FXUS61 KPHI 040840
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
340 AM EST FRI DEC 4 2009
.SYNOPSIS...
HIGH PRESSURE WILL SETTLE ACROSS OUR AREA TODAY BEFORE MOVING
NORTHWARD AND THEN BECOMING REESTABLISHED TO OUR WEST TONIGHT AND
SATURDAY. AN AREA OF LOW PRESSURE IS FORECAST TO DEVELOP NEAR THE
GULF COAST STATES TODAY INTO TONIGHT AND THEN MOVE NORTHEASTWARD
ALONG A FRONTAL BOUNDARY OFF THE EAST COAST. THE EXACT TRACK OF THIS
LOW STILL CARRIES SOME UNCERTAINTY, AS THIS WILL DETERMINE HOW MUCH
PRECIPITATION SPREADS ACROSS OUR AREA SATURDAY INTO SATURDAY
NIGHT. HIGH PRESSURE THEN BUILDS IN FROM THE WEST SUNDAY BEFORE
GRADUALLY SLIDING TO THE EAST MONDAY. THE NEXT POTENTIALLY
SIGNIFICANT STORM SYSTEM MAY ARRIVE WEDNESDAY INTO THURSDAY.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A 07Z SURFACE ANALYSIS PLACED HIGH PRESSURE NEAR THE TEXAS
PANHANDLE. MEANWHILE, A TROUGH WAS ACROSS THE CENTRAL GREAT LAKES
AND A FRONTAL BOUNDARY WAS WELL OFF THE EAST COAST BUT THEN DRAPED
BACK INTO THE GULF OF MEXICO. AN UPPER AIR ANALYSIS SHOWED A WIDE
300 MB JET ACROSS THE EASTERN HALF OF THE NATION AND THIS FEATURE
WAS CYCLONICALLY CURVED FROM THE INTERMOUNTAIN WEST TO THE
MISSISSIPPI VALLEY. A MIDLEVEL TROUGH WAS LOCATED FROM THE MIDWEST
TO THE SOUTHERN PLAINS WITH SEVERAL SHORT WAVES EMBEDDED WITHIN THE
FLOW. SOME WAA WAS BEGINNING AT 850 MB IN THE CENTRAL TO NORTHERN
GULF OF MEXICO.
A MUCH MORE TRANQUIL EARLY MORNING THAN JUST 24-HOURS AGO AS WE HAD
LOCALLY DAMAGING WINDS OCCURRING ALONG WITH NEAR RECORD HIGH
TEMPERATURES. THAT IS A THING OF THE PAST AS A COOLING TREND HAS
COMMENCED. THE LARGE SCALE PICTURE CONTINUES WITH AN UPPER-LEVEL
TROUGH FROM THE GREAT LAKES TO THE SOUTHERN PLAINS, WITH THE CORE OF
THE UPPER-LEVEL FEATURE NEAR HUDSON BAY. OUR REGION REMAINS ON THE
EAST SIDE OF THIS TROUGH WITH A SOUTHWESTERLY FLOW ALOFT CONTINUING.
THIS SETUP FAVORS THE COLDER AIR HANGING BACK TO OUR WEST WITH OUR
TEMPERATURES ONLY GRADUALLY TURNING COLDER. HIGH PRESSURE IS
FORECAST TO SETTLE ACROSS OUR AREA TODAY AS A BAROCLINIC ZONE
REMAINS WELL OFF THE MID ATLANTIC COAST BUT THEN IS POSITIONED
ACROSS THE GULF OF MEXICO. THE LINGERING CYCLONIC FLOW WITH GRADUAL
CAA HAS MAINTAINED SOME STRATOCUMULUS MOSTLY TO OUR WEST.
GIVEN THE SOUTHWESTERLY FLOW ALOFT, THERE WILL BE A TENDENCY OF SOME
MID TO ESPECIALLY HIGH LEVEL CLOUDINESS ARRIVING FROM THE SOUTHWEST
AS INCREASING LIFT OCCURS ALONG THE GULF COAST. AS A RESULT, WE WILL
CARRY MORE CLOUDS THIS AFTERNOON COMPARED TO THIS MORNING. THE
FORECAST SOUNDINGS INDICATE ENOUGH BOUNDARY LAYER MIXING TO PERHAPS
GET SOME STRATOCUMULUS TO REDEVELOP, HOWEVER THE CONVECTIVE
TEMPERATURES ARE FORECAST TO BE RATHER HIGH TODAY /PLUS THERE IS
SOME LOW-LEVEL DRYING FORECAST/.
AS FOR TEMPERATURES, WE MOSTLY UTILIZED A BLEND OF THE GFS AND NAM
MOS BUT LEANED TOWARD THE COOLER NAM MOS FOR SOME LOCALES GIVEN THE
COOLING AIR MASS ALOFT.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
THIS TIME FRAME WILL BE TRENDING RATHER INTERESTING. AS AN
UPPER-LEVEL TROUGH SWINGS THROUGH THE GREAT LAKES TO THE GULF COAST
REGION TONIGHT, LARGE SCALE LIFT WILL BECOME ENHANCED ALONG AND
NORTH OF A BAROCLINIC ZONE POSITIONED FROM THE GULF MEXICO TO OFF
THE SOUTHEASTERN UNITED STATES COAST. THIS HELPS TO ORGANIZE A
SURFACE LOW AS THE THERMAL GRADIENT STRENGTHENS SOME AND THE RIGHT
ENTRANCE REGION OF A 140-KNOT 250 MB JET COMES INTO PLAY. IN
ADDITION, THE INCOMING SHORT WAVE TROUGH IN THE SOUTHERN STATES
TENDS TO SHARPEN UP SOME MORE. THE COMPUTER MODEL GUIDANCE HAS BEEN
SHOWING THIS FEATURE FOR SOME TIME NOW, HOWEVER THE TRACK OF THE
SURFACE LOW AND HOW MUCH LIFT GETS PULLED NORTHWESTWARD AS THE
MIDLEVEL FEATURE EJECTS NORTHEASTWARD HAS BEEN IN QUESTION.
PER HPC, THE NAM/WRF IS ON THE MORE AMPLIFIED SIDE OF THE MODEL
GUIDANCE SPREAD STARTING LATE FRIDAY WITH PORTIONS OF THE MIDLEVEL
SHORT WAVE FORECAST TO CROSS THE EAST COAST SATURDAY NIGHT. AS A
RESULT, THE WESTERN ATLANTIC SURFACE LOW IS ONE OF THE FARTHER
WESTWARD TRACKS AMONG LATEST GUIDANCE. THE NAM/WRF HAS TRENDED
SLIGHTLY FASTER WITH THE MIDLEVEL ENERGY OVER THE PAST DAY. THE GFS
LEANS TOWARD THE QUICKER EDGE OF THE MODEL GUIDANCE ENVELOPE FROM
LATE FRIDAY ONWARD, WITH A WESTERN ATLANTIC SURFACE LOW EVOLUTION
THAT LEANS TOWARD THE FAST EDGE OF THE GUIDANCE. THE GFS HAS TRENDED
NOTICEABLY FASTER IN THE PAST DAY AS WELL SO ITS FASTER TIMING
CANNOT BE COMPLETELY DISCOUNTED. HOWEVER, THE 00Z ECMWF REMAINS
SLOWER THAN THE GFS, WITH ITS SOLUTION ALOFT COMPARING WELL TO THE
UKMET/CANADIAN GLOBAL, WHICH ARE SLIGHTLY STRONGER WITH THE TROUGH
THAN THE GFS. HPC MENTIONED THAT THE WESTWARD ADJUSTMENT OF THE 00Z
ECMWF FROM ITS PREVIOUS RUNS ALSO BRINGS IT TO THE MIDDLE OF THE
SPREAD BETWEEN THE NAM/WRF AND GFS. THE ECMWF MAY STILL BE A LITTLE
SLOW TO DEEPEN THE SURFACE LOW BASED ON REMAINING OPERATIONAL
GUIDANCE. SOME OF THE MODELS HAVE ALSO TRENDED A BIT WETTER AS WELL.
WE MAINLY UTILIZED A BLEND OF THE ECMWF AND UKMET FOR THE SATURDAY
AND SATURDAY NIGHT EVENT. BACKING UP A BIT, THE STRONG UPPER-LEVEL
JET IS FORECAST TO BE LIFTING GRADUALLY NORTHWARD TONIGHT AND EVEN
STRENGTHEN SOME MORE. THIS COMBINED WITH GRADUAL MOISTURE ADVECTION
ABOVE THE BOUNDARY LAYER WILL ALLOW FOR AN INCREASE AND THICKENING
OF THE CLOUDS TONIGHT. THESE CLOUDS MAY TEND TO KEEP TEMPERATURES UP
SOME DUE TO LESS CONDUCIVE RADIATIONAL COOLING CONDITIONS. IN
ADDITION, HIGH PRESSURE THAT SHIFTS NORTH OF OUR AREA LOOKS TO
ACTUALLY BECOME REESTABLISHED TO OUR WEST LATE TONIGHT INTO SATURDAY.
THIS WILL ALLOW THE WINDS TO SHIFT TO THE NORTH AND NORTHEAST AND
PERHAPS PICK UP SOME ESPECIALLY LATE TONIGHT. ALL OF THIS MAY TEMPER
THE LOWERING OF THE TEMPERATURES TO SOME EXTENT DESPITE LOWER
SURFACE DEW POINTS. AS THE SURFACE LOW ORGANIZES AND MOVES OFF THE
EAST COAST DURING SATURDAY, LARGE SCALE LIFT WILL SPREAD NORTHWARD.
THERE ARE SOME DIFFERENCES AMONG THE MODELS ON HOW MUCH
PRECIPITATION GETS FARTHER NORTH AND WEST, AND IT WILL BE
INTERESTING TO SEE HOW MUCH THE LOW-LEVEL DRYING HOLDS BACK THE
ADVANCING PRECIPITATION SHIELD. SOME OF THE FORECAST SOUNDINGS AND
EVEN THE GFS QPF FIELDS HINT AT DRY LOW-LEVEL AIR HOLDING FIRM FOR
AWHILE. DESPITE THIS, A DECENT AMOUNT OF MOISTURE TRANSPORT SHOULD
OCCUR NORTHWARD WITH TIME AS THE FLOW IS SOUTHWEST ALOFT AND EVEN
STRENGTHENS. FORECAST SOUNDINGS INDICATE THAT THE WESTERN ZONES ARE
COLD ENOUGH FOR MAINLY SNOW WITH RAIN TO START FARTHER TO THE EAST.
WITH A MILD OCEAN JUST TO OUR EAST, THE COASTAL AREAS WILL HAVE RAIN
BUT COULD MIX WITH OR END AS SOME SNOW. INTERESTING TO NOTE THAT
SOME GUIDANCE, LIKE THE NAM MOS, SHOWS LOWER SURFACE DEW POINTS
ESPECIALLY FOR THE INLAND AREAS. THIS MAY HELP TO EVENTUALLY COOL
THE COLUMN FURTHER ESPECIALLY IF THE PRECIPITATION INTENSITY
STRENGTHENS SOME. THERE IS A BAND OF LOW-LEVEL FRONTOGENETIC FORCING
THAT OVERSPREADS THE AREA, THEREFORE THAT COULD KICK UP THE
INTENSITY SOME. MODEL CROSS SECTIONS REVEAL THAT THE OMEGA FIELDS DO
INTERSECT THE SNOW GROWTH AREAS FOR A TIME SATURDAY INTO SATURDAY
NIGHT, HOWEVER THIS DOES NOT LOOK LIKE AN IDEAL SETUP AS THE
FORECAST OMEGA IS ON THE WEAKER SIDE. WE TRIED TO PRESERVE SOME
CONTINUITY WITH OUR PRECIPITATION TYPES, HOWEVER DID TWEAK POPS SOME
AND EVEN TIGHTEN THEM UP A BIT. BASICALLY CHC ACROSS THE WESTERN
AREAS TO LIKELY AND CATEGORICAL AS ONE HEADS EASTWARD. THE POPS
INCREASE FROM SOUTHEAST TO NORTHWEST DURING THE COURSE OF SATURDAY.
BASED ON THE ABOVE AND LOWER CONFIDENCE ON HOW MUCH SNOW ACTUALLY
STICKS, WE WILL PAINT IN A SWATCH OF AROUND AN INCH OF SNOW MOSTLY
CENTERED ALONG INTERSTATE 95. THIS IS CLOSE TO THE LATEST HPC WWD
SNOW GRAPHIC. WE WILL HAVE TO SEE HOW MUCH SNOW CAN ACTUALLY STICK
TO THE GROUND GIVEN THE BOUNDARY LAYER TEMPERATURES. WE WILL
CONTINUE TO HIGHLIGHT THIS EVENT IN THE HAZARDOUS WEATHER OUTLOOK.
STAY TUNED.
THE STORM EJECTS NORTHEASTWARD AND AWAY FROM OUR REGION EARLY
SUNDAY, THEREFORE WE TAPERED THE POPS DOWN FAIRLY QUICKLY SATURDAY
NIGHT WITH DRY CONDITIONS EXPECTED ON SUNDAY AS HIGH PRESSURE
RETURNS. THE SKY MAY TEND TO CLEAR QUICKLY SATURDAY NIGHT INTO
SUNDAY AND TEMPERATURES LOOK TO DROP BELOW FREEZING. WE MAY NEED TO
WATCH OUT FOR DEVELOPING ICY SPOTS DEVELOPING DUE TO THE FALLEN
RAIN/SNOW AND ANY REMAINING WET SURFACES.
AS FOR TEMPERATURES, WE TOOK A BLEND OF THE GFS AND NAM MOS BUT ALSO
ADJUSTED TOWARD SOME CONTINUITY AS WELL.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AN AREA OF HIGH PRESSURE OVER THE MID ATLANTIC REGION SUNDAY NIGHT
WILL MOVE OFFSHORE ON MONDAY. A WEAK FAST MOVING FRONTAL SYSTEM IS
FORECAST TO CROSS THE AREA WEST TO EAST LATE MONDAY OR MONDAY NIGHT
BUT THERE SEEMS TO BE LITTLE MOISTURE OR PRECIPITATION WITH IT. AS
OF NOW, TUESDAY LOOKS LIKE THE BEST DAY NEXT WEEK WITH FAIR WEATHER
AS HIGH PRESSURE MOVES BY.
THE OVERALL PATTERN THEN LOOKS TO RELOAD YET AGAIN AS ENERGY DIVES
SOUTHEASTWARD ACROSS THE WEST AND MAINTAINS OR AMPLIFIES THE
TROUGHING INTO THE PLAINS. AS THIS OCCURS, CYCLOGENESIS IS FORECAST
TO TAKE PLACE IN THE WESTERN SOUTHERN PLAINS. THIS FEATURE WILL THEN
BE DRIVEN EAST AND NORTHEASTWARD BY STRONG DYNAMICS. AS THE STORM
DEEPENS, THE TRACK LOOKS TO SLIDE TO OUR WEST AS THE TROUGH AXIS
HANGS BACK ACROSS THE MIDWEST. THIS SYSTEM COULD BE SIMILAR TO THE
ONE JUST EXPERIENCED WEDNESDAY NIGHT AND THURSDAY MORNING AS AN
OCCLUDED FRONT SWEEPS THROUGH AS THE WARM SECTOR TRIES TO LIFT
NORTHWARD. HOWEVER, THERE IS A SURFACE HIGH FORECAST TO BE SITTING
TO OUR NORTHEAST. THERE COULD EVEN BE A SURFACE LOW DEVELOPMENT
ALONG A POSSIBLE TRIPLE POINT. OF COURSE THE TRACK WILL HAVE TO BE
IRONED OUT, BUT THE MODEL CONSENSUS THUS FAR IS TO TRACK A POTENT
SURFACE LOW TO OUR WEST AND NORTH LATE WEDNESDAY INTO THURSDAY. IF
THE FORECAST STRENGTH OF THE SURFACE LOW BECOMES REALITY, RATHER
WINDY CONDITIONS MAY OCCUR HERE IN ITS WAKE. PRECIPITATION COULD
OVERSPREAD THE CWA BEFORE SUNRISE WEDNESDAY, IN THE FORM OF RAIN
SOUTH AND EAST OF PHILADELPHIA AND PERHAPS SNOW OR A RAIN/SNOW MIX
TO THE NORTHWEST AS SOME COLD AIR COULD LINGER FOR A TIME. THIS
EVENT IS SEVERAL DAYS AWAY AND THE FORECAST CARRIES MUCH UNCERTAINTY.
FOR THURSDAY, THE DEEPENING LOW PRESSURE SYSTEM SHOULD MOVE
NORTHEASTWARD INTO NEW ENGLAND, PULLING COLDER AND DRIER AIR INTO
THE REGION ALONG WITH THE POSSIBILITY OF WINDY CONDITIONS. OVERALL NO
SIGNIFICANT CHANGES WERE MADE, ALTHOUGH WE BLENDED IN A SMALL
PERCENTAGE OF THE 00Z MOSGUIDE FOR SOME FIELDS TO INTRODUCE SOME
NEWER GUIDANCE INTO THE FORECAST.
&&
.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
AT 0830Z, THE SKY OVER OUR REGION WAS MAINLY CLEAR, THERE WERE NO
VISIBILITY RESTRICTIONS AND THERE WAS A LIGHT WESTERLY WIND.
VFR CONDITIONS WILL CONTINUE THROUGH THE TAF PERIOD. THE LIGHT WEST
WIND SHOULD PERSIST THROUGH THE DAY, WITH A LIGHT NORTH OR VARIABLE
WIND EXPECTED FOR TONIGHT.
OUTLOOK...
A COASTAL LOW IS FORECAST TO PASS WELL TO OUR SOUTH AND EAST ON
SATURDAY AND SATURDAY NIGHT. PRECIPITATION IS EXPECTED TO SPREAD UP
FROM THE SOUTH ON SATURDAY. INITIALLY IT SHOULD BE RAIN FOR KMIV,
KACY, KILG, KPHL, KPNE AND KTTN AND A MIX OF RAIN AND SNOW AT KABE
AND KRDG. AS COLD AIR IS DRAWN DOWN FROM THE NORTH AND NORTHWEST ON
SATURDAY NIGHT, THE PRECIPITATION MAY CHANGE TO ALL SNOW AT KABE,
KRDG, KTTN, KPNE, KPHL AND KILG, WITH A MIX OF RAIN AND SNOW
POSSIBLE AT KACY AND KMIV. ANY CHANGE IN THE FORECAST TRACK OF THE
SYSTEM WILL HAVE AN IMPACT ON PRECIPITATION TYPE AND AMOUNTS.
DRY WEATHER IS ANTICIPATED TO BUILD IN FROM THE WEST FOR SUNDAY,
MONDAY AND TUESDAY.
&&
.MARINE...
HIGH PRESSURE WILL CONTINUE TO NOSE INTO OUR REGION FROM THE WEST
FOR TODAY AND TONIGHT.
LOW PRESSURE IS FORECAST TO DEVELOP OFF THE SOUTHEAST COAST TONIGHT
AND IT SHOULD PROGRESS TO THE NORTHEAST. THE LOW IS EXPECTED TO PASS
WELL TO THE EAST OF DELAWARE AND NEW JERSEY LATE ON SATURDAY. THE
SYSTEM WILL BRING INCREASING WIND SPEEDS AND BUILDING WAVES. AS A
RESULT, WE WILL ISSUE A SMALL CRAFT ADVISORY FOR SATURDAY INTO
SATURDAY NIGHT FOR OUR COASTAL WATERS AND FOR DELAWARE BAY. IT
APPEARS AS THOUGH WE MAY EVENTUALLY NEED TO EXTEND THE ADVISORY INTO
SUNDAY FOR OUR OCEAN WATERS.
HIGH PRESSURE IS FORECAST TO BEGIN BUILDING INTO OUR REGION FROM THE
WEST ON SUNDAY. WIND SPEEDS AND WAVE HEIGHTS SHOULD DIMINISH
GRADUALLY. THE AREA OF HIGH PRESSURE IS ANTICIPATED TO PASS OFF THE
MIDDLE ATLANTIC COAST EARLY IN THE NEW WEEK.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 6 AM SATURDAY TO 6 AM EST SUNDAY FOR
ANZ431-452>455.
SMALL CRAFT ADVISORY FROM 10 AM SATURDAY TO 6 AM EST SUNDAY
FOR ANZ430-450-451.
&&
$$
SYNOPSIS...GORSE
NEAR TERM...GORSE
SHORT TERM...GORSE
LONG TERM...AMC/GORSE
AVIATION...IOVINO
MARINE...IOVINO
