Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 281951
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
351 PM EDT TUE OCT 28 2014

.SYNOPSIS...
A COLD FRONT WILL MOVE FROM WEST TO EAST ACROSS THE REGION TONIGHT
AND THEN WILL MOVE OFFSHORE ON WEDNESDAY. HIGH PRESSURE WILL BUILD
INTO THE REGION FROM THE OHIO VALLEY WEDNESDAY NIGHT AND THURSDAY.
BY FRIDAY TWO LOW PRESSURE SYSTEMS WILL START TO IMPACT OUR REGION, ONE
OVER THE GREAT LAKES AND ANOTHER OFF THE CAROLINA COASTLINE. THESE
AREAS OF LOW PRESSURE WILL BE LOCATED OFFSHORE ON SATURDAY. BY
SUNDAY THE STRENGTHENING LOW PRESSURE SYSTEM WILL CONTINUE MOVING
NORTHEAST OFF THE NEW ENGLAND COASTLINE. HIGH PRESSURE WILL BUILD
BACK INTO THE REGION FOR MONDAY AND TUESDAY.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
THE MID LEVEL RIDGE WILL CONTINUE TO DRIFT EASTWARD AND OUT OVER THE
WESTERN NORTH ATLANTIC TONIGHT. MEANWHILE, A TROUGH WILL APPROACH
SLOWLY FROM THE WEST.

A SURFACE COLD FRONT EXTENDED ACROSS THE EASTERN GREAT LAKES AND THE
OHIO RIVER VALLEY AT MID AFTERNOON. THE BOUNDARY WILL CONTINUE TO
PROGRESS EASTWARD AND IT IS FORECAST TO BE LOCATED ALONG THE
INTERSTATE 81 CORRIDOR THROUGH PENNSYLVANIA, MARYLAND AND VIRGINIA
AROUND DAYBREAK.

A BAND OF RAIN SHOWERS ALONG AND BEHIND THE FRONT IS EXPECTED TO
MOVE INTO OUR NORTHWESTERN COUNTIES LATE TONIGHT.

WE ARE ANTICIPATING A LIGHT WIND, FAVORING THE SOUTH AND SOUTHWEST
IF ANY DIRECTION AT ALL. CLOUDS WILL BE ON THE INCREASE AND MINIMUM
TEMPERATURES SHOULD BE MILD FOR THIS TIME OF THE YEAR, RANGING
MAINLY IN THE 50S.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
THE COLD FRONT IS FORECAST TO PASS ACROSS THE REMAINDER OF OUR
AREA AND OFF THE COAST ON WEDNESDAY MORNING. THE BAND OF SHOWERS
IS EXPECTED TO TRAIL THE BOUNDARY AND WE WILL CONTINUE TO MENTION
A CHANCE OF SHOWERS THROUGH MUCH OF THE DAY. RAINFALL AMOUNTS
SHOULD BE MAINLY LESS THAN A QUARTER INCH.

A SOUTHWEST WIND AROUND 6 TO 12 MPH IN THE MORNING IS EXPECTED TO
VEER TO THE WEST NORTHWEST FOLLOWING THE COLD FRONTAL PASSAGE.
AFTERNOON TEMPERATURES SHOULD BE ABOUT 5 TO 7 DEGREES ABOVE NORMAL.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
WEDNESDAY NIGHT: A FRONTAL BOUNDARY WILL BE OFFSHORE TO START THE
PERIOD WHICH SHOULD RESULT IN CLEARING CONDITIONS, PERHAPS A FEW
SHOWERS STILL ALONG THE COAST EARLY. WINDS SHIFTING TO NORTHWEST BEHIND
THE FRONT. TEMPERATURES A COMPROMISE BETWEEN THE 12Z GFS AND THE
MAV/MET GUIDANCE.

THURSDAY THROUGH FRIDAY: HIGH PRESSURE BUILDS OVER THE REGION. DRY.
GENERAL NORTHWEST FLOW TILL THE HIGH PASSES BY LATE FRIDAY. EVEN
WITH TEMPERATURES THURSDAY MORNING STILL IN THE LOW TO MID 40`S WITH
NORTHWEST FLOW THIS FORECAST DOES UNDERCUT MAV/MET BY A COUPLE OF
DEGREES FOR HIGHS THURSDAY (MID-UPPER 50`S). FOR FRIDAY, USING
THE 925 MB TEMPS WOULD YIELD HIGHS IN THE UPPER 50`S AT PHL ON
FRI, THOUGH THINKING WITH CLOUDS AND A LOWER SUN ANGLE THIS SHOULD
BE KNOCKED BACK TILL ABOUT THE MID 50`S. COOLER NW BOTH DAYS.

FRIDAY NIGHT THROUGH SUNDAY NIGHT:

* STRONG WINDS AND POSSIBLE COASTAL STORM SATURDAY*

STORM OVERVIEW: TWO LOW PRESSURE CENTERS WILL BE MOVING TOWARD THE
REGION TO START OFF THIS PERIOD. ONE NEAR DETROIT AND THE OTHER OFF
HATTERAS. AN UNDERSTATEMENT WOULD BE THAT THE MODELS AND THE
RESPECTIVE ENSEMBLES HAVE BEEN GOING BACK AND FORTH ON THE OUTCOME.
MANY OF THE KEY PLAYERS INVOLVED ARE STILL NOT FIRMLY IN THE UPPER
AIR NETWORK TO WHICH MORE SAMPLED DATA WILL BECOME AVAILABLE. THIS
MAY REDUCE SOME UNCERTAINTY OVER THE NEXT DAY OR TWO. THE MODEL
SPREAD FROM THE GEFS, ECMWF, CMC, UKMET AND VARIOUS ENSEMBLE
PACKAGES SHOW TWO MAIN OUTCOMES. THE FIRST IS FOR A FRONTAL
PASSAGE WITH JUST SOME RAIN SHOWERS WITH THE NORTHERN WAVE COMING
EAST THROUGH THE REGION ON SATURDAY FOLLOWED BY A QUICK BUT POTENT
COLD SHOT WITH INTERACTION BETWEEN THE LOWS WELL TO OUR EAST AND
DISORGANIZED. THIS OUTCOME HAS BEEN GAINING TRACTION TODAY WITH
MOST DAY OPERATIONAL MODEL RUNS. POSSIBILITY NUMBER TWO INVOLVES
MORE INTERACTION BETWEEN THE LOW OFFSHORE AND THE LOW MOVING EAST
OUT OF THE GREAT LAKES (00Z ECMWF). THIS WOULD RESULT IN A RAINER
AND COOLER DAY WITH THE OUTSIDE POSSIBILITY OF RAIN CHANGING TO
SNOW DUE TO DYNAMICAL COOLING. EITHER WAY FRIDAY NIGHT LOOKS DRY
STILL WITH INCREASING CLOUDS AND LIGHT WINDS. SATURDAY WILL
FEATURE RAIN SHOWERS AND WINDY CONDITIONS AS THE LOW PRESSURE(S)
ORGANIZE AND STRENGTHEN. THE PRECIPITATION MAY BE MIXED AT TIMES AS
WELL WITH SNOW DEPENDING ON THE EXACT OUTCOME. BY SUNDAY WRAP-
AROUND PRECIPITATION WILL END WITH CLEARING BUT STILL WINDY AND
COOL.

THE WINDS WILL BE THE MAIN IMPACT FROM THIS SYSTEM.

SATURDAY AND SATURDAY NIGHT:  WITH A INCREASING PRESSURE GRADIENT
WINDS SHOULD GRADUALLY INCREASE THROUGHOUT THE DAY. FORTUNATELY WITH
PRECIPITATION AND A STABLE ENVIRONMENT IT DOES NOT APPEAR FAVORABLE
FOR MIXING. SUSTAINED WINDS FROM 15-20 MPH WITH GUSTS UP TO 30 MPH
ARE POSSIBLE. WINDS JUST OFF THE SURFACE AT ABOUT 900-925 MB LOOK TO
BE AROUND 50 MPH SO EVEN ISOLATED HIGHER GUSTS CAN NOT BE RULED OUT.
WINDS OFFSHORE MAY STRENGTHEN SOME SATURDAY NIGHT (SEE MARINE).

SUNDAY: THE LOW PRESSURE WILL START TO MOVE AWAY REDUCING THE
PRESSURE GRADIENT. THE 900 MB WINDS SHOULD RELAX. HOWEVER A STEEPER
LAPSE RATE WILL BE PRESENT ALLOWING FOR MIXING. STILL EXPECTING
WINDS FROM 15-20 MPH WITH GUSTS TO 30 MPH.

WINDS WILL DEPEND ON THE ACTUAL EVOLUTION OF THIS SYSTEM(S).
STRONGER LOW MEANS A BIGGER PRESSURE GRADIENT AND STRONGER WINDS.
THE FORECASTED WINDS REFLECT A COMPROMISE BETWEEN THE STRONGER 00Z ECMWF
FROM THIS EVENING AND THE MORE STRUNG OUT AND WEAKER 12Z GFS.

PRECIPITATION TYPE

THIS WILL HIGHLY DEPENDENT ON THE OVERALL MAKEUP OF THIS STORM.
OPTION ONE PRESENTED IN THE OVERVIEW SECTION WOULD MEAN RAIN SHOWERS
TO SCATTERED FLURRIES/SPRINKLES AS THE COLD AIR MOVES IN. OPTION TWO
WITH MORE INTERACTION BETWEEN THE LOWS IS MORE INTERESTING. A LOW
PRESSURE SYSTEM ORGANIZING MORE TO OUR SOUTH WOULD DRAW MORE WARM
AIR NORTHEAST (00Z ECMWF) AND KEEP THINGS ALL RAIN TILL PERHAPS
WRAP-AROUND STUFF SATURDAY NIGHT. IF THE LOW PRESSURE INTERACTIONS
TAKE PLACE OFF OUR COASTLINE THEN LESS WARM AIR WOULD BE PULLED IN
AND DYNAMIC COOLING MAY REALLY KEEP TEMPERATURES DOWN SATURDAY AND
ALLOW FOR CAA CHANGING RAIN TO SNOW NW OF PHL SATURDAY AFTERNOON AS
MID-LEVEL TEMPERATURES COOL BELOW 0C AT 925 AND 850 MB (06Z GFS). AN
INVERTED TROUGH FEATURE MAY DEVELOP AS WELL WHICH COULD LINGER
STEADIER PRECIPITATION INTO SATURDAY NIGHT AS WELL, USUALLY HARD TO
PIN THESE DOWN. IN THE UNLIKELY EVENT A SUSTAINED PERIOD OF SNOW WERE TO
OCCUR RATIOS WOULD BE 5:1 IF NOT LOWER DUE TO VERY WARM GROUND
TEMPERATURES AND SURFACE TEMPERATURES ABOVE FREEZING.

RIGHT NOW OPTION ONE APPEARS TO BE GAINING MORE TRACTION AND THAT IS
THE DIRECTION IN WHICH THIS FORECAST WILL GO, FOR BETTER OR WORSE.
THIS WOULD MINIMIZE SNOW CHANCES.

BOTTOM LINE
- STRONG WINDS ARE EXPECTED SATURDAY AND SATURDAY NIGHT WITH SOME
PERIODS OF COLD RAIN WITH THE THREAT OF VERY LIGHT MIXED
PRECIPITATION SATURDAY NIGHT.

- OF NOTE WHEN COMPARED TO THE LATE OCTOBER SNOWFALL IN 2011, THIS
SYNOPTIC SET-UP HAS CONSIDERABLE DIFFERENCES. THAT EVENT HAD A
CONSIDERABLE AMOUNT OF COLD AND DRY AIR ENTRAINED FROM A HIGH
PRESSURE SYSTEM WHICH ALLOWED FOR DYNAMICAL AND EVAPORATIONAL
COOLING. THIS SET-UP IS NOT EXPECTED TO HAVE EITHER OF THESE ATTM.

MONDAY AND TUESDAY: COOLER AND DRY WITH NORTHWEST FLOW GIVING WAY
TO SOUTHWESTERLY FLOW AS THE NEXT HIGH PRESSURE MOVES THROUGH.  DID
UNDERCUT MEX AND OTHER STATISTICAL GUIDANCE DUE TO THE NORTHWEST FLOW
FOR MONDAY. ON TUESDAY WITH A SOUTHWESTERLY  DID GO ABOVE THE
MODEL CONSENSUS ON TEMPERATURES.


&&

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

18Z TAFS VFR THRU THIS EVENING, UNCERTAIN ABOUT MVFR/IFR
CONDITIONS TOWARD WEDNESDAY MORNING AND A CHANCE OF SHOWERS LATER
WEDNESDAY. WE ADDED LLWS FOR KABE AND KRDG.

FOR THIS AFTERNOON VFR CIRRUS WITH SOUTH TO SOUTHWEST WINDS
AVERAGING CLOSE TO 10 KNOTS. A SLIGHT BACKING OF THE WIND DIRECTION
TOWARD EVENING.

THIS EVENING INTO THE OVERNIGHT. CONTINUED MAINLY CIRRUS BASED VFR
CIGS. VERY LIGHT WINDS FROM THE SOUTH IF NOT CALM. A LOW LEVEL JET
IS PREDICTED TO PASS ACROSS OUR NORTHWEST TERMINALS AND AIRPORTS.
SINCE THE COMBINATION OF MOST LIKELY CALM WINDS AND LOCATION OF
THE LLJ, WE DID ADD A LLWS PERIOD AT KABE AND KRDG AND WILL
MONITOR FOR THE REST OF THE TERMINALS.

LATE TONIGHT WE DID BRING MOST TERMINALS DOWN TO MVFR CONDITIONS
MAINLY DUE TO FOG AND ALSO SOME STRATUS AND STRATOCU AND SOME OF
THE MORE INLAND TERMINALS. CONFIDENCE THOUGH IS NOT HIGH AS IT
DEPENDS UPON HOW THICK THE CIRRUS WILL BE.

ON WEDNESDAY MORNING, VFR CONDITIONS PREDICTED TO RETURN AS A COLD
FRONT STARTS MOVING THROUGH THE AREA. WINDS ARE FORECAST TO BECOME
WEST. SHOWERS ARE POSSIBLE AT THE MORE INLAND TERMINALS WITH THEM
POSSIBLY REACHING THE INTERSTATE 95 CORRIDOR AIRPORTS BY THE END
OF THE TAF FCST PERIOD. WITH THE 30HR TAF AT KPHL WE DO SHOW A
WINDOW OF MAINLY VFR SHOWERS DURING THE AFTERNOON.


OUTLOOK...
WEDNESDAY NIGHT THROUGH FRIDAY NIGHT: VFR WITH WINDS UNDER 10
KNOTS.

SATURDAY: MAINLY MVFR CONDITIONS LIKELY THROUGHOUT MOST OF THE DAY
WITH CLOUDS AND RAIN, OCCASIONAL IMPROVEMENT TO MVFR CAN NOT BE
RULED OUT. NORTHWEST WIND INCREASING FROM 10 TO 20 KNOTS IN THE
AFTERNOON WITH HIGHER GUSTS UP TO 30 KNOTS.

SATURDAY NIGHT: MAINLY VFR CONDITIONS WITH SOME MVFR CONDITIONS IN
LIGHT RAIN SHOWERS, POSSIBLY MIXED WITH NON ACCUMULATING SNOW
FLURRIES. NORTHWEST WINDS 10-20 KNOTS WITH GUSTS UP TO 25 KNOTS.

SUNDAY: VFR. NORTHWEST WINDS 15-25 KNOTS WITH GUSTS UP TO 30
KNOTS.


&&

.MARINE...
WE WILL MAINTAIN THE SMALL CRAFT ADVISORY FOR OUR OCEAN WATERS FROM
MIDNIGHT UNTIL 200 PM ON WEDNESDAY. CONDITIONS WILL BE MARGINAL. THE
STEADY SOUTH TO SOUTHWEST FLOW MAY BUILD SEAS NEAR 5 FEET ON OUR
OUTER WATERS. OCCASIONAL WIND GUSTS AROUND 25 KNOTS ARE ANTICIPATED.

CONDITIONS ARE EXPECTED TO REMAIN BELOW THE SMALL CRAFT ADVISORY
CRITERIA ON DELAWARE BAY.

OUTLOOK...
WEDNESDAY NIGHT THROUGH FRIDAY NIGHT: SUB SCA SEAS AND WINDS WITH
BUILDING SEAS AND INCREASING WINDS LATE FRIDAY AND FRIDAY NIGHT.


SATURDAY THROUGH SUNDAY: SCA WINDS LIKELY DEVELOPING EARLY SATURDAY
WITH THE DEVELOPMENT OF LOW PRESSURE OFF THE COAST. GALE WIND GUSTS
POSSIBLE LATE SATURDAY AFTERNOON THROUGH SUNDAY. LINGERING SCA
GUSTS POSSIBLE SUNDAY NIGHT. SEAS ABOVE SCA CRITERIA.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 2 PM EDT
     WEDNESDAY FOR ANZ450>455.

&&

$$
SYNOPSIS...GAINES
NEAR TERM...IOVINO
SHORT TERM...IOVINO
LONG TERM...GAINES
AVIATION...GAINES/GIGI
MARINE...GAINES/IOVINO






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