AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
243 PM EDT THU JUL 7 2011

.SYNOPSIS...
A WEAK FRONT WILL REMAIN ACROSS CENTRAL NEW JERSEY AND SOUTHEAST
PENNSYLVANIA THIS AFTERNOON AND EVENING. THIS WILL BRING A CHANCE
OF SHOWERS AND THUNDERSTORMS THROUGH FRIDAY. HIGH PRESSURE WILL
PUSH THE FRONT AWAY TO THE SOUTHEAST BY SATURDAY MORNING AND WILL
BRING FAIR BUT WARM WEATHER FOR THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
SATELLITE IMAGES SHOW MOSTLY CLR SKIES ACROSS THE AREA AS OF THE
LATE MORNING. THE WEAK FRONT IS ACROSS NRN AND CNTRL NJ THEN
ACROSS SE PA ATTM. HIGHER DEW POINTS AND CAPE VALUES EXIST TO THE
SOUTH OF THE FRONT. THE DAYTIME HEATING WILL TRIGGER SCATTERED
SHOWERS/TSTMS ALONG THE FRONT THIS AFTERNOON WITH LOCAL DOWNPOURS
AND GUSTY WINDS NEAR THE CONVECTION. HEAVY DOWNPOURS MAY CREATE
LOCALIZED FLOODING CONCERNS...ESPECIALLY IF THEY FORM WHERE THEY
OCCURRED YESTERDAY (NRN BURLINGTON AND SRN MERCER COUNTIES).

MOST OF THE ACTIVITY WILL DIMINISH THIS EVENING WITH THE LOSS OF
DAYTIME HEATING AND PATCHY FOG WILL DEVELOP OVERNIGHT...ESPECIALLY
IN AREAS THAT RECEIVE RAIN TODAY. OVERNIGHT LOWS WILL BE VERY WARM
AND THE HUMIDITY WILL BE HIGH.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
BY THURSDAY NIGHT...THE SFC FRONT/TROF WILL STILL BE MORE OR LESS
IN PLACE ALTHO IT MAY SAG SWD A BIT. ANOTHER UPPER LVL SHRTWV TROF
IS FCST TO APPROACH FROM THE OH VLY WHICH WILL BEGIN TO PROVIDE
SOME LARGE-SCALE LIFT AND POTENTIALLY OVER-RUNNING ALONG THE
FRONT. WE HAVE MAINTAINED CHC POPS INTO THE OVERNIGHT PERIOD
TONIGHT AND ACTUALLY HAVE THEM INCRG TOWARDS FRI MORN.

FOR FRIDAY...MORE WIDESPREAD SHOWER/T-STORM ACTIVITY IS EXPECTED AS
GENERAL UVV CONTS AHEAD OF THE SHRTWV...ALSO AIDED BY DVLPMT OF AN
UPPER LEVEL JET MAX OVER NEW ENGLAND. ALTHO THE FRONT COULD SAG
SWD A BIT...SOME INSTBY SHOULD CONT N OF THE FRONT...PERHAPS SMWHT
ELEVATED. INDUCED LOW PRESSURE WILL TRACK ALONG THE FRONT LATER
FRIDAY INTO FRIDAY NIGHT. THE FORECAST POPS SHOW INCRG CHCS IN THE
MORNING BECOMING LIKELY BY LATE AFTN INTO EARLY EVENING.
CONSIDERABLE CLOUD COVER WILL TEND TO HOLD FRIDAY MAX TEMPS IN THE
MID 70S TO MID 80S FOR MOST AREAS.

FRIDAY NIGHT SHOULD SEE SOME T-STORM ACTVTY LINGERING INTO THE EVE
BUT THEN SHIFT OFFSHORE OVERNIGHT AS THE UPPER TROF PASSES AND
FLOW ALOFT BECOMES NWLY. HIGH PRESSURE WILL BUILD IN FOR
SATURDAY...ALTHO THE ASSOCD AIR MASS APPEARS TO BE ONLY SLIGHTLY
COOLER AND DRIER.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
THE NORTHERN FLOW REMAINS ACTIVE DURING THIS TIME FRAME AS
RIDGING REMAINS MOSTLY INTACT ACROSS THE SOUTHERN STATES. THIS
PATTERN REGIME WILL ALLOW SYSTEMS TO SLIDE ACROSS THE NORTHERN
TIER OF STATES WITH THEIR ASSOCIATED COLD FRONTS MOVING THROUGH
BUT THEN STALLING SOUTHWARD DUE TO THE RIDGING. THE ECMWF ENSEMBLE
MEAN HAS BEEN SHOWING GOOD CONTINUITY FOR QUITE SOME TIME. HPC
BLENDED IN THE LATEST ECMWF ENSEMBLE MEAN WITH THE PREVIOUS ONE.
WE INITIALIZED THE DATABASE WITH HPC GUIDANCE THEN MADE SOME
TWEAKS AFTER ADDITIONAL COLLABORATION WITH OUR NEIGHBORING
OFFICES.

BASED ON THE ABOVE, HIGH PRESSURE ACROSS THE AREA SATURDAY NIGHT AND
SUNDAY WILL EVENTUALLY SLIDE TO OUR EAST. THE MOISTURE AND THERMAL
ADVECTION ON THE BACKSIDE OF THIS HIGH AND AHEAD OF A COLD FRONT
SHOULD ALLOW A STALLED FRONT TO OUR SOUTH TO WORK NORTHWARD AS A
WARM FRONT MONDAY. AT THIS POINT, THERE DOES NOT LOOK LIKE MUCH OF A
TRIGGER FOR CONVECTION WITH THE WARM FRONT ITSELF. THE COLD FRONT
SETTLES ACROSS OUR AREA MONDAY NIGHT INTO TUESDAY, BUT WILL PROBABLY
TEND TO SLOW ITS SOUTHWARD MOVEMENT TUESDAY DUE TO BECOMING REMOVED
FROM THE STRONGER FLOW AND RIDGING FARTHER TO THE SOUTH. AS HIGH
PRESSURE MOVES ACROSS THE GREAT LAKES REGION TUESDAY AND WEDNESDAY,
THIS SHOULD PUSH THE FRONT SOUTH OF OUR DELMARVA ZONES. WE WILL
BRING IN SOME SLIGHT CHC POPS ACROSS OUR NORTHWEST ZONES MONDAY THEN
EXPAND THIS ALONG WITH LOW CHC POPS MONDAY NIGHT AND TUESDAY AS THE
FRONT ARRIVES. WE HELD ONTO SOME SLIGHT CHC POPS WEDNESDAY MAINLY
ACROSS PORTIONS OF OUR DELMARVA ZONES IN THE EVENT THE FRONT DOES
NOT SETTLE FAR ENOUGH SOUTH. THIS PATTERN LOOKS TO FAVOR WARM TO HOT
CONDITIONS THROUGH THE ENTIRE TIME FRAME, AND WE DID NOT MAKE ANY
SIGNIFICANT CHANGES TO THE HPC TEMPERATURE GUIDANCE.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

TODAY...VFR SCT CU NEAR 6000 WITH BRIEF IFR CONDS IN ISO/SCT
+TSRA NW G35 KT THIS AFTN. THE 12Z SPC WRF MAKES THIS A BIG DEAL
IN SE PA/SW NJ BY 00Z. THE NCEP MODEL MASS FIELDS SUGGEST LOOKING
FOR BETTER DEVELOPMENT FURTHER NORTH. NOT SURE OF THE BEST AREA.
WE HAVE CB IN MOST OF THE TAFS THRU 22Z AND WILL UPDATE ONCE WE
ARE SURE A CELL IS DESTINED TO HIT OR COME WITHIN 5 MI OF THE TAF
SITE.

LOCAL SEA BREEZE INFLUENCES KACY/KILG THIS AFTERNOON.

TONIGHT... VFR TO START WITH CONVECTION PROBABLY SETTLING DOWN BUT
NOT COMPLETELY CONVINCED IT CANNOT RE-FIRE DURING THE EARLY MORNING.
MVFR VSBY IN FOG/HAZE EXPECTED LATER TONIGHT....ESP IN THE FRONTAL
ZONE WHICH MAY END UP N OF PHL ALL NIGHT. CONFIDENCE BELOW AVG ON
CONVECTIVE OCCURRENCE AFTER 01Z.

OUTLOOK...
FRIDAY...VFR CIGS DEVELOP BY 17Z WITH CLUSTERS OF HEAVY RAIN SHOWERS
AND TSTMS...ISOLATED SEVERE TSTMS EXPECTED. WIDESPREAD MVFR CONDS
MAY DEVELOP IN THE AFTERNOON NNJ AND NE PA...ESP VCNTY KABE AND
THE POCONOS. LIGHT WIND TRENDING NE.

QUASI STATIONARY FRONT PROBABLY JUST N OF KPHL TO START THE DAY BUT
PROBABLY MOVES SOUTHWARD DURING THE AFTERNOON DOWN INTO N DEL.

FRIDAY NIGHT...MVFR CONDS PROBABLY SPREADING SEWD TO MOST TAF
LOCATIONS IN THE WAKE OF THE DEPARTING COLD FRONT AND ASSTD
CONVECTION.

THIS WEEKEND...WEAK HIGH PRESSURE BUILDING EAST FROM THE GREAT
LAKES SHOULD PROVIDE VFR CONDITIONS. THE ONLY EXCEPTION HERE
COULD BE SATURDAY EVENING...AS WIDELY SCATTERED THUNDERSTORMS
COULD AFFECT NORTHERN AREAS.

NEXT MONDAY...VFR TO START BUT MAY SEE TSTMS LATE AT NIGHT IN WARM
AIR ADVECTION ASSOCIATED WITH A WARM FRONTAL PASSAGE.

&&

.MARINE...
NO HEADLINES ATTM. LOW PROB WE WILL NEED AN SCA FRI NIGHT IN THE
ATLC WATERS OFF DEL.

CONVECTIVE GUSTS AND LIGHTNING ARE THE BIG PROBLEM THIS AFTERNOON
AND AGAIN FRIDAY INTO FRIDAY EVENING.

A DRY NICE WEEKEND IS ENVISIONED AS HIGH PRESSURE SETTLES IN WITH
A DRIER AIRMASS AND LIGHT WIND.

&&

.HYDROLOGY...
TODAY...PWAT IN THE 1.3 TO 1.6 INCH RANGE WITH A SMALL CHANCE OF
ISOLATED WET MICROBURSTS THIS AFTERNOON IN THE 92-94F HEAT ALONG
THE FRONTAL BOUNDARY WAVERING NEAR A NYC-PHL-DC LINE.

SMALL CELLS INCLUDING THUNDER IN PROGRESS SRN AND ERN PA INTO NJ
AND GENERAL STM MO IS 290 AT 14 KT.

TOMORROW...MUCH MORE CONCERN FOR FF POTENTIAL WITH PWAT INCREASING
A BIT...MUCH BETTER SFC CONVERGENCE ALONG THE QUASI STATIONARY
BOUNDARY NEAR OR JUST N OF PHL WITH WEAK SFC LOW FORMING IN THE
HOT AIRMASS ON THE BOUNDARY IN NE MD OR SE PA. THERE APPEARS TO BE
MORE THAN ADEQUATE SHEAR FOR SVR TOMORROW WITH LOW LVL SHEAR AS
WELL. 1 HR GRIDDED FFG IS AROUND 1.5INCHES ALONG AND N OF
I78...ESP IN NJ AND 6 HR FFG IS ONLY AROUND 4 INCHES IN THAT SAME
REGION. A VERY ACTIVE AFTERNOON EVENING IS ENVISIONED.

&&

.CLIMATE...
HEAT WAVE CONTINUES TODAY ILG/PHL REGION AND LOW PROBABILITY IT
MAY EXTEND INTO FRIDAY PER THE ULTIMATE POSITION OF THE QUASI
STATIONARY FRONT MIDDAY FRIDAY AND THE RESULTANT TIMING OF
PERSISTENT CONVECTION PRIOR OR SUBSEQUENT TO 18Z FRIDAY.

TODAY THE MODEST HEAT WAVE IS DAY5 FOR PHL AND DAY4 FOR ILG.

SINCE MAY 6TH AT KPHL...ONLY 8 DAYS BELOW NORMAL WITHIN A PERIOD
OF 61 DAYS....IE 53 AOA NORMAL IN THESE 61.

REGARDING TOMORROW... HAVE BEEN LOOKING ALOT AT PARALLEL NAM MOS
VS THE ACTUAL NAM MET MOS. IT SEEMS OVERALL TO BE PERFORMING SLIGHTLY
BETTER THAN NAM MOS. TODAYS 12Z GFS MAVMOS HAS AN IDEA THAT TOMORROW
COULD REACH 87 AT KILG...WHILE THE 12Z/7 METMOS HAS 82 BUT THE
PARALLEL METMOS 87. THE IDEA...ITS WORTHY OF COMPROMISING AND
PROBABLY RUNNING A BIT HIGHER THAN THE METMOS GUIDANCE.

MUCH IF NOT ALL OF THIS SECTION WILL PROBABLY BE DELETED IN SUBSEQUENT
AFD EFFORTS.

&&

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

&&

$$
SYNOPSIS...O`HARA