-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 201944
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
344 PM EDT MON MAY 20 2013

.SYNOPSIS...
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A FRONTAL BOUNDARY WILL BE LOCATED NORTH OF THE REGION THROUGH
WEDNESDAY WITH HIGH PRESSURE OFFSHORE. A COLD FRONT WILL MOVE
THROUGH THE REGION THURSDAY INTO FRIDAY. THIS FRONT WILL BE
FOLLOWED BY A HIGH PRESSURE SYSTEM WHICH WILL BE IN PLACE THROUGH
HOLIDAY THE WEEKEND.
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&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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THE WARM FRONT IS NOW NORTH/EAST OF THE AREA AND OUR ENTIRE CWA IS
IN THE ARM SECTOR. SEVERAL HUMID DAYS ARE AHEAD WITH OVERNIGHT
PERIODS OF LOW CLOUDS/FOG AND THEN SLOW RECOVERY THE FOLLOWING DAY.
TONIGHT...MOSTLY CLOUDY SKIES LATE THIS AFTERNOON WILL TRANSITION TO
PARTLY CLOUDY BY SUNSET. RADIATIONAL COOLING AND THE HUMID AIR MASS
WILL LEAD TO PLENTY OF FOG AGAIN TONIGHT. A FEW SCT SHOWERS MAY
OCCUR THIS EVENING ACROSS THE DELMARVA OR SRN NJ...BUT THE CHCS ARE
RATHER LOW. OVERNIGHT LOWS WILL BE IN THE LOW 60S NORTH AND MID 60S
ACROSS THE CENTRAL AND SRN AREAS. WINDS WILL BE LIGHT MOSTLY FROM
THE S OR SW.
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&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
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HIGH PRESSURE WILL REMAIN WELL OFF THE COAST...PUMPING IN WARM AND
HUMID AIR ACROSS THE REGION. A WEAK UPPER LOW WILL BE MEANDERING
ACROSS VA/MD DURING THE DAY. UPPER (H5/H7) HEIGHTS WILL BE SLOWLY
BUILDING EARLY...THEN BEGINNING TO LOWER LATE.

SLOW IMPROVEMENT IN THE CIGS/VSBYS EXPECTED TUE. AREAS OF FOG WILL
DISSIPATE BY MID MORNING AND SKIES SHOULD BECOME PARTLY SUNNY BY
AFTERNOON. THERE WILL BE MORE INSTABILITY THAN TODAY...SO A CHC FOR
SHOWERS/TSTMS WILL BE KEPT IN THE FCST FOR TUE. HIGHS WILL CLIMB
INTO THE LOW 80S NORTH AND MID 80S ACROSS THE METRO PHILADELPHIA
AREA. WINDS WILL BE SOUTHWEST AT AROUND 10 MPH.
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&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
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A FRONTAL BOUNDARY WILL BE LOCATED NORTH OF THE REGION THROUGH
WEDNESDAY, WITH HIGH PRESSURE OFFSHORE. MOISTURE ADVECTION WILL
ALSO BE ABUNDANT INTO THE REGION. THIS ADVECTION, ALONG A WITH A
WARM AND MUGGY AIRMASS WILL CONTRIBUTE TO SOME INSTABILITY DURING
THE DAY WEDNESDAY. THE INSTABILITY MAY BE ON THE MAGNITUDE OF 1000
J/KG COUPLED WITH STEEP LAPSE RATES. SHEAR WILL BE VERY WEAK ON
WEDNESDAY WITH LIMITED STORM MOTIONS. PULSE TYPE CONVECTION MAY BE
POSSIBLE PARTICULARLY CLOSER TO THE FRONT DURING THE DAY. FEEL
THIS ACTIVITY WILL BE SCATTERED BUT THE DEGREE OF INSTABILITY MAY
ALLOW FOR A SCATTERED STRONG STORM. THE OVERALL LACK OF SHEAR WILL
LIMIT ANY SEVERE THREAT WEDNESDAY. WITH THE SCATTERED NATURE OF
CONVECTION HIGH TEMPERATURES MAY DIFFER IN SPOTS. HAVE GONE ON THE
WARM SIDE GIVEN THE STRONG SOUTHWEST FLOW INTO THE REGION.

A COLD FRONT WILL APPROACH THE REGION ON THURSDAY AND RIGHT NOW
THE BEST TIMING FOR FRONTAL PASSAGE IS LATER THURSDAY. AS USUAL
THIS MAY NEED TO BE ADJUSTED AS WE GET CLOSER. RAISED POPS TO HIGH
CHANCE BASED ON CURRENT TIMING. THOUGH SEVERAL OF THE GFS ENSEMBLE
MEMBERS AND THE 12Z ECMWF HINT THE FRONT MAY BE A TOUCH SLOWER
THAN MODEL FCSTS. WENT COOLER ON TEMPERATURES THURSDAY DUE TO
CLOUD COVER. THIS MAY ALSO LIMIT THE INSTABILITY POTENTIAL
THURSDAY AHEAD OF THE FRONT THOUGH SLOWER TIMING COULD LEAD TO A
MORE UNSTABLE ENVIRONMENT. OVERALL WENT WITH ELEMENTS OF THE SREF
AND WPC FOR QPF FOR THE FRONTAL PASSAGE. OVERALL, THURSDAY LOOKS
TO HAVE THE HIGHEST POPS.

BEHIND THE FRONT, STRONG HIGH PRESSURE WILL BUILD IN WITH MORE
SUNSHINE AND COOLER TEMPERATURES. HIGHS GENLY IN THE LOWER TO MID
70S, LIGHT WINDS AND SUNNY SKIES ARE LIKELY TO DOMINATE THE
HOLIDAY WEEKEND! DID NOT STRAY MUCH FROM GUIDANCE HERE. THINK THE
GFS MAY BE TO QUICK WITH ANY SYSTEM THAT COMES IN NEXT MONDAY.
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&&

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

THE LONG SLOW CLIMB BACK TO VFR HAS CONTINUED IN MOST AREAS...A FEW
HIGH-END MVFR STILL AT 18Z. DRIER AIR HAS ARRIVED ON A SWRLY/WRLY
FLOW ALOFT...SO CONDITIONS ARE A BIT BETTER TODAY WHEN COMPARED TO
SUNDAY. WINDS HAVE BEEN SOUTHWEST AT 5 TO 10 KNOTS FOR THE MOST
PART.

CONDITIONS WILL LOWER AGAIN TONIGHT IN FOG AND SOME ST AS THE HUMID
AIRMASS REMAIN IN PLACE. IF HAVE FOLLOWED THE LAMP GUIDANCE FOR THE
MOST PART WITH WIDESPREAD IFR EXPECTED AGAIN. CONDITIONS WILL AGAIN
BE SLOW TO IMPROVE TUE MORNING...BUT EVENTUALLY VFR BY AFTERNOON.
SCT AFTERNOON SHOWERS/TSTMS POSSIBLE BUT NOT INCLUDED IN THE 18Z MON
TAFS.


OUTLOOK...
WEDNESDAY... MAINLY VFR WITH THE POTENTIAL FOR SCATTERED SHOWERS AND
THUNDERSTORMS AT ALL TAF SITES IN THE AFTERNOON TO REDUCE CONDITIONS
TO MVFR OR IFR FOR BRIEF PERIODS. SOUTHWEST WINDS 5 TO 10 KNOTS.

THURSDAY.... VFR TO MVFR IN SHOWERS AND A FEW THUNDERSTORMS.
SOUTHWEST WINDS 5 TO 15 KNOTS TURNING TO THE WEST AT NIGHT.  BEST
CHC FOR SHWRS AND TSTMS THIS WEEK OCCURS THU.

FRIDAY AND SATURDAY... VFR WITH HIGH PRESSURE BUILDING IN AND WINDS
BECOMING LIGHT NORTH OR VARIABLE.
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&&

.MARINE...
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LOOKS LIKE THE SCA CONDITIONS ON THE OCEAN WATERS HAVE JUST ABOUT
ENDED. IT HAS BEEN A VERY LOW-END EVENT AND WITH THE WARM AIR OVER
THE COLD WATERS AND THE DECREASING P-GRADIENT...IT APPEARS THAT A
PERIOD OF SUB-SCA CONDITIONS WILL BE OVER THE WATERS. THE FLAG WILL
BE DROPPED WITH THE 330 PM CWF ISSUANCE. IT APPEARS THE THE SW WINDS
WILL CONTINUE ON THE WATERS TONIGHT THROUGH TUESDAY. THERE MAY BE
AREAS OF FOG ON THE WATERS TONIGHT AND SCAT SHOWERS/TSTMS TUE
AFTERNOON.

OUTLOOK...
SEAS AND WINDS WILL BE BELOW SCA TILL EARLY WEDNESDAY. SEAS ARE
EXPECTED TO BE AT LEAST 5 FEET FROM WEDNESDAY MORNING TILL EARLY
FRIDAY. SEAS AND WINDS WILL DECREASE FRIDAY. WIND WILL ALSO
INCREASE AS THE CDFNT APPROACHES BY THU.  A SCA WILL LIKELY BE
NEEDED FOR A PORTION OF THIS TIME FRAME.
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&&

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

$$
SYNOPSIS...GAINES/NIERENBERG
NEAR TERM...O`HARA
SHORT TERM...O`HARA
LONG TERM...GAINES/NIERENBERG
AVIATION...GAINES/NIERENBERG/O`HARA
MARINE...GAINES/NIERENBERG/O`HARA