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000
FXUS61 KPHI 070920
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
420 AM EST SAT DEC 7 2013

.SYNOPSIS...
A COLD FRONT STILL REMAINS TO OUR SOUTH AND EAST TODAY AS A COLD
CANADIAN HIGH PRESSURE SYSTEM NOSES IN BRIEFLY BEFORE PUSHING OFF TO
THE NORTHEAST BY SUNDAY MORNING. A COMPLEX LOW PRESSURE SYSTEM WILL
THEN ENTER INTO THE LOWER GREAT LAKES SUNDAY EVENING WHILE A
SECONDARY LOW PRESSURE MAY FORM ALONG THE MID-ATLANTIC COAST ON
MONDAY. AN ASSOCIATED COLD FRONT IS FORECAST TO CROSS OUR AREA LATER
MONDAY WITH A SECONDARY FRONT MOVING THROUGH TUESDAY NIGHT OR
WEDNESDAY. A STRONG AREA OF HIGH PRESSURE THEN BUILDS IN DURING
WEDNESDAY AND THURSDAY BEFORE GRADUALLY SHIFTING TO OUR EAST FRIDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
LATEST RADAR IMAGERY SHOWED PRECIP CONTINUING TO EXIT STAGE RIGHT.
OVER THE NRN AND WRN SECTIONS, THE PRECIP HAS ENDED.  SOME VERY
LIGHT PRECIP WAS OCCURRING OVER CNTRL SECTIONS, WITH LINGERING
PRECIP ACRS THE S AND E. THE OVERALL TREND IS FOR AN END BY DAYBREAK
OR SHORTLY THEREAFTER.  WITH THE PRECIP OVER N AND W, WILL DROP THE
WINTER WEATHER ADVISORY FOR THE POCONOS AND SUSSEX COUNTY, NJ.
THERE COULD STILL BE SOME SLICK SPOTS, SO WILL ISSUE AN SPS TO
ACCOUNT FOR THIS.

OTHERWISE, GRADUALLY IMPROVING BUT WINDY CONDS TODAY WITH SUNSHINE
BY AFTN.  TEMPS WILL BE BELOW NRML AND WITH THE GUSTY NW WIND, THEY
WILL FEEL COLDER.  NEVERTHELESS, HIGH PRESSURE WILL BUILD IN FROM
THE MIDWEST AND MAKE FOR A DRY DAY ONCE THE CURRENT PRECIP MOVES
OUT.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
THE AFOREMENTIONED HIGH PRESSURE WILL BE OVER THE REGION TONIGHT, SO
EXPECT DRY WX WITH INCREASING CLOUDS IN ADVANCE OF THE NEXT SYS.
SOME WIND AND THE CLOUD COVER BY MRNG WILL PREVENT TEMPS FROM
BOTTOMING OUT.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
STILL EXPECTING A VERY COMPLEX SYSTEM TO EJECT INTO THE LOWER GREAT
LAKES SUNDAY NIGHT INTO MONDAY AS PRECIPITATION OVERSPREADS THE
REGION FROM THE SOUTH-SOUTHWEST DURING THIS TIMEFRAME. A COASTAL
WAVE COULD DEVELOP ALONG THE OLD BAROCLINIC ZONE, THE OLD ARCTIC
FRONT, AND MOVE TOWARDS THE REGION MONDAY MORNING PROVIDING BETTER
FRONTOGENETIC FORCING AND MODERATE PRECIPITATION...IT ALSO POSES
PTYPE ISSUES GIVEN THE THERMAL PROFILES. IT SHOULD BE NOTED THAT THE
00Z GFS LOOKED BETTER AT ALL THERMAL LEVELS WHEN COMPARED TO THE
NAM, THOUGH BOTH WERE A TAD COLDER UPSTREAM AND THE EC WAS SOMEWHERE
IN BETWEEN.

GETTING INTO IT...
SURFACE WAVE TO OUR WEST AND POSSIBLY TO THE EAST WILL ALLOW DECENT
WARM AIR ADVECTION TO KICK IN AS SURFACE RIDGING RETREATS FURTHER
EAST-NORTHEAST DURING THE DAY SUNDAY. THERMAL PROFILES SHOW THAT
EVERYONE SHOULD BE COLD ENOUGH TO SEE A LIGHT SNOWFALL SPREAD SOUTH
TO NORTH, THOUGH ALL THE WHILE THE MOISTURE ALOFT WILL BE COMBATING
DRY SURFACE AIR, SO NOT QUITE SURE HOW MUCH WILL ACTUALLY MAKE IT TO
THE GROUND, AND ULTIMATELY STICK. THE BETTER CHANCE FOR ACCUMULATION
WOULD BE ALONG PORTIONS OF THE EASTERN SHORE OF MARYLAND, DUE TO
SOME COLD AIR DAMMING FEATURE ALLOWING BOUNDARY LAYER TEMPERATURES
TO STAY RIGHT AROUND 30F, AND THEN NORTH AND WEST OF PHILADELPHIA,
BUT LATER IN THE EVENING AS STEADIER PRECIPITATION MOVES IN.

STILL EXPECTING A RAPID CHANGEOVER TO OCCUR ACROSS A MAJORITY OF OUR
ZONES BY MONDAY MORNING, THOUGH THE SURFACE TEMPERATURES WILL BE THE
TRICKY PART. DEPENDING ON THE PLACEMENT OF THE COASTAL LOW, ENOUGH
OF A NORTHEAST FLOW COULD STAY IN PLACE TO KEEP SURFACE TEMPERATURES
FROM WARMING ABOVE FREEZING FOR A FEW MORE HOURS, MORE THAN WHAT IS
CURRENTLY ANTICIPATED. THIS WOULD MEAN MORE FREEZING RAIN, THOUGH
ACTUAL ACCRETION AMOUNTS STILL NEED TO BE REFINED, PROVIDING AT
LEAST A WINTER WEATHER ADVISORISH TYPE OF EVENT...STILL NEED TO WORK
OUT A FEW MORE DETAILS.

PRECIPITATION SHOULD START TO TAPER OFF FROM NORTHWEST TO SOUTHEAST
LATER MONDAY, ALTHOUGH ANOTHER PIECE OF ENERGY RUNNING ALONG THE
BAROCLINIC ZONE COULD TOSS SOME MOISTURE BACK INTO AT LEAST OUR
SOUTHEAST ZONES MONDAY NIGHT. THIS IS OF LOWER CONFIDENCE.

FOR TUESDAY...AS AN UPPER-LEVEL TROUGH DIGS ACROSS THE MIDWEST AND
GREAT LAKES REGION, THIS MAY HELP TO INDUCE ANOTHER WAVE ALONG THE
BAROCLINIC ZONE TO OUR SOUTHEAST. THIS COULD RESULT IN A
PRECIPITATION SHIELD TRACKING ACROSS OUR SOUTHEAST ZONES ESPECIALLY
FOR A TIME. THE DETAILS IN THIS ARE OF LOW CONFIDENCE ESPECIALLY
RELATED TO THE TIMING OF THE ENERGY. THEREFORE, WE FAVORED MOSTLY
WPC POPS WHICH IS IN THE SLIGHT CHC TO CHC RANGE WITH THE HIGHEST
ACROSS THE SOUTHEAST.

FOR WEDNESDAY THROUGH FRIDAY...AN UPPER-LEVEL TROUGH WILL BE MOVING
THROUGH THE EAST. AT THE SURFACE, STRONG HIGH PRESSURE WILL BUILD
INTO THE MID ATLANTIC AND NORTHEAST WEDNESDAY AND ESPECIALLY
THURSDAY. THE CYCLONIC NORTHWESTERLY FLOW AND COLD AIR WILL RESULT
IN LAKE EFFECT SNOW AND SOME OF THIS MAY GET INTO OUR FAR NORTHWEST
ZONES. MOST OF THE ACTIVITY HOWEVER SHOULD BE CONFINED CLOSER TO THE
GREAT LAKES. THE FLOW THEN STARTS TO BACK THURSDAY NIGHT AND FRIDAY
AND SURFACE HIGH PRESSURE IS FORECAST TO GRADUALLY SHIFT OFF THE MID
ATLANTIC COAST. WE ARE ANTICIPATING COLD TEMPERATURES DURING THIS
TIME FRAME ALTHOUGH SOME MODERATION MAY START FRIDAY, HOWEVER AT
THIS POINT IT GENERALLY LOOKS DRY. WE ONLY CARRIED SOME FLURRIES
ACROSS THE POCONOS WEDNESDAY AND THURSDAY. THE WPC GUIDANCE WAS
MAINLY USED DURING THIS TIME FRAME AS MORE FOCUS WAS PUT ON THE
SUNDAY AND MONDAY EVENT.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

AFTER A MESSY ERLY MRNG CONDS SHUD IMPROVE TO VFR EVERYWHERE.
PRECIP HAS ENDED AT KABE AND KRDG.  IT WILL BE ENDING ACRS THE I-95
CORRIDOR ARPTS IN THE NEXT HOUR OR TWO AND FOR KMIV AND KACY LATER
THIS MRNG.  MANY SITES ALTERNATED BETWEEN VFR AND MVFR ALL NIGHT.
THIS TREND HAS CONTINUED.  THERE IS SOME LCL IFR IN PLACES AND THIS
CAN NOT BE RULED OUT ESPECIALLY FROM THE I-95 CORRIDOR S AND E THRU
THE ERLY MRNG.

HIGH PRESSURE WILL THEN BUILD IN FROM THE MIDWEST AND VFR CONDS ARE
EXPECTED TO RETURN LATER THIS MRNG AND CONTINUE FOR THE REMAINDER OF
THE TAF PD, IN ADVANCE OF THE NEXT SYS.

A GUSTY NW WIND IS EXPECTED TO DEVELOP LATER THIS MRNG AND CONTINUE
THRU THE DAY WITH GUSTS AS HIGH AS 20 KT.

OUTLOOK...
SUNDAY - MONDAY...INCREASING CLOUDS ALONG WITH CHANCES FOR
SNOW/RAIN/SLEET TO FALL BY LATE AFTERNOON. MVFR TO IFR CONDITIONS
WILL PREVAIL. TRANSITION OVER TO ALL RAIN BY EARLY MONDAY MORNING,
THOUGH THERE COULD BE A FEW HOURS OF FREEZING RAIN AT RDG/ABE BEFORE
DOING SO. HIGH CONFIDENCE IN PRECIPITATION TYPE WITH MODERATE
CONFIDENCE ON TRANSITION TIMING.

TUESDAY AND WEDNESDAY...SOME MVFR POSSIBLE MAINLY SOUTH AND EAST OF
KPHL TUESDAY, OTHERWISE GENERALLY VFR. SOME RAIN SNOW POSSIBLE
TUESDAY MAINLY SOUTH AND EAST OF KPHL, HOWEVER CONFIDENCE IS ON THE
LOW SIDE. NORTHWESTERLY WINDS 10-15 KNOTS WITH POSSIBLE GUSTS UP TO
25 KNOTS.

&&

.MARINE...
BASED ON LATEST OBS AND GUIDANCE WILL EXTEND THE SCA ON THE OCEAN
UNTIL 00Z.  IT MAY NEED TO BE EXTENDED FURTHER, ESPECIALLY ACRS THE
S.  WILL KEEP THE 1 PM EXPIRATION TIME FOR THE BAY AND MONITOR THIS
TO SEE IF ANY ADDITIONAL EXTENSIONS ARE NEEDED.  PRECIP WILL COME TO
AN END ACRS THE WATERS LATER THIS MRNG AS HIGH PRESSURE BUILDS IN
FROM THE MIDWEST.

OUTLOOK...
SUNDAY AND MONDAY...THE PRESSURE GRADIENT MAY RELAX SOME FOR
SUB-ADVISORY CONDITIONS FOR A TIME SUNDAY. AS THE FLOW TURNS TO THE
NORTHEAST AND INCREASES SOME, GUSTS COULD NEAR ADVISORY CRITERIA
LATER SUNDAY INTO MONDAY. THIS IS AS LOW PRESSURE TRACKS INTO THE
GREAT LAKES WITH A SECONDARY LOW POTENTIALLY DEVELOPING NEAR THE MID
ATLANTIC COAST. THE SEAS SHOULD ALSO BUILD SOME WITH THE
NORTHEASTERLY FLOW.

TUESDAY AND WEDNESDAY...MUCH COLDER AIR TO ARRIVE UNDER A WEST TO
NORTHWEST FLOW. THERE MAY BE ENOUGH FLOW ALONG WITH VERTICAL MIXING
FOR SOME GUSTS TO NEAR 30-35 KNOTS. AS OF NOW, ANY GALE POTENTIAL IS
OF LOW CONFIDENCE.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR
     ANZ450>455.
     SMALL CRAFT ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR ANZ430-
     431.

&&

$$
SYNOPSIS...GORSE/HEAVENER
NEAR TERM...NIERENBERG
SHORT TERM...NIERENBERG
LONG TERM...GORSE/HEAVENER
AVIATION...GORSE/HEAVENER/NIERENBERG
MARINE...GORSE/HEAVENER/NIERENBERG