Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 181611 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1211 PM EDT THU SEP 18 2014 .SYNOPSIS... A WEAK FRONTAL BOUNDARY WILL MOVE THROUGH OUR AREA THIS AFTERNOON AND EVENING. HIGH PRESSURE WILL THEN BUILD IN TONIGHT INTO FRIDAY, BEFORE SHIFTING OFFSHORE FRIDAY NIGHT. A WARM FRONT WILL LIFT TO OUR NORTHWEST SATURDAY, THEN A COLD FRONT IS EXPECTED TO ARRIVE LATE SUNDAY INTO MONDAY. THIS FRONT WILL SETTLE TO OUR SOUTH AND EAST DURING MONDAY, THEN AN EXPANSIVE AREA OF HIGH PRESSURE IS SCHEDULED TO BUILD IN FOR TUESDAY AND WEDNESDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... WITH THE MIDDAY UPDATE, WE ADDED SOME ISOLATED SHOWERS TO THE FORECAST FOR THE NEXT COUPLE OF HOURS ACROSS PORTIONS OF FAR SOUTHEASTERN PENNSYLVANIA, FAR NORTHERN DELAWARE, AND CECIL COUNTY MARYLAND. LATEST RADAR IMAGERY SHOWS A SMALL AREA OF LIGHT SHOWERS AND SPRINKLES HOLDING TOGETHER AND SLOWLY MOVING EAST INTO THESE AREAS. IN ADDITION, HOURLY TEMPS AND DEWPOINTS WERE ALSO TWEAKED THROUGH THE AFTERNOON USING THE LAV/LAMP GUIDANCE TO ACCOUNT FOR LATEST OBSERVATIONS AND TRENDS. OTHERWISE, THE MID-ATLANTIC IS LOCATED TOWARD THE BASE OF AN UPPER TROUGH AS SEEN ON WATER VAPOR SATELLITE IMAGERY. THIS LARGE- SCALE TROUGH IS ASSOCIATED WITH AN UPPER LOW LOCATED JUST TO THE EAST OF HUDSON BAY. A COLD FRONT STRETCHING FROM THE GULF OF ST LAWRENCE SOUTHEASTWARD INTO UPSTATE NY WAS RATHER DIFFUSE ON THE 13Z SFC ANALYSIS. THE COLD FRONT WILL MOVE SOUTHWARD INTO THE MID- ATLANTIC REGION THIS AFTERNOON. 12Z IAD, APG AND OKX SOUNDINGS ALL OBSERVED A SHALLOW SATURATED LAYER BETWEEN 800-700 MB WITH MOISTURE TRAPPED BELOW THE MID-LEVEL SUBSIDENCE INVERSION. MODEST LIFT ASSOCIATED WITH A SHORTWAVE TROUGH HAS LEAD TO A BAND OF BKN-OVC STRATOCU OVER EASTERN PA, NORTHWEST NJ AND THE EASTERN MD SO FAR THIS MORNING. TRIED TO TIME EASTWARD PROGRESSION OF THE TROUGH AND ASSOCIATED STRATOCU IN HOURLY SKY GRIDS WITH THE MORNING UPDATE. LATEST RAP MODEL, WHICH HAD INITIALIZED WELL WITH CURRENT CLOUD COVER, HANGS ON TO THE MORNING CLOUD THE LONGEST INTO THE AFTERNOON OVER SOUTHEASTERN PA AND THE DELMARVA. FORECAST MAX TEMPS TODAY IN THE MID 70S ARE ONLY A COUPLE OF DEGREES BELOW CLIMO. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... THE MID-LEVEL TROF AXIS MOVES OFF THE COAST THIS EVENING. A SURFACE HIGH BEHIND THE COLD FRONT BEGINS TO BUILD IN ACROSS THE AREA. TEMPERATURES WILL SETTLE IN THE LOWER 40S ACROSS THE SOUTHERN POCONOS TO THE MID 50S ACROSS THE COASTAL PLAIN. THIS IS A FEW DEGREES BELOW NORMAL. COULD BE A BIT MORE CLOUDINESS ACROSS THE SOUTHERN ZONES, BUT NO PRECIPITATION IS EXPECTED. SOME PATCHY FOG IS POSSIBLE TOWARD MORNING. NORTHWEST WINDS ON THE LIGHTER SIDE WILL SHIFT OUT OF THE NORTH OR NORTHEAST BY THE FRIDAY SUNRISE. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... THE OVERALL SYNOPTIC SETUP IS COMPRISED OF THE FLOW BECOMING MORE ZONAL FRIDAY ACROSS THE NORTHERN HALF OF THE NATION. SOME RIDGE DEVELOPMENT THOUGH OUT WEST LOOKS TO ALLOW A SHORT WAVE TO DIVE INTO THE MIDWEST SATURDAY, WHICH RESULTS IN A TROUGH AMPLIFYING ACROSS THE GREAT LAKES AND NORTHEAST SUNDAY THROUGH MONDAY. THIS TROUGH MAY THEN START TO LIFT OUT LATE TUESDAY. IT APPEARS THE MAIN FRONTAL PASSAGE OCCURS SUNDAY NIGHT INTO MONDAY, THEN AN EXPANSIVE SURFACE HIGH IS SCHEDULED TO BUILD ACROSS THE REGION TUESDAY AND WEDNESDAY. WE USED A GENERAL MODEL BLEND FOR FRIDAY THROUGH SUNDAY, THEN BLENDED IN THE 00Z WPC GUIDANCE THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE AFTER ADDITIONAL COLLABORATION WITH OUR SURROUNDING OFFICES. FOR FRIDAY...STRONG SURFACE HIGH PRESSURE SHOULD BE SHIFTING OFF THE NEW ENGLAND COAST WITH OUR LOW-LEVEL FLOW TURNING EAST AND SOUTHEAST. THERE IS SOME MOISTURE FORECAST TO BE LINGERING WELL OFFSHORE ESPECIALLY TO OUR SOUTHEAST, AND THE ONSHORE FLOW INTO OUR AREA MAY RESULT IN SOME CLOUDINESS ESPECIALLY AT NIGHT. THE POTENTIAL COMPLICATION IS THAT THE LOW-LEVEL FLOW MAY ACTUALLY VEER TO MORE SOUTHEAST OR SOUTH THROUGH FRIDAY NIGHT, FOCUSING AN INCREASE IN MOISTURE NORTHWEST OF THE FALL LINE. IT IS HERE WHERE PERHAPS SOME STRATUS AND/OR FOG DEVELOPS AS THE LOW-LEVEL MOISTURE POOLS BENEATH AN INVERSION. AS OF NOW, NOT QUITE SURE HOW MUCH STRATUS DEVELOPS DUE TO SOME QUESTION ON HOW QUICK THE LOWER LEVELS MOISTEN UP. FOR NOW, WE INCREASED THE CLOUDS ESPECIALLY AT NIGHT A BIT MORE. THE COMBINATION OF A NEW AIRMASS AND THE ONSHORE FLOW SHOULD RESULT IN A COOL DAY ACROSS THE CWA, AND POTENTIALLY BREEZY ALONG THE COAST. FOR SATURDAY AND SUNDAY...HIGH PRESSURE BECOMES ELONGATED INTO THE MID ATLANTIC AS IT WEAKENS AND SHIFTS FARTHER OFFSHORE. THIS OCCURS AS SOME WAA GETS UNDERWAY AHEAD OF THE NEXT SYSTEM AND HEIGHTS RISE SOME. THIS SHOULD RESULT IN A NORTHBOUND WARM FRONT THAT MOSTLY SLIDES JUST TO OUR NORTHWEST, AND WARMER AIR ARRIVES ACROSS OUR CWA ESPECIALLY SUNDAY WITH A MORE SOUTHWESTERLY LOW-LEVEL FLOW. A SHORT WAVE DIVING ACROSS THE GREAT LAKES WILL DRIVE A SURFACE LOW EASTWARD. THE AMPLIFICATION OF THE UPPER-LEVEL TROUGH SHOULD TAKE THE MAIN SURFACE LOW WELL TO OUR NORTH THOUGH DURING SUNDAY. THE ASSOCIATED COLD FRONT HOWEVER WILL ARRIVE INTO OUR AREA LATE SUNDAY WITH SOME SHOWERS. A BAND OF SHOWERS MAY END UP WEAKENING WITH A SOUTHEASTERN EXTENT DUE TO MUCH OF THE LARGE SCALE LIFT PEELING AWAY TO THE NORTH. THE INSTABILITY LOOKS LOW THEREFORE WE CONTINUED WITH NO THUNDER MENTION ATTM. WE GENERALLY FAVORED A BLEND OF CONTINUITY AND WPC GUIDANCE, WHICH PAINTS SLIGHT CHC TO LOW CHC POPS ACROSS THE CWA MAINLY SUNDAY NIGHT. MEANWHILE, A LEAD SHORT WAVE NEAR THE CAROLINAS MAY ORGANIZE A SURFACE LOW ALONG AN OLD BAROCLINIC ZONE. THIS FEATURE SHOULD TRACK NORTHEAST AND HAVE NO REAL AFFECT ON OUR SENSIBLE WEATHER. FOR MONDAY AND TUESDAY...THE MAIN UPPER-LEVEL TROUGH MAY AMPLIFY SOME MORE ACROSS THE NORTHEAST AND MID ATLANTIC REGIONS MONDAY. BASED ON SOME RIDGING ENTERING THE PLAINS, AN EXPANSIVE SURFACE HIGH IS FORECAST TO BUILD ACROSS THE MIDWEST AND GREAT LAKES LATER MONDAY INTO TUESDAY, WITH THIS FEATURE ARRIVING INTO OUR AREA DURING TUESDAY. SOME GUIDANCE SHOWS SOME INSTABILITY TYPE SHOWERS OCCURRING JUST TO OUR NORTH TUESDAY AS ANOTHER SHORT WAVE ROTATES AROUND THE BASE OF THE UPPER-LEVEL TROUGH. REGARDING POPS, KEPT SOME SLIGHT CHC TO LOW CHC POPS ESPECIALLY MONDAY MORNING WITH THE DEPARTING COLD FRONT. WE CARRIED A DRY FORECAST FOR TUESDAY AS THE UPPER-LEVEL TROUGH MAY START TO LIFT OUT SOME WITH ANY FOCUS GENERALLY TO OUR NORTH. FOR WEDNESDAY...AS A RIDGE SLIDES ACROSS THE GREAT LAKES, A POTENTIALLY STRONG SURFACE HIGH BUILDS ACROSS THE NORTHEAST AND MID ATLANTIC REGIONS. IF THE CENTER OF THIS HIGH ENDS UP ACROSS NEW ENGLAND, THEN WE WILL HAVE AN ONSHORE FLOW ONCE AGAIN. AS OF NOW, LEANED MUCH CLOSER TO THE 00Z WPC GUIDANCE FOR ALL WEATHER ELEMENTS. && .AVIATION /16Z THURSDAY THROUGH MONDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS VFR TDA AND TNGT. STRATOCU BETWEEN 5-9 KFT PROGRESSES EASTWARD ACROSS THE TERMINALS TDA. NW WINDS UNDER 10 KT TODAY WILL VEER TO THE N THIS EVE AND NE BY EARLY FRI MRNG. OUTLOOK... FRIDAY...VFR THROUGH THE DAY, HOWEVER SOME LOW CLOUDS OR EVEN SOME FOG COULD DEVELOP OVERNIGHT WITHIN AN ONSHORE FLOW. OUR CONFIDENCE IS ON THE LOWER SIDE. SATURDAY AND SUNDAY...SOME LOW CLOUDS AND/OR SOME FOG TO START EACH DAY, OTHERWISE MOSTLY VFR. A COLD FRONT ARRIVES SUNDAY NIGHT WITH POSSIBLE SHOWERS AND LOCAL SUB-VFR CONDITIONS. MONDAY...SOME SHOWERS POSSIBLE ESPECIALLY IN THE MORNING, OTHERWISE MOSTLY VFR WITH A WIND SHIFT TO THE NORTHWEST. && .MARINE... BUOY 44065 CAME BACK ON LINE ABOUT 10 PM LAST NIGHT. HOPEFULLY BUOY 44025 WILL NOT BE FAR BEHIND. TODAY...LONG PERIOD SWELLS GENERATED BY EDOUARD CONTINUE TO REACH THE EAST COAST TODAY. LATEST OBS SHOW 13-14 SEC WAVE PERIODS THIS MORNING. SEAS EXPECTED TO REMAIN JUST BELOW SCA LEVELS WIT WAVE HEIGHTS ARE 4 FT WHILE NORTHERLY WINDS WILL BE AROUND 10 KT (GUSTING TO 20 KT LATE IN THE DAY). TONIGHT...SWELLS ARE STILL FORECAST TO BE WITH US THROUGH TONIGHT. SEAS WILL BE LESS THAN 4 FEET. LIGHT NORTHERLY WINDS WILL INCREASE TO 20 KT OVERNIGHT ESPECIALLY ACROSS THE NORTHERN WATERS. OUTLOOK... FRIDAY...A NORTHEASTERLY WIND SURGE WITH AN INITIAL TIGHTENING OF THE PRESSURE GRADIENT AND CAA SHOULD THEN EASE SOME AS THE WINDS TURN EAST-SOUTHEAST BY LATE IN THE DAY AND AT NIGHT. THE SURGE COULD BE ENOUGH FOR SOME 25-KNOT GUSTS AND SEAS BUILDING TO 5 FEET ON THE COASTAL WATERS FOR A TIME. AS OF NOW THE WINDS AND SEAS ARE MARGINAL AND THEREFORE WILL HOLD OFF ON AN ADVISORY. SATURDAY AND SUNDAY...THE WINDS SHOULD TURN FROM THE SOUTH DURING THIS TIME FRAME AS HIGH PRESSURE DEPARTS TO THE EAST. THE NEXT COLD FRONT ARRIVES SUNDAY NIGHT, HOWEVER AN INCREASE IN THE WINDS SHOULD OCCUR AHEAD OF IT BUT THEY SHOULD BE BELOW ADVISORY CRITERIA. THE SEAS HOWEVER COULD BE RIGHT NEAR 5 FEET SATURDAY FROM THE EARLIER ONSHORE COMPONENT. MONDAY...THE CONDITIONS SHOULD BE BELOW ADVISORY CRITERIA OVERALL AS WINDS SHIFT FROM THE NORTH AS HIGH PRESSURE STARTS TO BUILD IN LATE. && .RIP CURRENTS... IN HOUSE GUIDANCE SUGGESTS A MODERATE RISK TODAY FOR NJ/DE BECAUSE OF LONG PERIOD SWELLS GENERATED BY EDOUARD. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GORSE NEAR TERM...KLEIN/KLINE SHORT TERM...KRUZDLO LONG TERM...GORSE AVIATION...GORSE/KLEIN/KRUZDLO MARINE...GORSE/KLEIN/KRUZDLO RIP CURRENTS...KRUZDLO/KLEIN

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