FXUS61 KPHI 272315
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
615 PM EST FRI NOV 27 2009
.SYNOPSIS...
A POTENT LOW PRESSURE SYSTEM WILL LIFT FROM NEAR NEW ENGLAND TO THE
CANADIAN MARITIMES TONIGHT AND SATURDAY. MEANWHILE, AN AREA OF HIGH
PRESSURE WILL BUILD ACROSS THE GULF COAST STATES SATURDAY INTO
SUNDAY. A COLD FRONT IS FORECAST TO MOVE THROUGH OUR AREA LATE
MONDAY, THEN HIGH PRESSURE BUILDS IN FOR TUESDAY AND WEDNESDAY. AN
AREA OF LOW PRESSURE IS SCHEDULED TO ARRIVE FROM THE SOUTHWEST
WEDNESDAY NIGHT AND ESPECIALLY THURSDAY, BEFORE MOVING AWAY THURSDAY
NIGHT INTO FRIDAY.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
AN 18Z SURFACE ANALYSIS PLACED A POTENT LOW JUST NORTHEAST OF CAPE
COD. A TROUGH OF LOW PRESSURE WAS FROM OFF THE NEW JERSEY COAST
SOUTHWESTWARD TO NORTHERN GEORGIA. A WARM FRONT WAS ACROSS THE
NORTHERN PLAINS WITH A COLD FRONT BACK ACROSS MONTANA. MEANWHILE,
HIGH PRESSURE WAS ALONG THE CENTRAL GULF COAST STATES. AN UPPER AIR
ANALYSIS PLACED A STRONG CYCLONICALLY CURVED 300 MB JET FROM THE
GREAT LAKES TO THE MID ATLANTIC, THEN UP INTO THE CANADIAN
MARITIMES. A CLOSED MIDLEVEL LOW WAS OVER THE NORTHEAST AND MID
ATLANTIC WITH A NEGATIVE TILT TO ITS ORIENTATION. SEVERAL STRONG
SHORT WAVES WERE EMBEDDED AROUND THIS CLOSED LOW.
A RAPIDLY DEEPENING SURFACE LOW /984 MB CENTRAL PRESSURE AS OF 18Z/
JUST NORTHEAST OF CAPE COD WILL CONTINUE TO INTENSIFY SOME MORE
THROUGH TONIGHT AS IT MERGES WITH THE UPPER-LEVEL SYSTEM INCOMING
FROM THE WEST, AND THEN MOVES INTO THE CANADIAN MARITIMES. THE
TIGHTENING PRESSURE GRADIENT ALONG WITH THE AMPLIFIED UPPER-LEVEL
TROUGH AS ALLOWED THE WIND FIELD TO INCREASE SUBSTANTIALLY TODAY.
THE CAA HAS STEEPENED THE LOW-LEVEL LAPSE RATES THIS AFTERNOON,
ALLOWING A DEEPER MIXED LAYER TO OCCUR. THERE HAVE BEEN WIND GUSTS
IN THE 30 TO 35 KNOT RANGE THUS FAR AND AS THE WIND FIELD INCREASES
SOME MORE, WIND GUSTS ARE EXPECTED TO INCREASE FURTHER. THIS
LEADS INTO A DECISION ON WHETHER TO RAISE A WIND ADVISORY.
THE FORECAST SOUNDINGS VIA BUFKIT INDICATE A STRENGTHENING WIND
FIELD THROUGH TONIGHT ABOVE THE SURFACE. WHILE THE MODEL GUIDANCE IS
NOT SHOWING 50 KNOTS OR MORE OF WIND AT 925 MB, SPEEDS NEAR THIS
LATE TONIGHT AND SATURDAY MORNING /THE NAM-WRF IS A BIT STRONGER
THAN THE GFS/. AN EXAMINATION OF THE FORECAST SOUNDINGS FROM SOUTH
TO NORTH INDICATES MUCH MORE EFFICIENT VERTICAL MIXING THROUGH THIS
EVENING, THEN AN INVERSION BEGINS TO DEVELOP AND LOWER. THE QUESTION
IS WHETHER THIS INVERSION WILL BE MORE PRONOUNCED OR WEAKER THAN THE
MODELS INDICATE AS IT WILL EITHER HINDER OR HELP THE STRONGER WINDS
FROM MAKING IT TO THE SURFACE. THERE IS NOT A LARGE PRESSURE RISE
COUPLET MOVING OVERHEAD AND THERE IS SHORT WAVE ENERGY FORECAST TO
SLIDE ACROSS THE AREA OVERNIGHT INSTEAD OF NVA, PLUS THE FLOW IS NOT
PERFECTLY DIRECTIONALLY ALIGNED. WE TYPICALLY DO NOT MIX AS DEEP
DURING THE NIGHT COMPARED TO THE DAYTIME, THEREFORE IT IS LOOKING
MORE LIKE A MARGINAL WIND ADVISORY EVENT. THERE IS SOME CONCERN OF
THE HIGHER ELEVATIONS WHERE THE STRONGEST GUSTS WOULD BE MORE
FOCUSED, AND IT LOOKS THE MOST MARGINAL ACROSS OUR FAR SOUTHERN
ZONES. SINCE WE DO BELIEVE THERE WILL BE SOME GUSTS TO 40 KNOTS, WE
DECIDED TO ERR ON THE SIDE OF CAUTION AN ISSUE A WIND ADVISORY
TONIGHT AND INTO SATURDAY /MORE ON SATURDAY IN THE SHORT TERM
SECTION/. THERE MAY BE A PERIOD OF RATHER GUSTY WINDS THIS EVENING
AND THEN A LITTLE BIT OF A LULL, WITH PERHAPS AN UPTICK IN GUSTS
AGAIN TOWARD DAYBREAK. FOR NOW, WE WILL GO WITH GUSTS TO AROUND
45 MPH /40 KNOTS/.
IT APPEARS THAT ENOUGH SUBSIDENCE HAS TAKEN HOLD ACROSS THE CWA THIS
AFTERNOON TO PREVENT MUCH IN THE WAY OF SHOWER ACTIVITY. WHERE THERE
WAS MORE SURFACE HEATING TO OUR SOUTHWEST, SHOWERS DID DEVELOP WITH
EVEN SOME ICE PELLETS/GRAUPEL REPORTED IN EASTERN VIRGINIA EARLIER.
WE HELD ONTO SOME SLIGHT CHC POPS FOR THE REMINDER OF THE AFTERNOON,
THEN JUST KEPT SOME SLIGHT CHC TO CHC POPS ACROSS THE FAR
NORTHWESTERN ZONES TONIGHT AS SOME WRAP AROUND AND UPSLOPING MAY
PRODUCE SOME RAIN AND SNOW SHOWERS. AS OF NOW, WE ARE EXPECTING
LITTLE TO NO SNOW ACCUMULATION. AS A SIDE NOTE, RADAR DATA SHOWING A
NARROW PLUME OF SHOWERS ORIGINATING OFF OF DELAWARE BAY. WE WILL
THROW IN SOME CHC POPS TO COVER THIS FEATURE THIS EVENING, ALTHOUGH
IT MAY END UP BEING TRANSIENT.
AS FOR TEMPERATURES, WE BLENDED THE GFS AND NAM MOS FOR MOST LOCALES
AS THEY SEEMED TO BE QUITE SIMILAR. AS FOR WINDS, WE WENT CLOSER TO
THE GFS FOR SPEEDS AS THE ACTUAL MOSGUIDE LOOKED TO LOW AND WE WENT
WITH WIND GUSTS NO HIGHER THAN 40 KNOTS.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
AN INTENSE AREA OF LOW PRESSURE WILL BE MOVING THROUGH THE CANADIAN
MARITIMES DURING SATURDAY. AS ENERGY DROPS DOWN THE WEST COAST,
RIDGING WILL BE BUILDING SOMEWHAT ACROSS THE PLAINS AND INTO THE
GREAT LAKES. THIS WILL KICK OUT THE AMPLIFIED TROUGH OVER THE EAST
AND A SURFACE HIGH WILL BUILD INTO THE SOUTHEASTERN UNITED STATES.
AS THIS OCCURS, THE PRESSURE GRADIENT ACROSS THE NORTHEAST AND MID
ATLANTIC WILL BE RELAXING DURING THE COURSE OF SATURDAY. THE TROUGH
AXIS IS FORECAST TO BE TO OUR EAST BY 12Z SATURDAY, THEREFORE A
MODERATION OF THE AIR MASS AT 850 MB IS FORECAST. ON THE WESTERN
SIDE OF THE TROUGH THOUGH, A STRONG WIND FIELD IS FORECAST TO
PERSIST ABOVE THE SURFACE THROUGH ABOUT MIDDAY BEFORE FINALLY
WEAKENING. THIS WILL CONTINUE TO PRODUCE WINDY CONDITIONS, ALTHOUGH
GUSTS ARE EXPECTED TO BE ON THE WAY DOWN THROUGH THE MORNING DUE TO
THE RELAXATION OF THE CAA, A LESSENING OF THE PRESSURE GRADIENT, AND
A MORE SHALLOW MIXED LAYER. THEREFORE, THE WIND ADVISORY WILL EXPIRE
AT 17Z SATURDAY FOR MOST OF THE AREA, EXCEPT 13Z FOR THE CENTRAL AND
SOUTHERN ZONES OF EASTERN MARYLAND AND DELAWARE. THIS ENDING TIME
MAY BE TO LONG GIVEN THE INVERSION FORECAST TO DEVELOP ON THE
SOUNDINGS. GIVEN THE NORTHWESTERLY FLOW AND LINGERING COLD AIR ALOFT
ACROSS THE NORTHERN ZONES, PERHAPS SOME LAKE MOISTURE COULD GET
PULLED INTO OUR FAR NORTHWESTERN ZONES IN THE FORM OF SNOW SHOWERS
OR FLURRIES. THIS ACTIVITY, IF PRESENT, IS EXPECTED TO DWINDLE AS
THE BOUNDARY LAYER MOISTURE WANES AND A SUBSIDENCE INVERSION LOWERS
SOME THROUGH THE DAY.
THE DRYING DOWNSLOPE FLOW SATURDAY SHOULD LEAD TO A GOOD AMOUNT OF
SUNSHINE ESPECIALLY ACROSS THE EASTERN HALF OF THE CWA. SOME
STRATOCUMULUS SHOULD LINGER ACROSS THE NORTHWESTERN ZONES DUE TO THE
RESIDUAL UPSLOPE COMPONENT INTO THE HIGHER TERRAIN AND PERHAPS SOME
LINGERING WRAP AROUND. HIGH PRESSURE THEN SETTLES TO OUR SOUTH
SATURDAY NIGHT INTO SUNDAY, BEFORE FLATTENING OUT SOME DURING
SUNDAY. AN EVOLVING CLOSED LOW ACROSS THE SOUTHWESTERN STATES AND
NORTHERN MEXICO WILL EVENTUALLY EJECT SOME ENERGY NORTHEASTWARD.
MEANWHILE, ENERGY DROPPING SOUTHEASTWARD OVER A RIDGE INTO WESTERN
CANADA WILL AMPLIFY AN UPPER-LEVEL TROUGH INTO THE MIDWEST SUNDAY.
THE INCREASING WAA DURING SUNDAY WILL TEND TO TOSS AN INCREASE IN
MOSTLY MID TO HIGH CLOUDS OUR WAY. AS THE AFOREMENTIONED UPPER-
LEVEL TROUGH AMPLIFIES SOME MORE AND SHORT WAVE ENERGY ROUNDS THE
BASE, A SURFACE LOW IS FORECAST TO TRACK ACROSS THE GREAT LAKES
REGION AND INTO SOUTHEASTERN CANADA SUNDAY NIGHT AND MONDAY. THIS
BOUNDARY WILL GRADUALLY MOVE INTO OUR AREA DURING MONDAY WITH A
DECENT CHANCE OF SOME RAIN. THE FRONT ITSELF ALMOST LOOKS MORE
LIKE AN ANAFRONT AS THE AXIS OF DEEPER MOISTURE IS MOSTLY FORECAST
ALONG AND BEHIND IT.
AS FOR TEMPERATURES, WE GENERALLY UTILIZED AN EVENLY WEIGHTED BLEND
OF THE GFS AND NAM MOS WITH SOME MINOR ADJUSTMENTS FOR SOME LOCAL
AFFECTS.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
THE 0000 UTC ECMWF WAS FAIRLY SIMILAR TO THE 1200 UTC RUN FROM
YESTERDAY FOR THE LONG TERM PERIOD OF THE FORECAST. HOWEVER, TODAY'S
1200 UTC RUN OF THE ECMWF IS A LITTLE MORE PROGRESSIVE THAN ITS
PREDECESSORS, LEANING A BIT MORE TOWARD THE TRENDS IN THE
OPERATIONAL GFS. WE WILL NOT MAKE ANY MAJOR CHANGES UNTIL WE SEE IF
THE FASTER TIMING IS CARRIED OVER TO FUTURE RUNS OF THE MODEL. IT
APPEARS AS THOUGH HPC IS FOLLOWING THE SAME IDEA.
A SURFACE COLD FRONT IS EXPECTED TO BE PUSHING OFF THE COAST ON
MONDAY EVENING. AN UPPER LEVEL TROUGH IS FORECAST TO EXTEND OVER THE
EASTERN GREAT LAKES AND THE UPPER OHIO RIVER VALLEY. THE TROUGH
SHOULD PROGRESS TO THE EAST AND IT WILL LIKELY PASS OVERHEAD LATE ON
MONDAY NIGHT. WE WILL CONTINUE TO MENTION A CHANCE OF SHOWERS FOR
MONDAY NIGHT. TEMPERATURES UP NORTH MAY BE COLD ENOUGH TO SUPPORT
SOME SNOW FLAKES.
HIGH PRESSURE IS FORECAST TO BUILD IN FROM THE WEST AND ITS CENTER
SHOULD PASS OVER OR NEAR OUR REGION ON WEDNESDAY MORNING. WE ARE
ANTICIPATING DRY WEATHER AND NEAR SEASONABLE TEMPERATURES FOR
TUESDAY AND WEDNESDAY.
AN UPPER LEVEL SHORT WAVE IS FORECAST TO APPROACH FROM THE SOUTHWEST
ON WEDNESDAY NIGHT AND IT SHOULD PASS OVERHEAD ON THURSDAY, WITH LOW
PRESSURE AT THE SURFACE FOLLOWING THE SAME TRACK. WE WILL CONTINUE
TO MENTION RAIN FOR WEDNESDAY NIGHT AND THURSDAY. THERE COULD BE A
FEW POCKETS OF BELOW FREEZING TEMPERATURES IN THE POCONOS FROM LATE
WEDNESDAY NIGHT INTO EARLY THURSDAY MORNING PERHAPS RESULTING IN A
SLIGHT ICE ACCUMULATION IN SPOTS.
AS THE LOW LIFTS TO OUR NORTHEAST, ANOTHER UPPER TROUGH IS EXPECTED
TO BECOME ESTABLISHED OVER THE GREAT LAKES REGION FOR FRIDAY.
&&
.AVIATION /23Z FRIDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
THE MAIN WEATHER IMPACT DURING THE TAF PERIOD WILL BE THE WIND.
STRONG LOW PRESSURE, LOCATED OFF THE NEW ENGLAND COAST THIS EVENING,
WILL DRIFT NORTHWARD OVER THE MARITIME PROVINCES ON SATURDAY. THE
STRONG CIRCULATION AROUND THE LOW WILL MAINTAIN A GUSTY WEST
NORTHWEST WIND IN OUR REGION INTO SATURDAY AFTERNOON. FOR THE
TONIGHT PERIOD INTO SATURDAY MORNING, SUSTAINED WIND SPEEDS WILL BE
15 TO 20 KNOTS WITH FREQUENT GUSTS INTO THE 30S. AS THE LOW DRIFTS
FARTHER AWAY FROM OUR REGION, WIND SPEEDS AND GUSTS SHOULD BEGIN TO
DIMINISH ON SATURDAY AFTERNOON.
VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. A MAINLY BROKEN
STRATOCUMULUS DECK WILL REMAIN OVERHEAD THIS EVENING. A DISTURBANCE
IN THE UPPER ATMOSPHERE IS EXPECTED TO PASS OVER OUR REGION AROUND
MIDNIGHT. AFTERWARD, THE CLOUD COVER SHOULD BECOME SCATTERED.
OUTLOOK...
HIGH PRESSURE IS FORECAST TO BUILD UP FROM THE SOUTHWEST FOR
SATURDAY NIGHT INTO SUNDAY NIGHT. A COLD FRONT FROM THE NORTHWEST
MAY BRING SOME RAIN FOR MONDAY INTO MONDAY NIGHT. ANOTHER AREA OF
HIGH PRESSURE SHOULD FOLLOW FROM THE WEST FOR TUESDAY INTO WEDNESDAY.
&&
.MARINE...
GALES WILL REMAIN IN EFFECT THROUGH EARLY SATURDAY EVENING. GALE
FORCE WINDS CONTINUE TO BLOW ACROSS THE DE BAY AND OUR SOUTHERN
WATERS AND SHOULD SPREAD NORTHWARD ALONG THE COAST LATER THIS
AFTERNOON AND EVENING. THE WINDS ARE EXPECTED TO PEAK OVERNIGHT WITH
GUST OF 45 KT EXPECTED. HOWEVER, THE GUSTY WINDS WILL CONTINUE
THROUGH SATURDAY BEFORE FINALLY STARTING TO DIMINISH SATURDAY
EVENING. AN OCCASIONAL GUST TO STORM FORCE CAN NOT BE RULED OUT AT
THIS TIME BUT CONFIDENCE IS NOT HIGH THAT THEY WILL OCCUR FREQUENTLY
ENOUGH TO WARRANT ISSUING STORM FORCE ON THE WATERS.
WINDS WILL DIMINISH SATURDAY EVENING FALLING BELOW GALE CRITERIA AND
THEN FINALLY FALL BELOW SCA CRITERIA ON SUNDAY. WINDS AND SEAS MIGHT
APPROACH SMALL CRAFT CRITERIA ON MONDAY AS A COLD FRONT APPROACHES
FROM THE WEST, ESPECIALLY IN THE COLD AIR ADVECTION LOCATED BEHIND
THE BOUNDARY ON TUESDAY.
1 TO 2 FOOT TIDAL DEPARTURES ARE EXPECTED TO OCCUR THROUGH SATURDAY.
HOWEVER, TIDES HAVE BEEN RUNNING ABOVE NORMAL OVER THE PAST SEVERAL
WEEKS AND THE 1 TO 2 FOOT PREDICTED DEPARTURES DO NOT LOOK TO BE
NEGATIVE ENOUGH TO CAUSE BLOWOUT TIDES AT THIS TIME.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...WIND ADVISORY UNTIL NOON EST SATURDAY FOR PAZ054-055-060>062-
067>071.
NJ...WIND ADVISORY UNTIL NOON EST SATURDAY FOR NJZ001-007>010-
012>027.
DE...WIND ADVISORY UNTIL NOON EST SATURDAY FOR DEZ001.
WIND ADVISORY UNTIL 8 AM EST SATURDAY FOR DEZ002>004.
MD...WIND ADVISORY UNTIL NOON EST SATURDAY FOR MDZ008.
WIND ADVISORY UNTIL 8 AM EST SATURDAY FOR MDZ012-015-019-020.
MARINE...GALE WARNING UNTIL 6 PM EST SATURDAY FOR ANZ430-431-450>455.
&&
$$
SYNOPSIS...GORSE
NEAR TERM...GORSE
SHORT TERM...GORSE
LONG TERM...IOVINO
AVIATION...IOVINO
MARINE...MEOLA
