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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 161742
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
142 PM EDT THU MAY 16 2013

.SYNOPSIS...
LOW PRESSURE WILL CONTINUE TO TRACK EASTWARD ACROSS NORTHERN NEW
ENGLAND THROUGH TODAY, THEN INTO THE CANADIAN MARITIMES TONIGHT
AND FRIDAY. AN ASSOCIATED COLD FRONT WILL SETTLE TO OUR SOUTH AND
STALL THROUGH THE WEEKEND INTO EARLY MONDAY. MEANWHILE, HIGH
PRESSURE BUILDS FROM EASTERN CANADA TO NEW ENGLAND FRIDAY AND
SATURDAY, BEFORE SETTLING SOUTHEASTWARD SUNDAY AND MONDAY. A WARM
FRONT IS THEN FORECAST TO LIFT NORTH OF OUR AREA DURING TUESDAY,
AS A COLD FRONT AND LOW PRESSURE SYSTEM TRACKS ACROSS THE GREAT
LAKES AND OHIO VALLEY WEDNESDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --
FOR THIS AFTERNOON, THE IDEA THAT ACTIVITY WOULD SLIDE FURTHER
SOUTH IS SUPPORTED BY CURRENT RADAR TRENDS. SURFACE BASED CAPE
VALUES ARE FORECAST TO INCREASE INTO THE 1000 TO 1500 J/KG RANGE
ACROSS OUR FAR SOUTHERN COUNTIES THIS AFTERNOON.

MEANWHILE, AREAS TO THE NORTH OF THE I-78 ARE EXPECTED TO REMAIN
RAIN FREE TODAY. THERE MAY BE A FEW CUMULUS AND A FAIR AMOUNT OF
CIRRUS OVERHEAD AT TIMES.

THE DAY WILL BEGIN RATHER MILD IN OUR REGION WITH TEMPERATURES
MAINLY IN THE 50S AND 60S. A WARM WESTERLY FLOW IS EXPECTED TO
CAUSE READINGS TO RISE INTO THE LOWER AND MIDDLE 80S AT MOST
LOCATIONS FOR THIS AFTERNOON (THE RISE WILL BE TEMPORARILY
DISRUPTED WHERE SHOWERS AND THUNDERSTORMS OCCUR). THE ONLY
EXCEPTIONS MAY BE THE ELEVATED TERRAIN UP NORTH WHERE TEMPERATURES
SHOULD PEAK IN THE MIDDLE AND UPPER 70S, AND LOCATIONS ALONG THE
IMMEDIATE COAST WHERE READINGS MAY REMAIN IN THE 60S AND 70S.
-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
A MID LEVEL TROUGH WILL REMAIN LOCATED OVER THE NORTHEASTERN
STATES FOR TONIGHT WITH AN IMPULSE PASSING OVERHEAD. THE IMPULSE
SHOULD HELP TO DRIVE A COLD FRONT SOUTHWARD THROUGH OUR REGION
DURING THE NIGHT.

THERE MAY BE A FEW LINGERING SHOWERS AND THUNDERSTORMS ACROSS OUR
FAR SOUTHERN COUNTIES THIS EVENING. HOWEVER, THE PRECIPITATION
WILL LIKELY SINK TO THE SOUTH. THE COLD FRONT SHOULD PASS THROUGH
OUR REGION WITHOUT ANY PRECIPITATION.

BEING THAT CONDITIONS WILL BE RATHER WARM TO START THE NIGHT, WE
HAVE FAVORED THE HIGHER END OF THE GUIDANCE TEMPERATURES FOR
TONIGHT`S MINIMA.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
THE OVERALL SYNOPTIC SETUP IS COMPRISED OF A TROUGH IN EASTERN
CANADA THAT GRADUALLY LIFTS OUT OF THE NORTHEAST FRIDAY AND
SATURDAY WITH A NORTHWESTERLY FLOW ALOFT OCCURRING. THE UPPER-
LEVEL FLOW THEN UNDERGOES AMPLIFICATION LATE IN THE WEEKEND AND
DURING THE FIRST HALF OF NEXT WEEK, AS A TROUGH EJECTS INTO THE
PLAINS ALLOWING DOWNSTREAM RIDGING TO TAKE PLACE. THIS GENERALLY
ALLOWS WARMING TO CONTINUE TO OCCUR INTO THE EAST, HOWEVER THE
RIDGE PLACEMENT ALLOWS SURFACE HIGH PRESSURE NEAR NORTHERN NEW
ENGLAND OVER THE WEEKEND TO SETTLE SOUTHWARD. THIS RESULTS IN AN
ONSHORE FLOW OCCURRING ACROSS OUR AREA, LEADING TO SOME COOLING
AND ALSO ADDITIONAL CLOUDS. THE PATTERN CONTINUES TO EVOLVE
THOUGH, AS THE RIDGE IS FORECAST TO TRANSLATE EAST ALLOWING A WARM
FRONT TO LIFT NORTHWARD TUESDAY. NOW THAT WE ARE IN THE WARM
SEASON, IT APPEARS THIS IS THROWING OFF THE MODELS SOME. AT LEAST
SOME OF THIS SEEMS TO BE TIED TO SOME GUIDANCE OVERDOING THE
SURFACE DEW POINTS. THIS COULD BE PLAYING A CONTINUED ROLE IN THE
GFS SHOWING MUCH MORE CONVECTION SATURDAY. WE ARE NOT REAL SURE
HOW THIS WILL TRANSLATE EAST WITH TIME, THUS POPS ARE ON THE LOWER
SIDE. THE UPPER-LEVEL TROUGH IN THE PLAINS THEN TRACKS EASTWARD,
DRIVING A SURFACE LOW AND COLD FRONT TOWARD OUR AREA WEDNESDAY. WE
USED A MODEL BLEND APPROACH FRIDAY INTO SUNDAY, THEN BLENDED A
DECENT AMOUNT OF NEW WPC GUIDANCE INTO CONTINUITY.

FOR FRIDAY...AN UPPER-LEVEL TROUGH ACROSS EASTERN CANADA WILL
MAINTAIN A NORTHWESTERLY FLOW ALOFT ACROSS THE REGION. THE MODEL
GUIDANCE INDICATES THAT THIS TROUGH STARTS TO LIFT NORTHEASTWARD
DURING THIS TIME AS RIDGING FROM THE MIDWEST STARTS TO SHIFT
EASTWARD. MEANWHILE, A SURFACE FRONT IS FORECAST TO BE STALLED
WELL TO OUR SOUTH. HIGH PRESSURE IS FORECAST TO START BUILDING
SOUTHWARD WHICH SHOULD PUSH THE SURFACE FRONT A BIT FURTHER SOUTH.
AS A RESULT, ANY CONVECTION SHOULD THEN REMAIN TO OUR SOUTH. WE
THEREFORE REMOVED THE SLIGHT CHC POPS ACROSS PORTIONS OF THE
DELMARVA. THE FLOW MAY BE LIGHT ENOUGH WITHIN THE BOUNDARY LAYER
TO RESULT IN SEA/BAY BREEZE CIRCULATIONS IN THE AFTERNOON.

FOR SATURDAY AND SUNDAY...HIGH PRESSURE CENTERED WELL TO OUR
NORTH AND NORTHEAST SATURDAY IS FORECAST TO SETTLE SOUTHWARD MORE
SUNDAY. THIS IS IN RESPONSE TO A TROUGH MOVING INTO THE PLAINS
WHICH DRIVES A RIDGE EASTWARD. THE TIMING AND POSITIONING OF THIS
SURFACE HIGH WILL HAVE AN IMPACT ON THE RETURN FLOW THAT
EVENTUALLY WILL SETUP. A WAA PATTERN SHOULD BE ONGOING UP THE OHIO
VALLEY DURING THIS TIME ALONG WITH AN INCREASING MOISTURE
GRADIENT. THIS WILL EVENTUALLY HELP TO TURN THE STALLED BOUNDARY
INTO A WARM FRONT. SOME GUIDANCE WANTS TO TOSS SOME CONVECTION
ACROSS A DECENT PORTION OF OUR AREA TIMES, HOWEVER WITH THE
SURFACE FRONT BEING FARTHER SOUTH IT MAY END UP PREVENTING THIS.
WE ARE NOT REAL CONFIDENT REGARDING ANY CONVECTIVE ORGANIZATION
SATURDAY. WE SHOULD ALSO HAVE AN ONSHORE FLOW OCCURRING DURING THE
WEEKEND, RESULTING IN COOLER TEMPERATURES /PROBABLY MORE CLOUDS/
ESPECIALLY CLOSER TO THE COAST. AS OF NOW, THE ONSHORE FLOW DOES
NOT LOOK TERRIBLY ROBUST THEREFORE WE HAVE LOWER CONFIDENCE FOR
THE POTENTIAL OF LOW CLOUDS INVADING THE CWA. WE MAINTAINED SOME
POPS NO HIGHER THAN LOW CHC GIVEN THE FRONTAL BOUNDARY POISED TO
OUR SOUTHWEST AND SOME GUIDANCE SHOWING AT LEAST SOME CONVECTIVE
POTENTIAL. HIGH TEMPERATURES ARE A LITTLE COOLER SUNDAY COMPARED
TO SATURDAY DUE TO THE ONSHORE FLOW THAT IS FORECAST. IF AN
ABUNDANCE OF CLOUDS PREVAIL IN COMBINATION WITH THE ONSHORE FLOW,
TEMPERATURES SHOULD BE COOLER THAN CURRENTLY FORECAST.

FOR MONDAY THROUGH WEDNESDAY...WE GENERALLY FOLLOWED CLOSER TO
WPC GUIDANCE WHICH HANGS THE WARM FRONT BACK A BIT. IT APPEARS THE
WARM FRONT LIFTS NORTH OF OUR CWA DURING TUESDAY, AS SURFACE LOW
PRESSURE ACROSS THE MIDWEST SLOWLY ADVANCES EASTWARD AS HIGH
PRESSURE DEPARTS. THERE MAY NOT BE MUCH WITH THE WARM FRONT, AS WE
THEN AWAIT FOR THE COLD FRONT TO APPROACH TUESDAY NIGHT AND
WEDNESDAY. GIVEN LOWER CONFIDENCE WITH THE TIMING AND CONVECTIVE
EVOLUTION, WE MAINTAINED MAINLY SLIGHT CHC TO LOW CHC POPS ACROSS
THE AREA. AS THE FLOW TURNS MORE SOUTH AND SOUTHWEST ALONG WITH
INCREASING WAA, TEMPERATURES ARE ANTICIPATED TO MODERATE A DECENT
AMOUNT DURING THIS TIME FRAME.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

SHOWER ACTIVITY HAD SLIPPED INTO THE MARYLAND EASTERN SHORE,
CENTRAL AND SOUTHERN DELAWARE AND FAR SOUTHERN NJ EARLY THIS
AFTERNOON. RADAR TRENDS SUGGEST THAT ONLY SOME LIGHT SHOWERS
THREATEN THE SOUTHEASTERN TAF SITES UNTIL AROUND DUSK. FURTHER
NORTH, THERE IS ONLY A SLIGHT CHANCE OF ANY ACTIVITY, AND SO ALL
THE TAFS ARE VFR.

THE LATEST MODELS SHOW WINDS PICKING UP FROM OUT OF THE WEST LATER
THIS AFTERNOON WITH SOME GUSTS ABOVE 20 KT POSSIBLE, THEN THEY
SHOULD RELAX BEFORE SHIFTING TO THE NORTH OVERNIGHT THANKS TO A
SECONDARY COLD FRONT. A SEA BREEZE HAD DEVELOPED AT ACY, BUT WE THINK
THE STRENGTHENING WEST WIND WILL OVERWHELM IT LATER THIS
AFTERNOON.

OUTLOOK...
FRIDAY...VFR. NORTHWESTERLY WINDS NEAR 10 KNOTS, TURNING
SOUTHEAST MAINLY AT KMIV AND KACY IN THE AFTERNOON BEFORE BECOMING
LIGHT AT NIGHT.

SATURDAY...MOSTLY VFR, HOWEVER AN ONSHORE FLOW MAY ALLOW FOR
INCREASING CLOUDS ALTHOUGH THE HEIGHT OF THE CLOUD BASES ARE OF
LOWER CONFIDENCE. A LOW CHANCE OF A SHOWER OR THUNDERSTORM IN THE
AFTERNOON AND EVENING. SOUTHEASTERLY WINDS NEAR 10 KNOTS.

SUNDAY AND MONDAY...MOSTLY VFR, HOWEVER AN ONSHORE FLOW MAY ALLOW
FOR LOWER CLOUDS TO OCCUR ALTHOUGH THIS IS OF LOWER CONFIDENCE. A
LOW CHANCE OF SOME SHOWERS AND THUNDERSTORMS ESPECIALLY EACH
AFTERNOON AND EVENING. SOUTHEASTERLY WINDS NEAR 10 KNOTS.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
ALTHOUGH WINDS ARE QUITE LIGHT OVER THE WATERS, A RESURGENT SWELL
ALONG THE FAR NORTHERN WATERS HAVE REQUIRED A SHORT-FUSED ADVISORY
FOR HAZARDOUS SEAS NORTH OF MANASQUAN INLET. MODELS SHOW THE SWELL
RETREATING BY THIS EVENING. THEN, CONDITIONS ARE EXPECTED TO
REMAIN BELOW THE SMALL CRAFT ADVISORY CRITERIA THROUGH TONIGHT. A
VARIABLE WIND FOR TODAY AND THIS EVENING IS FORECAST TO BECOME
NORTHERLY OVERNIGHT AS A COLD FRONT DROPS ACROSS THE COASTAL
WATERS OF NEW JERSEY AND DELAWARE.

OUTLOOK...
A FRONTAL BOUNDARY IS FORECAST TO REMAIN STALLED TO OUR SOUTH AS
HIGH PRESSURE BUILDS SOUTHWARD SOME FROM NEW ENGLAND. THIS SURFACE
HIGH WILL ALLOW A SOUTHEASTERLY FLOW TO OCCUR FRIDAY AFTERNOON AND
CONTINUE INTO EARLY NEXT WEEK. THE ONSHORE FLOW DOES NOT APPEAR TO
BE ALL THAT ROBUST, ALTHOUGH SOME ENHANCEMENT COULD TAKE PLACE AT
TIMES ESPECIALLY NEAR-SHORE AND UP DELAWARE BAY. WE MAINTAINED THE
WINDS BELOW ADVISORY CRITERIA, HOWEVER GIVEN THE WIND DIRECTION
THIS COULD BUILD THE SEAS TO AROUND 5 FEET DURING MONDAY. THE
WAVEWATCH GUIDANCE COULD BE ON THE HIGH SIDE AS IT IS TIED TO
STRONGER WINDS BY THE GFS, THEREFORE WE UNDERCUT THIS SOME FOR
MONDAY.
-- End Changed Discussion --

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 5 PM EDT THIS
     AFTERNOON FOR ANZ450.
-- End Changed Discussion --

&&

$$
SYNOPSIS...GORSE
NEAR TERM...IOVINO/DELISI
SHORT TERM...IOVINO
LONG TERM...GORSE
AVIATION...GORSE/IOVINO/DELISI
MARINE...GORSE/IOVINO/DELISI