Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
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/...
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.

&&

.SHORT TERM /TONIGHT/...
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.

&&

.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/...
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.

&&

.MARINE...
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.

&&

.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...
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/

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
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.

&&

$$
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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