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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 182151
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
551 PM EDT SAT MAY 18 2013

.SYNOPSIS...
A STATIONARY FRONT TO OUR SOUTHWEST IS FORECAST TO SLOWLY DISSIPATE
THROUGH MONDAY. HIGH PRESSURE TO OUR NORTHEAST WILL DROP SOUTH AND
TAKE ON THE CHARACTERISTICS OF A BERMUDA HIGH. A FRONTAL BOUNDARY
FROM THE NORTH WILL APPROACH OUR AREA ON TUESDAY AND STALL NEARBY.
THE FRONT MAY LIFT BACK NORTH LATER IN THE WEEK. A COLD FRONT
APPROACHING FROM THE WEST MAY CROSS OUR AREA LATE IN THE WEEK.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
-- Changed Discussion --
WITH THE EARLY EVENING UPDATE, WE INCREASED POPS FROM EAST-CENTRAL
PA INTO CENTRAL NJ TO REFLECT THE STEADIER, SCATTERED SHOWERS
CURRENTLY PASSING THROUGH THESE AREAS. QPF AMOUNTS WERE ALSO
RAISED SOME, AS A FEW HUNDREDTHS OF AN INCH OF RAIN ARE EXPECTED
FOR THESE AREAS. SLIGHT CHANCE POPS WERE LEFT IN PLACE FOR THE
SOUTHERN POCONOS AND NORTHERN NJ, AND THESE AREAS WILL LIKELY HAVE
A BREAK IN MEASURABLE PRECIP FOR THE NEXT FEW HOURS. PRECIP
COVERAGE THROUGH THE LATE EVENING HOURS WAS ADJUSTED TO REFLECT
SCATTERED SHOWERS, AND THE TIMING OF INCREASING POPS FROM SOUTH TO
NORTH LATER TONIGHT LOOKS REASONABLE AS COMPARED TO THE HRRR,
WHICH WAS REFLECTING CURRENT RADAR TRENDS FAIRLY WELL. WE ALSO
ADJUSTED HOURLY TEMPERATURES AND DEWPOINTS THROUGH THIS EVENING
ACCORDINGLY TO REFLECT CURRENT TRENDS, INCLUDING WHERE SHOWERS
HAD PASSED THROUGH.

OTHERWISE, HIGH PRESSURE TO THE NORTH/EAST AND AN APPROACHING
WARM FRONT TO THE WEST WILL CREATE DETERIORATING WEATHER
CONDITIONS ACROSS THE AREA TONIGHT. THE GFS MODEL BRING SHOWERS TO
THE EXTREME NORTH EARLY TONIGHT THEN LIGHT SHOWERS TO ALL AREAS
AFTER MIDNIGHT. THE NAM IS MORE ROBUST WITH THE QPF AND BRINGS IT TO
MOST AREAS BY MIDNIGHT AND MAKES IT LAST INTO SUNDAY. WE HAVE
FOLLOWED A BLENDED APPROACH WITH LOW LIKELY POPS TO MOST AREAS
TONIGHT. THE ONSHORE FLOW WILL KEEP CONDITIONS MILD...SO THE LOWS
WILL MOSTLY BE IN THE UPPER 50S/LOW 60S SOUTH AND LOW TO MID 50S
NORTH. WINDS WILL CONTINUE FROM THE E/SE AT AROUND 10 MPH.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
THE FRONT WILL BE SLOW TO CROSS THE AREA. A WEAK UPPER LOW WILL ALSO
BE INTERACTING WITH THE FRONT...SO ANOTHER DAY OF ABUNDANT
CLOUDINESS AND SCATTERED SHOWERS IS EXPECTED. WE WILL KEEP THE LOW
LIKELY POPS ACROSS THE AREA EARLY...THEN LOWER THEN AFTER THAT. THIS
IS MORE LIKE THE NAM STAT GUIDANCE...BUT CONFID IN THE AMOUNT/QPF
FOR SUNDAY IS RATHER LOW ATTM. HIGH TEMPERATURES WILL MOSTLY BE IN
THE MID TO UPPER 60S FAR NORTH...LOW 70S CENTRAL AREAS AND PERHAPS
INTO THE MID OR UPPER 70S FAR SOUTH...ESPECIALLY IF ANY BREAKS
DEVELOP IN THE CLOUDS LATE.  QPF FCST...MOSTLY 1/10 TO 1/4 INCH WITH
THE HIGHER TOTALS ACROSS THE DELMARVA.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
THE MID LEVELS STILL START WITH A VORTEX OVER EASTERN CANADA, A
RIDGE BUILDING FROM THE WESTERN ATLANTIC AND A LOW CROSSING THE
ROCKIES. THERE ALSO ARE THE REMAINS OF THE LOW THAT CAUSED THE SPLIT
FLOW EARLIER THIS WEEK, AND THEY ARE FORECAST TO MOVE SLOWLY TOWARD
AND THEN ACROSS OUR AREA INTO TUESDAY. IT LOOKS THOSE REMAINS AND
THE VORTEX TO THE NORTH WILL COMBINE TO KEEP THE RIDGE FROM BUILDING
TOO MUCH UP THE EASTERN SEABOARD THROUGH THE FIRST PART OF THE LONG
TERM, AND THEN THE LOW APPROACHING FROM THE WEST WILL BEGIN TO PUSH
THE RIDGE TO THE EAST. THAT LOW IS EXPECTED TO OPEN DURING THE
MID-WEEK PERIOD AND EVENTUALLY CROSS OUR LONGITUDE. WHETHER IS DOES
SO BEFORE THE END OF THE LONG TERM IS UP IN THE AIR. THE GFS KEEPS
SOMETHING OF A REX BLOCK OVER THE CENTER OF THE NATION GOING INTO
THURSDAY, AND IS THEREFORE NOT AS PROGRESSIVE AS THE ECMWF. THE 12Z
GEFS SUPPORT THE OPERATIONAL GFS, AND THE 00Z ECMWF ENSEMBLES
SUPPORT THE OPERATIONAL 00Z AND 12Z ECMWF. WE THEREFORE HAVE SIDED
WITH THE FORECAST FROM HPC, WHICH LEANS TOWARD THE LATTER SUITE AND
MAINTAINS DECENT CONTINUITY.

THE MODELS AGREE ON GRADUALLY MOVING THE CENTER OF SURFACE HIGH
PRESSURE FROM NORTH OF 40N TO SOUTH OF IT, AND THAT TRANSITIONS US
FROM A MARITIME FLOW WITH AN EASTERLY COMPONENT TO A MORE SOUTHERLY
AND HUMID FLOW AND A MORE (ESPECIALLY AWAY FROM THE OCEAN) UNSTABLE
FLOW. THE VORTEX TO THE NORTH STILL TRIES TO PUSH A COLD FRONT DOWN
INTO OUR AREA AROUND TUESDAY NIGHT, AND IT MAY STALL NEARBY. ALL THIS
WILL SEND US FROM A PERIOD OF SHOWERS TO A PERIOD WHEN THUNDERSTORMS
ARE POSSIBLE. AT THIS POINT, WE REALLY CAN`T CARVE OUT A TIME PERIOD
WHEN WE AREN`T CARRYING A CHANCE OF THUNDERSTORMS UNTIL THE SYSTEM
FROM THE WEST MOVES THROUGH WITH A SURFACE COLD FRONT. SINCE WE HAVE
SIDED WITH THE MORE PROGRESSIVE SOLUTION, OUR POPS DO DROP BELOW
CHANCE BY SATURDAY. AS NOTED BY THE PREVIOUS LONG TERM FORECASTER,
THUNDERSTORM ACTIVITY WILL NOT BE CONSTANT. IN THE ABSENCE OF ANY
FOCUSED ENERGY KICKING OUT OF THE SYSTEM TO THE WEST, ACTIVITY WOULD
BE MOST LIKELY DURING THE AFTERNOON AND EVENING HOURS.

NIGHTS ARE FORECAST TO BE WARMER THAN NORMAL AND RATHER HUMID UNTIL
THE FRONTAL PASSAGE TOWARD THE WEEKEND. DAYS ARE ALSO FORECAST TO BE
HUMID, WITH TEMPERATURES STARTING AROUND NORMAL BUT RISING TO ABOVE
NORMAL FOR MUCH OF THE WEEK. IF THE REMNANTS OF THE MID LEVEL LOW
PASS US IN TIME ON TUESDAY, THEN THAT MAY BE THE WARMEST DAY OF THE
LONG TERM. WE PRESENTLY ARE FORECASTING DRIER AND COOLER AIR FOR THE
END OF THE PERIOD.

&&

.AVIATION /22Z SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

A WEALTH OF MID LEVEL CLOUDS ARE ACROSS THE TERMINALS AT LATE DAY
WITH MOSTLY LIGHT WINDS. THESE VFR CONDITIONS WILL PROBABLY
CONTINUE INTO THE EARLY EVENING BEFORE POORER CONDITIONS ARRIVE.
THE PERSISTENT ONSHORE FLOW WILL BRING DEEPER MOISTURE THIS
EVENING AND THEN OCCASIONAL SHOWERS TONIGHT INTO SUNDAY. WE HAVE
SPED UP THE TIMING OF THE LOWER CONDITIONS BY A FEW HOURS WHEN
COMPARED TO THE PREVIOUS TAFS. BOTH THE GFS AND NAM ARE SHOWING
THE DETERIORATING CIGS/VSBYS...SO CONFID IN THEM OCCURRING IS
GOOD...BUT THE TIMING IS STILL SOMEWHAT UNCERTAIN. LOOKS LIKE THE
LOW CIGS/VSBYS WILL CARRY ON INTO SUNDAY...SO I FAILED TO WRITE IN
ANY IMPROVEMENT AFTER 12Z ANYWHERE. WINDS SHOULD REMAIN MOSTLY
ERLY/SERLY AT 5 TO 10 KTS IN MOST AREAS.

OUTLOOK...
SUNDAY NIGHT...MAINLY MVFR CEILINGS WITH POSSIBLE IFR CONDITIONS AT
TIMES. A CHANCE OF SHOWERS. CONFIDENCE IS MODERATE.

MONDAY THROUGH THURSDAY...MAINLY VFR CONDITIONS FROM LATE MORNING
THROUGH THE EVENING. THERE WILL BE A CHANCE OF SHOWERS AND
THUNDERSTORMS WHICH COULD LOWER CEILINGS AND REDUCE THE VISIBILITY,
AND THEY ARE SOMEWHAT MORE LIKELY IN THE AFTERNOON AND EVENING.
ALSO, MVFR AND IFR CONDITIONS ARE POSSIBLE ESPECIALLY DURING THE
LATE NIGHT AND EARLY MORNING HOURS. CONFIDENCE IS MODERATE.
-- End Changed Discussion --

&&

.MARINE...
THE ONSHORE FLOW BETWEEN THE HIGH WELL OFF TO THE NORTHEAST AND THE
APPROACHING FRONT TO THE WEST WILL CAUSE WINDS (AND THEN SEAS) TO
SLOWLY INCREASE TONIGHT INTO SUNDAY. IT APPEARS THAT SEAS WILL REACH
SCA CRITERIA (5 FT) ACROSS THE SRN WATERS FIRST (TONIGHT) AND THEN
ACROSS THE NRN COASTAL WATERS SUNDAY. WE WILL ISSUE SCA FLAGS TO
COVER THIS EXPECTED INCREASE IN SEAS. SCA FLAGS WILL EXTEND THRU
SUNDAY FOR NOW. SPRINKLES THIS EVENING THEN SCATTERED/OCNL SHOWERS
OVERNIGHT AND SUNDAY.

OUTLOOK...
SUSTAINED WINDS ARE FORECAST TO REMAIN BELOW 25 KNOTS THROUGH
WEDNESDAY NIGHT, ALTHOUGH THERE MAY BE SOME OCCASIONS WHEN 25 KNOT
GUSTS OCCUR MAINLY ON MONDAY. WINDS MAY BEGIN TO INCREASE AGAIN ON
THURSDAY. SEAS ON OUR OCEAN WATERS ARE FORECAST TO REMAIN AT AROUND
5 FEET THROUGH MONDAY NIGHT. THEY MAY REMAIN THERE LONGER IN THE
SOUTH TO SOUTHWEST FLOW, ALTHOUGH THAT FLOW IS FORECAST TO RELAX SOME
FOR THE MID-WEEK PERIOD.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 6 AM SUNDAY TO 6 AM EDT MONDAY FOR
     ANZ450>452.
     SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 6 AM EDT
     MONDAY FOR ANZ453>455.

&&

$$
SYNOPSIS...DELISI
NEAR TERM...KLINE/O`HARA
SHORT TERM...O`HARA
LONG TERM...DELISI
AVIATION...DELISI/O`HARA
MARINE...DELISI/O`HARA