FXUS61 KPHI 292036
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
336 PM EST SUN NOV 29 2009
.SYNOPSIS...
HIGH PRESSURE OFF THE EASTERN SEABOARD WILL CONTINUE EAST. A COLD
FRONT WILL APPROACH TONIGHT AND CROSS THE AREA ON MONDAY. HIGH
PRESSURE WILL BUILD IN FOR TUESDAY AND RECEDE EAST ON WEDNESDAY.
LOW PRESSURE WILL APPROACH FROM THE GULF REGION ON WEDNESDAY NIGHT
AND MOVE BY ON THURSDAY.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
IT SHOULD TAKE A BIT OF TIME FOR CLOUDS AHEAD OF THE APPROACHING
COLD FRONT AND MID LEVEL TROUGH TO START TO AFFECT THE AREA, AND
THERE COULD BE SOME PARTIAL DECOUPLING IN THE MOST SHELTERED
SPOTS. HOWEVER, THE H925 WIND IS FORECAST TO PICK UP QUICKLY
TONIGHT, AND THAT LIKELY WILL PRECLUDE WHOLESALE RADIATING. WE
HAVE BUMPED MINIMUM TEMPERATURES UP A BIT IN RESPONSE, AND THEY
BASICALLY MATCH THE MILDER STAT GUIDANCE WHERE THE MAV AND THE MET
DIFFER /WHERE THEY DON'T, WE MATCH GUIDANCE/. WE PUT THE MINS
AT AROUND MIDNIGHT AND THEN KEEP TEMPERATURES STEADY FOR THE REST
OF THE NIGHT. WE MAINTAIN THE WIND FORECAST, WHICH KEEPS A
SURFACE FLOW GOING OUT OF THE SOUTHWEST. ALTHOUGH THE NAM LIKELY
IS A BIT SLOW WITH THE APPROACHING SYSTEM, THE REST OF THE MODELS
ARE ONLY SLIGHTLY FASTER AND SO WE CONFINE CHANCE OR SLIGHT CHANCE
POPS TO THE NORTHWEST. IT SEEMS THAT THE BULK OF THE RAIN WILL
FALL AFTER THE FRONT PASSES.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
THE H925 WINDS BEHIND THE EXTENSION OF THE SURFACE FRONT NOW LOOK
SLOWER THAN THE SURFACE FRONT ITSELF, AND THE H8 WINDS LOOK ABOUT
AS SLOW AS THE FRONT. SOUNDINGS BEHIND THE FRONT DO NOT GO DRY
ADIABATIC UP TO A SUBSIDENCE INVERSION UNTIL SOME TIME AFTER THE
FROPA /FROPA LOOKS TO OCCUR DURING THE FIRST HALF OF THE DAY/, AND THE
ASSOCIATED MID LEVEL TROUGH HAS A POSITIVE TILT. THESE ARE ALL
ANAFRONT CHARACTERISTICS, WHICH IS WHY WE FORECAST THE GREAT BULK
OF THE RAIN AFTER THE SURFACE FRONT PASSES. THERE ISN'T NORMAL
ISENTROPIC LIFT OR ANY INSTABILITY ASSOCIATED WITH THIS EVENT, BUT
THERE IS DECENT LOWER LEVEL FRONTOGENESIS, UPPER LEVEL Q-VECTOR
CONVERGENCE AND A BRUSH WITH THE RIGHT-REAR QUAD OF AN UPPER JET
TO WORK ON THE FAIR MOISTURE /H8 DEW POINTS AROUND 5 DEG C WITH
THE THETA-E AXIS/, SO WE WENT WITH UP TO ABOUT ONE-QUARTER INCH
OF RAIN WITH THE SYSTEM. THERE MAY BE A BIT MORE, BUT NOTHING THAT
WOULD BE THREATENING. WE MAINTAIN THE TEMPERATURE FORECAST ON THE
COOL SIDE AT MOST LOCATIONS, WHICH MATCHES THE COOLER STAT
GUIDANCE.
GENERALLY, CONDITIONS IMPROVE ON MONDAY NIGHT, ALTHOUGH THERE
STILL IS A WEAK SECONDARY IMPULSE THAT APPROACHES AND MOVES
THROUGH EARLY TUESDAY. WE MAINTAIN THE SLIGHT CHANCE POPS IN THE
NORTHWEST JUST IN CASE /THERE IS SOME WEAK I280 ISENTROPIC LIFT/,
ALTHOUGH STAT GUIDANCE SAYS NOTHING WILL HAPPEN OTHER THAN THE
PASSING OF SOME CLOUDS. STAT GUIDANCE AND CONTINUITY AGREE ON THE
MONDAY NIGHT MINS AND TUESDAY MAXES AND WERE ACCEPTED. WINDS
SHOULD PICK UP BY MONDAY NIGHT ON THE DECENT COLD AIR ADVECTION
AND CONTINUE INTO TUESDAY.
AS FAR AS WE CAN TELL, TUESDAY NIGHT SHOULD HAVE NOTHING OTHER
THAN SOME HIGH CLOUDS, AND WINDS SHOULD DIMINISH. WE MAY WELL
DECOUPLE, AND SO MINIMUM TEMPERATURE MAINTAIN CONTINUITY AND FAVOR
THE COLDER GUIDANCE.
ON WEDNESDAY, THE NEXT SYSTEM WILL APPROACH. THERE IS DECENT
ISENTROPIC LIFT AT I300 AND LOWER LEVEL FRONTOGENESIS THAT JUST
MOVES INTO THE SOUTHERN PART OF THE AREA BY 00Z THURSDAY, BUT THE
ECMWF ISN'T BRINGING ANYTHING MEASURABLE INTO THE AREA EXCEPT FOR
THE FAR SOUTHWESTERN PART /VERY SMALL AMOUNTS THERE/, AND SO FOR
NOW WE MAINTAIN SLIGHT CHANCE POPS THERE ONLY.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
THE AREA OF LOW PRESSURE THAT WILL BE DEVELOPING AND STRENGTHENING
IN THE SOUTH-CENTRAL STATES WILL BE MOVING ALONG THE APPALACHIAN
RANGE AND TOWARD THE NORTHEAST WEDNESDAY NIGHT. THIS WILL LEAD TO A
PERIOD OF STEADY RAINFALL OVERNIGHT WEDNESDAY INTO THURSDAY MORNING.
WITH A FAIRLY PROLONGED PERIOD OF RAINFALL, TOTAL AMOUNTS SHOULD
AVERAGE AROUND AN INCH, BUT THERE COULD BE SOME ISOLATED AREAS AS
MUCH AS 1.5 TO 2 INCHES. THERE IS NOT MUCH IN THE WAY OF
INSTABILITY, AND BEING WE SHOULD BE ON THE COOL SIDE OF THE
WARM/OCCLUDED FRONT, WE DO NOT EXPECT MUCH IN THE WAY OF CONVECTION
AT THIS TIME. THE LOW PRESSURE WILL NORTHEAST INTO NEW ENGLAND ON
THURSDAY, THEN MAKE ITS WAY INTO THE CANADIAN MARITIMES ON FRIDAY.
HIGH PRESSURE IS THEN EXPECTED TO BUILD INTO THE REGION FROM THE
SOUTHWEST FOR THE WEEKEND AND PROVIDE A MOSTLY DRY FORECAST THROUGH
SUNDAY.
TEMPERATURES FOR THE EXTENDED BEYOND THURSDAY SHOULD BE CLOSE TO OR
A FEW DEGREES BELOW NORMAL.
&&
.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
AN AREA OF HIGH PRESSURE TO OUR SOUTH WILL CONTINUE TO SLIDE
EASTWARD THROUGH TONIGHT. A WEAK AREA OF LOW PRESSURE ACROSS THE
GREAT LAKES REGION WILL TRACK TO NEW ENGLAND TONIGHT AND MONDAY.
THIS WILL PULL A COLD FRONT INTO AND THROUGH OUR AREA ON MONDAY.
AHEAD OF THIS FRONT, A SOUTHWEST FLOW WILL INCREASE ABOVE THE
SURFACE AND THIS WILL TEND TO ALLOW THE SURFACE WINDS TO HOLD UP
SOME AT MOST TERMINALS TONIGHT /ISOLATED GUSTS TO AROUND 15 KNOTS
THROUGH LATE THIS AFTERNOON/. AS MOISTURE IS ON THE INCREASE, CLOUDS
WILL ALSO BE INCREASING DURING TONIGHT AND THESE WILL GRADUALLY
LOWER AS WELL. IT APPEARS THAT VFR CONDITIONS WILL CONTINUE THROUGH
TONIGHT, THEN AS THE MOISTURE DEEPENS FURTHER THE CEILINGS WILL
BEGIN TO LOWER DURING MONDAY MORNING. WE ARE EXPECTING THIS TO OCCUR
AFTER SUNRISE WITH CEILINGS EVENTUALLY GETTING TO MVFR. WE DECIDED
NOT TO GO ANY LOWER WITH THE CEILINGS AT THIS TIME AS CONFIDENCE IS
NOT AS HIGH REGARDING THE RAIN INTENSITY, WHICH MAY END UP DRIVING
ANY LOWER CEILINGS GIVEN THE EXPECTED WIND DIRECTION. A BAND OF RAIN
IS EXPECTED TO OCCUR WITH AND BEHIND THE FRONT AND WE STEPPED THE
VISIBILITIES DOWN TO MVFR THROUGH THE MORNING INTO THE EARLY
AFTERNOON. IF SOME HEAVIER RAIN OCCURS, THE LOCAL VISIBILITY MAY
LOWER EVEN MORE FOR MOSTLY A BRIEF TIME.
THE LIGHT SOUTHWEST SURFACE WINDS WILL TEND TO SHIFT TO THE WEST AND
NORTHWEST DURING MONDAY AS THE FRONT MOVES THROUGH. WE ARE NOT
ANTICIPATING GUSTS AHEAD OF THE FRONT, HOWEVER AS COLDER AIR
ARRIVES BEHIND THE FRONT, SOME GUSTS WILL BE POSSIBLE AND WE WENT
WITH 20 KNOTS FOR NOW.
OUTLOOK...
AS THE THE COLD FRONT SLIDES EASTWARD, THE RAIN WILL TAPER OFF FROM
WEST TO EAST MONDAY AFTERNOON AND EVENING. HIGH PRESSURE THEN BUILDS
INTO THE OHIO VALLEY MONDAY NIGHT, HOWEVER A NORTHWEST WIND
/POSSIBLY GUSTY AT TIMES/ WILL CONTINUE. THESE WINDS LOOK TO
DIMINISH TUESDAY AS HIGH PRESSURE GRADUALLY SETTLES ACROSS THE AREA.
DURING WEDNESDAY, THE HIGH PRESSURE SYSTEM WILL BE SHIFTING TO OUR
EAST ALLOWING THE WINDS TO BECOME SOUTHERLY. A POTENTIALLY STRONG
AND MOISTURE LADEN STORM SYSTEM THEN ARRIVES LATE WEDNESDAY AND
THURSDAY FROM THE SOUTHWEST. IN ADDITION TO THE POSSIBLE LOWER
CEILINGS AND VISIBILITIES, GUSTY WINDS MAY OCCUR AS WELL WEDNESDAY
NIGHT AND THURSDAY. THIS STORM MOVES AWAY THURSDAY NIGHT WITH A
GUSTY NORTHWEST WIND IN ITS WAKE.
&&
.MARINE...
HIGH PRESSURE NEAR THE SOUTHEASTERN UNITED STATES WILL CONTINUE TO
SLIDE EASTWARD. A LOW PRESSURE SYSTEM IS THEN FORECAST TO TRACK TO
OUR NORTH TONIGHT AND MONDAY, PULLING A COLD FRONT ACROSS OUR AREA
DURING MONDAY. A SOUTHWEST WIND MOSTLY UNDER 15 KNOTS THIS AFTERNOON
WILL TEND TO INCREASE SOME TONIGHT AS A LOW-LEVEL JET INCREASES.
THERE IS SOMEWHAT OF A FORECAST CHALLENGE TONIGHT INTO MONDAY AS THE
WINDS INCREASE ABOVE THE SURFACE. THIS IS WITHIN A WAA REGIME AND
THE FORECAST SOUNDINGS INDICATE THAT A LOW-LEVEL INVERSION HOLDS
TONIGHT AND FOR A TIME MONDAY. THE NAM/WRF IS LOWER WITH THE
INVERSION HEIGHT COMPARED TO THE GFS, HOWEVER BOTH SUGGEST THAT
ENOUGH WIND DEVELOPS BENEATH THE INVERSION TO ALLOW WINDS TO
POTENTIALLY 25 KNOTS TO REACH THE SURFACE. THIS APPEARS TO BE A
MARGINAL TYPE SMALL CRAFT ADVISORY EVENT DURING THE WAA PHASE AND
WAVEWATCH JUST GETS SEAS TO 5 FEET. MANY TIMES IT IS MORE DIFFICULT
TO GET BETTER WINDS TO MIX DOWN TO THE SURFACE IN A WAA REGIME AND
THIS COULD BE ONE OF THOSE TIMES. HOWEVER, GIVEN THE FORECAST
LOW-LEVEL WIND FIELD AND COLLABORATION WITH OUR NEIGHBORING OFFICES,
WE OPTED TO ISSUE AN ADVISORY STARTING AT 03Z TONIGHT. BASED ON SOME
POINT FORECAST SOUNDINGS FOR DELAWARE BAY, WE WILL GO AHEAD AND
ISSUE AN ADVISORY JUST FOR THE LOWER BAY FOR NOW. OUR CONFIDENCE IS
RATHER LOW REGARDING CRITERIA BEING MET IN THE UPPER PORTION.
THE ADVISORY WILL RUN THROUGH 11Z TUESDAY FOR NOW. IT LOOKS LIKE
THERE COULD BE A LULL IN THE WINDS DURING MONDAY AFTERNOON, THEN A
RAMPING UP TREND OCCURS AS CAA GETS UNDERWAY AND ALLOWS THE
LOW-LEVEL LAPSE RATES TO STEEPEN AND IMPROVE THE VERTICAL MIXING. TO
KEEP IT SIMPLE, WE CARRIED THE ADVISORY RIGHT THROUGH FOR NOW. HIGH
PRESSURE THEN GRADUALLY BUILDS IN TUESDAY INTO WEDNESDAY. DURING
WEDNESDAY, THE HIGH PRESSURE SYSTEM WILL BE SHIFTING TO OUR EAST
ALLOWING THE WINDS TO BECOME SOUTHERLY. A POTENTIALLY STRONG AND
MOISTURE LADEN STORM SYSTEM THEN ARRIVES LATE WEDNESDAY AND THURSDAY
FROM THE SOUTHWEST. THIS SYSTEM MAY PRODUCE STRONG WINDS OVER THE
WATERS /AND BUILDING SEAS/, HOWEVER THERE IS UNCERTAINTY REGARDING
THE TRACK OF THE SURFACE LOW. GIVEN THIS UNCERTAINTY, WE DID NOT GO
WITH THE 12Z WAVEWATCH GUIDANCE ALTHOUGH DID BUMP SEAS UP SOME FROM
CONTINUITY. THIS STORM MOVES AWAY THURSDAY NIGHT WITH A GUSTY
NORTHWEST WIND AND CAA IN ITS WAKE.
REGARDING THE LATE WEDNESDAY AND THURSDAY STORM POTENTIAL, THERE
COULD BE SOME COASTAL IMPACTS ALTHOUGH THERE IS UNCERTAINTY WITH THE
STORM TRACK. A MORE INLAND TRACK WOULD KEEP THE WINDS MORE SOUTH AND
SOUTHEAST, WHICH IS LESS DAMAGING TO OUR COASTAL LOCALES. A FULL
MOON OCCURS ON WEDNESDAY, THEREFORE THE ASTRONOMICAL TIDES WILL BE
ON THE HIGH SIDE, PERHAPS LEADING TO SOME COASTAL FLOODING CONCERNS.
WE WILL MONITOR THIS AS IT WILL DEPEND ON THE STORM TRACK AND THE
STRENGTH AND DIRECTION OF THE WINDS. FOR NOW, WE CONTINUED A MENTION
IN THE HAZARDOUS WEATHER OUTLOOK.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 6 AM EST
TUESDAY FOR ANZ431-450>455.
&&
$$
SYNOPSIS...DELISI
NEAR TERM...DELISI
SHORT TERM...DELISI
LONG TERM...ROBERTSON
AVIATION...GORSE
MARINE...GORSE
