Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 200736
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
336 AM EDT MON OCT 20 2014

.SYNOPSIS...
A HIGH PRESSURE SYSTEM NEAR NORFOLK WILL MOVE OFFSHORE TODAY.
A LOW PRESSURE SYSTEM WITH AN ASSOCIATED COLD FRONT OVER LAKE
SUPERIOR WILL DIVE SOUTHEAST REACHING OUR REGION DURING THE DAY ON
TUESDAY. ANOTHER LOW PRESSURE SYSTEM WILL FORM OFF THE MID ATLANTIC
COAST LINE ON TUESDAY AND THEN DRIFT SLOWLY NORTHEAST, REACHING CAPE
COD ON THURSDAY AND NOVA SCOTIA ON FRIDAY. HIGH PRESSURE WILL
THEN BRIEFLY MOVE IN FROM THE WEST LATE FRIDAY. A COLD FRONT
SHOULD PASS THROUGH THE NORTHEAST AROUND SATURDAY NIGHT, WITH
ANOTHER HIGH PRESSURE SYSTEM REACHING THE GREAT LAKES ON SUNDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THE FROST ADVISORY AND FREEZE WARNING REMAINS IN EFFECT FOR EARLY
THIS MORNING, AS MANY AREAS ARE WELL DOWN INTO THE 30S. THE HIGH
LEVEL CLOUDS THOUGH MAY HAVE SLOWED THE TEMPERATURE DROP A LITTLE
FOR SOME SPOTS.

HIGH PRESSURE WILL BE SHIFTING OFFSHORE TODAY ALLOWING A
SOUTHWESTERLY FLOW AT THE SURFACE TO DEVELOP. THIS FLOW WILL BE MUCH
LESS COMPARED TO THE GUSTINESS THAT WAS OBSERVED YESTERDAY. A ROBUST
SHORT WAVE DIVING SOUTHEASTWARD FROM THE MIDWEST WILL HELP CARVE OUT
ANOTHER UPPER-LEVEL TROUGH ACROSS THE GREAT LAKES AND OHIO VALLEY
DURING THE COURSE OF TODAY. DOWNSTREAM FROM THIS, SOME WEAK WAA IS
FORECAST TO OCCUR ACROSS THE MID ATLANTIC. THIS COMBINED WITH THE
PRESENCE OF AN UPPER-LEVEL JET WILL SPREAD AREAS OF MID AND HIGH
LEVEL CLOUDINESS ACROSS THE REGION. THE MAIN LIFT ASSOCIATED WITH
THE AMPLIFYING UPPER-LEVEL TROUGH IS FORECAST TO REMAIN TO OUR WEST,
THEREFORE WE MAINTAINED A DRY FORECAST TODAY. WE DID CARRY SOME
ADDITIONAL CLOUDINESS THOUGH FOR MANY AREAS.

AS FOR HIGH TEMPERATURES, WE USED A MODEL/MOS BLEND WHICH RESULTS
IN MILDER TEMPERATURES COMPARED TO YESTERDAY. THIS LINES UP WITH THE
WEAK WAA THAT IS ALSO FORECAST THROUGH THE DAY ALONG WITH A
SOUTHWESTERLY SURFACE FLOW.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
AN UPPER-LEVEL TROUGH WILL CONTINUE TO AMPLIFY ACROSS THE GREAT
LAKES AND NORTHEAST. AS THIS OCCURS, LOW PRESSURE ORGANIZING AT THE
SURFACE IS FORECAST TO BE IN THE GENERAL VICINITY OF THE EASTERN
GREAT LAKES LATER TONIGHT.

THERE IS SOME WAA BEING MAINTAINED AHEAD OF THIS SYSTEM, BUT OVERALL
THE BEST FOCUS FOR THIS IS FORECAST TO BE TO OUR SOUTH AND EAST. IN
ADDITION, A DECENT SHOT OF LOW-LEVEL THETA-E ADVECTION IS FORECAST
TO ARRIVE THROUGH THE NIGHT. AS THE ATMOSPHERE MOISTENS AND THE
LARGE SCALE ASCENT BEGINS TO OVERSPREAD THE REGION LATE, SOME
SHOWERS COULD DEVELOP. THIS LOOKS TO BE ACROSS OUR WESTERN ZONES
WHICH IS WHERE WE HAVE THE HIGHEST /CHC/ POPS LATE. THERE MAY ALSO
BE ANOTHER AREA OF FOCUS, WHICH IS OFFSHORE WHERE THE LEADING EDGE
OF THE STRONGER THETA-E ADVECTION INTERACTS WITH SOME INSTABILITY
PARTIALLY DUE TO THE GULF STREAM. OVERALL, THE CLOUDS ARE FORECAST
TO LOWER SOME THROUGH THE NIGHT FROM WEST TO EAST AND THE POPS WERE
GRADUALLY INCREASED AS WELL.

AS FOR LOW TEMPERATURES, WITH THE THICKENING CLOUDS AND A WEAK
SOUTHWESTERLY FLOW IN PLACE IT WILL BE A MILDER NIGHT. OVERALL, WE
USED A MOS BLEND WITH SOME MINOR ADJUSTMENTS.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
TUESDAY THROUGH THURSDAY NIGHT: A COASTAL LOW PRESSURE SYSTEM
WILL DEVELOP OFFSHORE AND BE SLOW TO MOVE NORTHEAST THROUGHOUT
THIS PERIOD. THE END RESULT WILL BE GRAY GLOOMY COOLER DAYS
FEATURING RAIN SHOWERS AND SOME BRISK NORTHWESTERLY WINDS
WEDNESDAY AND THURSDAY AFTERNOONS. THE FORMATION OF THIS LOW
PRESSURE WILL START WITH TWO PIECES, A STRONG UPPER LEVEL LOW AND
COLD FRONT DIVING FROM THE GREAT LAKES INTO THE MID-ATLANTIC AND A
LOW PRESSURE FORMING OFF THE CAROLINA`S. THE UPPER LOW AND COLD
FRONTAL BOUNDARY WILL LEAD TO CONTINUED SCATTERED SHOWERS ON
TUESDAY TO THE REGION WITH A MOISTURE PLUME FROM THE CAROLINA LOW
WELL OFFSHORE. BY TUESDAY NIGHT WE BEGIN TO SEE MORE INTERACTION
BETWEEN THE FEATURES, PHASING. A PHASED LOW FORMS OFF THE SOUTHERN
NEW ENGLAND COASTLINE BY WEDNESDAY WITH THE MAJORITY OF ATLANTIC
MOISTURE BROUGHT INTO SOUTHERN NEW ENGLAND. TO COMPARE OUR REGION
WOULD BE FAVORED FOR JUST SOME WRAP AROUND SHOWERS.

OVERALL THE OPERATIONAL MODELS HAVE COME INTO BETTER CONSENSUS TODAY
THAT THE ABOVE OUTCOME WILL OCCUR. THIS IS REFLECTED IN BOTH THE 00Z
ECMWF ENSEMBLE MEAN COMPARED TO THE OPERATIONAL RUN AND THE 06Z
GEFS. WITH THAT BEING SAID, CONFIDENCE CONTINUES TO INCREASE THAT
THIS PERIOD WILL BE DOMINATED BY SOME SCATTERED SHOWERS LASTING
THROUGH THURSDAY. AREAS FURTHER NORTHEAST CLOSER TO THE LOW
STAND THE BEST CHANCE TO SEE THE MOST IN TERMS OF SHOWER ACTIVITY.
TIMING DIFFERENCES ON THE SHOWERS ARE STILL PRESENT LEAVING SOME
UNCERTAINTY WITH POPS, KEPT AT HIGH CHANCE TO LOW END LIKELY.
TOTAL RAINFALL WILL BE UNDER ONE INCH FOR THIS EVENT. THE 12Z
ECMWF AND NAM FROM TODAY DO INDICATE THE POTENTIAL FOR SOME
HEAVIER SHOWERS ACROSS THE NORTH TUESDAY NIGHT INTO WEDNESDAY AS
THE MID-LEVEL ENERGY BEGINS TO TRANSFER TO THE COAST, THIS WILL
NEED TO BE WATCHED AS NEW DATA COMES IN. WITH PLENTY OF CLOUDS, LOW
TEMPERATURES WILL STAY UP AT NIGHT CLOSE TO 50 FOR MOST OF US
WHILE HIGHS STRUGGLE TOWARD 60, COOLER NW. NOT MUCH SPREAD IN THE
MODELS AND THERE ENSEMBLES/ STATISTICAL GUIDANCE ON TEMPERATURES,
WENT ON THE WARMER END EACH NIGHT AND THE COOLER END DURING EACH
DAY. IN TERMS OF TIDES IT LOOKS AS THOUGH THE WIND DIRECTION WILL
NOT CREATE DEPARTURES HIGH ENOUGH FOR MINOR COASTAL FLOODING OR
CREATE LOW ENOUGH DEPARTURES FOR BLOWOUT TIDES ATTM.

FRIDAY: LOW PRESSURE SYSTEM FINALLY DEPARTS WITH HIGH PRESSURE
BUILDING BACK IN. THIS ALLOWS FOR CLEARING FROM SOUTH TO NORTH AND
THE FIRST DRY DAY IN A WHILE. TEMPERATURES ARE FORECASTED TO BE
CLOSER TO MEX GUIDANCE AND THE 12Z ECMWF MODELED TWO METER
TEMPERATURES. CONTINUED NORTHWEST WINDS WITH THE BEST CHANCE OF
MIXING TO LEAD TO SOME AFTERNOON WIND GUSTS AROUND 20 MPH.

FRIDAY NIGHT THROUGH SUNDAY: DURING D+6 AND D+7, THE NEGATIVE
NAO/POSITIVE PNA PATTERN OF THE PAST TWO WEEKS IS PROJECTED TO
REVERSE. THIS TREND IS UNDERWAY, AND IS EVIDENT IN LESS HIGH-
LATITUDE BLOCKING. THE MAIN MID-LEVEL FEATURES IN THIS TIMEFRAME
ARE A CLOSED LOW LIFTING INTO THE CANADIAN MARITIMES ON SATURDAY,
FOLLOWED BY A SHORT-WAVE MOVING THROUGH A MORE ZONAL FLOW ON
SUNDAY. THERE IS MODEL DISAGREEMENT WITH THESE FEATURES, AS THE
GFS EJECTS THE CLOSED LOW SLOWER THAN THE ECMWF, RESULTING IN A
DELAYED RETURN TO A MORE ZONAL FLOW. THIS FURTHER RESULTS IN THE
GFS MOVING THE SHORTWAVE FURTHER NORTHEAST, WHILE THE ECMWF TAKES
IT MUCH FURTHER TO THE SOUTH OVER NEW ENGLAND. SOME OF THE GFS
ENSEMBLE MEMBERS ALSO SUPPORT THE ECMWF SOLUTION. GIVEN THE GFS
INITIALIZED MORE ROBUST WITH THE LEAD SHORT-WAVE /LOCATED OVER
NORTHERN SASKATCHEWAN AS OF THIS WRITING/ THAT RESULTS IN THE CUT-
OFF LOW, AND PREVIOUS GFS RUNS WERE MORE IN LINE WITH THE ECMWF,
FEEL THE GFS SOLUTION IS UNREALISTIC. THE ECMWF SOLUTION IS ALSO
MORE REPRESENTATIVE OF THE PROJECTED LACK OF HIGH-LATITUDE
BLOCKING.

OR SATURDAY, SHORT-WAVE RIDGING ALOFT WILL ALLOW HIGH PRESSURE
TO BUILD IN FROM THE WEST, WITH TEMPS AT 850 HPA SUPPORTING HIGH
TEMPERATURES AT SEASONABLE LEVELS. A COLD FRONT IS PROJECTED TO MOVE
THROUGH THE REGION SOMETIME IN THE LATE SATURDAY INTO EARLY SUNDAY
TIMEFRAME. AT THIS TIME, THE ECMWF INDICATES THE BEST DYNAMICS
SITUATED TO THE NORTH AND LIMITED MOISTURE, BUT IT IS TOO FAR OUT TO
SPECULATE ON PRECIP CHANCES. IF THE TIMING OF THE FRONT HOLDS,
PROJECTED 850 HPA TEMPS WOULD SUPPORT BELOW NORMAL HIGHS ON SUNDAY.

&&

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

TODAY...VFR, WITH A CEILING AT TIMES MAINLY AT OR ABOVE 15000 FEET.
LIGHT AND VARIABLE WINDS, BECOMING SOUTHWESTERLY AND INCREASING TO
AROUND 10 KNOTS.

TONIGHT...VFR, WITH A CEILING LOWERING TO BETWEEN 5000-8000 FEET.
SOME SHOWERS MAY APPROACH KABE AND KRDG TOWARD DAYBREAK.
SOUTH-SOUTHWEST WINDS DIMINISHING TO 5 KNOTS, AND EVEN BECOMING
LIGHT AND VARIABLE AT SOME TERMINALS.

OUTLOOK...
TUESDAY...SOME RESTRICTIONS TO MVFR WITH SCATTERED SHOWERS.

TUESDAY NIGHT THROUGH THURSDAY... SOME MVFR RESTRICTIONS WITH
SCATTERED SHOWERS. NORTH TO NORTHWEST WINDS WEDNESDAY AFTERNOON
THROUGH THURSDAY FROM 10-15 KNOTS WITH HIGHER GUSTS.

THURSDAY NIGHT AND FRIDAY: VFR, NORTHWEST WIND GUSTS FRIDAY
AFTERNOON FROM 15-20 KNOTS.

&&

.MARINE...
TODAY AND TONIGHT...THE CONDITIONS ARE EXPECTED TO BE BELOW SMALL
CRAFT ADVISORY CRITERIA. HIGH PRESSURE SHIFTS TO THE EAST ALLOWING A
SOUTH-SOUTHWEST FLOW TO DEVELOP. THIS WILL BE ON THE LIGHTER SIDE
FOR MUCH OF TODAY, HOWEVER IS IS FORECAST TO INCREASE SOME LATER
TODAY AND TONIGHT FOR A TIME. THE OVERALL BOUNDARY LAYER FLOW SHOULD
BE LIGHT ENOUGH THOUGH TO KEEP THE WINDS BELOW 25 KNOTS. THE SEAS
ARE ANTICIPATED TO BE AT OR BELOW 4 FEET.

OUTLOOK...
TUESDAY THROUGH WEDNESDAY: SEAS AND WINDS BELOW SCA CRITERIA
BUT INCREASING WEDNESDAY WITH THE DEVELOPMENT OF A LOW PRESSURE TO
OUR NORTHEAST.

WEDNESDAY NIGHT THROUGH FRIDAY: OVERALL THINKING IS THAT WAVEWATCH
IS UNDERDONE BY ABOUT A FOOT ON THE SEAS. SEAS WILL LIKELY BE AT OR
OVER FIVE FEET THROUGH MOST OF THIS PERIOD WITH SOME DECREASE IN THE
SEAS FRIDAY. NORTHWEST WIND GUSTS OVER 25 KNOTS ARE ALSO POSSIBLE
EACH AFTERNOON. SCA POSSIBLE FOR MOST OF THIS TIMEFRAME.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...FREEZE WARNING UNTIL 8 AM EDT THIS MORNING FOR PAZ054-055-061-
     062.
     FROST ADVISORY UNTIL 8 AM EDT THIS MORNING FOR PAZ060-101>106.
NJ...FREEZE WARNING UNTIL 8 AM EDT THIS MORNING FOR NJZ001-007>010.
     FREEZE WARNING UNTIL 8 AM EDT THIS MORNING FOR NJZ020>022-027.
     FROST ADVISORY UNTIL 8 AM EDT THIS MORNING FOR NJZ012-013-
     015>019-023.
DE...NONE.
MD...NONE.
MARINE...NONE.

&&

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



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