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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 012255
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
555 PM EST SUN DEC 1 2013

.SYNOPSIS...
-- Changed Discussion --
LOW PRESSURE IS FORECAST TO DEVELOP OFF THE NORTH CAROLINA COAST
TONIGHT INTO MONDAY, THEN TRACK NORTHEASTWARD AND INTENSIFY TOWARD
THE CANADIAN MARITIMES MONDAY AND TUESDAY. A WEAK HIGH PRESSURE
SYSTEM THEN BRIEFLY BUILDS IN TUESDAY NIGHT INTO WEDNESDAY BEFORE
SHIFTING OFFSHORE. LOW PRESSURE TRACKING ACROSS THE MIDWEST INTO
SOUTH CENTRAL CANADA WEDNESDAY AND THURSDAY WILL SEND A COLD FRONT
TO THE EAST COAST FRIDAY. THERE IS THE POTENTIAL THAT THIS FRONT
STALLS ALONG THE COAST AS PIECES OF ENERGY RIDE ALONG IT FRIDAY
AND SATURDAY. STRONG HIGH PRESSURE FROM THE MIDWEST TO THE PLAINS
IS THEN FORECAST TO BUILD TOWARD THE MID ATLANTIC SUNDAY.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
-- Changed Discussion --
CONSIDERABLE MID-LVL CLOUDINESS SHOULD REMAIN ACROSS THE
AREA...ESPECIALLY N OF DELMARVA. THE CLOUDS SHOULD LIMIT
RADIATIONAL COOLING OVERNIGHT...IN SPITE OF LIGHT TO CALM WINDS
ASSOCD WITH THE ILL-DEFINED SFC PRES PATN AND WEAK PRES GRADIENT.
TONIGHTS MINS ARE A BIT ON THE WARM SIDE OF MOS GUIDANCE AND
SHOULD BE A FEW DEGREES WARMER THAN LAST NIGHT.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
-- Changed Discussion --
FOR MONDAY...THERE SHOULD BE A GENERAL INCREASE IN HIGHER-LEVEL
CLOUDS AHEAD OF A BROAD BUT INCREASINGLY NEG-TILT TROF MOVING FROM
THE MS VLY INTO THE ERN U.S. EXPECT THERE WILL STILL BE SOME SUN
VSBL THRU HIGHER CLOUDS AND WITH TEMPS STARTING OUT NOT QUITE AS
COLD AS TODAY...MAX TEMPS ON MON SHOULD BE SIMILAR TO TODAY OR
PERHAPS A DEG OR TWO WARMER. WINDS WILL REMAIN LIGHT IN A RATHER
WEAK SFC PRES PATN...HWVR THE UPPER TROF IS FCST TO INDUCE SFC LOW
PRES EAST OF CAPE HAT BY 00Z TUES. WINDS MAY PICK UP SMWHT FROM
THE NE OVER DE AND SRN NJ BUT LIKELY MORE SO OVER THE ADJ COASTAL
WATERS. HAVE ALSO INCLUDED A SLGT CHC FOR RAIN LATE AFTN OVER SRN
COASTAL AREAS BUT CONFIDENCE IS LOW FOR MEASURABLE PRECIP.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
-- Changed Discussion --
THE OVERALL SYNOPTIC SETUP IS FORECAST TO BECOME MORE AMPLIFIED
WITH TIME WITH A TROUGH MAINLY ANCHORED ACROSS THE WEST. WE START
OUT WITH A NEGATIVE TILT TROUGH SHIFTING TO OUR EAST MONDAY NIGHT
AND TUESDAY. THIS WILL TAKE AN INTENSIFYING SURFACE LOW TO OUR
NORTHEAST, HOWEVER THE ORIENTATION AND SPEED OF THE TROUGH SHOULD
KEEP NEARLY ALL OF THE PRECIPITATION OFF THE COAST. AS THIS
FEATURE MOVES AWAY TUESDAY, SOME SHORT WAVE RIDGING MOVES IN
ALLOWING SURFACE HIGH PRESSURE TO SETTLE IN WEDNESDAY BEFORE
SHIFTING OFFSHORE THURSDAY. A SIGNIFICANT UPPER-LEVEL TROUGH IS
FORECAST TO BE CARVED OUT ACROSS THE WEST, WITH SOME OF THIS
ENERGY EVENTUALLY EJECTING EASTWARD. THIS SHOULD OCCUR IN PIECES
AS A RIDGE IS NEAR THE SOUTHEASTERN U.S. THERE IS INCREASING
UNCERTAINTY FROM ABOUT THURSDAY ONWARD WITH THE TIMING OF ENERGY
AND AN ASSOCIATED SURFACE COLD FRONT. IT APPEARS THAT A
STRENGTHENING SURFACE LOW MOVES INTO SOUTH CENTRAL CANADA
THURSDAY, AND ITS TRAILING COLD FRONT ARRIVES IN THE EAST. THIS
BOUNDARY MAY TEND TO STALL THOUGH AS THE FLOW BECOMES PARALLEL TO
IT AND ALSO SOUTHEAST U.S. RIDGING MAY HOLD ENOUGH. GIVEN THE
TROUGH STILL IN THE WEST WITH SHORT WAVES EJECTING NORTHEASTWARD
WITHIN THE SOUTHWESTERLY FLOW ALOFT, A MOISTURE CONDUIT MAY BECOME
SETUP IN THE EAST WITH POTENTIAL OVERRUNNING EVENTS.

OUR CONFIDENCE IS MUCH LOWER ESPECIALLY FOR FRIDAY THROUGH SUNDAY
AS THE DETAILS ARE LESS CERTAIN GIVEN TIMING, STRENGTH OF THE
FEATURES AND ASSOCIATED OVERRUNNING SETUP AND THE THERMAL
PROFILES. WE USED MOSTLY A MODEL BLEND MONDAY NIGHT THROUGH
WEDNESDAY, THEN WPC GUIDANCE WEDNESDAY NIGHT ONWARD. SOME
ADJUSTMENTS WERE THEN MADE FACTORING IN OUR CONFIDENCE AND ALSO
FOLLOWING ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES.

FOR MONDAY NIGHT...A NEGATIVE TILT TROUGH IS FORECAST TO BE
MOVING ACROSS THE AREA. THIS WILL TAKE A SURFACE LOW OFFSHORE AND
TOWARD THE CANADIAN MARITIMES. GIVEN THE UPPER-LEVEL FLOW PATTERN,
IT DOES APPEAR THAT THE LARGE SCALE LIFT AND ASSOCIATED
PRECIPITATION SHIELD WITH THE OCEAN STORM REMAINS TO OUR EAST. WE
THEREFORE LOWERED POPS BUT DID STILL KEEP SOME SLIGHT CHC TO LOW
CHC POPS RIGHT NEAR THE COAST ON EASTWARD. THERE SHOULD THEN BE
SOME SORT OF A BOUNDARY LURKING FROM THE OHIO VALLEY TO THE
MIDWEST AS WAA OCCURS. THIS WAA SHOULD GENERATE SOME CLOUDS THAT
MAY GET PULLED INTO OUR AREA WITHIN THE INITIAL NORTHWESTERLY FLOW
ALOFT. SOME LIGHT WAA INDUCED PRECIPITATION IS POSSIBLE AS WELL,
HOWEVER THE MAIN FORCING FOR THIS IS FORECAST TO REMAIN TO OUR
WEST. THEREFORE, WE CARRIED A DRY FORECAST INLAND.

FOR TUESDAY AND WEDNESDAY...AS A TROUGH IS TO OUR WEST SOME SHORT
WAVE RIDGING MOVES IN. THE UPPER-LEVEL PATTERN IS FORECAST TO BE
UNDERGOING AMPLIFICATION WITH LOTS OF ENERGY BEING CARVED OUT
ACROSS THE WEST. SOME OF THIS ENERGY IS FORECAST TO EJECT
NORTHEASTWARD ACROSS THE PLAINS AND MIDWEST, WHICH DRIVES A
SURFACE LOW ACROSS THE MIDWEST WEDNESDAY. AS WE LOOK DOWNSTREAM,
WEAK HIGH PRESSURE ACROSS THE MID ATLANTIC SHIFTS OFFSHORE AND A
RETURN FLOW STARTS TO SET UP. AN INCREASING WAA PATTERN GETTING
UNDERWAY WEDNESDAY ESPECIALLY WILL ALLOW A WARM FRONT TO BECOME
BETTER ORGANIZED ACROSS THE OHIO VALLEY TO THE CAROLINAS. THIS
FEATURE WILL GRADUALLY LIFT NORTHWARD THROUGH WEDNESDAY NIGHT. A
COLD FRONT WILL BE APPROACHING THE AREA LATE WEDNESDAY NIGHT,
HOWEVER THE WAA AND ISENTROPIC LIFT MAY GET SOME SHOWERS CLOSE TO
OUR NORTHWEST ZONES. THEREFORE, SOME LOW POPS WERE CARRIED
NORTHWEST WEDNESDAY NIGHT.

FOR THURSDAY AND FRIDAY...THE UPPER-LEVEL PATTERN CONTINUES TO
AMPLIFY WITH STRONG TROUGHING IN THE WEST SLOWLY EJECTING
EASTWARD. THE TIMING OF THE INITIAL ENERGY APPEARS TO HAVE SPED
UP, THEREFORE A COLD FRONT IS FORECAST TO MOVE IN LATER THURSDAY
INTO FRIDAY BUT ITS FORWARD MOTION MAY SLOW WITH THE MAIN ENERGY
TRACKING WELL TO OUR NORTHWEST. AS THE FRONT SLOWS, ENERGY RIDING
ALONG IT MAY HELP TO INCREASE THE WAA AND ALSO TIGHTEN UP THE
BAROCLINIC ZONE ESPECIALLY ALOFT. AS A RESULT, AN AREA OF
EXPANDING PRECIPITATION DUE TO ISENTROPIC LIFT AND FRONTOGENETIC
FORCING MAY MOVE ACROSS THE AREA ESPECIALLY FRIDAY AND FRIDAY
NIGHT /ALTHOUGH THE TIMING CAN CERTAINLY CHANGE/. THERE IS BETTER
AGREEMENT WITH THE MODEL GUIDANCE OF THIS SCENARIO THEREFORE
INCREASED POPS TO LOW LIKELY VALUES FRIDAY AND FRIDAY NIGHT FROM
WEST TO EAST. THE POPS DO INCREASE DURING THURSDAY, HOWEVER THERE
APPEARS TO BE A LESSER CHC ATTM.

A LOOK AT SOME FORECAST SOUNDINGS INDICATE THAT DESPITE THE WAA,
A NORTHERLY LOW-LEVEL FLOW DEVELOPS BEHIND THE SLOW MOVING SURFACE
FRONT OR PRE-FRONTAL TROUGH. THERE DOES NOT APPEAR TO BE STRONG
PUSH OF COLD LOW-LEVEL AIR, HOWEVER PROFILES ESPECIALLY ACROSS OUR
NORTHWEST ZONES INDICATE SLEET AND/OR FREEZING RAIN IS A
POSSIBILITY ESPECIALLY FRIDAY NIGHT. THIS IS A POTENTIALLY MESSY
AND CHALLENGING FORECAST AS IT DEPENDS ON THE AMOUNT OF FORCING
AND ESPECIALLY WHAT THE THERMAL PROFILES OF THE ATMOSPHERE
ULTIMATELY ARE. AS OF NOW GIVEN THE LOWER CONFIDENCE AND
UNCERTAINTY WITH THE DETAILS, WE OPTED TO NOT GET TO SPECIFIC WITH
PRECIPITATION TYPES. A MENTION REMAINS HOWEVER IN THE HAZARDOUS
WEATHER OUTLOOK FOR THE CHC OF SOME MIXED WINTRY PRECIPITATION
ACROSS THE NORTHWESTERN ZONES.

FOR SATURDAY AND SUNDAY...A BATTLE BETWEEN A LINGERING SOUTHEAST
U.S. RIDGE AND STRONG ARCTIC HIGH PRESSURE ACROSS THE PLAINS AND
MIDWEST WILL DETERMINE WHAT SENSIBLE WEATHER WE GET. A SECONDARY
COLD FRONT MAY ARRIVE SATURDAY AS COLDER AIR GETS ADVECTED
EASTWARD. PRIOR TO THIS THOUGH, A PERSISTENT TROUGH IS FORECAST TO
BE IN THE WEST WITH THE EAST UNDER MOSTLY A WEST-SOUTHWEST FLOW
ALOFT. THERE SHOULD BE A BOUNDARY LURKING OFF THE COAST WITH SHORT
WAVES RIPPLING ALONG IT, HOWEVER IT APPEARS THAT THE LARGE DOME OF
HIGH PRESSURE BUILDS IN ENOUGH TO PUSH THE ASSOCIATED MOISTURE
CONDUIT TO OUR SOUTH AND EAST. THIS CARRIES LESS CONFIDENCE AS THE
UPPER-LEVEL FLOW SUGGESTS THE BOUNDARY/FORCING MAY BE SLOWER TO
LEAVE. WE GENERALLY FOLLOWED WPC`S LEAD AT THIS POINT GIVEN THE
UNCERTAINTY, WHICH BASICALLY IS CHC POPS SATURDAY THEN LOWERING TO
A DRY FORECAST SUNDAY.
-- End Changed Discussion --

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

VFR CONDS AND VERY LIGHT TO CALM WINDS ARE EXPECTED THROUGHOUT THE
TAF FORECAST TIME PERIOD...OR THROUGH MONDAY. A MID-LVL CLOUD DECK
HAS OVER-SPREAD THE REGION WITH CIGS GENERALLY OVC090. THESE CLOUDS
SHOULD PERSIST MUCH OF THE NIGHT AND MAY LOWER A BIT...BUT CIGS WILL
STAY ABOVE 050.

OUTLOOK...
MONDAY NIGHT...VFR WITH CEILINGS AROUND 5000 FEET. NORTHEAST
WINDS 5-10 KNOTS, BECOMING NORTH.

TUESDAY AND WEDNESDAY...OVERALL VFR, ALTHOUGH CLOUDS SHOULD
INCREASE WEDNESDAY. NORTHWESTERLY WINDS LESS THAN 10 KNOTS.

THURSDAY AND FRIDAY...VFR CEILINGS TO POTENTIALLY MVFR DURING
THURSDAY, THEN A CHANCE OF MVFR/IFR FRIDAY. THIS IS DUE TO A COLD
FRONT ARRIVING AND SLOWING WITH AT LEAST SOME PRECIPITATION
OVERSPREADING THE AREA, ESPECIALLY FRIDAY AND FRIDAY NIGHT.
SOUTHWEST WINDS AROUND 10 KNOTS, BECOMING NORTHWEST FRIDAY. OUR
CONFIDENCE IS ON THE LOWER SIDE REGARDING TIMING AND DETAILS.
-- End Changed Discussion --

&&

.MARINE...
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LIGHT WINDS AND SEAS 3 FT OR LESS SHOULD PREVAIL THROUGH TONIGHT
AND MONDAY. W WINDS TONIGHT WILL BECOME NE ON MONDAY AND INCREASE
SMWHT AS LOW PRES BEGINS TO DEVELOP LATE IN THE DAY OFF OF CAPE
HAT. WINDS AND SEAS SHOULD REMAIN WELL BELOW SCA LEVELS HWVR.

OUTLOOK...
MONDAY NIGHT THROUGH TUESDAY...A SMALL CRAFT ADVISORY MAY BE
NEEDED MAINLY FOR THE ATLANTIC COASTAL WATERS. THIS IS ASSOCIATED
WITH LOW PRESSURE THAT TRACKS WELL OFFSHORE, HOWEVER A TIGHTENING
PRESSURE GRADIENT MAY ALLOW FOR WIND GUSTS TO NEAR 25 KNOTS FOR A
TIME. LOWER CONFIDENCE HOWEVER GIVEN A MORE OFFSHORE TRACK.

WEDNESDAY THROUGH THURSDAY...THE CONDITIONS APPEAR TO BE BELOW
ADVISORY CRITERIA. A COLD FRONT OR PRE-FRONTAL TROUGH IS EXPECTED
TO ARRIVE LATER THURSDAY NIGHT WITH A WIND SHIFT FROM THE SOUTH-
SOUTHWEST TO THE WEST. WHILE SOME INCREASE IS ANTICIPATED IT IS
FORECAST TO BE BELOW 25 KNOTS.

FRIDAY...A COLD FRONT WILL PROBABLY BE SLOWLY SHIFTING EASTWARD
OR EVEN STALL IN THE VICINITY AS ENERGY RIDES ALONG IT. WHILE THE
FLOW LOOKS TO GO NORTHWESTERLY, THE PRESENCE OF THE SURFACE FRONT
SHOULD RESULT IN LESS WIND. LOW CONFIDENCE REGARDING THE POSITION
OF THE ACTUAL SURFACE FRONT.
-- End Changed Discussion --

&&

.PHI WATCHES/WARNINGS/ADVISORIES...

PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...GORSE
NEAR TERM...AMC
SHORT TERM...AMC
LONG TERM...GORSE
AVIATION...AMC/GORSE
MARINE...AMC/GORSE