Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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924
FXUS61 KPHI 292003
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
403 PM EDT FRI APR 29 2016

.SYNOPSIS...
A WEAK SYSTEM MOVES ACROSS OUR AREA THROUGH THIS EVENING, THEN HIGH
PRESSURE BUILDS DOWN FROM THE NORTH SATURDAY. LOW PRESSURE IS
FORECAST TO TRACK ACROSS OUR AREA SUNDAY INTO EARLY MONDAY BEFORE
SHIFTING OFFSHORE DURING MONDAY. HIGH PRESSURE MAY EXTEND INTO OUR
AREA TUESDAY INTO WEDNESDAY. AS LOW PRESSURE TRACKS NORTHWARD
OFFSHORE THURSDAY INTO FRIDAY, A COUPLE OF COLD FRONTS ARE FORECAST
TO APPROACH OR MOVE THROUGH OUR AREA.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
THE FORECAST AREA THIS AFTERNOON REMAINS UNDER EXTENSIVE LOW
CLOUD COVER WITH COOL ONSHORE FLOW FROM THE ATLANTIC OCEAN. THE
CLOUD COVER IS KEEPING TEMPS WELL BELOW NORMAL IN THE LOWER 50S.
THIS BASIC PATTERN WILL NOT CHANGE MUCH THROUGH TONIGHT AND
TOMORROW ALTHOUGH SOMEWHAT DRIER AIR IS EXPECTED TO PUSH IN FROM
THE NORTH FOR A WHILE ON SATURDAY.

FOR TONIGHT...A SHORTWV TROF NOW LOCATED APPROX OVER LAKE ERIE WILL
MOVE ESE ACROSS THE AREA WITH SOME WEAK LOW-LEVEL WARM ADVECTION AND
UVV AHEAD OF IT. THIS WILL RESULT IN INCREASE SHOWERS AS CAN ALREADY
BE SEEN ON THE REGIONAL RADAR LOOP. INDICATIONS ARE THAT THE MOST
CONCENTRATED SHOWER ACTIVITY WILL BE ACROSS THE POCONOS, LEHIGH VLY
AND NORTHERN NJ. PRECIP AMOUNTS SHOULD BE SOMEWHAT HIGHER THERE ALSO
ALTHOUGH PROBABLY NO MORE THAN ONE-QUARTER INCH OR SO...WITH LESSER
AMOUNTS FOR PHL AND SOUTH. THE SHOWERS SHOULD TAPER OFF SHORTLY
AFTER MIDNIGHT. COOLING OVERNIGHT WILL BE LIMITED BY THE CLOUD COVER
AND LOWS IN THE LOW TO MID 40S ARE EXPECTED.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
FOR SATURDAY...WEAK HIGH PRESSURE WILL BUILD IN FROM THE NORTH AND
THERE WILL ALSO BE SOME RIDGING ALOFT BEHIND THE SHRTWV TROF. A
DRIER AIRMASS WILL BE IN PLACE PROVIDING CONSIDERABLY MORE SUNSHINE
THAN TODAY. THUS DAYTIME HEATING WILL ALLOW FOR MILDER AFTERNOON
TEMPS ON SATURDAY WITH HIGHS IN THE LOW 60S...EXCEPT COOLER NEAR THE
ATLANTIC COAST SINCE WINDS WILL STILL BE COMING OFFER THE OCEAN.
SOME MID TO HIGH-LEVEL CLOUDS WILL BE SPREADING IN FROM THE SW IN
THE AFTERNOON AHEAD OF THE NEXT SYSTEM. HOWEVER THE ASSOCD PRECIP
SHOULD NOT REACH THE AREA UNTIL AFTER DARK.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
THE SYNOPTIC PATTERN IS FORECAST TO BE COMPRISED OF A RIDGE THAT
QUICKLY SLIDES ACROSS THE EAST SATURDAY NIGHT. PLENTY OF ENERGY
STRETCHES FROM THE GREAT LAKES BACK INTO THE FOUR CORNERS AREA, AND
THE UPPER-LEVEL FLOW ACROSS THE EAST BACKS TO MORE SOUTHWESTERLY. AS
THE NORTHERN PORTION OF A TROUGH AMPLIFIES ACROSS THE GREAT LAKES
SUNDAY NIGHT INTO MONDAY THEN EASTWARD DURING MONDAY, LOW PRESSURE
TRACKS FROM THE PLAINS TO THE UPPER OHIO VALLEY THEN ACROSS OUR
REGION. THERE LOOKS TO BE PLENTY OF MOISTURE TRANSPORT AHEAD OF AND
WITH THIS FEATURE, WHICH SHOULD RESULT IN A DECENT AMOUNT OF
RAINFALL FROM LATE SATURDAY NIGHT INTO MONDAY. THE TROUGH THEN LIFTS
OUT THEREAFTER, HOWEVER A MORE SIGNIFICANT TROUGH IS FORECAST TO
AMPLIFY INTO THE EAST WEDNESDAY AND THURSDAY. WHILE SOME INDIVIDUAL
MODEL RUNS SHOW THE POTENTIAL FOR THE UPPER-LEVEL TROUGH TO CLOSE
OFF FRIDAY SOMEWHERE OVER THE EASTERN STATES, THERE IS A LACK OF
CONSISTENCY/AGREEMENT. THIS WOULD RESULT IN COOLER AND MORE
UNSETTLED WEATHER ACROSS THE EAST. WE USED A MODEL/CONTINUITY BLEND
INTO MONDAY, THEN BLENDED IN THE 12Z WPC GUIDANCE THEREAFTER. SOME
ADJUSTMENTS WERE THEN MADE FOLLOWING ADDITIONAL COLLABORATION WITH
OUR NEIGHBORING OFFICES.

FOR SATURDAY NIGHT AND SUNDAY...AS AN UPPER-LEVEL RIDGE AXIS QUICKLY
SHIFTS TO OUR EAST SATURDAY NIGHT, SURFACE HIGH PRESSURE ALSO EASES
OFFSHORE. ON ITS HEELS IS ENERGY EJECTING OUT OF THE PLAINS WITHIN A
BACKING UPPER-LEVEL FLOW. THIS WILL RESULT IN INCREASING DOWNSTREAM
WAA AND MOISTURE ADVECTION ALONG WITH ISENTROPIC LIFT. AS A RESULT,
WE ARE ANTICIPATING RAIN OVERSPREADING THE ENTIRE REGION BY LATE
SATURDAY NIGHT WITH IT CONTINUING FOR MUCH OF SUNDAY. THE MODEL
GUIDANCE SHOWS THE PW VALUES SURGING INTO THE 1.0-1.5 INCH RANGE
THROUGH SUNDAY. THIS COMBINED WITH AMPLE LIFT MAY ALLOW THE RAIN TO
BE MODERATE/HEAVY AT TIMES. RAINFALL AMOUNTS BY LATE SUNDAY OF
AROUND AN INCH ARE POSSIBLE FOR MUCH OF THE AREA, HOWEVER THIS
SHOULD FALL OVER A LONG ENOUGH PERIOD OF TIME. THE FORECAST
SOUNDINGS OVERALL INDICATE A PRONOUNCED VEERING PROFILE IN THE LOWER
LEVELS AS A LOW-LEVEL JET MOVES THROUGH DURING A PORTION OF SUNDAY.
THE LEADING EDGE OF THE WAA SURGE AND INCREASING 850 MB FLOW COULD
ALLOW THE RAIN TO RAMP UP QUICKLY TOWARD 12Z SUNDAY. DESPITE THE
SHOWERY WEATHER OF LATE, THE REGION COULD USE MORE RAIN.

THERE IS ALSO AT LEAST SOME INSTABILITY FORECAST SUNDAY AFTERNOON
AND EVENING MAINLY SOUTH OF PHILADELPHIA. THIS WILL BE DETERMINED BY
HOW FAR NORTH THE INCOMING WARM FRONT GETS. GIVEN THE FORECAST ATTM,
WE KEPT A MENTION OF SOME THUNDER ACROSS THE SOUTHERN ZONES SUNDAY
AFTERNOON INTO THE EVENING. THE BEST ISENTROPIC LIFT MAY START TO
SHIFT TO OUR NORTHEAST BY SUNDAY AFTERNOON AND EVENING, ALLOWING THE
STEADY RAIN TO END AND BECOME MORE SHOWERY. THIS OCCURS AS SURFACE
LOW PRESSURE ARRIVES RIGHT OVER OUR AREA BY DAYBREAK MONDAY.

FOR MONDAY AND TUESDAY...AS AN UPPER-LEVEL TROUGH AMPLIFIES ACROSS
THE NORTHEAST AND MID ATLANTIC REGIONS MONDAY, SURFACE LOW PRESSURE
WILL BE SHIFTING OFFSHORE. WHILE MONDAY IS LOOKING DRIER WITH TIME
AS THE SURFACE LOW DEPARTS, RESIDUAL MOISTURE AND LIFT WITH THE
INCOMING TROUGH SHOULD PRODUCE SHOWERS ESPECIALLY THE FIRST HALF OF
THE DAY. IT APPEARS THE WARM SECTOR IS IN OUR SOUTHERN AREAS MONDAY
BEFORE THE SURFACE LOW SHIFTS OFFSHORE. WHILE SOME THUNDER CANNOT BE
RULED OUT WITHIN THE WARM SECTOR, THE SURFACE LOW IS FORECAST TO
EXIT TO THE EAST DURING THE FIRST PART OF MONDAY. GIVEN LESS
CERTAINTY FOR SOME THUNDER MONDAY, WE OPTED TO NOT INCLUDE A
MENTION. ANY LEFTOVER SHOWERS SHOULD END EARLY MONDAY NIGHT AS THE
TROUGH AXIS SHIFTS OFFSHORE AND THE LOW-LEVEL FLOW TURNS MORE FROM
THE NORTH AND NORTHWEST. A WEAK AREA OF HIGH PRESSURE MAY THEN
EXTEND INTO OUR AREA FROM THE WEST TUESDAY.

FOR WEDNESDAY THROUGH FRIDAY...AN UPPER-LEVEL TROUGH IS FORECAST TO
AMPLIFY INTO THE EAST DURING THIS TIME FRAME. AS THIS STARTS TO
OCCUR, A FRONTAL BOUNDARY TO OUR SOUTH AND EAST MAY HAVE A WAVE OF
LOW PRESSURE RUNNING UP THE FRONT. THIS COULD AT LEAST BRUSH OUR
EASTERN AND SOUTHERN ZONES WEDNESDAY, HOWEVER THERE IS LOW
CONFIDENCE WITH THIS. AS THE MAIN TROUGH TO OUR WEST ARRIVES
THURSDAY, A SURFACE COLD FRONT WILL ALSO ARRIVE AND MOVE THROUGH.
THE WAA AHEAD OF THE FRONT SHOULD ALLOW FOR WARMER TEMPERATURES
WEDNESDAY AND THURSDAY BEFORE SOME COOLING TAKES PLACE ON FRIDAY.
THE COOLING ON FRIDAY MAY ALSO BE ACCOMPANIED BY A SECONDARY COLD
FRONT APPROACHING. THE SETUP FOR THURSDAY INTO FRIDAY COULD BE MORE
UNSETTLED AS ENERGY OFF THE COAST ALONG AN OLD FRONT MAY ALLOW FOR A
STRENGTHENING SURFACE LOW. THIS FEATURE, DEPENDING ON ITS TRACK AND
ALSO STRENGTH/POSITION OF THE UPPER-LEVEL TROUGH, COULD ENHANCE
PRECIPITATION OVER OUR AREA THURSDAY INTO FRIDAY ALONG WITH AN
INCOMING COLD FRONT FROM THE WEST. GIVEN THE UNCERTAINTY ON THE
SYNOPTIC EVOLUTION AND ASSOCIATED DETAILS, WE KEPT POPS NO HIGH THAN
CHC.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG,KMIV, KACY AND SURROUNDING AREAS.

DETERIORATING CONDITIONS ARE EXPECTED FOR ALL TAF SITES FOR THE
REST OF THIS AFTERNOON AND THIS EVENING. CEILINGS HAVE ALREADY
FALLEN INTO THE MVFR RANGE FOR MOST SITES. THEY WILL CONTINUE TO
DROP THROUGH THIS EVENING AND MAY REACH IFR ESPECIALLY PHL AND
SOUTH. CONFIDENCE IS NOT VERY HIGH ON OCCURRENCE OR TIMING OF
IFR. HOWEVER IF IFR CIGS DO DEVELOP THEY MAY LAST FOR MOST OF THE
NIGHT EVEN THOUGH THE MOS GUIDANCE SUGGEST SOME IMPROVEMENT AFTER
MIDNIGHT. VSBY SHOULD NOT BE TOO MUCH OF AN ISSUE ALTHOUGH COULD
BE TEMPORARILY REDUCED IN SHOWERS THIS EVENING. CONDITIONS WILL
IMPROVE TO VFR SAT MORNING AND CONTINUE THROUGH THE DAY. WINDS
WILL REMAIN LIGHT OVERALL.

OUTLOOK...
SATURDAY NIGHT THROUGH MONDAY...THE CONDITIONS LOWER TO MVFR/IFR
SATURDAY NIGHT AND SUNDAY WITH PERIODS OF RAIN, THEN IMPROVE LATER
MONDAY WITH SOME SHOWERS STILL EXPECTED DURING MONDAY. A FEW
THUNDERSTORMS ARE POSSIBLE SUNDAY AFTERNOON AND EVENING, MAINLY
SOUTH OF KPHL. EAST OR SOUTHEAST WINDS 10 KNOTS OR LESS.

TUESDAY AND WEDNESDAY...VFR OVERALL AS WEAK HIGH PRESSURE ARRIVES.

&&

.MARINE...
NORTHEAST WIND WITH A FAIRLY LONG FETCH IS BLOWING INTO THE NJ
COASTAL WATERS. THIS RESULTS IN BUILDING SEAS WHICH HAVE REACHED 5
TO 6 FEET AT BUOYS 44009...91 AND 65. HIGHER SEAS ARE EXPECTED TO
CONTINUE THROUGH TONIGHT HENCE A SCA FOR HAZ SEAS HAS BEEN EXTENDED
UNTIL 600 AM SAT. THIS SCA MAY NEED TO BE EXTENDED FURTHER INTO THE
DAY ON SAT.

OUTLOOK...
SATURDAY NIGHT THROUGH MONDAY...NORTHEAST WINDS MAY BRIEFLY GUST TO
25 KNOTS ACROSS MAINLY THE NORTHERN ATLANTIC COASTAL WATERS SUNDAY
AHEAD OF LOW PRESSURE. WHILE SEAS SHOULD BE MOSTLY IN THE 2-4 FOOT
RANGE, TIMES OF 5 FOOTERS ARE POSSIBLE ON THE ATLANTIC COASTAL
WATERS.

TUESDAY AND WEDNESDAY...THE WINDS SHOULD BE BELOW SMALL CRAFT
ADVISORY CRITERIA, HOWEVER SEAS COULD BUILD TO 5 ABOUT FEET DURING
WEDNESDAY ON THE ATLANTIC COASTAL WATERS.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 AM EDT
     SATURDAY FOR ANZ450>455.

&&

$$
SYNOPSIS...GORSE
NEAR TERM...AMC
SHORT TERM...AMC
LONG TERM...GORSE
AVIATION...AMC/GORSE
MARINE...AMC/GORSE



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