Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 271955 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 355 PM EDT SAT JUN 27 2015 .SYNOPSIS...
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LOW PRESSURE OVER THE OHIO VALLEY WILL REDEVELOP OVER OUR REGION TONIGHT AND MOVE INTO NEW ENGLAND ON SUNDAY. HIGH PRESSURE WILL BRIEFLY MOVE INTO THE AREA FOR MONDAY. A COLD FRONT WILL SETTLE ACROSS OUR REGION LATER TUESDAY AND WEDNESDAY...BEFORE STALLING TO OUR SOUTH ON THURSDAY. THIS FRONT MAY BEGIN TO LIFT NORTHWARD ACROSS OUR AREA ON FRIDAY AND SATURDAY.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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PLENTY TO KEEP TRACK OF IN THE NEAR TERM. LOW PRESSURE WILL MOVE ACROSS OHIO/PA TONIGHT AND CAUSE A WARM FRONT TO LIFT NORTHWARD OVER OUR AREA. A SECOND LOW WILL FORM NEAR THE POTOMAC AND LIFT OVER THE DEL VALLEY OVERNIGHT. RAIN AND SCT TSTMS EXPECTED. THE BEST CHC FOR TSTMS WILL BE ACROSS THE SRN AREAS. QPF WILL RANGE FROM 2 TO 3 INCHES OVER THE WRN AREAS (BERKS,CHESTER AND LEHIGH VALLEY) TO 1 TO 2 INCHES OVER SRN DELAWARE AND ERN NJ. FLOOD WATCH...WE WILL MAINTAIN AS IS. THERE COULD BE SOME HIGHER TOTALS ACROSS THE SRN POCONOS AND NRN NJ...BUT IT APPEARS THE THE HIGHEST TOTALS WILL BE JUST SOUTH OF THAT ACROSS THE LEHIGH VALLEY. A SECOND LOW WILL DEVELOP SOUTH OF THE AREA THIS EVENING THEN TRACK ACROSS THE DEL VALLEY TONIGHT. IT WILL TEND TO KEEP THE STEADY RAINS N/W WITH MORE SHOWERY PRECIP S/E. TORNADO WATCH...IN EFFECT ACROSS MUCH OF THE MD ERN SHORE AND THE SRN 2/3RD OF DELAWARE THRU 800 PM. CONVECTION WILL DEVELOP/MOVE ACROSS THESE AREAS AND THERE IS GOOD LOW LEVEL SHEAR ON THIS SIDE OF THE FRONT.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
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THE STRONG LOW WILL BE ACROSS NRN NJ SUNDAY MORNING. THE PRESSURE GRADIENT WILL FAVOR A DRYING WRLY FLOW ACROSS THE AREA...SO THE STEADY PRECIP ACROSS THE NORTH EARLY WILL LIFT OUT...LEAVING OUR AREA IN AN IMPROVING PATTERN. A COUPLE SCT SHOWERS POSSIBLE EARLY...THEN POPS DECREASE THROUGH THE DAY. SKIES WILL BECOME SUNNY FROM S TO N AS THE DAY PROGRESSES. HIGH TEMPERATURES WILL RISE INTO THE LOW 80S ACROSS THE SRN AREAS...WHERE WE HAVE THE GREATEST DURATION OF SUNSHINE. ACROSS THE NRN AREAS TEMPS WILL TOP OUT IN THE MID/UPPER 70S. WINDS...MOSTLY WRLY AND BECOME GUSTY (20 TO 25 MPH) DURING THE AFTERNOON.
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&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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OVERVIEW... AMPLIFIED MID-LEVEL PATTERN DURING THE D+3 THRU D+7 PERIOD FEATURES A RIDGE ALONG THE WEST COAST OF NOAM AND A TROUGH OVER THE GRT LKS. STRONG HIGH LATITUDE BLOCKING BY JUNE STANDARDS IS ALSO PRESENT... AND THIS IS REFLECTED IN THE -NAO/+PNA PATTERN...THAT IS EXPECTED TO PERSIST AT LEAST INTO THE 4TH OF JULY WEEKEND. THE MAIN UNCERTAINTY IN THE FORECAST IS WITH REGARD TO THE AMPLITUDE AND TIMING OF S/WV ENERGY TRAVERSING THE WEST COAST RIDGE...AS THE GRT LAKES TROUGH TAKES ON AN INCREASINGLY NEGATIVE TILT BY MID-WEEK. OVERALL...A CYCLONIC FLOW ALOFT AND BLW AVG HEIGHTS WILL LEAD TO UNSETTLED WEATHER THRU THE PERIOD WITH TEMPS GENERALLY AOB SEASONAL NORMS. DETAILS... SUN NIGHT AND MON...LOW LEVEL MOISTURE ASSOCIATED WITH COMMA HEAD WILL GRADUALLY DECREASE AS LOW PRES DEPARTS AND FLOW BECOMES WEST. A -SHRA IS POSSIBLE EARLY SUN NIGHT OVER THE POCONOS. INCREASING SUNSHINE EXPECTED ON MON...AS S/WV RIDGING AND THE LEFT ENTRANCE REGION OF THE JET MOVE IN ALOFT...SUPPORTING A WEAK RIDGE OF HIGH PRES AT THE SURFACE. MAX TEMPS WILL AVERAGE AROUND 5 DEGREES BELOW AVG...WITH MUCH MORE COMFORTABLE HUMIDITY LEVELS. TUE...LOW PRES MOVING THRU THE GRT LKS WILL LEAD TO A WARM FROPA... BUT ONSHORE FLOW MAY INHIBIT THIS...AND THE FRONT COULD STALL FOR A TIME ACROSS THE REGION. LOW AND MID-LEVEL MOIST WILL INCREASE AS A S/WV APPROACHES THE REGION...WITH CONSIDERABLE CLOUDINESS EXPECTED. ATTM...BEST CHANCE OF PRECIP IS NORTHWEST OF THE I-95 CORRIDOR... WHERE DEEPER MOISTURE AND LIFT COINCIDE. THERE IS THE POTENTIAL FOR CONVECTION...WHICH WILL BE DEPENDANT ON THE LOCATION OF THE WARM FRONT AND AMOUNT OF INSOLATION. ALTHOUGH CAPE AND SHEAR ARE BOTH UNCERTAIN...MODEL SOLUTIONS INDICATE A CONSIDERABLE AMOUNT OF LOW- LEVEL HELICITY INVOF THE BOUNDARY...SO THIS WILL BEAR WATCHING. WED...LOW PRES MOVES THRU THE ST. LAWRENCE VALLEY...AS A BONAFIED COLD FRONT APPROACHES FROM THE WEST. THIS IS WHERE MODEL SOLUTIONS BEGIN TO DIVERGE WITH RESPECT TO TIMING OF THE COLD FROPA...WHICH WILL DETERMINE CONVECTIVE POTENTIAL. ATTM...MODELS HAVE THE FRONT TO THE I-95 CORRIDOR BY 18Z...WHICH PLACES THE EMPHASIS FOR CONVECTION ALONG AND EAST OF HERE. THE FRONT WILL ALSO SLOW DOWN...WHICH COULD PROLONG CONVECTIVE CHANCES INTO WED NIGHT OVER DELMARVA. MAX TEMPS ARE EXPECTED TO BE AOA SEASONAL LEVELS. THU...HIGH PRES BRIEFLY MOVES IN...BUT STALLED FRONT NEAR DELMARVA COULD LEAD TO CONSIDERABLE CLOUDINESS AND EVEN SOME -SHRA OVER THIS AREA. TO THE NORTH...ENOUGH DRY AIR SHOULD FILTER IN FOR AT LEAST PARTIAL SUNSHINE. FRI AND SAT...CONSIDERABLE SPATIAL AND TEMPORAL MODEL SPREAD EXISTS IN HANDLING S/WV ENERGY TRAVERSING GRT LKS TROUGH. SOLUTIONS VARY... FROM THE FLATTER UKMET TO THE MORE AMPLIFIED ECMWF. THE LATTER WOULD LEAD TO ANOTHER STORM SYSTEM MOVING THRU THE GRT LKS W/REDEVELOPMENT OVER THE MID-ATLANTIC...AND THE POTENTIAL FOR MORE HEAVY RAINFALL. THIS WILL HAVE TO BE MONITORED...GIVEN RAINFALL OCCURING THIS WEEKEND...THUS ANTICIPATED WET ANTEDENT CONDITIONS.
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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. THE LOWER CONDITIONS ACROSS THE DEL VALLEY AND EAST TOOK LONGER TO DEVELOP THAN EXPECTED EARLIER...BUT WE HAVE CONTINUED WITH THE OVERALL TREND IN THE EARLIER TAFS OF A DECENT PERIOD OF IFR CONDITIONS AND HEAVY RAINS OVERNIGHT. A WARM FRONT AND LOW PRESSURE MOVING ACROSS THE AREA WILL CONTINUE TO CREATE SHOWERS/TSTMS SOUTH AND STEADY RAINS AND LOW CIGS N/W. THE TREND TOWARD IMPROVING CONDITIONS WILL BEGIN AROUND DAWN SUNDAY SOUTH AND SPREAD NORTHWARD. WINDS TONIGHT MOSTLY ERLY/SERLY THEN SWITCHING TO WRLY LATE TONIGHT. OUTLOOK... SUN NIGHT AND MON...VFR CONDITIONS EXPECTED. TUE THRU WED...MVFR POSSIBLE IN SHRA/TSRA...PARTICULARLY I-95 CORRDIDOR TERMINALS AND POINTS NORTHWEST. THU...VFR CONDITIONS. MVFR POSSIBLE IN SHRA/TSRA...ESPECIALLY SOUTH NJ AND DELMARVA TERMINALS. LOW CONFIDENCE.
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&& .MARINE...
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WE WILL CONTINUE WITH THE SCA FLAG FOR THE OCEAN WATERS INTO SUNDAY. WE HAVE EXTENDED THE SCA FLAG FOR DEL BAY BEYOND THE PREVIOUS (11PM TONIGHT)...INTO PRE-DAWN HOURS OF SUNDAY. THE DEVELOPING LOW LOOKS A BIT SLOWER AND THE SE FLOW MAY CONTINUE UP THE BAY A LITTLE LONGER THAN PREVIOUSLY EXPECTED. RAIN WITH A CHC OF THUNDER OVERNIGHT. SMW`S FOR GUSTY WINDS POSSIBLE OVERNIGHT FOR THE SRN COASTAL WATERS DUE TO TSTMS NEARBY. OUTLOOK... SUN NIGHT...SCA NOW IN EFFECT THRU 21Z SUN MAY NEED TO BE EXTENDED INTO SUNDAY NIGHT FOR RESIDUAL 5 FOOT SEAS. MONDAY...WINDS AND SEAS ARE ANTICIPATED TO BE BLW SCA THRESHOLDS. TUESDAY...INCREASE IN SOUTHERLY FLOW MAY BUILD SEAS ON THE OCEAN SCA CRITERIA. WEDNESDAY...SUBSIDING SEAS WITH SUB-SCA CONDITIONS EXPECTED ATTM.
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&& .HYDROLOGY... A FLOOD WATCH IS IN EFFECT FOR BERKS COUNTY, THE LEHIGH VALLEY AND SOUTHEASTERN PENNSYLVANIA FROM NOON TODAY UNTIL 500 AM SUNDAY. ALSO, THE FLOOD WATCH INCLUDES CECIL COUNTY IN MARYLAND AND NEW CASTLE COUNTY IN DELAWARE. WE ARE ANTICIPATING WIDESPREAD RAINFALL AMOUNTS OF 1.5 TO 2.5 INCHES IN THE WATCH AREA. LOCALLY HIGHER AMOUNTS ARE LIKELY. THE LOWER SCHUYLKILL RIVER VALLEY IS PARTICULARLY VULNERABLE TO NEW FLOODING DUE TO THE SATURATED CONDITIONS THERE. RADAR INDICATED LOCALIZED RAINFALL AMOUNTS OF GREATER THAN 4 INCHES FROM AROUND PHOENIXVILLE AND COLLEGEVILLE DOWN TO CONSHOHOCKEN DURING THE HOURS AROUND MIDNIGHT. GENERALLY, SMALL STREAMS AND CREEKS WILL BE MOST VULNERABLE DURING THIS EVENT ALONG WITH AREAS OF POOR DRAINAGE. THE MAIN RIVERS SUCH AS THE LEHIGH, THE SCHUYLKILL AND THE DELAWARE ARE NOT EXPECTED TO FLOOD. && .TIDES/COASTAL FLOODING...
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A STRONG SOUTHEAST FLOW UP THE DELAWARE BAY WILL RESULT IN HIGHER THAN NORMAL WATER LEVELS THIS EVENING INTO THE OVERNIGHT HOURS. THE LATEST DBOFS/CBOFS MODEL RUNS KEEP WATER LEVELS SHY OF MINOR TIDAL FLOODING LEVELS. WE NORMALLY BEGIN TO ISSUE STATEMENTS OR ADVISORIES WHEN LEVELS EXCEED MINOR LEVELS BY 1/4 FOOT...SO WE ARE GOING TO HOLD OFF FOR NOW. THERE IS NOT A GREAT DEAL OF ROOM FOR ERROR...HOWEVER...SO PAY ATTENTION FOR POSSIBLE FUTURE UPDATES.
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&& .RIP CURRENTS...
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THE MODERATE TO STRONG EAST TO SOUTHEAST FLOW WILL LEAD US TO CONTINUE THE FORECAST FOR A HIGH RISK OF RIP CURRENTS THIS EVENING ALONG THE NEW JERSEY SHORE. WE WILL KEEP THE RISK AT MODERATE FOR THE DELAWARE BEACHES BASED ON OUTPUT FROM OUR LOCAL PROGRAM.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...FLOOD WATCH THROUGH LATE TONIGHT FOR PAZ060>062-070-071- 101>106. NJ...HIGH RIP CURRENT RISK UNTIL 10 PM EDT THIS EVENING FOR NJZ014- 024>026. DE...FLOOD WATCH THROUGH LATE TONIGHT FOR DEZ001. MD...FLOOD WATCH THROUGH LATE TONIGHT FOR MDZ008. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT SUNDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL 6 AM EDT SUNDAY FOR ANZ430-431.
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&& $$ SYNOPSIS...FRANCK/GORSE NEAR TERM...O`HARA SHORT TERM...O`HARA LONG TERM...FRANCK/GORSE AVIATION...FRANCK/GORSE/O`HARA MARINE...FRANCK/GORSE/O`HARA HYDROLOGY...O`HARA TIDES/COASTAL FLOODING...O`HARA RIP CURRENTS...O`HARA

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