Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 122000 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 400 PM EDT SAT JUL 12 2014 .SYNOPSIS...
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HIGH PRESSURE WILL CONTINUE TO MOVE OFFSHORE TONIGHT. THE HEAT AND HUMIDITY WILL BUILD SUNDAY AND MONDAY AS SOUTHERLY RETURN FLOW STRENGTHENS AROUND THE HIGH. A COLD FRONT WILL SLOWLY MOVE THROUGH THE AREA TUESDAY AND OFFSHORE WEDNESDAY. HIGH PRESSURE BUILDS INTO THE REGION THURSDAY AND MOVES OFFSHORE BY THE END OF THE WEEK.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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IN GENERAL...HIGH PRESSURE PREVAILS ACROSS MOST OF THE AREA. THE WEATHER IS DRY IN MOST AREAS...BUT SOME SCT SHOWERS AND TSTMS HAVE DEVELOP ACROSS THE WRN EDGES OF THE FORECAST AREA...AND THEY MAY AFFECT THERE AREAS INTO THE EARLY EVENING. A FEW SHORT TERM WARNINGS HAVE BEEN ISSUED DUE TO THE SLOW NATURE OF THE CELLS. WE WILL LEAVE MOSTLY CHC POPS FOR THOSE AREAS...WITH A LOW LIKELY POP FOR BERKS OCOUNTY THRU 00Z. A QUIET EVENING AND OVERNIGHT EXPECTED WITH SOME PATCHY FOG OVERNIGHT AND A MUGGY MILD NIGHT EXPECTED. LOW TEMPS A MET/MAV MOS BLEND.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
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HIGH PRESSURE WILL LOSE ITS INFLUENCE ON OUR WEATHER. AN APPROACHING UPPER TROUGH AND SFC FRONTS WILL BRING INCREASING CHCS FOR AFTERNOON SHOWERS/TSTMS TO MOST AREAS. POPS ARE IN THE CHC RANGE FOR THE MOST PART. ANOTHER VERY WARM AND MUGGY DAY EXPECTED WITH HIGH TEMPS IN THE LOW/MID 80S NORTH AND CENTRAL AND UPPER 80S AND LOW 90S SOUTH/EAST.
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&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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SYNOPTIC SETUP EARLY NEXT WEEK WILL FEATURE A DIGGING TROUGH TO OUR WEST AS AN ANOMALOUSLY STRONG UPPER LOW FOR THIS TIME OF YEAR MOVES SOUTHEASTWARD OVER THE GREAT LAKES. DEEP S-SW FLOW DOWNSTREAM OF THE TROUGH AND UPSTREAM OF A BERMUDA RIDGE WILL STRENGTHEN OVER THE EASTERN CONUS. AN ACTIVE WEATHER PATTERN IS EXPECTED UNDER THIS SETUP THROUGH TUESDAY. A SFC TROUGH ASSOCIATED WITH LOPRES MOVING JUST EAST OF JAMES BAY IS FORECAST TO EXTEND SOUTHWARD FROM THE LOW INTO UPSTATE NY AND THEN BACK TO THE SOUTHWEST ACROSS WESTERN PA PRIOR SUNSET SUNDAY EVENING. UPSTREAM SHOWERS AND THUNDERSTORMS THAT DEVELOP IN WESTERN/CENTRAL PA ALONG AND AHEAD OF THE SFC TROUGH DURING THE DAYTIME WOULD MOST LIKELY PROGRESS EASTWARD INTO THE FORECAST AREA SUNDAY NIGHT. NOCTURNAL CONVECTION MAY BE ABLE TO BE MAINTAINED SOMEWHAT BY A SWLY LLVL JET, BUT IT SHOULD WEAKEN LATER INTO THE EVENING WITH THE LOSS OF DAYTIME HEATING. POPS ARE HIGHEST TOWARD THE LEHIGH VALLEY/POCONOS (LIKELY) AND DECREASE TO THE SOUTHEAST (TO SLIGHT CHANCE BY THE NJ/DE COAST). THE ENTIRE EASTERN SEABOARD WILL BE POSITIONED WITHIN THE PRE-FRONTAL WARM SECTOR THAT IS WELL AHEAD OF THE UPPER LOW/COLD FRONT OVER THE MIDWEST/GREAT LAKES ON MONDAY. HOT AND HUMID ARE FORECAST FOR MONDAY WITH SLY RETURN FLOW AROUND THE HIGH AND THE LLVL THERMAL RIDGE OVERHEAD. HOWEVER, THE EXTENT OF LEFTOVER DEBRIS CLOUDS FROM OVERNIGHT CONVECTION IS UNCERTAIN, BUT IF CLOUDS LINGER LATER INTO THE DAY THAN CURRENTLY ANTICIPATED, FORECAST MAX TEMPS IN THE LOWER 90S MAY NOT BE REALIZED. ASSUMING SUFFICIENT BREAKS IN CLOUD COVER, MODERATE TO STRONG INSTABILITY MAY DEVELOP OVER THE REGION (FCST MEDIAN SBCAPE OF 1500-2000 J/KG FROM THE 09Z SREF). MODELS INDICATE THE DEVELOPMENT OF A LEE SFC TROUGH ON MONDAY. CONVERGENCE ALONG THE BOUNDARY AND OVER THE HIGHER TERRAIN WOULD PROVIDE THE NECESSARY LIFT FOR DEEPER CONVECTION TO INITIATE DURING THE PEAK HEATING. STRONGER SW WINDS ALOFT WILL SPREAD EASTWARD AHEAD OF THE TROUGH, HELPING TO INCREASE DEEP-LAYER SHEAR OVER THE AREA (FCST MEDIAN 0-6 KM SHEAR FROM THE 09Z SREF INCREASES TO 40 KT ACROSS NERN PA LATE IN THE DAY). THERE IS A POTENTIAL FOR SEVERE THUNDERSTORMS MONDAY AFTERNOON AND EVENING GIVEN THE FORECAST ENVIRONMENT. THE AREA IS OUTLOOKED IN A SLIGHT RISK BY SPC FOR MONDAY. DAMAGING WINDS WOULD BE THE PRIMARY THREAT BUT LARGE HAIL, ISOLATED TORNADOES AND FLASH FLOODING ARE ALSO POSSIBLE. WHILE THE MODELS HAVE COME INTO BETTER AGREEMENT WITH THE HANDLING OVER THE GREAT LAKES UPPER LOW, THERE ARE STILL SOME DIFFERENCES REGARDING THE TIMING OF THE COLD FRONT ON TUESDAY. THE POTENTIAL FOR ANOTHER ROUND OF SEVERE THUNDERSTORMS AHEAD OF THE COLD FRONT ON TUESDAY WOULD BE HIGHER IN THE SLOWER SOLUTION THAT WAS DEPICTED BY THE 00Z/12Z ECMWF. 12Z GFS CONTINUES TO BE MORE PROGRESSIVE WITH THE FRONT, SHIFTING THE CORE OF THE WARM, MOIST AND UNSTABLE AIR SOUTH AND EAST OF THE REGION. THIS WOULD LIMIT THE POTENTIAL FOR A MORE SIGNIFICANT SEVERE THUNDERSTORM EVENT. DESPITE THESE UNCERTAINTIES, POPS WERE INCREASED TO LIKELY FOR MOST OF THE AREA TUESDAY WITH FAVORABLE SYNOPTIC LIFT ALONG THE FRONT AND IN THE RIGHT ENTRANCE REGION OF A STRONG UPPER-LEVEL JET. THE COLD FRONT SHOULD BE OFFSHORE ON WEDNESDAY. POST-FRONTAL NW FLOW WILL ADVECT MUCH COOLER, DRIER CANADIAN AIR. BOTH WEDNESDAY AND THURSDAY BOTH 5-10F BELOW NORMAL. FCST MAX TEMPS RANGING FROM THE LOW 70S IN THE POCONOS TO LOW 80S ALONG AND EAST OF I-95 COMBINED WITH DEWPOINTS AOB 60F WILL BE A RESPITE FROM THE SUMMER HEAT AND HUMIDITY.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDITIONS CONTINUE AT THE TERMINALS THIS AFTERNOON. SHOWERS AND ISOLATED TSTMS CONTINUE WEST OF KRDG EARLY THIS AFTERNOON AND THEY MAY BEGIN TO AFFECT KRDG AROUND 19Z THRU 21Z SO AMDS THERE ARE POSSIBLE. ELSEWHERE...FEW-SCT CU AND A DECENT S/SW WINDS INLAND AND MOSTLY SE WIND ACROSS DE/NJ. GOOD CONDITIONS WILL CONTINUE THIS EVENING...THEN SOME PATCHY FOG WILL DEVELOP OVERNIGHT. MVFR VSBYS MAY DEVELOP AFTER 06Z ACROSS MOST AREAS. THE MORE METRO TAF SITES MAY REMAIN 6SM HZ/BR HOWEVER. SUNDAY...A BIT OF MORNING FOG...THEN MORE VFR CONDITIONS WITH BUILDING DAYTIME CU. SHOWERS/TSTMS MAY DEVELOP LATER DURING THE AFTERNOON. WINDS MOSTLY SRLY 10-15 KTS. OUTLOOK... SUNDAY NIGHT THROUGH TUESDAY NIGHT...UNSETTLED WX PATTERN WITH THE POTENTIAL FOR MVFR/IFR IN SEVERAL ROUNDS OF SHRA/TSRA. THE BEST CHANCE FOR PRECIP WILL BE DURING THE AFTN/EVE PERIODS ON MONDAY AND TUESDAY. S-W WINDS AHEAD OF THE COLD FRONT AROUND 10-15 KT EACH AFTN, AND 5-10 KT EACH NIGHT. WEDNESDAY-THURSDAY...CANADIAN HIGH PRESSURE BUILDS INTO THE AREA WITH VFR CONDITIONS.
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&& .MARINE...
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WINDS AND SEAS WILL REMAIN SRLY OR SERLY OVERNIGHT AND SUN MORNING. WINDS SPEEDS AND SEAS WILL BE SUB-SCA IN THOSE PERIODS. SUN AFTERNOON WILL SEE AN INCREASE IN WINDS WITH SEAS TO FOLLOW. WE WILL BRING OUT THE SCA FOR SUN AFTERNOON WITH WIND GUSTS AROUND 25 KTS AND SEAS INCREASING TO AROUND 4 FT. SCT TSTMS POSSIBLE LATER SUN. OUTLOOK... SUNDAY NIGHT THROUGH TUESDAY... SLY WINDS EXPECTED IN ADVANCE OF A SLOW-MOVING COLD FRONT WILL BECOME GUSTY EACH AFTERNOON AND EVENING. SCA WAS ISSUED FOR SUNDAY NIGHT FOR THE ATLANTIC COASTAL WATERS WITH GUSTS TO 25 KT AND SEAS 4-5 FT. SCA MAY BE NEEDED AGAIN MONDAY AND TUESDAY.
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&& .TIDES/COASTAL FLOODING...
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THE HIGH TIDES TONIGHT AND SUNDAY NIGHT MAY APPROACH THE MINOR FLOOD LEVEL ALONG THE ATLANTIC COASTAL AREAS, BUT ARE NOT EXPECTED TO REACH HIGH ENOUGH LEVELS TO REQUIRE A COASTAL FLOOD ADVISORY.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY FROM NOON SUNDAY TO 6 AM EDT MONDAY FOR ANZ450>455.
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&& $$ SYNOPSIS...KLEIN NEAR TERM...O`HARA SHORT TERM...O`HARA LONG TERM...KLEIN AVIATION...KLEIN/O`HARA MARINE...KLEIN/O`HARA TIDES/COASTAL FLOODING...O`HARA

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