Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 111938 CCA
AFDPHI

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
337 PM EDT FRI JUL 11 2014

.SYNOPSIS...
HIGH PRESSURE WILL CONTINUE TO BUILD ACROSS THE NORTHEAST STATES
TONIGHT, THEN PUSH OFFSHORE SATURDAY. A WARM FRONT MAY TRY TO LIFT
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY. A PRE FRONTAL OR LEE
SIDE TROUGH WILL DEVELOP ACROSS THE MID ATLANTIC STATES MONDAY INTO
TUESDAY, BEFORE A COLD FRONT SWEEPS ACROSS THE AREA TUESDAY INTO
EARLY WEDNESDAY. HIGH PRESSURE WILL RETURN TO THE NORTHEAST BY THE
END OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
THE MID-ATLANTIC REGION WAS POSITIONED ON THE SRN SIDE OF BROAD
HIPRES THAT IS CENTERED OVER THE NORTHEAST STATES THIS AFTN. CU
FIELD HAS BEEN RATHER FLAT SO FAR THIS AFTN ACROSS MOST OF THE CWA
AND HAS EVEN SEEN DISSIPATION OF CLOUDS OVER CENTRAL NJ AS DRIER AIR
ADVECTS IN FROM NORTHEAST. THE ONE EXCEPTION IS TOWARD THE POCONOS,
WHERE A MATURE CU FIELD HAS DEVELOP LIKELY IN RESPONSE TO A MID-LVL
SHORTWAVE TROUGH THAT IS APPROACHING FROM CENTRAL PA. DO NOT EXPECT
MUCH THAN A FEW SHOWERS OR SPRINKLES IN THE POCONOS/LEHIGH
VALLEY/EXTREME NW NJ WITH MINIMAL INSTABILITY. FARTHER SOUTH TOWARD
EXTREME SERN PA, SWRN NJ AND THE DELMARVA- SFC DEWPOINTS ARE IN THE
UPPER 60S AND THE 19Z SPC MESOANALYSIS INDICATES MLCAPE VALUES
AROUND 1000 J/KG. ISOLATED SHOWERS AND THUNDERSTORMS MAY DEVELOP
ACROSS THIS AREA THRU ABOUT SUNSET.

SFC HIPRES BUILDS TOWARD THE NEW ENGLAND AND MID-ATLANTIC COAST
TONIGHT. DIURNALLY-DRIVEN CU FIELD AND SHOWERS/STORMS WILL DISSIPATE
AFTER DARK. THE 12Z NAM INDICATES THE POTENTIAL FOR CLOUDS TO LINGER
INTO THE OVERNIGHT ALONG AND EAST OF THE DELAWARE BASED ON HIGH RH
VALUES AT 850 MB, BUT THIS MODEL WAS AN OUTLIER AND RH VERIFIED TOO
HIGH THIS AFTN BASED ON NEARBY ACARS SOUNDINGS. ACCORDINGLY, A GOOD
SETUP FOR RADIATIONAL COOLING IS FORECAST FOR TNGT UNDER CLEARING
SKIES AND LIGHT WINDS. LEANED TOWARD THE COOLER MAV GUIDANCE FOR MIN
TEMPS TONIGHT. FOG AND/OR STRATUS MAY DEVELOP TOWARD MORNING,
ESPECIALLY ALONG THE COAST OF SRN NJ AND DELMARVA WHERE THERE IS
MOISTURE POOLING.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
THE HIGH WILL MOVE OFF THE NEW ENGLAND AND MID-ATLANTIC COAST
SATURDAY. SOUTHERLY RETURN FLOW AROUND THE HIGH WILL BE LIGHT OVER
THE FORECAST AREA SO DO NOT EXPECT A BIG SURGE OF WARM/MOIST AIR
BACK INTO THE REGION. LLVL THETA-E RIDGE DOES DRAW NORTHWARD INTO
CENTRAL PA, SO DIURNALLY-DRIVEN SHOWERS SHOULD STAY WEST OF THE CWA.
UNDER PLENTY OF SUNSHINE, MAX TEMPS ARE IN THE MID TO UPPER 80S
EXCEPT COOLER NEAR THE WATERS AND IN THE POCONOS.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
A WET PERIOD CONTINUES TO LOOKS TO BE IN STORE EARLY NEXT WEEK,
ALTHOUGH THERE IS SOME DISAGREEMENT BETWEEN OPERATIONAL MODELS AND
HOW THEY HANDLE THE SYSTEM.

SATURDAY NIGHT IS FORECAST TO BE THE LAST DRY PERIOD IN THE FIRST
HALF OF THE LONG TERM FORECAST. THERE MAY BE A WARM FRONT LIFT
ACROSS THE AREA OVERNIGHT SATURDAY INTO SUNDAY MORNING, BUT FOR NOW
WE WILL KEEP DRY WEATHER ACROSS THE AREA.

THEN WE ENTER A PERIOD THROUGH AT LEAST TUESDAY WHEN WE HAVE A
CHANCE OF RAIN EACH PERIOD, DAY AND NIGHT. STARTING SUNDAY, A SERIES
OF FRONTAL BOUNDARIES WILL BEGIN MOVING OUT OF THE UPPER MISSISSIPPI
RIVER VALLEY AND INTO THE MIDWEST. AT THE SAME TIME, A PRE-FRONTAL
OR LEE-SIDE TROUGH WILL SET UP ACROSS THE MID-ATLANTIC REGION. THE
FRONTAL BOUNDARIES TO OUR WEST WILL SLOW DOWN INTO MONDAY, BEFORE
THE INITIAL ONE BEGINS TO TAKE OVER, WHILE THE SURFACE TROUGH ACROSS
THE MID-ATLANTIC REMAINS IN PLACE. SEVERAL SHORT WAVE/VORTICITY
IMPULSES WILL SWING AROUND THE MID-UPPER LOW ACROSS THE GREAT LAKES
REGION THROUGH THE PERIOD, KEEPING HIGH CHANCES OF SHOWERS AND
THUNDERSTORMS EACH PERIOD.

THE GFS AND ECMWF HAVE SPLIT IN THEIR SOLUTIONS IN REGARDS TO HOW
FAST THE FRONT MOVES THROUGH THE AREA. THE GFS IN ITS LATEST MODEL
RUN HAS SPEND THE FRONT UP AND MOVED IT THROUGH BY TUESDAY MORNING,
WHICH BASICALLY ENDS ALL PRECIPITATION BY TUESDAY. MEANWHILE, THE
ECMWF KEEPS THE FRONT SLOWLY MOVING INTO THE AREA AND THROUGH LATE
TUESDAY INTO WEDNESDAY MORNING WHICH IS MORE IN LINE WITH PREVIOUS
RUNS. FOR NOW WE ARE GOING TO KEEP CLOSER TO WPC/ECMWF SOLUTION AND
KEEP AN ENHANCED CHANCE OF SHOWERS AND THUNDERSTORMS THROUGH TUESDAY
NIGHT.

DURING THE SUNDAY THROUGH TUESDAY PERIOD, THERE WILL BE THE THREAT
FOR VERY HEAVY RAINFALL WITH FLOODING POSSIBLE AS PW VALUES WILL BE
NEAR OR OVER 2 INCHES. IN ADDITION, WITH THE WARM/UNSTABLE AIRMASS
IN PLACE, DEPENDING ON THE MID-UPPER JET DYNAMICS AND FORECAST
SHEAR, THERE COULD BE A PERIOD OF STRONG TO SEVERE STORMS. MONDAY
AND TUESDAY LOOK TO BE THE PERIOD OF HIGHEST STRONG/SEVERE THREAT.

REGARDLESS OF WHICH SOLUTION IS RIGHT, WE EXPECT A DRYING OUT PERIOD
STARTING LATE WEDNESDAY INTO THURSDAY AS PW VALUES LOWER TO AN INCH
OR LESS ACROSS THE AREA AND HIGH PRESSURE BUILDS BACK ACROSS THE
NORTHEAST. HOWEVER, ISOLATED SHOWERS AND THUNDERSTORMS MAY RETURN BY
FRIDAY AS RETURN FLOW DEVELOPS AND MOISTURE BEGINS TO CREEP BACK
NORTHWARD.

AFTER ABOVE NORMAL TEMPERATURES FOR THE FIRST HALF OF THE EXTENDED
SUNDAY-TUESDAY, NEAR OR EVEN SLIGHTLY BELOW NORMAL TEMPERATURES
COULD RETURN FOR THE SECOND HALF OF NEXT WEEK.

&&

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

ISO POP-UP SHRA SOUTH AND WEST OF KPHL THIS AFTN. COVERAGE WAY TOO
LOW TO INCLUDE IN TAFS. LOW CHANCE OF TSRA IN VC OF KILG. OTHERWISE
VFR THRU 06Z. PATCHY FOG POSSIBLE BETWEEN 06Z-12Z AT THE TERMINALS
TO THE SOUTH AND WEST OF KPHL. IFR CIGS IN STRATUS ALSO POSSIBLE
TOWARD SUNRISE AT ACY/MIV. VFR DURING THE DAYTIME HOURS SATURDAY
WITH HIPRES JUST OFFSHORE.

OUTLOOK...
SATURDAY NIGHT...MOSTLY VFR.

SUNDAY-MONDAY...GENERALLY VFR WITH A CHANCE FOR SHOWERS AND
THUNDERSTORMS. LOCALLY MVFR/IFR CONDITIONS POSSIBLE WITH SHOWERS OR
THUNDERSTORMS. GUSTY AFTERNOON WINDS 15-20 KNOTS.

TUESDAY-TUESDAY NIGHT...SHOWERS AND THUNDERSTORMS EXPECTED WITH A
COLD FRONTAL PASSAGE. MVFR/IFR CONDITIONS LIKELY WITH SHOWERS OR
THUNDERSTORMS. GUSTY WINDS IN THE AFTERNOON AROUND 20 KNOTS, WITH
STRONGER WIND GUSTS POSSIBLE WITH THUNDERSTORMS.

WEDNESDAY...SHOWERS AND THUNDERSTORMS POSSIBLE IN THE MORNING, THEN
CLEARING THROUGH THE DAY.

&&

.MARINE...
EASTERLY WINDS 5-10 KT THIS AFTN WILL BECOME SOUTH-SOUTHEASTERLY
TONIGHT AND SOUTHERLY SATURDAY MORNING AS HIPRES MOVES OFF THE
COAST. WINDS WILL BE LIGHT DURING THIS TIME. SOUTHERLY FLOW
STRENGTHENS SATURDAY AFTERNOON BUT WILL BE BELOW SCA LEVELS WITH
GUSTS AROUND 15 KT.

OUTLOOK...
SUNDAY-TUESDAY NIGHT...NEAR OR LOWER END SMALL CRAFT ADVISORY
CONDITIONS ARE POSSIBLE THROUGH THE OUTLOOK PERIOD AS SOUTHWEST
WINDS INCREASE AHEAD OF AN APPROACHING COLD FRONT AND HIGH PRESSURE
REMAINS WELL OFF THE COAST.

WEDNESDAY...NEAR SMALL CRAFT POSSIBLE EARLY IN THE DAY WITH GUSTY
WINDS BEHIND FRONTAL BOUNDARY, THEN DIMINISHING THROUGH THE DAY.

&&

.TIDES/COASTAL FLOODING...
THE HIGH TIDES FRIDAY NIGHT, SATURDAY NIGHT, AND SUNDAY NIGHT MAY
APPROACH THE MINOR FLOOD LEVEL ALONG THE ATLANTIC COASTAL AREAS,
BUT ARE NOT EXPECTED TO REACH HIGH ENOUGH LEVELS TO REQUIRE A
COASTAL FLOOD ADVISORY.

&&

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

&&

$$
SYNOPSIS...ROBERTSON
NEAR TERM...KLEIN
SHORT TERM...KLEIN
LONG TERM...ROBERTSON
AVIATION...KLEIN/ROBERTSON
MARINE...KLEIN/ROBERTSON
TIDES/COASTAL FLOODING...ROBERTSON





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