Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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587 FXUS61 KPHI 040516 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 116 AM EDT WED MAY 4 2016 .SYNOPSIS... WAVES OF LOW PRESSURE WILL RIDE ALONG A FRONTAL BOUNDARY STALLED TO THE SOUTH OF OUR REGION INTO THURSDAY. A STRONGER LOW IS EXPECTED TO DEVELOP NEAR THE VIRGINIA CAPES THURSDAY NIGHT AND SLOWLY MOVE NORTH ALONG THE DELAWARE AND NEW JERSEY COAST, BEFORE MOVING OUT TO SEA SATURDAY INTO SUNDAY. A WEAK COLD FRONTAL PASSAGE IS ANTICIPATED SUNDAY, FOLLOWED BY HIGH PRESSURE MOVING IN FROM THE OHIO VALLEY MONDAY AND TUESDAY. && .NEAR TERM /THROUGH TODAY/...
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1230 AM ESTF: LITTLE CHANGE FROM THE 1045 PM UPDATE FOR EARLY THIS MORNING. SHOWERS DEVELOPING NEWD INTO E MD AND E PA ATTM. TEMPS NEARLY STEADY THROUGH DAYBREAK. LIGHT NE WIND. AFTER SUNRISE WEDNESDAY...PERIODS OF SHOWERY RAINS AND DRIZZLE, ESPECIALLY I95 CORRIDOR WESTWARD. ISOLATED THUNDER POSSIBLE DELMARVA OR EVEN SE PA OR S NJ IN RESPONSE TO A POCKET OF INSTABILITY ALOFT ASSOCIATED WITH A KI POOL 30+ AND TT NEAR 52 AS WELL AS A WEAK 850 TROUGH. QPF IS THAT FROM WPC. COULD BE POCKETS OF .25 TO .5 INCHES TODAY, SINCE PWAT INCREASES TO ABOUT 1 INCH. NE WIND GUSTY 15-20 MPH THIS AFTERNOON I95 CORRIDOR EASTWARD IN CYCLONIC FLOW WITH A GRADUALLY INCREASING PRESSURE GRADIENT. 50 50 BLENDED 00Z/4 GFS/NAM MOS...FAVORING THE COLDER SIDE AS WE DRAW FROM THE COOLER WET BULB RESERVOIR OVER SOUTHERN NEW ENGLAND.
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&& .SHORT TERM /TONIGHT/...
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PWAT DRIES TO 0.75 INCHES AND INSTABILITY ALOFT DECREASES SOMEWHAT BUT A CONTD MOIST CYCLONIC CIRCULATION WITH PROBABLY PERIODS OF MEASURABLE DRIZZLE AND MAYBE A FEW POCKETS OF SHOWERS. 50 50 BLENDED 00Z/4 GFS NAM GUIDANCE. MORE LATER.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/... THE SYNOPTIC SCALE MID-LEVEL FEATURES THROUGH FRIDAY INCLUDE A MEAN VORTEX NEAR THE CLIMATOLOGICAL FAVORED NORTHERN HUDSON`S BAY WITH AN OMEGA BLOCK SETTING UP A SPLIT FLOW OVER NOAM. A VIGOROUS SHORTWAVE OVER THE OHIO VALLEY WED NIGHT WILL CARVE OUT A CLOSED MID-LEVEL LOW OVER THE MIDDLE ATLANTIC THU, WHICH WILL SLOWLY MEANDER NORTH AND GRADUALLY FILL THROUGH SATURDAY. THIS SETS THE STAGE FOR CONTINUED UNSETTLED WEATHER THRU EARLY THIS WEEKEND. A STOUT SHORTWAVE MOVING ALONG THE WESTERN SHORE OF HUDSON`S BAY FRIDAY INTO SATURDAY WILL BREAK DOWN THE OMEGA BLOCK, AND EJECT THE AFOREMENTIONED CLOSED LOW SATURDAY INTO SUNDAY. THIS SHORTWAVE WILL LEAD TO A COLD FRONTAL PASSAGE LATE THIS WEEKEND. MID-LEVEL RIDGING WILL GRADUALLY BUILD OVER THE MID ATLANTIC EARLY NEXT WEEK, WITH A RETURN TO FAIR WEATHER, AND A MODERATION IN TEMPERATURES. WEDNESDAY NIGHT AND THURSDAY...OFFSHORE LOW PRESSURE RIDING ALONG STALLED FRONTAL BOUNDARY TO OUR SOUTH WILL MAINTAIN A COOL AND MOIST NORTHEAST FLOW ACROSS THE REGION. THERE WILL BE WEAK SUBSIDENCE ACROSS THE REGION WITHIN THE LEFT-REAR QUADRANT OF THE UPPER-LEVEL JET, MAINTAINING A WEAK OF RIDGE OF HIGH PRESSURE AT THE SURFACE, WHICH WILL NOSE DOWN FROM THE BAY OF FUNDY. THE COLUMN WILL BE VERY MOIST WITH WEAK STEERING CURRENTS, FAVORING LIGHT AND SPOTTY PRECIP MAINLY WEST OF THE FALL LINE, WHERE OROGRAPHIC LIFT IS ENHANCED. THURSDAY NIGHT THRU SATURDAY...DEEP MID-LEVEL LOW, WITH HEIGHTS OF NEGATIVE 3-4 STANDARD DEVIATIONS, CLOSES OFF OVER THE MID ATLANTIC THU NIGHT INTO EARLY FRI, AND GRADUALLY FILLS, AS IT MOVES NORTHEAST TOWARD THE NEW ENGLAND COAST SAT. THE VORT MAX ASSOCIATED WITH THIS FEATURE LEADS TO MODEST CYCLOGENESIS NEAR THE VA CAPES THU NIGHT, AS THE SYSTEM BECOMES VERTICALLY STACKED NEAR THE DE/NJ COAST FRI NIGHT INTO EARLY SAT. THERE IS SOME MODEL DISAGREEMENT REGARDING THE PLACEMENT OF THE SURFACE LOW, PARTICULARLY HOW FAR SOUTH IT DEVELOPS THU NIGHT, THEN HOW FAST IT MOVES OFFSHORE SAT. THE NAM IS FURTHEST TO THE SOUTH THU NIGHT, WITH A GREATER PRESSURE GRADIENT NORTHWARD INTO FRIDAY, RESULTING IN LONGER DURATION OF GUSTY WINDS ALONG THE COAST. FORTUNATELY, THE CONFLUENT REGION OF THE UPPER-LEVEL JET IS NOT FAVORABLE FOR THE MAINTENANCE OF SURFACE HIGH PRESSURE NORTH OF THE LOW, WHICH SHOULD REDUCE THE WIND POTENTIAL, I.E., LACK OF A ROBUST LOW LEVEL EASTERLY JET. THE ECMWF MAY BE LIFTING THE LOW TOO QUICKLY NORTHEAST SATURDAY, GIVEN THE VERTICALLY STACKED NATURE OF THE SYSTEM, AND IS AN OUTLIER. OVERALL, A WET PERIOD DURING THIS TIME FRAME. THE HEAVIEST RAINFALL IS ANTICIPATED JUST TO THE SOUTH AND WEST OF OUR REGION, WHERE THE DEEPEST MOISTURE ALIGNS WITH THE STRONGEST PVA. WITH THE LACK OF A ROBUST LOW-LEVEL JET, AS WELL AS THE SYNOPTIC SETUP, THE HIGHER RAINFALL AMOUNTS WILL FAVOR THE EAST SLOPES OF THE APPALACHIANS. THUS, EXPECT RAINFALL AMOUNTS TO INCREASE AWAY FROM THE COASTLINE, WITH EARLY ESTIMATES UP TO AROUND 1.5 INCHES NORTHWEST OF I-95. GIVEN THE DURATION OF THE RAINFALL, URBAN AND POOR DRAINAGE FLOODING IS NOT ANTICIPATED TO BE A MAJOR ISSUE. WHILE WE HAVE NOT INSERTED THUNDER AT THIS POINT IN THE FORECAST, MID-LEVEL COLD POOL WILL BE OVER DELMARVA FRIDAY, WITH 500 HPA TEMPS APPROACHING -24C! MID-LEVEL LAPSE RATES ARE MODELED TO APPROACH 7C/KM, WITH MODEST ELEVATED CAPE. IF THUNDERSTORMS ARE ABLE TO DEVELOP, THEY WOULD BE CAPABLE OF PRODUCING SMALL HAIL. AS THE MID-LEVEL COLD POOL SLOWLY MOVES NORTH ACROSS THE REGION SATURDAY, CANNOT RULE OUT A CONTINUED CHANCE OF THUNDER. WITH THE PRESSURE GRADIENT IN PLACE, WINDS COULD GUST UP TO AROUND 30 MPH ALONG THE COAST. SUNDAY...CLIPPER-TYPE SHORTWAVE QUICKLY FOLLOWING ON THE HEELS OF THE CLOSED MID-LEVEL LOW IS ANTICIPATED TO LEAD TO A COLD FRONTAL PASSAGE ACROSS THE REGION. THE MODELS TEND TO AMPLIFY THIS SHORT- WAVE ACROSS THE NORTHEAST CONUS, WHICH WOULD LEAD TO AN INCREASED CHANCE OF PRECIP, AS WELL AS GUSTY POST-FRONTAL NORTHWEST WINDS. A PATTERN CHANGE WILL ALSO BE UNDERWAY AT THIS TIME, SO THERE IS SOME UNCERTAINTY AS TO HOW AMPLIFIED THIS FEATURE WILL BE. MONDAY AND TUESDAY...FAIR WEATHER DURING THIS TIME FRAME WITH TEMPERATURES AOA SEASONABLE LEVELS. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. EARLY TODAY...GENERALLY IFR CIGS WITH PATCHY 2 TO 5 MI FOG. SHOWERS AND DRIZZLE DEVELOPING, ESPECIALLY KRDG/KABE/KILG WHICH WILL RESULT IN PATCHY LIFR CONDITIONS. LIGHT NE WIND. TODAY AFTER 12Z...GENERALLY IFR CIGS WITH PATCHY 2-5 MI IN NUMEROUS SHOWERS/ PATCHY DRIZZLE-FOG. ISOLATED THUNDER NOT IMPOSSIBLE PER NAM/GFS INSTABILITY ALOFT, MAINLY DELMARVA OR SE PA/S NJ. NE WIND WITH A FEW GUSTS 15-20 KT VCNTY KPHL/KACY. TONIGHT...GENERALLY IFR CIGS WITH PATCHY 2-5 MI IN SCT SHOWERS/ PATCHY DRIZZLE-FOG. POSSIBLE LIFR CIGS. NE WIND G 15-20 KT POSSIBLE KPHL-KTTN-KACY. OUTLOOK... OVERALL, MODERATE CONFIDENCE THURSDAY NIGHT THRU SUNDAY TAF PERIOD. THU NIGHT AND FRI...PREDOMINANTLY MVFR IN SHRA. POCKETS OF IFR POSSIBLE, PARTICULARLY ACY AND MIV THU NIGHT INTO EARLY FRI. NORTHEAST WINDS COULD GUST AROUND 20 KNOTS AT TERMINALS ALONG AND SOUTHEAST OF I-95, MAINLY FRI. FRI NIGHT...MVFR. IMPROVEMENT TO VFR POSSIBLE SOUTHEAST OF I-95. SAT AND SUN...PREDOMINANTLY VFR. GUSTY NORTHWEST WINDS POSSIBLE SUN.
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&& .MARINE...
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SCA FOR SEAS CONTINUED. WILL BE UPGRADED TO INCLUDE WIND GUSTS 25-30KT IN THE 330 AM FORECAST FOR AT LEAST NNJ 450-451 LATE TODAY AND TONIGHT. SST`S ARE NEAR OR SLIGHTLY ABOVE NORMAL. WAVES NEAR 4 FT NOW WILL STEADILY BUILD SO THAT TONIGHT THEY SHOULD BE WIDESPREAD 5-6 FT, POSSIBLY 7 FT VCNTY 44091. OUTLOOK... A VERY PERSISTENT NORTHEAST FLOW CONTINUES OVER THE COASTAL WATERS THURSDAY THRU SATURDAY. THE STRONGEST WINDS ARE ANTICIPATED LATE THU NIGHT INTO FRI AS DEVELOPING LOW PRESSURE MOVES NORTHWARD NEAR THE MID ATLANTIC COAST. STILL SOME UNCERTAINTY REGARDING THE WIND FIELDS ASSOCIATED WITH THIS SYSTEM, BUT A SCA IS PROBABLE, GIVEN BUILDING SEAS IN A NORTHEAST FETCH WED NIGHT THRU FRI. A SCA IS NOW IN EFFECT THRU 12Z THU, FOR WAVE HEIGHTS NEAR 5FT, AND WILL LIKELY NEED TO BE EXTENDED FURTHER INTO FRI. SATURDAY...SEAS SHOULD BE SUBSIDING, BUT CANNOT RULE OUT RESIDUAL 5FT WAVES, THUS LOW PROBABILITY SCA MAY BE NEEDED. LOW CONFIDENCE. SUN...A COLD FRONT IS EXPECTED TO CROSS THE COASTAL WATERS, WITH SCA LEVEL WINDS POSSIBLE, MAINLY IN THE NORTHWEST FLOW BEHIND THE FRONT. LOW CONFIDENCE.
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&& .TIDES/COASTAL FLOODING... A LONG DURATION NORTHEASTERLY FETCH WILL DEVELOP IN THE WED THRU AT LEAST FRI TIME FRAME. IN ADDITION, ASTRONOMICAL TIDES WILL BE ON THE INCREASE AS WE APPROACH THE NEW MOON FRI. ALL AVAILABLE GUIDANCE SUGGESTS THERE COULD BE SOME MINOR TIDAL FLOODING AROUND THE TIMES OF HIGH TIDE ON WEDNESDAY EVENING, THURSDAY EVENING, AND MORE LIKELY FRIDAY EVENING. THERE IS ALSO A SLIGHT CHANCE OF REACHING A MODERATE THRESHOLD FRIDAY EVENING, BUT CONFIDENCE IS LOW. AS A SIDE NOTE: IT IS OUR UNDERSTANDING THAT EVENTUALLY WE WILL BEGIN REFERENCING COASTAL FLOODING WITH RESPECT TO MHHW WHICH WILL EQUATE TO INUNDATION DEPTH WITH RESPECT TO NORMALLY DRY GROUND. THERE WILL LIKELY BE TRAINING REFERENCES DURING THIS SIGNIFICANT COASTAL FLOODING REFERENCING TRANSITION FROM MLLW TO MHHW. && .RIP CURRENTS...
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WE WILL BE TESTING THE SRF THIS MORNING FOR AN HOUR AROUND 630A TO ENSURE CORRECT POSTING OF THE SRF PRODUCT FOR ITS MAY 20 530 AM START UP. HERE`S A SHORT USEFUL REVIEW OF RIP CURRENT SCIENCE PRODUCED BY A PARTNERSHIP OF NWS AND OCEANS TODAY. HTTP://OCEANTODAY.NOAA.GOV/RIPCURRENTSCIENCE/
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 9 AM THIS MORNING TO 8 AM EDT THURSDAY FOR ANZ450>453.
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&& $$ SYNOPSIS...FRANCK NEAR TERM...DRAG 115 SHORT TERM...DRAG 115 LONG TERM...FRANCK AVIATION...DRAG/FRANCK 115 MARINE...DRAG/FRANCK 115 TIDES/COASTAL FLOODING... RIP CURRENTS...DRAG 115

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