FXUS61 KPHI 230451
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1151 PM EST TUE DEC 22 2009
.SYNOPSIS...
THE SOUTHERN END OF HIGH PRESSURE CENTERED OVER SOUTHERN CANADA
WILL CONTINUE TO NOSE ITS WAY ACROSS THE AREA THROUGH AT LEAST
THURSDAY. AN AREA OF LOW PRESSURE WILL BE LIFTING THROUGH THE
CENTRAL STATES AND THROUGH THE GREAT LAKES LATE IN THE WEEK AND
INTO THE WEEKEND. THIS WILL DRAG A FRONTAL BOUNDARY ACROSS OUR
AREA OVER THE WEEKEND. A STEADY NORTHWEST FLOW WILL DEVELOP ACROSS
THE AREA EARLY NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
THE TREND TOWARD CLEARING CONTINUED IN OUR REGION THIS EVENING AS
DRY AIR PUSHED DOWN FROM THE NORTH. WE WILL CARRY A MOSTLY CLEAR
FORECAST FOR THE OVERNIGHT PERIOD...EXCEPT FOR THE FAR
NORTHWESTERN POCONOS ZONES WHERE SOME STRATOCUMULUS WAS FILTERING
SOUTHWARD. TEMPERATURES WILL DROP MAINLY INTO THE TEENS. WE
SHOULD HOLD ONTO A BIT OF A NORTHWEST WIND THROUGH THE NIGHT.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
WEDNESDAY THROUGH THURSDAY SHOULD BE RELATIVELY QUIET DAYS AS HIGH
PRESSURE ACROSS SOUTHERN CANADA NOSES ITS WAY DOWN INTO OUR AREA.
A MID/UPPER LOW SLIDES TO OUR NORTH TONIGHT INTO WEDNESDAY, BEFORE
RIDGING TRIES TO TAKE PLACE FROM THURSDAY INTO FRIDAY. FOR HIGH
TEMPERATURES ON WEDNESDAY AND THURSDAY, WE DECIDED TO GO A COUPLE OF
DEGREES ABOVE MOS SINCE THEY HAVE BEEN UNDER DOING THE HIGHS THE
LAST COUPLE OF DAYS EVEN WITH THE SNOW PACK. CONVERSELY, WE WENT A
COUPLE OF DEGREES BELOW GUIDANCE FOR THE LOW TEMPERATURES DUE TO THE
SNOW PACK AND RELATIVELY MINIMALLY CLOUDY SKIES.
BY THURSDAY NIGHT INTO FRIDAY HOWEVER, THE HIGH MOVES INTO EASTERN
CANADA, SO WE WILL BE GETTING MORE OF AN ONSHORE FLOW, AND BUILDING
THICKNESSES, WHICH SHOULD HELP MODERATE OUR TEMPERATURES. AN AREA OF
LOW PRESSURE WILL BE LIFTING THROUGH THE CENTRAL STATES AND INTO THE
GREAT LAKES REGION LATE IN THE WEEK, WITH A FRONTAL BOUNDARY
APPROACHING THE AREA FROM THE SOUTH AND SOUTHWEST. WARM AIR
ADVECTION PRECIPITATION COULD START DURING THE DAY FRIDAY, AND IF IT
STARTS EARLY ENOUGH, IT MAY LEAD TO SOME WINTRY PRECIPITATION,
BEFORE CHANGING TO MOSTLY LIQUID RAIN. PRECIPITATION IS EXPECTED TO
BEGIN IN OUR SOUTHWEST AREAS, THEN SPREAD TO THE NORTHEAST LATE IN
THE DAY.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AN EXPANSIVE CLOSED LOW IS FORECAST TO BE IN THE PLAINS AND MIDWEST
DURING THE START OF THIS TIME FRAME. THE MODEL GUIDANCE OVERALL HAS
CONTINUED TO BE IN DECENT AGREEMENT ON THE PATTERN ALOFT, WITH
RIDGING ACROSS THE WEST COAST AND ALSO ALONG THE EAST COAST. THERE
HAS BEEN A TENDENCY IN THE MODEL GUIDANCE TO SLOW DOWN THE EASTWARD
PROGRESSION OF THIS LARGE SYSTEM AND ITS ASSOCIATED SURFACE FRONT.
THE DEEP SURFACE LOW WILL LIKELY OCCLUDE GIVEN THE ADVERTISED
UPPER-LEVEL PATTERN, WHICH WILL DRIVE THE BOUNDARY OUR WAY ALONG
WITH A WARM FRONT OR EVEN A COASTAL FRONT LIFTING NORTHWARD.
MEANWHILE, A STRONG SURFACE HIGH IS FORECAST TO BE IN SOUTHEASTERN
CANADA BUT TRENDING TO BE TRANSIENT. HPC WENT WITH THE ECMWF
ENSEMBLE 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 LEAVING THE AREA
FRIDAY NIGHT AS THE OCCLUDED FRONT ARRIVES FROM THE WEST. PLENTY OF
ENERGY ROUNDING THE STRONG UPPER-LEVEL TROUGH TO OUR WEST,
THEREFORE A SURFACE LOW MAY FORM ALONG THE TRIPLE POINT. THERE
ARE HINTS THAT A WARM FRONT OR EVEN A COASTAL FRONT WILL BE WORKING
NORTHWARD, HOWEVER JUST HOW FAR NORTH THIS FEATURE GETS IS IN
QUESTION. IT APPEARED THAT THIS SETUP WAS MORE CHARACTERISTIC OF
COLD AIR DAMMING, HOWEVER THE TREND OF SLOWING THE ARRIVAL OF THE
SYSTEM DOWN SOME MORE WILL GIVE THE LINGERING COLD AIR AT THE
SURFACE TIME TO BE ERODED. THERE IS STRONG WAA FORECAST TO BE
OCCURRING AHEAD OF THIS SYSTEM, AND THAT WILL TRANSPORT MILDER AND
MORE MOIST AIR ACROSS OUR AREA FROM SOUTH TO NORTH. THIS COULD ALLOW
THE PRECIPITATION TO ARRIVE SOONER AND ALSO SOME FOG TO BECOME AN
ISSUE IF ENOUGH SNOW COVER EXISTS. SINCE THERE IS SOME SNOW COVER
STILL EXPECTED TO BE AROUND, THIS MAY KEEP THE SURFACE TEMPERATURES
COLDER A LITTLE LONGER THAN THE MODELS ARE PORTRAYING. IN ADDITION,
SOME ICING COULD OCCUR FOR A TIME DESPITE THE AIR TEMPERATURES BEING
ABOVE FREEZING. BASED ON THE FORECAST SOUNDINGS, A MOSTLY PLAIN RAIN
EVENT WOULD BE IN STORE FOR OUR AREA, HOWEVER WE WILL STILL MENTION
A MOSTLY BRIEF PERIOD OF ICE/MIX ACROSS OUR FAR NORTHWESTERN ZONES.
IT APPEARS THAT ANY WINTRY PRECIPITATION WOULD BE SLEET OR FREEZING
RAIN INSTEAD OF SNOW GIVEN THE STRENGTH OF THE WAA. FOR NOW, WE
SLOWED DOWN THE INCREASING POPS SOME FROM WEST TO EAST AND DID NOT
GO ANY HIGHER THAN HIGH LIKELY ATTM. TEMPERATURES MAY ACTUALLY START
TO RISE FRIDAY NIGHT INTO SATURDAY MORNING AS THE WAA AND BOUNDARY
LAYER FLOW STRENGTHENS. WITH THE EXPECTED RAINFALL AND SNOW MELT, WE
WILL MONITOR FOR THE POTENTIAL OF SOME FLOODING.
AS THE MAIN SURFACE LOW TRACKS ACROSS THE GREAT LAKES LATE SATURDAY
INTO SUNDAY, THE POSSIBLE SECONDARY LOW SHOULD BE JUST TO OUR EAST
WITH THE OCCLUDED FRONT CLEARING OUR AREA EARLY SUNDAY. THIS ENTIRE
SYSTEM THEN SLIDES ACROSS NEW ENGLAND AND SOUTHEASTERN CANADA
MONDAY, HOWEVER ADDITIONAL ENERGY LOOKS TO MAINTAIN AN AMPLIFIED
UPPER-LEVEL TROUGH FROM THE GREAT LAKES TO THE NORTHEAST MONDAY.
THIS COULD PRODUCE SOME FLURRIES OR SNOW SHOWERS GIVEN THE COLDER
NORTHWESTERLY FLOW ALOFT, HOWEVER FOR NOW WE WILL JUST HOLD FLURRIES
TO THE FAR NORTHWESTERN ZONES SUNDAY NIGHT THROUGH MONDAY NIGHT. WE
THEN SHOULD REMAIN UNDER A CYCLONIC FLOW AS LOW PRESSURE MOVES INTO
THE CANADIAN MARITIMES TUESDAY AND HIGH PRESSURE SLIDES INTO THE
OHIO VALLEY. AN ARCTIC FRONT MAY THEN BE WAITING JUST NORTH OF THE
GREAT LAKES REGION.
&&
.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
SKIES ALMOST CLEAR ACROSS THE REGION WITH THE EXCEPTION OF A SMALL
PATCH EXTENDING TO THE NORTHERN POCONOS. WILL REMAIN VFR OVERNIGHT
AND WED.
FOR WEDNESDAY, OUR REGION LOOKS TO BE SANDWICHED BETWEEN THE SYSTEM
TO THE NORTH/NORTHEAST AND A DEVELOPING STORM ACROSS THE CENTRAL
PLAINS. WE ARE ANTICIPATING SOME STRATOCUMULUS TO REDEVELOP MAINLY
AFTER DAYTIME HEATING GETS GOING AND WE PLACED THE GREATEST COVERAGE
/BROKEN/ AT KRDG AND KABE. PERHAPS THIS CAN SEEP SOUTHEASTWARD AT
TIMES BUT FOR NOW WE THINNED THESE CLOUDS OUT FARTHER SOUTH AND
EAST. THERE IS SOME INDICATION THAT SOME SUB-VFR CEILINGS DEVELOP
DURING THE AFTERNOON, HOWEVER AT THIS TIME WE BELIEVE THIS MAY BE
OVERDONE THEREFORE WE MAINTAINED VFR CONDITIONS. THE PRESSURE
GRADIENT ALONG WITH ENOUGH VERTICAL MIXING ONCE AGAIN SHOULD PROMOTE
SOME GUSTINESS TO THE NORTHWESTERLY WINDS AT MOST TERMINALS
WEDNESDAY FROM ABOUT MID/LATE MORNING THROUGH MID/LATE AFTERNOON
BEFORE DIMINISHING. THE STORM SYSTEM WELL TO OUR WEST, MAY TOSS SOME
MID TO HIGH LEVEL CLOUDS OUR WAY MAINLY LATER IN THE DAY.
OUTLOOK...
HIGH PRESSURE IS FORECAST TO PARTIALLY SETTLE INTO OUR AREA THURSDAY
INTO CHRISTMAS DAY BEFORE GRADUALLY MOVING AWAY. A STRONG STORM
SYSTEM IN THE PLAINS IS FORECAST TO MOVE INTO THE GREAT LAKES REGION
ON CHRISTMAS DAY. A FRONTAL BOUNDARY WILL MOVE INTO OUR AREA LATE
CHRISTMAS DAY WITH POSSIBLY A SECONDARY STORM DEVELOPING ALONG IT. A
PERIOD OF PRECIPITATION IS EXPECTED TO MOVE ACROSS THE AREA,
ALTHOUGH THE TIMING STILL HAS TO BE PINNED DOWN, BUT FOR NOW LATE
DAY CHRISTMAS DAY THEN TAPERING OFF FROM SOUTHWEST TO NORTHEAST ON
SATURDAY. WHILE RAIN IS EXPECTED TO BE THE PREDOMINANT PRECIPITATION
TYPE, THERE LOOKS TO BE A PERIOD OF SLEET AND FREEZING RAIN MAINLY
FOR KABE AND KRDG. THE KPHL METRO AREA TO KTTN COULD SEE A BRIEF
PERIOD OF SLEET/FREEZING RAIN, ALTHOUGH IT WILL DEPEND ON HOW FAST
THE SURFACE TEMPERATURES CLIMB. KABE MAY HAVE A CHANCE OF A LONGER
DURATION OF SOME ICING. AREAS OF ICING SHOULD CHANGE TO PLAIN RAIN
AS MILDER AIR MOVES IN. THIS SYSTEM WILL BRING REDUCED CEILINGS AND
VISIBILITIES. THE MILDER AIR ARRIVING OVER THE REMAINING SNOW COVER
MAY LEAD TO AREAS OF FOG FRIDAY INTO SATURDAY. AN UPPER-LEVEL
WEATHER DISTURBANCE POSSIBLY MOVING THROUGH SUNDAY INTO MONDAY MAY
BRING CLOUDINESS AND PERHAPS SOME FLURRIES/SNOW SHOWERS.
&&
.MARINE...
AT 1130 PM SEAS AT 44009 ARE 4 FT EVERY 4 SECONDS WITH WINDS 300
DEGREES AT 17-21 KTS. AMBROSE BUOY HAS WINDS 310 DEGREES AT 25 TO
29 KT WITH 4 FT SEAS. TEXAS TOWER BUOY AT HUDSON CANYON IS 300
DEGREES AT 23 TO 31 KT WITH 9 FT SEAS.
HAVE LOWERED THE SMALL CRAFT ADVISORY FOR THE SOUTHERN WATERS.
WILL HAVE TO REVISIT AGAIN WITH THE FULL MORNING PACKAGE. WINDS
ARE OCCASIONALLY HITTING 20 KT AND WILL HOLD THAT FOR THE
REMAINDER OF THE NIGHT INTO WED.
A HIGH PRESSURE RIDGE WILL MOVE ACROSS OUR REGION THURSDAY AND
THURSDAY NIGHT BEFORE MOVING OFF TO THE EAST CHRISTMAS DAY. LOW
PRESSURE MOVING INTO THE WESTERN GREAT LAKES AREA WILL PUSH A COLD
FRONT TOWARD OUR REGION FRIDAY NIGHT. SECONDARY LOW PRESSURE IS
FORECAST TO DEVELOP ON THE FRONT OVER VIRGINIA FRIDAY NIGHT AND
TRACK NE ACROSS OUR AREA SATURDAY. THIS SYSTEM WILL MORE THAN
LIKELY BRING OUR NEXT ROUND OF ADVISORY OR WARNING CONDITIONS.
WITH A FAIRLY STRONG ONSHORE FLOW DEVELOPING FRIDAY NIGHT INTO
SATURDAY, TIDAL DEPARTURES WILL BE INCREASING. FORTUNATELY NORMAL
TIDE HEIGHTS WILL BE QUITE LOW AND THE EVENT WILL BE RELATIVELY
SHORT LIVED, SO THE THREAT FOR COASTAL TIDAL FLOODING WILL BE
MINIMAL.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 10 AM EST WEDNESDAY FOR ANZ450-451.
&&
$$
SYNOPSIS...ROBERTSON
NEAR TERM...IOVINO/
SHORT TERM...ROBERTSON
LONG TERM...GORSE
AVIATION...EBERWINE/GORSE
MARINE...EBERWINE/RPW
