Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 211051 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 651 AM EDT TUE OCT 21 2014 .SYNOPSIS... LOW PRESSURE OVER LAKE ONTARIO WILL SLIDE SOUTHEAST TO THE NEW JERSEY COAST THIS EVENING. IT SLOWLY INTENSIFIES WEDNESDAY AND PASSES SOUTHEAST OF CAPE COD THURSDAY NIGHT. HIGH PRESSURE OVER THE OHIO VALLEY LATE IN THE WEEK WILL AWAIT THE PASSAGE OF A COLD FRONT SATURDAY NIGHT THEN BUILD OVER THE MID ATLANTIC STATES SUNDAY AND MONDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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AN UPPER-LEVEL TROUGH WILL CONTINUE TO AMPLIFY INTO THE NORTHEAST THROUGH TODAY. AN INITIAL STRONG AND COMPACT SHORT WAVE CARVING OUT THE TROUGH CONTINUES TO WORK ITS WAY ACROSS PENNSYLVANIA EARLY THIS MORNING. THIS FEATURE IS WELL EVIDENT ON THE WATER VAPOR IMAGERY AS IT LIFTS EAST-NORTHEASTWARD, AND APPEARS TO BE STRONGER THAN EARLIER GUIDANCE INDICATED. AS A RESULT, THE DOWNSTREAM WAA AND LOWER LEVEL CONVERGENCE/LIFT HAS BEEN STRONG ENOUGH TO DEVELOP AND ORGANIZE SOME SHOWERS, WHICH ARE NOW LIFTING TO OUR NORTH OVERALL. A STRONGER MID/UPPER LEVEL JET DIVING DOWN THE WEST SIDE OF THE TROUGH WILL PUSH STRONGER SHORT WAVE ENERGY ALONG. THIS WILL ASSIST IN CUTTING OFF THE TROUGH FROM THE MAIN FLOW, THEREFORE THIS UPPER-LEVEL TROUGH WILL BE CLOSING OFF DURING THE COURSE OF THE DAY. THIS WILL ALSO TAKE LOW PRESSURE NEAR THE EASTERN GREAT LAKES EARLY THIS MORNING, AND THEN MOVE IT OVER OUR AREA BEFORE IT STARTS TO EVENTUALLY CONSOLIDATE OFFSHORE. THE MAIN FORECAST CHALLENGE IS THE TIMING AND COVERAGE OF THE ASSOCIATED SHOWERS. AFTER SOME INITIAL SHOWERS EARLY THIS MORNING MAINLY ACROSS THE WESTERN ZONES, THERE SHOULD BE A BREAK BEFORE ADDITIONAL SHOWERS DEVELOP ESPECIALLY LATER THIS AFTERNOON AS ANOTHER STRONG SHORT WAVE ROUNDS THE BASE OF THE TROUGH. THE SOUNDINGS SHOW SOME INSTABILITY DEVELOPING, BUT THIS IS MOSTLY CONFINED TO THE LOWEST LEVELS WITH PERHAPS AN ISOLATED LOW-TOPPED STORM. GIVEN LESS CERTAINTY, WE HELD OFF ON ADDING A THUNDER MENTION ATTM. WE CONTINUED SLIGHT CHC TO CHC POPS FOR ISOLATED/SCATTERED SHOWERS THROUGH THE DAY, ALTHOUGH A TIME OF LIKELY POPS ACROSS THE WESTERN AREAS CLOSER TO THE INCOMING TROUGH. THE AIRMASS IS MODERATING AHEAD OF THE MAIN UPPER-LEVEL TROUGH AND THE ASSOCIATED WAA WILL YIELD WARMER AFTERNOON TEMPERATURES. THERE MAY BE A SQUEEZE PLAY THOUGH AS THE WARMEST AIR MAY SLIDE UP ACROSS OUR DELMARVA AND EASTERN ZONES. THEREFORE, A BLEND OF THE NAM/GFS MOS RESULTED IN THE WARMEST HIGH TEMPERATURES IN THESE AREAS. OTHERWISE, THE FLOW SHOULD START TO SHIFT AROUND FROM THE SOUTHWEST TO THE NORTHWEST DURING THE COURSE OF THE DAY AS LOW PRESSURE DEVELOPS OVER OUR AREA BEFORE CONSOLIDATING SOME JUST TO OUR EAST TOWARD EVENING.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... A CLOSED LOW WILL STRENGTHEN ACROSS THE MID ATLANTIC AND NORTHEAST THROUGH TONIGHT. AS THIS OCCURS, SURFACE LOW PRESSURE SHOULD CONSOLIDATE SOME MORE OFF OF OUR COAST. THE MODEL GUIDANCE OVERALL SHOWS A SIGNIFICANT SHORT WAVE ROUNDING THE BASE OF THE CLOSED LOW OVERNIGHT. THIS FEATURE LOOKS TO NEAR OUR SOUTHEASTERN ZONES TOWARD DAYBREAK. AS THIS OCCURS, LARGE SCALE LIFT IN CONJUNCTION WITH SOME POTENTIAL FRONTOGENETIC FORCING ON THE WEST SIDE OF THE SURFACE LOW SHOULD ORGANIZE AND AREA OF RAIN. THIS LOOKS TO GENERALLY BE ACROSS THE EASTERN HALF OF THE CWA. AS A RESULT, LIKELY POPS ARE CARRIED ACROSS MUCH OF THE CWA ESPECIALLY LATE WITH THE SLIGHTLY HIGHER VALUES ACROSS THE EASTERN ZONES. WHILE ISOLATED THUNDER CANNOT BE RULED OUT ESPECIALLY ACROSS THE EASTERN AREAS AS AT LEAST SOME MID LEVEL INSTABILITY COULD BE PRESENT, THE CHC APPEARS TO BE RATHER LOW AND THEREFORE IT WAS NOT CARRIED ATTM. THE POTENTIALLY DEVELOPING RAIN AREA HAS THE SIGNATURE OF WHAT COULD BE THE START OF A PIVOT REGION ACROSS AT LEAST A PORTION OF OUR AREA STARTING NEAR DAYBREAK. THIS WOULD BE DUE TO THE CLOSED LOW MOVING OVERHEAD AND THE STRONG SHORT WAVE PIVOTING UP FROM THE SOUTHWEST AS THE SURFACE LOW ORGANIZES SOME MORE OFFSHORE. AS FOR LOW TEMPERATURES, WE UTILIZED MAINLY AN EVEN NAM/GFS MOS BLEND. WHILE THE WINDS SHOULD BE LIGHT FOR MOST, A NORTHERLY WIND SHOULD START TO INCREASE SOME MAINLY LATE AS THE SYSTEM AS A WHOLE STARTS TO BECOME BETTER ORGANIZED TO OUR EAST. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... 500 MB: A LARGE AND VERTICALLY DEEP CLOSED LOW ALONG THE MID ATLANTIC COAST TO START THE PERIOD WILL SLIDE TO THE EAST OF NEW ENGLAND FRIDAY. A POTENTIALLY STRONG SHORT WAVE IS SLATED TO MOVE FROM SOUTH CENTRAL CANADA SATURDAY THROUGH SOUTHEAST CANADA SUNDAY THEN TO BE FOLLOWED BY TEMPORARY RIDGING NEXT MONDAY. TEMPERATURES: CALENDAR DAY AVG TEMPS FOR OCTOBER WERE ABOUT 2 DEGREES ABOVE NORMAL THROUGH THE 20TH AND DIFFICULT TO BELIEVE THIS MONTH CAN NOW AVERAGE NORMAL OR BELOW. DAILY AVERAGES WILL B A LITTLE ABOVE NORMAL THROUGH FRIDAY WITH MINIMUM TEMPS SIGNIFICANTLY ABOVE NORMAL AND MAXIMUMS NEAR OR SLIGHTLY BELOW NORMAL. ABOVE NORMAL TEMPS CONTINUE SATURDAY WITH A POSSIBLE BRIEF COOLING TO NEAR NORMAL SUNDAY BEFORE WARMING WELL ABOVE NORMAL EARLY NEXT WEEK. FORECAST BASIS: UNLESS OTHERWISE NOTED THE LONG TERM PERIOD OF THIS FORECAST IS GENERALLY BASED ON A 50 50 BLEND OF THE 00Z/21 NAM/GFS MOS FOR THE PERIOD WEDNESDAY-THURSDAY...THE 00Z/21 GFS MOS THURSDAY NIGHT AND FRIDAY...THEN THEREAFTER (FRIDAY NIGHT ONWARD) THE 0502Z/21 WPC GRIDDED GUIDANCE. THE 00Z/21 NCEP GUIDANCE MAXIMUM TEMPS MAY BE SIGNIFICANTLY TOO WARM WEDNESDAY, THURSDAY AND NEXT SUNDAY. THE WED/THU 00Z/21 NCEP MOS GUIDANCE WAS BLENDED DOWN WITH THE 00Z/21 ECMWF TEMPS. WEDNESDAY AND THURSDAY COULD BE EVEN COOLER THAN THE 330 AM FCST ISSUANCE INDICATED. PRECIPITATION PROBABILITY GUIDANCE IS CHECKED AGAINST THE 21Z/20 SREF 3HRLY POPS FOR .01 THROUGH 12Z FRIDAY AND THEREAFTER THE 00Z/21 GEFS 6HR POPS FOR 0.05. THE DAILIES BELOW... WED-THU...PERIODS OF SHOWERS IN THE DEEP CYCLONIC FLOW WITH UNSTABLE MID LVLS..EVEN SMALL POTENTIAL OF THUNDER NNJ WHERE SWI IS SUB ZERO AT TIMES. A TROWAL CURLS WESTWARD AROUND THE NORTHWEST SIDE OF THE DEEP CYCLONIC CIRCULATION. RAIN SHOULD BE HEAVY AT TIMES WEDNESDAY ALONG THE COAST AND THEN POSSIBLY THURSDAY IN NNJ NEAR THE AXIS OF THE 850 MB WIND SHIFT (850 MB VORTICITY AXIS) FROM NE TO NW AND COINCIDENT WITH THE TROWAL. CONFIDENCE: ABOVE AVERAGE. THU NIGHT-FRIDAY...AS THE LOW ALOFT MOVES AWAY TO OUR NORTHEAST THE POTENTIAL FOR RAIN SHOWERS SHOULD GRADUALLY DIMINISH IN OUR AREA. CLOUD COVER WILL STILL BE PREDOMINANT. CONFIDENCE: AVERAGE SINCE TIMING OF THE IMPROVEMENT IS UNCERTAIN. THIS WEEKEND...A SHORT WAVE WITH A 12 HR HFC OF OVER 120 METERS PASSES THRU NYS AND NEW ENGLAND SAT AND SAT NIGHT. 850 TEMPS IN ITS WAKE COOL 6C ON THE ECMWF FOR NEXT SUNDAY. THE SHORT WAVE IS NOT EXPECTED TO HAVE MUCH MOISTURE ASSOCIATED WITH IT. THEREFORE, WE ARE NOT ANTICIPATING ANY RAIN. CONFIDENCE: AVERAGE...JUST A MATTER OF INTENSITY OF THE SHORT WAVE DIVING SEWD TOWARD THE NE USA SAT EVENING AND THE RESULTANT COOLER 850MB TEMPERATURES ON SUNDAY. NEXT MONDAY...A MID LEVEL RIDGE FROM THE WEST SHOULD BUILD TOWARD OUR REGION WHEN THE NICEST WEATHER OF THIS 6 DAY EXTENDED PERIOD SHOULD OCCUR. CONFIDENCE: AVERAGE FOR A DAY 7 FORECAST. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...MOSTLY VFR. SOME SHOWERS WILL BE AROUND THE AREA AS LOW PRESSURE DEVELOPS OVERHEAD BEFORE STARTING TO CONSOLIDATE SOME JUST TO OUR EAST TOWARD EVENING. WHILE MVFR CONDITIONS CAN OCCUR FOR A TIME WITH SHOWERS, THERE IS SOME LOWER CONFIDENCE ON THE TIMING AND AREAL COVERAGE. THERE IS THE POTENTIAL FOR A LOW-TOPPED THUNDERSTORM TO DEVELOP THIS AFTERNOON, HOWEVER THIS LOOKS TO BE ISOLATED IF IT WERE TO DEVELOP. A SOUTH-SOUTHWEST WIND WILL SHIFT TO THE WEST AND NORTHWEST DURING THE COURSE OF THE DAY, HOWEVER SPEEDS ARE EXPECTED TO BE AROUND 5 KNOTS. TONIGHT...VFR CEILINGS OVERALL. THERE IS THE POTENTIAL FOR MVFR VISIBILITIES AT TIMES WITH SOME SHOWERS. A MORE ORGANIZED AREA OF RAIN SHOULD DEVELOP ESPECIALLY LATE, WHERE SOME MVFR CEILINGS SHOULD START TO DEVELOP. LOWER CONFIDENCE ON THE MVFR CEILINGS. THE WINDS ARE ANTICIPATED TO BECOME NORTH TO NORTHEAST NEAR 5 KNOTS, BUT INCREASE SOME TOWARD DAYBREAK. OUTLOOK... WEDNESDAY THROUGH THURSDAY...CONDITIONS VARYING BETWEEN VFR CIGS AND MVFR CONDITIONS IN PERIODS OF SHOWERY RAINS. POTENTIAL BRIEF IFR CONDITIONS KABE...KTTN AND KACY. NORTH NORTHWEST WIND GUSTS 20 KT WEDNESDAY AND 25 TO 30 KT THURSDAY. CONFIDENCE: ABOVE AVERAGE. THURSDAY NIGHT AND FRIDAY...MAINLY VFR CIGS WITH A CHANCE OF SHOWERS. NORTHWEST WIND GUSTS 20-25 KT. CONFIDENCE: ABOVE AVERAGE. SATURDAY...VFR SCT-BKN AOA 5000 FT. NORTHWEST WIND GUSTS 15 TO 20 KT. CONFIDENCE: ABOVE AVERAGE.
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&& .MARINE... TODAY AND TONIGHT...LOW PRESSURE DEVELOPING OVERHEAD WILL START TO CONSOLIDATE SOME OFFSHORE TONIGHT. THIS WILL RESULT A SOUTHWESTERLY WIND TURNING TO THE WEST AND NORTHWEST TODAY THEN NORTH-NORTHEAST DURING TONIGHT. GIVEN THE NEARBY LOCATION OF THE ORGANIZING SURFACE LOW, THE FLOW IS FORECAST TO BE ON THE LIGHTER SIDE. AFTER SOME SURGE IN THE SEAS OFFSHORE EARLIER, THE SEAS ARE EXPECTED TO BE BELOW ADVISORY CRITERIA THROUGH TONIGHT. THE NORTHERLY WINDS MAY START TO INCREASE THOUGH TOWARD DAYBREAK WEDNESDAY. OUTLOOK... MIDWEEK...A GALE WATCH WAS ISSUED FOR MOST OF OUR WATERS...FOR OCNL GUSTS AROUND 35 KT WEDNESDAY AFTN POSSIBLY INTO MIDDAY THURSDAY. ONLY THE UPPER PART OF DELAWARE BAY IS WITHOUT A GALE WATCH AND THERE WE ISSUED AN SCA. FUTURE FORECASTS WILL DETERMINE WHETHER THE GALE WATCH IS A BIT TOO ROBUST AND WE`LL NEED TO SETTLE FOR A STRONG SCA. FOR NOW...BE PREPARED FOR THE POSSIBILITY OF GALES. AT THIS TIME...AM 60 PERCENT CONFIDENT THAT AT LEAST THE S NJ AND DE COASTAL WATERS WILL VERIFY A GALE BY THURSDAY. CONFIDENCE: A BIT ABOVE AVERAGE. THURSDAY NIGHT THROUGH FRIDAY NIGHT...NORTHWESTERLY WIND GUSTS OF 25 TO 30 KNOTS AT TIMES. SCA LIKELY. CONFIDENCE: ABOVE AVERAGE SATURDAY...NO MARINE HEADLINES ARE ANTICIPATED. NORTHWEST WIND GUSTS 15-20 KT. CONFIDENCE: ABOVE AVERAGE. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...GALE WATCH FROM WEDNESDAY AFTERNOON THROUGH LATE WEDNESDAY NIGHT FOR ANZ431-450>455. SMALL CRAFT ADVISORY FROM NOON WEDNESDAY TO 6 AM EDT THURSDAY FOR ANZ430. && $$ SYNOPSIS...DRAG NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...DRAG AVIATION...DRAG/GORSE MARINE...DRAG/GORSE

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