Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 171756
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
156 PM EDT SUN AUG 17 2014

.SYNOPSIS...
A COLD FRONT OVER THE GREAT LAKES EARLY THIS MORNING WILL PROGRESS
SOUTHEASTWARD THROUGH EASTERN PENNSYLVANIA AND NEW JERSEY TODAY AND
THE DELMARVA TONIGHT. THE FRONT WILL STALL JUST SOUTH OF THE AREA
MONDAY. A WAVE OF LOW PRESSURE IS EXPECTED TO TRACK EASTWARD ALONG
THE STALLED BOUNDARY MONDAY NIGHT INTO TUESDAY. ANOTHER LOW PRESSURE
SYSTEM WILL APPROACH THE AREA WEDNESDAY INTO THURSDAY. THE
AFOREMENTIONED FRONTAL BOUNDARY IS EXPECTED TO REMAIN JUST SOUTH OF
THE AREA THROUGH THE REMAINDER OF THE WEEK AS MORE WAVES OF LOW
PRESSURE RIDE ALONG IT.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
AN EVER SLOWING COLD FRONT SLINKS ACROSS THE GREAT LAKES INTO
NORTHWESTERN PENNSYLVANIA AND EXTREME WESTERN NEW YORK EARLY THIS
MORNING AND HAS PUSHED INTO PHILADELPHIA METROPOLITAN AREA. AN AREA OF
SHOWERS IS OUT AHEAD OF THIS FRONTAL BOUNDARY BUT A GRADUAL
WEAKENING TREND HAS BEEN NOTICED ON RADAR WITH THESE SHOWERS.

THE FRONT WILL CONTINUE TO SAG TOWARDS THE SOUTH THIS AFTERNOON. A WEAK
MID- LEVEL IMPULSE MOVES OVERHEAD IN TANDEM WITH THE SURFACE FRONT
PROGRESSION. THE AMOUNT OF FRONTAL FORCING BEGINS TO WASH OUT AS
THE FLOW ALOFT BECOMES MORE ALIGNED ALONG THE FRONTAL BOUNDARY AND
LESS OF A COLD AIR PUSH BEHIND THE FRONT. BETTER HEATING AHEAD THE
OF THE BOUNDARY WITH SURFACE BASED CAPES PUSHING CLOSE TO 500J/KG
COULD BE ENOUGH OF A SPARK TO SEE BETTER CHANCES FOR SHOWERS WITH
ISOLATED THUNDER ACROSS OUR SOUTHERN HALF.

TEMPERATURES TODAY, UNDER SLIGHTLY STRONGER WARM AIR ADVECTION AHEAD
OF THE APPROACHING COLD FRONT, WILL BE A COUPLE DEGREES WARMER THAN
SATURDAY. STAT GUIDANCE IS PRETTY CLOSE TO ONE ANOTHER AND BOTH THE
GFS AND NAM INITIALIZED PRETTY WELL THERMALLY SO TOOK AN EVEN SPLIT
OF THE MET/MAV. SLOWED THE ADVECTION OF LOWER DEWPOINTS AND MADE
SOME SLIGHT CHANGES TO THE TEMPERATURES BASED ON THE 16Z METAR
OBS WITH THE 12;30 PM UPDATE.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
THE COLD FRONT WILL BE TO OUR SOUTH LATE TONIGHT AND A DRYING
NORTHWEST WIND COMMENCES. WEAK HIGH PRESSURE OVERHEAD SHOULD ALLOW
FOR MOSTLY CLEAR SKIES, NORTH OF THE STALLED FRONTAL BOUNDARY,
TONIGHT AND A LIGHT WIND SO LOWS WILL BE ABLE TO RADIATE DOWN INTO
THE MID TO UPPER-50S IN A LOT OF PLACES.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
AN OLD FRONTAL BOUNDARY IS EXPECTED TO STALL OVER THE SOUTHERN
DELMARVA AND SOUTHERN VA ON MONDAY. THE AIRMASS OVER THE SOUTHERN
FRINGE OF THE CWA WILL REMAIN RELATIVELY MOIST WITH DEWPOINTS IN THE
MID 60S. A NOTICEABLY DRIER AIRMASS (DEWPOINTS IN THE 50S) WILL
RESIDE FARTHER INTO PA/NJ AS A RESULT OF NORTHERLY FLOW AROUND
HIPRES OVER THE GREAT LAKES/UPSTATE NY. FORECAST MAX TEMPS RANGE
FROM THE UPPER 70S IN THE POCONOS TO MID 80S IN THE I-95 URBAN
CORRIDOR. DESPITE WARMER H8 TEMPS FARTHER SOUTH ACROSS THE
DELMARVA, INCREASING CLOUD COVER LATE IN THE DAY AND AN EAST-
SOUTHEAST WIND OFF THE ATLANTIC SHOULD KEEP AFTERNOON HIGHS IN THE
MID 80S.

A WEAK SHORTWAVE TROUGH OVER KY IS FORECAST TO MOVE EASTWARD MONDAY
AND TOWARD THE MOUTH OF THE CHSPK BAY MONDAY NIGHT INTO TUESDAY
MORNING. WEAK SFC CYCLOGENESIS CAN BE EXPECTED AS THE UPPER IMPULSE
INTERACTS THE OLD FRONTAL BOUNDARY. THE MOST RECENT 00Z MODELS HAVE
COME INTO BETTER AGREEMENT FOR MONDAY NIGHT-TUESDAY AND HAVE
TRENDED TOWARD A PROGRESSIVE/SUPPRESSED SYSTEM, WHICH WOULD MAKE
SENSE GIVEN A RATHER FLAT/ZONAL STEERING FLOW PATTERN. THERE IS
ALSO AN UPSTREAM KICKER SYSTEM THAT DOES NOT HAVE MUCH OF A
SEPARATION DISTANCE FROM THIS LEADING SHORTWAVE TROUGH. HAVE
LOWERED POPS ACROSS THE NORTHERN HALF OF THE CWA. WE CURRENTLY
MENTION A HEAVY RAINFALL THREAT IN THE HWO FOR EXTREME SOUTHERN
NJ/DELMARVA. ALTHOUGH THE LATEST TREND FROM THE MODEL GUIDANCE IS
SHIFTING AWAY FROM THIS POTENTIAL HEAVY RAIN EVENT, THESE SAME
LOCATIONS RECEIVED 5-10 INCHES OF RAINFALL AUGUST 12-13 AND THUS
WOULD REMAIN RATHER SUSCEPTIBLE TO FLOODING. WILL KEEP IT IN THE
HWO FOR NOW BUT ADD CONDITIONAL WORDING.

THE OLD FRONTAL BOUNDARY IS EXPECTED TO REMAIN STALLED JUST TO THE
SOUTH AND WEST OF THE CWA WEDNESDAY AND THURSDAY AS EASTERLY FLOW
OFF THE ATLANTIC KEEPS THE COASTAL MID ATLANTIC IN A COOLER REGIME.
THE AFOREMENTIONED KICKER SYSTEM, A NORTHERN STREAM LOW OVER THE
UPPER MIDWEST, WILL DIVE SOUTHEASTWARD AROUND THE PERIPHERY OF A
BUILDING GULF OF MEXICO RIDGE AND INTO THE NORTHERN MID-ATLANTIC
STATES DURING THIS TIME. THIS SYSTEM WILL BE ACCOMPANIED BY SHOWERS
AND THUNDERSTORMS BOTH DAYS. CONVECTION PREFERENTIALLY WOULD FOCUS
ALONG THE FRONTAL BOUNDARY TO OUR SOUTH AND WEST. FOR NOW, BROAD
BRUSHED THE AREA WITH LOW CHANCE POPS AS THERE IS STILL TOO MUCH
UNCERTAINTY THIS FAR OUT TO DETERMINE HOW QUICKLY PRECIP MAKES IT
TO THE AREA AND WHERE IT DEVELOPS.

FORECAST UNCERTAINTY IS HIGH FOR THE END OF THE PERIOD. WHILE MODEL
CONSENSUS POINTS TOWARD A BUILDING RIDGE OVER THE CENTRAL CONUS LATE
IN THE WEEK, THEY DISAGREE WITH HOW QUICKLY THE UPPER LOW TO THE
NORTHEAST OF THIS RIDGE OPENS UP AND EXITS THE MID-ATLANTIC STATES.
TRENDED TOWARD A DRIER FORECAST FOR FRIDAY AND SATURDAY WITH HIPRES
OVER EASTERN CANADA TRYING TO WEDGE DOWN THE EASTERN SEABOARD.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

A COLD FRONT WITH SOME ASSOCIATED MID-LEVEL AND OCCASIONALLY MVFR
CEILINGS IS MOVING SOUTHEAST ACROSS THE REGION. AS THE FRONT MOVES
THROUGH MIXING WILL INCREASE ALLOWING FOR A RETURN TO VFR
CONDITIONS BY LATE AFTERNOON. WINDS WILL ALSO INCREASE SLIGHTLY THIS
AFTERNOON WITH A FAVORABLE SET-UP FOR SOME WIND GUSTS CLOSE TO 20
KT FOR THE MID AND PERHAPS LATE AFTERNOON HOURS FROM THE
NORTHWEST.

WINDS WILL RELAX BY THIS EVENING AND CLOUDS WILL CONTINUE TO CLEAR
OUT. NO FOG OR LOW VISIBILITIES ARE EXPECTED TONIGHT. VFR TONIGHT.
SOME MID-LEVEL CLOUDS MAY ENTER THE PICTURE TOMORROW AFTERNOON,
BUT STILL VFR WITH WEST-SOUTHWEST WINDS UNDER 10 KTS AFTER
STARTING THE DAY LIGHT AND VARIABLE.

OUTLOOK...

MONDAY NIGHT AND TUESDAY...LO PRES TRACKS SOUTH OF THE AREA. BEST
CHANCE FOR SHRA AND POSSIBLY TSRA NEAR ILG/MIV WITH CHANCES
DECREASING FARTHER NORTH. NRN FRINGE OF PRECIP MAY SET UP CLOSE
TO PHILADELPHIA TERMINALS. A PERIOD OF MVFR-IFR CONDITIONS POSSIBLE
AT TIMES OF HEAVIER SHRA. PRECIP MOST LIKELY EXITS THE SRN TERMINALS
TUESDAY AFTN.

TUESDAY NIGHT...VFR

WEDNESDAY THROUGH THURSDAY...SCT SHRA/TSRA AS MULTIPLE DISTURBANCES
TRACK THRU THE REGION. SOME FLIGHT RESTRICTIONS POSSIBLE.

&&

.MARINE...
SUB-SCA CONDITIONS EXPECTED ACROSS OUR WATERS TODAY AND TONIGHT.
WINDS WILL INCREASE THIS AFTERNOON FROM THE SOUTHWEST BETWEEN 10-15
KNOTS AND SEAS WILL SLOWLY BUILD UPWARDS OF 3 FEET. COLD FRONT WILL
PASS THROUGH THE WATERS LATER THIS EVENING AND WINDS WILL BACK
TOWARDS THE WEST-NORTHWEST LATE.

OUTLOOK...
MONDAY...LIGHT W-NW WINDS.

MONDAY NIGHT THROUGH TUESDAY NIGHT...LIGHT SLY WINDS MONDAY EVE
BACK OVERNIGHT AND ACQUIRE MORE OF AN ONSHORE COMPONENT AS LOPRES
APPROACHES THE DE COAST FROM THE WEST. A TIGHTENING PRESSURE
GRADIENT WILL STRENGTHEN THE WINDS JUST TO THE NORTH OF THE LOW
TUESDAY. BASED ON THE CURRENT FORECAST TRACK OF THIS LOW, THE
DELAWARE AND SRN NJ ATLANTIC BEACHES AND EVEN THE LOWER DELAWARE
BAY MAY APPROACH SCA CRITERIA.

WEDNESDAY THROUGH THURSDAY...ONSHORE FLOW CONTINUES BUT WILL WEAKEN
OVER TIME.

&&

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

&&

$$
SYNOPSIS...KLEIN
NEAR TERM...GAINES/HEAVENER
SHORT TERM...HEAVENER
LONG TERM...KLEIN
AVIATION...GAINES//KLEIN
MARINE...HEAVENER/KLEIN






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