Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 171756 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 156 PM EDT SUN AUG 17 2014 .SYNOPSIS... A COLD FRONT OVER THE GREAT LAKES EARLY THIS MORNING WILL PROGRESS SOUTHEASTWARD THROUGH EASTERN PENNSYLVANIA AND NEW JERSEY TODAY AND THE DELMARVA TONIGHT. THE FRONT WILL STALL JUST SOUTH OF THE AREA MONDAY. A WAVE OF LOW PRESSURE IS EXPECTED TO TRACK EASTWARD ALONG THE STALLED BOUNDARY MONDAY NIGHT INTO TUESDAY. ANOTHER LOW PRESSURE SYSTEM WILL APPROACH THE AREA WEDNESDAY INTO THURSDAY. THE AFOREMENTIONED FRONTAL BOUNDARY IS EXPECTED TO REMAIN JUST SOUTH OF THE AREA THROUGH THE REMAINDER OF THE WEEK AS MORE WAVES OF LOW PRESSURE RIDE ALONG IT. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... AN EVER SLOWING COLD FRONT SLINKS ACROSS THE GREAT LAKES INTO NORTHWESTERN PENNSYLVANIA AND EXTREME WESTERN NEW YORK EARLY THIS MORNING AND HAS PUSHED INTO PHILADELPHIA METROPOLITAN AREA. AN AREA OF SHOWERS IS OUT AHEAD OF THIS FRONTAL BOUNDARY BUT A GRADUAL WEAKENING TREND HAS BEEN NOTICED ON RADAR WITH THESE SHOWERS. THE FRONT WILL CONTINUE TO SAG TOWARDS THE SOUTH THIS AFTERNOON. A WEAK MID- LEVEL IMPULSE MOVES OVERHEAD IN TANDEM WITH THE SURFACE FRONT PROGRESSION. THE AMOUNT OF FRONTAL FORCING BEGINS TO WASH OUT AS THE FLOW ALOFT BECOMES MORE ALIGNED ALONG THE FRONTAL BOUNDARY AND LESS OF A COLD AIR PUSH BEHIND THE FRONT. BETTER HEATING AHEAD THE OF THE BOUNDARY WITH SURFACE BASED CAPES PUSHING CLOSE TO 500J/KG COULD BE ENOUGH OF A SPARK TO SEE BETTER CHANCES FOR SHOWERS WITH ISOLATED THUNDER ACROSS OUR SOUTHERN HALF. TEMPERATURES TODAY, UNDER SLIGHTLY STRONGER WARM AIR ADVECTION AHEAD OF THE APPROACHING COLD FRONT, WILL BE A COUPLE DEGREES WARMER THAN SATURDAY. STAT GUIDANCE IS PRETTY CLOSE TO ONE ANOTHER AND BOTH THE GFS AND NAM INITIALIZED PRETTY WELL THERMALLY SO TOOK AN EVEN SPLIT OF THE MET/MAV. SLOWED THE ADVECTION OF LOWER DEWPOINTS AND MADE SOME SLIGHT CHANGES TO THE TEMPERATURES BASED ON THE 16Z METAR OBS WITH THE 12;30 PM UPDATE. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... THE COLD FRONT WILL BE TO OUR SOUTH LATE TONIGHT AND A DRYING NORTHWEST WIND COMMENCES. WEAK HIGH PRESSURE OVERHEAD SHOULD ALLOW FOR MOSTLY CLEAR SKIES, NORTH OF THE STALLED FRONTAL BOUNDARY, TONIGHT AND A LIGHT WIND SO LOWS WILL BE ABLE TO RADIATE DOWN INTO THE MID TO UPPER-50S IN A LOT OF PLACES. && .LONG TERM /MONDAY THROUGH SATURDAY/... AN OLD FRONTAL BOUNDARY IS EXPECTED TO STALL OVER THE SOUTHERN DELMARVA AND SOUTHERN VA ON MONDAY. THE AIRMASS OVER THE SOUTHERN FRINGE OF THE CWA WILL REMAIN RELATIVELY MOIST WITH DEWPOINTS IN THE MID 60S. A NOTICEABLY DRIER AIRMASS (DEWPOINTS IN THE 50S) WILL RESIDE FARTHER INTO PA/NJ AS A RESULT OF NORTHERLY FLOW AROUND HIPRES OVER THE GREAT LAKES/UPSTATE NY. FORECAST MAX TEMPS RANGE FROM THE UPPER 70S IN THE POCONOS TO MID 80S IN THE I-95 URBAN CORRIDOR. DESPITE WARMER H8 TEMPS FARTHER SOUTH ACROSS THE DELMARVA, INCREASING CLOUD COVER LATE IN THE DAY AND AN EAST- SOUTHEAST WIND OFF THE ATLANTIC SHOULD KEEP AFTERNOON HIGHS IN THE MID 80S. A WEAK SHORTWAVE TROUGH OVER KY IS FORECAST TO MOVE EASTWARD MONDAY AND TOWARD THE MOUTH OF THE CHSPK BAY MONDAY NIGHT INTO TUESDAY MORNING. WEAK SFC CYCLOGENESIS CAN BE EXPECTED AS THE UPPER IMPULSE INTERACTS THE OLD FRONTAL BOUNDARY. THE MOST RECENT 00Z MODELS HAVE COME INTO BETTER AGREEMENT FOR MONDAY NIGHT-TUESDAY AND HAVE TRENDED TOWARD A PROGRESSIVE/SUPPRESSED SYSTEM, WHICH WOULD MAKE SENSE GIVEN A RATHER FLAT/ZONAL STEERING FLOW PATTERN. THERE IS ALSO AN UPSTREAM KICKER SYSTEM THAT DOES NOT HAVE MUCH OF A SEPARATION DISTANCE FROM THIS LEADING SHORTWAVE TROUGH. HAVE LOWERED POPS ACROSS THE NORTHERN HALF OF THE CWA. WE CURRENTLY MENTION A HEAVY RAINFALL THREAT IN THE HWO FOR EXTREME SOUTHERN NJ/DELMARVA. ALTHOUGH THE LATEST TREND FROM THE MODEL GUIDANCE IS SHIFTING AWAY FROM THIS POTENTIAL HEAVY RAIN EVENT, THESE SAME LOCATIONS RECEIVED 5-10 INCHES OF RAINFALL AUGUST 12-13 AND THUS WOULD REMAIN RATHER SUSCEPTIBLE TO FLOODING. WILL KEEP IT IN THE HWO FOR NOW BUT ADD CONDITIONAL WORDING. THE OLD FRONTAL BOUNDARY IS EXPECTED TO REMAIN STALLED JUST TO THE SOUTH AND WEST OF THE CWA WEDNESDAY AND THURSDAY AS EASTERLY FLOW OFF THE ATLANTIC KEEPS THE COASTAL MID ATLANTIC IN A COOLER REGIME. THE AFOREMENTIONED KICKER SYSTEM, A NORTHERN STREAM LOW OVER THE UPPER MIDWEST, WILL DIVE SOUTHEASTWARD AROUND THE PERIPHERY OF A BUILDING GULF OF MEXICO RIDGE AND INTO THE NORTHERN MID-ATLANTIC STATES DURING THIS TIME. THIS SYSTEM WILL BE ACCOMPANIED BY SHOWERS AND THUNDERSTORMS BOTH DAYS. CONVECTION PREFERENTIALLY WOULD FOCUS ALONG THE FRONTAL BOUNDARY TO OUR SOUTH AND WEST. FOR NOW, BROAD BRUSHED THE AREA WITH LOW CHANCE POPS AS THERE IS STILL TOO MUCH UNCERTAINTY THIS FAR OUT TO DETERMINE HOW QUICKLY PRECIP MAKES IT TO THE AREA AND WHERE IT DEVELOPS. FORECAST UNCERTAINTY IS HIGH FOR THE END OF THE PERIOD. WHILE MODEL CONSENSUS POINTS TOWARD A BUILDING RIDGE OVER THE CENTRAL CONUS LATE IN THE WEEK, THEY DISAGREE WITH HOW QUICKLY THE UPPER LOW TO THE NORTHEAST OF THIS RIDGE OPENS UP AND EXITS THE MID-ATLANTIC STATES. TRENDED TOWARD A DRIER FORECAST FOR FRIDAY AND SATURDAY WITH HIPRES OVER EASTERN CANADA TRYING TO WEDGE DOWN THE EASTERN SEABOARD. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. A COLD FRONT WITH SOME ASSOCIATED MID-LEVEL AND OCCASIONALLY MVFR CEILINGS IS MOVING SOUTHEAST ACROSS THE REGION. AS THE FRONT MOVES THROUGH MIXING WILL INCREASE ALLOWING FOR A RETURN TO VFR CONDITIONS BY LATE AFTERNOON. WINDS WILL ALSO INCREASE SLIGHTLY THIS AFTERNOON WITH A FAVORABLE SET-UP FOR SOME WIND GUSTS CLOSE TO 20 KT FOR THE MID AND PERHAPS LATE AFTERNOON HOURS FROM THE NORTHWEST. WINDS WILL RELAX BY THIS EVENING AND CLOUDS WILL CONTINUE TO CLEAR OUT. NO FOG OR LOW VISIBILITIES ARE EXPECTED TONIGHT. VFR TONIGHT. SOME MID-LEVEL CLOUDS MAY ENTER THE PICTURE TOMORROW AFTERNOON, BUT STILL VFR WITH WEST-SOUTHWEST WINDS UNDER 10 KTS AFTER STARTING THE DAY LIGHT AND VARIABLE. OUTLOOK... MONDAY NIGHT AND TUESDAY...LO PRES TRACKS SOUTH OF THE AREA. BEST CHANCE FOR SHRA AND POSSIBLY TSRA NEAR ILG/MIV WITH CHANCES DECREASING FARTHER NORTH. NRN FRINGE OF PRECIP MAY SET UP CLOSE TO PHILADELPHIA TERMINALS. A PERIOD OF MVFR-IFR CONDITIONS POSSIBLE AT TIMES OF HEAVIER SHRA. PRECIP MOST LIKELY EXITS THE SRN TERMINALS TUESDAY AFTN. TUESDAY NIGHT...VFR WEDNESDAY THROUGH THURSDAY...SCT SHRA/TSRA AS MULTIPLE DISTURBANCES TRACK THRU THE REGION. SOME FLIGHT RESTRICTIONS POSSIBLE.
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&& .MARINE... SUB-SCA CONDITIONS EXPECTED ACROSS OUR WATERS TODAY AND TONIGHT. WINDS WILL INCREASE THIS AFTERNOON FROM THE SOUTHWEST BETWEEN 10-15 KNOTS AND SEAS WILL SLOWLY BUILD UPWARDS OF 3 FEET. COLD FRONT WILL PASS THROUGH THE WATERS LATER THIS EVENING AND WINDS WILL BACK TOWARDS THE WEST-NORTHWEST LATE. OUTLOOK... MONDAY...LIGHT W-NW WINDS. MONDAY NIGHT THROUGH TUESDAY NIGHT...LIGHT SLY WINDS MONDAY EVE BACK OVERNIGHT AND ACQUIRE MORE OF AN ONSHORE COMPONENT AS LOPRES APPROACHES THE DE COAST FROM THE WEST. A TIGHTENING PRESSURE GRADIENT WILL STRENGTHEN THE WINDS JUST TO THE NORTH OF THE LOW TUESDAY. BASED ON THE CURRENT FORECAST TRACK OF THIS LOW, THE DELAWARE AND SRN NJ ATLANTIC BEACHES AND EVEN THE LOWER DELAWARE BAY MAY APPROACH SCA CRITERIA. WEDNESDAY THROUGH THURSDAY...ONSHORE FLOW CONTINUES BUT WILL WEAKEN OVER TIME. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...KLEIN NEAR TERM...GAINES/HEAVENER SHORT TERM...HEAVENER LONG TERM...KLEIN AVIATION...GAINES//KLEIN MARINE...HEAVENER/KLEIN

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