FXUS61 KPHI 230845
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
345 AM EST WED DEC 23 2009
.SYNOPSIS...
A RIDGE OF HIGH PRESSURE FROM THE GREAT LAKES TO THE CENTRAL MID
ATLANTIC REGION TODAY WILL CONTINUE THURSDAY BUT MOVE EASTWARD
FRIDAY. LOW PRESSURE WILL INTENSIFY OVER THE CENTRAL PLAINS THURSDAY
NIGHT AND MOVE SLOWLY TO THE MID AND UPPER MISSISSIPPI VALLEY BY
SATURDAY. SECONDARY LOW PRESSURE IS EXPECTED TO FORM OVER THE
CENTRAL MID ATLANTIC REGION FRIDAY NIGHT AND SATURDAY AND MOVE
THROUGH OUR AREA BY SUNDAY MORNING. HIGH PRESSURE WILL RETURN FOR
THE NEW WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
WITH THE THERMAL TROUGH DRIFTING EASTWARD THROUGH OUR AREA
TODAY...MAINLY THIS MORNING...TODAY SHOULD BE THE COLDEST DAY OF
THIS RUN, AS WARM ADVECTION WILL FOLLOW FOR THE REST OF THE WEEK.
WARM ADVECTION CLOUDS WERE NOTED SOUTHWEST OF OUR AREA. MOSTLY
SUNNY SKIES ARE FORECAST FOR TODAY AS THE PASSAGE OF THE
AFOREMENTIONED THERMAL TROUGH...DRIER AIR AT THE LOWER LEVELS...
AND BUILDING SURFACE HIGH PRESSURE ARE EXPECTED TO LEAD TO
RELATIVELY CLOUD-FREE CONDITIONS WITH ONLY SOME SCATTERED
CUMULUS, AND THAT MAINLY NORTHWEST.
NAM MOS WAS SHOWING ITS USUAL COLD BIAS, AND SEEMED A BIT TOO COLD
FOR MOST SPOTS, SO EITHER THE GFS MOS WAS USED OUTRIGHT OR A HEDGE
TOWARD THE GFS MOS WAS TAKEN.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/...
TONIGHT AND THURSDAY SHOULD BE RELATIVELY QUIET PERIODS AS HIGH
PRESSURE ACROSS SOUTHERN CANADA WILL NOSE DOWN INTO OUR AREA. A
RIDGE OF HIGH PRESSURE WILL REPLACE THE SOMEWHAT CYCLONIC FLOW OF
THE PAST SEVERAL DAYS, AND THIS IS FORECAST TO PERSIST INTO
FRIDAY. FOR HIGH TEMPERATURES THURSDAY, IT WAS 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 MINIMALLY CLOUDY SKIES.
BY THURSDAY NIGHT INTO FRIDAY HOWEVER, THE HIGH IS SEEN TO MOVE
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 SECONDARY LOW AND ASSOCIATED FRONTAL BOUNDARY APPROACHING
OUR AREA FROM THE SOUTHWEST. WARM AIR ADVECTION PRECIPITATION
COULD START DURING THE DAY FRIDAY, AND MODEL GUIDANCE IS UNIFORM
IN SHOWING HIGH RELATIVE HUMIDITIES BY LATE IN THE DAY. IF THE
PRECIPITATION STARTS EARLY ENOUGH, IT MAY LEAD TO SOME WINTRY
PRECIPITATION ESPECIALLY NORTH BEFORE CHANGING TO PRIMARILY IF NOT
EXCLUSIVELY LIQUID RAIN. PRECIPITATION IS EXPECTED TO BEGIN IN OUR
SOUTHWEST AREAS, THEN SPREAD TO THE NORTHEAST LATE IN THE DAY
FRIDAY.
&&
.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 /09Z WEDNESDAY THROUGH SUNDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
VFR CONDITIONS FOR THE NEXT SEVERAL DAYS WITH SFC WINDS FROM THE
WEST NORTHWEST THROUGH TOMORROW AFTERNOON. WIND WILL GUST THIS
AFTERNOON 16-18 KTS.
OUTLOOK...
THE FAIR WEATHER HIGH PRESSURE WILL MOVE EAST OF THE AREA ON FRIDAY
AS A WEAK LOW DEVELOPS ON THE COAST AND THE WINDS SHIFT TO THE
SOUTHEAST 30 KT. 5,000 FT WINDS WILL BE FROM THE SOUTHEAST 50 TO 60
KT. PCPN WILL MOVE INTO THE REGION AFTER DAYBREAK ON FRIDAY INTO
FRIDAY NIGHT. MVFR/IFR FRIDAY AFTERNOON INTO SATURDAY AFTERNOON.
&&
.MARINE...
AT 245 AM...BUOY 44009 HAS A NORTHWEST WIND(330 DEGREES) AT 17-21 KT
WITH A 4 FT SEA EVERY 5 SECONDS. AMBROSE TOWER 300 DEGREES AT 21-29
KT WITH A 3 FT SEA EVERY 4 SECONDS, AND THE TEXAS TOWER BUOY AT
HUDSON CANYON 300 DEGREES AT 23-29 KT WITH A 9 FT SEA EVERY 7
SECONDS.
WILL MAINTAIN SMALL CRAFT ADVISORY NORTH OF LITTLE EGG INLET UNTIL
AROUND 10 AM. WIND GRADIENT STILL PRODUCING WIND GUST NEAR 25 KT.
THE SURFACE FEATURE HAS HIGH PRESSURE OVER THE COASTAL WATERS BUT A
FAST MOVING UPPER LOW WILL DROP SOUTH TODAY WITH THE WIND GRADIENT
POSSIBLY INCREASING FARTHER SOUTH DOWN THE COAST. BUT WILL HOLD OFF
AT THIS TIME ISSUING THE SMALL CRAFT FARTHER SOUTH.
MEANWHILE...HIGH PRESSURE WILL REMAIN OVER THE WATERS INTO FRIDAY
MORNING BEFORE MOVING OFFSHORE. A PRIMARY LOW PRESSURE WILL DEVELOP
OVER THE CENTRAL PLAINS AND MOVE INTO NORTHERN PLAINS FRIDAY
AFTERNOON. A WEAK SECONDARY LOW WILL FORM ON THE COAST TIGHTENING THE
WIND GRADIENT WITH NEAR GALE FORCE SOUTHEAST WINDS FRIDAY INTO
SATURDAY.
THERE ARE NO GALES UP FOR THE CANYONS FOR THE NEXT COUPLE DAYS.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 10 AM EST THIS MORNING FOR ANZ450-
451.
&&
$$
SYNOPSIS.../
NEAR TERM.../
SHORT TERM...ROBERTSON /
LONG TERM...GORSE
AVIATION...EBERWINE
MARINE...EBERWINE
