Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 082327 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 727 PM EDT TUE JUL 8 2014 .SYNOPSIS... AN AREA OF LOW PRESSURE WILL CONTINUE TO MOVE INTO EASTERN CANADA THROUGH THURSDAY, WHICH WILL SLOWLY PULL A COLD FRONT ACROSS OUR AREA WEDNESDAY, BEFORE SAGGING TO OUR SOUTH THURSDAY. BEHIND THIS COLD FRONT, HIGH PRESSURE WILL BRIEFLY BUILD ACROSS THE NORTHEAST FRIDAY INTO SATURDAY, BEFORE IT PUSHES OFFSHORE LATER ON SATURDAY. THEN A SERIES OF COLD FRONTS ARE EXPECTED TO MOVE ACROSS THE AREA EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... DANGEROUS LINE OF SEVERE THUNDERSTORMS APPROACHING OUR CWA. PLEASE TAKE THE WARNINGS SERIOUSLY. ONCE WARNINGS ARE ISSUED, ITS RECOMMENDED ALL NON EMERGENCY DRIVING SHOULD BE HALTED UNTIL THE LEADING EDGE GUST FRONT PASSES YOUR AREA. HRRR AND COSPA HAVE BEEN PRETTY MUCH SPOT ON WITH THE PROGRESSION OF SQUALL LINE. WITH THE LINE ORGANIZED AND 90+ AIR AND LARGE TEMP/ DEW POINT SPREAD PRECEDING IT, NO REASON TO SEE WEAKENING OVER THE NEXT COUPLE OF HOURS. LESS CERTAINTY NEAR THE COAST HAS THE SEA BREEZE FRONT IS STARTING SOME STABILIZATION. BASED ON HRRR/COSPA BLEND, SQUALL LINE WINDS GET TO READING AND ELKTON ABOUT 8 PM, STROUDSBURG, TRENTON, PHILADELPHIA, WILMINGTON 830 PM TO 900 PM AND A WEAKENING LINE FROM FREEHOLD TO HAMMONTON TO GEORGETOWN ABOUT 10 PM. HEAT ADVISORY WILL BE CANCELLED FOR NEW CASTLE COUNTY AS ILG HEAT INDEX HAS DROPPED TO 95. TONIGHT...AS THE UPPER LEVEL TROUGH AND COLD FRONT APPROACH THE REGION, WE SHOULD SEE CONSIDERABLY MORE COVERAGE OF THUNDERSTORMS BETWEEN 8 PM AND MIDNIGHT. INSTABILITY SHOULD DECREASE THROUGH THIS TIME AS 0-6KM BULK SHEAR VALUES INCREASE TO NEAR 40KT IN THE VICINITY OF THE APPROACHING FRONT, WHICH SHOULD INCLUDE MUCH OF THE AREA NORTH AND WEST OF THE I95 CORRIDOR. AS SUCH, THE SEVERE THREAT, PRIMARILY FOR STRONG WINDS WILL CONTINUE FOR SOME OF THE REGION THROUGH THE EVENING HOURS, T MLCAPE THIS EVENING 1000J..TT50...SHEAR LOOKS ADEQUATE KI POPS TO NEAR 40C. A SMALL CONCERN FOR CONVECTION MAKING IT PAST THE DELAWARE RIVER IS THE DRY ECMWF TONIGHT. THIS MAY BE A CONVECTIVE MODELING ISSUE OR IT COULD BE REAL. IN ANY CASE...CONVECTIVE DECAY AFTER 01Z IS ANTICIPATED NO MATTER WHAT CONVECTION. AS FOR THE HEAVY RAIN THREAT, MODELS CONTINUE TO SHOW PWAT VALUES NEAR OR JUST BELOW 2 INCHES THIS EVENING. HOWEVER, FAST STORM MOTIONS SHOULD MEAN THAT ANY FLOODING THREAT WILL BE LIMITED TO POOR DRAINAGE AREAS. WITH HIGHER DEW POINTS LINGERING IN THE REGION AS THE COLD FRONT DRIFTS EAST, COULD SEE SOME THIN FOG DEVELOPMENT LATE TONIGHT, IN AREAS WHERE STORMS CLEAR OUT BY LATE EVENING AND OF COURSE WHERE IT RAINED. ELSEWHERE...JUST SOME HAZE TOMORROW MORNING...MAINLY NW NJ AND E PA COUNTRYSIDE. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... THE COLD FRONT ALOFT HAS PASSED BUT IT IS WEAK. THE AIRMASS RECOVERS... ESPECIALLY IN S NJ/DE WHERE LITTLE CONVECTION IS EXPECTED TONIGHT AND TEMPS SHOULD QUICKLY RUN UP TO 90F BETWEEN 11AM AND 1 PM...BARRING ANY CONVECTION. I THINK THE NAM IS TOO ROBUST ON QPF WEDNESDAY MORNING AND THEREFORE THIS COOLS ITS 2M AND MOS GUIDANCE FOR WEDNESDAY. EVEN PHL TO ME STILL LOOKS GOOD FOR 90 OR 91F. IF THAT OCCURS...ITS THE SECOND HEAT WAVE (ALBEIT SHORT) OF THE SEASON FOR PHL. IT APPEARS TO ME THAT TSTMS WILL DEVELOP MUCH SOONER TOMORROW...(MIDDAY) AND BE POTENTIALLY SVR FROM CAROLINE AND TALBOT COUNTIES IN MD THROUGH SUSSEX COUNTY DE AND POSSIBLY TO CAPE MAY NJ. ALSO...THE ECMWF HAS SPREAD MUCH HIGHER INSTABILITY THROUGH THE ENTIRE FORECAST AREA AND WE MAY SEE A LINE OF GUSTY TSTMS DEVELOP OVER NE PA AND HEAD EWD LATE IN THE DAY. GUSTY WINDS IN THE FCST. OTRW...USED THE WARMER OF THE AVBL GUIDANCE. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
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THE COLD FRONT IS EXPECTED TO CONTINUE TO SLOWLY SAG SOUTH OF THE AREA WEDNESDAY NIGHT INTO THURSDAY, AND REMAIN TO OUR SOUTH THROUGH FRIDAY. THIS WILL ALLOW MUCH OF THE AREA TO BEGIN TO DRY OUT AS PW VALUES BEGIN TO LOWER BEHIND THE BOUNDARY. 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. 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 AFTERNOON, 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 RETURN TO A PATTERN SIMILAR TO THE LAST SEVERAL DAYS. AN AREA OF LOW PRESSURE WILL BE SLIDING INTO EASTERN CANADA, WHILE A SERIES OF FRONTAL BOUNDARIES CIRCLE AROUND THE LOW ACROSS THE GREAT LAKES AND NORTHEAST. AHEAD OF THESE BOUNDARIES, A PRE-FRONTAL/LEE-SIDE TROUGH IS POSSIBLE EACH DAY. AS SEVERAL SHORT WAVE/VORTICITY IMPULSES CROSS OUR AREA IN THE SOUTHWEST-WEST FLOW ALOFT, SHOWERS AND THUNDERSTORMS ARE POSSIBLE EACH DAY UNTIL THE MAIN COLD FRONT MOVES ACROSS THE AREA. THIS IS NOT EXPECTED UNTIL TUESDAY NIGHT INTO WEDNESDAY. SO WE WILL HAVE AT LEAST A CHANCE OF SHOWERS/THUNDERSTORMS EACH DAY FROM SUNDAY THROUGH TUESDAY. INSTABILITY WILL BE INCREASING, AND PW VALUES WILL AS WELL. SO WE IT REMAINS POSSIBLE FOR PERIOD OF HEAVY RAINFALL AND STRONG STORMS POSSIBLE AS WELL.
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&& .AVIATION /23Z TUESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. NEAR SEVERE, POSSIBLY SEVERE THUNDERSTORMS EXPECTED TO AFFECT MOST OF THE TERMINALS AND NEARLY ALL OF OUR AIRPORTS AWAY FROM THE COAST THIS EVENING. 00Z TAFS HAVE WEST WIND GUSTS OF 40 TO 50 KTS WITH IFR VSBYS AS THE TSTMS MOVE THROUGH. OVERNIGHT NO CHANGE TO PREVIOUS TAF WITH SKIES CLEARING, SOME LIGHT MVFR RESTRICTIONS DUE TO FOG OR HAZE REMAINS POSSIBLE. ON WEDNESDAY WE ARE EXPECTING VFR CONDITIONS WITH A CUMULUS BASED CIG POSSIBLE. SOME SHOWERS AND TSTMS MAY OCCUR, BUT FOR NOW WE ARE MOST CONFIDENT SOUTH OF THE TERMINALS, SO NO INCLUSION WITH THIS PACKAGE. SOUTHWEST TO WEST WINDS WILL AVERAGE AROUND 10 KTS. OUTLOOK... WEDNESDAY NIGHT THRU 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...SHOWERS AND THUNDERSTORMS POSSIBLE, WHICH COULD LOWER CIGS/VSBYS.
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&& .MARINE... SCA FOR DELAWARE BAY EXTENDED UNTIL 1 AM UNTIL THE LLJ PASSES TO THE EAST. ALBEIT IT MAY BECOME TOUGHER TO MIX ONCE THE SQUALL LINE MOVES THROUGH, BUT IT (SQUALL LINE) SHOULDNT ARRIVE UNTIL AFTER 8 PM. SW WIND GRADIENT WILL INCREASE DURING THE AFTERNOON AND EVENING WITH GUSTS 25 KT ALONG THE NEARSHORE POINTS SHORTLY. SEAS WILL RESPOND TONIGHT AND REACH 5 FT THROUGHOUT THE ATLC WATERS. EVEN THOUGH SW WINDS DIMINISH CONSIDERABLY ON WEDNESDAY...ATLANTIC SEAS MAY BE SLOW TO SUBSIDE. TSTMS...SMALL CHANCE NEAR MIDNIGHT TONIGHT. A BETTER CHC FOR AN SMW TSTM DE AND FAR S NJ COASTAL WATERS EARLY WED AFTN. OUTLOOK... WEDNESDAY NIGHT-THURSDAY NIGHT...SUB-ADVISORY CONDITIONS EXPECTED. CHANCE OF SHOWERS/THUNDERSTORMS, MAINLY SOUTHERN WATERS. HIGHER WINDS/SEAS NEAR THUNDERSTORMS. FRIDAY-SATURDAY NIGHT...SUB-ADVISORY CONDITIONS EXPECTED. SUNDAY...SUB-ADVISORY CONDITIONS EXPECTED, BUT INCREASING WINDS. BETTER CHANCE OF SHOWERS/THUNDERSTORMS. HIGHER WINDS/SEAS NEAR THUNDERSTORMS. && .RIP CURRENTS... THE THREAT FOR RIP CURRENTS ALONG THE NEW JERSEY SHORE IS MODERATE TODAY AND THIS EVENING. WATERS TEMPS ARE A BIT COOLER THAN NORMAL IN THE WAKE OF ARTHURS PASSAGE...IN THE LOW MID 60S MUCH OF THE NJ COAST AND UPPER 60S TO MID 70S DE COAST. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 2 PM EDT WEDNESDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL 1 AM EDT WEDNESDAY FOR ANZ430-431.
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&& $$ SYNOPSIS...ROBERTSON NEAR TERM...DRAG/GIGI SHORT TERM...DRAG LONG TERM...ROBERTSON AVIATION...GIGI/ROBERTSON MARINE...DRAG/ROBERTSON RIP CURRENTS...

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