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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 090314
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1014 PM EST SUN DEC 8 2013

.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL MOVE THROUGH THE GREAT LAKES REGION
THROUGH 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 MONDAY MORNING/...
-- Changed Discussion --
WITH THE LATE EVENING UPDATE, WE DECIDED TO EXTEND THE WINTER
WEATHER ADVISORY FOR A FEW MORE HOURS INTO THE OVERNIGHT FOR THE
EASTERN SHORE OF MARYLAND, AS WELL AS, KENT DE AND INTO ATLANTIC
AND CUMBERLAND NJ. THESE AREAS STILL HAVE TEMPERATURES AT OR BELOW
FREEZING, AND WITH THE NEXT BATCH OF PRECIP APPROACHING ON RADAR,
WE EXPECT SOME LIGHT FREEZING RAIN/FREEZING DRIZZLE.

OTHERWISE, THE HEAVY SNOW FROM EARLIER TODAY HAS MOVED WELL
OFFSHORE AND NOW WE ARE IN SOMEWHAT OF A LULL IN THE PRECIP. THUS
THE WINTER STORM WARNING WAS TAKEN DOWN AND REPLACED WITH A WINTER
WEATHER ADVISORY FOR LIGHT FREEZING RAIN. SFC COLD AIR IS HANGING
IN A LITTLE MORE THAN EXPECTED...WHICH MAY BE PARTLY DUE TO
SEVERAL INCHES OF SNOW COVER ACROSS PARTS OF THE AREA. TIMING OF
THE CURRENT ADVISORIES WAS BASED ON THE ASSUMPTION OF MILDER AIR
COMING IN OFF THE ATLANTIC BUT THE ADVISORIES ENDING TIMES MAY
NEED TO BE ADJUSTED.

ANOTHER ROUND OF PRECIP IS APPROACHING FROM THE SW AND WILL LIKELY
REACH OUR FCST AREA AFTER MIDNIGHT. BY THE TIME IT GETS HERE THERE
SHOULD BE A WARMER LAYER ALOFT SO P-TYPE IS EXPECTED TO BE MAINLY
ZR AND/OR IP...OR JUST RAIN WHERE SFC TEMP IS ABOVE FREEZING.
DEPENDING ON HOW MUCH QPF FALLS AS ICE...SOME NWRN ADVISORIES
MIGHT POSSIBLY NEED TO BE UPGRADED OVERNIGHT.

A VERY IMPRESSIVE EVENT UNFOLDED TODAY ACROSS A PORTION OF OUR AREA
AND THE RESULTS HAD SIGNIFICANT IMPACTS. THIS ONGOING WINTRY
PRECIPITATION EVENT WILL CONTINUE, HOWEVER A TRANSITION TO ICE AND
RAIN IS EXPECTED FROM SOUTHEAST TO NORTHWEST INTO MONDAY MORNING.

A RATHER ROBUST LOW-LEVEL WAA REGIME IS OCCURRING ACROSS THE MID
ATLANTIC, AND THE INITIAL SURGE OF THIS HELPED TO RAPIDLY TIGHTEN UP
THE THERMAL GRADIENT ALOFT. THIS RESULTED IN A TIGHTENING AREA OF
WEST TO EAST ORIENTATED FRONTOGENETIC FORCING. THIS FORCING
WAS SEEN IN THE RADAR DATA AS A BANDED FEATURE ACROSS NORTHERN
MARYLAND TO PORTIONS OF SOUTHERN NEW JERSEY. THERE APPEARED TO BE
SOME SLANTWISE INSTABILITY THAT PLAYED A ROLE ALONG WITH SIGNIFICANT
ISENTROPIC UPGLIDE COMBINING WITH THE SNOW GROWTH REGION. THE END
RESULT WAS SNOWFALL RATES OF 1-3 INCHES PER HOUR! THE SNOW WAS FLUFFY
AS WELL GIVEN THE COLD AND DRY AIR THAT WAS IN PLACE. STORM TOTALS
WILL BE ABOUT 6-12 INCHES ACROSS SOME AREAS THAT WERE UNDER THIS
BAND. SO, WHERE DO GO FROM HERE?

THE WAA OCCURRING ALOFT WHICH IS HELPING TO DRIVE THE ONGOING SNOW
IS ALSO HELPING TO PRODUCE A WARMING LAYER. THIS WILL RESULT IN A
TRANSITION TO SLEET, FREEZING RAIN AND RAIN FROM SOUTHEAST TO
NORTHWEST THROUGH THE NIGHT. THIS IS ALREADY OCCURRING ACROSS THE
DELMARVA AND PORTIONS OF SOUTHERN NEW JERSEY. AN EXCEPTION IS FROM
ABOUT THE LEHIGH VALLEY, POCONOS AND PORTIONS OF NORTHWESTERN NEW
JERSEY WHERE THE LOW-LEVEL COLD AIRMASS SHOULD REMAIN LOCKED IN THE
LONGEST. THIS WILL RESULT IN SLEET AND FREEZING RAIN HOLDING ON
THROUGH MUCH OF THE NIGHT, WITH THE POCONOS PROBABLY NOT GOING OVER
TO PLAIN RAIN UNTIL SOMETIME MONDAY MORNING. DUAL-POL DATA SHOWING
MIXED PHASES ACROSS MARYLAND, DELAWARE AND SOUTHERN NEW JERSEY WHICH
IS ACTUAL SLEET AT THE SURFACE.

THE PRECIPITATION MAY BECOME INTERMITTENT AT TIMES THROUGH THIS
EVENING AS THE INITIAL WAA/FRONTOGENETIC LIFT SHIFTS TO OUR EAST,
THEN ADDITIONAL LIFT ARRIVES WITH AN OCCLUSION TYPE FEATURE AND A
SECONDARY LOW DEVELOPS NEAR THE MID ATLANTIC COAST. OVERALL, POPS
REMAIN IN THE CATEGORICAL RANGE. REGARDING THE WARNINGS AND
ADVISORIES, WE WILL MAINTAIN AS IT BUT THE END TIMES WILL LIKELY
NEED SOME FURTHER ADJUSTMENTS. THE AMOUNT OF ICING NORTH AND WEST OF
INTERSTATE 95 WILL DEPEND ON THE CHANGEOVER TIME AND ALSO HOW MUCH
QPF IS LEFT. EAST OF OF HERE, SOME ICE IS ANTICIPATED ON TOP OF THE
SNOW HOWEVER AMOUNTS SHOULD BE LIGHT. AS OF NOW, WE ARE EXPECTING
0.20 INCHES OF ICE OR LESS NORTH AND WEST AND THEREFORE WILL STAY
WITH THE ADVISORY. THE SNOW AND ICE WILL CONTINUE TO RESULT IN
HAZARDOUS TRAVEL AS TEMPERATURES SHOULD TEND TO SLOWLY RISE.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
THE ACTIVE WEATHER SHOULD BE TAPERING DOWN AS WE GO THROUGH MONDAY.
THIS IS AS LOW PRESSURE LIFTS ACROSS THE GREAT LAKES AND INTO
SOUTHEASTERN CANADA, AND A SECONDARY LOW NEAR THE TRIPLE POINT LIFTS
TOWARD SOUTHEASTERN NEW ENGLAND THROUGH THE EARLY AFTERNOON. THIS
SHOULD RESULT IN THE LARGE SCALE LIFT GRADUALLY WANING, WITH
PRECIPITATION GRADUALLY COMING TO AN END. THERE MAY BE SOME LINGERING
ICING ACROSS THE POCONOS AND WILL RUN THE ADVISORY UNTIL 9 AM MONDAY.
A WEAK COLD FRONT WILL THEN PUSH IN FROM THE WEST AND EFFECTIVELY
PUT AN END TO PRECIPITATION, BUT IN DOING SO COLDER AIR BEGINS TO
FILTER BACK INTO THE REGION.

NO MAJOR CHANGES WERE MADE TO THIS TIME FRAME ATTM.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
NOT MANY CHANGES TO THE EXTENDED DUE TO ONGOING WEATHER IN THE
NEAR/SHORT TERM PORTION OF THE FORECAST. BLENDED IN SOME NEWER
GUIDANCE TO THE FORECAST AND ADJUSTED POPS FOR THE TUESDAY EVENT.

MODELS CONTINUE TO SHOW A DISCONTINUITY WITH EACH OTHER IN TERMS OF
THE FINAL WAVE ON TUESDAY...DOES IT SKIRT BY TO OUR SOUTH OR HAVE
ENOUGH LATITUDE TO BRUSH BY OVERHEAD. UPPER LEVEL SUPPORT IN TERMS
OF THE RIGHT ENTRANCE TO THE STRONG JET AND WEAK Q-VEC CONVERGENCE
COUPLED WITH WEAK FGEN IN THE 700-500MB LAYER, SHOULD ALLOW FOR SOME
MORE MOISTURE TO BE SQUEEZED OUT ACROSS AT LEAST THE SOUTHERN HALF
OF THE CWA TUESDAY AFTERNOON. THERMAL PROFILES WILL BE CONDUCIVE FOR
ALL SNOW TO FALL THOUGH THE ONE MAJOR QUESTION BECOMES HOW MUCH
ENERGY IS STILL LEFT IN THE MID-LEVELS. BY TUESDAY THE MID-LEVEL
ENERGY BECOMES VERY STRUNG OUT AND MAY HAVE GIVEN ALL IT CAN SO ONLY
TIME WILL TELL IN THE AFTERMATH OF TONIGHTS SYSTEM TO SEE IF IF CAN
RECOVER. SPEAKING OF SNOWFALL, NOT EXPECTING MUCH IN THE WAY OF
ACCUMULATION THOUGH SOME OF THE MODELS ARE TRYING TO SHOW A QUICK
BURST TUESDAY AFTERNOON WITH DECENT DENDRITIC GROWTH POSSIBLE WITH
UPWARDS OF AN INCH IN SPOTS...MOST SOUTH AND EAST OF PHILLY.

WITH THE FINAL WAVE GONE, HIGH PRESSURE WORKS BACK IN ON WEDNESDAY
AND TEMPERATURES PLUMMET TO WELL BELOW SEASONAL AVERAGES...THROUGH
AT LEAST THE END OF THE WORK WEEK. A SLIGHT MODERATION IS EXPECTED
BY SATURDAY AS THE FLOW BEGINS TO VEER SLIGHTLY TOWARDS THE
WEST-SOUTHWEST. THE NEXT POTENTIAL SYSTEM LOOKS TO SKIRT BY THE
COAST SATURDAY NIGHT INTO SUNDAY THROWING SOME MOISTURE BACK ACROSS
THE REGION.

&&

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

TONIGHT...A TRANSITION OF THE PRECIPITATION IS GRADUALLY
OCCURRING FROM SOUTHEAST TO NORTHWEST, WITH SOME SLEET CHANGING TO
FREEZING RAIN/FREEZING DRIZZLE AND THEN RAIN. KABE AND KRDG WILL
HANG ONTO THE FROZEN/FREEZING PRECIPITATION THE LONGEST, WITH KMIV
AND KACY HAVING ALL RAIN SOONER. MVFR TO EVEN IFR CONDITIONS
/ESPECIALLY CEILINGS/ ARE EXPECTED. NORTHEAST WINDS GENERALLY
AROUND 5 TO 10 KNOTS, HOWEVER BECOMING EAST-SOUTHEAST MAINLY AT
KACY OVERNIGHT.

MONDAY...SOME LIGHT RAIN WILL CONTINUE THROUGH THE MORNING TO
EARLY AFTERNOON ACROSS THE REGION, WITH ANY IFR CONDITIONS
GRADUALLY IMPROVING TO LOW-END MVFR. MAINLY SOUTHEAST WINDS UNDER
10 KNOTS ARE EXPECTED THROUGH THE DAY, BECOMING MORE SOUTHWEST TO
WEST LATE.

OUTLOOK...
MONDAY NIGHT THROUGH TUESDAY...MVFR TO VFR CONDITIONS ARE EXPECTED
AT THE TERMINALS. SNOW/RAIN IS POSSIBLE. BETTER CHANCES FOR
PRECIPITATION SOUTH AND EAST OF KPHL ON TUESDAY. 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 AND FRIDAY...MAINLY VFR CONDITIONS EXPECTED. WEST TO
NORTHWEST WINDS AROUND 10 KNOTS OR LESS.

&&

.MARINE...
HIGH PRESSURE WILL SLIDE INTO NEW ENGLAND THROUGH TONIGHT.
MEANWHILE, LOW PRESSURE WILL TRACK UP THE OHIO VALLEY WITH A
SECONDARY WEAKER LOW DEVELOP NEAR THE MID ATLANTIC COAST. AS THIS
OCCURS, THE NORTHEASTERLY WIND WILL INCREASE SOME AND THEN TURN
EASTERLY TONIGHT ESPECIALLY ACROSS THE NORTHERN ZONES. BASED ON THE
FORECAST SOUNDINGS FROM THE NAM/GFS AND ECMWF, A SMALL CRAFT
ADVISORY IS IN EFFECT FOR OUR OCEAN ZONES ENDING DOWN SOUTH FIRST.
WE HELD OFF ON AN ADVISORY FOR DELAWARE BAY AS THE GREATER FLOW
LOOKS TO BE MOVING NORTHWARD ACROSS THE OCEAN ZONES. SEAS WILL BE
NEARING 5 FEET INTO MONDAY GIVEN THE FLOW INCREASING SOME AND
TURNING MORE NORTHEAST AND EAST. LOW PRESSURE WILL BE SHIFTING TO
OUR NORTHEAST DURING MONDAY WITH WINDS SHIFTING TO THE SOUTHWEST AND
PROBABLY WILL LOWER FOR A TIME. IT IS POSSIBLE THAT THE ADVISORY
ESPECIALLY UP NORTH THOUGH MAY NEED TO BE EXTENDED THROUGH MUCH OF
MONDAY, HOWEVER DUE TO ONGOING WEATHER THIS CAN BE ADJUSTED LATER ON.

OUTLOOK...
MONDAY NIGHT THROUGH AND WEDNESDAY...A FAIRLY TIGHT GRADIENT WILL
EXIST FOR THE MONDAY NIGHT 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 AND FRIDAY...WINDS AND SEAS WILL SUBSIDE BELOW SMALL CRAFT
ADVISORY LEVELS AS HIGH PRESSURE BUILDS ACROSS THE REGION AND REMAIN
BELOW AS WE END THE WORK WEEK.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...WINTER WEATHER ADVISORY UNTIL 6 AM EST MONDAY FOR PAZ060>062.
     WINTER WEATHER ADVISORY UNTIL 3 AM EST MONDAY FOR PAZ101-
     103>106.
     WINTER WEATHER ADVISORY UNTIL 1 AM EST MONDAY FOR PAZ070-071-
     102.
     WINTER WEATHER ADVISORY UNTIL 9 AM EST MONDAY FOR PAZ054-055.
NJ...WINTER WEATHER ADVISORY UNTIL 6 AM EST MONDAY FOR NJZ007-008.
     WINTER WEATHER ADVISORY UNTIL 3 AM EST MONDAY FOR NJZ009.
     WINTER WEATHER ADVISORY UNTIL 1 AM EST MONDAY FOR NJZ010-012-
     013-015>022-027.
     WINTER WEATHER ADVISORY UNTIL 9 AM EST MONDAY FOR NJZ001.
DE...WINTER WEATHER ADVISORY UNTIL 1 AM EST MONDAY FOR DEZ001-002.
MD...WINTER WEATHER ADVISORY UNTIL 1 AM EST MONDAY FOR MDZ008-012-
     015-019-020.
MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR ANZ452>455.
     SMALL CRAFT ADVISORY UNTIL 6 AM EST MONDAY FOR ANZ450-451.
-- End Changed Discussion --

&&

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