FXUS61 KPHI 032351
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
651 PM EST THU DEC 3 2009
.SYNOPSIS...
HIGH PRESSURE WILL RESUME CONTROL OF THE REGION THROUGH FRIDAY
BEFORE A COASTAL LOW PRESSURE RIDES ALONG THE EASTERN SEABOARD ON
SATURDAY. THE EXACT TRACK OF THIS LOW IS STILL IN QUESTION, HOWEVER,
IT DOES APPEAR THAT WE WILL SEE SOME EFFECTS FROM THIS SYSTEM.
MASSIVE HIGH PRESSURE WILL SETTLE IN FROM THE WEST ON SUNDAY THROUGH
EARLY NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
A 20Z SURFACE ANALYSIS PLACES LAST NIGHTS LOW PRESSURE OVER NORTHERN
MAINE WITH ITS COLD FRONT WELL OFFSHORE. MID-WEST HIGH PRESSURE WILL
CONTINUE TO BUILD INTO THE REGION THIS EVENING WHILE WINDS WILL
REMAIN OUT OF THE WEST SOUTHWEST. A SLIGHT TURN TO THE NORTHWEST MAY
OCCUR FOR A FEW HOURS AS THE HIGH NEARS.
TODAY'S GUSTY WINDS WILL CONTINUE FOR THE NEXT FEW HOURS BUT AS WE
LOSE ANY LEFT OVER SOLAR INSOLATION AND THE BOUNDARY LAYER BEGINS TO
DECOUPLE THIS EVENING, THE WINDS WILL START TO SUBSIDE. WE WILL ALSO
SEE A GRADUAL CLEARING TONIGHT WITH THE HIGH PRESSURE SETTLING IN.
MODEL SOUNDINGS INDICATE DECENT LOW AND MID-LEVEL DRYING, BUT UPPER
LEVELS, UNDER THE STRONG SOUTHWEST FLOW ASSOCIATED WITH THE
TREMENDOUS UPPER LEVEL JET WILL MORE THAN LIKELY DEVELOP CIRRUS, SO
TONIGHT AND TOMORROW MORNING DO NOT APPEAR TO BE COMPLETELY CLEAR.
TEMPERATURES WERE PRIMARILY A BLEND OF THE MAV/MET MOS GUIDANCE, BUT
WERE HEDGED CLOSER TO THE COLDER METMOS.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
FRIDAY SEEMS TO BE A RATHER DULL DAY IN COMPARISON TO SATURDAY WHICH
MAY POTENTIALLY BE THE REGION'S FIRST WIDESPREAD SNOWFALL OF THE
LATE FALL/EARLY WINTER SEASON. AS WAS STATED A FEW DAYS AGO,
DECEMBER 5TH SEEMS TO BE OUR BENCHMARK FOR ACCUMULABLE SNOW IN THE
PHILADELPHIA REGION AS IT HAS HAPPENED IN 2002, 2003, 2005, AND
2007. AS WAS ALSO STATED BEFORE, TO SEE A DECENT ACCUMULATION ON THE
5TH, TEMPERATURES ON THE 4TH HISTORICALLY WERE IN THE 30S; THIS IS
NOT THE CASE THIS TIME...FRIDAY HIGHS WILL BE IN THE LOW 50S ACROSS
MUCH OF THE CWA.
THIS SHORT TERM FORECAST FOR SATURDAY INTO SUNDAY HAS VERY LITTLE
CONFIDENCE ASSOCIATED WITH IT AS THERE IS NOT REALLY A MODELING
CONSENSUS REGARDING THE PLACEMENT OF THE SURFACE LOW AND IT TRACK.
TRIED TO USE A GOOD MIDDLE OF THE ROAD COMPROMISE BETWEEN THE GFS,
ECMWF, AND THE GEM FOR SATURDAY. 1000-850MB THICKNESSES SHOW 1300M
OVER THE PHILADELPHIA METRO AREA ON SATURDAY RIGHT AS THE
PRECIPITATION BEGINS TO FALL, SO THESE AREA WILL START AS MOSTLY
RAIN WITH POSSIBLY WET SNOW FLAKES MIXED IN. FREEZING LEVELS HAVE
DROPPED A COUPLE HUNDRED FEET OVER THE PAST FEW MODEL RUNS, AND NOW
THEY ARE PROGGED TO BE AROUND 1000'. THE LOW-LEVEL FLOW WILL BE OUT
OF THE NORTHEAST DURING THE DAY SATURDAY WITH THE MID AND UPPER
LEVELS OUT OF THE SOUTHWEST, SO AGAIN THE ADVECTION OF DRIER AIR
INTO THE REGION IS STILL A PROBLEM.
THERE ARE SOME INDICATIONS OF MID-LEVEL LIFT ASSOCIATED WITH THE
SHARPENING TROUGH AS THE MODEL CONSENSUS PLACES ANOTHER AREA OF
ENHANCED PRECIPITATION JUST TO THE SOUTHWEST OF THE REGION. THIS
LINES UP WELL WITH PIECES OF ENERGY DIVING INTO THE BASE OF THE
MID-LEVEL TROUGH. IT DOES LOOK LIKE THAT MOISTURE WILL NOT
COMPLETELY MAKE INTO OUR NECK OF THE WOODS AS IT SHOULD SLIDE JUST
TO THE SOUTH OF OUR REGION. AS THE TROUGH GOES NEGATIVE ON SATURDAY
THIS WOULD HELP TO INCREASE THE MOISTURE FLOW FROM THE SOUTHWEST
INTO THE MID-ATLANTIC STATES, HOWEVER, IT IS STILL UNCLEAR IF WE
HAVE A SHOT AT TAPPING INTO ANY OF IT.
THE GFS SEEMS TO BE THE DRIER OF THE THREE MODELS WITH ONLY 0.05''
OF LIQUID PRECIPITATION. THIS MAY BE DUE TO THE FASTER PROGRESSION
AND PROXIMITY OF THE LOW PRESSURE TO THE COAST. THE ECMWF AND
CANADIAN BOTH HAVE ABOUT 0.10'' INCHES FOR PHILADELPHIA. THESE
NUMBERS INCREASE FURTHER SOUTHEAST TOWARDS THE COAST AND DECREASE TO
THE NORTHWEST, AGAIN BASED ON THE CURRENT TRACK.
THE MILLION DOLLAR QUESTION EVERYONE IS ASKING IS, HOW MUCH SNOW IS
EXPECTED. WELL THERE ARE A COUPLE OF FACTORS TO CONSIDER WHEN TRYING
TO ANSWER THIS QUESTION, OTHER THAN THE TRACK OF THE LOW. THE FIRST
BEING, HOW COLD DO WE ACTUALLY GET FRIDAY NIGHT/SATURDAY MORNING,
WITH THE SOUTHWEST FLOW ALOFT, WILL THERE BE ANY CLOUDS AROUND TO
DISRUPT A DECENT SHOT TO RADIATE. THOUGH THE PRECIPITATION IS NOT
PROGGED TO START UNTIL LATE SATURDAY MORNING THE OVERNIGHT LOWS WILL
PLAY A BIG PART FOR THE INITIAL ON-SET OF PRECIPITATION. ALSO, WITH
A WARM DAY ON FRIDAY, WHAT WILL THE GROUND TEMPERATURES BE. EVEN
WITH LIGHT SNOW FALLING, SURFACE TEMPERATURES MAY BE AT OR ABOVE
FREEZING AND LIGHT SNOW WOULD MORE THAN LIKELY NOT STICK.
ALL IN ALL, CURRENT THINKING IS THAT ONCE WE ARE ABLE TO COOL
ENOUGH, MAINLY SATURDAY NIGHT, SNOW ACCUMULATION IS POSSIBLE IN AND
AROUND THE PHILADELPHIA METRO AREA. RIGHT NOW, BASED ON CURRENT QPFS
AND DYNAMICS, THERE IS POTENTIAL FOR AN INCH TO FALL THROUGH SUNDAY
MORNING. ALTHOUGH IT MAY NOT BE MUCH, THIS MAY INDEED BE OUR FIRST
WIDESPREAD SNOWFALL FOR THE REGION.
HIGH PRESSURE WILL THEN MOVE IN BEHIND THE DEPARTING LOW CLEARING
OUT THE SKIES, RATHER RAPIDLY, WITH WINDS OUT OF THE NORTHWEST.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
THE 12Z GFS SEEMED TO BE MORE OR LESS IN LINE WITH THE HPC DAY 3-7
PROGS SO THE GRIDS WERE POPULATED MAINLY WITH THE EXTENDED DIGITAL
MOS GUIDANCE...WITH SOME ADJUSTMENTS FOR CONSISTENCY WITH OTHER
OFFICES.
AN AREA OF HIGH PRESSURE OVER THE MID-ATLANTIC REGION SUNDAY NIGHT
WILL MOVE OFFSHORE ON MONDAY. A WEAK FAST-MOVG FRONTAL SYSTEM IS
FORECAST TO CROSS THE AREA WEST TO EAST LATE MONDAY OR MONDAY NIGHT
BUT THERE SEEMS TO BE LITTLE MOISTURE OR PRECIP WITH IT. WE HAVE
INCLUDED JUST A SLIGHT CHANCE OF RAIN SHOWERS...OR SNOW SHOWERS
NORTH.
AS OF NOW TUESDAY LOOKS LIKE THE BEST DAY NEXT WEEK WITH FAIR WX AND
ABOVE NORMAL MAX TEMPS AS HIGH PRESSURE MOVE BY.
THEN THE NEXT STORM SYSTEM BEGINS DEVELOPING TUESDAY NIGHT OVER THE
LOWER MS VLY AND SPREADS CLOUDS NEWD INTO THE MID ATLANTIC REGION.
PRECIP COULD OVERSPREAD THE FORECAST AREA BEFORE SUNRISE WED...IN
THE FORM OF RAIN SOUTH AND EAST OF PHILA AND SNOW OR A RAIN/SNOW MIX
TO THE NW. OF COURSE THIS EVENT IS SEVERAL DAYS AWAY AND THE
FORECAST CARRIES MUCH UNCERTAINTY...BUT FOR NOW IT LOOKS LIKE MOST
OF THE ASSOCD PRECIP DURG THE DAY WED SHOULD BE RAIN.
FOR THURSDAY THE DEEPENING LOW PRESSURE CENTER SHOULD MOVE NEWD INTO
NEW ENGLAND...PULLING SEASONABLY COLDER AND DRIER AIR INTO THE
REGION.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
THE STLT IMAGERY SHOWS STRATO-CU RAPIDLY DISSIPATING OVER SEPA AN
VCNTY AS EXPECTED. WINDS ARE ALSO DIMINISHING AS PREVIOUSLY FCST.
WE EXPECT SKIES WILL BECOME CLEAR DURING THE EVENING WITH LIGHT
WNW WINDS. WINDS SHOULD REMAIN LIGHT ON FRIDAY AS A RIDGE OF HIGH
PRESSURE BUILDS OVER THE AREA. A FEW STRATOCU ARE POSSIBLE DURING
THE DAY WITH PBL MIXING. ALSO SOME HIGH TO MID CLOUDS MAY APPEAR
LATE IN THE DAY AHEAD OF THE NEXT WEATHER SYSTEM. VFR CONDS
PREVAIL.
OUTLOOK...
ON SATURDAY IS THE NEXT THREAT OF PRECIPITATION. LOW PRESSURE OFF
THE EAST COAST COULD BRING RAIN TO THE COAST AND RAIN AND/OR SNOW
FARTHER WEST TO AROUND PHL.
&&
.MARINE...
SCA ARE NOW IN EFFECT UNTIL 1 AM. GUSTY WINDS ASSOCIATED WITH COLDER
AIR ADVECTING INTO THE REGION WILL CONTINUE THIS EVENING. HOWEVER,
THE GRADIENT WILL WEAKEN OVERNIGHT AND WINDS SHOULD DROP BELOW 25 BY
MIDNIGHT. SEAS SHOULD ALSO COME DOWN QUICKLY TONIGHT.
FOR FRIDAY AND FRIDAY NIGHT...HIGH PRESSURE WILL NOSE INTO THE
REGION FROMT HE WEST WITH A PERIOD OF TRANQUIL WEATHER.
LOW PRESSURE IS EXPECTED TO DEVELOP OFF THE SOUTHEAST COAST ON
FRIDAY NIGHT AND SATURDAY. THE LOW SHOULD MOVE TO THE NORTHEAST,
PASSING WELL TO THE EAST OF DELAWARE AND NEW JERSEY ON SATURDAY
NIGHT. SMALL CRAFT ADVISORY CONDITIONS ARE LIKELY OVER THE WEEKEND
AND THERE IS THE POSSIBILITY OF GALES.
HIGH PRESSURE IS FORECAST TO BUILD OVER THE AREA SUNDAY WITH WINDS
DIMINISHING ONCE AGAIN. A WEAK FRONT MAY MOVE THROUGH THE AREA ON
MONDAY NIGHT, BUT WINDS SHOULD STAY BELOW 25 KT INTO MIDWEEK ANYWAY.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 1 AM EST FRIDAY FOR ANZ430-431-
450>455.
&&
$$
SYNOPSIS...HEAVENER
NEAR TERM...HEAVENER
SHORT TERM...HEAVENER
LONG TERM...AMC
AVIATION...AMC/STAUBER
MARINE...STAUBER
