FXUS61 KPHI 220832
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
332 AM EST TUE DEC 22 2009
.SYNOPSIS...
HIGH PRESSURE WILL BRING FAIR WEATHER TO PARTS OF THE MID ATLANTIC
AND NORTHEAST TODAY THROUGH EARLY FRIDAY. LOW PRESSURE WILL MOVE
FROM THE FOUR CORNERS OF THE SOUTHWEST UNITED STATES AND INTENSIFY
OVER THE CENTRAL PLAINS THURSDAY NIGHT. THE LOW WILL MOVE TO THE
NORTHERN GREAT LAKES BY SATURDAY BUT SPREAD PRECIPITATION INTO OUR
REGION SOMETIME DURING THE DAY ON CHRISTMAS.
&&
.NEAR TERM /THROUGH TONIGHT/...
COMPACT UPPER LOW WILL SCOOT DOWN FROM CANADA INTO NEW ENGLAND
TODAY WITH COLD AIR ADVECTION AT 80H CONTRIBUTING TO THE LOW
CLOUDS ACROSS THE REGION THIS MORNING. THEY WILL BE AROUND FOR
MUCH OF THE DAY BUT THINNING OUT AT TIMES. SHORT WAVE AT 50H ALSO
BRINGING IN SOME MID AND HIGH LEVEL MOISTURE LATER TODAY MAINLY
ACROSS THE SOUTHERN HALF. HIGH TEMPERATURES WILL BE ABOUT 5 TO 10
DEGREES BELOW NORMAL RANGING FROM 25 IN THE POCONOS TO NEAR 40
SOUTHERN DELAWARE. SINGLE DIGITS UP NORTH TONIGHT AND AROUND 20
SOUTH. A SMALL WARM-UP IS IN STORE BY THE WEEKS END.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
THE SURFACE SETTING IS PEACEFUL ENOUGH WITH HIGH PRESSURE CENTER
NORTH OF THE GREAT LAKES ON WEDNESDAY AND WILL EXTEND SOUTHEAST
TO THE MID ATLANTIC COAST. MEANWHILE, THE UPPER ATMOSPHERE
UNDERGOING MAJOR CHANGES AS DEEP LOW AT 50H MOVES INTO THE GULF OF
MAINE WITH A RIDGE BUILDING OVER THE GREAT LAKES. THE WEATHER-
MAKER HOWEVER IS A DEEPENING LOW OVER THE FOUR CORNERS OF THE
SOUTHWEST UNITED STATES THAT WILL TRIGGER SURFACE DEVELOPMENT ON
WEDNESDAY AND CAUSE A RAPIDLY INTENSIFYING LOW TO MOVE TO MISSOURI
ON THURSDAY. WHILE THINGS REMAIN TRANQUIL OVER OUR REGION
WEDNESDAY AND THURSDAY THE WESTERN PART OF THE COUNTRY WILL SEE
SIMILAR WEATHER CONDITIONS TO WHAT THE EAST COAST JUST EXPERIENCED.
TEMPERATURES HERE REMAIN UNSEASONABLY COLD FOR WEDNESDAY AND
THURSDAY.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
ONLY DIFFERENCE FROM EARLIER LONG TERM DISC IS TO SLOW THE ONSET
OF PRECIPITATION UNTIL AROUND DAYBREAK. OTHERWISE...
AS RIDGING IS FORECAST INTO THE WESTERN UNITED STATES BY THE TIME
THIS PERIOD BEGINS, THIS TENDS TO SUPPORT AN AMPLIFYING TROUGH IN
THE MIDDLE OF THE NATION. IN ADDITION, SOME RIDGING WILL BE
DOWNSTREAM ACROSS THE EAST FOR A TIME. WHILE THE OVERALL MODEL
GUIDANCE SUPPORTS THIS IDEA, THERE ARE SOME DIFFERENCES IN TIMING
AND ALSO THE AMPLIFICATION OF THE UPPER-LEVEL TROUGH. THIS WILL
HAVE AN IMPACT ON THE STRENGTH OF THE SURFACE LOW AS WELL AS THE
DOWNSTREAM SURFACE HIGH IN SOUTHEASTERN CANADA. HPC WENT MORE WITH
A BLEND OF THE ECMWF ENSEMBLE MEAN AND ECMWF, WITH A HIGHER WEIGHT
TOWARD THE MEAN. WE INITIALIZED THE DATABASE WITH HPC GUIDANCE,
HOWEVER SOME MOSTLY MINOR ADJUSTMENTS WERE MADE BASED ON
ADDITIONAL COLLABORATION WITH OUR SURROUNDING OFFICES.
BASED ON THE ABOVE, HIGH PRESSURE IS FORECAST TO BE WEDGED DOWN INTO
THE MID ATLANTIC THURSDAY NIGHT AS UPPER-LEVEL RIDGING AMPLIFIES
ACROSS THE EAST. A DEEPENING SURFACE LOW IS FORECAST TO TRACK FROM
IOWA FRIDAY MORNING TO NEAR LAKE SUPERIOR SATURDAY MORNING. A
STRENGTHENING SOUTHWESTERLY FLOW ALOFT AHEAD OF THIS SYSTEM WILL
TRANSPORT GULF OF MEXICO MOISTURE NORTHWARD INTO OUR AREA ON
CHRISTMAS DAY. SOME WAA-INDUCED PRECIPITATION MAY BEGIN TO EDGE
CLOSER TO OUR WESTERN CWA CHRISTMAS EVE NIGHT HOWEVER. THERE APPEARS
TO BE AT LEAST SOME COLD AIR DAMMING TAKING PLACE, GIVEN THE TRACK
OF THE SURFACE LOW SO FAR TO OUR WEST. THE COLD AIR RIGHT AT THE
SURFACE MAY ALSO BE HELD IN PLACE LONGER DUE TO THE SNOW COVER,
WHICH SHOULD STILL BE DEEP ENOUGH BY THIS TIME /ALTHOUGH SOME
MELTING WILL OCCUR PRIOR/. GIVEN THE WAA ALOFT BUT SOME LINGERING
COLDER AIR AT THE SURFACE, THIS SETUP LOOKS TO BE MORE OF A MIX/ICE
SCENARIO BEFORE CHANGING OVER TO PLAIN RAIN. THE DETAILS WILL HAVE
TO BE PINNED DOWN MORE AS WE GET CLOSER, HOWEVER AREAS ESPECIALLY
FROM INTERSTATE 95 NORTH AND WEST COULD GET A PERIOD OF ICE/MIX
BEFORE WARMER AIR GETS DRAWN IN TO WARM THE SURFACE TEMPERATURES
ABOVE FREEZING. JUST TO NOTE, THE 12Z ECMWF IS SLOWER, WHICH IF
CORRECT, MAY THEN LOWER THE ICE/MIX POTENTIAL. AT THIS POINT, WE
UTILIZED MOSTLY THE TOP-DOWN METHOD TO DRAW IN THE MIX/ICE
POTENTIAL. SOMETHING TO WATCH IS THE POTENTIAL DEVELOPMENT OF A
SECONDARY SURFACE LOW ALONG THE OCCLUDED FRONT IN OUR VICINITY. IF
THIS SYSTEM DOES DEVELOP AND IF IT IS FARTHER TO THE SOUTH, THE
LOW-LEVEL COLD AIR MAY BE TRAPPED LONGER IN OUR NORTHERN AND WESTERN
ZONES AS THE LOW-LEVEL FLOW MAY REMAIN AGEOSTROPHIC LONGER. WE DID
RAMP UP POPS FRIDAY INTO SATURDAY, BUT GIVEN SOME TIMING
UNCERTAINTY, WE WENT NO HIGHER THAN LIKELY ATTM.
AS THE SURFACE LOW TRACKS WELL TO OUR NORTH LATE SATURDAY INTO
SUNDAY, THE ASSOCIATED SURFACE FRONT WILL CLEAR OUR AREA. AN
UPPER-LEVEL TROUGH THEN SETTLES INTO THE NORTHEAST WITH A COLDER
CYCLONIC FLOW REGIME SETTING UP INTO MONDAY. THERE COULD BE SOME
RESPONSE FROM THE EASTERN GREAT LAKES, THEREFORE WE CARRIED A CHC
OF FLURRIES IN THE POCONOS AND FAR NORTHWESTERN SUSSEX COUNTY, NEW
JERSEY SATURDAY NIGHT THROUGH SUNDAY NIGHT.
&&
.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
THE PERSISTENT COLD AIR ADVECTION ON THE WEST-NORTHWEST FLOW HAS
CAUSED A CONTINUATION OF THE COLD AIR STRATOCUMULUS OVERNIGHT AND
EARLY THIS MORNING. HOWEVER, THESE CLOUDS HAVE BEEN VFR. AS SURFACE
HIGH PRESSURE BUILDS OVER OUR AREA FROM THE WEST TODAY, THIS
STRATOCUMULUS IS FORECAST TO DIMINISH LATER THIS MORNING, AND BE
SCATTERED LATE THIS MORNING AND THIS AFTERNOON BEFORE DISSIPATING
TONIGHT. WEST TO WEST-NORTHWEST WINDS WILL AGAIN BE SOMEWHAT GUSTY
TODAY, ALTHOUGH NOT QUITE AS MUCH AS MONDAY AS THE GRADIENT IS LESS
TIGHT. WIND GUSTS ARE EXPECTED TO DIMINISH FAIRLY QUICKLY TOWARD
EVENING AS THE BOUNDARY LAYER SEPARATES FROM THE SURFACE.
OUTLOOK...
NO SIGNIFICANT WEATHER IS EXPECTED WEDNESDAY AS HIGH PRESSURE MOVES
ACROSS OUR AREA. A POSSIBLE EXCEPTION IS WEDNESDAY AFTERNOON AND
NIGHT, AS ENOUGH MOISTURE COULD BECOME TRAPPED UNDER A STRENGTHENING
INVERSION TO POSSIBLY BRING ADDITIONAL STRATOCUMULUS. THE NEXT STORM
IS FORECAST TO ARRIVE LATE IN THE WEEK. MODEL GUIDANCE IS ACTUALLY
SLOWING THESE FEATURES DOWN. WE WILL HAVE TO SEE IF LATER MODEL RUNS
REINFORCE THIS TREND OR OVERRULE IT. BUT, ONCE THE SYSTEM ARRIVES,
THERE COULD BE A PERIOD OF MIXED PRECIPITATION AND/OR ICE, MOSTLY
NORTH AND WEST OF KPHL. HOWEVER, THE TIMING WILL BE KEY REGARDING
WHAT THE SURFACE TEMPERATURES END UP BEING. OTHERWISE, ANY MIXED
PRECIPITATION OR ICE SHOULD CHANGE TO PLAIN RAIN DURING CHRISTMAS
DAY AS MILDER AIR WORKS IN, OR IT MAY BE JUST RAIN IF PRECIPITATION
ONSET IS LATER IN THE DAY OR FRIDAY NIGHT. THIS SYSTEM WILL BRING
REDUCED CEILINGS AND VISIBILITIES, ALTHOUGH THE TIMING MAY CHANGE.
THE MILDER AIR ARRIVING OVER THE REMAINING SNOW COVER COULD LEAD TO
FOG DEVELOPMENT. THIS SYSTEM MAY LINGER SATURDAY BEFORE GRADUAL
IMPROVEMENT OCCURS.
&&
.MARINE...
THE STRONG GRADIENT THAT WE'VE BEEN EXPERIENCING THE PAST SEVERAL
DAYS WILL EASE ONLY SLIGHTLY TODAY. WIND GUSTS HAVE DROPPED A BIT
OVER LOWER DELAWARE BAY...AND THE SMALL CRAFT ADVISORY HAS BEEN
TAKEN DOWN THERE, ALTHOUGH A FEW GUSTS UP TO 25 KNOTS COULD YET
OCCUR THIS MORNING, AND WILL BE SO MENTIONED.
OTHERWISE THE ADVISORY WILL CONTINUE ON THE OCEAN, AND WILL BE
EXTENDED THROUGH WEDNESDAY (OUR THIRD PERIOD) AT THIS TIME.
AS THE INTENSE STORM EAST OF THE CANADIAN MARITIMES CONTINUES MOVING
OFF TO THE EAST AND NORTHEAST, AND HIGH PRESSURE TRIES TO PUSH IN
FROM THE WEST, WEST TO NORTHWEST WINDS WILL CONTINUE ACROSS OUR
WATERS. A WEAK UPPER LOW DROPPING DOWN ACROSS THE GREAT LAKES WILL
LACK SIGNIFICANT WEATHER BUT WILL REINFORCE THE COLD AIR AND TEND TO
KEEP THE PRESSURE GRADIENT FAIRLY TIGHT THROUGH TONIGHT. IT IS
CONCEIVABLE THAT A FEW GUSTS COULD REACH UP TO NEAR 35 KNOTS AT
TIMES THROUGH TONIGHT ON OUR OCEAN WATERS, BUT NOT FREQUENT ENOUGH
TO ISSUE A GALE WARNING. HIGH PRESSURE WILL MOVE ACROSS OUR REGION
WEDNESDAY THROUGH THURSDAY BEFORE A LOW PRESSURE SYSTEM, MOVING
ACROSS THE GREAT LAKES, DRAGS A COLD FRONT ACROSS OUR AREA LATE
CHRISTMAS NIGHT OR EARLY SATURDAY. HOWEVER, MODEL GUIDANCE HAS
TRENDED SLOWER WITH THESE FEATURES. THIS SYSTEM COULD BRING OUR NEXT
ROUND OF ADVISORY OR WARNING CONDITIONS.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST WEDNESDAY FOR ANZ450>455.
&&
$$
SYNOPSIS...EBERWINE
NEAR TERM...EBERWINE
SHORT TERM...EBERWINE
LONG TERM...EBERWINE/GORSE
AVIATION.../
MARINE.../
