Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 280731
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
331 AM EDT THU MAY 28 2015

.SYNOPSIS...
A COLD FRONT WILL MOVE ACROSS THE AREA TODAY. HIGH PRESSURE
REESTABLISHES ITSELF OFF THE EAST COAST FRIDAY INTO SATURDAY. A
COLD FRONT IS FORECAST TO MOVE ACROSS THE AREA SATURDAY NIGHT INTO
SUNDAY. HIGH PRESSURE WILL RETURN TO THE NORTHEAST EARLY NEXT WEEK
WHILE THE FRONTAL BOUNDARY STALLS TO OUR SOUTH.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
COLD FRONT WILL BEGIN CROSSING OUR REGION TODAY. INTERESTINGLY, MOST
MODELS AGREE THAT THE FRONT WILL BE MOVING THROUGH OUR WESTERN
SECTIONS BY 18Z OR SHORTLY THEREAFTER DESPITE LARGE DIFFERENCES IN
THE TIMING OF THE FRONT FOR OUR EASTERN COASTAL PLAINS (MORE ON THAT
IN THE SHORT TERM SECTION). COULD BE A FEW SHOWERS THIS MORNING AS
THE RIGHT REAR QUADRANT OF THE UPPER LEVEL JET PROPAGATES CLOSER TO
THE REGION. HOWEVER, THE MAIN FOCUS FOR ANY STORMS, AND THUS HIGHEST
POPS, LOOK TO BE AFTER 18Z IN THE VICINITY OF THE FRONT. ONE CHANGE
FROM THE PREVIOUS FORECAST IS THAT IT NOW LOOKS LIKE THE HIGHEST
CHANCES FOR STORMS WILL BE IN THE NORTHERN HALF OF THE REGION WHICH
WILL BE CLOSER TO THE MID AND UPPER LEVEL TROUGH AXIS. MEANWHILE IN
THE SOUTHERN HALF OF OUR CWA, AN UPPER LEVEL RIDGE LOOKS TO BUILD IN
BY LATE THIS AFTERNOON, AND WHILE ANY ASSOCIATED SUBSIDENCE MAY NOT
BE ENOUGH TO COMPLETELY SUPPRESS CONVECTIVE INITIATION IN THIS AREA,
IT SHOULD BE A FACTOR IN LIMITING STORM COVERAGE.

AS FOR HAZARDS, THERE IS THE POTENTIAL FOR GUSTY WINDS, PRIMARILY
ACROSS NW NJ AS 0-6KM SHEAR VALUES COULD BE NEAR 40 KT (PRIMARILY
SPEED SHEAR) WITH MODEST (LESS THAN 500 J/KG CAPE) INSTABILITY. WILL
MENTION POTENTIAL FOR STRONG STORMS IN THIS AREA IN THE HWO. SHEAR
VALUES, AND THUS STRONG STORM THREAT, DROPS OFF QUICKLY AS YOU GO
FURTHER SOUTH THANKS AGAIN TO THE HIGH BUILDING IN. WITH THIS HIGH,
ANY STORM MOTIONS ACROSS THE SOUTHERN HALF OF THE REGION SHOULD BE
QUITE SLOW (15 KT OR LESS), BUT OTHER CONTRIBUTING FACTORS FOR A
HEAVY RAIN THREAT ARE LIMITED, SO WILL HOLD OFF ON MENTIONING ANY
HEAVY RAIN IN THE HWO.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
AS MENTIONED EARLIER, THERE ARE SOME BIG DIFFERENCES AMONG MODELS
FOR THE TIMING OF THE FRONT FROM DELAWARE VALLEY AND POINTS FURTHER
EAST. SOME MODELS, MOST NOTABLY THE NAM, BRING THE FRONT IN QUICKLY
TO THE WESTERN ZONES, BUT THEN DON/T SHOW THE FRONT MOVING THROUGH
THE EASTERN COASTAL PLAINS UNTIL NEAR OR AFTER 06Z. THIS DOESN/T
SEEM REALISTIC EVEN WITH THE HIGH BUILDING IN. THE LOW ASSOCIATED
WITH THIS COLD FRONT SHOULD BE QUICKLY PROPAGATING EAST THROUGH THIS
TIME, SO SEE LITTLE REASON THAT THE FRONT WILL STALL. THUS FORECAST
FAVORS A FASTER SOLUTION, HAVING THE FRONT MOVE OFF SHORE AROUND
06Z. REGARDLESS OF THE FRONTAL TIMING, LOSS OF DAYTIME HEATING AND
THE RIDGE BUILDING IN SHOULD LEAD TO CHANCES FOR STORMS DECREASING
THROUGH THE EVENING HOURS, AND WOULD EXPECT MOST, IF NOT ALL OF THE
AREA TO BE DRY BY MIDNIGHT.

THE ONE AREA WHERE THE TIMING DIFFERENCES COULD HAVE CONSIDERABLE
IMPACT WILL BE WITH LOW TEMPERATURES OVERNIGHT. FOR NOW HAVE GONE
WITH A BLEND OF THE FASTER SOLUTIONS (CMC, GFS, AND ECMWF), BUT WITH
DRIER AIR MOVING IN BEHIND THE FRONT, THERE IS THE POTENTIAL FOR
CONSIDERABLE RADIATIONAL COOLING IF THE FRONT PUSHES THROUGH FASTER
THAN PREVIOUSLY EXPECTED.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
HIGH PRESSURE IS FORECAST TO REESTABLISH ITSELF ACROSS THE ATLANTIC
ON FRIDAY, WITH OUR AREA ON THE WESTERN EDGE, WHILE THE RIDGE ALOFT
BUILDS TO OUR EAST AS WELL. THIS SHOULD HELP KEEP THE WEATHER MOSTLY
DRY INTO FRIDAY. HOWEVER, WITH RETURN FLOW ACROSS THE AREA,
INSTABILITY IS FORECAST TO DEVELOP ACROSS THE THE AREA, ESPECIALLY
FOR WESTERN AREAS. THIS DAYTIME INSTABILITY COULD LEAD TO A FEW
ISOLATED SHOWERS/THUNDERSTORMS WITH ANY VORTICITY IMPULSE THAT MOVES
ACROSS THE WESTERN EDGE OF THE RIDGE.

THE SURFACE HIGH AND RIDGING ALOFT PUSH EASTWARD SLIGHTLY SATURDAY,
WITH SOUTHWEST FLOW AT THE SURFACE ALOFT DEVELOPING. THIS WILL ALLOW
FOR A COUPLE OF SHORT WAVE/VORTICITY IMPULSES TO MOVE ACROSS THE
AREA LATE SATURDAY WHILE DAYTIME INSTABILITY DEVELOPS AS WELL. AN
INCREASE IN SHOWER/THUNDERSTORM ACTIVITY IS POSSIBLE, ESPECIALLY FOR
THE WESTERN PORTIONS OF THE AREA.

A COLD FRONT IS THEN FORECAST TO MOVE ACROSS THE AREA SATURDAY NIGHT
INTO SUNDAY. THE LATEST GFS AND ECMWF HAVE PRETTY GOOD AGREEMENT
WITH THE TIMING OF THE PRECIPITATION. BOTH AGREE THAT SUNDAY LOOKS
TO BE THE PERIOD WITH HIGHEST PROBABILITY FOR PRECIPITATION AS THE
FRONT MOVES ACROSS AND SOUTH OF THE AREA. PW VALUES INCREASE TO NEAR
2 INCHES, SO THERE COULD BE A PERIOD OF HEAVY RAINFALL WITH ANY
SHOWERS THAT DEVELOP DURING THE TIME PERIOD. THERE REMAINS
INSTABILITY FORECAST AHEAD OF THE FRONT, SO WE WILL KEEP
THUNDERSTORMS IN THE FORECAST, BUT ONCE THE FRONT PASSES,
THUNDERSTORM POTENTIAL DECREASES.

HIGH PRESSURE RETURNS TO THE NORTHEAST EARLY NEXT WEEK AS THE
FRONTAL BOUNDARY PUSHES SOUTH AND LIKELY STALLS JUST SOUTH OF OUR
AREA. WITH THE HIGH TO OUR NORTHEAST, THIS WILL KEEP EASTERLY FLOW
ACROSS THE AREA. SOUTHWEST-WESTERLY FLOW ALOFT WILL REMAIN ACROSS
THE AREA AS WELL. SEVERAL SHORT WAVE/VORTICITY IMPULSES WILL LIKELY
MOVE ACROSS THE AREA EARLY NEXT WEEK, WHICH COULD HELP CREATE
PRECIPITATION ACROSS THE AREA. WITH THE EASTERLY FLOW ACROSS THE
AREA, THE ATMOSPHERE SHOULD BE STABLE, SO WE HAVE REMOVED
THUNDERSTORMS FROM THE FORECAST MONDAY AND TUESDAY DUE TO LACK OF
INSTABILITY.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

PATCHY FG/BR WILL LIKELY CONTINUE AT KRDG AND KABE THROUGH 12Z. FOR
THE DELAWARE VALLEY AND COASTAL SITES (KPHL, KPNE, KTTN, KMIV, KACY
AND KILG), EXPECT BRIEF INTERMITTENT IMPACTS (PRIMARILY MVFR EXCEPT
AT KTTN) THROUGH THIS TIME AS WELL. AFTER SUNRISE, WINDS SHOULD
SETTLE IN OUT OF THE SW. THERE MAY BE ISOLATED SHRA BETWEEN 12 AND
15Z, BUT COVERAGE WILL BE TOO LIMITED TO MENTION IN THE TAFS.

A COLD FRONT IS EXPECTED TO APPROACH THE REGION AROUND 18Z. JUST
AHEAD OF THE FRONT, COULD SEE ISOLATED TO SCATTERED THUNDERSTORMS,
THOUGH HIGHER CHANCES LOOK TO STAY NORTH OF THE TAF SITES, WILL BE
KEEPING A CLOSE EYE ON THIS THROUGH THE DAY THOUGH. AS FOR THE EXACT
TIMING OF THE FRONT, AND THUS A SHIFT TO NORTHWESTERLY WINDS,
RELATIVELY HIGH CONFIDENCE OF IT ARRIVING AT KRDG AND KABE BY 21Z.
CONSIDERABLY LESS CONFIDENCE FOR THE OTHER TAF SITES. HAVE CHOSEN TO
GO WITH A FASTER SOLUTION THAN WHAT THE NAM OR GFS LAMP ARE SHOWING
GIVEN A RELATIVELY PROGRESSIVE OVERALL PATTERN, WITH AN ARRIVAL IN
THE DELAWARE VALLEY BETWEEN 00 AND 03Z, AND AT THE COASTAL SITES BY
06Z.

OUTLOOK...

FRIDAY...GENERALLY VFR. ISOLATED SHOWERS/THUNDERSTORMS POSSIBLE FOR
WESTERN TAFS.

FRIDAY NIGHT...VFR EARLY, THEN LOWERING CIGS/VSBYS WITH
STRATUS/FOG POSSIBLE OVERNIGHT.

SATURDAY...LOWER CONDITIONS POSSIBLE EARLY, THEN BECOMING VFR DURING
THE DAY. SCATTERED SHOWERS AND THUNDERSTORMS POSSIBLE WHICH MAY
LOCALLY REDUCE CIGS/VSBYS. GUSTY SOUTH-SOUTHWEST WINDS AROUND 20
KNOTS.

SATURDAY NIGHT-MONDAY...AN EXTENDED PERIOD OF MVFR/IFR CONDITIONS
POSSIBLE. A CHANCE OF RAIN EACH DAY. BEST POTENTIAL FOR
THUNDERSTORMS IS SUNDAY.

&&

.MARINE...
A FEW SITES CONTINUE TO SHOW WAVE HEIGHTS NEAR 5 FT, SO WILL KEEP
THE SMALL CRAFT ADVISORY GOING THROUGH 6AM, BUT DO NOT ANTICIPATE
ANY EXTENSIONS AT THIS TIME. THIS AFTERNOON, A FEW GUSTS NEAR OR
JUST ABOVE 20 KT ARE POSSIBLE ON THE ATLANTIC COASTAL WATERS, BUT
SHOULD REMAIN BELOW SCA CRITERIA. A WIND SHIFT WITH A COLD FRONT IS
EXPECTED THIS EVENING INTO THE OVERNIGHT HOURS.

OUTLOOK...

FRIDAY-FRIDAY NIGHT...SUB-SMALL CRAFT ADVISORY CONDITIONS CURRENTLY
EXPECTED, ALTHOUGH WINDS MAY GUST AROUND 20 KNOTS AT TIMES.

SATURDAY-MONDAY...SEAS MAY RETURN TO 5 FEET OR GREATER LATE ON
SATURDAY AHEAD AHEAD OF AN APPROACHING COLD FRONT. SEAS MAY REMAIN
ELEVATED INTO MONDAY, AND WINDS MAY INCREASE TO 25 KNOTS.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT EARLY THIS MORNING FOR
     ANZ450>455.

&&

$$

SYNOPSIS...ROBERTSON
NEAR TERM...JOHNSON
SHORT TERM...JOHNSON
LONG TERM...ROBERTSON
AVIATION...JOHNSON/ROBERTSON
MARINE...JOHNSON/ROBERTSON


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