FXUS61 KPHI 012107
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
407 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 /21Z TUESDAY THROUGH SUNDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
HIGH PRESSURE, CENTERED JUST TO OUR SOUTH, BROUGHT US GOOD VFR
FLYING CONDITIONS TODAY. SOME SC AND AC WERE CONFINED TO OUR
NORTHERN SECTIONS WITH MOSTLY CLEAR SKIES SOUTH. EVEN HAD A FEW
SNOW FLURRIES THIS MORNING IN THE NORTHERN MOUNTAINS. WESTERLY
WINDS AVERAGED AROUND 10 KT WITH GUSTS TO AROUND 20 KT. ONCE THE
HEATING ABATES THIS EVENING, SKIES WILL CLEAR THROUGHOUT AND WINDS
WILL DROP OFF TO LESS THAN 5 KT. AS THE HIGH PULLS OFF TO THE
EAST WEDNESDAY, HIGH CLOUDS WILL BE INCREASING AND THICKENING.
BY THE END OF THE DAY, MOISTURE FROM THE LOW MOVING OUT OF THE
GULF STATES WILL BE SPREADING IN FROM THE SOUTH AND SOUTHWEST.
CIGS WILL LOWER THROUGH AC TO SC TOWARD EVENING AND RAIN WILL
BEGIN TO PUSH IN.
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 LOWER TO MVFR AND 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. 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...RPW
MARINE...RPW
