FXUS61 KPHI 262015
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
315 PM EST THU NOV 26 2009
.SYNOPSIS...
A STRONG COLD FRONT IS FORECAST TO CROSS OUR AREA LATE TONIGHT AND
EARLY FRIDAY MORNING. MEANWHILE, AN AREA OF LOW PRESSURE IN THE
GREAT LAKES REGION WILL GRADUALLY MOVE EASTWARD. A SECONDARY LOW
PRESSURE SYSTEM OFF THE MID ATLANTIC COAST TONIGHT WILL STRENGTHEN
AND COMBINE WITH THE FIRST LOW IN NEW ENGLAND ON FRIDAY. HIGH
PRESSURE SLIDING EASTWARD ACROSS THE SOUTHERN STATES WILL GRADUALLY
BUILD INTO OUR AREA OVER THE WEEKEND. THE NEXT COLD FRONT IS
FORECAST TO MOVE THROUGH LATE MONDAY WITH HIGH PRESSURE TO FOLLOW
TUESDAY INTO WEDNESDAY. ANOTHER STORM SYSTEM MAY APPROACH OUR AREA
FROM THE SOUTHWEST WEDNESDAY NIGHT AND THURSDAY.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
AN 18Z 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 MIDLEVEL 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 MIDLEVEL SHORT WAVES /AS DEPICTED ON THE
WATER VAPOR IMAGERY THIS AFTERNOON/ DIGS EAST 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.
THE POSITIONING OF THE TWO AFOREMENTIONED STORM SYSTEMS HAS PUT OUR
CWA IN A LIGHT FLOW REGIME /FOR NOW/. THIS HAS NOT ALLOWED MUCH
MIXING OF THE LOWEST LEVELS WITH EVEN A LIGHT EASTERLY FLOW
PERSISTING. SOME DRYING ALONG WITH SUBSIDENCE ON THE NORTHWEST
SIDE OF THE OCEAN LOW HAS HELPED ERODE THE LOW CLOUDS THIS AFTERNOON
ACROSS THE NORTHEASTERN PORTIONS OF THE CWA. THIS HAS BEEN SLOWLY
EXPANDING SOUTHWESTWARD. OVERALL, THE AREAS THAT SAW CLEARING SHOULD
TEND TO HAVE A BROKEN TO OVERCAST DECK RETURN THROUGH THE EVENING
AS THE LOW CLOUD DECK FARTHER WEST MAY TEND TO EXPAND BACK EASTWARD.
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 HAS 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 MIDLEVEL
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 /20Z THURSDAY THROUGH TUESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
PARTS OF THE PHL AREA HAVE CLEARED AS THERE IS SOME SINKING AIR
BETWEEN THE LOW PRESSURE SYSTEM MOVING OFFSHORE EAST OF US AND THE
APPROACHING COLD FRONT.
WHILE THIS HAS PRODUCED SOME VFR CONDITIONS, IT HAS ALSO REDUCED
FORECAST CONFIDENCE. THERE IS STILL A SWATH OF MVFR CLOUDS OVER MD
AND DE AS WELL AS PARTS OF SERN PA THAT WE BELIEVE WILL SPREAD
THROUGHOUT OUR TERMINAL SITES /IF THEY EVER LEAVE AT ALL/ LATER
THIS AFTERNOON INTO THIS EVENING. THE CLEAR SKIES ALSO INCREASES
THE CHANCES FOR SOME MVFR FOG TO FORM AS TEMPERATURES WOULD FALL
FASTER EARLY THIS EVENING.
AS EVENING ARRIVES AND CONTINUES, THIS CLEARING PROCESS WILL REVERSE
AND THE 22Z-04Z CIG IS AN AVERAGE FOR THE TIME PERIOD AS A WHOLE,
SLIGHTLY HIGHER CIGS EARLY AND LOWER LATER. AS PER ABOVE WE
MAINTAINED THE POSSIBILITY OF SOME MVFR FOG REFORMING THIS EVENING
AS WINDS SHOULD STILL BE LIGHT.
ABOUT A FOUR HOUR PERIOD OF SHOWERS IS FORECAST OVERNIGHT AS THE COLD
FRONT MOVES THROUGH THE REGION. PCPN INTENSITY IS NOT EXPECTED TO
GET HEAVY AND WE MAINTAINED MVFR CONDITIONS AS THIS BAND OF
SHOWERS MOVES THROUGH. ONCE THE COLD FRONT REACHES THE COAST AND
THE LOW PRESSURE SYSTEM INTENSIFIES, WINDS WILL INCREASE AND BECOME
QUITE GUSTY ON FRIDAY. THE WIND GUSTS DURING THE EARLY MORNING
FORECAST PERIOD IS MORE OF A BRIDGE TO THIS INCREASE IN GUSTINESS
AFTER THE SUN RISES. IT WILL BE PRETTY COLD ALOFT AND THIS SHOULD
MAKE IT EASY FOR CU OR STRATOCU TO BE AROUND DURING THE DAY, BUT
CURRENT EXPECTATIONS ARE FOR THE CIGS TO REMAIN VFR. WIND GUSTS FRIDAY
AFTERNOON /AS REFLECTED IN THE PHL 30 HR TAF/ SHOULD REACH AROUND
35 KNOTS.
OUTLOOK...
STRONG GUSTY WINDS WITH VFR CONDITIONS SHOULD PERSIST INTO FRIDAY
NIGHT AND MOST OF SATURDAY BEFORE WINDS DIMINISH SATURDAY NIGHT.
HIGH PRESSURE SHOULD BUILD TO OUR SOUTH FOR LATE SATURDAY, SUNDAY
AND EARLY MONDAY WITH BASICALLY VFR CONDITIONS. A COLD FRONTAL
PASSAGE LATER MONDAY WOULD BRING THE NEXT CHANCE FOR EITHER MVFR OR
IFR CONDITIONS.
&&
.MARINE...
ALL MARINE HEADLINES REMAIN AS IS. A SCA IS IN EFFECT FOR LATE
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 FROM 10 PM THIS EVENING TO 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...GIGI
MARINE...GIGI/STAUBER
