Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 292020 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 420 PM EDT SAT AUG 29 2015 .SYNOPSIS... HIGH PRESSURE WILL BE CENTERED NEAR THE MID ATLANTIC COAST INTO THURSDAY WITH A HEAT WAVE LIKELY. A WEAK COLD FRONT SHOULD SLIDE SOUTH INTO OUR REGION LATE THURSDAY WITH A COOLER ONSHORE FLOW DEVELOPING NEXT FRIDAY AND SATURDAY AS HIGH PRESSURE BECOMES DOMINANT OVER COASTAL EASTERN NEW ENGLAND. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... HIGH PRESSURE AT THE SURFACE ACROSS THE AREA WILL CONTINUE TO BECOME MORE CENTERED OFFSHORE, AND THIS WILL MAINTAIN A SOUTHERLY FLOW REGIME. MEANWHILE, A SHORT WAVE TROUGH FROM THE MIDWEST TO THE UPPER GREAT LAKES WILL GRADUALLY SHIFT EASTWARD. OUR WEATHER THROUGH TONIGHT WILL BE MAINLY DOMINATED BY THE DEPARTING SURFACE HIGH, THEREFORE A DRY NIGHT IS ANTICIPATED. THE CUMULUS THIS AFTERNOON IS EXPECTED TO FLATTEN AND DISSIPATE THIS EVENING WITH THE LOSS OF HEATING, THEN MOSTLY SOME HIGH LEVEL CLOUDINESS AROUND AT TIMES. THE LIGHT ENOUGH FLOW COMBINED WITH AMPLE BOUNDARY LAYER HEATING THIS AFTERNOON RESULTED IN A SEA BREEZE. THIS WILL CONTINUE TO MOVE INLAND SOME BEFORE WASHING OUT EARLY THIS EVENING. THE SOUTHERLY FLOW HAS HELPED TO INCREASE THE SURFACE DEW POINTS SOME, ALTHOUGH SOME LOWERING IN SPOTS HAS BEEN NOTED THIS AFTERNOON DUE TO BOUNDARY LAYER HEATING AND SOME MIXING. THESE SHOULD EDGE UP A BIT THROUGH THE NIGHT AS COOLING OCCURS AND THE MOISTURE STARTS TO POOL CLOSEST TO THE SURFACE. THIS COULD ALSO LEAD TO GROUND FOG IN LOCALIZED SPOTS. AS FOR THE LOW TEMPERATURES, WE USED MAINLY A NAM/GFS MOS BLEND AND THESE ARE A LITTLE HIGHER OVERALL WITH THE EXPECTATION THAT THE DEW POINTS WILL BE HIGHER THAN PREVIOUS NIGHTS. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... A SHORT WAVE TROUGH IS FORECAST TO BE ARRIVING ACROSS THE NORTHEAST LATER SUNDAY, AND AS IT DOES IT SHOULD TEND TO WEAKEN. A WEAK COLD FRONT AT THE SURFACE IS TIED TO THIS FEATURE, AND WITH SOME MOISTURE ON THE INCREASE THERE SHOULD BE SOME SHOWERS AND THUNDERSTORMS WITH IT TO OUR WEST. THE QUESTION IS WHETHER THIS ACTIVITY CAN BE MAINTAINED AS IT APPROACHES OUR WESTERN ZONES MAINLY LATER IN THE AFTERNOON. THERE IS SOME INSTABILITY DURING THE DAY AND INTO THE EVENING, WITH THIS PROBABLY BETTER ACROSS THE WESTERN ZONES. HOWEVER, THE FORECAST SOUNDINGS MOSTLY SHOW A SKINNY CAPE PROFILE WHICH TENDS TO KEEP UPDRAFTS ON THE WEAKER SIDE. THE BULK OF THE LIFT ASSOCIATED WITH THE TROUGH AXIS IS FORECAST TO BE TO OUR WEST DURING PEAK HEATING, HOWEVER TERRAIN INFLUENCES AND A WEAK SURFACE TROUGH COULD COME INTO PLAY AND THEREFORE WE INCLUDED A SLIGHT CHC POP DURING THE AFTERNOON ACROSS THE NORTHWESTERN ZONES. IT WILL BE RATHER WARM TO HOT ACROSS MUCH OF THE CWA, HOWEVER DEW POINTS MAY BE HIGHER IN THE MORNING DUE TO HEATING OF THE BOUNDARY LAYER ALLOWING FOR SOME DECREASE IN THE AFTERNOON. THE PRESSURE GRADIENT IS NOT FORECAST TO BE ALL THAT TIGHT, THEREFORE LIGHT ENOUGH FLOW SHOULD RESULT IN A SEA BREEZE ONCE AGAIN IN THE AFTERNOON. AS FOR THE HIGH TEMPERATURES, WE USED AN EVEN MOS BLEND THEN MADE SOME LOCAL TWEAKS. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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500 MB: A RIDGE OF WARM HIGH PRESSURE CENTERED NEAR BERMUDA DEVELOPS NORTHWESTWARD THIS WEEK WHILE A WEAK TROUGH REMAINS LODGED VICINITY OF THE LOWER MISSISSIPPI VALLEY. TEMPERATURES: AUGUST THROUGH THE 28TH AVERAGED NEAR OR ABOVE NORMAL. KMPO AND KGED WERE THE ONLY TWO OF THE 8 CLIMATE SITES BELOW NORMAL. KTTN, KACY AND KPHL WERE AVERAGING 1 TO ~2F ABOVE NORMAL. CALENDAR DAY DEPARTURES SUNDAY AND MONDAY WILL WARM THE MONTHLY AVERAGES COMPARED TO NORMAL. AS IT STANDS FROM THE 12Z/29 MODEL GUIDANCE TEMPERATURES SHOULD AVERAGE 6 TO 11 DEGREES ABOVE NORMAL MONDAY- THURSDAY. THE ONLY OPPORTUNITY FOR SIGNIFICANT COOLING OCCURS FRIDAY- SATURDAY BEHIND A SOUTHWARD DRIFTING COLD FRONT AND THERE IS NO CERTAINTY THAT THE COLD FRONT ARRIVES THURSDAY. IT COULD BE DELAYED OR LESS EFFECTIVELY COOLER THAN CURRENTLY FORECAST FOR FRIDAY AND SATURDAY. THE OUTCOME IS IN PART DEPENDENT ON THE AMPLITUDE AND LONGITUDE OF A TROUGH EAST OF THE MARITIMES LATE THIS COMING WEEK. THE GREATEST POSITIVE DEPARTURES WITH RESPECT TO NORMAL THROUGH THURSDAY SHOULD RESIDE NEAR AND N OF I-78. FORECAST BASIS: UNLESS OTHERWISE NOTED, A 50 50 BLEND 12Z/29 GFS/NAM MOS GUIDANCE SUNDAY NIGHT-MONDAY NIGHT - FAVORING THE WARMER OF THE AVBL GUIDANCE SINCE THE 12Z NCEP AND ECMWF 2M TEMPS ARE RATHER WARM AND 850 TEMPS 16-18C. THIS APPROACH WAS EXTENDED THROUGH THURSDAY EXCEPT THE 12Z/29 MEX MOS WAS APPLIED TUESDAY THROUGH THURSDAY WHICH WAS BLENDED WITH THE 1521Z WPC GUIDE. THE 1521Z/29 WPC GRIDDED ELEMENTS OF MAX/MIN TEMP, 12 HOUR POP, 6 HOUR DEWPOINT- SKY-WIND WAS USED AS IS FROM THURSDAY NIGHT ONWARD. HAZARDS THROUGH DAY 7: OTHER THAN RIP CURRENT MODERATE RISK TODAY-THEN POSSIBLY AGAIN SUNDAY AND THE END OF NEXT WEEK; ITS ABOUT A PROBABLE HEAT WAVE AND HOW LONG. FOR NOW, THE MAX HEAT INDEX IS FORECAST TO BE REMAIN BELOW ADVISORY CRITERIA...DEWPOINTS STILL ON THE LOWER SIDE OF WHAT THEY COULD BE. HEAT WAVE BEGINS SUNDAY OR MONDAY AFTERNOON DEPENDING ON LOCATION AND PROBABLY EXTENDS THROUGH AT LEAST THURSDAY. OUR MAX HEAT INDEX FORECAST RIGHT NOW IS IN THE MID 90S. THE DAILIES... SUNDAY NIGHT...VARIABLE CIRRUS, ESPECIALLY KPHL SOUTH OTHERWISE FAIR. LIGHT WIND. SMALL CHC OF A SHOWER OR TSTM NW OF I-95, WITH HIGHEST CHANCE APPEARING TO BE THE NORTHERN MOUNTAINS IN MONROE AND SUSSEX COUNTIES OF NE PA AND NW NJ. CONFIDENCE: ABOVE AVERAGE. MONDAY...PARTLY SUNNY SOUTH AND BECOMING SUNNY NORTH (CI FROM TROPICAL SYSTEM NEAR FL). HOT, ESPECIALLY KPHL NORTH. WESTERLY WIND GUSTS 15 MPH DURING THE AFTERNOON, POSSIBLY 20 MPH DURING THE EVENING I-95 EASTWARD. SMALL CHANCE OF AN AFTERNOON TSTM E PA OR THE N 2/3RDS NJ AHEAD A WEAK WIND SHIFT. CONFIDENCE: ABOVE AVERAGE. TUESDAY...SUNNY AND HOT. LIGHT N TO NW WIND, GUSTS UNDER 15 MPH. CONFIDENCE: ABOVE AVERAGE. WEDNESDAY...MOSTLY SUNNY AND HOT. COULD BE A PERIOD OF THICK CIRRUS. LIGHT SW WIND. CONFIDENCE: AVERAGE. THURSDAY...SUNNY AND HOT. LIGHT NW WIND. CONFIDENCE: ABOVE AVERAGE. FRIDAY AND SATURDAY...MAX TEMPS DEPEND IN PART ON THE COLD FRONTAL POSITION AND THE STRENGTH OF GEFS ONSHORE FLOW OFF THE WARMER THAN NORMAL ATLANTIC WATERS. COULD STILL BE HOT IN THE INTERIOR? LOOKS TO BE MORE HUMID WITH THE OCEAN INFLOW OFF THE SSTS IN THE 70S. EVENTUALLY A CHANCE OF TSTMS? PROBABLY MOST FAVORED IN THE UPSLOPE REGIONS OF E PA AND NW NJ BUT RATHER FAR IN THE FUTURE TO BE CONFIDENT. CONFIDENCE: BELOW AVERAGE (POSITION OF COLD FRONT).
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. REST OF THIS AFTERNOON...VFR WITH SOME CUMULUS AT AROUND 5000 FEET. SOUTH-SOUTHWEST WINDS UP TO 10 KNOTS. A SEA BREEZE SHOULD TURN THE WINDS MORE SOUTH OR SOUTH-SOUTHEAST AT KACY, WITH THIS ALSO OCCURRING AT KILG DUE TO A BAY BREEZE. TONIGHT...VFR OVERALL WITH REMAINING CUMULUS DISSIPATING IN THE EVENING. THERE IS A CHANCE FOR LOCALIZED MVFR FOG TOWARD SUNDAY MORNING. WINDS BECOMING LIGHT SOUTHWEST OR LIGHT AND VARIABLE AT MOST TERMINALS, TO LOCALLY CALM. SUNDAY...PERHAPS LOCALIZED MVFR FOG EARLY, OTHERWISE VFR WITH SOME CUMULUS AROUND 5000 FEET. SOUTHWESTERLY WINDS INCREASING UP TO 10 KNOTS, WHICH SHOULD TURN MORE SOUTHERLY AT KACY AND PERHAPS KILG DUE TO A SEA/BAY BREEZE. OUTLOOK... SUNDAY NIGHT...VFR MAINLY CIRRUS. LOCALIZED MVFR POSSIBLE WITH COUNTRYSIDE FOG MONDAY MORNING. AN ISOLATED SHOWER OR TSTM POSSIBLE VCNTY KMPO/KABE DURING THE EVENING? MONDAY...VFR SCT-BKN CLOUDS AOA 5000 FT. WEST WIND GUST 15-20 KT 16Z THROUGH 00Z/1. SMALL CHANCE OF ISOLATED TSTMS KPHL NORTHWARD. CONFIDENCE: AVERAGE. MONDAY NIGHT... VFR. LOCALIZED MVFR POSSIBLE WITH COUNTRYSIDE FOG EARLY TUESDAY MORNING. WIND TURNING NW-N LATE. CONFIDENCE: ABOVE AVERAGE. TUESDAY...VFR SCT CLOUDS AOA 5000 FT. LIGHT N TO NW WIND...GUSTS UNDER 15 KT. CONFIDENCE: ABOVE AVERAGE. WEDNESDAY...VFR SCT CLOUDS AOA 5000 FT. LIGHT SW WIND. ANOTHER BATCH OF CIRRUS POSSIBLE. CONFIDENCE: ABOVE AVERAGE THURSDAY...VFR. LIGHT W WIND BECOMING N OR NW. CONFIDENCE: AVERAGE. && .MARINE... HIGH PRESSURE BECOMING MORE CENTERED OFFSHORE WILL ALLOW FOR A SOUTHERLY FLOW THROUGH SUNDAY. WHILE THE WIND SPEEDS ARE EXPECTED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA, SOME INCREASE IS EXPECTED THROUGH THIS EVENING MOSTLY DUE TO A SEA BREEZE INFLUENCE NEARSHORE. THIS MAY ALSO OCCUR AGAIN SUNDAY AFTERNOON. SEAS MAINLY 3 FEET OR LESS. OUTLOOK... SUNDAY NIGHT- THURSDAY...A FEW GUSTS NEAR OR ABOVE 20 KT POSSIBLE SUNDAY NIGHT AND/OR MONDAY EVENING, OTHERWISE WINDS AND SEAS SHOULD STAY WELL BELOW SMALL CRAFT ADVISORY CRITERIA. WATER TEMPERATURES ARE ABOVE NORMAL. CONFIDENCE: ABOVE AVERAGE && .RIP CURRENTS...
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A LONG PERIOD /AROUND 11 SECONDS/ EAST-SOUTHEAST SWELL CONTINUES INTO TONIGHT, WITH SEAS IN THE 2-3 FOOT RANGE. A FULL MOON /HIGHER TIDE LEVELS/ AND A SOUTHERLY WIND WILL ALLOW FOR TRICKY CONDITIONS AT TIMES IN THE SURF ZONE ESPECIALLY FOR NEW JERSEY. AS A RESULT A MODERATE RISK OF DANGEROUS RIP CURRENTS ALONG THE NEW JERSEY COAST CONTINUES THROUGH THIS EVENING, HOWEVER A LOW RISK IS MAINTAINED FOR THE DELAWARE BEACHES. OUTLOOK... SUNDAY...APPEARS TO BE LOW ENHANCED WITH RESIDUAL IMPACT FROM TODAYS 3 FT 11 SECOND SE SWELL BUT THE SWELL SHOULD BE SUBSIDING SOMEWHAT ON SUNDAY. STILL FULL MOON IMPACT SO LARGER THAN NORMAL TIDAL EXCHANGE. MONDAY THROUGH THURSDAY...CURRENTLY LOOKING TO BE A DAILY LOW RISK. THE RISK MAY INCREASE SLIGHTLY NEXT FRIDAY-SATURDAY DEPENDING ON THE STRENGTH OF THE ONSHORE FLOW AND SIZE-PERIOD OF THE SWELL. CONCERN: ABOVE NORMAL SST`S (UPPER 70S) AND ABOVE NORMAL TEMPS THIS LAST FULL WEEK OF SUMMER AND SWIMMERS-WADERS BEING TOO CASUAL IN THE SURF ZONE SINCE THE RC RISK IS LOW. FOR GREATEST SAFETY... SWIM IN THE PRESENCE OF LIFE GUARDS AND DURING THEIR COVERAGE HOURS. SWIMMING AT JETTIES, PIERS, GROINS IS ILL ADVISED SINCE RIP CURRENTS REPEATEDLY FORM THERE. SWIMMING AT NIGHT OR NOT IN SIGHT OF LIFE GUARDS IS RISKY. WATER TROUBLE CAN QUICKLY TURN TO RECOVERY INSTEAD OF RESCUE.
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&& .CLIMATE...
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WE HAVE LOOKED AT RECORDS FOR NEXT WEEK (NEAR 100F IN 1953) AND SO WHILE CONFIDENCE IS VERY HIGH THAT A HEAT WAVE OCCURS NEXT WEEK, NOT ENOUGH HEAT IS INDICATED TO CHALLENGE THE RECORDS. RECORD HIGHS NEXT FRIDAY, SATURDAY AND SUNDAY ARE LOWER BUT NOT SURE HOW MUCH ONSHORE FLOW PREVAILS, THEREFORE KEEPING IT COOLER THAN RECORD.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...DRAG NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...DRAG 420 AVIATION...DRAG/GORSE MARINE...DRAG/GORSE RIP CURRENTS...420 CLIMATE...420

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