Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 312146 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 546 PM EDT SUN MAY 31 2015 .SYNOPSIS...
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A COLD FRONT HAS SETTLED SOUTH ACROSS ACROSS NORTHERN PENNSYLVANIA AND NORTHERN NEW JERSEY LATE TODAY WITH AREAS OF LOW PRESSURE IN SOUTHERN PENNSYLVANIA AND EASTERN OHIO. THIS COLD FRONT AND AREAS OF LOW PRESSURE WILL INCH ITS WAY SOUTHEASTWARD THROUGH THE REMAINDER OF OUR FORECAST AREA MONDAY AND TUESDAY. HIGH PRESSURE WILL BUILD SOUTHEASTWARD BEHIND FOR THE MIDDLE AND LATTER HALF OF NEXT WEEK. THIS HIGH WILL BE FOLLOWED BY ANOTHER COLD FRONT DROPPING SOUTHEAST INTO THE REGION BY NEXT WEEKEND.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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530 PM ESTF: A COLD FRONT HAS SETTLED SOUTH TO NEAR I-78 AND WILL PROBABLY BECOME NEARLY STATIONARY ABOUT 20 MILES SOUTH OF THIS POSITION LATE THIS EVENING. OVERRUNNING HEAVY SHOWERS AND TSTMS WERE OCCURRING NEAR AND NORTH OF THE FRONT AND THE FLOOD WATCH CONTINUES WITH PWAT NEAR 1.7 INCHES AND MODEL GUIDANCE SUGGESTING EXPANSION AND INTENSIFICATION OF RAINFALL BETWEEN NOW AND 10 PM. WE MAY NEED TO EXPAND THE WATCH SWD ONE TIER OF COUNTIES AT 630 PM. AS YET UNDECIDED. MEANWHILE CUT THE POPS THROUGH 04Z FROM NEAR KBLM TO KTTN AND KPHL SEWD TO THE COASTS WHERE AM NOT EXPECTING ANY SHOWERS AND STORMS BEFORE MIDNIGHT. AS FOR A SEVERE THUNDERSTORM THREAT, THE BEST BULK SHEAR IS TO OUR NORTH AND WEST, HOWEVER WITH PLENTY OF INSTABILITY INTO THIS EVENING ANY ROBUST CONVECTIVE CORES COULD PRODUCE A LOCAL DOWNBURST/DAMAGING WIND GUST IN COMBINATION WITH VERY HEAVY RAIN. THIS IS MAINLY FOR OUR WESTERN TO NORTHWESTERN ZONES. AS FOR THE LOW TEMPERATURES, WE MAINLY USED A NAM/GFS MOS BLEND. THE HOURLY TEMPERATURE AND DEW POINT GRIDS HAD THE LAMP/LAV GUIDANCE INCORPORATED INTO THEM. DID LOWER THE TEMPS SHARPLY N OF I-80 IN NNJ THIS EVENING IN OUTFLOWS AND BACKDOOR COLD FRONT.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
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...FLASH FLOOD WATCH MAY BE NEEDED FOR E PA AND MUCH OF THE NRN THIRDS OF NJ MONDAY... AS PER BELOW WE WILL NOT ISSUE TODAY TRAINING OF BANDS OF 1.8 INCH PWAT TSTORMS MONDAY AFTN/EVENING COULD BECOME A SERIOUS PROBLEM FOR URBAN AREAS THAT THEY TRAVERSE. CENTRAL A FRONTAL BOUNDARY SHOULD BE BISECTING OUR AREA FROM WEST TO EAST DURING THE COURSE OF THE DAY. THE FRONT IS NOT EXPECTED TO SAG ALL THE WAY TO THE SOUTH DUE TO ENOUGH RIDGING HOLDING ON COMBINED WITH A SLOW MOVING WEAK SURFACE LOW. AN UPPER-LEVEL TROUGH IS FORECAST TO UNDERGO SOME AMPLIFICATION ACROSS THE GREAT LAKES, AND THIS SHOULD TEND TO HOLD THE BOUNDARY AND WEAK SURFACE LOW IN OUR AREA THROUGH THE DAY. AS A RESULT, AT LEAST THE SOUTHERN HALF OF OUR AREA WILL BE WITHIN THE WARM SECTOR ALTHOUGH THE NORTHERN ZONES WILL BE MUCH COOLER WITH AN EASTERLY WIND. THIS MAY TEND TO HOLD IN LOWER CLOUDS THROUGH MUCH OF THE DAY, WITH MORE INSTABILITY FARTHER SOUTH. AS A RESULT, A POTENTIALLY TRICKY HIGH TEMPERATURE FORECAST. WE BLENDED THE NAM/GFS MOS OVERALL. FOR AREAS ALONG AND SOUTH OF THE FRONT, A HIGH PW AIRMASS REMAINS AND WITH ENOUGH LIFT AND FOCUS WITH THE SURFACE FRONT COMBINED WITH WEAK SURFACE LOW PRESSURE IS EXPECTED TO RESULT IN NUMEROUS SHOWERS AND THUNDERSTORMS ACROSS MUCH OF THE AREA. THIS MAY BE FOCUSED INITIALLY ALONG THE INTERSTATE 95 CORRIDOR BEFORE DRIFTING SOUTH, HOWEVER THEN MORE DEVELOPMENT NORTHWARD IS POSSIBLE WITH LIFT OVER THE FRONT WITH THE ARRIVAL OF WEAK SURFACE LOW PRESSURE. IT IS ACROSS THE SOUTHERN AREAS WHERE ENOUGH INSTABILITY COMBINED WITH FORCING COULD BUILD CONVECTIVE CORES ENOUGH TO ALLOW FOR LOCALLY STRONG WINDS AND PERHAPS SOME HAIL. THIS WILL DEPEND ON HOW MUCH INSTABILITY CAN DEVELOP PRIOR TO CONVECTIVE INITIATION OR LEFTOVER EARLIER CONVECTION. THERE IS THE POTENTIAL FOR TRAINING CELLS WITH CONVECTIVE ORGANIZATION AND THEREFORE STRONGER CORES COULD BE CAPABLE OF PRODUCING LOCALLY EXCESSIVE RAINFALL RATES. DEPENDING ON HOW THE CONVECTIVE ORGANIZATION BEHAVES, A FLASH FLOOD WATCH MAY BE NEEDED FOR PORTIONS OF THE CWA ESPECIALLY FOR THE URBAN AREAS ALONG THE INTERSTATE 95 CORRIDOR.
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&& .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... MONDAY NIGHT THROUGH TUESDAY NIGHT: MID-LEVEL FLOW WILL CONTINUE TO SLOW DOWN MONDAY NIGHT, ALMOST ALLOWING THE FRONT TO STALL OUT. SEVERAL FACTORS SUGGEST HEAVY, POTENTIALLY TRAINING SHOWERS AND A FEW THUNDERSTORMS WILL OCCUR MONDAY NIGHT INTO TUESDAY. SEVERAL AREAS OF LOW PRESSURE AND ASSOCIATED MID LEVEL DISTURBANCES WILL PASS THROUGH THE REGION. MOISTURE WILL CONTINUE TO STREAM NORTHWARD AHEAD OF THE FRONT LEADING TO SURGING PW VALUES CLOSE TO 2 INCHES. A TALL SKINNY CAPE PROFILE IS ALSO MODELED ALONG WITH VERY SLOW STORM MOTIONS. HOWEVER, AS STATED IN THE OVERNIGHT DISCUSSION THE SATURATION OF ATMOSPHERIC PROFILE DOES NOT HAVE A IDEAL LOOK FOR HEAVY RAINFALL WHICH MAY LIMIT THE EXCESSIVENESS OF THE RAIN SOMEWHAT. WITH MORE IN THE WAY OF SHOWERS OVERALL, INSTABILITY WILL BE LESS LEADING TO A MORE ISOLATED THREAT FOR ANY STRONG THUNDERSTORMS. THE HIGHEST CHANCES FOR RAIN WILL GRADUALLY SHIFT SOUTHEASTWARD MONDAY NIGHT AND TUESDAY. THE FRONTAL BOUNDARY SHOULD BEGIN TO TRANSITION EASTWARD BY TUESDAY NIGHT WITH GRADUALLY DECREASING CHANCES OF RAIN FROM NORTHWEST TO SOUTHEAST. COMPARED TO YESTERDAY, RAINFALL AMOUNTS LOOK SLIGHTLY HIGHER IN THESE PERIODS THAN WITH THE LAST FEW FORECAST UPDATES. THIS MAKES SENSE LOOKING AT ENVIRONMENTAL FACTORS IN PLACE AND THE POTENTIAL FOR DECENT SYNOPTIC LIFT AHEAD OF A MORE ORGANIZED AND SLOWER MOVING LOW PRESSURE SYSTEM. THIS FORECAST GOES WITH THE RFC QPF AS A STARTING POINT, WITH TIMING ON THE ECMWF AND UKMET MODELS FACTORED IN AS WELL, WHICH ARE SLOWER COMPARED TO THE GFS/CMC. WILL MAINTAIN CATEGORICAL POPS FOR MONDAY NIGHT AND RAISE POPS SOME ON TUESDAY AS WELL. TRENDS CONTINUE TO SHOW SOME SHOWERS MAY LINGER THROUGH TUESDAY NIGHT IN THE DELMARVA AND SOUTHEAST NJ. TOTAL RAINFALL MONDAY NIGHT AND TUESDAY IS LIKELY TO RANGE FROM 1 TO 3 INCHES WITH LOCALLY HIGHER AMOUNTS. A GENERAL CONSENSUS AT THIS TIME YIELDS THE HIGHEST RAINFALL TOTALS ACROSS EASTERN PA AND NORTHERN NJ. MET/MAV MOS ARE STARTING TO PICK UP ON THE POTENTIAL FOR TEMPERATURES TO BE KEPT UP AT NIGHT AND LOWER DURING THE DAY DUE TO CLOUDS AND PRECIPITATION. WEDNESDAY THROUGH FRIDAY: HIGH PRESSURE BUILDS OVER THEN PASSES EAST OF THE REGION FOR THE MIDDLE AND LATER HALF OF THE WEEK. COOL REFRESHING AIRMASS TO START THEN WARMER AND MUGGY BY WEEKS END. THE POTENTIAL STILL DOES EXIST FOR AN AREA OF LOW PRESSURE TO DEVELOP WELL TO OUR SOUTHEAST NEAR THE FRONTAL BOUNDARY WHICH PASSES THROUGH OUR REGION TUESDAY. RIGHT NOW FOR THIS TIMEFRAME IT STILL LOOKS LIKE THE HIGH PRESSURE HAS ENOUGH PUSH TO KEEP OUR WEATHER PARTLY TO MOSTLY CLOUDY WITH THE MOST CLOUDS ACROSS THE SOUTHERN DELMARVA REGION. FRIDAY NIGHT THROUGH SUNDAY: ANOTHER COLD FRONT IS LIKELY TO MOVE INTO THE REGION POSSIBLY DECAYING OVER THE REGION. TIMING DIFFERENCES AS USUAL ARE PRESENT WITH THIS FEATURE WITH THE FASTER, STRONGER GFS AND THE SLOWER ECMWF. WARM AND MORE HUMID CONDITIONS ARE LIKELY PRECEDE THE FRONT. SOME SCATTERED THUNDERSTORMS MAY FORM AHEAD OF THE FRONT AS WELL. OPTED FOR LOW CHANCE POPS ATTM CENTERED ON SATURDAY AFTERNOON AND EVENING, CLOSER TO THE ECMWF TIMING. GIVEN THE UNCERTAINTY WITH THE FRONTAL TIMING AND THE POTENTIAL FOR MORE CLOUDS, KEPT TEMPERATURES FAIRLY CLOSE TO THE GFS/ECMWF/WPC ENSEMBLE SETS. && .AVIATION /21Z SUNDAY THROUGH FRIDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THROUGH 00Z...VFR EVERYWHERE EXCEPT IFR IN SHOWERS AND THUNDERSTORMS CLOSEST TO KABE TO KRDG WHERE GUSTY NE WINDS MAY DEVELOP THIS EVENING. OTHERWISE SOUTH- SOUTHWEST WINDS GUSTY 20 KT IN SE PA AND S NJ THROUGH DE. TONIGHT...A COLD FRONT WILL SETTLE SOUTHWARD BUT PROBABLY STALL. THIS SHOULD ALLOW FOR SHOWERS AND THUNDERSTORMS TO ARRIVE FROM THE WEST, BUT THEN WEAKEN AFTER 04Z/01. THE TIMING AND OVERALL ORGANIZATION/PLACEMENT CARRIES SOME LOWER CONFIDENCE, AND THEREFORE ONLY CARRIED THUNDER IN THE FAR INLAND TERMINALS TO START THE EVENING. PLEASE SEE TAFS FOR DETAILS. HAVE DELAYED SHOWERS FOR ABOUT 6 HRS IN THE TAFS FOR KTTN KPHL AREA. MVFR TO NEAR IFR CEILINGS ARE ANTICIPATED FOR MANY OF THE TERMINALS OVERNIGHT. SOUTH-SOUTHWEST WINDS BECOMING SOUTHEAST AT LESS THAN 10 KNOTS, ALTHOUGH EASTERLY AT KABE AND KTTN. MONDAY...SHOWERS AND THUNDERSTORMS EXPECTED, WITH THE MOST WIDESPREAD ACTIVITY DURING THE AFTERNOON. AS A RESULT, MVFR AND LOCALIZED IFR ESPECIALLY DURING SHOWERS AND THUNDERSTORMS. SOUTHEAST OR EAST WIND UP TO 10 KNOTS. OUTLOOK... MONDAY NIGHT THROUGH TUESDAY NIGHT: MVFR AND IFR RESTRICTIONS IN SHOWERS AND SCATTERED THUNDERSTORMS. EAST TO NORTHEAST WINDS UNDER 10 KNOTS. WEDNESDAY THROUGH FRIDAY: VFR. EAST WINDS UNDER 10 KNOTS BECOMING MORE SOUTHERLY BY FRIDAY.
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&& .MARINE...
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MAY ISSUE AN MWS AT 6 PM FOR GUSTY S WIND TO 25 KT THROUGH 9 PM. A SOUTHERLY FLOW WILL CONTINUE AHEAD OF A COLD FRONT DRIFTING SOUTHWARD THROUGH MONDAY. THIS BOUNDARY WILL ALLOW FOR A WIND SHIFT FROM THE SOUTH TO SOUTHEAST AND THEN EAST ESPECIALLY LATE TONIGHT AND MONDAY ACROSS THE NORTHERN COASTAL WATERS. THE FLOW IS EXPECTED TO BE LIGHT ENOUGH TO KEEP THE WINDS BELOW 25 KNOTS. SOME GUSTINESS IS EXPECTED INTO THIS EVENING THOUGH ESPECIALLY NEARSHORE WITH BETTER MIXING AND ONCE AGAIN ON MONDAY SOUTH OF THE FRONT. THE SEAS ARE EXPECTED TO BE AT OR BELOW 4 FEET THROUGH MONDAY. OUTLOOK... MONDAY NIGHT THROUGH FRIDAY: SEAS THREE TO FOUR FEET FOR MOST OF THE WEEK. WINDS SHIFTING TO THE EAST AND NORTHEAST WITH GUSTS UNDER 20 KNOTS THROUGH TUESDAY NIGHT. SOME LOCALIZED GUSTS FROM 20-25 ARE POSSIBLE WEDNESDAY MORNING. WINDS SHIFTING TO MORE SOUTHERLY ON FRIDAY. STILL SOME UNCERTAINTY WITH SEAS GIVEN THE POTENTIAL FOR LOW PRESSURE TO FORM SOUTHEAST OF THE REGION FOR THE MIDDLE OF THE WEEK, ATTM IT DOES NOT LOOK LIKE A INCREASE IN SEAS FROM THIS.
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&& .RIP CURRENTS... THE RIP CURRENT RISK FOR THE JERSEY SHORE AND THE DELAWARE BEACHES IS MODERATE THROUGH THIS EVENING, BASED ON THE CONTINUED SOUTHERLY FLOW AND LONGER WAVE PERIOD. && .CLIMATE... NOTE: SEE BOTTOM OF THIS SECTION ON KPHL FIRST 90 OF THE SEASON. MAY 2015...A TOP 4 WARMEST ON RECORD FOR LARGE PORTIONS OF OUR AREA, AND RATHER DRY THOUGH WE STILL HAVE POTENTIAL FOR SIGNIFICANT RAINFALL THIS EVENING WHICH WOULD SIGNIFICANTLY ALTER THE FINAL MONTH OF MAY PRECIPITATION RANKING. ALL ACTUAL AND FORECAST INFORMATION CHECKED THROUGH AROUND 2 PM TODAY - SUNDAY MAY 31. ALLENTOWN WILL PROBABLY AVERAGE VERY CLOSE TO 66.4 OR AT LEAST 6 DEGREES ABOVE NORMAL. POR BACK TO 1922. NORMAL 59.9 PROBABLY THE 2ND WARMEST ON RECORD. 1991 67.2 2015 66.4 2012 66.1 1944 66.0 NORMAL PCPN 4.14. AS OF 2 PM TODAY ALLENTOWN SECOND DRIEST MAY ON RECORD SO FAR WITH 0.27 INCHES. DRIEST MAY 0.09 1964. -- PHILADELPHIA WILL PROBABLY AVERAGE CLOSE TO 70.1 DEGREES OR AT LEAST 6 DEGREES ABOVE NORMAL. SECOND WARMEST ON RECORD. NORMAL 63.9 1991 70.8 NUMBER 3 WOULD BE 69.2 IN 2004. NORMAL RAINFALL 3.71 THE 1.19 INCHES SO FAR IS 13TH DRIEST ON RECORD. -- ATLANTIC CITY MAY 2015 66.5 OR OVER 5 DEGREES ABOVE NORMAL AND PROBABLE #2 POR BACK TO 1874 NORMAL 61.1 2004 66.9 2015 66.5 1991 66.0 NORMAL PCPN 3.35 THE 0.71 INCHES SO FAR MAKES THIS AROUND THE 7TH DRIEST MAY ON RECORD. -- WILMINGTON DE SOLID POR BACK TO 1916 LOCKED INTO #4 WARMEST, SMALL CHANCE EQUAL NUMBER 3 WARMEST. NORMAL 62.8 1896 70.1 1991 69.1 2004 68.2 2015 AROUND 68.1 NORMAL PCPN 3.95 THE 2.39 INCHES IS MIDDLE OF THE PACK AND NOT ESPECIALLY OF STANDOUT DRY INTEREST FOR THIS STATION NO AVAILABLE MONTHLY HISTORICAL DATA FOR KMPO KGED KTTN AND KRDG. AN ADDITIONAL TIDBIT... PER TONY... SECOND 90F OF THE MONTH OCCURRED TODAY AT BOTH KRDG AND KABE KPNE HAS HAD 3 DAYS OF 90 SO FAR. KPHL WITH ITS 2ND WARMEST MAY EVER...AND FINALLY THE FIRST 90 OCCURRED TODAY... 92 AT 213PM. THE HISTORICAL RECORD DATING BACK TO 1874 FINDS PHILADELPHIA WITH ITS MEAN FIRST 90 AROUND MAY 29. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...FLASH FLOOD WATCH UNTIL 11 PM EDT THIS EVENING FOR PAZ054-055- 062. NJ...FLASH FLOOD WATCH UNTIL 11 PM EDT THIS EVENING FOR NJZ001-007- 008. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GAINES NEAR TERM...DRAG/GORSE 545P SHORT TERM...GORSE LONG TERM...GAINES AVIATION...DRAG/GAINES/GORSE 545P MARINE...DRAG/GAINES/GORSE 545P RIP CURRENTS... CLIMATE...

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