Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 031940
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
340 PM EDT TUE MAY 3 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 /UNTIL 6 AM WEDNESDAY MORNING/...
THE AREA OF LOW PRESSURE THAT AFFECTED OUR REGION DURING THE NIGHT
AND THIS MORNING WAS CONTINUING TO MOVE OUT TO SEA THIS AFTERNOON.
MEANWHILE, ANOTHER LOW WAS DEVELOPING OVER CENTRAL VIRGINIA. IT
SHOULD DRIFT SOUTHEASTWARD REACHING THE COAST NEAR THE VIRGINIA AND
NORTH CAROLINA BORDER AROUND DAYBREAK.

THE BACK EDGE OF THE DECK OF HIGH CLOUDS ABOVE THE STRATUS WAS
BEGINNING TO MOVE OFF THE COAST AROUND MID AFTERNOON. THE INCREASING
INSOLATION SHOULD CAUSE THE BASES OF THE STRATUS TO LIFT A BIT
DURING THE BALANCE OF THE AFTERNOON. ALSO, IT SHOULD BRING AN END TO
ANY PATCHY DRIZZLE IN OUR REGION.

THE STRATUS SHOULD BEGIN TO LOWER AGAIN AFTER DARK. THE NORTHERN
EDGE OF THE SHOWERS AND THUNDERSTORMS THAT WERE IN WESTERN VIRGINIA
AROUND 330 PM MAY AFFECT SOME OF OUR COUNTIES IN NORTHEASTERN
MARYLAND AND DELAWARE THIS EVENING. ANOTHER BATCH OF SHOWERS
DEVELOPING IN WEST VIRGINIA MAY LIFT NORTHEASTWARD AND INTO OUR
NORTHWESTERN COUNTIES LATE TONIGHT. OTHERWISE, THE REST OF OUR
FORECAST AREA SHOULD RECEIVE LITTLE OR NO PRECIPITATION TONIGHT.

THE SURFACE PATTERN WILL MAINTAIN A NORTHEASTERLY FLOW IN OUR
REGION. MINIMUM TEMPERATURES SHOULD FAVOR THE UPPER 4OS AND LOWER
50S.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
WEAK LOW PRESSURE IS FORECAST TO LIFT FROM THE COASTAL WATERS OF
VIRGINIA ON WEDNESDAY MORNING TO THE WATERS OFF DELAWARE AND
SOUTHERN NEW JERSEY LATE ON WEDNESDAY AFTERNOON. LOW CLOUDS AND A
NORTHEAST WIND ARE AGAIN EXPECTED IN OUR REGION

THE AREA OF SHOWERS THAT IS ANTICIPATED TO AFFECT OUR NORTHWESTERN
COUNTIES LATE TONIGHT SHOULD LIFT NORTHEASTWARD AND OUT OF OUR
REGION DURING THE MORNING HOURS. HOWEVER, A SHORT WAVE TROUGH
TRAVELING IN THE SOUTHWESTERLY MID LEVEL FLOW IS EXPECTED TO PASS
OVERHEAD DURING THE MID TO LATE AFTERNOON HOURS AND IT SHOULD
ENHANCE THE POTENTIAL FOR SHOWERS THROUGHOUT OUR FORECAST AREA AT
THAT TIME.

DAYTIME TEMPERATURES ARE EXPECTED TO BE BELOW NORMAL DUE TO THE
NORTHEAST WIND AND THE CLOUD COVER. HIGHS SHOULD FAVOR THE UPPER 50S
AND LOWER 60S.

&&

.LONG TERM /WEDNESDAY NIGHT 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 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.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
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. 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 LATE TONIGHT AROUND KRDG AND KABE. SCATTERED
SHOWERS ARE EXPECTED AT ALL EIGHT OF OUR TAF SITES ON WEDNESDAY
AFTERNOON.

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.

&&

.MARINE...
THE SURFACE PATTERN WITH LOW PRESSURE REMAINING TO OUR SOUTH AND
EAST SHOULD MAINTAIN A NORTHEASTERLY FLOW ON OUR COASTAL WATERS FOR
TONIGHT AND WEDNESDAY. WHILE WIND SPEEDS AND GUSTS ARE FORECAST TO
STAY BELOW 25 KNOTS, WAVE HEIGHTS ON OUR OCEAN WATERS MAY BUILD TO 5
FEET, ESPECIALLY ON THE WATERS OFF NEW JERSEY. AS A RESULT, WE HAVE
ISSUED A SMALL CRAFT ADVISORY FOR SEAS FOR OUR COASTAL WATERS FROM
SANDY HOOK TO CAPE MAY. IT BEGINS AT 900 AM WEDNESDAY.

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 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.

&&

.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 THE TRANSITION.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 9 AM WEDNESDAY TO
     8 AM EDT THURSDAY FOR ANZ450>453.

&&

$$
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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