FXUS61 KPHI 260203
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
903 PM EST FRI DEC 25 2009

.SYNOPSIS...
LOW PRESSURE OVER THE CENTRAL PORTION OF THE NATION WILL MOVE
SLOWLY NORTHEASTWARD. A WARM FRONT EXTENDING FROM THIS LOW WILL
CROSS THE MID-ATLANTIC REGION. A SECOND AREA OF LOW PRESSURE WILL
FORM NEAR THE VIRGINIA CAPES AND MOVE NORTHEASTWARD AS WELL. RAIN
IS EXPECTED OVER MOST OF THE AREA, WITH SOME FREEZING RAIN OVER
MAINLY THE HIGHER ELEVATIONS OF THE POCONOS AND NORTHERN NEW
JERSEY. TEMPERATURES ARE EXPECTED TO RISE THROUGH THE NIGHT. HIGH
PRESSURE WILL THEN BUILD IN FOR SUNDAY. A COLD FRONT WILL SWING
THROUGH ON MONDAY, FOLLOWED BY HIGH PRESSURE FOR THE MIDWEEK PERIOD.

&&

.NEAR TERM /THROUGH SATURDAY/...
A LARGE AREA OF LOW PRESSURE WAS LOCATED OVER THE CNTRL CONUS AND
WILL SLOWLY SPIN AND EVENTUALLY MOVE NEWD TWD THE GRTLKS. AS IT
SPINS, THE ATTENDANT WMFNT WILL CROSS THE REGION TONIGHT. A
SECONDARY SFC WAVE MAY THEN DEVELOP ALONG THE VA CAPES AND MOVE
NEWD.  

THE PUBLIC PRODUCTS ARE BEING UPDATED TO REMOVE THE FREEZING RAIN
ADVISORY FROM THE LEHIGH VALLEY COUNTIES OF PA AND ALL THE NJ
COUNIES EXCEPT SUSSEX. SFC TEMPERATURES HAVE WARMED ENOUGH THE
LAST FEW HOURS TO PRECLUDE ANY FURTHER THREAT FROM ICE. THE
ADVISORY WILL CONTINUE FURTHER NORTH...WHERE SOME ICE COATING HAS
BEEN REPORTED FROM SPOTTERS.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
PERIODS OF RAIN WILL CONTINUE ON SATURDAY, POSSIBLY HEAVY AT
TIMES, BUT THEN WILL TAPER OFF FROM SW TO NE SATURDAY EVENING INTO
SATURDAY NIGHT. ALL LOCATIONS ARE FCST TO BE ABOVE FREEZING ON
SATURDAY, SO ANY PRECIP WILL BE LIQUID RAIN. BY SUNDAY, THE LOW
FILLS AND MOVES NEWD AND HIGH PRESSURE AT THE SFC BEGINS TO NOSE
IN. HOWEVER, THE LARGE H5 TROF IS NOW CENTERED OVER THE ERN CONUS,
SO DON'T EXPECT MUCH IN THE WAY OF SUNSHINE. ON SUNDAY, THE LOW
PULLS FURTHER AWAY. BY MONDAY, THE LAST VESTIGES OF THE UPR/SFC
LOW SWINGS A CDFNT THROUGH THE AREA AND THERE COULD BE SOME SNOW
SHOWERS AT THAT TIME. ATMOSPHERIC PROFILES AND TEMPS INDICATE THAT
WITH THE CORE OF THE COLD AIR ALOFT ABOVE US, THAT ANY PRECIP
WOULD BE IN THE FORM OF SNOW. HOWEVER, AMTS SHOULD BE GENLY LIGHT. 

TEMPERATURES EXPECTED TO RISE QUITE NICELY DURG THE DAY ON
SATURDAY, WITH TEMPS AROUND 50 DEGREES IN THE PHL AREA AND EVEN IN
THE LOW 40S IN THE LEHIGH VLY. ACRS SRN AREAS, TEMPS MAY EVEN
APPROACH 60!

THE WARM TEMPS AND STEADY RAIN WILL MAKE A SIGNIFICANT DENT IN THE
CURRENT SNOW PACK.  PLS SEE THE HYDROLOGY SECTION BELOW FOR THE
LATEST ON ANY POTENTIAL HYDRO ISSUES.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
HIGH PRESSURE IS EXPECTED TO BUILD IN FROM THE MIDWEST ON TUE, THEN 
MOVE OFF THE MID-ATLANTIC COAST ON WED. AN UPPER LEVEL DISTURBANCE 
MAY BRING SOME RELATIVELY LIGHT SNOW TO THE AREA LATE WED AND WED 
NIGHT. THE BIG ELEPHANT IN THE ROOM IS THE POTENTIAL FOR ANOTHER 
COASTAL STORM LATE NEW YEARS DAY AND SATURDAY AS STRONG NEG AO/NAO 
AND EL NINO CONDITIONS CONTINUE TO PROVIDE A FAVORABLE ENVIRONMENT 
FOR SUCH STORMS. NEED TO WATCHFUL TO SEE HOW THINGS TURN OUT.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY AND SURROUNDING AREAS.

CEILINGS HAVE BEEN SLOWLY IMPROVING DURING THE LATE AFTERNOON AND
EVENING HOURS, EVEN AS RAIN HAS BEEN MOVING INTO THE REGION. THE
TAFS HAVE BEEN ADJUSTED TO ACCOUNT FOR THIS SLIGHT IMPROVEMENT.
HOWEVER, CEILINGS UNDER 1000 FEET ARE STILL EXPECTED DURING THE
OVERNIGHT HOURS, AND VSBYS UNDER 2SM ARE STILL POSSIBLE IF FOG
DEVELOPS AS WARMER AIR MOVES OVER THE SNOWPACK.

CONDITIONS ARE NOT EXPECTED TO IMPROVE UNTIL SATURDAY AFTERNOON
AS LOW PRESSURE MOVES PAST.

AFTER THAT, THE LOW MOVES TO THE NORTHEAST AND CONDITIONS IMPROVE. 
THE WEATHER WILL THEN BE VFR INTO SUNDAY AFTERNOON. 

OUTLOOK...
A COLD FRONT WILL APPROACH FROM THE WEST SUNDAY NIGHT WITH COLD AIR 
ADVECTION RETURNING AND WITH POSSIBLE SNOW SHOWERS ACROSS THE TAF 
SITES NORTH OF PHL-PNE FROM MONDAY MORNING INTO THE EVENING HOURS. A 
COOL NORTHWEST FLOW WILL CONTINUE INTO MONDAY NIGHT WITH IMPROVING 
FLYING CONDITIONS.

&&

.MARINE...
GUIDANCE IS STILL BRINGING WINDS UP TO GALE FORCE TONIGHT, BUT
THE WARMER AIR OVER THE COLDER WATER /ESPECIALLY OVER THE BAY AND
SOUTHERN ATLANTIC WATERS/ MAY MAKE THIS A MARGINAL GALE. STILL, WE
WILL MAINTAIN OUR HEADLINES AS IS AND CAP WIND GUSTS AT AROUND 35
KNOTS.

WE STILL EXPECT IMPROVING CONDITIONS FROM SOUTH TO NORTH LATER IN 
THE DAY INTO THE EVENING SATURDAY AS WINDS SHIFT AND LOW PRESSURE 
MOVES INTO THE WATERS NEAR LONG ISLAND. THIS WILL ALLOW WINDS AND 
SEAS TO DIMINISH FOR ABOUT A 36 HOUR PERIOD BEFORE A FRONT MOVES IN 
FROM THE WEST LATE SUNDAY WITH SHIFTING AND INCREASING NORTHWEST 
WINDS. 

REGARDING TIDES, DEPARTURES FRI AFTERNOON GENERALLY WERE AROUND
1.25 FT /A BIT LESS OVER CHESAPEAKE BAY AND A BIT MORE UP DELAWARE
BAY INTO THE TIDAL DELAWARE/. BECAUSE WE ARE NEAR NEAP TIDE, WE
WOULD NEED SIGNIFICANTLY GREATER DEPARTURES TO REACH MINOR TIDAL
FLOODING LEVELS. THAT IS NOT EXPECTED TO OCCUR AT THIS TIME, BUT
WE WILL MONITOR THE SITUATION. GIVEN THE PRESENT DEPARTURES, THE
AREAS OF GREATEST CONCERN WOULD BE DELAWARE BAY AND THE TIDAL
DELAWARE. THE FIRST CHANCE OF MINOR FLOODING WOULD BE WITH THE
HIGH TIDE THAT OCCURS FROM AROUND 330 AM TO 545 AM SATURDAY UP THE
BAY AND FROM ABOUT 600 AM TO AROUND 900 AM SATURDAY UP THE TIDAL
DELAWARE.

&&

.HYDROLOGY...
THE LATEST ASSESSMENT OF THE HYDRO SITUATION HAS NOT CHANGED ALL
THAT MUCH. THE RAIN IS EXPECTED TO COME OVER A FAIRLY LONG
DURATION 12-24 HOURS AND WITH QPFS AROUND OR SLIGHTLY ABOVE 1.00
INCH, WE EXPECT A SIGNIFICANT DENT IN THE SNOWPACK.  

WITH TEMPERATURES TOPPING IN THE 40S N, LOWER 50S CENTRAL AND MID
50S S ON SATURDAY ON SATURDAY, COUPLED WITH HIGH DEW POINTS, SOME WIND,
AND THE RAIN, MELTING SNOW IS MOST DEFINITE. THE QUESTION IS HOW
MUCH SNOW WILL MELT? WE FEEL THAT 75% OF THE WATER LOCKED UP IN
THE SNOW IS GOING TO TRANSLATE INTO RUNOFF.

SNOW WATER EQUIVALENTS RANGE FROM LESS THAN A .5 INCH ACROSS THE 
NORTHERN HSA TO ABOUT 1.5 INCHES ACROSS THE CENTRAL AND SOUTHERN 
SNOW-PACK.

SO IF YOU ADD THE NUMBERS AND AN INCH OF RAINFALL, COMBINED WITH
UP TO 1.10 INCHES OF LIQUID WATER FROM THE SNOW, WE'RE LOOKING AT
POSSIBLY OVER 2 INCHES. 

ALTHOUGH THE HSA'S CAPACITY TO HOLD WATER HAS INCREASED, FLOODING IS 
STILL POSSIBLE, THAT IS FOR CREEKS AND STREAMS. NUISANCE FLOODING 
IN LOW LYING AND IN POOR DRAINAGE AREAS IS GOING TO HAPPEN. FOR OUR 
CREEKS AND STREAMS, WE THINK WE'LL BE O.K. IF WE ONLY RECEIVE 0.75 
INCHES OF RAIN. IF WE GET 1.00 INCH OF RAIN, MOST OF THE WATER WILL 
REMAIN IN THE CHANNELS. IF WE GET 1.25 INCHES, CREEK AND STREAM 
FLOODING WILL BE LIKELY...THE FAST RESPONDERS. IF WE RECEIVE 1.50 
INCHES, CREEK AND STREAM FLOODING IS ALMOST A DEFINITE.

THE QUICK RESPONDERS INCLUDE THOSE IN NORTHERN DELAWARE, SOUTHEAST 
PENNSYLVANIA, AND THE ASSUNPINK AND MILLSTONE IN JERSEY.

IF THE SCHUYLKILL BASIN RECEIVES 1.50 INCHES, 3/4 BANKFULL TO 
BANKFULL ISN'T OUT OF THE QUESTION. THE DELAWARE WOULD SEE 1/2 TO 
3/4 BANKFULL. HOWEVER, CURRENT FCSTS ARE NOT CALLING FOR QPF TO BE
THAT HIGH.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...FREEZING RAIN ADVISORY UNTIL 9 AM EST SATURDAY FOR PAZ054-055.
NJ...FREEZING RAIN ADVISORY UNTIL 9 AM EST SATURDAY FOR NJZ001.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 1 AM EST SATURDAY FOR ANZ450>452.
     GALE WARNING FROM 1 AM TO 4 PM EST SATURDAY FOR ANZ450>452.
     GALE WARNING UNTIL 10 AM EST SATURDAY FOR ANZ430-431-453>455.

&&

$$
SYNOPSIS...NIERENBERG
NEAR TERM...NIERENBERG/O'HARA
SHORT TERM...NIERENBERG
LONG TERM...NIERENBERG
AVIATION...MIKETTA
MARINE...MIKETTA
HYDROLOGY...