Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 121952 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 352 PM EDT SAT APR 12 2014 .SYNOPSIS...
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A WARM FRONT WILL LIFT NORTH OF THE REGION TONIGHT. TOMORROW, A HIGH CENTERED IN THE NORTH ATLANTIC WILL BUILD, BECOMING THE PREDOMINANT FEATURE FOR OUR WEATHER THROUGH MONDAY. LATE TUESDAY, A STRONG COLD FRONT IS EXPECTED TO PUSH THROUGH THE REGION. HIGH PRESSURE IS EXPECTED TO BUILD AND REMAIN ENTRENCHED OVER OUR REGION THROUGH THE LATER HALF OF THE WORK WEEK.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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HIGH PRESSURE WILL CONTINUE TO SLIDE OVERHEAD TONIGHT WHILE A WARM FRONT TO OUR SOUTH PUSHES NORTHWARD. AN INCREASE IN ATLANTIC MOISTURE, ON THE NOSE OF A SOUTHEAST SURFACE FLOW, SHOULD ALLOW FOR AREAS OF STRATUS TO DEVELOP BY EARLY SUNDAY MORNING AS A LOW-LEVEL INVERSION LOWERS OVERNIGHT. PATCHY FOG, MAINLY IN THE SHELTERED SPOTS AND RIVER VALLEYS, COULD ALSO FORM, BUT THINKING TONIGHT IS MORE OF A STRATUS EVENT. THAT BEING SAID, THE MAVMOS, WHICH HAS VERY LITTLE IN THE WAY OF LOWER CLOUDS, SEEMED A BIT TOO COLD SO SIDED WITH THE WARMER MET NUMBERS. THIS SHOULD YIELD WELL ABOVE OVERNIGHT LOWS AROUND 50F.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
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THE WARM FRONT WILL SLIDE THROUGH THE REGION PLACING US IN THE WARM SECTOR LATE TOMORROW MORNING. STRENGTHENING SOUTHERLY FLOW, COMBINED WITH DAYTIME HEATING, SHOULD ALLOW THE STRATUS TO LIFT AND BURN-OFF. THERE SHOULD BE A FAIR AMOUNT OF SUNSHINE WITHIN THE WARM SECTOR, OTHER THAN FAIR WEATHER CUMULUS, AS LOW-LEVEL THERMAL FIELDS INCREASE QUITE NICELY. A CURSORY LOOK AT THE 850 AND 925MB TEMPERATURES SHOWED THAT BOTH THE NAM AND GFS WERE A TAD TOO COLD JUST DOWNSTREAM, WHILE THE NAM WAS A BIT WARMER AND BETTER THAN THE GFS. SEEING AS THOUGH WE MADE A PRETTY GOOD RUN AT 80F ON FRIDAY IT LOOKS WE MAY HAVE ANOTHER SHOT TOMORROW BUT WITH THE WINDS BEING MORE SOUTHERLY, WITHOUT MUCH OF A WEST COMPONENT DID NOT GO THAT ROBUST BUT DID GO A COUPLE DEGREES ABOVE GUIDANCE. SEA AND BAY BREEZES SHOULD NOT BE MUCH AN ISSUE BEYOND THE IMMEDIATE SHORE POINTS TOMORROW GIVEN THE STRONGER LOW-LEVEL FLOW IN PLACE. WINDS SHOULD BECOME GUSTY BY THE MID-AFTERNOON HOURS AS THE LAPSE RATES INCREASE AND CONVECTIVE TEMPERATURES ARE CLOSE TO BEING MET.
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&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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HE MAIN CONCERN THROUGH THIS PERIOD IS THE HEAVY RAIN POTENTIAL MONDAY INTO TUESDAY AHEAD OF THE NEXT COLD FRONT. WE REMAIN IN THE WARM SECTOR ON MONDAY, AND COULD SEE A FEW SHOWERS WITH SOME LEADING UPPER LEVEL SHORT WAVE TROUGHS. MODEL PRECIPITABLE WATER VALUES ARE AROUND 1.25 TO 1.50 DURING THE OVERNIGHT HOURS MONDAY NIGHT THROUGH MID DAY TUESDAY. WHILE NOT UNPRECEDENTED, THESE VALUES WOULD BE HIGHER THAN THE 75TH PERCENTILE FOR PWATS THIS TIME OF YEAR. IN ADDITION, ON TUESDAY MORNING ESPECIALLY, THE 0 TO 6 KM MEAN FLOW IS NEARLY PARALLEL TO THE APPROACHING COLD FRONT. THEREFORE IF THE COLD FRONT IS A SLOW MOVER (NOT UNCOMMON FOR A LATE SPRING COLD FRONT), SOME LOCATIONS COULD SEE SEVERAL HOURS OF TRAINING STORMS. THE MEAN RH IS ALSO QUITE HIGH THROUGH THIS PERIOD (>90 PERCENT). ON THE FLIP SIDE HOWEVER, THERE ARE LIMITING FACTORS FOR THE HEAVY RAIN POTENTIAL. FIRST, THE WARM CLOUD LAYER AT ITS PEAK IS ABOUT 9000 FT DEEP, WHICH IS MARGINAL FOR AN ENHANCED HEAVY RAIN THREAT. THE LOW LEVEL JET REMAINS A SOUTHWESTERLY JET THROUGH THE PERIOD, WITH LITTLE TO NO ON SHORE FLOW, LIMITING MOISTURE TRANSPORT DURING THE PRECIPITATION EVENT. THE MEAN FLOW IS ALSO RATHER FAST (40 TO 50KT) FOR AN ENHANCED HEAVY RAIN THREAT, BUT THIS COULD BE NEGATED BY STORM TRAINING. FINALLY, AS MENTIONED BY THE PREVIOUS SHIFT, THE MODELS HAVE RECENTLY TENDED TO BE A BIT TOO HIGH BOTH WITH QPF AND FORECAST PWAT VALUES. FOR NOW, AGREE WITH THE PREVIOUS SHIFT THAT THE POTENTIAL IS THERE FOR MODERATE TO HEAVY RAIN, BUT AT THIS TIME THE THREAT FOR FLOODING IS RATHER LOW. WHAT WOULD MAKE THIS THREAT HIGHER IS IF THE FRONT SLOWS OR EVEN STALLS (THE ECMWF IS SHOWING A SLOWER FRONT) OR IF AN AREA OF TRAINING CELLS DEVELOPS OVER A MORE URBANIZED LOCATION, LIKE THE I95 CORRIDOR. BEHIND THE FRONT, THE FORECAST PICTURE BECOMES A BIT MORE MUDDLED. THE GFS SHOWS THE FRONT PUSHING ALL THE WAY THROUGH THE REGION BY TUESDAY EVENING, WHILE THE ECMWF SLOWS AND EVEN STALLS THE FRONT OFF THE COAST. THIS HAS IMPLICATIONS FOR OUR REGION IN TWO WAYS. FIRST, WITH HIGHS ON TUESDAY; FOR NOW HAVE GONE WITH A MIDDLE OF THE ROAD SOLUTION OF HIGHS IN THE 50S AND 60S BEING REACHED EARLY IN THE DAY. IF THE GFS SOLUTION IS TRUE, HIGHS COULD ONLY BE A BIT LOWER. THE OTHER IMPLICATION RELATES TO PRECIPITATION BEHIND THE FRONT. THE ECMWF SHOWS A BROAD AREA OF PRECIPITATION LASTING 24 TO 36 HOURS BEHIND THE FRONT, PRIMARILY FOR LOCATIONS NEARER THE SHORE. WITH HOW COLD THE AIR IS EXPECTED TO BE BEHIND THE FRONT, THIS COULD MEAN A WINTRY MIX FOR HIGHER ELEVATIONS IN THE POCONOS. HOWEVER, GIVEN THE CONTINENTAL SOURCE REGION OF THE POLAR AIR MASS, EXPECT CONSIDERABLE DRY AIR ADVECTION BEHIND THE FRONT, AND THUS HAVE TRENDED THE FORECAST CLOSER TO THE GFS BEHIND THE FRONT. ONCE THE FRONT FULLY CLEARS THE REGION, EXPECT A SURFACE HIGH TO BUILD, AND THEN TRANSITION TO A POSITIVELY TILTED RIDGE BY FRIDAY. THE NEXT LOW PRESSURE SYSTEM COULD AFFECT THE REGION AS EARLY AS SATURDAY OR SUNDAY, BUT THERE ARE CONSIDERABLE DIFFERENCES AMONG THE LONG RANGE MODELS IN THE TRACK OF THIS SYSTEM.
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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. TONIGHT...VFR TO START THEN TRENDING TOWARDS THE MVFR/IFR RANGE BY MID-MORNING. SOUTHERLY WINDS WILL SLIGHTLY VEER TOWARDS THE SOUTHEAST TONIGHT ALLOWING MORE MOISTURE TO MOVE INTO THE REGION. HIGH PRESSURE SLIDING THROUGH THE REGION WILL ALLOW A LOW-LEVEL TEMPERATURE INVERSION TO SETUP BY TOMORROW MORNING POOLING MOISTURE NEAR THE SURFACE. THIS COULD PROVIDE AREAS OF STRATUS AND PATCHY FOG THROUGH THE LATE MORNING HOURS. HAD THE HIGHEST CONFIDENCE OUTSIDE OF I-95 CORRIDOR TERMINALS, WHICH STILL SHOW A TEMPO GROUP FOR MVFR CIGS. TOMORROW...STRATUS/FOG LIFT AND BURN OFF BY LATE MORNING GIVING WAY TO POCKETS OF FAIR WEATHER CUMULUS. WINDS TURN TOWARDS THE SOUTH BEHIND A WARM FRONT PASSAGE AND STRENGTHEN BECOMING GUSTY, AROUND 20 KNOTS, BY THE AFTERNOON HOURS. OUTLOOK... MONDAY...MOSTLY VFR. MVFR CONDITIONS IN -SHRA POSSIBLE LATE MONDAY AFTERNOON. 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...CONDITIONS IMPROVING TO VFR FROM WEST TO EAST.
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&& .MARINE...
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WARM FRONT WILL LIFT THROUGH THE REGION LATE TONIGHT TURNING THE WINDS FROM SOUTHEAST TO SOUTH AND STRENGTHENING THEM. SEAS AND WINDS SHOULD INCREASE ENOUGH TOWARDS THE AFTERNOON HOURS TO REACH SMALL CRAFT CRITERIA THROUGH THE REMAINDER OF THE DAY. OUTLOOK... MONDAY AND TUESDAY...SMALL CRAFT ADVISORY CONDITIONS ARE LIKELY TO CONTINUE. WEDNESDAY...WINDS DECREASING BELOW SCA CONDITIONS BY MID DAY.
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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...JOHNSON NEAR TERM...HEAVENER SHORT TERM...HEAVENER LONG TERM...JOHNSON AVIATION...HEAVENER/JOHNSON MARINE...HEAVENER/JOHNSON

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