FXUS61 KPHI 042030
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
330 PM EST FRI DEC 4 2009
.SYNOPSIS...
HIGH PRESSURE OVER OUR AREA THIS AFTERNOON WILL WEAKEN AND DRIFT
NORTH TONIGHT AS AN AREA OF LOW PRESSURE DEVELOPS OVER NORTHERN
FLORIDA. 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 BEGINS TO GATHER STRENGTH
TO OUR SOUTH, CLOUDINESS WILL THICKEN AND LOWER OVERNIGHT.
RAIN WILL BE APPROACHING 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.
&&
.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 /21Z FRIDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
CLOUDS AROUND 5 THSD FT THAT WERE LOCATED TO THE SW HAVE SPREAD
ACROSS THE REGION. EVEN THOUGH THE COMPUTER MODELS DO NOT SHOW THEM,
I THINK THEY WILL STAY IN PLACE THROUGHOUT TONIGHT SINCE THERE ARE
NO MECHANISMS TO DISSIPATE THEM. OTHERWISE, VFR CONDITIONS PREVAIL
THROUGH TONIGHT.
A COASTAL LOW PRESSURE SYSTEM HAS FORMED OFF THE COAST OF GEORGIA.
THIS 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. RAIN IS EXPECTED FROM
PHL-PNE SOUTH AND EAST WITH A MIX AT TTN AT THE ONSET. TIMING OF
STARTING THE RAIN IS AROUND 12Z SAT AT ACY/MIV, BY 15Z AT
PHL/PNE/ILG AND 15Z FOR R/S AT TTN AND SNOW AT ABE/RDG WITH
CONDITIONS LOWERING TO MVFR AT ALL SITES. IFR CONDITIONS MIGHT
DEVELOP AT ABE/RDG/TTN IN THE AFTN.
AFTER 21Z, COLDER AIR WILL BE MOVING IN FROM THE N/W AND CHANGING
THE PCPN TO SNOW WITH ALL PCPN THEN ENDING FROM THE WEST BY MIDNIGHT
SAT NIGHT. IFR CONDITIONS SHOULD DEVELOP AT ALL SITES FOR A FEW HRS
DURING THE EVENING BEFORE IMPROVING 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 THEN 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...
WE SHOULD BE LUCKY WITH THIS SYSTEM IN RESPECT TO COASTAL FLOODING.
HIGH TIDE OCCURS LATE SAT AFTN, BUT THIS TIDE IS MUCH LOWER THAN THE
HIGHER OF THE HIGH TIDES WHICH OCCURS EARLY SUNDAY MORNING. WE WILL
NEED DEPARTURES OF OVER 2 FT FOR MINOR FLOODING SAT AFTN AND THIS
APPEARS UNLIKELY. EARLY SUNDAY MORNINGS HIGH TIDE, WINDS SHOULD BE
OFFSHORE AND TIDES SHOULD BE CLOSER TO NORMAL.
ON THE OTHER HAND, SEAS WILL BE GETTING ROUGH SATURDAY EVENING AS
GALE FORCE NE WINDS DEVELOP. THIS MIGHT EVEN 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...NONE.
DE...NONE.
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...RPW
NEAR TERM...RPW
SHORT TERM...RPW
LONG TERM...DELISI
AVIATION...STAUBER
MARINE...STAUBER
TIDES/COASTAL FLOODING...STAUBER
