Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 100110 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 910 PM EDT WED JUL 9 2014 .SYNOPSIS... A COLD FRONT WILL MOVE INTO THE AREA FROM THE NORTHWEST TONIGHT BEFORE STALLING NEAR THE DELMARVA ON THURSDAY. HIGH PRESSURE WILL BRIEFLY BUILD ACROSS THE NORTHEAST FRIDAY INTO SATURDAY, BEFORE IT PUSHES OFFSHORE LATER IN THE DAY SATURDAY. THEN A SERIES OF SURFACE TROUGHS WILL AFFECT THE AREA EARLY NEXT WEEK, FOLLOWED BY A SLOW MOVING COLD FRONT TUESDAY INTO WEDNESDAY. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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REMOVED THE SEVERE THUNDERSTORM WATCH HEADLINES. POPS WILL REMAIN IN THE FORECAST FOR MOST OF US DURING THE OVERNIGHT WITH THE STALLED FRONT OVERHEAD. BUMPED UP POPS THIS EVENING ACROSS THE DELMARVA. KEPT THUNDER IN THE FORECAST FROM ABOUT THE I-95 CORRIDOR SOUTHWARD. PREVIOUS DISCUSSION... SEVERE THUNDERSTORM WATCH NUMBER 407 HAS JUST BEEN ISSUED. THIS WATCH BOX IS IN EFFECT THRU 10 PM INCLUDES MOST OF THE CWA WITH THE EXCEPTION OF THE SRN TIP OF NJ AND THE SRN DELMARVA. DAMAGING WIND GUSTS ARE THE PRIMARY THREAT. PREVIOUS DISCUSSION... A 986 MB SFC LOW IS ANALYZED OVER CENTRAL QUEBEC. ATTENDANT COLD FRONT EXTENDS TO THE SOUTH INTO THE ADIRONDACKS AND TO THE SW INTO NRN PA AND OH. NUMEROUS SHOWERS AND STORMS HAVE DEVELOPED ALONG THE FRONT. FARTHER DOWNSTREAM...MORE SCT CONVECTION IS OCCURRING ALONG A PRE-FRONTAL TROUGH INTO CENTRAL AND NORTHEASTERN PA. SPC MESOANALYSIS SHOWS BETWEEN 500-1000 J/KG OF MLCAPE OVER MUCH OF THE AREA WITH LOCALLY HIGHER AMOUNTS ANALYZED OVER THE DELMARVA. BULK SHEAR VALUES OF 35-45 KT COMBINED WITH THIS AMOUNT OF INSTABILITY WILL BE SUPPORTIVE OF A FEW DAMAGING DOWNBURSTS, ESPECIALLY FARTHER NORTH AND WEST, WHERE THE BETTER WIND FIELD AND MORE SIGNIFICANT INTRUSION OF MID-LVL DRY AIR RESIDES. MODEST LIFT SHOULD LIMIT COVERAGE OF CONVECTION SO POPS ARE LIMITED TO CHANCE. THIS ACTIVITY WILL PROGRESS EWD TOWARD PHILADELPHIA, SRN NJ AND THE DELMARVA THIS EVE AS THE COLD FRONT MOVES SOUTHEASTWARD ACROSS THE REGION. SHOWERS MAY LINGER OVERNIGHT NEAR THE FRONT ACROSS SRN NJ/DELMARVA. A BAND OF SHOWERS ALONG THE PRE-FRONTAL SHORTWAVE TROUGH WILL MOVE DOWNSTREAM FROM THE CHSPK BAY INTO THE DELMARVA AND SRN NJ LATE THIS MRNG AND EARLY THIS AFTN. MAY SEE AN ISO TSTM DEVELOP WITH THIS ACTIVITY BUT OVERALL COVERAGE AND STRENGTH OF CONVECTION WILL BE LIMITED WITHOUT MUCH OF AN OPPORTUNITY FOR THE BOUNDARY LAYER TO DESTABILIZE BEFOREHAND. EXPECT ADDITIONAL CONVECTION TO DEVELOP IN CENTRAL PA JUST AHEAD OF THE COLD FRONT DURING THE PEAK HEATING HRS THIS AFTN. THESE SHOWERS AND STORMS ARE THEN EXPECTED TO PROGRESS EWD INTO ERN PA LATER IN THE AFTN. LIMITED POPS TO CHANCE WITH SYNOPTIC LIFT RATHER WEAK.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... AN AMPLIFIED RIDGE OVER THE ATLANTIC OCEAN WILL BE ASSOCIATED WITH AN OMEGA BLOCK THAT DEVELOPS OVER THE GREENLAND. UPSTREAM RAMIFICATIONS OF THIS BLOCKING PATTERN WILL ALLOW THE UPPER LOW TO REMAIN CUTOFF OVER QUEBEC AND ITS ASSOCIATED LONGWAVE TROUGH OVER THE GREAT LAKES AND MIDWEST. OPERATIONAL MODEL GUIDANCE IN FAIRLY GOOD AGREEMENT WITH THE POSITION OF THE COLD FRONT IN SRN NJ/DELMARVA AT 12Z THURSDAY. THE FRONT WILL BECOME ORIENTED PARALLEL TO THE S-SWLY STEERING FLOW IN BETWEEN THE UPSTREAM TROUGH AND DOWNSTREAM RIDGE, CAUSING THE FRONTAL BOUNDARY TO STALL OVER THE SRN THIRD OF THE CWA ON THURSDAY. THE EXPECTED POSITION OF THE STATIONARY FRONT, POSITION OF THE UPPER-LVL JET STREAK, AND TRACK OF A MID-LVL SHORTWAVE TROUGH ALL CONTRIBUTE TO LARGE-SCALE LIFT FOR SRN NJ, DE, AND THE ERN SHORE OF MD. POPS WERE INCREASED IN THESE SRN ZONES BUT DID NOT QUITE HAVE THE FCST CONFIDENCE TO GO WITH LIKELY POPS DUE TO UNCERTAINTIES IN TIMING OF PRECIP. CLOUDS EXPECTED TO LIMIT CONVECTIVE POTENTIAL AND THUS THE SETUP FOR SEVERE TSTMS NOT NEARLY AS FAVORABLE AS YESTERDAY AND TODAY. CLOUD COVER AND SHOWER CHANCES DECREASE FARTHER NORTH. KEPT FCST DRY NORTH OF INTERSTATES 195 AND 76. MAX TEMP FCST WEIGHTED MORE WITH THE MET GUIDANCE. LIKED THE GRIDDED OUTPUT WITH THE WARMEST TEMPS IN THE PHILA METRO AND CENTRAL NJ, JUST NORTH, WHICH MAY BE JUST NORTH OF THE THICKER CLOUD CLOVER. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... AT THE BEGINNING OF THE LONG TERM PERIOD, THE FRONTAL BOUNDARY WILL REMAIN STALLED OUT OFFSHORE OF THE EAST COAST, WHILE PW VALUES LOWER SLIGHTLY ACROSS THE AREA INTO FRIDAY. HOWEVER, THERE COULD REMAIN JUST ENOUGH MOISTURE TO INTERACT WITH ANY SHORT WAVE/VORTICITY IMPULSES THAT SLIDE ACROSS THE AREA WITHIN THE BROAD TROUGH ALOFT THAT WILL REMAIN ACROSS THE EAST COAST. THE GREATEST LIKELIHOOD IS ACROSS OUR FAR SOUTHERN NEW JERSEY AND SOUTHERN DELMARVA ZONES, WHICH WILL BE CLOSER TO ANY INFLUENCE OF THE FRONT TO OUR SOUTH AND WHERE ANY MOISTURE REMAINS POOLED. HIGH PRESSURE WILL CONTINUE TO SLIDE ACROSS THE NORTHEAST FRIDAY INTO FRIDAY NIGHT WHICH SHOULD HELP REINFORCE THE DRYING POTENTIAL. THE HIGH BUILDS OFF THE NORTHEAST COAST SATURDAY, WHICH WILL ALLOW A RETURN FLOW TO DEVELOP ACROSS THE AREA. WITH THIS RETURN FLOW, MOISTURE RETURNS, AND WITH A VORTICITY IMPULSE APPROACHING THE AREA SATURDAY, A FEW SCATTERED SHOWERS/THUNDERSTORMS COULD DEVELOP. THESE WILL LIKELY BE MAINLY AFTERNOON/DIURNALLY DRIVEN AND DIMINISH AFTER SUNSET. AS WE MOVE INTO SUNDAY AND EARLY NEXT WEEK, WE ALMOST COPY AND PAST THE FORECAST FROM THE LAST SEVERAL DAYS, AND PASTE IT INTO THE FORECAST SUNDAY THROUGH WEDNESDAY PERIOD NEXT WEEK. AN AREA OF LOW PRESSURE IS EXPECTED TO MOVE INTO SOUTHEASTERN CANADA, WHILE A SERIES OF FRONTAL BOUNDARY CIRCLE AROUND THE LOW ACROSS THE GREAT LAKES AND NORTHEAST. AHEAD OF THESE BOUNDARIES, A PRE-FRONTAL/LEE-SIDE TROUGH IS POSSIBLE EACH DAY. SEVERAL SHORT WAVE/VORTICITY IMPULSES ARE EXPECTED TO MOVE ACROSS OUR AREA EACH DAY, WHICH WILL MAKE SHOWERS AND THUNDERSTORMS POSSIBLE EACH DAY UNTIL THE MAIN COLD FRONT MOVES ACROSS THE AREA. THIS IS NOT EXPECTED UNTIL AT LEAST TUESDAY NIGHT INTO WEDNESDAY. SO WE WILL HAVE AT LEAST A CHANCE OF SHOWERS/THUNDERSTORMS EACH DAY FROM SUNDAY THROUGH TUESDAY. EVEN THOUGH THERE IS A CHANCE EACH DAY, IT IS NOT EXPECTED TO BE A COMPLETE WASHOUT EVERYWHERE EACH DAY. STILL, INSTABILITY WILL BE INCREASING, AND PW VALUES WILL AS WELL. SO WE IT REMAINS POSSIBLE FOR PERIOD OF HEAVY RAINFALL AND STRONG STORMS AS WELL. ANY SEVERE POTENTIAL WILL DEPEND ON EACH DAY`S INSTABILITY AND WIND/SHEAR PROFILES WHICH WILL BECOME MORE EVIDENT IN THE DAYS TO COME. && .AVIATION /01Z THURSDAY THROUGH MONDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. MAINLY VFR TONIGHT. THE EXCEPTION WILL BE IN SHOWERS AND SOME FOG. ADDED SOME MVFR CONDITIONS. THE COLD FRONT WILL PROGRESS SWD THRU THE TERMINALS TNGT AND WILL BE ASSOCIATED WITH A WIND SHIFT FROM S TO NW OVNGT AND EVENTUALLY N-NE BY THU. ADDITIONAL SHRA EXPECTED IN VC OF ILG/MIV/ACY ON THU. TSRA CHANCES WILL BE LOW. OUTLOOK... THURSDAY NIGHT-FRIDAY...MOSTLY VFR. A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS, MAINLY ACROSS OUR SOUTHERN TAF SITES. FRIDAY NIGHT-SATURDAY NIGHT...MVFR CIGS POSSIBLE WITH EASTERLY FLOW. SUNDAY-MONDAY...SHOWERS AND THUNDERSTORMS POSSIBLE, WHICH COULD LOWER CIGS/VSBYS.
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&& .MARINE...
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AFTERNOON MODELS KEEP THE WINDS AND OCEAN SEAS BELOW SCA LEVELS. HEADLINES HAVE BEEN REMOVED. EXPECTING TO MAX OUT AHEAD OF THE FRONT IN THE 15-20 KT RANGE WITH 4 FOOT SEAS. WINDS SHOULD BE LIGHT ON THURSDAY WITH THE FRONTAL BOUNDARY STALLING OVER THE WATERS. POTENTIAL FOR A FEW TSTMS ON THURSDAY NEAR THE DELAWARE WATERS. OUTLOOK... THURSDAY NIGHT-FRIDAY...SUB-ADVISORY CONDITIONS EXPECTED. CHANCE OF SHOWERS/THUNDERSTORMS, MAINLY SOUTHERN WATERS. HIGHER WINDS/SEAS NEAR THUNDERSTORMS. FRIDAY NIGHT-SATURDAY NIGHT...SUB-ADVISORY CONDITIONS EXPECTED. SUNDAY-MONDAY...SUB-ADVISORY CONDITIONS EXPECTED, BUT WINDS WILL BE INCREASING IN THE SOUTHWESTERLY FLOW AHEAD OF AN APPROACHING FRONTAL BOUNDARY. CHANCE OF SHOWERS/THUNDERSTORMS. HIGHER WINDS/SEAS NEAR THUNDERSTORMS.
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&& .TIDES/COASTAL FLOODING... TIDAL LEVELS WILL BE INCREASING LATER IN THE WEEK INTO THE WEEKEND AS WE APPROACH FULL MOON ON SATURDAY. HOWEVER, CURRENT GUIDANCE KEEPS THE FORECAST BELOW ADVISORY LEVELS THROUGH SATURDAY. && .RIP CURRENTS...
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THE THREAT FOR RIP CURRENTS ALONG THE NEW JERSEY AND DELAWARE COASTS SHOULD DIMINISH TO LOW TOMORROW.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE.
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&& $$ SYNOPSIS...ROBERTSON NEAR TERM...KLEIN/KRUZDLO SHORT TERM...KLEIN LONG TERM...ROBERTSON AVIATION...KLEIN/ROBERTSON/KRUZDLO MARINE...KLEIN/KRUZDLO/ROBERTSON TIDES/COASTAL FLOODING...ROBERTSON RIP CURRENTS...KRUZDLO

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