Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 131955 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 355 PM EDT SUN APR 13 2014 .SYNOPSIS...
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HIGH PRESSURE CONTINUES TO SLIDE EAST OFF THE SHORE TONIGHT. A COLD FRONT WILL APPROACH FROM THE WEST TOMORROW NIGHT AND PUSH THROUGH THE REGION TUESDAY AFTERNOON. IN THE WAKE OF THE COLD FRONT, HIGH PRESSURE WILL SETTLE IN OVER THE REGION THROUGH THE REMAINDER OF THE WORK WEEK. AN UPPER LEVEL TROUGH COULD SLIDE OVER OUR REGION EARLY NEXT WEEKEND.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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STRONG WARM AIR ADVECTION AND PLENTY OF SUNSHINE HAVE ALLOWED TEMPERATURES TO EXCEED EXPECTED HIGHS AND BASICALLY BLEW STAT GUIDANCE AWAY. THE DEEPER MIXING HAS FINALLY TAPPED INTO SOME OF THE STRONGER LOW-LEVEL WINDS AND THE GUSTS ARE STARTING TO INCREASE FOR THE NEXT FEW HOURS BEFORE DROPPING OFF SHORTLY AFTER SUNSET. MID AND HIGHER LEVEL CLOUDS WILL BE ON THE INCREASE TONIGHT FROM THE WEST. STILL UNSURE HOW MUCH STRATUS AND OR FOG FORMS LATE TONIGHT ACROSS THE REGION. DEWPOINTS ARE MUCH HIGHER THAN THEY WERE EARLIER THIS MORNING BUT THE BOUNDARY LAYER WINDS WERE ALSO MUCH WEAKER ALLOWING BETTER MOISTURE POOLING TO OCCUR. THINKING THAT TONIGHT THE BEST CHANCES FOR STRATUS ARE ALONG THE COASTAL AREAS AND POSSIBLY DOWNWIND OF THE UPPER CHESAPEAKE BAY...SLIGHT BAY ENHANCEMENT POSSIBLE. EITHER WAY WITH CLOUDS OVERHEAD AND A MUCH WARMER STARTING POINT TEMPERATURES SHOULD BE SEVERAL DEGREES WARMER THAN THIS MORNING WITH LOWS IN THE UPPER-50S TO LOW 60S IN SOME SPOTS.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
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ANY LOWER CLOUDS AND FOG SHOULD BURN OFF LATE MORNING GIVING WAY TO THE MID AND HIGHER LEVEL CLOUDS. THE RIDGING OFFSHORE SHOULD CONTINUE TO PUSH EASTWARD AND SOME LOWER HEIGHTS AND THICKNESSES ADVECT INTO THE REGION FROM THE WEST. THE GRADIENT FLOW WILL STILL BE FROM THE SOUTH-SOUTHWEST WHERE THE GUIDANCE IS SHOWING SLIGHTLY COOLER LOW-LEVEL TEMPERATURES. ALL INDICATIONS SHOW MONDAY BEING A COUPLE DEGREES COOLER THAN SUNDAY WITH THE NEUTRAL/COOLER AIR ADVECTION OCCURRING AND MORE CLOUD COVER IN PLACE. THAT BEING SAID STILL WENT ABOVE GUIDANCE FOR TOMORROW AS THE AIRMASS ON A WHOLE REMAINS UNCHANGED. NUMERICAL GUIDANCE AND PROBABILISTIC QPF GUIDANCE SHOW THE MAIN SHOWERY ACTIVITY WITH THE COLD FRONT, AGAIN WELL TO OUR WEST TOMORROW, HOLDING OFF THROUGH THE DAYTIME. THEREFORE WE KEEP TOMORROW DRY.
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&& .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
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THE BIG WEATHER STORY OF THE WEEK IS GOING TO BE THE STRONG COLD FRONT AND ASSOCIATED PRECIPITATION TO BEGIN THE LONG TERM PERIOD. OVERVIEW...THERE IS MUCH BETTER MODEL AGREEMENT TODAY WITH THE TIMING AND TRACK OF THIS COLD FRONT, WITH THE TREND GENERALLY TOWARDS A MORE PROGRESSIVE SOLUTION. STILL EXPECTING STRONG SOUTHERLY/SOUTHWESTERLY FLOW TO DEVELOP IN THE WARM SECTOR, AND WITH THAT WIDESPREAD PRECIPITATION AHEAD OF THE FRONT. THE FRONT IS NOW EXPECTED TO COMPLETELY PUSH THROUGH THE REGION BETWEEN 18Z TUESDAY AND 00Z WEDNESDAY. THERE MAY BE A BRIEF PERIOD (LESS THAN 6 HR) OF PRECIPITATION BEHIND THE FRONT, BUT CONSIDERING THE SOURCE REGION OF THE POLAR AIR MASS, EXPECT CONSIDERABLE DRY AIR ADVECTION BEHIND THE FRONT. HEAVY RAIN...MODELS CONTINUE TO SHOW MAXIMUM PRECIPITABLE WATER VALUES AROUND 1.5 INCHES...OR ABOUT 2 STANDARD DEVIATIONS ABOVE NORMAL FOR THIS TIME OF THE YEAR. IN ADDITION, THE 0-6KM MEAN FLOW TUESDAY NIGHT CONTINUING INTO TUESDAY MORNING IS NEARLY PARALLEL TO THE APPROACHING FRONT, INCREASING THE RISK FOR TRAINING STORMS. HOWEVER, WARM CLOUD LAYER IS MARGINAL FOR AN ENHANCED HEAVY RAIN THREAT, PWAT VALUES ACTUALLY DECREASE BEFORE THE MAXIMUM LIFT ARRIVES OVER THE REGION, AND WITH THE TREND TOWARDS A FASTER COLD FRONT THE PERIOD FOR HEAVY RAIN POTENTIAL IS SHORTER THAN PREVIOUSLY EXPECTED. WILL CONTINUE WITH SIMILAR WORDING IN THE HWO HIGHLIGHTING THE POTENTIAL FOR HEAVY RAIN. THUNDERSTORMS...MODELS DEPICT MARGINAL ML CAPE VALUES (<100 J/KG) IN THE WARM SECTOR. HOWEVER, THERE IS POTENTIAL FOR ELEVATED INSTABILITY AS WELL THROUGH THE ENTIRE PERIOD THAT THE REGION IS IN THE WARM SECTION. WINTRY MIX OF PRECIPITATION BEHIND THE FRONT...AS MENTIONED PREVIOUSLY, EXPECT THE PERIOD OF PRECIPITATION BEHIND THE FRONT TO BE RATHER BRIEF. THE HIGHER TERRAIN OF THE POCONOS COULD SEE SOME WINTRY MIX THROUGH THIS PERIOD, BUT GIVEN HIGH GROUND TEMPERATURES, DO NOT EXPECT MUCH IN THE WAY OF ACCUMULATION. EXPECT THE SURFACE RIDGE TO BE THE DOMINANT FEATURE FOR THE REGION WEDNESDAY AND THURSDAY. EXPECT ONLY A MODEST WARMING TREND THROUGH THIS PERIOD MAINLY DUE TO AIR MASS MODIFICATION. BEGINNING THURSDAY, WE`RE WATCHING AN UPPER LEVEL THROUGH DIGGING SOUTHEAST OVER THE GREAT BASIN REGION. THAT MUCH THE MODELS AGREE ON. BY FRIDAY MODEL DIFFERENCES AND ENSEMBLE SPREAD INCREASE CONSIDERABLY. THE GFS SHOWS THE TROUGH CUTTING OFF, DEEPENING AND INTENSIFYING IN THE THE NORTHERN STREAM, EVENTUALLY PROPAGATING TO THE GREAT LAKES REGION. WITH THIS SOLUTION, OUR REGION COULD BE IN THE WARM SECTOR, WITH STEADY RAIN THROUGH THE WEEKEND. THE ECMWF ON THE OTHER HAND, CUTS OFF THE LOW IN THE SOUTHERN STREAM, AS IT PROPAGATES OFF THE COAST OF THE CAROLINAS BY SUNDAY. THIS WOULD RESULT IN COOLER CONDITIONS, AND ONLY A BRIEF PERIOD OF PRECIPITATION FOR MOST OF OUR REGION. CONSIDERING THE LOW CONFIDENCE, HAVE STAYED CLOSE TO THE PREVIOUS FORECAST AND WPC GUIDANCE THROUGH THIS PERIOD.
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&& .AVIATION /20Z SUNDAY THROUGH FRIDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THIS EVENING - TONIGHT...MOSTLY VFR. SOUTH-SOUTHWESTERLY WINDS WILL CONTINUE TO GUST INTO THE LOW-20 KNOTS RANGE THROUGH THE EVENING HOURS. A SEA-BREEZE FRONT HAS BEEN PUSHING INLAND TODAY NEAR ACY AS THE WINDS ARE LESS THAN EXPECTED ALOFT BUT SHOULD HAVE HARD TIME MOVING MUCH FURTHER. SHORTLY AFTER SUNSET WE SHOULD LOSE THE GUSTS BUT KEEP THE HIGHER SUSTAINED WINDS. THERE IS STILL A QUESTION ABOUT HOW MUCH STRATUS FORMS TONIGHT. HIGHER CONFIDENCE EXISTS CLOSER TO THE COAST AT MIV/ACY SO KEPT IT THERE BUT STILL HINTED AT IT ELSEWHERE...WE BARELY RECEIVED ANY THIS MORNING. TOMORROW...ANY STRATUS/FOG THAT DOES FORM LATE TONIGHT SHOULD LIFT/BURN OFF BY LATE MORNING. SOUTHERLY WINDS WILL PICK UP AGAIN AND BEGIN TO GUST, SLIGHTLY STRONGER, TOMORROW AFTERNOON. OUTLOOK... MONDAY NIGHT AND TUESDAY...DETERIORATING CONDITIONS TO WIDESPREAD MVFR AND POSSIBLY WIDESPREAD IFR. RAIN COULD BE HEAVY AT TIMES, AND ISOLATED THUNDERSTORMS ARE POSSIBLE DURING THE DAY TUESDAY. WEDNESDAY THROUGH THURSDAY NIGHT...GENERALLY VFR CONDITIONS EXPECTED.
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&& .MARINE...
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SOUTHERLY WINDS WILL CONTINUE TO INCREASE TONIGHT AND TOMORROW SO EVEN THOUGH WE HAVE NOT MUCH SCA ACTIVITY TODAY WE SHOULD BY LATE TONIGHT AND TOMORROW. SEAS SHOULD ALSO RESPOND, AS THEY HAVE NOT YET, TO THE BETTER SOUTHERLY SURGE COMING TOMORROW AHEAD OF THE APPROACHING COLD FRONT. OUTLOOK... TUESDAY...SMALL CRAFT ADVISORY CONDITIONS ARE LIKELY. A COLD FRONT WILL MOVE THROUGH LATE TUESDAY AFTERNOON BRINGING AN ABRUPT SHIFT FROM SOUTHERLY TO NORTHWESTERLY WINDS. WEDNESDAY...SMALL CRAFT ADVISORY CONDITIONS POSSIBLE ESPECIALLY EARLY IN THE DAY, BUT EXPECT WINDS TO DECREASE WEDNESDAY AFTERNOON. WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...WINDS NEAR OR JUST BELOW 25KT. HOWEVER, WAVE HEIGHTS COULD BE ABOVE 5 FT THROUGH THE ENTIRE PERIOD.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ430-431.
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&& $$ SYNOPSIS...JOHNSON NEAR TERM...HEAVENER SHORT TERM...HEAVENER LONG TERM...JOHNSON AVIATION...HEAVENER/JOHNSON MARINE...HEAVENER/JOHNSON

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