453
FXUS61 KPHI 270245
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
945 PM EST THU NOV 26 2009
SYNOPSIS
LOW PRESSURE WILL MOVE EASTWARD THROUGH THE GREAT LAKES REGION AND
ANOTHER LOW PRESSURE SYSTEM OFF THE EAST COAST WILL LIFT NORTHWARD
TONIGHT. A COLD FRONT BRIDGING THE LOWS WILL MOVE THROUGH OUR AREA
OVERNIGHT. THE LOWS WILL MERGE ALONG THE NEW ENGLAND SEABOARD
FRIDAY. AS THIS MAIN LOW INTENSIFIES TO OUR NORTHEAST, WINDY
CONDITIONS WILL DEVELOP DURING FRIDAY AND CONTINUE FRIDAY NIGHT AND
INTO SATURDAY. HIGH PRESSURE WILL BUILD GRADUALLY INTO THE MID
ATLANTIC REGION DURING SATURDAY AND MOVE EASTWARD AND OFFSHORE BY
MONDAY. THE NEXT COLD FRONT IS EXPECTED TO TRACK THROUGH MONDAY
NIGHT...AND YET ANOTHER STORM SYSTEM MAY APPROACH OUR AREA FROM THE
SOUTHWEST WEDNESDAY NIGHT AND THURSDAY.
NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
CLOUDS HAD DECREASED SOMEWHAT AT MANY LOCATIONS DURING THE
AFTERNOON, BUT WERE RE-COAGULATING EARLY THIS EVENING. EVEN SOME
LIGHT ECHOES WERE NOTED OVER DELAWARE BAY AND ALONG THE CENTRAL
AND SOUTHERN NEW JERSEY COAST AS LOW LEVEL CONVERGENCE WAS
BEGINNING TO HAVE AN EFFECT.
AN EARLY AFTERNOON SURFACE ANALYSIS PLACED AN AREA OF LOW
PRESSURE OFF THE NORTH CAROLINA COAST. ANOTHER LOW WAS NEAR
WESTERN LAKE HURON WITH A TRAILING COLD FRONT FROM WESTERN NEW
YORK/PENNSYLVANIA SOUTHWARD TO THE WESTERN FLORIDA PANHANDLE. AN
UPPER AIR ANALYSIS PLACED A CYCLONICALLY CURVED JET FROM THE
MIDWEST TO THE SOUTHEASTERN U.S. THEN TO NEW ENGLAND. A SHARP MID-
LEVEL TROUGH WAS FROM THE GREAT LAKES TO THE SOUTHEASTERN U.S.
WITH SEVERAL STRONG SHORT WAVES EMBEDDED.
THE PATTERN AMPLIFICATION WILL CONTINUE AS A WELL-DEFINED UPPER-
LEVEL LOW AND SOME MID-LEVEL SHORT WAVES /AS DEPICTED ON THE WATER
VAPOR IMAGERY THIS AFTERNOON/ DIGS EASTWARD AND SOUTHEASTWARD.
THE INCOMING ENERGY ARRIVING ABOVE A SHARPENING BAROCLINIC ZONE TO
OUR EAST HAS ALLOWED A SURFACE LOW TO DEVELOP OFF THE NORTH
CAROLINA COAST. THIS LOW IS FORECAST TO LIFT NORTHWARD AND DEEPEN
AS THE INCOMING CLOSED LOW CAPTURES IT. THE MAIN SURFACE LOW WILL
DEEPEN QUITE A BIT OVER NEW ENGLAND, HOWEVER OUR WEATHER WILL
MOSTLY BE DRIVEN BY THE STRONG UPPER-LEVEL TROUGH ARRIVING FROM
THE WEST ALONG WITH A STRONG COLD FRONT.
THERE MAY BE SOME FOG AROUND AGAIN ESPECIALLY THE FIRST HALF OF
THE NIGHT, AND FOR NOW WE PLACED PATCHY FOG ACROSS THE WESTERN
ZONES WHERE THE STRATUS HAD BEEN MORE SOLID TODAY. A POTENT SHORT
WAVE ROUNDING THE BASE OF THE SHARPENING UPPER-LEVEL TROUGH WILL
PLOW INTO OUR AREA LATER TONIGHT ALONG WITH THE COLD FRONT. THE
ASSOCIATED SYNOPTIC SCALE LIFT WILL GENERATE SHOWERS ACROSS THE
AREA FROM WEST TO EAST, AND THESE MAY TEND TO ORGANIZE INTO BANDS
WITH OR JUST AHEAD OF THE NORTH TO SOUTH PVA GRADIENT. THERE MAY
END UP BEING ABOUT TWO ORGANIZED AREAS OF SHOWERS, ONE UP NORTH
CLOSER TO THE CENTER OF THE INCOMING CLOSED LOW, AND ANOTHER DOWN
SOUTH WITH THE MAIN SHORT WAVE IN THE BASE OF THE TROUGH. THERE IS
CAA FORECAST TO DEVELOP MAINLY TOWARD DAYBREAK, WHICH MAY BE
ENOUGH TO ALLOW FOR SOME SNOW TO MIX IN ACROSS THE HIGHEST TERRAIN
OF THE NORTHWESTERN ZONES. IT WAS DECIDED TO PLACE THE HIGHEST
POPS /CATEGORICAL/ ACROSS THE FAR NORTHWESTERN ZONES DUE TO ONE
SYSTEM TO OUR EAST AND THEN THE MAIN FORCING /PVA AND MID-LEVEL
Q-VECTOR CONVERGENCE/ ARRIVING FROM THE WEST. IF RADAR TRENDS
PORTRAY MORE COVERAGE WITH TIME, THEN POPS CAN BE INCREASED AND
EXPANDED WITH LATER UPDATES /OR VICE-VERSA/.
AS FOR TEMPERATURES, WE GENERALLY UTILIZED AN EVENLY WEIGHTED BLEND
OF THE GFS AND NAM MOS.
SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/
AT LEAST FOR THE FIRST PORTION OF THIS PERIOD, A SHOT OF COLDER AIR
WILL SETTLE ACROSS OUR AREA. THE AFOREMENTIONED SURFACE LOW TO OUR
EAST WILL BECOME CAPTURED BY THE CLOSED LOW. THE GFS AND SREF MEAN
ARE FARTHEST WEST WITH THE SURFACE LOW IN THE VICINITY OF MAINE
FRIDAY AFTERNOON. THE UKMET AND CMC GEM SURFACE LOW POSITIONS, ALONG
WITH THE ECMWF/NAM/WRF KEEP THE CENTER NEAR THE MAINE COAST FRIDAY
AFTERNOON, AND THE LATTER IS MORE PREFERRED. HPC MENTIONED THAT THE
DEEPER GFS AND ECMWF SOLUTIONS ARE MORE FAVORED GIVEN THE STRONG
UPPER-LEVEL DYNAMICS AND SATELLITE PRESENTATION SO FAR. AS A STRONG
UPPER-LEVEL JET ROTATES AROUND THE BASE OF THE TROUGH, THE SURFACE
LOW WILL INTENSIFY FRIDAY AS IT MOVES INTO NEW ENGLAND. THIS WILL
TIGHTEN UP THE PRESSURE GRADIENT ALONG WITH A STRONGER WIND FIELD.
THE 3-HOUR PRESSURE RISES/FALLS ARE NOT ALL THAT IMPRESSIVE, AND
MOST FALLS ARE ACTUALLY CENTERED MORE TOWARD THE SURFACE LOW TO OUR
NORTHEAST COMPARED A STRONGER RISE/FALL COUPLET ARRIVING FROM THE
WEST. THERE IS GOOD CAA THOUGH, WHICH WILL ALLOW FOR MORE EFFICIENT
VERTICAL MIXING THROUGH THE DAY FRIDAY AS THE LOW-LEVEL LAPSE RATES
STEEPEN. THE FORECAST SOUNDINGS INDICATE THAT BETTER VERTICAL MIXING
OCCURS IN THE AFTERNOON AND ALSO AT NIGHT. BASED ON THE MOMENTUM
TRANSFER SCHEME OFF OF BUFKIT, WIND GUSTS APPEAR TO BE MARGINAL FOR
A WIND ADVISORY. WE WOULD LIKE TO SEE A MORE ORGANIZED/QUICKER
PRESSURE RISE MOVING OVERHEAD IN CONJUNCTION WITH THE STRENGTHENING
CAA TO GET THE STRONGER WINDS TO THE SURFACE. THAT DOES NOT APPEAR
TO BE THE CASE, ALTHOUGH IT WILL TURN WINDY. FOR NOW, WE DECIDED TO
BUMP UP THE MOSGUIDE SUSTAINED WINDS BY ABOUT 5 KNOTS AND WE CAPPED
THE GUSTS AT 35 KNOTS. SINCE THE STRONG WIND POTENTIAL HAS BEEN
CARRIED IN THE HAZARDOUS WEATHER OUTLOOK, WE WILL CONTINUE TO PLACE
A MENTION HERE BUT PUT MORE FOCUS ON THE VALUES.
FRIDAY AND FRIDAY NIGHT WILL BE DOMINATED BY CYCLONIC FLOW AND
COLDER AIR BEING ADVECTED INTO OUR AREA. THE CORE OF THE COLDER AIR
IS FORECAST TO LINGER TO OUR WEST, ALTHOUGH 850 MB TEMPERATURES ARE
FORECAST TO LOWER TO ABOUT -5C TO -6C TOWARD 00Z SATURDAY. GIVEN THE
PROXIMITY OF THE CLOSED LOW AND COLDER AIR ALOFT, COMBINED WITH
CYCLONIC FLOW AND SHORT WAVE ENERGY, SOME INSTABILITY SHOWERS SHOULD
BE AROUND WITH BETTER COVERAGE PROBABLY ACROSS THE NORTHERN ZONES.
IF ENOUGH INSTABILITY CAN MATERIALIZE, PERHAPS LOW-TOPPED CONVECTION
CAN OCCUR WITH MAYBE SOME GRAUPEL. THE FORECAST SOUNDINGS INDICATE
SOME WEAK INSTABILITY DEVELOPING, SO WE WILL HAVE TO SEE HOW THIS
PANS OUT. THE COLDER AIR WILL ALLOW FOR SOME SNOW SHOWERS, MAINLY
ACROSS THE NORTHWESTERN ZONES BUT BOUNDARY LAYER TEMPERATURES COULD
BE A PROBLEM FOR ANY REAL ACCUMULATIONS AT LEAST DURING THE DAY. FOR
NOW, WE PLACED SNOW ACCUMULATIONS OF AROUND AN INCH AT AND ABOVE
1500 FEET IN THE POCONOS. IT WILL BE RATHER BLUSTERY FRIDAY NIGHT AS
THE CAA CONTINUES TO TEAM UP WITH THE TIGHTENED PRESSURE GRADIENT.
THERE COULD BE SOME WRAP AROUND MOISTURE INTO OUR NORTHERN ZONES,
ALTHOUGH AN ALIGNED TRAJECTORY OFF THE EASTERN GREAT LAKES IS A
LITTLE UNCERTAIN ATTM. WE CARRIED SOME SLIGHT CHC TO CHC POPS ACROSS
THE NORTH. THIS COULD PERHAPS TOSS SOME SMALL SNOW ACCUMULATIONS
THERE MAINLY ACROSS THE HIGHER TERRAIN.
AS ENERGY DIVES INTO THE WEST, THE FLOW ACROSS THE CENTRAL AND
EASTERN PART OF THE NATION WILL TEND TO FLATTEN OUT. THIS WILL KICK
OUT THE CLOSED LOW DURING SATURDAY WITH THE GUSTY NORTHWEST WINDS
GRADUALLY DIMINISHING. AS THIS OCCURS, THE AIR MASS IS FORECAST TO
BEGIN MODERATING ON SATURDAY WITH SOME WAA TAKING PLACE AT 850 MB.
THIS WILL TEND TO ORGANIZE A WARM FRONT TO OUR WEST AS A WEAK
SURFACE LOW TRACKS ACROSS SOUTHERN CANADA. A COLD FRONT ASSOCIATED
WITH THIS LOW IS FORECAST TO BE LURKING WELL TO OUR WEST SUNDAY.
LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/
ON SUNDAY NIGHT, AN UPPER LEVEL TROUGH IS FORECAST TO BEGIN DIGGING
OVER THE GREAT LAKES REGION. THE TROUGH AXIS SHOULD PUSH TO THE
EAST, PASSING ACROSS THE NORTHEASTERN STATES ON TUESDAY. A SURFACE
COLD FRONT, ASSOCIATED WITH THE TROUGH, SHOULD PASS THROUGH OUR
REGION LATE ON MONDAY. WE WILL MENTION A CHANCE FOR SHOWERS FROM
MONDAY AFTERNOON INTO MONDAY NIGHT. IT COULD BE COLD ENOUGH FOR SOME
SNOW FLAKES UP NORTH.
WE MAY HOLD ON TO SOME CLOUDS AND SHOWERS, ESPECIALLY IN THE NORTH,
IN THE COLD ADVECTION ON TUESDAY.
HIGH PRESSURE IS ANTICIPATED TO BUILD ACROSS OUR REGION ON TUESDAY
NIGHT AND WEDNESDAY, BRINGING A PERIOD OF DRY WEATHER WITH
SEASONABLE TEMPERATURES.
THE CONSENSUS SEEMS TO BE THAT THE OPERATIONAL 1200 UTC GFS IS A BIT
FAST AND OVERDONE WITH THE LOW FOR THURSDAY. WE WILL FAVOR THE 1200
UTC ECMWF AND HPC SOLUTIONS. AS A RESULT, WE WILL FORECAST
PRECIPITATION TO MOVE INTO OUR REGION ON WEDNESDAY NIGHT AND
CONTINUE IT INTO THURSDAY. WITH BORDERLINE TEMPERATURES EXPECTED UP
NORTH, WE COULD SEE SOME ICE IN THE POCONOS AND FAR NORTHERN NEW
JERSEY.
AVIATION /03Z FRIDAY THROUGH TUESDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
AT 0230Z, CEILINGS WERE IN THE MVFR RANGE AT KRDG, KTTN, KILG,
KMIV AND KACY, AND IN THE VFR RANGE AT KPHL, KPNE AND KABE. AS
THE COLD FRONT AND SHOWERS CONTINUE TO APPROACH FROM THE WEST,
MVFR CEILINGS SHOULD REMAIN PREVALENT AT ALL EIGHT OF OUR TAF
SITES DURING THE OVERNIGHT PERIOD.
THE MAIN BAND OF SHOWERS FROM THE WEST SHOULD REACH OUR REGION
LATE TONIGHT, WITH SOME SHOWERS ALSO DRIFTING OFF THE OCEAN.
AS LOW PRESSURE WELL OFF THE COAST CONTINUES TO STRENGTHEN OVERNIGHT
AND ON FRIDAY, WE WILL EXPERIENCE AN INCREASING WEST TO NORTHWEST
WIND. AROUND 0600Z, MOST LOCATIONS WILL SETTLE INTO A NORTHWEST WIND
AROUND 4 TO 8 KNOTS. SPEEDS SHOULD INCREASE TO 8 TO 12 KNOTS BY
DAYBREAK, WITH SOME GUSTS AROUND 16 TO 20 KNOTS POSSIBLE. DURING THE
DAYLIGHT HOURS ON FRIDAY, THE WEST NORTHWEST WIND SHOULD INCREASE TO
15 TO 20 KNOTS WITH GUSTS IN EXCESS OF 30 KNOTS.
A FAIR AMOUNT OF STRATOCUMULUS, WITH BASES AROUND 4500 FEET, IS
EXPECTED FOR FRIDAY, WITH PERHAPS A GRADUAL DECREASE IN CLOUD COVER
DURING THE AFTERNOON.
OUTLOOK...
AS STRONG LOW PRESSURE PASSES OVER THE COASTAL WATERS OF NEW ENGLAND
AND UP OVER THE ATLANTIC PROVINCES OF CANADA FROM FRIDAY NIGHT INTO
SATURDAY, IT WILL LIKELY REMAIN QUITE BRISK IN OUR REGION WITH A
GUSTY WEST WIND. WIND SPEEDS ARE FORECAST TO DIMINISH LATE ON
SATURDAY. DRY WEATHER IS FORECAST FOR SATURDAY, SUNDAY AND EARLY
MONDAY AS HIGH PRESSURE BUILDS ACROSS OUR REGION. A COLD FRONT FROM
THE NORTHWEST MAY BRING SHOWERS FROM MONDAY AFTERNOON INTO EARLY
TUESDAY.
MARINE
ALL MARINE HEADLINES REMAIN AS IS. A SCA IS IN EFFECT FOR TONIGHT
AND GALE WARNINGS ARE IN EFFECT FOR FRIDAY AND FRIDAY NIGHT. THEY
MIGHT HAVE TO BE EXTENDED INTO SATURDAY DAY.
INITIALLY WE REMAIN IN LIGHT WINDS BETWEEN SYSTEMS, AHEAD OF THE
COLD FRONT AND TOO FAR WEST FROM THE OFFSHORE LOW. HOWEVER, ONCE A
COLD FRONT MOVES THROUGH FROM THE NW TONIGHT, WINDS WILL INCREASE
DUE TO BOTH THE INCREASED PRESSURE GRADIENT AND ALSO COLDER AIR
MOVING OVER RELATIVELY WARMER WATERS. THE GRADIENT ONLY SUPPORTS
WINDS TO 25 KT LATE TONIGHT, BUT ON FRIDAY, THE GRADIENT SUPPORTS
GUSTS TO 35-40 KT AND PERHAPS AS HIGH AS 45 KT FRIDAY NIGHT.
THE GALES MAY CONTINUE INTO SATURDAY. HOWEVER, THE GRADIENT SLOWLY
RELAXES AS HIGH PRESSURE NEARS. WINDS SHOULD DECREASE AS SATURDAY
CONTINUES AND ESPECIALLY ON SATURDAY NIGHT.
WINDS AND SEAS SHOULD REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA
SUNDAY INTO MOST OF MONDAY PRECEDING THE NEXT COLD FRONT. WINDS AND
OR SEAS MIGHT REACH SCA CRITERIA AGAIN LATER MONDAY INTO TUESDAY AS
A COLD FRONT APPROACHES THE REGION ON MONDAY AND THEN IN THE COLD
AIR ADVECTION BEHIND THE FRONTAL BOUNDARY ON TUESDAY.
ALSO, TIDES SHOULD BECOME BELOW NORMAL WITH NEGATIVE DEPARTURES OF 1
TO 2 FT FORECAST LATER FRIDAY INTO SATURDAY. HOWEVER, THESE
DEPARTURES DO NOT APPEAR LARGE ENOUGH FOR ANY LOW WATER ADVISORIES.
ALSO WE HAVE TO GET THERE ALSO, TIDAL DEPARTURES ARE CURRENTLY
HIGHER THAN GUIDANCE IS FORECASTING.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST FRIDAY FOR ANZ430-431-
450>455.
GALE WARNING FROM 6 AM FRIDAY TO 6 AM EST SATURDAY FOR ANZ430-
431-450>455.
SYNOPSIS...GORSE/
NEAR TERM...GORSE/
SHORT TERM...GORSE
LONG TERM...IOVINO
AVIATION...IOVINO
MARINE...GIGI
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