Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 192051
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
351 PM EST FRI DEC 19 2014

.SYNOPSIS...
HIGH PRESSURE JUST NORTH OF LAKE SUPERIOR WILL GRADUALLY MOVE
EASTWARD INTO NORTHERN NEW ENGLAND THRU MONDAY. A WAVE OF LOW
PRESSURE WILL FORM ALONG THE MID-ATLANTIC COASTLINE ON MONDAY
AND MOVE NORTHEASTWARD JUST OFFSHORE ON TUESDAY. MEANWHILE...
A STRONG AREA OF LOW-PRESSURE WILL FORM OVER THE MISSISSIPPI
VALLEY AND MOVE THRU THE GREAT LAKES REGION DURING THE MIDDLE
OF THE WEEK...BRINGING A STRONG COLD FRONT THRU THE REGION
BY THURSDAY. HIGH PRESSURE IS PROJECTED TO BUILD IN ON FRIDAY.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY/...
EXTENSIVE LOW CLOUD DECK THAT COVERED THE AREA THIS MORNING HAS
ERODED CONSIDERABLY THIS AFTN. CLOUD COVER PERSISTS OVER DELMARVA
AND OVER NWRN NJ AND ADJ PA. GIVEN THE NWLY LOW-LVL FLOW...THINK THE
CLOUDS DOWN SOUTH WILL CONT TO ERODE WHILE THE NRN AREA WILL BE MORE
PERSISTENT INTO THIS EVENING. TEMPS IN CLEARING AREAS HAVE RESPONDED
ONLY SLIGHTLY DUE TO THE LOW DEC SUN ANGLE.

FOR TONIGHT...NW WINDS WILL CONTINUE BUT WILL BECOME LIGHTER AS
CANADIAN LOW PRES MOVES AWAY AND HIGH PRES MOVES CLOSED WITH
RESULTING RELAXED PRES GRAD. MOSTLY CLEAR TO PARTLY CLOUDY SKIES
TONIGHT SHOULD ALLOW FOR DECENT COOLING WITH OVERNIGHT MINS GENLY 5
TO 10 DEGS COOLER THAN LAST NIGHT.

&&

.SHORT TERM /6 AM TO 6 PM SATURDAY/...
FOR SATURDAY...HIGH PRES CENTERED OVER CANADA SHIFTS EWD FROM
ONTARIO INTO QUEBEC. A RIDGE AXIS IS FCST TO EXTEND SWD THROUGH THE
MID-ATLANTIC REGION RESULTING IN ONLY LIGHT NLY WINDS. SOME LOW-LVL
MOISTURE SHOULD REMAIN TRAPPED BELOW THE LARGE-SCALE SUBSIDENCE
INVERSION BUT HARD TO SAY HOW EXTENSIVE ANY LOW CLOUDS MAY BE. THE
12-KM NAM SHOWS A THIN LOW CLOUD LAYER DEVELOPING DURG THE DAY BUT
HIGHER-RES ARW/NMM AND THE GFS DO NOT. THERE WILL BE SOME HIGHER
CLOUDS ALSO ASSOCD WITH THE SHRTWV NOW MOVING ENEWD OUT OF THE SRN
PLAINS...HWVR POPS REMAIN NEAR ZERO.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
HIGHLIGHTS...

* SLIGHT CHANCE OF SNOW SHOWERS SUNDAY MORNING MAINLY NORTH.
* SNOW POSSIBLE NORTHWEST OF THE I-95 CORRIDOR LATE MONDAY
  THRU EARLY TUESDAY.
* POTENTIAL FOR HEAVY RAIN INCREASING ON CHRISTMAS EVE DAY.

OVERVIEW...

MID-LEVEL BLOCKING PATTERN OVER NOAM BEGINS TO DISLODGE IN RESPONSE
JET ENERGY MOVING INTO THE PACIFIC NORTHWEST THIS WEEKEND...CARVING
OUT A DEEP TROUGH OVER THE MS VALLEY EARLY EARLY NEXT WEEK...WHICH
LEADS TO INCLEMENT WEATHER IN THE TUESDAY THRU WEDNESDAY TIME FRAME.

DETAILS...

SUNDAY...
SHORTWAVE LIFTING THROUGH THE REGION EARLY IN THE DAY MAY GENERATE
ENOUGH LIFT ALONG WITH MARGINAL MOISTURE IN THE COLUMN TO PRODUCE
SOME LIGHT SNOW SHOWERS...MAINLY DURING THE PRE-DAWN HOURS. LITTLE
IF ANY ACCUMULATION EXPECTED AS MOISTURE IS VERY LIMITED. RIDGING
THEN BUILDS IN SO FAIR WEATHER IS EXPECTED THE REMAINDER OF THE DAY.

MONDAY AND TUESDAY...
HIGH PRESSURE ANCHORS ALONG THE LEE OF THE APPALACHIANS. A SOUTHERN
STREAM SHORTWAVE WILL INDUCE LOW-PRESSURE OF THE MID-ATLANTIC COAST.
MODELS BRING QPF NORTHWARD INTO THE AREA ON MONDAY NIGHT INTO EARLY
TUESDAY. THERMAL PROFILES ARE COLD ENOUGH FOR SNOW TO THE NORTHWEST
OF THE I-95 CORRIDOR...BUT THE BEST LIFT IS FOCUSED JUST SOUTHEAST
OF THIS AREA...AND THE SYSTEM COULD TRACK FURTHER TO THE SOUTH PER
12Z UKMET MODEL. STILL A LOT OF UNCERTAINTY WITH ULTIMATE TRACK.

WEDNESDAY...
A MID-LEVEL RIDGE WILL MOVE THROUGH THE REGION TUESDAY NIGHT INTO
EARLY WEDNESDAY LEADING TO A BRIEF RESPITE BETWEEN WEATHER SYSTEMS.
THEN A MID-LEVEL TROUGH IS PROJECTED TO BECOME NEGATIVELY TILTED
OVER THE OHIO VALLEY ON WED...LEADING TO A MERIDIONAL FLOW ALONG
THE EAST COAST...WITH THE ENTIRE COLUMN EXPECTED TO BE WELL ABOVE
FREEZING ACROSS THE CWA FAVORING A RAIN EVENT. THERE ARE SEVERAL
INGREDIENTS COMING TOGETHER FOR HEAVY RAIN. IN PARTICULAR...DEEP
GULF MOISTURE...LOW-LEVEL ISENTROPIC LIFT...MID-LEVEL PVA...AND
THE RIGHT-REAR QUADRANT OF A 140 KNOT UPPER-LEVEL JET JUST NORTH.
THE SYSTEM SHOULD BE FAIRLY PROGRESSIVE BUT WILL HAVE TO MONITOR
POTENTIAL FOR FLOODING.

THU AND FRI...
LOW-PRESSURE MOVES NORTHWARD INTO QUEBEC AND HIGH-PRESSURE BEGINS
TO BUILD IN. TEMPERATURES WILL RETURN TO SEASONABLE LEVELS AND
THERE COULD BE SNOW SHOWERS IN THE BLUSTERY NORTHWEST FLOW.

&&

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
SMWHAT GUSTY NW WINDS WILL CONTINUE FOR A COUPLE MORE HOURS BUT
SHOULD DIE DOWN SOME BY SUNSET AS THE SFC COOLS/DECOUPLES AND THE
LARGER SCALE PRES GRADIENT RELAXES. LIGHT NW WINDS WILL CONTINUE
OVERNIGHT. THE EARLIER LOW CLOUDS HAVE MOSTLY DISSIPATED AND ATTM
ARE NOT EXPECTED TO RETURN TONIGHT. SOME LOW CLOUDS ARE POSSIBLE
ON SATURDAY BUT SHOULD NOT BE AS EXENSIVE AS THIS MORNING. WINDS
ON SATURDAY WILL BE LIGHT NORTHERLY AS A HIGH PRESSURE RIDGE MOVES
OVER HEAD.

OUTLOOK...
SUNDAY...VFR CONDITIONS EXPECTED.
MONDAY AND TUESDAY...IFR POSSIBLE IN SHRA AND SHSN.
WEDNESDAY...IFR POSSIBLE IN RA AND FG.

&&

.MARINE...
SUB-SCA CONDS ARE EXPECTED FOR THE NEXT 24 HOURS AT LEAST. SMWHT
GUST NW WINDS THIS EVENING WILL GRADUALLY DIMINISH TONIGHT THROUGH
SATURDAY AS A RIDGE OF HIGH PRES MOVES OVERHEAD. SEAS ARE
CURRENTLY RUNNING 2 TO 3 FT BUT THEY SHOULD GRADUALLY DIMINISH
ALSO.

OUTLOOK...

SUNDAY AND MONDAY...SUB-SCA CONDITIONS EXPECTED.
TUESDAY...SCA MAY BE NEEDED FOR BUILDING SEAS.
WEDNESDAY...GALE WARNING MAY BE NEEDED.

&&

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

&&

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





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