FXUS61 KPHI 012300
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
600 PM EST TUE DEC 1 2009

.SYNOPSIS...
HIGH PRESSURE OFF THE MID ATLANTIC SEABOARD WILL RECEDE EAST. LOW 
PRESSURE WILL DEVELOP OVER THE GULF REGION TONIGHT, LIFT NORTHEAST 
ON WEDNESDAY AND BE NEAR LAKE ONTARIO BY EARLY THURSDAY. THE LOW 
WILL THEN CONTINUE RAPIDLY NORTHEAST AND AWAY FROM THE REGION. HIGH 
PRESSURE WILL BUILD IN SLOWLY BEGINNING FRIDAY. LOW PRESSURE MAY 
DEVELOP OFF THE SOUTHEAST COAST AND LIFT AWAY FROM THE MAINLAND OVER 
THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
SKIES SHOULD CLEAR AND WINDS SHOULD GO LIGHT THIS EVENING. THERE IS 
A POSSIBLE FLY IN THE RADIATING OINTMENT, AND THAT WOULD BE ENOUGH 
HIGH CLOUDS MOVING NORTH AHEAD OF THE NEXT SYSTEM TO TEMPER 
RADIATING. OVER THE SOUTHERN ZONES, WHERE THIS IS MORE LIKELY, WE'VE 
RAISED THE MINS JUST A BIT. OVER THE NORTHERN ZONES, WE'VE BASICALLY 
STAYED PAT.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
WE STILL GENERALLY ARE LOOKING AT THE ECMWF RESEMBLING THE TIMING OF 
THE GFS AND THE STRENGTH OF THE NAM WITH THE UPCOMING SYSTEM. THE 
GFS CONTINUES TO TRACK THE LOW FURTHEST EAST AS THE MID LEVEL 
IMPULSE KICKING OUT AROUND THE H5 VORTEX IS MORE BOISTEROUS THAN IT 
IS ON EITHER THE ECMWF OR THE NAM, AND THE ECMWF IS A NICE AND 
FAIRLY CONSISTENT COMPROMISE BETWEEN THE TWO AMERICAN MODELS. WE ARE 
CONTINUING TO GO WITH IT, WITH AN ACKNOWLEDGMENT THAT THE MODELS ALL 
HAVE SPED UP SOME. 

ISENTROPIC LIFT AT I300 SPREADS INTO AT LEAST THE SOUTHWESTERN HALF 
OF THE FORECAST AREA BY 00Z THURSDAY, AND UPPER LEVEL Q-VECTOR 
CONVERGENCE AND LOWER LEVEL FRONTOGENESIS START TO COME TOGETHER. 
THERE ALSO IS SOME ELEVATED INSTABILITY TO ACT ON THE AMPLE MOISTURE 
/H8 DEW POINTS RISE TO AT OR ABOVE 10 DEG C/, BUT ALL THIS IS RATHER 
PROGRESSIVE AS THE SYSTEM IS NOT BLOCKED AND MOVES TOWARD AND THEN 
BY US RAPIDLY. THE FOCUS OF THE GREATEST AMOUNT OF RAINFALL IS 
WEDNESDAY NIGHT, AND THE GFS AND THE ECMWF WANT TO TAKE EVERYTHING OUT
OF HERE BY 12Z THURSDAY. IN RESPONSE TO ALL OF THIS, WE HAVE
LEANED TOWARD THE HIGHER MAV POPS ON WEDNESDAY, GONE ALL THE WAY
TO 100 ON WEDNESDAY NIGHT /AND MENTIONED THE CHANCE OF THUNDER/ AND
LEANED TOWARD THE LOWER MAV POPS ON THURSDAY. QPF VALUES LOOK TO
BE IN EXCESS OF AN INCH, BUT FFG AND FFH VALUES INDICATE THAT WE
CAN TAKE THIS. THE ONLY POSSIBLE PROBLEM WOULD BE IF CONVECTION
GENERATED LOCALLY HEAVIER AMOUNTS. WE WILL MENTION THIS IN THE
HWO.

WINDS START TO BECOME A FACTOR LATER WEDNESDAY NIGHT INTO THURSDAY 
AS 70 KT WINDS AT H925 ARE A REAL POSSIBILITY. NOT ALL OF THAT CAN
MIX DOWN PRIOR TO FRONTAL PASSAGE, AFTER WHICH TIME THEY BEGIN TO
DIMINISH /HOPEFULLY, ANY CONVECTION WEDNESDAY NIGHT REMAINS
ELEVATED/, BUT PERHAPS WE WILL EVENTUALLY BE ISSUING A WIND
ADVISORY FOR LATER WEDNESDAY NIGHT AND/OR THURSDAY. WE WILL
MENTION THIS ALSO IN THE HWO.

ON TEMPERATURES, FOR WEDNESDAY WE SHOOT THE MIDDLE TO UPPER END OF
GUIDANCE UP NORTH AND OVER OUR EASTERN ZONES, THE FORMER BECAUSE
ANY RAIN WOULD ARRIVE LATER AND THE LATTER BECAUSE OF SOME
POSSIBLE WARM AIR ADVECTION. MOVING SOUTHWEST, WE MOVE TOWARD THE
COOLER GUIDANCE. FOR WEDNESDAY NIGHT, WE GO WITH A NON-DIURNAL
OSCILLATION AS WE FORECAST TEMPERATURES TO RISE FOR A GOOD PORTION
OF THE NIGHT. WE DO PUT THE MINS AT THE END OF THE NIGHT, BECAUSE
WE THINK THE COLD FRONT WILL JUST MAKE IT THROUGH. WE ACCEPTED
GUIDANCE ON THURSDAY.

THURSDAY NIGHT SHOULD BE DRY WITH DIMINISHING WINDS, AND FRIDAY ALSO 
SHOULD BE DRY. GUIDANCE AGAIN WAS ACCEPTED ON TEMPERATURES.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
5-WAVE MODEL GUIDANCE SHOWS A STAUNCH LATITUDINAL TROUGH PLACED OVER 
THE EASTERN HALF OF THE UNITED STATES. THE TROUGH BEGINS TO 
RETROGRADE A BIT WITH A MASSIVE WEST COAST RIDGE BUILDING IN AND 
MOVING NORTHWARD. A POLAR VORTEX LOOKS TO TAKE SHAPE OVER FAR 
NORTHEASTERN CANADA AND SLOWLY SINK SOUTHWEST LATE IN THE PERIOD.

AS THE LOW PRESSURE IN THE EARLIER PERIOD WINDS DOWN AND MOVES 
FURTHER OFFSHORE SURFACE HIGH PRESSURE WILL BEGIN TO BUILD INTO THE 
REGION. FRIDAY NIGHT LOOKS TO BE PLEASANTLY COLD WITH CALMING WINDS. 
NOT TO SOUND CLIQUE BUT FRIDAY NIGHT MAY BE THE CALM BEFORE THE 
STORM, DECEMBER 5TH.  

HERE IS A LITTLE CLIMATIC TIDBIT THAT TG MENTIONED REGARDING OUR 
INFAMOUS DECEMBER 5TH SNOWFALLS OVER THE PAST DECADE. IN THE YEARS 
IT SNOWED, 2002, 2003, 2005, AND 2007, THE 4TH OF DECEMBER HAS 
ALWAYS HAD DAYTIME HIGHS THAT NEVER GOT OUT OF THE 30S SO WE HAVE 
ALWAYS HAD COLD AIR LOCKED INTO PLACE IN PREVIOUS YEARS. FROM WHAT 
THE MODELS ARE SHOWING, AND WHAT STAT GUIDANCE HAS SUGGESTED, 2009 
WILL NOT FALL INTO THIS PATTERN; THE COLD AIR JUST DOES NOT SEEM TO 
BE THERE. HOWEVER, WITH THAT BEING SAID, FORECAST SOUNDINGS ARE 
SPITTING OUT RAIN AND SNOW SHOWERS ALL ACROSS THE REGION. FREEZING 
LEVELS DURING THE DAY HOVER AROUND 1500 TO 2000 FEET IN THE 
PHILADELPHIA METRO AREA WITH WETBULB TEMPERATURES NEAR THE SURFACE 
IN THE LOW TO MID 30S. THERE DOES APPEAR TO BE AN INDICATION OF 
LOW-LEVEL DRYNESS WHICH MAY TAKE A WHILE TO OVERCOME WITH FALLING 
PRECIPITATION. IF WE GET A NICE HEAVY BURST OF SNOW, SINCE ABOVE 
950MB IS BELOW FREEZING AND THE SNOW GROWTH ZONE IS MOIST ADIABATIC, 
WE COULD SEE ADIABATIC COOLING TAKE PLACE DUE TO SUBLIMATION. 
 
HOWEVER, EVERYTHING IS CONTINGENT ON THE PLACEMENT AND TRACK OF THE 
COASTAL LOW. TODAY'S 12Z RUN OF THE ECMWF HAS THE CENTER OF THE LOW 
PRESSURE CLOSER TO SHORE WHEN COMPARED TO THE 12Z GFS. THE PREVIOUS 
06Z GFS RUN FROM TODAY HAD THE LOW PRESSURE MUCH CLOSER TO THE NEW 
JERSEY COAST AND THE PREVIOUS 00Z RUN OFF THE ECMWF HAD A SLOWER 
MOVING SYSTEM. BASICALLY THE MODELS ARE NOT SURE WHAT THEY WANT TO 
DO WITH THIS NEXT LOW PRESSURE SYSTEM. DEPENDING ON HOW STRONG THE 
SURFACE HIGH PRESSURE BECOMES, AND HOW FAST IT MOVES IN, THE FARTHER 
OFFSHORE AND FASTER PROGRESSION MAY WIN OUT. THEN AGAIN, IF THE HIGH 
IS SLOW TO BUILD IN AND ALLOWS AMPLE TIME FOR A TREMENDOUS 180KT JET 
STREAK AT 250MB TO DIVE INTO THE BASE OF THE UPPER LEVEL TROUGH IT 
MAY PROVIDE ENOUGH ENERGY TO DRAW THE LOW PRESSURE BACK TO THE WEST 
A TAD. WITH ALL THAT BEING SAID, STILL FELT IT WAS NECESSARY TO ADD 
CHANCE POPS FOR RAIN AND SNOW SHOWERS ON SATURDAY AFTERNOON THROUGH 
EARLY SUNDAY MORNING.

ONCE THIS COASTAL STORM PULLS AWAY A MID-WEST HIGH PRESSURE SYSTEM 
WILL ENCOMPASS THE REGION AND DRIVE OUR SENSIBLE WEATHER FOR THE 
REMAINDER OF THE PERIOD.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY AND SURROUNDING AREAS.

THE SOON TO BE ISSUED TAFS WILL BE TAKING CONDITIONS IN REVERSE
OVER THE NEXT 24 HOURS AS RAIN IS SCHEDULED TO ARRIVE IN THE
REGION WEDNESDAY AFTERNOON. FOR TONIGHT VFR CONDITIONS ARE EXPECTED AT
MOST OF THE AIRPORTS WITH NOT MUCH IN THE WAY OF CLOUDS AND LIGHT
IF NOT CALM WINDS. WE DID CARRY MVFR CONDITIONS DUE TO FOG AT ONLY
KRDG AS PER THEIR GREATEST TENDENCY FOR FOG TO FORM OF OUR EIGHT
AIRPORTS.

SOME CIRRUS SHOULD START ARRIVING AFTER MIDNIGHT AND CONTINUE TO
THICKEN THROUGH THE MORNING. NOT REFLECTED IN THE CURRENT TAFS
BECAUSE OF ITS EXPECTED HEIGHT (GREATER THAN 10K), BUT AN AC OR AS CIG
IS LIKELY TO BE PRESENT DURING OR BY THE AFTERNOON.

WE BRING RAIN IN SLIGHTLY FASTER BASED ON THE LATEST 18Z GFS
MODEL, 20Z-22Z, FROM THE SW TO THE NE. IN GENERAL A MVFR AVERAGE
IS CURRENTLY FORECAST FOR THE FIRST COUPLE OF HOURS OF
PRECIPITATION. PRECIPITATION INTENSITY IS EXPECTED TO INCREASE
DURING THE EVENING AND WE LOWERED CIGS AND VSBYS TO IFR CONDITIONS
AT KRDG, KILG AND KPHL AND IN ALL LIKELIHOOD THIS WILL OCCUR AT
ALL OF OUR TERMINALS WEDNESDAY NIGHT.

WINDS THROUGH THE 24 HOUR TAF PERIOD SHOULD GENERALLY BE LIGHT, BUT
INCREASE FROM THE KPHL AREA AIRPORTS EASTWARD WEDNESDAY EVENING.
 

OUTLOOK...
RAIN WILL INCREASE IN INTENSITY WEDNESDAY NIGHT AS THE LOW MOVES
BY TO THE WEST. THE RAIN MAY BE MODERATE TO HEAVY AT TIMES AND
THERE IS A POSSIBILITY FOR A FEW ISOLATED THUNDERSTORMS. CONDITIONS
ARE EXPECTED TO AVERAGE IFR, AND THERE COULD EVEN BE LIFR. SE
WINDS WILL BECOME MORE SWLY AS THE LOW MOVES BY AND WIND GUSTS
COULD HIT THE 20 TO 25 KT RANGE WITH SOME 30 KT GUSTS NOT OUT OF
THE QUESTION. LLWS MAY BE NEEDED TO BE ADDED FOR WEDNESDAY NIGHT
AS THE LLJ IS FORECAST TO REACH AROUND 70 KNOTS FROM THE SOUTH. THE
STORM MOVES AWAY DURING THE DAY ON THURSDAY AND AN EXPANSIVE AREA
OF HIGH PRESSURE BUILDS IN FROM THE PLAINS STATES. THERE WILL
LIKELY BE SOME GUSTY WINDS INTO THURSDAY NIGHT DUE TO THE PRESSURE
GRADIENT, BUT THINGS SHOULD SETTLE DOWN LATER THURSDAY NIGHT INTO
FRIDAY AS THE CENTER OF THE HIGH MOVES CLOSER. LOW PRESSURE
FORECAST TO DEVELOP OFF THE MID ATLANTIC COAST COULD AFFECT
PORTIONS OF OUR AREA ON SATURDAY, MAINLY SOUTHERN AND EASTERN
SECTIONS.

&&

.MARINE...
HIGH PRESSURE JUST TO OUR SOUTH HAS BROUGHT A DOWNWARD TREND IN
BOTH WINDS AND SEAS TODAY. THIS RATHER TRANQUIL PATTERN WILL
PERSIST THROUGH TONIGHT AND INTO WEDNESDAY. THE HIGH WILL MOVE
OFF TO THE EAST WEDNESDAY AS LOW PRESSURE HEADS NORTHEAST FROM
THE GULF COAST STATES. THE CURRENT TRACK FOR THIS SYSTEM WILL
KEEP IT INLAND, CROSSING WV, PA AND INTO NYS AND EVENTUALLY
NEW ENG ON THURSDAY. THIS IS EXPECTED TO BE A STRONG MOISTURE-
LADEN SYSTEM DUE TO THE UPPER AIR SUPPORT AND ITS GULF ORIGINS.
SOUTHEAST WINDS WILL BE INCREASING LATE WEDNESDAY INTO WEDNESDAY
NIGHT. GALE FORCE GUSTS ARE POSSIBLE WEDNESDAY NIGHT INTO
THURSDAY. FOR THIS REASON, A GALE WATCH HAS BEEN ISSUED FROM 5 PM
WEDNESDAY UNTIL NOON THURSDAY. THESE WINDS WILL PRODUCE INCREASING
SEAS AS WELL. IN ADDITION, POUNDING WAVES OF 6 TO 8 FEET IN THE
SURF ARE POSSIBLE WEDNESDAY NIGHT. AND WITH THE FULL MOON OCCURRING
WEDNESDAY, ASTRONOMICAL TIDES WILL BE QUITE HIGH. THE ONSHORE FLOW
LATE WEDNESDAY INTO WEDNESDAY NIGHT IS EXPECTED TO PRODUCE
INCREASING TIDAL DEPARTURES AND SOME MINOR TIDAL FLOODING COULD
OCCUR AROUND THE TIME OF HIGH TIDE THURSDAY MORNING. THIS WILL BE
DEPENDENT ON THE SPEED OF THE SYSTEM. IF THE STORM MOVE FAST,
WINDS WILL SHIFT TO THE SOUTHWEST PRIOR TO THURSDAY MORNINGS
HIGH TIDE AND THE THREAT OF FLOODING WILL BE MINIMIZED. IF THE
STORM MOVES SLOWER, WINDS AROUND THE TIME OF HIGH TIDE WILL STILL
BE SOUTHERLY AND THE THREAT OF MINOR TIDAL FLOODING WILL BE
INCREASED. TIMING WILL BE A MAJOR FACTOR WITH THIS SYSTEM AND A
MATTER OF HOUR COULD MEAN THE DIFFERENCE BETWEEN MINOR TIDAL
FLOODING AND, VIRTUALLY, NO FLOODING AT ALL. WHATEVER HAPPENS,
THERE WILL NOT BE THE MAJOR DEVASTATION THAT OCCURRED WITH THE
LAST STORM. WE WILL CONTINUE TO MONITOR THIS DEVELOPING SITUATION.
WE HAVE REFRESHED OUR PNS AND MAKE MENTION OF OUR CONCERNS IN THE
HWO. ALL MARINE INTERESTS SHOULD STAY TUNED.

ONCE THE STORM MOVES AWAY FROM OUR AREA THURSDAY NIGHT, HIGH
PRESSURE WILL PUSH IN FOR FRIDAY AND FRIDAY NIGHT. THEN COMES THE
NEXT WEATHER MAKER --- LOW PRESSURE FORECAST TO DEVELOP OFF THE
CAROLINA COAST. THIS SYSTEM WILL INTENSIFY AND HEAD NORTHEAST
UP THE COAST SATURDAY. THE EXACT TRACK AND INTENSITY OF THIS
SYSTEM WILL DETERMINE HOW OUR AREA IS AFFECTED. ONCE AGAIN, 
STAY TUNED.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...GALE WATCH FROM WEDNESDAY AFTERNOON THROUGH THURSDAY MORNING 
     FOR ANZ431-450>455.

&&

$$
SYNOPSIS...DELISI
NEAR TERM...DELISI
SHORT TERM...DELISI
LONG TERM...HEAVENER
AVIATION...GIGI/RPW
MARINE...RPW