Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 241954 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 354 PM EDT TUE MAR 24 2015 .SYNOPSIS...
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HIGH PRESSURE EXTENDING OVER THE NORTHEAST AND MID ATLANTIC STATES WILL GRADUALLY MOVE OFFSHORE BY EARLY WEDNESDAY. A WARM FRONT IS THEN FORECAST TO LIFT NORTH THROUGH THE REGION WEDNESDAY NIGHT, FOLLOWED BY A STRONG COLD FRONT CROSSING THE MID ATLANTIC THURSDAY EVENING. A SECONDARY COLD FRONT SHOULD THEN PASS THROUGH THE REGION LATE FRIDAY. HIGH PRESSURE IS EXPECTED TO FOLLOW OVER THE WEEKEND, WITH ANOTHER COLD FRONT REACHING THE AREA MONDAY.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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THE SYNOPTIC SETUP IS COMPRISED OF A TROUGH IN THE NORTHEAST AND INTO THE MID ATLANTIC. AT THE SURFACE, HIGH PRESSURE CENTERED NEAR THE EASTERN GREAT LAKES EXTENDS DOWN INTO THE MID ATLANTIC. THIS IS ALLOWING FOR LIGHT WINDS AND WILL DOMINATE OUR WEATHER THROUGH TONIGHT. THE LINGERING OVERCAST THIS AFTERNOON COMBINED WITH A LACK OF MIXING HAS KEPT TEMPERATURES ACROSS MUCH OF THE AREA IN THE 30S. HOWEVER WHERE THINNING AND CLEARING IS TAKING PLACE THIS AFTERNOON, THE TEMPERATURES ARE RESPONDING AND GETTING INTO THE 40S. A SHORT WAVE WITH ITS VORTICITY BECOMING MORE CHANNELIZED IS FORECAST TO CLEAR OUR AREA THROUGH EARLY THIS EVENING. THIS IS ASSOCIATED WITH THE EXTENSION OF A SHORT WAVE TROUGH AXIS THAT WILL ALSO SHIFT TO OUR EAST EARLY THIS EVENING. THE MOISTURE ASSOCIATED WITH THIS FEATURE COMBINED WITH A SUBSIDENCE INVERSION AND A NEARBY THERMAL GRADIENT ALOFT, HAS ALLOWED THE CLOUD DECK TO HANG ON LONGER FOR MUCH OF THE CWA. THERE IS DRYING THOUGH WORKING SOUTHWARD THIS AFTERNOON, WHICH WILL ERODE THE CLOUD DECK SOUTHWARD BENEATH THE SUBSIDENCE INVERSION. AS A RESULT, THE CLOUDS ARE EXPECTED TO THIN AND CLEAR FROM NORTH TO SOUTH THROUGH EARLY THIS EVENING. AS THE AFOREMENTIONED SURFACE HIGH BEGINS TO SHIFT EASTWARD THROUGH THE NIGHT, A LIGHT SOUTHEASTERLY FLOW WILL START TO DEVELOP. THIS WILL ALLOW THE SURFACE DEW POINTS TO START CREEPING UPWARD, HOWEVER A COLD NIGHT IS EXPECTED WITH LIGHT WINDS AND ANY LINGERING CLOUDS DISSIPATING. AS FOR THE LOW TEMPERATURES, WE USED MOSTLY A NAM/GFS MOS BLEND.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
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HIGH PRESSURE AT THE SURFACE WILL BE SHIFTING TO OUR EAST DURING THE MORNING AS A SHORT WAVE RIDGE MOVES ACROSS. AS THIS OCCURS, AN UPPER- LEVEL TROUGH WILL AMPLIFY SOME FROM THE MIDWEST TO THE OHIO VALLEY AND EVEN TAKE ON A NEGATIVE TILT. THE FLOW ALOFT WILL BACK AND ALLOW FOR WAA TO INCREASE ACROSS THE REGION, ESPECIALLY FROM THE EASTERN GREAT LAKES DOWN THE OHIO VALLEY. IT IS IN THESE AREAS WHERE THE STRONGEST LOW-LEVEL JET IS FORECAST TO MOVE THROUGH DURING THE COURSE OF THE DAY. AS THE WAA OCCURS DURING THE DAY, WE ARE EXPECTING AN INCREASE IN CLOUDS ACROSS THE ENTIRE AREA. THESE WILL LOWER AS THE FORECAST SOUNDINGS INDICATE MID LEVEL MOISTURE INCREASING MORE QUICKLY AT FIRST /ESPECIALLY WESTERN AREAS INITIALLY/ THEN THE LOWER LEVELS GRADUALLY MOISTEN UP. AS THIS IS OCCURRING, AN INCOMING WARM FRONT AND THE SOUTHEASTERN EXTENSION OF THE TROUGH GOING NEGATIVELY TILTED SHOULD PRODUCE SOME SHOWERS OR A BAND OF SHOWERS FROM THE GREAT LAKES REGION SOUTHEASTWARD. THE BEST FORCING HOWEVER APPEARS TO BE MAINLY FOCUSED TO OUR NORTHWEST. AS A RESULT, WE ADJUSTED THE POPS TO SHOW THE HIGHEST CHC ACROSS OUR WESTERN ZONES IN THE AFTERNOON. THE FORECAST SOUNDINGS DO SUGGEST THAT AS THE MOISTENING IS OCCURRING, SOME LOW-LEVEL DRY AIR MAY HANG ON. IT APPEARS THOUGH AS THE AIRMASS MODIFIES AND BY THE TIME THE PRECIPITATION ARRIVES, IT WILL BE MILD ENOUGH TO BE ALL RAIN. BASED ON THE QPF FORECAST AND THE STRONGEST FORCING HANGING BACK TO OUR WEST, WENT WITH SHOWERY WORDING. AS FOR THE HIGH TEMPERATURES, MODERATION OF THE AIRMASS IS EXPECTED AS WAA OCCURS. HOWEVER, THIS SHOULD BE TEMPERED SOME DUE TO INCREASING CLOUDS AND A DEVELOPING ONSHORE FLOW AHEAD OF THE WARM FRONT. OVERALL, WE USED A NAM/GFS MOS BLEND THEN MADE SOME TWEAKS.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
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AN ACTIVE PATTERN WITH A BRIEF WARM-UP WILL BE ONGOING AT THE START OF THE LONG TERM, BEFORE ANOTHER MID/UPPER LEVEL TROUGH RETURNS ALONG WITH CANADIAN HIGH PRESSURE FOR OVER THE WEEKEND. BY WEDNESDAY NIGHT, WARM ADVECTION WILL BE TAKING HOLD ACROSS THE REGION AS A SURFACE WARM FRONT CONTINUES TO LIFT NORTHWARD. WE HAVE MAINTAINED HIGH CHANCE POPS THROUGH WEDNESDAY NIGHT, INCREASING POPS A LITTLE INTO DAYBREAK THURSDAY. AS NOTED BY THE PREVIOUS SHIFT, WE HAVE ALSO KEPT A MENTION OF DRIZZLE AND FOG THROUGH THE OVERNIGHT WEDNESDAY, AS FORECAST SOUNDINGS SHOW SOME DRIER AIR ALOFT WITH VERY SATURATED LOW LEVELS. INTO THURSDAY, AN INCREASING SOUTHWEST FLOW WILL BE SETTING UP ACROSS THE REGION AHEAD OF AN APPROACHING STRONG COLD FRONT. SOUTHWEST WINDS MAY GUST TO AROUND 25 MPH INTO THURSDAY AFTERNOON AHEAD OF THE ADVANCING FRONT AS TEMPERATURES WARM INTO THE 60S, WITH SOME LOWER 70S POSSIBLE ACROSS SOUTHERN AREAS. INCREASING LOW LEVEL MOISTURE WILL ALSO BE APPARENT ACROSS THE REGION AS DEWPOINTS ARE FORECAST TO RISE INTO THE 50S. WITH THE APPROACHING COLD FRONT BY LATE-DAY, WE INCREASE POPS TO LIKELY FOR THURSDAY AFTERNOON AND EVENING AND MAINTAIN A CHANCE FOR TSTORMS AS CAPE VALUES ARE FORECAST TO REACH UP TO A FEW HUNDRED J/KG. BRIEF DOWNPOURS AND A FEW STRONGER WIND GUSTS ARE POSSIBLE WITH ANY DEVELOPING TSTORMS AS PWAT VALUES ARE FORECAST TO RISE TO A LITTLE OVER AN INCH AND FORECAST SOUNDINGS SHOW BULK SHEAR FROM 0-6 KM RANGING BETWEEN 40 TO 50 KT AS THE COLD FRONT NEARS THE REGION INTO THURSDAY EVENING. OVERALL QPF AMOUNTS STILL LOOK TO RANGE MAINLY BETWEEN A QUARTER TO THREE QUARTERS OF AN INCH. THROUGH THE REMAINDER OF THURSDAY OVERNIGHT, WE STEP-DOWN POPS TO CHANCE FROM WEST TO EAST ACROSS THE FORECAST AREA AS THE COLD FRONT PASSES OFFSHORE. MODEL CONSENSUS THEN INDICATES A SECONDARY COLD PASSAGE LATE FRIDAY TO FRIDAY NIGHT, WITH A LONGWAVE TROUGH ALSO MOVING IN ACROSS THE EASTERN UNITED STATES. FRIDAY LOOKS TO BE A MAINLY CLOUDY DAY ACROSS OUR REGION, WITH ISOLATED SHOWERS POSSIBLE, ESPECIALLY ACROSS NORTHERN AREAS. OVER THE WEEKEND, DRY AND COOL CONDITIONS ARE ANTICIPATED AS THE LONGWAVE TROUGH PASSES OVERHEAD AND SURFACE HIGH PRESSURE BUILDS DOWN ACROSS THE AREA. THEREAFTER, A LOW PRESSURE SYSTEM MOVING ACROSS SOUTHERN CANADA IS EXPECTED TO SEND A COLD FRONT ACROSS OUR REGION MONDAY. ANY RAIN/SNOW SHOWERS AND PRECIP AMTS LOOK TO BE LIGHT AT THIS TIME AND MAINLY ACROSS OUR NORTHERN ZONES AS MOST OF THE FORCING WITH THIS SYSTEM IS EXPECTED TO BE TO OUR NORTH. AS THAT SYSTEM PASSES OFFSHORE INTO MONDAY NIGHT, MORE HIGH PRESSURE IS ANTICIPATED TO BUILD ACROSS THE REGION INTO TUESDAY.
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&& .AVIATION /20Z TUESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. REST OF THIS AFTERNOON...VFR CEILINGS /6000-10000 FEET/ WILL SCATTER OUT FROM NORTH TO SOUTH INTO THE EVENING. THE WINDS WILL BE MAINLY LIGHT AND VARIABLE. TONIGHT...VFR WITH ANY LINGERING CLOUDS EARLY DISSIPATING SOUTHWARD. LIGHT AND VARIABLE TO LOCALLY CALM WINDS. WEDNESDAY...VFR WITH INCREASING CLOUDS. A DEVELOPING CEILING MAY LOWER TO MVFR MAINLY LATE IN THE AFTERNOON ESPECIALLY NORTH AND WEST OF KPHL. SOME SHOWERS SHOULD DEVELOP DURING THE AFTERNOON MOSTLY WEST OF KPHL. THE CHANCE AS OF NOW IS LOW ENOUGH, AND THEREFORE A MENTION WAS NOT INCLUDED IN THE TAFS AT KRDG AND KABE. SOUTHEASTERLY WINDS GENERALLY 5-10 KNOTS. OUTLOOK... WEDNESDAY NIGHT INTO THURSDAY MORNING...IFR CONDITIONS WITH LOW CLOUDS, FOG AND A CHANCE OF RAIN/DRIZZLE. LOW LEVEL WIND SHEAR IS POSSIBLE ON THURSDAY MORNING TO MIDDAY DUE TO THE POSSIBLE PRESENCE OF A LOW LEVEL SOUTHWESTERLY JET OVERHEAD. THURSDAY AFTERNOON INTO THURSDAY NIGHT...MAINLY VFR WITH OCCASIONAL MVFR AND IFR CONDITIONS IN SHOWERS AND SCATTERED THUNDERSTORMS. FRIDAY...VFR CONDITIONS WITH NORTHWEST WINDS. SATURDAY AND SUNDAY...VFR CONDITIONS.
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&& .MARINE...
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HIGH PRESSURE EXTENDS ACROSS OUR AREA FROM THE EASTERN GREAT LAKES INTO TONIGHT. THIS HIGH WILL THEN SHIFT OFF THE COASTS OF NEW ENGLAND AND THE MID ATLANTIC WEDNESDAY MORNING, RESULTING IN A SOUTHEASTERLY FLOW TO BECOME MORE ESTABLISHED. THE FLOW WILL INCREASE SOME DURING THE COURSE OF WEDNESDAY, HOWEVER THE WINDS AND AND SEAS ARE EXPECTED TO REMAIN WELL BELOW SMALL CRAFT ADVISORY CRITERIA. OUTLOOK... WEDNESDAY NIGHT...SUB-ADVISORY CONDITIONS ARE EXPECTED. THURSDAY AND FRIDAY...SCA CONDITIONS ARE EXPECTED TO DEVELOP DURING THURSDAY MORNING AND LAST INTO EARLY FRIDAY WITH THE APPROACH AND PASSAGE OF A COLD FRONT. WIND GUSTS WILL REACH INTO THE 25 TO 30 KNOT RANGE, WITH A WIND SHIFT FROM SOUTHWEST TO NORTHWEST OCCURRING AS THE COLD FRONT PASSES OVER THE WATERS LATE THURSDAY NIGHT. IN ADDITION, SEAS WILL STEADILY BUILD INTO THE 5 TO 8 FOOT RANGE FOR THE COASTAL WATERS DURING THURSDAY AND THURSDAY NIGHT, BEFORE SUBSIDING EARLY FRIDAY. SATURDAY AND SUNDAY...MAINLY SUB-SCA CONDITIONS ARE EXPECTED. SOME NORTHWEST WIND GUSTS AROUND 20 KNOTS PLUS ARE POSSIBLE FOR THE COASTAL WATERS SATURDAY.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...KLINE NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...KLINE AVIATION...GORSE/IOVINO/KLINE MARINE...GORSE/KLINE

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