Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 211858 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 258 PM EDT THU AUG 21 2014 .SYNOPSIS... LOW PRESSURE FROM LAKE ONTARIO TO VIRGINIA PRODUCES OCCASIONALLY UNSETTLED WEATHER HERE THROUGH FRIDAY. QUEBEC HIGH PRESSURE BECOMES OUR PRIMARY WEATHER INFLUENCE LATER THIS WEEKEND THROUGH THE MIDDLE OF NEXT WEEK AS THE HIGH SETTLES SOUTHWARD TO THE MID ATLANTIC STATES. && .NEAR TERM /THROUGH TONIGHT/...
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THROUGH MIDNIGHT TONIGHT...UNSETTLED WITH POTENTIAL FOR BRIEF POOR DRAINAGE FLOODING AND SMALL HAIL PRODUCING THUNDERSTORMS (G35KT)...PARTICULARLY NE PA AND NW NJ...AND THINKING AKIN TO THE 00Z/21 NSSL WRF IN WEAK WAA AHEAD OF THE SFC TROUGH IN CENTRAL PA WHERE SBLI AT 18Z NEAR -7. EXPLAINING THE AXIS OF THE ONGOING STORMS AT 1830Z...I CANNOT EASILY DO. IT APPEARS INSTABILITY AND PROXIMITY TO THE COLD TROUGH ALOFT HAS FOCUSED IN OUR CWA MORE TO THE NORTH RATHER THAN TO THE SOUTH. PWAT NEAR 1.5 INCHES. MLCAPE 1200J. MARGINAL 0-6KM BULK SHEAR. THE SREF AND GEFS POPS ARE 20-30 PCT HIGHER THAN WHAT WE ARE ISSUING AT 330 PM. AS NOTED EARLIER: THE 12Z NAM CONTG A THEME OF 2 INCH IN ONE HOUR TSTMS SOMEWHERE IN E CENTRAL PA INTO CENTRAL NJ THIS EVENING. VIL NEAR 60 AT 1845Z CENTRAL PA IS EITHER VERIFYING THAT RAIN OR SUGGESTING LARGE HAIL. WHILE THE PLACEMENT OF THE NAM SHORT TERM QPF IS POSSIBLY WRONG...THE IDEA I THINK IS CORRECT. A PTN OF E CENTRAL OR NE PA IN N OR CENTRAL NJ SHOULD RECEIVE SOME STRONG TSTORMS VERY LATE THIS AFTN OR EVENING. OTRW CONSIDERABLE HIGH CLOUDINESS DELMARVA AS BLOWOFF CLOUD DEBRIS FROM THE OHIO VALLEY CONVECTION SPREADS EWD. AFTER MIDNIGHT...NORMALLY ANY EVENING CONVECTION DIMINISHES BUT THE ECMWF TRIES TO INCREASE RFALL AFTER 06Z WITH THE SHORT WAVE MOVING SEWD FROM NYS. JUST VERY UNSURE OF WHAT EXISTS AFTER 06Z TONIGHT. PLEASE FOLLOW ANY UPDATED SWOMCD`S SWODY1 AND LOCAL PHI CONVECTIVE RELATED PRODUCTS ISSUED THIS EVENING. FCST BASIS: TEMPS/DEWS/WINDS ARE A 50 50 BLEND OF THE 12Z/21 GFS/NAM MOS.
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&& .SHORT TERM /FRIDAY/...
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1000J OF MLCAPE AND SLIGHTLY STRONGER 0-6KM BULK SHEAR CUES INTEREST IN CONVECTION FRI AFTN. SREF HAS DECENT PROBS FOR SHOWERS...ESPECIALLY E PA...S NJ AND THE DELMARVA. FOR NOW HAVE PLAYED THE SHOWER AND TSTM RISK CONSERVATIVELY AND MAINTAINED THE 330 AM THURSDAY FCST POPS FOR FRIDAY...ABOUT 10 PCT BELOW THE 12Z/21 GFS/NAM MOS BLEND. IT WILL BE SLIGHTLY COOLER AS THE FLOW TURNS MORE EASTERLY AS THE SFC LOW CONSOLIDATES TO THE S OF THE DELMARVA. FCST BASIS: TEMPS/DEWS/WINDS ARE A 50 50 BLEND OF THE 12Z/21 GFS/NAM MOS.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... FRIDAY NIGHT THROUGH SATURDAY...THE REGION REMAINS UNDER NORTHWEST FLOW AS THE STOUT RIDGE REMAINS OVER THE MISSISSIPPI VALLEY, AND THE OTHER HIGH REMAINS OVER EASTERN CANADA. WITH THE NORTHWEST FLOW, EXPECT A FEW EMBEDDED SHORT WAVE TROUGHS TO BRING CHANCES FOR THUNDERSTORMS THROUGH THIS PERIOD. HOWEVER, THE TIMING OF THE INDIVIDUAL SHORT WAVE TROUGHS REMAINS UNCERTAIN. SUNDAY THROUGH THURSDAY...THE HIGH OVER EASTERN CANADA BUILDS SOUTH. WITH THE ASSOCIATED COLD AIR ADVECTION, COULD SEE HIGHS ESPECIALLY EARLY IN THE WEEKEND 5 TO 10 DEGREES BELOW NORMAL. BY TUESDAY HOWEVER, THE HIGH STARTS TO SHIFT OFF SHORE, LEAVING THE REGION UNDER SOUTHERLY FLOW AND LEADING TO A MODEST WARMING TREND. HOWEVER, ALSO TOWARDS THE END OF THIS FORECAST PERIOD THE GFS AND ECMWF SOLUTIONS DIFFER GREATLY ON THE TIMING OF AN UPPER LEVEL TROUGH AND ASSOCIATED SURFACE COLD FRONT THAT WILL BE PROPAGATING EAST ON THE HEALS OF THE HIGH. STILL, BOTH SOLUTIONS SHOW THESE FEATURES JUST BEYOND THE SEVEN DAY FORECAST. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. REMAINDER THIS AFTERNOON...SPOTTY MVFR CIGS IN E PA SHOULD LIFT THE VFR SCT-BKN AOA 4000 FT ELSEWHERE WITH A LIGHT SOUTHERLY FLOW. LOCAL IFR CONDS IN SCT SHOWERS AND TSTMS LATE THIS AFTN...MAINLY VCNTY KRDG AND KABE. A NW WIND GUST TO 35 KT POSSIBLE ASSOCIATED WITH A LATE AFTN TSTM. TONIGHT...SCT SHOWERS AND TSTMS THIS EVENING WITH NW WIND G25-35 KT AND BRIEF IFR CONDS...MAINLY IN THE 23Z-03Z TIME FRAME THOUGH SHOWERS MAY LINGER LATE AT NIGHT VCNTY KACY. OTRW VFR CIGS MAY DEGRADE TO MVFR OR IFR CONDS IN ST/FOG TOWARD 09Z. CONFIDENCE ON DEGRADED CIGS/VSBY LATE AT NIGHT IS BELOW AVG. FRIDAY...CIGS 2500-4000 FT WITH LOWER IFR CONDS IN SCT SHOWERS AND TSTMS AND THE WIND TURNING LIGHT EASTERLY. OUTLOOK... FRIDAY AND SATURDAY...MOSTLY VFR. ISOLATED TO SCATTERED TSRA ARE POSSIBLE ACROSS THE REGION. UNDER ANY TSRA MVFR CEILINGS AND BRIEF IFR VISIBILITIES WILL BE POSSIBLE. SUNDAY THROUGH MONDAY...GENERALLY VFR.
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&& .MARINE... SUB-SMALL CRAFT ADVISORY CONDITIONS EXPECTED THROUGH FRIDAY WITH SEAS 3 FEET OR LESS AND SOUTH TO SOUTHEAST WINDS 5 TO 10 KNOTS BECOMING EASTERLY FRIDAY. WE`VE NOT SEEN ANY NEW MAREPS THIS WEEK FROM MARINERS IN OUR EASY USE (INTERNET AND/OR SMART PHONE) LINK WWW.WEATHER.GOV/PHI/MAROBSFORM THIS HAS BEEN DERIVED FOR THE MARINER TO EASILY POST INFO INSTANTLY TO THE NWS FOR USE IN OUR MARINE PRODUCTS. OUTLOOK... FRIDAY NIGHT...SCA NE WIND GUSTS MAY DEVELOP LATE AT NIGHT ON THE ATLC WATERS. SATURDAY...OCCASIONAL GUSTS NEAR 25 KT AND WAVE HEIGHTS APPROACHING 5 FT ARE POSSIBLE ESPECIALLY SATURDAY AFTERNOON THROUGH SATURDAY NIGHT. SUNDAY AND MONDAY...WAVE HEIGHTS AND WINDS SLOWLY FALLING BELOW SMALL CRAFT ADVISORY CRITERIA SUNDAY MORNING AND SHOULD REMAIN BELOW CRITERIA THROUGH MONDAY. && .CLIMATE... WE RCD INQUIRY ON HOW THE CLIMATE PROGRAM SELECTS FOR OUR 530 PM CLI. OUR PROGRAM SEARCHES MAX/MIN TEMP DATA FOR THE DAY ENDING 5PM SHARP. THAT DATA IS INGESTED INTO THE 530 PM POSTED CLI. IF A MAX TEMP OCCURS THEREAFTER...IT IS REFLECTED IN THE END OF DAY SUMMARY POSTS AROUND 230 AM EDT THE NEXT DAY AND ALSO YOU CAN CHECK THE 8 PM RTPPHI WHICH POSTS AROUND 815 PM EDT. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...DRAG/JOHNSON NEAR TERM...DRAG 257 SHORT TERM...DRAG 257 LONG TERM...JOHNSON AVIATION...DRAG/JOHNSON 257 MARINE...DRAG/JOHNSON 257 CLIMATE...

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