Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 010115
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
915 PM EDT TUE SEP 30 2014

.SYNOPSIS...
A WEAKENING COLD FRONT WILL SLOWLY SAG THROUGH THE REGION TONIGHT
ALLOWING HIGH PRESSURE TO WORK IN FROM THE NORTH LATER ON WEDNESDAY.
THE HIGH WILL SLIDE TO OUR EAST BY FRIDAY BEFORE A MORE POTENT COLD
FRONT SWEEPS THROUGH FRIDAY NIGHT INTO SATURDAY MORNING. ANOTHER
BREAK BETWEEN COLD FRONTS IS EXPECTED THROUGH MONDAY.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
A LINE OF SHOWERS AND THUNDERSTORMS CONTINUES TO PROGRESS OUT OF
SOUTH CENTRAL PENNSYLVANIA INTO SOUTHEASTERN PENNSYLVANIA THIS
EVENING AND IS EVER SO SLOWLY MOVING TOWARDS OUR AREA. THIS
ACTIVITY IS ASSOCIATED WITH A FRONTAL BOUNDARY MOVING ACROSS THIS
AREA AND IS BEING ENHANCED BY A STRONG DIFFLUENT AREA ALOFT AND
VORTICITY IMPULSE AHEAD OF AN APPROACHING MID-UPPER LOW MOVING
INTO WESTERN PENNSYLVANIA. MEANWHILE, A WEAKENING BACKDOOR COLD
FRONT WILL CONTINUE TO SLOWLY SETTLE SOUTHWARD ACROSS THE AREA
THROUGH THE OVERNIGHT WHICH WILL KEEP A CONTINUED EASTERLY TO
NORTHEAST FLOW ACROSS THE AREA AND PROVIDE AMPLE MOISTURE. SHORT
TERM MODEL GUIDANCE INDICATES THE LINE OF SHOWERS AND
THUNDERSTORMS MOSTLY WEAKENING BEFORE IT GETS TO OUR AREA,
HOWEVER, SINCE IT IS APPROACHING THE AREA, HAVE DECIDED TO
INCREASE THE POPS ACROSS OUR WESTERN ZONES AND EXTEND THE CHANCE
OF THUNDERSTORMS A FEW HOURS. ELSEWHERE ISOLATED TO SCATTERED
SHOWERS MAY STILL DEVELOP ANYWHERE AS THE COLD POOL ALOFT SLIDES
ACROSS THE AREA.

GUIDANCE WAS ALSO INDICATING THE POTENTIAL FOR PATCHY FOG, AND WE
KEPT THIS IN THE FORECAST WITH THE EAST-NORTHEAST FLOW AND AMPLE
MOISTURE. FOR OVERNIGHT TEMPERATURES, WE MOSTLY TOOK A BLEND OF
MET/MAV GUIDANCE AND EXPECT LOWS MOSTLY IN THE 50S, EXCEPT SOME
LOWER 60S ALONG THE COAST AND IN MORE URBAN AREAS.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
THROUGH THE DAYTIME WEDNESDAY, THE PREVIOUSLY MENTIONED UPPER LOW
WILL BE SWINGING BY TO OUR NORTHEAST, AND BY LATE IN THE DAY,
SURFACE HIGH PRESSURE TO OUR NORTH WILL BEGIN TO SLOWLY BUILD TOWARD
OUR REGION. THERE WILL STILL BE THE POSSIBILITY FOR ISOLATED TO
SCATTERED SHOWERS, ESPECIALLY THROUGH MORNING TO ABOUT MIDDAY, AND
WE SLOWLY TRAIL POPS OFF THROUGH THE AFTERNOON. SKIES WILL BE MAINLY
CLOUDY THROUGH MIDDAY BEFORE SOME SLOW THINNING OCCURS LATE-DAY.
MAXIMUM TEMPERATURES WERE A BLEND OF MET/MAV GUIDANCE WITH
CONTINUITY, AND WE EXPECT HIGHS MOSTLY IN THE LOW TO MID 70S.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
OPERATIONAL MODELS ARE IN PRETTY GOOD AGREEMENT WITH THE LARGE SCALE
FEATURES THROUGH THE WEEKEND. THE FIRST SUCH FEATURE BEING THE
DEPARTING UPPER LEVEL CUT-OFF LOW THAT SHOULD BE TO OUR IMMEDIATE
EAST. THEN WE HAVE THE POTENTIAL PHASING OF A STRONG NORTHERN AND
SOUTHERN STREAM SYSTEM TO OUR WEST THAT CARVES OUT A VERY LARGE AND
DEEP CLOSED LOW/TROUGH ACROSS THE UPPER MID-WEST BY LATE FRIDAY
NIGHT.

THURSDAY...RATHER DRY DAY EXCEPT FOR SOME LINGERING SHOWERS EARLY ON
ACROSS OUR EASTERN PORTIONS. THERE COULD STILL BE SOME MID-LEVEL
INSTABILITY TO WORK WITH AS THE MID-LEVEL COLD POOL SCRAPES BY BUT
NOT EXPECTING MUCH QPF WITH. MID AND UPPER LEVEL RIDGING BECOME MORE
PROMINENT ON THURSDAY WHICH SHOULD GIVE WAY TO LATE DAY SUNSHINE.
TEMPERATURES WILL BE IN THE LOW-70S; AT OR SLIGHTLY BELOW NORMAL.

FRIDAY...MODEL GUIDANCE MAY BE BREAKING DOWN THE RIDGING OVERHEAD A
BIT TOO FAST, ESPECIALLY GIVEN THE DOWNSTREAM UPPER LEVEL LOW IS
STILL LINGERING BY AND THE APPROACH OF A DEEPENING TROUGH UPSTREAM,
THE RIDGE SHOULD BUILD SLIGHTLY BEFORE BREAKING. ONSHORE FLOW AHEAD
OF THE NEXT TROUGH AND ATTENDANT SURFACE FRONT MAY ALLOW FOR
SCATTERED SHOWERS TO BREAK OUT ALONG THE HIGHER ELEVATION LOCATIONS
ACROSS OUR WESTERN ZONES BY LATER FRIDAY AFTERNOON. DO NOT SEE MUCH
IN THE WAY OF CONVECTION WITH THIS ACTIVITY GIVEN THE STABLE LOWER
ATMOSPHERE. WE SEE A INCREASE IN SHOWER COVERAGE AND POSSIBLY
INTENSITY BY LATE FRIDAY NIGHT AS A STRONGER COLD FRONT INCHES
CLOSER. DAYTIME TEMPERATURES SHOULD REMAIN MUCH THE SAME, LOW-70S
WITH INCREASING COLD COVER.

SATURDAY...TRANSITION DAY WITH A STRONG FRONT EXPECTED TO SWEEP
THROUGH DURING THE MORNING HOURS. DEEP SOUTHWEST FLOW AHEAD OF THE
FRONT WILL ALLOW PWATS TO CLIMB TO WELL ABOVE NORMAL MAKING FOR
HEAVIER RAINFALL. ANTECEDENT CONDITIONS ARE STILL PRETTY DRY ACROSS
THE REGION SO NOT EXPECTING ANYTHING OUT OF THE ORDINARY TO OCCUR
WITH THE POSSIBLE HEAVIER RAIN. LOTS OF CLOUD COVER AND COLD AIR
ADVECTION OCCURRING DROPPING TEMPERATURES BACK INTO THE MID TO
UPPER-60S.

SUNDAY - TUESDAY...CLOSED MID-LEVEL LOW ESTABLISHES ITSELF OVER
NORTHERN ONTARIO DURING THE SATURDAY THROUGH TUESDAY TIMEFRAME.
PREFERRED THE CMC AND UKMET EVOLUTION OF THE MID-LEVEL HEIGHT
FIELD OVER THE GFS AND ECMWF...BOTH OF WHICH HAVE A MORE
NEGATIVELY TILTED TROUGH AND PLACEMENT OF THE CLOSED LOW FURTHER
SOUTH AND EAST. THERE IS STILL QUITE A BIT UNCERTAINTY AS SHOWN BY
BOTH THE GEFS AND ECENS SPREAD IN MID-LEVEL HEIGHT FIELDS FROM THE
MEAN AND THIS THINKING IS SUPPORTED BY THE LATEST MODEL
VERIFICATIONS WHICH INDICATE A LESS AMPLIFIED SOLUTION.

EXPECT WINDS TO DECREASE SATURDAY NIGHT AS A RIDGE OF HIGH PRES
NOSES INTO THE REGION. IF THE BOUNDARY LAYER DECOUPLES ENOUGH W/
LIGHT WINDS...COULD SEE LOW TEMPS IN THE 35-40 RANGE IN THE
NORTHWEST INTERIOR OF OUR CWA. SUNDAY IS SHAPING UP TO BE THE
COOLEST DAY OF THE PERIOD...WITH 850 HPA TEMPS SUPPORTING HIGHS
SEVERAL DEGREES BELOW NORMAL...MID 50S IN THE POCONOS TO MID 60S
IN SOUTH JERSEY. A WEAK COLD FRONT IS PROGGED TO MOVE THROUGH
THE REGION EARLY ON TUESDAY...PRESENTING THE BEST CHANCE OF
PRECIPITATION DURING THIS TIMEFRAME. TEMPERATURES WILL RETURN
TO SEASONABLE LEVELS ON MONDAY AND CONTINUE THROUGH TUESDAY

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

LATE EVENING THROUGH OVERNIGHT...VFR CONDITIONS TO START OUT,
BEFORE MVFR/IFR CONDITIONS DEVELOP OVERNIGHT. ISOLATED/SCATTERED SHOWERS
MAY IMPACT SEVERAL OF THE TAF SITES LATER THIS EVENING INTO THE
OVERNIGHT HOURS, WITH THE HEAVIEST SHOWERS MOST LIKELY AT
ABE/RDG. THERE REMAINS SOME THUNDERSTORM ACTIVITY TO OUR WEST, BUT
WE EXPECT MUCH OF THIS TO WEAKEN BEFORE REACHING THE AREA; WILL
AMEND IF THE STORMS GET WITHIN A COUPLE OF HOURS FROM A TAF SITE,
WHICH SOULD MOST LIKELY BE RDG AND AFTER LOCAL MIDNIGHT.

WEDNESDAY...POSSIBLE MVFR/IFR CONDITIONS WILL LIKELY LAST THROUGH
THE MORNING, BEFORE BECOMING VFR AROUND MIDDAY TO EARLY AFTERNOON
FOR THE TAF SITES. AN ISOLATED TO SCATTERED SHOWER REMAINS
POSSIBLE THROUGH THE MORNING. NORTHEASTERLY WINDS ARE EXPECTED,
MOSTLY IN THE 8 TO 10 KNOT RANGE.

OUTLOOK...
THURSDAY...MVFR EARLY BECOMING VFR. EASTERLY WINDS EXPECTED.
POSSIBLE LINGERING SHOWER EARLY AT MIV/ACY, OTHERWISE DRY.

FRIDAY...MOSTLY VFR. RAIN, HEAVY AT TIMES LATE, OVERSPREADS THE AREA
FROM THE WEST. REDUCED VSBYS AND CIGS IN HEAVY SHOWERS. WINDS BACK SOUTH-SOUTHWEST.

SATURDAY...MVFR/IFR EARLY IN HEAVY RAIN, TRENDING VFR. WINDS
CONTINUE TO BACK TO THE WEST-NORTHWEST.

&&

.MARINE...
AN EAST-NORTHEAST FLOW WILL BECOME MORE NORTHEASTERLY ACROSS OUR
AREA WATERS THROUGH THIS EVENING AND TONIGHT. SPEEDS ARE EXPECTED TO
INCREASE THROUGH THE OVERNIGHT, AND FROM EARLY MORNING WEDNESDAY
THROUGH THE DAYTIME, SOME GUSTS BETWEEN 20 TO 25 KNOTS ARE POSSIBLE.
IN ADDITION, SEAS WILL ALSO BE BUILDING IN THE INCREASING NORTHEAST
FLOW. SEAS ARE EXPECTED TO BUILD TO AROUND 4 FEET BY AROUND DAYBREAK
WEDNESDAY, AND FORECAST LEVELS SHOULD REACH 5 FEET FROM ABOUT GREAT
EGG INLET NORTHWARD DURING THE DAYTIME WEDNESDAY. WE THEREFORE
DECIDED TO RAISE A SMALL CRAFT ADVISORY FOR OUR NORTHERN ATLANTIC
COASTAL WATERS, FROM GREAT EGG INLET NORTHWARD TO SANDY HOOK,
BEGINNING AT 15Z WEDNESDAY.

FOR DELAWARE BAY, WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL
CRAFT ADVISORY LEVELS THROUGH TONIGHT AND WEDNESDAY.

OUTLOOK...
THURSDAY - FRIDAY...SCA CONDITIONS WILL LIKELY PERSIST ON OUR
WATERS THROUGH EARLY FRIDAY AS WE CONTINUE WITH THE EASTERLY ONSHORE
FLOW. SEAS WILL CONTINUE TO RUN AROUND 5 FEET. WINDS BEGIN TO BACK
TOWARDS THE SOUTH-SOUTHEAST BY FRIDAY AHEAD OF THE NEXT COLD FRONT.

SATURDAY...STRONG COLD FRONT MOVES THROUGH. WINDS BACK TOWARDS THE
WEST-NORTHWEST LATER IN THE DAY AND WITH STRONGER COLD AIR
ADVECTION OCCURRING, WE COULD SEE A RETURN TO SCA CONDITIONS.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 11 AM WEDNESDAY TO 6 AM EDT THURSDAY
     FOR ANZ450>452.

&&

$$
SYNOPSIS...HEAVENER
NEAR TERM...KLINE/ROBERTSON
SHORT TERM...KLINE
LONG TERM...FRANCK/HEAVENER
AVIATION...HEAVENER/KLINE/ROBERTSON
MARINE...HEAVENER/KLINE




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