FXUS61 KPHI 050217
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
917 PM EST FRI DEC 4 2009
.SYNOPSIS...
HIGH PRESSURE WILL WEAKEN AND DRIFT NORTH TONIGHT AS AN AREA OF
LOW PRESSURE DEVELOPS OVER THE SOUTHEASTERN UNITED STATES. THE
LOW WILL THEN MOVE NORTHEAST UP THE COAST SATURDAY INTO SATURDAY
NIGHT. HIGH PRESSURE WILL BUILD IN FROM THE WEST SUNDAY BEFORE
GRADUALLY SLIDING OFF TO THE EAST MONDAY. THE NEXT POTENTIALLY
SIGNIFICANT STORM SYSTEM ARRIVES WEDNESDAY INTO WEDNESDAY NIGHT.
HIGH PRESSURE WILL FOLLOW FOR THE END OF THE WEEK.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
AS THE HIGH PRESSURE WEAKENS AND THE LOW TO OUR SOUTH BEGINS TO
GATHER STRENGTH, INCREASED CLOUDINESS IS EXPECTED TO CONTINUE
THROUGH TONIGHT. RADAR INDICATES THE PRECIPITATION IS STILL WELL
TO THE SOUTH OF THE AREA BUT WILL SLOWLY MAKE ITS WAY NORTHWARD
OVERNIGHT. RAIN WILL APPROACH DURING THE EARLY MORNING HOURS AND
COULD BEGIN TO MOVE INTO OUR SOUTHERN SECTIONS TOWARD DAYBREAK.
TEMPERATURES WILL FALL INTO THE UPPER 20S AND 30S.
UPDATED THE FORECAST TO BETTER REFLECT CURRENT OBSERVATIONS AND
TRENDS.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
STILL MUCH UNCERTAINTY WITH THE COASTAL LOW. WE OPTED TO NOT GO WITH
ANY ADVISORIES WITH THE AFTERNOON PACKAGE, MAINLY TO REMAIN
CONSISTENT WITH WWD AND OUR SURROUNDING OFFICES. OUR SNOW AMOUNTS
WILL BE JUST BELOW ADVISORY CRITERIA. WITH THIS SAID, NOW THAT
THE UK HAS COME IN LINE WITH THE 12Z NAM AND GFS, IT WOULD NOT
SURPRISE ME TO SEE SNOW AMOUNTS BUMPED UP LATER TONIGHT. BUT THAT
WILL HINGE ON THE NEXT ROUND OF MODEL RUNS. THE 12Z RUNS SHARPEN
THE UPPER TROUGH AND BRING 1/2 TO 3/4 INCH WATER EQUIVALENT TO
OUR AREA. IT SHOULD START OUT AS RAIN IN OUR SOUTHERN AREAS WITH
MIXED RAIN AND SNOW NORTH AND WEST OF THE PHILLY METRO AREA AND
MOSTLY ALL SNOW NORTH. DURING THE AFTERNOON THE RAIN SNOW LINE
WILL SHIFT SOUTH AND EAST. THE EXPECTED CHANGEOVER IN THE PHILLY
AREA SHOULD BE BY 4 OR 5 PM. WITH RELATIVELY WARM GROUND
TEMPERATURES, THE SNOW WILL HAVE A TOUGH TIME ACCUMULATING ON
ROADWAYS UNTIL THE EVENING HOURS. TEMPERATURES WILL ONLY RISE A
FEW DEGREES DURING THE DAY WITH HIGHS IN THE MID 30S TO MID 40S.
BY EVENING, TEMPERATURES WILL BEGIN FALLING BELOW FREEZING IN OUR
NORTHERN AREAS AND WILL DROP INTO THE MID 30S IN THE PHILLY AREA.
THE CHANGEOVER TO SNOW WILL CONTINUE TO MARCH SOUTH AND EAST AND
SHOULD REACH THE COASTAL REGION BY THE TIME THE PRECIPITATION IS
ENDING AROUND OR SHORTLY AFTER MIDNIGHT. WHILE THE SNOWFALL RATE
WILL LOOK QUITE IMPRESSIVE FOR A WHILE LATE SATURDAY OR EARLY
SATURDAY NIGHT, THE SOGGY WET SNOW WILL ONLY ACCUMULATE AN INCH
OR TWO IN THE PHILLY METRO AREA. NORTHERN SECTIONS COULD GET 2 TO
3 INCHES. THE STORM WILL MOVE RAPIDLY OFF TO THE NORTHEAST LATE
SATURDAY NIGHT INTO SUNDAY. THIS WILL ALLOW SKIES TO CLEAR AND
TEMPERATURES TO DROP INTO THE 20S AND 30S. SHOULD SEE PLENTY OF
SUNSHINE SUNDAY AS AN AREA OF HIGH PRESSURE MOVES IN. HIGHS WILL
BE IN THE MID 30S TO LOWER 40S. SKIES WILL BEGIN MOSTLY CLEAR
SUNDAY NIGHT, BUT WE COULD GET SOME INCREASE IN CLOUDS TOWARD
MORNING AS THE HIGH MOVES OFF TO THE EAST. LOWS WILL BE IN THE 20S
TO LOW 30S. EXPECT PARTLY CLOUDY SKIES MONDAY AS A WEAK FRONTAL
SYSTEM CROSSES OUR REGION. COULD EVEN BE A FEW SNOW FLURRIES IN
OUR NORTHERN AREAS. HIGHS WILL BE IN THE UPPER 30S AND 40S.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
HPC HAS RELIED HEAVILY ON THE 00Z ECMWF FOR THE LONG TERM FORECAST,
AND THE 12Z ECMWF LOOKS FAIRLY SIMILAR AROUND OUR REGION AND SO WAS
COMBINED WITH THE 00Z RUN FOR THIS FORECAST. HIGH PRESSURE FOR
MONDAY NIGHT WILL MOVE EAST OF THE AREA ON TUESDAY, AND THEN PRESENT
THINKING IS THAT A PRECIPITATION EVENT THAT STARTS WITH OVERRUNNING
AND ISENTROPIC LIFT AND EVENTUALLY INCORPORATES DYNAMICS AND PERHAPS
EVEN SOME INSTABILITY DEVELOPS AS LOW PRESSURE IS EXPECTED TO MOVE
FROM THE OHIO RIVER VALLEY TO LOCALES JUST TO OUR NORTH. SOME
CONVECTION AND SIGNIFICANT WIND MAY BE ASSOCIATED WITH THIS EVENT,
BUT WE'LL KEEP OUR POWDER DRY FOR NOW. PRECIPITATION TYPE MAINLY
LOOKS TO BE RAIN, BUT OVER OUR FAR NORTHWESTERN AREAS SOME SORT OF
MIXED OR SOLID PRECIPITATION COULD FALL FOR A TIME BOTH BEFORE AND
AFTER THE LOW PASSES.
THURSDAY THROUGH FRIDAY LOOK DRY THANKS TO HIGH PRESSURE, THEN
ANOTHER SYSTEM MAY GET CLOSE ENOUGH TO BRING ANOTHER CHANCE OF
PRECIPITATION LATE FRIDAY NIGHT. RIGHT NOW, WE HAVE MADE THIS JUST
A SLIGHT CHANCE.
TEMPERATURES THROUGH THE PERIOD OSCILLATE AROUND NORMAL.
&&
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
CONDITIONS AROUND THIS EVENING WERE VFR WITH MAINLY MID LEVEL
CLOUDINESS.
A COASTAL LOW PRESSURE SYSTEM HAD FORMED OFF THE COAST OF GEORGIA.
THE LOW WILL COMBINE WITH AN UPPER AIR TROUGH LIFTING THROUGH
THE REGION ON SATURDAY. THIS MEANS CONDITIONS WILL DETERIORATE
DURING THE DAY SATURDAY FROM SOUTH TO NORTH. PRECIP WILL START AS
RAIN OVER THE SOUTHEASTERN SITES AND MOST OF THE DELAWARE VALLEY
SITES, BUT WILL START AS MIXED AT TTN AND AS SNOW AT THE
NORTHWESTERN SITES. THAT MIX WILL MOVE SOUTH ACROSS THE DELAWARE
VALLEY SITES DURING THE AFTERNOON. TIMING OF STARTING THE
PRECIPITATION IS SHORTLY AFTER DAYBREAK AT ACY/MIV, BY LATE MORNING
AT THE DELAWARE VALLEY SITES AT BY NOON AT THE NORTHWESTERN SITES.
BY LATE AFTERNOON, COLDER AIR WILL BE CHANGING THE PCPN TO SNOW OVER
THE DELAWARE VALLEY SITES. SOME MIXING IS POSSIBLE TOWARD THE END OF
THE TAF PERIOD OVER THE SOUTHEASTERN SITES. THEY MAY WELL CHANGE
OVER TO ALL SNOW BEFORE PRECIPITATION ENDS. THAT IS EXPECTED TO
HAPPEN FROM THE WEST BY MIDNIGHT SATURDAY. IFR CONDITIONS SHOULD
DEVELOP FOR TIME BEFORE CONDITIONS IMPROVE RAPIDLY LATE AT NIGHT.
WINDS WILL BE TRANQUIL INTO SAT MORNING AND THEN PICK UP FROM THE NE
IN THE AFTN/EVENING. SUSTAINED WINDS OF 15 KT SHOULD DEVELOP
ILG/PHL/PNE SOUTH AND EAST WITH WINDS GUSTS TO 30 KT PSBL IN THE
AFTN AT ACY/MIV.
OUTLOOK...
NO SIGNIFICANT WEATHER IS EXPECTED THROUGH TUESDAY. ON WEDNESDAY,
LOW PRESSURE WILL PROBABLY BRING RAIN TO THE AREA.
&&
.MARINE...
LOW PRESSURE HAS FORMED OFF THE GEORGIA COAST. THIS LOW WILL
INTENSIFY AS IT HEADS NE THROUGH SATURDAY WHILE STAYING WELL TO
THE EAST OF THE FORECAST WATERS. HOWEVER, THE GRADIENT ON THE WEST
SIDE OF THE LOW SHOULD BE ENOUGH FOR GALE FORCE GUSTS TO DEVELOP SAT
AFTN WITH GUSTS TO 45 KT POSSIBLE IN THE EVENING OVER THE WATERS
SOUTH OF LITTLE EGG INLET AND ON LOWER DELAWARE BAY. SATURDAY NIGHT,
WINDS WILL SHIFT TO N AND NW BUT ENOUGH GRADIENT SHOULD REMAIN FOR
POTENTIAL GALE FORCE GUSTS OVER THE REST OF THE FORECAST WATERS
INCLUDING UPPER DELAWARE BAY.
MORE SPECIFICALLY, A GALE WARNING HAS BEEN ISSUED FOR THE WATERS
SOUTH OF LITTLE EGG INLET AND ALSO FOR LOWER DELAWARE BAY FOR
SAT/SAT NIGHT. ON THE WATERS TO THE N OF LITTLE EGG INLET AND FOR
THE UPPER DEL BAY, SCA IS IN EFFECT 10 AM TO 6 PM SAT WITH A GALE
WATCH SAT NIGHT.
ON THE AREA WATERS, MOSTLY RAIN IS ANTICIPATED WITH THE SYSTEM,
HOWEVER, SOME CHANGE OVER TO SNOW COULD OCCUR SAT EVENING.
HIGH PRESSURE WILL BUILD OVER THE REGION SUNDAY AND MONDAY AND THEN
OFF THE COAST TUESDAY WITH TRANQUIL CONDITIONS EXPECTED.
ON WEDNESDAY, ANOTHER LOW PRESSURE SYSTEM SHOULD AFFECT THE REGION
WITH POTENTIAL GALES.
&&
.TIDES/COASTAL FLOODING...
DESPITE THE RELATIVELY LIGHT FLOW THIS FRIDAY EVENING, TIDAL
DEPARTURES WERE BEGINNING TO INCREASE. THEY WERE ABOUT 0.5 FT AS WE
WERE MOVING INTO THE EVENING HIGH TIDE, AND WE ONLY NEED BETWEEN 0.5
AND 0.8 FT WORTH OF A POSITIVE DEPARTURE TO GIVE MINOR TIDAL
FLOODING DURING THE SATURDAY MORNING HIGH TIDE ALONG THE COAST AND
ADJACENT BACK BAYS FROM OCEAN COUNTY, NJ SOUTHWARD. WE THEREFORE
HAVE PUT UP AN ADVISORY ALONG THE COAST AND ADJACENT BACK BAYS FROM
OCEAN COUNTY SOUTH. THIS IS A QUICK EVENT, AND FOR NOW WE ARE
LEAVING MONMOUTH COUNTY, NJ, DELAWARE BAY, THE TIDAL DELAWARE AND
CHESAPEAKE BAY OUT OF THIS. AS NOTED PREVIOUSLY, THE SATURDAY
EVENING HIGH TIDE IS MUCH LOWER THAN THE HIGHER HIGH TIDE. WE WOULD
NEED DEPARTURES OF OVER 2 FT FOR MINOR FLOODING SAT EVENING AND THIS
APPEARS UNLIKELY. BY EARLY SUNDAY MORNING'S HIGH TIDE, WINDS SHOULD
BE OFFSHORE AND TIDES SHOULD BE CLOSER TO NORMAL.
SEAS WILL BE GETTING ROUGH THROUGH SATURDAY EVENING AS GALE FORCE NE
WINDS DEVELOP. THIS SHOULD CAUSE SOME BEACH EROSION DUE TO THE NE
WINDS AND SURF. WE MAY EVENTUALLY NEED A HEAVY SURF ADVISORY DUE TO
THESE CONDITIONS.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...COASTAL FLOOD ADVISORY FROM 8 AM TO 1 PM EST SATURDAY FOR
NJZ020-022>027.
DE...COASTAL FLOOD ADVISORY FROM 8 AM TO 1 PM EST SATURDAY FOR
DEZ003-004.
MD...NONE.
MARINE...GALE WARNING FROM 6 AM SATURDAY TO 5 AM EST SUNDAY FOR ANZ431-
452>455.
GALE WATCH FROM SATURDAY EVENING THROUGH LATE SATURDAY NIGHT
FOR ANZ430-450-451.
SMALL CRAFT ADVISORY FROM 10 AM TO 6 PM EST SATURDAY FOR
ANZ430-450-451.
&&
$$
SYNOPSIS...MEOLA/RPW
NEAR TERM...MEOLA/RPW
SHORT TERM...RPW
LONG TERM...DELISI
AVIATION...DELISI/STAUBER
MARINE...STAUBER
TIDES/COASTAL FLOODING...DELISI/STAUBER
