Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 311946
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
346 PM EDT FRI JUL 31 2015

.SYNOPSIS...
HIGH PRESSURE ACROSS THE APPALACHIANS WILL GIVE WAY TO A WEAK
COLD FRONT, WHICH IS FORECAST TO CROSS OUR AREA LATE SATURDAY
INTO SUNDAY. A STRONGER COLD FRONT IS FORECASTED TO CROSS OUR
REGION LATE MONDAY INTO EARLY TUESDAY, THEN STALL OFFSHORE ON
WEDNESDAY INTO THURSDAY. HIGH PRESSURE MAY ARRIVE ON FRIDAY.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
A RATHER PLEASANT SUMMER AFTERNOON IS UNDER WAY WITH LIGHT NORTHWEST
WINDS, TEMPERATURES IN THE MID/UPPER 80S BUT DEWPTS IN THE 50S. SCT
DIURNAL CU HAVE FORMED OVER MOST OF THE AREA BUT THEY WILL THIN OUT
AND DISSIPATE TOWARDS EVENING. KDIX RADAR SHOWS A SEA BREEZE ALONG
PARTS OF THE NJ SHORE BUT IT WILL NOT BE ABLE TO MOVE INLAND MUCH
AGAINST THE PREVAILING NW FLOW.

FOR TONIGHT...LIGHT WINDS AND CLEAR SKIES WILL ALLOW TEMPS TO FALL
INTO THE 60S MOST AREAS...EXCEPT POSSIBLY UPPER 50S IN THE POCONOS
AND LOW 70S IN AND NEAR PHILADELPHIA AND NEAR THE OCEAN AND BAYS.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
FOR SATURDAY...THE FLOW ALOFT IS BROADLY CYC BUT WITHOUT NOTEWORTHY
DISTURBANCES AND THE AIRMASS CONTINUES RATHER DRY. ONCLY EXPECTED
CLOUDS ARE SOME DIURNAL CU SIMILAR TO TODAY. THE SFC PRES PATTERN
SHOULD BE SIMILAR TO TODAY AS WELL SO GENLY WLY WIND SHOULD DEVELOP
IN THE MORNING AND CONT THROUGH AFTN. THE 850MB WINDS ARE FCST TO BE
SMWHT STRONGER SO THERE COULD BE A LITTLE MORE GUSTINESS WITH AFTN
MIXING. HAVE INCLUDED A SLGT CHC FOR LATE AFTN T-STORMS OVER NRN NJ
AND ADJ PA WITH SOME MARGINAL INSTBY EXPECTED.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...

OVERVIEW...

DOMINANT MID-LEVEL FEATURE THRU THE LONG-TERM PERIOD IS A CLOSED
LOW INVOF HUDSON`S BAY ALONG W/ SEVERAL S/WV DISTURBANCES MOVING
THRU IT. THIS FEATURE WILL BE MAINTAINED BY A DEVELOPING RIDGE
OVER WESTERN NOAM AND HIGH-LATITUDE BLOCKING OVER DAVIS STRAIT.
ALTHOUGH THERE IS UNCERTAINTY IN THE TIMING AND STRENGTH OF THE
INDIVIDUAL S/WV IMPULSES...AND HOW THEY AFFECT THE AMPLITUDE OF
THE TROUGH...A DEVELOPING OMEGA BLOCK OVER NOAM SHOULD LOCK IN THE
OVERALL PATTERN THRU AT LEAST D+7. THE MOST APPARENT MODEL TRENDS
ARE TO SPEED THE TIMING OF A PRIMARY COLD FRONT THRU THE AREA ON
MON NIGHT /AS OPPOSED TO TUE NIGHT/ ...WITH THE FRONT BECOMING
STATIONARY NEAR THE NJ COAST AND DELMARVA THRU THU.

THE STALLED FRONT SOLUTION IS PLAUSIBLE...GIVEN THE MID-LEVEL
LOW OVER HUDSON`S BAY MOVING SLOWLY NORTHEAST THRU THE PERIOD...
WHICH WILL LEAD TO A MORE ZONAL FLOW OVER THE AREA PARALLELING
THE FRONT BY MID-WEEK. THIS SOLUTION IS ALSO SUPPORTED BY THE
ECENS/GEFS MEANS...WITH OVERALL SUPPORT FROM THE INDIVIDUAL
MEMBERS AS WELL. THEREFORE...RELIED MORE HEAVILY ON THE EURO
GIVEN ITS RECENT PERFORMANCE AS WELL AS THE MORE STABLE ECENS/
GEFS MEANS...AND DISCOUNTED THE MORE PROGRESSIVE GFS AFTER
00Z THU ESPECIALLY GIVEN THE MORE ROBUST NOAM BLOCKING PATTERN.

OVERALL...THE MAIN CONCERNS ARE THE POTENTIAL FOR CONVECTION
AND LOCALIZED FLASH FLOODING IN THE MON THRU THU TIME FRAME.
TEMPS WILL BE AOA NORMAL THRU AT LEAST WED...WITH ABOVE AVG
UNCERTAINTY GOING FORWARD...DUE TO THE QUESTIONABLE LOCATION
OF THE FRONT AND ASSOCIATED CLOUDINESS.

DALIES...

SUNDAY...S/WV RIDGING ALOFT W/ HIGH PRES MOVING IN BEHIND THE
DEPARTING COLD FRONT. THIS WILL PROMOTE A MOSTLY SUNNY AND DRY
DAY. THE GRADIENT MAY RELAX ENOUGH FOR A SEA-BREEZE TO DEVELOP
ALONG PORTIONS OF THE COAST.

MONDAY...SHRA/TSRA ARE POSSIBLE MON AFTN AS S/WV IMPULSE SKIRTS
TO THE NORTH AND A STRONGER COLD FRONT APPROACHES FROM THE WEST.
THE APPROACH OF THE S/WV WILL LEAD TO STEEPER LAPSE RATES...BUT
MOISTURE IS LIMITED...SO POPS WERE FOCUSED TO THE WEST OF I-95
WHERE BETTER FORCING SHOULD RESIDE. THE CONVECTIVE POTENTIAL IS
STILL IN QUESTION AT THIS POINT...AND MAY BE MORE FOCUSED JUST
TO OUR WEST. THE MODELS APPEAR TO BE OVERDOING VERTICAL MIXING
AHEAD OF THE FRONT...BUT THERE IS THE POTENTIAL FOR 20-25 KNOT
WIND GUSTS.

MONDAY NIGHT AND TUESDAY...THE AFOREMENTIONED COLD FRONT WILL
MOVE JUST OFFSHORE MON NIGHT WHERE IT IS EXPECTED TO BECOME
STATIONARY. THERE IS STILL UNCERTAINTY AS TO THE EXTENT OF
SHRA/TSRA CROSSING THE CWA MON NIGHT...SO LOW POPS CONFINED
N/W OF I-95 FOR NOW. ON TUESDAY...THE CWA IS SITUATED BETWEEN
THE STALLED FRONT OFFSHORE AND ANOTHER S/WV DISTURBANCE JUST
TO OUR NORTH. W/ SUCH A SETUP...COULD EASILY SEE SOME PRECIP
IN DELMARVA AND ESPECIALLY OVER THE POCONOS AND LEHIGH VALLEY.
HAVE LOW POPS CONFINED N/W OF I-95 FOR NOW.

WED THRU FRI...THERE REMAINS ABOVE AVERAGE UNCERTAINTY DURING
THIS TIME FRAME. THE SYNOPTIC SETUP FAVORS A STATIONARY FRONT
IN THE VICINITY AND THE MODELS ALSO ADVERTISE A WAVE OF LOW-
PRESSURE TRAVERSING THIS BOUNDARY ON THURSDAY. THE MODELS ARE
ALSO SUFFERING CONVECTIVE FEEDBACK ISSUES DURING THIS PERIOD
WHICH FURTHER ADDS TO THE UNCERTAINTY. THE MAIN CONCERN IS THE
POTENTIAL FOR SOME HEAVY RAINFALL DURING THIS TIME FRAME...AS
WPC HAS THEIR MAX QPF AXIS ACROSS THE SRN HALF OF OUR CWA.

&&

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

HI CONFIDENCE FOR VFR CONDS TO CONTINUE THROUGH TONIGHT AND SATURDAY
AT ALL TAF SITES. WINDS WILL BECOME LIGHT/VRBL TONIGHT AS THE SFC
LAYER COOLS AND DECOUPLES FROM WINDS ALOFT. WLY WINDS WILL REDEVELOP
ON SATURDAY MORNING AND MAY BE SMWHT GUSTY 15 TO 20 KT AT TIMES IN
THE AFTN DUE TO SLIGHTLY STRONGER WINDS ALOFT.

OUTLOOK...

SAT NIGHT AND SUNDAY...VFR.

MONDAY THRU WEDNESDAY...SHRA/TSRA ARE POSSIBLE...ESPECIALLY EACH
AFTERNOON. OTHERWISE VFR.

&&

.MARINE...
WINDS AND SEAS WILL CONT RATHER LIGHT OVER THE FORECAST WATERS
TONIGHT AND TOMORROW MORNING. TODAYS NW FLOW WILL TURN TO THE S AND
THEN SW TONIGHT AND SATURDAY AS A SFC TROF BECOMES MORE PRONOUNCED
ALONG THE MID-ATLANTIC SEABOARD. SEAS OF 2 TO 3 FT TONIGHT WILL
BUILD SLIGHTLY ON SATURDAY AS SWLY WINDS INCRESE...GUSTING TO 15 OR
20KT SAT AFTN.

OUTLOOK...

SUNDAY THROUGH WEDNESDAY...

WEAK HIGH PRESSURE OVER THE CENTRAL APPALACHIANS WILL EXTEND OVER
THE WATERS ON SUNDAY INTO MONDAY. A STRONGER COLD FRONT WILL MOVE
OVR THE WATERS MON NIGHT AND STALL IN THE VICINITY THRU WEDNESDAY.

THERE MAY BE A PERIOD OF WIND GUSTS TO ABOUT 20 KNOTS ASSOCIATED
WITH THE PASSAGE OF A COLD FRONT LATE MONDAY INTO EARLY TUESDAY.
THIS WILL RESULT IN SEAS INCREASTING...BUT THEY ARE EXPECTED TO
REMAIN BELOW 5 FEET ATTM.

OTHERWISE SUB-SCA CONDITIONS ARE ANTICIPATED THRU THE PERIOD.

&&

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

&&

$$
SYNOPSIS...FRANCK
NEAR TERM...AMC
SHORT TERM...AMC
LONG TERM...FRANCK
AVIATION...AMC/FRANCK
MARINE...AMC/FRANCK


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