Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 242306 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 706 PM EDT THU APR 24 2014 .SYNOPSIS... A NARROW AREA OF HIGH PRESSURE WILL SLIDE ACROSS OUR REGION THROUGH TONIGHT, THEN WEAKEN AND SHIFT OFFSHORE FRIDAY. LOW PRESSURE IS FORECAST TO TRACK ACROSS THE OHIO VALLEY AND MID ATLANTIC REGION FRIDAY INTO SATURDAY MORNING. HIGH PRESSURE WILL THEN FOLLOW FOR LATE SATURDAY INTO MONDAY. LOW PRESSURE, DEVELOPING OVER THE MIDDLE OF THE NATION MONDAY AND TUESDAY, WILL BE A SLOW MOVER AND IT SHOULD RESULT IN AN EXTENDED PERIOD OF UNSETTLED WEATHER FOR OUR REGION STARTING TUESDAY AND LASTING THROUGH THURSDAY. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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FOR TONIGHT...THE FCST AREA WILL COME UNDER THE INFLUENCE OF A SFC HIGH PRES RIDGE WHICH WILL EXTEND FROM HUDSON BAY SWD ACROSS THE MID-ATLANTIC REGION TO OFF THE SE US COAST. AS A RESULT THE GUSTY WINDS WILL DIMINISH BY SUNSET THIS EVENING AND THEN BECOME LIGHT AND VARIABLE OVERNIGHT. GENERALLY GOOD RADIATIONAL CONDS WILL ALLOW MIN TEMPS TO REACH NEAR OR BELOW FREEZING AT MANY PLACES N OF PHL AND POSSIBLY ALSO IN THE SRN NJ PINE BARRENS. A FREEZE WARNING HAS BEEN ISSUED FOR PARTS OF NJ AND ERN PA WHERE SUB-FREEZING TEMPS ARE EXPECTED. BECAUSE OF THE DRY AIR...LITTLE FROST IS EXPECTED EVEN IN COLDER AREAS. ALSO, AS THE UPPER RIDGE AXIS NOW OVER THE MIDWEST MOVE EAST...SOME HI LVL CLOUDINESS SHOULD BEGIN TO SPILL OVER AND MAY LIMIT COOLING OVER ERN PA.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... FOR FRIDAY...THE SFC RIDGE AXIS WILL BE OVER THE AREA IN THE MORNING BUT WILL MOVE OFFSHORE IN THE AFTN. WINDS WILL PICK UP FROM THE SE TO S BY MID DAY. HI AND MID LVL CLOUDS WILL BE INCREASING AHEAD OF AN UPPER SHRTWV TROF APPROACHING FROM THE OHIO VLY. EVEN SO SUNSHINE THROUGH THE CLOUDINESS AND LOW LVL WARM ADVECTION SHOULD RESULT IN MAX TEMPS A FEW DEGS WARMER THAN TODAY. NO PRECIP IS FCST FOR FRI MORN BUT BY AFTN POPS BEGIN TO INCREASE FROM WEST TO EAST ACROSS THE FCST AREA. SCT SHRA ARE EXPECTED BY LATE AFTN WEST OF PHL BUT ANY RAINFALL AMOUNTS SHOULD BE JUST A FEW HUNDREDTHS AT MOST. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... THE OVERALL SYNOPTIC SETUP IS COMPRISED OF AN INITIALLY PROGRESSIVE FLOW WITH A SHORT WAVE TROUGH SLIDING ACROSS THE AREA FRIDAY NIGHT AND SATURDAY. THE FLOW THEN LOOKS TO UNDERGO SIGNIFICANT AMPLIFICATION AS BLOCKING DEVELOPS. THIS ALLOWS FOR A CLOSED LOW TO DEVELOP SOUTHEAST OF NEW ENGLAND SUNDAY, WITH ANOTHER ONE EJECTING OUT INTO THE PLAINS. AN INITIAL SHARP/NARROW RIDGE BETWEEN THESE TWO SYSTEMS SHOULD GET KNOCKED DOWN AS ENERGY ROTATES ACROSS THE GREAT LAKES BEFORE BEING ABSORBED BY THE CLOSED SYSTEM FROM THE PLAINS. DUE TO BLOCKING DOWNSTREAM, A LARGE CLOSED LOW SHOULD RESULT DURING NEXT WEEK FROM THE GREAT LAKES TO THE TENNESSEE VALLEY. THIS PLACES OUR AREA ON THE EAST SIDE OF THE CLOSED LOW, WHICH IS TYPICALLY A FAVORABLE AREA FOR MOISTURE TO SURGE NORTHWARD. IF THIS PANS OUT LIKE THIS, A PERIOD OF UNSETTLED AND COOLER WEATHER WILL OCCUR ACROSS OUR AREA. WE USED A GENERAL MODEL BLEND FROM FRIDAY NIGHT INTO SUNDAY, THEN FAVORED WPC GUIDANCE THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE FOLLOWING ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES. FRIDAY NIGHT AND SATURDAY...A SHORT WAVE TROUGH IS FORECAST TO MOVE THROUGH DURING AT LEAST A PORTION OF THIS TIME FRAME. THE AXIS OF THE TROUGH LOOKS TO START TAKING ON A NEGATIVE TILT FOR A TIME BEFORE IT WEAKENS AND GIVES WAY TO INCREASING HEIGHT FALLS WITH THE CLOSED LOW NEAR THE UPPER GREAT LAKES. THIS WILL PROVIDE A RIBBON OF ENHANCED LIFT ACROSS THE AREA, WHICH SHOULD RESULT IN A DECENT AMOUNT OF SHOWERS DURING AT LEAST FRIDAY EVENING. THERE MAY BE ENOUGH INSTABILITY FRIDAY EVENING COMBINED WITH THE FORCING FOR SOME THUNDER ESPECIALLY ACROSS PORTIONS OF THE SOUTHERN ZONES. AS LOW PRESSURE SLIDES ACROSS THE AREA LATER FRIDAY EVENING THEN SHIFTS TO OUR NORTHEAST SATURDAY MORNING, THE SHOWERS ARE EXPECTED TO CLEAR OUR CWA. HOWEVER, THE MAIN UPPER-LEVEL TROUGH/CLOSED LOW IS THEN FORECAST TO DROP DOWN ACROSS THE NORTHEAST AND NORTHERN MID ATLANTIC REGION. THIS ALONG WITH COLDER AIR ALOFT AND A SECONDARY FRONTAL BOUNDARY SHOULD TRIGGER SOME ADDITIONAL SHOWERS. WHILE THERE COULD BE SOME INSTABILITY TO ALLOW FOR THUNDER, WE MAY HAVE JUST SOME LOW-TOPPED CONVECTIVE CELLS DURING SATURDAY AFTERNOON AND THUS NO THUNDER WAS ADDED FOR SATURDAY ATTM. WE WENT WITH LIKELY POPS FOR A PORTION OF FRIDAY NIGHT, THEN LOWERED TO THE CHC/SLIGHT CHC RANGE THROUGH SATURDAY. THE SHOWER THREAT SHOULD END VERY EARLY SATURDAY EVENING AS THE SYSTEM SHIFTS TO THE EAST AND THE AIR MASS STABILIZES. SUNDAY AND MONDAY...IT APPEARS THAT THIS TIME FRAME WILL FEATURE OUR AREA BEING BETWEEN WEATHER SYSTEMS. A CLOSED LOW TO OUR NORTHEAST IS FORECAST TO SHIFT FARTHER OUT TO SEA, HOWEVER THIS FEATURE MAY ALSO HELP IN THE MAIN FLOW BECOMING SLOWER. A NARROW AREA OF HIGH PRESSURE LOOKS TO WEDGE DOWN INTO THE MID ATLANTIC DURING SUNDAY INTO MONDAY. THE MAIN SURFACE HIGH IS FORECAST TO BE CENTERED WELL TO OUR NORTH AS A SYSTEM CLOSES OFF ACROSS THE CENTRAL PARTS OF THE NATION. AS DOWNSTREAM BLOCKING LOOKS TO GET GOING, THE SYSTEMS AS A WHOLE SHOULD MOVE RATHER SLOWLY EASTWARD. THIS WOULD INITIALLY PLACE OUR REGION WITHIN AN AREA OF GENERAL SUBSIDENCE, HOWEVER THE FLOW TURNING ONSHORE ESPECIALLY LATER MONDAY SHOULD ALLOW FOR MORE CLOUDS TO START DEVELOPING. THIS TIME FRAME IS DRY, WITH THE EXCEPTION OF SOME SLIGHT CHC TO LOW CHC POPS LATE MONDAY NIGHT AS THE ONSHORE FLOW BECOMES BETTER ESTABLISHED ALONG WITH THE DEVELOPMENT OF A WARM FRONT TO OUR SOUTH AND GRADUAL ISENTROPIC LIFT. TUESDAY THROUGH THURSDAY...A SIGNIFICANT CLOSED LOW DRIFTING EASTWARD FROM THE MID MISSISSIPPI VALLEY TUESDAY WILL SPELL AN UNSETTLED PERIOD OF WEATHER FOR OUR ENTIRE REGION. THIS WILL DRIVE A SURFACE LOW THAT WILL PROBABLY OCCLUDE INTO THE MID ATLANTIC LATER WEDNESDAY AND THURSDAY. THERE MAY BE A LINGERING SURFACE WEDGE OF HIGH PRESSURE DOWN INTO THE MID ATLANTIC INITIALLY, ALLOWING FOR A BETTER OVERRUNNING SURFACE TO BE PRESENT. THE INITIAL WAA AND ASSOCIATED ISENTROPIC LIFT COUPLED WITH MOISTURE ADVECTION SHOULD ALLOW FOR RAIN TO DEVELOP ESPECIALLY LATER TUESDAY. THIS LOOKS TO CONTINUE RIGHT THROUGH THURSDAY, HOWEVER THE RAIN MAY MOVE THROUGH IN STAGES AND BE HEAVY AT TIMES ESPECIALLY WHEN TIED TO THE ARRIVAL OF EMBEDDED SHORT WAVE ENERGY EJECTING AHEAD OF THE CLOSED LOW. THE INITIAL SURGE IN MOISTURE THOUGH MAY HAVE A TOUGHER TIME GETTING TO OUR NORTHERN ZONES FOR A TIME AS SOME DRIER AIR MAY HANG ON. WE THEREFORE WENT WITH HIGH CHC TO LIKELY POPS THROUGH MUCH OF THIS TIME FRAME. THE LOW-LEVEL FLOW LOOKS TO BE ONSHORE WHICH TENDS TO LIMIT OR SUBDUE THE INSTABILITY /ESPECIALLY SURFACE-BASED/, HOWEVER SOME ELEVATED INSTABILITY IS POSSIBLE WHICH COULD LEAD TO SOME EMBEDDED THUNDER. GIVEN IT BEING THIS FAR OUR IN TIME AND LOWER CONFIDENCE REGARDING THE THERMAL PROFILES AND THEREFORE ASSOCIATED INSTABILITY, THUNDER WAS NOT INCLUDED ATTM. && .AVIATION /23Z THURSDAY THROUGH TUESDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDS ARE EXPECTED FOR THE NEXT 24 HOURS OR SO. THE GUSTY NW WINDS WILL DIMINISH THIS EVENING AND BECOMING LIGHT AND VARIABLE OVERNIGHT AS A SFC HIGH PRES RIDGE MOVES OVERHEAD. LIGHT WINDS WILL CONTINUE TOMORROW MORNING BUT WILL START TO PICK UP FROM THE SE TO S BY MIDDAY. HIGH TO MID-LVL CLOUDS WILL BE INCREASING DURING THE DAY BUT CIGS WILL REMAIN WELL ABOVE MVFR LIMITS UNTIL LATE IN THE DAY. OUTLOOK... FRIDAY NIGHT AND SATURDAY...MVFR TO AT TIMES IFR WITH SHOWERS /SOME THUNDER CANNOT BE RULED OUT ESPECIALLY SOUTH OF KPHL FRIDAY EVENING/, THEN CONDITIONS IMPROVING TO VFR EARLY SATURDAY MORNING. SOME ADDITIONAL SHOWERS ARE ANTICIPATED FOR SATURDAY AFTERNOON. SOUTHERLY WINDS GENERALLY 5-10 KNOTS, BECOMING WEST AND NORTHWEST 10-15 KNOTS SATURDAY. SUNDAY AND MONDAY...OVERALL VFR. NORTHERLY WINDS 10-15 KNOTS SUNDAY, BECOMING LIGHT AND VARIABLE SUNDAY NIGHT AND MONDAY. CLOUDS INCREASE MONDAY NIGHT WITH A CHANCE OF SOME MVFR CEILINGS TOWARD DAYBREAK TUESDAY. TUESDAY...MVFR CEILINGS SHOULD DEVELOP WITH AN ONSHORE FLOW ESPECIALLY LATER IN THE DAY. SOME RAIN SHOULD OVERSPREAD THE AREA FROM SOUTH TO NORTH LATE IN THE DAY AND AT NIGHT WITH SUB-VFR CONDITIONS ANTICIPATED. && .MARINE... WINDS WILL CONTINUE TO DIMINISH AS LOW PRES WELL EAST OF NEW ENGLAND MOVES FARTHER OUT TO SEA AND THE PRES GRADIENT RELAXES. SEAS SHOULD ALSO SUBSIDE. THE SCA HAS BEEN DROPPED. WINDS SHOULD BE RATHER LIGHT OVERNIGHT AND FRIDAY MORNING BUT WILL BEGIN TO INCREASE FROM THE SE TO S DURG THE AFTN TMRW. OUTLOOK... FRIDAY NIGHT AND SATURDAY...SOUTHERLY WINDS AHEAD OF A COLD FRONT WILL SHIFT TO THE NORTHWEST LATER FRIDAY NIGHT AND SATURDAY. THE FLOW MAY BE STRONG ENOUGH TO ALLOW FOR ADVISORY LEVEL GUSTS TO OCCUR. THE SEAS WILL BUILD IN THE SOUTHERLY FLOW, HOWEVER THE SOUTHERLY DIRECTION IS NOT ANTICIPATED TO BE PROLONGED. THE CONDITIONS SHOULD THEN BE MAINLY SUB-ADVISORY SATURDAY NIGHT. SUNDAY AND MONDAY...GENERALLY SUB-ADVISORY NORTHWESTERLY FLOW SUNDAY, THEN WINDS DIMINISH AND START TO TURN ONSHORE MONDAY. TUESDAY...EASTERLY WINDS INCREASE, HOWEVER PROBABLY REMAINING BELOW ADVISORY CRITERIA. THE SEAS HOWEVER SHOULD BUILD TO NEAR 5 FEET DURING THIS TIME FRAME. && .FIRE WEATHER... THE RED FLAG WARNING REMAINS IN EFFECT THROUGH EARLY THIS EVENING, AS GUSTY WINDS CONTINUE ALONG WITH RATHER LOW RELATIVE HUMIDITY VALUES. THE FUELS HAVE DRIED OUT MORE TODAY AS WELL, AND SOME BRUSH FIRES HAVE BEEN REPORTED. RADAR SHOWED A LARGE SMOKE PLUME EARLIER FROM A FIRE IN OCEAN COUNTY. THE WINDS ARE EXPECTED TO DIMINISH THIS EVENING. FOR FRIDAY, THERE MAY BE AN ENHANCED RISK OF FIRE WEATHER /SPS ISSUANCE POSSIBLE/ ESPECIALLY FOR EASTERN PENNSYLVANIA AND NEW JERSEY, HOWEVER THE WINDS ARE ANTICIPATED TO BE MUCH LESS COMPARED TO THE LAST FEW DAYS. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...RED FLAG WARNING UNTIL 8 PM EDT THIS EVENING FOR PAZ054-055- 060>062-070-071-101>106. FREEZE WARNING FROM 2 AM TO 8 AM EDT FRIDAY FOR PAZ060>062-101- 103-105. NJ...RED FLAG WARNING UNTIL 8 PM EDT THIS EVENING FOR NJZ001- 007>010-012>027. FREEZE WARNING FROM 2 AM TO 8 AM EDT FRIDAY FOR NJZ001-007>010. DE...RED FLAG WARNING UNTIL 8 PM EDT THIS EVENING FOR DEZ001>004. MD...RED FLAG WARNING UNTIL 8 PM EDT THIS EVENING FOR MDZ008-012- 015-019-020. MARINE...NONE.
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&& $$ SYNOPSIS...GORSE NEAR TERM...AMC SHORT TERM...AMC LONG TERM...GORSE AVIATION...AMC/GORSE MARINE...AMC/GORSE FIRE WEATHER...GORSE

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