Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 311022 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 622 AM EDT FRI OCT 31 2014 .SYNOPSIS... LOW PRESSURE OVER THE GREAT LAKES REGION WILL DIG SOUTHEAST THROUGH THE DAY TODAY, EVENTUALLY MERGING WITH AN OFF SHORE LOW TOMORROW. THAT STORM MOVES TO THE MARITIMES SUNDAY. HIGH PRESSURE SETTLES INTO THE CAROLINAS EARLY NEXT WEEK THEN SLIPS EASTWARD INTO THE CENTRAL ATLANTIC NEXT WEDNESDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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AN OVERALL QUIET DAY TODAY BEFORE CONDITIONS DETERIORATE. AN AREA OF LOW PRESSURE OVER THE EASTERN GREAT LAKES REGION THIS MORNING WILL MOVE SOUTHWARD THROUGH THE DAY, WHILE ANOTHER AREA OF LOW PRESSURE WILL CONTINUE TO STRENGTHEN OFF THE CAROLINA COASTS. OUR AREA WILL BE BETWEEN THE TWO SYSTEMS, SO WE DO NOT EXPECT ANY PRECIPITATION THROUGH THE DAY ALTHOUGH AN INCREASE IN CLOUD COVER IS EXPECTED. THERE WILL BE SOME SUN TO START THE DAY FOR MANY AREAS AS IT IS MOSTLY CLEAR FOR A PORTION OF THE AREA THIS MORNING, BUT WE EXPECT CLOUDS TO SPREAD ACROSS THE AREA THROUGH THE MORNING AND INTO THE AFTERNOON. TEMPERATURES WILL WARM THROUGH MIDDAY, THEN AS CLOUDS CONTINUE TO DEVELOP AND SPREAD ACROSS THE AREA BY THE AFTERNOON, TEMPERATURES SHOULD LEVEL OFF. HIGHS WERE A BLEND OF MAV/MET MOS AND BLENDED ECMWF 925MB TEMPS.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... THE LOW MOVING OUT OF THE GREAT LAKES REGION WILL WEAKEN AND COMBINE WITH YET ANOTHER LOW SOUTH OF OUR AREA TONIGHT, WHILE THE INITIAL COASTAL LOW STRENGTHENS AND BEGINS MOVING NORTHWARD. AS THIS LOW BEGINS DRIFTING NORTHWARD, SEVERAL VORTICITY IMPULSES ALOFT AND PLENTY OF LOW LEVEL MOISTURE WILL LIFT NORTHWARD AND SWING ACROSS OUR AREA. THIS WILL LEAD TO RAINFALL DEVELOPING TO OUR SOUTH AND EAST OVERNIGHT THAT SHOULD SWING ACROSS OUR AREA, GENERALLY AROUND OR AFTER MIDNIGHT. && .LONG TERM /SATURDAY THROUGH THURSDAY/... BY SATURDAY THE SURFACE LOW (BY THIS POINT THE CONTENTION LOW AND OFF SHORE LOW HAVE MERGED) BEGINS TO LIFT NORTHEAST, AS THE CUTOFF UPPER LEVEL LOW CONTINUES TO TRUDGE EASTWARD. THE MAIN IMPACTS WE`LL BE WATCHING WITH THIS SYSTEM WILL BE PRECIP, TEMPS, COASTAL FLOODING (SEE SECTION BELOW) AND WINDS: WINDS WILL LIKELY BE THE MAIN STORY BOTH ON LAND AND MARINE. THE MARINE CONCERNS ARE DESCRIBED BELOW. AS FOR WIND ON LAND, CONTINUE TO BE CONCERNED ABOUT THE POTENTIAL FOR NEAR WIND ADVISORY CONDITIONS ESPECIALLY NEARER THE COAST. HOWEVER, THERE ARE A FEW THINGS LIMITING THE WIND. FIRST, THE TIGHTEST SURFACE PRESSURE GRADIENT AND GREATEST MID LEVEL HEIGHT GRADIENT ARE NOT JUXTAPOSED EITHER TEMPORALLY OR GEOGRAPHICALLY. THE TIGHTEST PRESSURE GRADIENT WILL LIKELY BE OVER THE EASTERN HALF OF THE REGION SATURDAY NIGHT INTO EARLY SUNDAY, HOWEVER AT THIS TIME THE MID AND UPPER LEVEL TROUGH AXIS SHOULD BE BISECTING THE REGION. ALSO A MID LEVEL INVERSION WILL LIMIT MIXING. INSTEAD, THE STRONGEST WINDS LIKELY SUNDAY AFTERNOON INTO EARLY SUNDAY EVENING WHEN THE TIGHTEST MID AND UPPER LEVEL HEIGHT GRADIENT WILL BE OVER THE REGION. ALSO, 6 HR PRESSURE RISES THROUGH THIS PERIOD ARE FORECAST TO BE BETWEEN 2 AND 6 MB, WHILE NOT NEARLY AS IMPRESSIVE AS THE 10MB PLUS PRESSURE RISES WELL OFF THE COAST THAT THE MODELS SHOW, IT COULD BE ENOUGH FOR A SMALL COMPONENT OF AN ISALLOBARIC WIND. HAVING SAID ALL THAT HOWEVER, BASED ON LOCAL HIGH WIND GUIDANCE WE STILL APPEAR TO BE ON THE LOWER END OF A WIND ADVISORY THREAT EVEN ALONG THE COAST. THEREFORE, WILL JUST KEEP MENTION IN THE HWO AT THIS TIME. TEMPS...IN THE WAKE OF THE COLD FRONT ON SATURDAY, TEMPERATURES BY SUNDAY SHOULD BE 10 TO 15 DEGREES BELOW NORMAL. THE COLDEST WEATHER IS EXPECTED SUNDAY NIGHT WITH DECREASING WINDS AND CLEARING SKIES. STILL EXPECTING THE VAST MAJORITY OF THE REGION TO BE NEAR OR BELOW FREEZING SUNDAY NIGHT. HOWEVER, AS MENTIONED BY THE PREVIOUS SHIFT, THE FALL FROST/FREEZE PROGRAM ENDS NOV. 1 AS WE ARE PAST THE MEAN FIRST FREEZE DATE. PRECIP...MODELS ARE IN MUCH BETTER AGREEMENT OF THE TIMING OF THE PRECIP, WHICH WILL MAINLY BE DURING THE DAY SATURDAY, WITH SOME LINGERING INTO SATURDAY NIGHT. THROUGH THIS PERIOD, ALL OF THE REGION IS EXPECTED TO BE WELL ABOVE FREEZING, SO PRECIP TYPE IS EXPECTED TO BE RAIN. FROM THE MODEL SOUNDINGS, THE MELTING LAYER THROUGH THIS PERIOD IS FORECAST TO BE AT OR ABOVE 4000 FT AGL. WITH SUCH A DEEP WARM LAYER, EVEN FLURRIES ARE VERY UNLIKELY. MONDAY AND TUESDAY...SURFACE HIGH BUILDS NORTHEAST AS THE UPPER LEVEL RIDGE SLIDES OVER THE REGION. STILL EXPECT A WARMING TREND THROUGH THIS PERIOD DUE TO BOTH AIR MASS MODIFICATION AND INCREASING THICKNESSES. HOWEVER, INTERESTINGLY, THE GFS IS NOW SHOWING A MUCH MORE DRAMATIC WARMING TREND THROUGH THIS PERIOD AS COMPARED TO YESTERDAYS RUNS, WITH HIGHS IN THE UPPER 60S POSSIBLE BY TUESDAY. WEDNESDAY THROUGH FRIDAY...STILL CONSIDERABLE UNCERTAINTY IF THE COLD FRONT THAT WILL APPROACH FROM THE WEST WILL STALL WEST OF THE REGION UNTIL LATE THURSDAY WHEN AN UPPER LEVEL TROUGH DIGS SE TOWARD THE REGION. GIVEN THE UNCERTAINTY AND MODEL DIFFERENCES HAVE STAYED CLOSE TO THE PREVIOUS FORECAST. && .AVIATION /10Z FRIDAY THROUGH TUESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDITIONS ARE EXPECTED DURING THE DAY, ALTHOUGH CLOUDS WILL INCREASE THROUGH THE DAY IN BETWEEN TWO LOW PRESSURE SYSTEMS, ONE TO OUR WEST AND ONE TO OUR SOUTH. CLOUDS CONTINUE TO INCREASE AND LOWER THROUGH THE EVENING AND OVERNIGHT TONIGHT AND MVFR CIGS ARE EXPECTED TO SPREAD TO ALL TAF SITES DURING THE OVERNIGHT, WITH THE POSSIBILITY FOR SOME IFR, ESPECIALLY CLOSER TO THE COAST. RAINFALL WILL ALSO BEGIN TO SPREAD FROM EAST TO WEST OVERNIGHT AND TOWARD DAYBREAK SATURDAY. MOSTLY LIGHT AND VARIABLE WINDS THIS MORNING ARE EXPECTED TO BECOME MORE NORTH TO NORTHEAST DURING THE DAY AND CONTINUE THROUGH THE PERIOD. WIND WILL BEGIN TO INCREASE OVERNIGHT AND TOWARD DAYBREAK SATURDAY, ALTHOUGH GUSTS ARE NOT EXPECTED TO OCCUR UNTIL AROUND OR AFTER AFTER DAYBREAK. OUTLOOK... SATURDAY...MVFR CEILINGS EXPECTED ACROSS THE REGION. LOCALIZED IFR CONDITIONS POSSIBLE ESPECIALLY CLOSER TO THE COAST INCLUDING KACY AND KMIV. BREEZY NORTHERLY WINDS THROUGH THE DAY. SATURDAY NIGHT INTO SUNDAY...CONDITIONS WILL SLOWLY IMPROVE FROM WEST TO EAST. BREEZY NORTHERLY AND NORTHWESTERLY WINDS EXPECTED ESPECIALLY NEAR THE COAST. MONDAY THROUGH TUESDAY...VFR CONDITIONS EXPECTED.
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&& .MARINE... SUB-SMALL CRAFT ADVISORY CONDITIONS WILL CONTINUE TODAY INTO MOST OF TONIGHT, BEFORE AN INCREASE IN WINDS AND SEAS TOWARD DAYBREAK. SMALL CRAFT ADVISORY LEVEL WINDS MAY BEGIN AROUND DAYBREAK SATURDAY, BUT SINCE WE`VE ISSUED A GALE WARNING IN THE SUBSEQUENT PERIODS, THE ADVISORY HAS BEEN REMOVED. OUTLOOK... SATURDAY THROUGH SUNDAY NIGHT...GALE CONDITIONS EXPECTED ON THE ATLANTIC WATERS AND LOWER DELAWARE BAY WITH PEAK GUSTS NEAR 45 KT. SEAS AS HIGH AS 10FT POSSIBLE ON THE ATLANTIC WATERS. ON THE UPPER DELAWARE BAY...SMALL CRAFT ADVISORY GUSTS EXPECTED PRIMARILY SATURDAY NIGHT INTO SUNDAY. MONDAY...CONDITIONS SHOULD FALL BELOW SCA CRITERIA BY MONDAY AFTERNOON. TUESDAY...WINDS AND SEAS ARE EXPECTED TO BE BELOW SCA CRITERIA. && .TIDES/COASTAL FLOODING... AN ONSHORE COMPONENT OF THE BREEZY TO WINDY CONDITIONS ON SATURDAY WILL LEAD TO ELEVATED WATER LEVELS THIS WEEKEND. MINOR TIDAL FLOODING MAY OCCUR WITH THE HIGH TIDE CYCLE ON SATURDAY. IT IS POSSIBLE BUT VERY UNLIKELY TO ALSO OCCUR WITH THE HIGH TIDE CYCLE ON SATURDAY NIGHT. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...GALE WARNING FROM 2 PM EDT SATURDAY TO 5 AM EST SUNDAY FOR ANZ431-450>455. && $$ SYNOPSIS...JOHNSON NEAR TERM...ROBERTSON SHORT TERM...ROBERTSON LONG TERM...JOHNSON AVIATION...JOHNSON/ROBERTSON MARINE...JOHNSON/ROBERTSON TIDES/COASTAL FLOODING...

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