Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 160233
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
933 PM EST MON DEC 15 2014

.SYNOPSIS...
HIGH PRESSURE ALONG THE EAST COAST WILL MOVE OFFSHORE OVERNIGHT.
LOW PRESSURE IN THE GREAT LAKES TUESDAY WILL PUSH A WARM FRONT
NORTH INTO THE MID ATLANTIC STATES, WITH SECONDARY LOW PRESSURE
DEVELOPING NEAR LONG ISLAND TUESDAY NIGHT. THE COLD FRONT PASSES
OFFSHORE WEDNESDAY MORNING AS THE LOWS COMBINE AND HEAD FOR THE
CANADIAN MARITIMES THURSDAY. HIGH PRESSURE IN THE GREAT LAKES
ASSERTS CONTROL HERE ON FRIDAY. LOW PRESSURE IN GEORGIA SATURDAY
MORNING IS FORECAST TO INTENSIFY AS IT MOVES NORTHEASTWARD OFF THE
MID ATLANTIC COAST SUNDAY.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
HIGH PRESSURE AT THE SURFACE IS ELONGATED FROM NEW ENGLAND TO THE
EASTERN CAROLINAS THIS EVENING. THIS FEATURE WILL EASE OFFSHORE
OVERNIGHT AS AN UPPER-LEVEL RIDGE ALSO SHIFTS TO OUR EAST. THE
STRONG SUBSIDENCE INVERSION THAT HAS PERSISTED WHILE STILL PRESENT
HAS NOW WEAKENED SOME. THIS IS EVIDENT BY COMPARING THE 00Z
STERLING, VA RAOB TO THE 12Z AND EVEN YESTERDAY`S 00Z. THE LOW-LEVEL
FLOW CONTINUES TO SHIFT MORE FROM THE SOUTH-SOUTHWEST AHEAD OF THE
NEXT SYSTEM, AND THIS ALONG WITH SOME DRYING ERODED THE EARLIER
LOW CLOUDS. SOME LOW CLOUDS THOUGH ARE STILL HOLDING ON NEAR THE
POCONOS ON WESTWARD. IT APPEARS THAT MUCH OF THE AREA WILL HAVE
LITTLE IN THE WAY OF CLOUDS FOR AWHILE OTHER THAN SOME HIGH
CLOUDINESS, HOWEVER SOME FORECAST SOUNDINGS SHOW A LAYER BENEATH
THE INVERSION MOISTENING AGAIN OVERNIGHT. THIS COULD BE ENHANCED
SOME BY WAA AHEAD OF A WARM FRONT. THEREFORE, WE STILL MAINTAIN
SOME INCREASE IN CLOUDS THROUGH THE OVERNIGHT HOWEVER OUR
CONFIDENCE HAS DECREASED REGARDING THE EXTENT OF LOW CLOUD
REDEVELOPMENT.

IF THE LOW CLOUDS DO REDEVELOP ACROSS THE AREA OVERNIGHT, THEN
COMBINED WITH A LIGHT DEVELOPING SOUTHEASTERLY SURFACE FLOW MAY
RESULT IN PATCHY DRIZZLE. THE NORTHWEST ZONES PROBABLY HAVE THE
BETTER CHC OF THIS GIVEN SOME LIGHT UPSLOPE COMPONENT. SOME FOG
/FREEZING FOG/ IS ONGOING ACROSS THE HIGHER TERRAIN OF THE POCONOS,
AND THEREFORE PATCHY FOG IS CARRIED ACROSS PORTIONS OF THE NORTHWEST
ZONES. GIVEN LOWER CONFIDENCE REGARDING THE LOW CLOUD REDEVELOPMENT,
DRIZZLE WAS NOT INCLUDED. A PATCHY FOG MENTION WAS EXPANDED THOUGH
SOME ACROSS PORTIONS OF EASTERN PENNSYLVANIA, NORTHWESTERN NEW
JERSEY AND INTERIOR SOUTHERN NEW JERSEY.

THE HOURLY GRIDS WERE ADJUSTED BASED ON THE LATEST OBSERVATIONS,
WHICH INCLUDED SHOWING COLDER TEMPERATURES IN SEVERAL PLACES SO
FAR GIVEN THE LACK OF CLOUDS AND LIGHT WINDS. THE LOW TEMPERATURES
NEEDED TO BE LOWERED SOME FOR SEVERAL LOCALES.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
TUESDAY IS EXPECTED TO START OUT DRY AND CLOUDY, BUT PRECIPITATION
IS EXPECTED BY THE END OF THE DAY. A WARM FRONT IS EXPECTED TO LIFT
ACROSS THE AREA DURING THE DAY AS AN AREA OF LOW PRESSURE LIFTS INTO
THE GREAT LAKES REGION. LOW LEVEL LIFT WILL INCREASE AS THE WARM
FRONT LIFTS ACROSS THE AREA AND A COLD FRONT APPROACHES FROM THE
WEST. AS AN INITIAL SHORT WAVE/VORTICITY IMPULSE LIFTS ACROSS THE
AREA DURING THE AFTERNOON, SHOWERS WILL SPREAD ACROSS THE AREA FROM
SOUTHWEST TO NORTHEAST. PW VALUES DO APPROACH AN INCH, SO IT WOULD
NOT BE SURPRISING TO SEE A FEW BRIEF HEAVIER DOWNPOURS, MAINLY FOR
THE DELMARVA AND SOUTHERN NEW JERSEY. HIGHS WERE A BLEND OF MAV/MET
MOS AND MOSGUIDE.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
500 MB: A NEGATIVE TILT SHORT WAVE IN WESTERN PA TO START TUESDAY
EVENING LIFTS EAST NORTHEAST AND BEGINS THE PROCESS OF PULLING A
CLOSED LOW EASTWARD FROM THE GREAT LAKES REGION INTO THE MARITIMES
BY THURSDAY. THEN SEVERAL SHORT WAVES NOW APPROACHING CALIFORNIA
WILL HAVE REACHED THE SOUTHERN PLAINS FRIDAY MORNING. THEY WILL
MOVE EAST AND OFF THE MID ATLANTIC COAST SUNDAY. THE QUESTION:
AMPLITUDE... EITHER WEAKENING AS PER THE 00Z AND 12Z/15 GEFS OR
WELL DEFINED AND SIGNIFICANT AS PER THE 00Z AND 12/15 ECMWF ENS.

TEMPERATURES: DECEMBER THROUGH THE 14TH HAS AVERAGED NEAR NORMAL
NORTHWEST FRINGE OF OUR FORECAST AREA (KRDG/KMPO) AND A BIT ABOVE
NORMAL ELSEWHERE. WEDNESDAY WILL BE ABOUT 10 DEGREES ABOVE NORMAL
AND THE REST OF THE LONG TERM FORECAST PERIOD THROUGH NEXT MONDAY
WITHIN 4 DEGREES OF NORMAL. THERE IS POSSIBLY SOME SUBTLY COOLER
AIR COMING INTO OUR AREA THURSDAY AND FRIDAY AND AGAIN NEXT SUNDAY
NIGHT...MODELED BY THE ECMWF AND NOT BY THE GFS.

FORECAST BASIS:  IN A NUTSHELL AND UNLESS OTHERWISE NOTED WITHIN THE
DAILIES. THIS FORECAST IS A 50 50 BLEND OF THE 12Z/15 MAV/MET FOR
TUESDAY NIGHT-WEDNESDAY NIGHT. THE 12Z/15 MEX MOS WAS NOT USED
THURSDAY... INSTEAD RELYING HEAVILY ON OUR PHI OFFICE PREVIOUS
330 AM FCST. THEREAFTER THE 1523Z/15 WPC D4-8 ELEMENTS OF DEWPOINTS/
WIND/SKY/POP/MAX-MIN TEMPS. SREF AND GEFS PROBS FOR QPF AND
12Z/15 ECMWF 2METER TEMPERATURES WERE CHECKED.

THE DAILIES...

CONFIDENCE: OVERALL ABOVE AVERAGE THROUGH FRIDAY THEN AVERAGE OR
BELOW FOR THE WEEKEND.

TUESDAY NIGHT...LEFTOVER POPS ASSTD WITH CFP AND THE EVENING
NEGATIVE TILT SHORT WAVE PASSAGE (500 MB VORT MAX AND ASSOCIATED
120M 12 HR HFC VCNTY KAVP AT 06Z/17). PROBABLY DRY AFTER MIDNIGHT
WITH PARTIAL CLEARING POSSIBLE. SHOWERS MAY HAVE ENDED
PHILADELPHIA AREA SOUTHWESTWARD THROUGH TO CHESAPEAKE BAY AND ALL
OF DELAWARE BY THE START OF THIS FORECAST TUESDAY EVENING. IT IS
POSSIBLE THE VORT MAX WILL HAVE A CLUSTER OF SHOWERS PASSING
THROUGH THE POCONOS JUST BEFORE MIDNIGHT. (NO SNOW EXPECTED
THERE... FAR TOO WARM BELOW 6000 FEET). WE HAVE ADDED PATCHY FOG
TO NORTHERN NEW JERSEY LATE AT NIGHT AND MAY NEED TO EXPAND THE
COVERAGE PATCHY FOG IN FUTURE FORECASTS FOR TUESDAY NIGHT.

WEDNESDAY...MAINLY DRY WITH VARIABLE CLOUDS...A BIT OF SUN AT TIMES.
A SECOND SHORT WAVE PASSAGE WEDNESDAY NIGHT (100M 12 HR HFC THROUGH
E PA) ASSOCIATED WITH THE EASTWARD PASSAGE OF THE CLOSED LOW ACROSS
NEW YORK STATE MAY GENERATE MIDDAY SHOWERS AHEAD OF IT IN THE POCONOS
(BOUNDARY LAYER STILL ON THE WARM SIDE FOR ANY SNOW) AND THEN SOME
SNOW SHOWERS...ALSO OVER THE POCONOS AT NIGHT...A WEAK WINDEX
EVENT. NW WIND GUST 20-25 MPH. -1C AT 850MB AROUND 18Z.

THURSDAY...PARTLY SUNNY. EXCEPT POCONOS AND EXTREME NORTHWEST NJ WHERE
IT SHOULD BE MOSTLY CLOUDY WITH A POSSIBILITY OF NW FLOW FLURRIES.
NW WIND GUST 25-30 MPH WITH SOMEWHAT MORE UNSTABLE LAPSE RATES
(850MB SLIGHTLY COLDER, AROUND -4C, FOLLOWING THE LATE WEDNESDAY
NIGHT SHORT WAVE- TROUGH PASSAGE) AND SLIGHTLY STRONGER GRADIENT
FLOW ASSOCIATED WITH A SOMEWHAT INVIGORATED MARITIMES LOW. 12Z/15
GFS MOS TEMPS LOOKED ABOUT 5 TO 8 DEGREES TOO WARM FOR A VARIABLY
CLOUDY DAY. RAISED THE 330 AM FCST TEMPS BY 2 DEGREES BUT NO MORE
THAN THAT DUE TO THE SIGNIFICANTLY COOLER 00Z/15 ECMWF 2M TEMPS.

FRIDAY...PARTLY TO MOSTLY SUNNY. NW WIND GUST 20 MPH. 850MB -5C.

NEXT WEEKEND...ALL DIRECTLY ASSOCIATED WITH THE INTENSITY OF THE
SHORT WAVE AND SFC LOW TRACK. MARGINAL LOW LEVEL THERMAL PROFILE
AOB 800MB FROM I95 SEWD (RAIN I95 SEWD AND SNOW NW OF I95 IF PCPN
REACHES THAT FAR NORTH). COULD BE A NOREASTER? THE 12Z ECMWF ENSEMBLES
ARE MUCH STRONGER WITH THIS SYSTEM THAN THE GEFS...FORMING A CLOSED
LOW OVER PA BY SUNDAY MORNING...IN OTHER WORDS STRONGER THAN EVEN
THE 12Z ECMWF OP RUN. PART OF THIS STRONGER ECMWF ENSEMBLE APPEARS
TO BE RELATED TO THE 12Z/15 ECMWF CONTROL WHICH APPEARS TO BE TOO
INTENSE AT ALL LEVELS. NEVERTHELESS, NEED TO MONITOR MODEL TRENDS
FOR THIS POTENTIAL WINTER EVENT.

WE SAW THE 12Z/15 GGEM OP RUN HAS EDGED NORTH.

FOR NOW WE USED THE WPC GRIDDED GUIDANCE.

MONDAY...WPC GRIDDED GUIDANCE STRAIGHT UP.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

OVERNIGHT...VFR FOR AWHILE, HOWEVER MVFR CEILINGS REMAIN WEST OF
KABE AND KRDG. SOME REDEVELOPMENT OF THE MVFR CEILINGS ARE
ANTICIPATED, HOWEVER OUR CONFIDENCE HAS DECREASED. SOME FURTHER
DELAY OF THIS WAS INDICATED IN THE LATEST AMENDMENTS. SOME FOG
SHOULD DEVELOP ESPECIALLY AROUND KABE AND KRDG AND PERHAPS KMIV.
WINDS MAINLY LIGHT AND VARIABLE.

TUESDAY...VFR/MVFR CEILINGS /MVFR MAY IMPROVE TO VFR FOR A TIME/,
HOWEVER LOWER CLOUDS SHOULD BECOME MORE DOMINANT IN THE AFTERNOON AS
A WARM FRONT LIFTS THROUGH. SHOWERS ARE EXPECTED TO ARRIVE FROM
SOUTHWEST TO NORTHEAST IN THE AFTERNOON, AND THERE IS THE POTENTIAL
FOR IFR CEILINGS TO DEVELOP BY LATE IN THE DAY. THE VISIBILITIES
WILL BE REDUCED TO MVFR DURING HEAVIER SHOWERS. LIGHT AND VARIABLE
WINDS, BECOMING SOUTHEASTERLY 5-8 KNOTS.

OUTLOOK...
TUESDAY NIGHT...MVFR CONDS IN SHOWERS ENDING EARLY, THEN PATCHY
IFR CONDITIONS IN STRATUS/FOG IS EXPECTED. WIND LIGHT BECOMING
WEST LATE. CAUSE: CLEARING ALOFT WITH LIGHT WIND IN THE SATURATED
BOUNDARY LAYER. CONFIDENCE; ABOVE AVERAGE

WEDNESDAY...VFR BKN CIGS AOA 3000 FT. NW WIND GUST 20-25 KT.
CONFIDENCE ABOVE AVERAGE.

THURSDAY...VFR SCT-BKN AOA 3500 FT. NW WIND GST 25-30 KT.
CONFIDENCE ABOVE AVERAGE.

FRIDAY...VFR SCT-BKN AOA 3000 FT. NW WIND G 20 KT. CONFIDENCE
ABOVE AVERAGE.

SATURDAY... VFR CIGS AOA 10000 FT POSSIBLY LOWERING TO MVFR OR IFR
CONDITIONS AT NIGHT IN PCPN. LIGHT WIND BECOMING INCREASING NE.
CONFIDENCE: AVERAGE.

&&

.MARINE...
SUB-SMALL CRAFT ADVISORY CONDITIONS TONIGHT AS HIGH PRESSURE BUILDS
EAST OF THE WATERS TONIGHT. SUB-SMALL CRAFT ADVISORY CONDITIONS
CONTINUE INTO TUESDAY, ALTHOUGH WINDS AND SEAS INCREASE ALONG WITH
SHOWERS AS A WARM FRONT LIFTS ACROSS THE AREA.

OUTLOOK...
TUESDAY NIGHT...SUB-ADVISORY CONDITIONS ARE EXPECTED. CONFIDENCE
ABOVE AVERAGE.

WEDNESDAY AND THURSDAY...WHILE SEAS ARE EXPECTED TO REMAIN GENERALLY
BELOW SCA LEVELS, NORTHWEST WIND GUSTS SHOULD REACH THE SCA THRESHOLD
OF 25 KNOTS AT TIMES DURING WEDNESDAY AFTERNOON THROUGH THURSDAY...
POSSIBLY 30 KT.  SCA EXPECTED.   CONFIDENCE: ABOVE AVERAGE.

FRIDAY...MOSTLY SUB-ADVISORY CONDITIONS ARE EXPECTED. SOME NORTHWEST
WIND GUSTS COULD STILL BE IN THE 20 PLUS KNOT RANGE, THOUGH.
CONFIDENCE: ABOVE AVERAGE.

SATURDAY...SCA LIKELY AT NIGHT...POSSIBLY A GALE BUT FOR NOW SCA
IS FAVORED FOR A START.  CONFIDENCE: AVERAGE.

&&

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

&&

$$
SYNOPSIS...DRAG
NEAR TERM...GORSE
SHORT TERM...ROBERTSON
LONG TERM...DRAG
AVIATION...DRAG/GORSE
MARINE...DRAG/ROBERTSON




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