Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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066 FXUS61 KPHI 031932 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 332 PM EDT TUE MAY 3 2016 .SYNOPSIS...
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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.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... LOW PRESSURE WAS CENTERED OFF THE NEW JERSEY COAST AROUND 130 PM. THE LOW WILL DRIFT EASTWARD AND FARTHER OUT TO SEA THIS AFTERNOON. A SECONDARY LOW IS FORECAST TO DEVELOP OVER SOUTHEASTERN VIRGINIA AND NORTHEASTERN NORTH CAROLINA. THE CIRCULATION AROUND THE DEPARTING LOW WILL KEEP OUR FORECAST AREA IN A NORTHEASTERLY SURFACE FLOW. SOMEWHAT MILDER AIR ABOVE THE MARINE LAYER SHOULD MAINTAIN THE LOW CLOUDS OVER OUR REGION. THE BACK EDGE OF THE DECK OF HIGH CLOUDS ABOVE THE STRATUS IS EXPECTED TO WORK ITS WAY FROM WEST TO EAST OVER OUR FORECAST AREA DURING THE MID TO LATE AFTERNOON. THE INCREASING INSOLATION MAY CAUSE THE LOW CLOUD DECK TO RISE A BIT AT THAT TIME. THE MAIN AREA OF RAIN SHOWERS WAS WELL TO OUR EAST EARLY THIS AFTERNOON. WE ARE NOT ANTICIPATING MUCH MORE THAN SCATTERED LIGHT RAIN SHOWERS AND PATCHY DRIZZLE THROUGH THE BALANCE OF THE DAYLIGHT HOURS. HOWEVER, SHOWERS AND PERHAPS ISOLATED THUNDERSTORMS MAY BEGIN TO APPROACH NORTHEASTERN MARYLAND AND DELAWARE FROM THE WEST LATE IN THE DAY BASED ON SOME OF THE MODEL GUIDANCE. THE CLOUD COVER AND NORTHEASTERLY FLOW WILL KEEP TEMPERATURES FROM GETTING MUCH ABOVE THE UPPER 50S AND LOWER 60S IN MOST OF OUR FORECAST AREA. READINGS WILL FALL SHORT OF THAT RANGE IN THE FAR NORTH AND THEY WILL BE A BIT ABOVE THOSE VALUES IN PARTS OF SOUTHERN DELAWARE. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... THE AFOREMENTIONED UPPER-LEVEL TROUGH IS FORECAST TO SHARPEN SOME TO OUR WEST DURING THE COURSE OF TONIGHT. THERE DOES NOT APPEAR TO BE A MORE FOCUSED SHORT WAVE WITHIN THE SOUTHWESTERLY FLOW ALOFT UNTIL TOWARD MORNING. THE 250 MB JET IS FORECAST TO MOVE RIGHT OVER OUR AREA TONIGHT, REMOVING THE REGION FROM THE MORE FAVORABLE AREA OF LIFT. AS A RESULT, WE KEPT POPS IN THE SLIGHT CHC TO LOW CHC RANGE AS SOME SHOWERS CANNOT BE RULED OUT. THE IDEA OF LOW CLOUDS CONTINUES ACROSS THE AREA GIVEN THE MARINE INFLUENCE, AND THEREFORE SOME DRIZZLE IS POSSIBLE AS THE FORECAST SOUNDINGS INDICATE SOME MID LEVEL DRYING IN PLACE. WHILE SOME FOG MAY BE AROUND IT IS NOT ANTICIPATED TO BE SIGNIFICANT AS THE STRATUS MAY LIMIT THE ACTUAL DEVELOPMENT OVERALL. THEREFORE, OPTED TO NOT INCLUDE FOG ATTM BUT THIS WILL BE REVISITED LATER. AS FOR THE LOW TEMPERATURES, WE USED A MOS BLEND OVERALL. TEMPERATURES SHOULD NOT FALL A LOT GIVEN THE CLOUD COVER AND DEW POINTS GENERALLY REMAINING UP DUE TO NEAR LOW-LEVEL SATURATION. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
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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 VIRGOROUS 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 CYCLOGENSIS 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 APPOACH 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.
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&& .AVIATION /19Z TUESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. CEILINGS ARE FORECAST TO RISE INTO THE MVFR CATEGORY FOR THE LATE AFTERNOON AND EARLY EVENING HOURS WITH SCATTERED LIGHT RAIN SHOWERS AND PATCHY DRIZZLE AFFECTING OUR REGION. CEILINGS ARE FORECAST TO LOWER BACK INTO THE IFR RANGE AFTER DARK AND THEY SHOULD REMAIN THERE WELL INTO WEDNESDAY MORNING. CLOUD BASES MAY LIFT SLIGHTLY FROM LATE WEDNESDAY MORNING INTO WEDNESDAY AFTERNOON BUT THEY SHOULD REMAIN IN THE HIGH END IFR TO LOW END MVFR RANGE. WE ARE ANTICIPATING SCATTERED SHOWERS AGAIN ON WEDNESDAY. THE WIND WILL FAVOR THE NORTHEAST AND EAST THROUGH THE TAF PERIOD, AT SPEEDS MAINLY BETWEEN 5 AND 10 KNOTS. OUTLOOK... OVERALL, MODERATE CONFIDENCE THU NIGHT THRU SUN 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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WEAK LOW PRESSURE EAST AND SOUTH OF THE AREA THIS AFTERNOON INTO TONIGHT WILL KEEP AN ONSHORE FLOW IN PLACE. WHILE THIS MAY SOME INCREASE FOR A TIME ESPECIALLY LATER TODAY AND TONIGHT ACROSS THE NORTHERN ATLANTIC COASTAL WATERS, IT SHOULD REMAIN BELOW 25 KNOTS. SINCE THE FLOW IS FORECAST TO BE WEAK ENOUGH, SEAS ARE ANTICIPATED TO BE 4 FEET OR LESS. THEREFORE, THE CONDITIONS ARE EXPECTED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA THROUGH TONIGHT. OUTLOOK... A VERY PERSISTENT NORTHEAST FLOW CONTINUES OVER THE COASTAL WATERS WED NIGHT THRU SAT. THE STRONGEST WINDS ARE ANTICIPATED LATE THU NIGHT INTO FRI AS DEVELOPING LOW PRESSURE MOVES NORTHWARD NEAR THE MID ATLANTIC COAST. STILL LOW CONFIDENCE 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...
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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 THE TRANSITION.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...FRANCK NEAR TERM...IOVINO SHORT TERM...IOVINO LONG TERM...FRANCK AVIATION...FRANCK/IOVINO MARINE...FRANCK/IOVINO TIDES/COASTAL FLOODING...STAFF

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