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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 080128
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
828 PM EST SAT DEC 7 2013

.SYNOPSIS...
HIGH PRESSURE WILL MOVE OVER THE REGION TONIGHT AND THEN MOVE OFF TO
THE NORTHEAST ON SUNDAY. A LOW PRESSURE SYSTEM WILL MOVE THROUGH THE
GREAT LAKES REGION ON SUNDAY AND MONDAY, DRAGGING A COLD FRONT
THROUGH OUR AREA LATE MONDAY. MEANWHILE, A LOW PRESSURE SYSTEM WILL
DEVELOP AND MOVE UP ALONG THE MIDDLE ATLANTIC COAST ON MONDAY. A
SECONDARY FRONT WILL MOVE THROUGH THE REGION LATE TUESDAY INTO
WEDNESDAY. HIGH PRESSURE WILL THEN BUILD INTO THE REGION FROM THE
WEST ON WEDNESDAY BEFORE SHIFTING EAST OF THE AREA AT THE END OF THE
WEEK.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
-- Changed Discussion --
THE STRATOCUMULUS THAT HAD BEEN HOLDING ACROSS A GOOD PART OF THE
REGION EARLIER HAS SINCE DISSIPATED THIS EVENING. SOME HIGH CLOUDS
WILL CONTINUE TO STREAM IN ACROSS THE FORECAST AREA FROM SOUTHWEST
TO NORTHEAST IN ADVANCE OF OUR NEXT STORM SYSTEM. A FEW
ADJUSTMENTS WERE MADE TO HOURLY WINDS, TEMPERATURES, AND DEWPOINTS
THIS EVENING, BUT THE OVERALL FORECAST THROUGH THE NIGHT LOOKS TO
BE ON TRACK.

OTHERWISE, THE CALM BEFORE THE NEXT SYSTEM AFFECTS OUR REGION. A
STRONG AREA OF HIGH PRESSURE IN THE MIDWEST WILL EXPAND EASTWARD
THROUGH TONIGHT AND BECOME CENTERED NEAR NEW YORK AND PENNSYLVANIA
TOWARD DAYBREAK. A COLDER AND DRIER AIRMASS WILL CONTINUE TO BE
DRIVEN INTO OUR AREA WITH A NORTHERLY LOW-LEVEL FLOW.

THE CAA AT 850 MB IS FORECAST TO LESSEN AND BECOME MOSTLY NEUTRAL
TOWARD DAYBREAK. THIS IS IN RESPONSE TO OUR NEXT SYSTEM GRADUALLY
ORGANIZING TO OUR SOUTHWEST. THE WAA ASSOCIATED WITH THIS SYSTEM TO
OUR SOUTHWEST WILL HELP PUSH SOME HIGHER CLOUDINESS ACROSS THE AREA
ESPECIALLY LATE. GIVEN THE FORECAST OF DRIER AIR SETTLING SOUTHWARD
AND THE WAA INDUCED THERMAL GRADIENT STAYING TO OUR SOUTH THROUGH
DAYBREAK, WE CONTINUED WITH A DRY FORECAST THROUGH THE NIGHT.

AS FOR LOW TEMPERATURES, WE USED AN EVEN BLEND OF THE GFS/NAM MOS.
THE HOURLY TEMPERATURES INCORPORATED THE LAMP/LAV GUIDANCE THROUGH
THIS EVENING TO HELP WITH TRENDS. THE WINDS ARE FORECAST TO LESSEN
AND ENOUGH DECOUPLING SHOULD OCCUR TO ALLOW TEMPERATURES TO FALL A
DECENT AMOUNT THROUGH THE EVENING.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
THE ARRIVAL OF A WINTRY PRECIPITATION EVENT GETS UNDERWAY AS WE GO
THROUGH SUNDAY. A WINTER WEATHER ADVISORY IS BEING ISSUED FOR A
PORTION OF OUR CWA FOR THE COMBINATION OF SNOW AND ICE.

THE OVERALL SYNOPTIC SETUP IS COMPRISED OF A WAVE OF LOW PRESSURE
THAT DEVELOPS ALONG AN EXISTING BAROCLINIC ZONE TO OUR SOUTH AND
EAST. THIS IS FORECAST TO RESULT IN A SURFACE LOW TRACKING UP THE
OHIO VALLEY AS ENERGY EJECTS OUT OF THE PERSISTENT WESTERN U.S
TROUGH. MEANWHILE, COLD HIGH PRESSURE AT THE SURFACE IS FORECAST TO
BE SLIDING ACROSS THE NORTHEAST. THIS RESULTS IN A LOW-LEVEL COLD
AIR DAMMING SETUP, WHICH TENDS TO LEAD TO A VARIETY OF PRECIPITATION
TYPES ACROSS THE AREA.

THE FEATURES INVOLVED DO NOT APPEAR TO BE ALL THAT ROBUST, AS THE
MAIN FORCING LOOKS TO BE TIED TO WAA AND ISENTROPIC ASCENT ABOVE A
COLD LOW-LEVEL LAYER. THE WAA PUSH IS DECENT ENOUGH THOUGH TO
INITIATE AN AREA OF PRECIPITATION THAT EXPANDS NORTH AND
NORTHEASTWARD DURING THE COURSE OF THE DAY. THE FORECAST SOUNDINGS
CONTINUE TO SHOW A PRONOUNCED DRY LAYER WHICH WOULD KEEP THE
PRECIPITATION FROM REACHING THE GROUND FOR AWHILE. THE FORECAST
CHALLENGE IS WHEN THE SATURATION OCCURS TO ALLOW PRECIPITATION TO
REACH THE GROUND. THE FORECAST SOUNDINGS OVERALL SHOW THE THERMAL
PROFILE IS COLD ENOUGH NEARLY EVERYWHERE TO START THE PRECIPITATION
AS SNOW, ESPECIALLY WHEN ACCOUNTING FOR SOME INITIAL EVAPORATIONAL
COOLING. THE EXCEPTION IS ACROSS THE FAR SOUTH AND THE COASTAL
LOCALS WHERE QUICKER WARMING SHOULD RESULT IN ANY SNOW MIXING WITH
SOME SLEET THEN CHANGING OVER TO RAIN AS WE GO THROUGH THE
AFTERNOON. BASED ON THE SOUNDINGS, WE SLOWED THE INCREASE IN POPS
FROM SOUTH TO NORTH. OUR FAR NORTHERN ZONES MAY NOT SEE ANY SNOW
UNTIL THE EARLY EVENING. IT APPEARS THAT ANY FREEZING RAIN IS
LIMITED TO PERHAPS SOME OF OUR INTERIOR DELMARVA AREAS DURING THE
PRECIPITATION TRANSITION.

WE OPTED TO GO WITH A WINTER WEATHER ADVISORY FOR OUR EASTERN
MARYLAND COUNTIES DUE TO A PERIOD OF MIXED SNOW/SLEET WITH EVEN SOME
POCKETS OF FREEZING RAIN BEFORE GOING OVER TO PLAIN RAIN. THE
SNOW/SLEET AND ICE AMOUNTS HERE LOOK TO BE ON THE LIGHT SIDE, BUT IT
DOES NOT TAKE MUCH ICING TO LEAD TO SLIPPERY SPOTS. THE ADVISORY
THEN EXPANDS TO INCLUDE AREAS NORTH AND WEST OF PHILADELPHIA DURING
THE AFTERNOON. THE START TIMES OF THE ADVISORIES MAY HAVE TO BE
ADJUSTED BASED ON HOW THE NORTHWARD PROGRESSION OF THE SNOW REACHING
THE GROUND ENDS UP BEHAVING. WE TRIED TO GIVE SOME WIGGLE ROOM. THE
MAIN ICING LOOKS TO OCCUR IN THE START OF THE LONG TERM. DUE TO
LOWER CONFIDENCE REGARDING ANY ICING, WE HELD OF ON AN ADVISORY
FARTHER SOUTHEAST /MENTION STILL IN THE HAZARDOUS WEATHER OUTLOOK/.

AS FOR TEMPERATURES, A NAM/GFS MOS BLEND WAS USED. THE CLOUDS SHOULD
INCREASE AND THICKEN FAIRLY QUICKLY LIMITING THE SURFACE HEATING.
THIS RESULTS IN A COLD DAY, PLUS ONCE THE PRECIPITATION REACHES THE
GROUND SOME LOWERING OF THE TEMPERATURES SHOULD OCCUR.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
WINTER WEATHER ADVISORIES ARE IN EFFECT FOR PORTIONS OF THE REGION
THROUGH LATE SUNDAY NIGHT/MONDAY MORNING....

A VERY MESSY FORECAST FOR THE START OF THE EXTENDED AS A COMPLEX LOW
PRESSURE SYSTEM OVER THE GREAT LAKES AND LOW PRESSURE DEVELOPING
ALONG THE MIDDLE ATLANTIC COAST AFFECT THE REGION.

SUNDAY NIGHT...PRECIPITATION SHOULD ALREADY BE FALLING ACROSS THE
REGION AS RAIN/SNOW AT THE START OF THE PERIOD. THE COLD AIR WILL
REMAIN IN PLACE ON SUNDAY NIGHT BUT WE WILL START TO SEE SOME
WARMING DEVELOPING AT THE SURFACE AND IN THE MID LEVELS AND THAT
WILL SLOWLY BUT SURELY MOVE FROM SOUTH TO NORTH THROUGH THE REGION.
MODEL SOUNDINGS SHOW THE COLD LAYER IN PLACE AND WE WILL SEE A
PERIOD OF TRANSITIONING PRECIPITATION FROM SOUTH TO NORTH. AREAS TO
SOUTH WILL TRANSITION TO ALL RAIN OVERNIGHT WITH AREAS TO THE NORTH
SEEING SLEET MIX IN WITH SNOW AND THEN CHANGEOVER TO A MIX OF SLEET
AND FREEZING RAIN AS THE SURFACE LAYER STARTS TO WARM. POTENTIAL FOR
ICY CONDITIONS WILL MAINLY EXIST NORTH AND WEST OF THE PHILADELPHIA
METRO AREA BUT A BRIEF PERIOD OF FREEZING RAIN CANNOT BE RULED OUT
ALONG THE I-95 CORRIDOR AS THE PRECIPITATION CHANGES OVER TO RAIN.
IT WILL ALL DEPEND ON JUST HOW FAST THE COLUMN MOISTENS UP AND
WHETHER OR NOT THE SURFACE TEMPERATURES HAVE WARMED ABOVE FREEZING.

MONDAY THROUGH TUESDAY...ALL AREAS SHOULD SEE A CHANGEOVER TO ALL
RAIN BY MONDAY MORNING AS WARM AIR ADVECTION CONTINUES TO SPREAD
ACROSS THE REGION. THE WRENCH IN THE FORECAST HERE IS THE LOCATION
AND STRENGTH OF THE DEVELOPING COASTAL LOW. GFS CONTINUES TO SHOW
MORE OF A COLD AIR DAMMING EVENT FROM THE DEPARTING HIGH PRESSURE
ACROSS OUR AREA WHILE THE NAM DEEPENS THE COASTAL LOW A BIT MORE.
SHOULD IT REMAIN COLDER ACROSS THE NORTHERN AREAS, WE COULD SEE A
LONGER PERIOD OF FREEZING RAIN WHICH MEANS ICIER CONDITIONS.

AS THE COASTAL LOW CONTINUES ITS MARCH UP THE MIDDLE ATLANTIC AND
INTO NEW ENGLAND, A WEAK COLD FRONT WILL MOVE THROUGH THE AREA. THIS
WILL HELP TO PUT A STOP TO THE PRECIPITATION FROM NORTHWEST TO
SOUTHEAST AS DRIER AIR MOVES IN FROM THE NORTHWEST.

WEDNESDAY THROUGH SATURDAY...HIGH PRESSURE STARTS TO BUILD INTO THE
REGION FROM THE WEST WHICH WILL ALLOW FOR A PERIOD OF DRY WEATHER
ACROSS OUR FORECAST AREA. A MID-LEVEL SHORTWAVE WILL ROTATE THROUGH
THE REGION WEDNESDAY NIGHT WHICH MAY HELP TO PUSH SOME LAKE EFFECT
SNOW SHOWERS INTO THE POCONOS ON THE NORTHWESTERLY FLOW ON WEDNESDAY
AND MAYBE INTO THURSDAY. THE CLOCKWISE ROTATION AROUND THE BUILDING
HIGH WILL ALSO USHER IN SOME COLDER AIR AND WE SHOULD BE ON THE
COLDER SIDE THROUGH THE MID WEEK PERIOD. AS WE HEAD INTO THE WEEKEND
AND THE HIGH STARTS TO SLIDE TO THE EAST OF THE AREA, THE AIR MASS
SHOULD START TO MODIFY A BIT AND WE WILL WARM SLIGHTLY BY THE TIME
THE WEEKEND ROLLS AROUND.

WITH A BIG EMPHASIS PUT ON THE EVEN SUNDAY NIGHT/MONDAY, WE
GENERALLY FOLLOWED WPC GUIDANCE AND BLENDED WITH CONTINUITY FOR THE
EXTENDED PERIOD.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

TONIGHT...VFR. HIGH CLOUDINESS INCREASES ESPECIALLY LATE FROM SOUTH
TO NORTH. NORTHWEST WINDS EARLY BECOMING NORTH-NORTHEAST OVERNIGHT
AND AVERAGING AROUND 5 KNOTS.

SUNDAY...THICKENING AND LOWERING CLOUDS/CEILINGS DURING THE DAY.
SNOW IS ANTICIPATED TO OVERSPREAD THE AREA FROM SOUTH TO NORTH
STARTING NEAR MIDDAY AROUND KILG TO KACY THEN LATER IN THE AFTERNOON
AT KABE AND KTTN. THE SNOW SHOULD START TO MIX WITH SOME SLEET NEAR
KPHL ON SOUTH AND EAST TOWARD EVENING. AS A RESULT, VFR CEILINGS
WILL LOWER TO MVFR ESPECIALLY DURING THE AFTERNOON. NORTHEAST WINDS
5-8 KNOTS. OUR CONFIDENCE IS ON THE LOWER SIDE REGARDING THE START
TIME OF THE SNOW.

OUTLOOK..
SUNDAY NIGHT THROUGH MONDAY...MVFR CONDITIONS WITH POSSIBLE IFR WILL
BE PROMINENT IN A MIXED PRECIPITATION EVENT ACROSS THE REGION.
TERMINALS TO THE SOUTH WILL SEE MOSTLY RAIN WITH A MIX OF
RAIN/SNOW/SLEET AS YOU MOVE NORTHWARD. FREEZING RAIN IS POSSIBLE
MAINLY AT THE NORTHERN TERMINALS. ALL SITES SHOULD TRANSITION OVER
TO RAIN BY MONDAY MORNING. NORTHEAST TO EAST WINDS AROUND 10 KNOTS
OR LESS.

TUESDAY...MVFR TO VFR CONDITIONS ARE EXPECTED AT THE TERMINALS.
SNOW/RAIN IS POSSIBLE, MAINLY ACROSS THE SOUTHERN TERMINALS AS
PRECIPITATION EXITS THE REGION. NORTHWEST WINDS AROUND 5 TO 10
KNOTS.

WEDNESDAY...MAINLY VFR CONDITIONS EXPECTED. WEST WINDS AROUND 10 TO
15 KNOTS WITH GUSTS UP AROUND 20 KNOTS.

THURSDAY...MAINLY VFR CONDITIONS EXPECTED. WEST TO NORTHWEST WINDS
AROUND 10 KNOTS OR LESS.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
THE NORTHWEST FLOW CONTINUES AS HIGH PRESSURE BUILDS INTO THE
NORTHEAST STATES. THIS SHOULD DIMINISH SOME, ESPECIALLY ACROSS THE
NORTH, AS THE PRESSURE GRADIENT RELAXES INTO SUNDAY. WE HAVE
ALLOWED THE SCA FOR OUR NORTHERN WATERS TO EXPIRE EARLIER THIS
EVENING BASED ON OBSERVATIONS AND IN COLLABORATION WITH OUR
NEIGHBORING OFFICE. FARTHER SOUTH, WHILE THE WINDS ARE MAINLY
UNDER 25 KNOTS, THE SEAS ARE ELEVATED BUT HAVE COME DOWN TO AROUND
5 FEET. AS THE FLOW TURNS TO THE NORTHEAST AND INCREASES SOME
ESPECIALLY SUNDAY, GUSTS COULD NEAR ADVISORY CRITERIA MAINLY
ACROSS OUR SOUTHERN WATERS. THIS COULD KEEP SEAS CLOSE TO 5 FEET
AS WELL. THEREFORE, THE SOUTHERN WATERS ADVISORY WAS EXTENDED
THROUGH THE DAY SUNDAY. AS OF NOW, CONDITIONS ARE ANTICIPATED TO
BE BELOW ADVISORY CRITERIA ON DELAWARE BAY.

OUTLOOK...
SUNDAY NIGHT THROUGH MONDAY...EASTERLY WINDS WILL GRADUALLY INCREASE
AS LOW PRESSURE DEVELOPS AND MOVES UP THE MIDDLE ATLANTIC COAST.
GUSTS WILL NEAR 25 KNOTS AND SEAS WILL BUILD IN THE EASTERLY FLOW. A
SMALL CRAFT ADVISORY LOOKS TO BE NEEDED FOR SUNDAY NIGHT THROUGH
MONDAY.

TUESDAY AND WEDNESDAY...A FAIRLY TIGHT GRADIENT WILL EXIST FOR THE
TUESDAY THROUGH WEDNESDAY TIME FRAME WITH WINDS PICKING UP OUT OF
THE WEST OR NORTHWEST. WE SHOULD HAVE ENOUGH MIXING TO BRING SOME
HIGHER WINDS FROM ALOFT TO THE SURFACE AND WE MAY NEAR GALE FORCE
GUSTS TUESDAY NIGHT AND WEDNESDAY MORNING, ESPECIALLY ACROSS THE
NORTHERN OCEAN WATERS. CONFIDENCE IS HIGH THAT A SMALL CRAFT WILL BE
NEEDED BUT NOT THAT HIGH FOR POTENTIAL GALES.

THURSDAY...WINDS AND SEAS WILL SUBSIDE BELOW SMALL CRAFT ADVISORY
LEVELS AS HIGH PRESSURE BUILDS ACROSS THE REGION.
-- End Changed Discussion --

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...WINTER WEATHER ADVISORY FROM 3 PM SUNDAY TO 5 AM EST MONDAY
     FOR PAZ060>062.
     WINTER WEATHER ADVISORY FROM 2 PM SUNDAY TO 3 AM EST MONDAY
     FOR PAZ101>106.
     WINTER WEATHER ADVISORY FROM 6 PM SUNDAY TO 7 AM EST MONDAY
     FOR PAZ054-055.
NJ...WINTER WEATHER ADVISORY FROM 3 PM SUNDAY TO 5 AM EST MONDAY
     FOR NJZ007-008.
     WINTER WEATHER ADVISORY FROM 2 PM SUNDAY TO 3 AM EST MONDAY
     FOR NJZ009.
     WINTER WEATHER ADVISORY FROM 6 PM SUNDAY TO 7 AM EST MONDAY
     FOR NJZ001.
DE...NONE.
MD...WINTER WEATHER ADVISORY FROM 9 AM TO 6 PM EST SUNDAY FOR
     MDZ008-012-015-019-020.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EST SUNDAY FOR ANZ452>455.
-- End Changed Discussion --

&&

$$
SYNOPSIS...MEOLA
NEAR TERM...GORSE/KLINE
SHORT TERM...GORSE
LONG TERM...MEOLA
AVIATION...GORSE/KLINE/MEOLA
MARINE...GORSE/KLINE/MEOLA