-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 171940
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
340 PM EDT FRI MAY 17 2013

.SYNOPSIS...
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A FRONTAL BOUNDARY WILL REMAIN STALLED TO OUR SOUTH THROUGH THE
UPCOMING WEEKEND. THE BOUNDARY IS EXPECTED TO RETURN NORTHWARD AS A
WARM FRONT LATE MONDAY INTO TUESDAY. THE FRONT MAY SAG BACK
SOUTHWARD TOWARD OUR AREA TUESDAY INTO WEDNESDAY AND COMBINE WITH A
BACKDOOR FRONT THAT SAGS SOUTH TOWARD OUR AREA FROM SOUTHERN
CANADA. THIS FRONT MAY WOBBLE NEAR OUR AREA OR JUST NORTH OF THE
AREA WEDNESDAY INTO THURSDAY, BEFORE A COLD FRONT PUSHES THROUGH
THE AREA LATE THURSDAY INTO EARLY FRIDAY.
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&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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WE EXPECT TO START THE PERIOD WITH DRY AIR, MAINLY CLEAR SKIES AND
LIGHT WINDS. BY THE END OF THE PERIOD, IT`S LIKELY THAT AT LEAST A
FAIR AMOUNT OF MID LEVEL CLOUDS WILL BE OVER THE AREA. WE ALLOWED
FOR SOME RADIATING TO OCCUR DURING THE FIRST PART OF THE NIGHT, AND
SO WE LEANED TOWARD THE COOLER SIDE OF STAT GUIDANCE.

THE U.S. MODELS BRING A LITTLE BIT OF RAIN IN ON THE DEVELOPING
ALBEIT MODEST EASTERLY SURFACE FLOW, A SLOWLY MOISTENING H8 SOUTHERLY
FLOW AND THE GRADUAL WEAKENING OF THE SHORT WAVE RIDGE OUT AHEAD OF
THE MID LEVEL LOW. THE ECMWF STOPPED THE ADVANCE OF RAIN JUST AT OUR
SOUTHWESTERN DOORSTEP. THE CANADIAN IS THE SLOWEST OF THE FOUR TO
MOVE RAIN NORTHEAST. WE KEPT THE FORECAST THROUGH 10Z DRY.
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&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
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THE MID LEVEL LOW WILL CONTINUE TO MOVE SLOWLY TOWARD THE AREA AND
THE MID LEVEL HIGH WILL CONTINUE TO WEAKEN SLOWLY, BUT THERE ARE
STILL SIGNS OF IT JUST TO OUR WEST BY THE END OF THE DAY. WE ONLY
BRING IN SLIGHT CHANCE TO CHANCE POPS DURING THE COURSE OF THE DAY
SOUTHWEST, AND THAT IS LARGELY IN KEEPING WITH CONTINUITY. WE DO
PUSH THE SLIGHT CHANCE POPS FURTHER NORTH OVER OUR WESTERN ZONES AS
PERHAPS ENERGY MOVING OUT OF THE GREAT LAKES CAN TRIGGER SOMETHING
THERE; OTHERWISE THERE`S SOME WEAK ISENTROPIC LIFT AT I295 TO I300K
TO GO WITH THE GRADUAL INCREASE IN LOW LEVEL MOISTURE. THUNDER DOES
NOT SEEM TO BE A CONCERN THIS FAR NORTHEAST. GIVEN THE EXPECTED
CLOUDINESS AND THE MODEST ONSHORE SURFACE FLOW, WE CONTINUE TO
FORECAST COOLER TEMPERATURES ON SATURDAY.
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&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
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HIGH PRESSURE BUILDS OFF THE NEW ENGLAND COAST SATURDAY NIGHT AND
PUSHES WELL TO OUR EAST THROUGH EARLY NEXT WEEK. THE FRONTAL
BOUNDARY TO OUR SOUTH WILL REMAIN NEARLY STATIONARY THROUGH SUNDAY,
THEN AS THE HIGH BUILDS TO OUR EAST, THE FRONT SHOULD BEGIN MOVING
BACK NORTHWARD AS A WARM FRONT. THE WARM FRONT SHOULD PASS THROUGH
OUR AREA LATE MONDAY INTO TUESDAY, THEN MAY COMBINE WITH A BACKDOOR
FRONT SINKING SOUTHWARD FROM SOUTHERN CANADA. THIS FRONT MAY WOBBLE
SOMEWHERE NEAR OUR AREA, OR JUST NORTHWARD WEDNESDAY INTO THURSDAY,
BEFORE A COLD FRONT PUSHES THROUGH THE AREA LATE THURSDAY INTO
EARLY FRIDAY.

SUNDAY LOOKS TO BE THE COOLEST DAY WITH THE ONSHORE FLOW EXPECTED
WITH HIGH PRESSURE TO OUR NORTHEAST. HOWEVER, TEMPERATURES WILL
SLOWLY RISE THROUGH MID-WEEK AS THE WARM FRONT MOVES THROUGH THE
AREA, AND THICKNESSES INCREASE. TUESDAY AND WEDNESDAY ARE EXPECTED
TO BE THE WARMEST DAYS IN THE FORECAST, THEN COOLING TEMPERATURES
TOWARD LATE WEEK.

THE EXTENDED PERIOD HAS THE POTENTIAL TO BE RATHER UNSETTLED WITH
THE FRONTAL BOUNDARIES MEANDERING THEIR WAY BACK AND FORTH ACROSS
THE AREA AND THE LIKELIHOOD OF SEVERAL SHORT WAVES/VORT MAXES
TRAVERSING THE AREA AS WELL. WITH THE UNCERTAINTY OF THE TIMING OF
EACH EVENT, WE WILL KEEP A CHANCE OF PRECIPITATION IN THE FORECAST
EACH DAY WITH THE GREATEST PROBABILITIES TIED TO THE POSSIBLE
FRONTAL PASSAGES AND VORT MAXES CURRENTLY FORECAST. THUNDERSTORMS
ARE POSSIBLE EACH DAY FROM MONDAY THROUGH THURSDAY AS THERE IS
INSTABILITY BEING FORECAST. SUNDAY WOULD MORE LIKELY BE SHOWERS AS
NO INSTABILITY IS CURRENTLY FORECAST.
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&&

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

VFR CONDITIONS ARE FORECAST THROUGH THE TAF PERIOD. A SEA/BAY BREEZE
IS FORECAST FOR ACY AND ILG LATE THIS AFTERNOON, THEN A LIGHT EAST
TO SOUTHEAST FLOW IS EXPECTED TO DEVELOP AND INCREASE SLIGHTLY
DURING THE DAY ON SATURDAY. WE EXPECT NO VISIBILITY RESTRICTIONS
THROUGH THE TAF PERIOD. A RULE OF THUMB IS THAT WE NEED ABOUT 18
HOURS OF AN ONSHORE FLOW BEFORE WE START TO SEE EITHER STRATUS OR
FOG. WE DON`T EXPECT TO HAVE THAT BY 18Z SATURDAY/00Z SUNDAY. WE
START THE BEGINNING OF THE TAF PERIOD WITH CLEAR SKIES OR CIRRUS,
AND GRADUALLY HIGH AND THEN MID LEVEL CLOUDS ARE FORECAST TO INVADE.

OUTLOOK...
SATURDAY NIGHT...MAINLY VFR WITH LOWERING CLOUDS. A CHANCE OF
SHOWERS.

SUNDAY-MONDAY NIGHT...SUB-VFR CONDITIONS POSSIBLE, ESPECIALLY WITH
ANY SHOWERS, OR THUNDERSTORMS MONDAY.

TUESDAY-WEDNESDAY...GENERALLY VFR, POSSIBLE MVFR CIGS/VSBYS,
ESPECIALLY WITH ANY SHOWERS/THUNDERSTORMS.
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&&

.MARINE...
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WE ARE FORECASTING SUB-ADVISORY WINDS AND SEAS THROUGH THE DAYLIGHT
PORTION OF SATURDAY. LIGHT WINDS WILL DEVELOP A SOUTHEASTERLY
COMPONENT OVERNIGHT AND INCREASE A BIT ON SATURDAY, BUT NOT ENOUGH
TO REQUIRE AN ADVISORY. SEAS WILL INCREASE A BIT AS WINDS DO.

OUTLOOK...
AS HIGH PRESSURE CONTINUES BUILD ACROSS THE NORTHEAST SATURDAY NIGHT
AND OFFSHORE SUNDAY INTO MONDAY, WINDS MAY APPROACH SMALL CRAFT
LEVELS AS THE PRESSURE GRADIENT TIGHTENS. ALSO, SEAS COULD APPROACH
5 TO 6 FEET SUNDAY INTO MONDAY AS A STEADY SOUTHEAST FLOW DEVELOPS.
ALTHOUGH WINDS MAY NOT REACH ADVISORY LEVELS AS WE GO INTO TUESDAY
AND WEDNESDAY AS THE PRESSURE GRADIENT WEAKENS, WINDS COULD STILL
GUST NEAR 20 KNOTS, AND SEAS MAY REMAIN NEAR 5 TO 6 FEET.
-- End Changed Discussion --

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...ROBERTSON
NEAR TERM...DELISI
SHORT TERM...DELISI
LONG TERM...ROBERTSON
AVIATION...DELISI/ROBERTSON
MARINE...DELISI/ROBERTSON