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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 100905
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
405 AM EST WED FEB 10 2010

.SYNOPSIS...
-- Changed Discussion --
AN AREA OF LOW PRESSURE OFF THE DELMARVA COAST EARLY THIS MORNING
WILL RAPIDLY INTENSIFY DURING TODAY INTO A POTENT STORM. THIS STORM
WILL THEN LIFT AWAY FROM OUR AREA TONIGHT INTO THURSDAY. AN AREA OF
HIGH PRESSURE WILL THEN GRADUALLY APPROACH FROM THE WEST THROUGH
FRIDAY. THE NEXT SYSTEM IS FORECAST TO ARRIVE AROUND MONDAY.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
AN 08Z SURFACE ANALYSIS PLACED A SURFACE LOW MAINLY NEAR THE MOUTH
OF CHESAPEAKE BAY. A SECONDARY LOW WAS LOCATED IN NORTHWESTERN
PENNSYLVANIA. AN UPPER AIR ANALYSIS PLACED A STRONG CLOSED LOW OVER
OHIO WITH DIFFLUENT FLOW OVER THE MID ATLANTIC. THE STRONGEST WAA AT
850 MB WAS LOCATED OVER THE DELMARVA AND ACROSS SOUTHERN NEW JERSEY.
THIS WAA SHOT HAS BEEN SEEN ON THE KDIX DOPPLER RADAR IMAGERY AS A
BAND OF HIGHER REFLECTIVITY WORKING NORTHWARD. THIS SIGNIFIES THE
LEADING EDGE OF THE SLEET AND FREEZING RAIN. THE WAA SNOWS
ACCUMULATED, ON AVERAGE, 5-8 INCHES DURING THE NIGHT MOSTLY ALONG
THE INTERSTATE 95 CORRIDOR WITH LESSER AMOUNTS ON EITHER SIDE.

A RATHER DYNAMIC SETUP TODAY INTO TONIGHT AS WE HAVE A SURFACE LOW
THAT IS FORECAST TO BOMB OFF OF OUR COAST. THIS IS IN RESPONSE TO
TREMENDOUS PRESSURE FALLS ACCOMPANYING A POTENT MIDLEVEL CLOSED LOW.
THE MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THE SYNOPTIC EVOLUTION,
HOWEVER THERE STILL REMAINS SOME UNCERTAINTY REGARDING THE QPF
AMOUNTS. THE NAM/WRF THERMAL FIELDS SEEMED TO HAVE INITIALIZED
BETTER WITH THE 00Z RAOBS ESPECIALLY AT THE 850 MB LEVEL. MEANWHILE
AT 500 MB, THE GFS MAY BE BETTER WITH THE VORTEX AS IT APPEARS TO BE
ON THE FASTER EDGE SO FAR. THE WATER VAPOR IMAGERY SHOWING THE
MIDLEVEL CLOSED LOW RATHER NICELY SEEMS TO SUGGEST THE SOMEWHAT
QUICKER DEPICTION OF THE GFS. DESPITE THE NAM/WRF LOOKING BETTER
WITH THE THERMAL FIELDS, IT APPEARS THE WARM NOSE IS MORE DEFINED
AND GETTING A BIT FARTHER INLAND THAN THE MODELS ARE SHOWING. AN
EXAMPLE IS THE BUFKIT SOUNDINGS FOR KDCA WHICH SHOWED PREDOMINATELY
SNOW, HOWEVER THE PRECIPITATION CHANGED TO FREEZING RAIN AT 05Z.
BASED ON THE NORTHWARD PUSH OF THE WARM NOSE, WE WILL BRING THE
FREEZING/LIQUID PRECIPITATION A BIT FARTHER NORTHWARD THROUGH EARLY
THIS MORNING BEFORE COLDER AIR BEGINS TO WORK IN. THE QUICKER THE
OFFSHORE LOW DEEPENS, THE FASTER THE ATMOSPHERE WILL COOL ALLOWING
ALL SNOW TO OCCUR. BASED ON THE WARMER AIR SURGING INTO THE
PHILADELPHIA METRO, WE HAD TO ADJUST THE WEATHER GRIDS TO BRING IN
FREEZING/MIXED PRECIPITATION SOONER. WE ARE ANTICIPATING THE LIQUID
AND/OR FREEZING PRECIPITATION TO CHANGE OVER TO ALL SNOW DURING THE
MORNING AS THE SURFACE LOW DEEPENS AND HEIGHT FALLS BEGIN TO OCCUR
IN EARNEST.

DESPITE THE WAA SHOT DURING THE NIGHT BEING RATHER ROBUST, WE DID
NOT MAKE ANY SIGNIFICANT CHANGES TO THE SNOWFALL TOTALS. THERE MAY
BE A PRECIPITATION LULL FOR A TIME THIS MORNING AS WE AWAIT THE
FORCING TO RAMP UP WITH THE CLOSED LOW AND SURFACE LOW
INTENSIFICATION. THIS LESSENING OF THE PRECIPITATION INTENSITY MAY
ALLOW FOR POCKETS OF LIGHT SNOW OR EVEN FREEZING DRIZZLE. THE
NAM/WRF MAY BE A BIT ON THE HIGH SIDE REGARDING QPF, HOWEVER WE ARE
CONCERNED THAT BANDING WILL OCCUR AS THE CLOSED MIDLEVEL CENTER
SLIDES JUST TO OUR SOUTH. THIS IN CONJUNCTION WITH THE RAPIDLY
DEEPENING SURFACE LOW WILL ALLOW FOR STRONG FRONTOGENETIC FORCING TO
BECOME ESTABLISHED ACROSS A GOOD PART OF OUR CWA. AN EXAMINATION OF
MODEL CROSS SECTIONS REVEALS THAT THE STRONG OMEGA FIELDS DO NOT
COMPLETELY LINE UP WITH THE SNOW GROWTH REGION. THIS WOULD TEND TO
KEEP THE SNOWFALL RATES MORE IN CHECK, HOWEVER GIVEN THE STRENGTH OF
THE VERTICAL MOTION, WE BELIEVE THAT ENHANCED SNOWFALL RATES WILL
OCCUR FOR A TIME TODAY, ESPECIALLY THIS AFTERNOON INTO THE EVENING.
THIS BRINGS US TO THE CURRENT HEADLINES /WARNINGS/ THAT ARE IN
EFFECT.

THERE IS GOOD MODEL AGREEMENT THAT STRONG WINDS IN THE 925 MB LAYER
INCREASE TO ABOUT 40-50 KNOTS THIS AFTERNOON INTO TONIGHT. THE
FORECAST SOUNDINGS INDICATE THAT AS THE PRESSURE GRADIENT TIGHTENS
SUBSTANTIALLY AS THE COASTAL STORM BOMBS, THERE WILL BE A GOOD
POTENTIAL FOR THE STRONGER WINDS TO MIX DOWN TO THE SURFACE. THE
STRENGTHENING SURFACE WINDS IN CONJUNCTION WITH THE FALLING SNOW
WILL CAUSING BLOWING AND DRIFTING SNOW ALONG WITH GREATLY REDUCED
VISIBILITIES. THERE WAS QUITE A BIT OF DISCUSSION ABOUT GOING WITH A
BLIZZARD WARNING AND WE DECIDED TO GO THIS ROUTE FOR A FEW REASONS.
FIRST, THE POTENTIAL FOR BANDING AND SECOND THE SNOW GETTING DRIER
AS COLDER AIR WRAPS IN ON THE WEST SIDE OF THE STORM. DESPITE SOME
AREAS SEEING MIXED, FREEZING OR LIQUID PRECIPITATION FOR A TIME, A
CHANGE TO ALL SNOW IS EXPECTED AND THIS WILL BE MODERATE TO HEAVY AT
TIMES. NOT ALL AREAS UNDER THE BLIZZARD WARNING MAY REACH THE
CRITERIA, HOWEVER GIVEN THAT IT LOOKS TO BE REALLY CLOSE FOR A TIME
LATER THIS AFTERNOON INTO TONIGHT, PLUS FACTORING IN THE SOCIETAL
IMPACT, A BLIZZARD WARNING WILL BE ISSUED FOR SOUTHEASTERN
PENNSYLVANIA, NEW JERSEY SOUTH OF MORRIS COUNTY AND THE DELMARVA.
THE WEST/NORTHWEST PART OF THE CWA WILL REMAIN UNDER A WINTER STORM
WARNING AS THERE MAY BE A SHARP DROP OFF IN THE STRONGER WINDS,
ALTHOUGH SOME BLOWING AND DRIFTING OF SNOW IS EXPECTED HERE AS WELL.
BUT, WE ARE JUST NOT AS CERTAIN WITH BLIZZARD CONDITIONS FARTHER
INLAND. WE RAN THE BLIZZARD WARNING UNTIL 05Z TONIGHT, HOWEVER THE
HEAVIEST SNOW SHOULD HAVE ENDED BY THEN. DESPITE THE SNOW COMING TO
AN END DURING THE EARLY EVENING FOR MOST AREAS, THE WINDS WILL BE
GUSTY PRODUCING AREAS OF BLOWING AND DRIFTING. THIS HAS BEEN ADDED
TO THE WEATHER GRIDS.

AS FOR TEMPERATURES, WE USED A GENERAL BLEND OF THE NAM/GFS MOS
ALONG WITH CONTINUITY ALTHOUGH WE NEED TO MAKE SOME MANUAL
ADJUSTMENTS BASED ON TRENDS SO FAR EARLY THIS MORNING. THANKS TO
THE SURROUNDING OFFICES FOR THE COLLABORATION EARLY THIS MORNING!
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
-- Changed Discussion --
AS HIGH PRESSURE GRADUALLY BUILDS INTO THE OHIO VALLEY THURSDAY, OUR
AREA WILL REMAIN WITHIN A COLD CYCLONIC FLOW REGIME AS THE STORM
CONTINUES TO MOVE AWAY. THIS WILL MAINTAIN A GUSTY NORTHWESTERLY
WIND, WHICH WILL TEND TO PRODUCE SOME BLOWING AND DRIFTING SNOW
MAINLY IN THE OPEN AREAS. THERE WILL PROBABLY BE SOME LAKE EFFECT
COMING OF THE EASTERN GREAT LAKES, AND PERHAPS SOME OF THIS MAY GET
PULLED ALL THE WAY INTO OUR NORTHWESTERN ZONES. THERE MAY BE ENOUGH
SUBSIDENCE HOWEVER BEHIND THE DEPARTED MAJOR STORM TO KEEP THE
CLOUDS OUT OF OUR AREA AND PERHAPS LIMIT ANY SNOW TO JUST FLURRIES
ACROSS OUR FAR NORTHWESTERN ZONES.

THE SURFACE HIGH GRADUALLY EDGES CLOSER DURING FRIDAY, ALLOWING THE
PRESSURE GRADIENT TO RELAX. GIVEN THE SNOWPACK THAT WILL BE ON THE
GROUND, WE STUCK CLOSER TO CONTINUITY BUT DID EDGE A BIT BELOW MOST
OF THE MOS GUIDANCE FOR SOME LOCALES. IF THE WINDS ARE ABLE TO
DECOUPLE SOME AT NIGHT, THE TEMPERATURES WILL TEND TO DROP OFF MORE
THAN FORECAST. OVERALL, IT LOOKS LIKE FAIRLY TRANQUIL WEATHER
RELATIVELY SPEAKING FOR ALL THE CLEAN UP AND DIGGING OUT THAT WILL
NEED TO BE DONE.
-- End Changed Discussion --

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
-- Changed Discussion --
THE UPPER AIR PATTERN CONTINUES TO SHOW A DEEP UPPER CLOSED LOW OFF
THE CANADIAN MARITIME PROVINCES AND WEAK RIDGING OVER THE ROCKY
MOUNTAINS. THE UPPER LOW SLOWLY RETROGRADES BACK ACROSS NORTHERN
QUEBEC WHILE THE UPPER RIDGE OUT WEST SHARPENS. THESE FEATURES ALONG
WITH PLENTIFUL SNOW COVER ACROSS THE AREA WILL ENSURE BELOW NORMAL
TEMPERATURES THROUGH THE EXTENDED PERIOD. HIGH TEMPERATURES SHOULD
ONLY REACH THE LOW TO MID 30S EACH DAY.

THERE ARE NO SIGNIFICANT WEATHER SYSTEMS IN THE EXTENDED PERIOD, BUT
A SHORT WAVE ROTATING SOUTHEAST ALONG THE SOUTHERN PERIPHERY OF THE
CANADIAN UPPER LOW WILL CAUSE LOW PRESSURE AND A FRONTAL SYSTEM TO
CROSS THE AREA MONDAY AND MONDAY NIGHT. THE POPS HAVE BEEN RAISED
SLIGHTLY FROM THE PREVIOUS FORECAST WITH SLIGHT CHC AND CHC POPS IN
THE NORTHERN AND CENTRAL SECTIONS OF OUR CWA.
-- End Changed Discussion --

&&

.AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

SNOW OVERSPREAD THE AREA EARLIER LAST NIGHT...AND CEILINGS AND
VISIBILITIES PLUNGED. AS WARM AIR ENTERED AHEAD OF THE INTENSIFYING
SURFACE LOW...PRECIPITATION CHANGED OVER TO FREEZING RAIN AT THE
SOUTHEASTERN TAF SITES OF KACY AND KMIV, AND EVEN AT KILG...AND WILL
ALSO LIKELY BRUSH KPHL AND KPNE FOR A SHORT WHILE WITH MIXED SNOW/
SLEET/FREEZING RAIN POSSIBLE, AT LEAST UNTIL THE SURFACE LOW LIFTS
NORTHWARD TO OUR LATITUDE AND SHIFTS THE WINDS AROUND TO NORTH-
NORTHEAST TOWARD MORNING. KABE AND KRDG SHOULD RECEIVE ALL SNOW.
THERE IS ALSO THE POSSIBILITY THAT THE PRECIPITATION MAY END FOR A
BRIEF PERIOD DURING THIS TIME. HOWEVER, SNOW IS EXPECTED TO PICK UP
AND INCREASE IN INTENSITY BY MID MORNING, AND LAST THROUGH MID TO
LATE AFTERNOON...OR EVEN INTO THE EARLY EVENING. AS SNOW BEGINS TO
DIMINISH AS WE APPROACH SUNDOWN TODAY, CEILINGS AND VISIBILITIES
WILL BEGIN TO IMPROVE. WE EXPECT THE SNOW TO END BEFORE MIDNIGHT,
WITH A RETURN TO VFR CONDITIONS OVERNIGHT.

ON TOP OF THE SNOW, WINDS WILL BEGIN TO INCREASE THROUGH THE DAY
TODAY AND INTO TONIGHT. HOWEVER, IT MAY TURN OUT...AND BE FORTUNATE
FOR OPERATIONS...THAT THE STRONGEST WINDS WILL NOT BE COINCIDENT
WITH THE HEAVIEST SNOW. WIND GUSTS ARE EXPECTED TO INCREASE TO 25
TO 30 KNOTS LATER THIS MORNING, AND TO 30 TO 36 KNOTS DURING THIS
AFTERNOON, WHICH WILL PRODUCE BLOWING AND DRIFTING SNOW LATER THIS
AFTERNOON AND TONIGHT.

OUTLOOK...
GENERALLY VFR CONDITIONS ARE EXPECTED FOR THE REST OF THE WEEK AND
INTO THE EARLY WEEKEND. EACH DAY THERE MAY BE SOME GUSTY WINDS
DURING THE AFTERNOON, ESPECIALLY THURSDAY, ALONG WITH SOME AFTERNOON
CLOUDS WHICH MAY DEVELOP AROUND 2500-3500 FEET.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
THE MAJOR WINTER COASTAL STORM IS DEVELOPING JUST SOUTH OF OUR AREA
OFF THE MID-ATLANTIC COAST EARLY THIS MORNING...AND IT WILL MOVE
NORTHEASTWARD ALONG THE COAST TO OUR LATITUDE DURING THIS MORNING.
WINDS WERE INCREASING ACROSS OUR AREA WELL BEFORE SUNRISE, AND SEAS
WERE BEGINNING TO RESPOND AS WELL. AS THE STORM APPROACHES THE
DELAWARE AND NEW JERSEY COASTAL WATERS, WINDS WILL REALLY BEGIN TO
INCREASE, REACHING GALE FORCE DURING THIS MORNING, PROBABLY BY MID
MORNING, AND INCREASE EVENTUALLY TO STORM FORCE DURING THE DAY AND
INTO THIS EVENING. SO, THE STORM WARNING REMAINS IN EFFECT FOR THE
OCEAN MARINE ZONES AS WELL AS LOWER DELAWARE BAY. A GALE WARNING
WAS INHERITED FOR THE UPPER BAY, BUT AS WINDS ARE THOUGHT TO BE
ABLE TO GUST TO 45 TO 50 KNOTS ON THE UPPER BAY (BASED ON 925 HPA
WINDS), THE STORM WARNING WILL BE EXTENDED TO THE UPPER BAY AS WELL.

THE WINDS WILL LIKELY DIMINISH BACK TO GALE FORCE OVERNIGHT TONIGHT,
AND POSSIBLY PERSIST INTO THURSDAY, BUT SUBSEQUENT SHIFTS WILL BE
ABLE TO DOWNGRADE TO A GALE WARNING AFTER THE STORM FORCE WINDS ARE
OVER. HIGH PRESSURE WILL TRY TO BUILD INTO THE REGION LATE IN THE
WEEK AND INTO THE WEEKEND, BUT WILL NOT MAKE IT AS AN AREA OF LOW
PRESSURE REMAINS ACROSS EASTERN CANADA. THIS WILL KEEP A STEADY
NORTHWEST FLOW FOR THE END OF THE WEEK AND INTO THE WEEKEND, WHICH
COULD KEEP SMALL CRAFT ADVISORY CONDITIONS ACROSS THE WATERS.
-- End Changed Discussion --

&&

.TIDES/COASTAL FLOODING...
-- Changed Discussion --
TIDAL DEPARTURES WITH THE APPROACHING COASTAL STORM WILL BE
INCREASING WITH THE INCREASING WINDS TODAY. IT LOOKS LIKE THE
STRONGEST WINDS WILL BE INCREASING LATER THIS AFTERNOON AND INTO
TONIGHT. THIS MORNING`S HIGH TIDE AND THIS AFTERNOON`S HIGH TIDE
BOTH ARE EXPECTED TO REMAIN BELOW MINOR FLOODING LEVELS. HOWEVER,
THE HIGH TIDE THURSDAY MORNING STILL LOOKS LIKE IT COULD REACH MINOR
TIDAL FLOODING AS ANOMALIES WILL BE HIGHEST THEN TO COINCIDE WITH
THE HIGHER OF THE TWO DAILY HIGH TIDES, SO WE MAY NEED AN ADVISORY
LATER TODAY.
-- End Changed Discussion --

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...WINTER STORM WARNING UNTIL MIDNIGHT EST TONIGHT FOR PAZ054-055-
     060>062.
     BLIZZARD WARNING UNTIL MIDNIGHT EST TONIGHT FOR PAZ067>071.
NJ...WINTER STORM WARNING UNTIL MIDNIGHT EST TONIGHT FOR NJZ001-007-
     008.
     BLIZZARD WARNING UNTIL MIDNIGHT EST TONIGHT FOR NJZ009-010-
     012>027.
DE...BLIZZARD WARNING UNTIL MIDNIGHT EST TONIGHT FOR DEZ001>004.
MD...BLIZZARD WARNING UNTIL MIDNIGHT EST TONIGHT FOR MDZ008-012-015-
     019-020.
MARINE...STORM WARNING UNTIL 6 AM EST THURSDAY FOR ANZ430-431-450>455.
-- End Changed Discussion --

&&

$$
SYNOPSIS...GORSE
NEAR TERM...GORSE
SHORT TERM...GORSE
LONG TERM...O`HARA
AVIATION.../
MARINE.../
TIDES/COASTAL FLOODING.../