY HEAVY OR WIDESPREAD UNDER THIS SETUP. THE COLD FRONT WILL MOVE OFFSHORE WHILE HIGH PRESSURE BUILDS IN FROM THE MIDWEST STATES. NORTHWEST WINDS BEHIND THE COLD FRONT WILL USHER IN NOTICEABLY COOLER AND DRIER AIR ON MONDAY IN A TIMELY FASHION FOR THE FIRST DAY OF AUTUMN. MAX TEMPS RANGE FROM NEAR 60F IN THE POCONOS TO MID 70S IN THE DELMARVA/SOUTHERN NJ. CLOUDS WILL LIMIT SUNSHINE ESPECIALLY ACROSS THE NORTHERN AND WESTERN TIER OF THE CWA. MODELS OFTEN UNDER DO THE POST-FRONTAL STRATOCU DEVELOPMENT DURING SIGNIFICANT CAA REGIMES. A QUIET WX PATTERN WILL CONTINUE INTO AT LEAST THE MIDDLE OF THE WEEK WITH HIGH PRESSURE BUILDING IN DURING THIS TIME. A CUTOFF LOW IS FORECAST TO DEVELOP OVER THE SOUTHEAST STATES DURING THE FIRST HALF OF THE WEEK. THERE WAS SOME HINT AT THIS LOW DRIFTING NORTHWARD UP THE EASTERN SEABOARD AND THEN POSSIBLY IMPACTING PORTIONS OF THE FORECAST AREA LATE IN THE WEEK. HOWEVER, PREDICTABILITY IN THIS SETUP IS LOWER THAN NORMAL DUE TO A LACK OF STEERING FLOW UNDERNEATH THE RIDGE. ASIDE FROM THE 12Z OPERATIONAL ECMWF, DID NOT HAVE ENOUGH SUPPORT FROM NWP GUIDANCE TO WARRANT A SIGNIFICANT CHANGE TOWARD A MORE PESSIMISTIC (I.E., CLOUDY AND RAINY) FORECAST FOR LATE IN THE WEEK. CONFINED SLIGHT CHANCE POPS TO THE DELMARVA THURSDAY. OTHERWISE, A DRY FORECAST IS ADVERTISED THRU THE END OF THE LONG-TERM PERIOD. NEAR TO SLIGHTLY BELOW NORMAL TEMPS EXPECTED EARLY IN THE WEEK BEHIND THE COLD FRONT AND CONTINUE THRU THE END OF THE WEEK WITH PERSISTENT ONSHORE FLOW. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDS PREVAIL EVERYWHERE EARLY THIS EVE. KACY HAD SOME BRIEF MVFR EARLIER AND IT CAN NOT BE RULED OUT AGAIN, BUT THE OVERALL TREND IS DOWNWARD AS THE ONSHORE FLOW FAVORS A SLOW LOWERING OF CIGS AND VSBYS IN FOG OVERNIGHT. SOME LIGHT SHOWERS OR PATCHY DRIZZLE MAY OCCUR CLOSE TO THE SHORE. THIS WAS PLACED IN A TEMPO GROUP FOR KACY. SUNDAY...SLOW RECOVERY BACK TO VFR WITH AN APPROACHING COLD FRONT AND A GRADUAL SWITCH IN WINDS TO SW. IT IS LIKELY THAT MOST SITES WILL BE BACK TO VFR 14Z- 16Z. OUTLOOK... SUNDAY NIGHT...COLD FRONT MOVES THRU THE TERMINALS. SCT SHRA ALONG AND AHEAD OF THE FRONT BUT GENERALLY VFR CONDITIONS EXPECTED. WIND SHIFT FROM SW TO NW WILL OCCUR WITH THE FROPA. MONDAY...NW WIND GUSTS AROUND 20 KT ARE POSSIBLE MONDAY IN ASSOCIATION WITH POST-FRONTAL PRESSURE SURGE. STRATOCU FAVORED IN THIS SETUP, WHICH MAY RESULT IN A PERIOD MVFR CIGS FOR PHILLY TERMINALS NORTH AND WEST. MONDAY NIGHT THROUGH THURSDAY...VFR AND LIGHT WINDS EXPECTED.
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&& .MARINE... THE SCA FLAG OUT PRESENTLY FOR THE COASTAL WATERS WILL BE EXTENDED IN TIME...SINCE THE APPROACHING LOW WILL NOT DO ANYTHING TO REDUCE THE POTENTIAL FOR ENHANCED SEAS. WE WILL ADD THE NRN-MOST COASTAL ZONE TO THE MIX THIS EVENING...WHEN THE HIGHER SEAS WILL (PROBABLY) ARRIVE THERE. THE SCA FLAG WILL CONTINUE THRU NOON SUNDAY. BY THEN THE BEST PRESSURE GRADIENT WITH THE OFFSHORE LOW WILL HAVE WEAKENED ACROSS THE WATERS. SCT SHOWERS ARE EXPECTED TONIGHT AND EARLY SUNDAY. OUTLOOK... SUNDAY NIGHT THROUGH MONDAY...A COLD FRONT WILL MOVE THRU THE WATERS LATE SUNDAY NIGHT. SW FLOW AHEAD OF THE FRONT WILL SHIFT OUT OF THE NW. POST-FRONTAL NW WINDS OF 15-20 KT GENERALLY EXPECTED BUT CANNOT RULE OUT LOCALLY STRONGER GUSTS LATE SUNDAY NIGHT INTO MONDAY. LATEST GUIDANCE ALSO SHOWS SEAS INCREASE TO 4-6 FT IN THE ATLANTIC JUST OFF THE DE/NJ COAST DURING THIS TIME. OPTED TO HOLD OF ON ISSUING A SCA WITH ANOTHER SCA IN EFFECT THRU NOON SUNDAY AND A LULL IN SCA CONDITIONS EXPECTED FOR 6-12 HOURS. MONDAY NIGHT THROUGH THURSDAY...SUB-SCA CONDITIONS EXPECTED ATTM. && .RIP CURRENTS... A MODERATE RISK FOR ENHANCED RIP CURRENTS WILL CONTINUE TONIGHT AS THE DECENT ONSHORE FLOW CONTINUES. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT SUNDAY FOR ANZ451>455. SMALL CRAFT ADVISORY UNTIL NOON EDT SUNDAY FOR ANZ450.
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&& $$ SYNOPSIS...KLEIN NEAR TERM...NIERENBERG/O`HARA SHORT TERM...O`HARA LONG TERM...KLEIN AVIATION...KLEIN/NIERENBERG/O`HARA MARINE...KLEIN/O`HARA RIP CURRENTS...

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