FXUS61 KPHI 250949 AAC
AFDPHI

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
449 AM EST FRI DEC 25 2009

.SYNOPSIS...
LOW PRESSURE WILL INTENSIFY OVER THE CENTRAL PLAINS TODAY 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 TONIGHT AND SATURDAY AND MOVE THROUGH OUR AREA BY 
SUNDAY MORNING. A WESTERLY FLOW WITH WEAK HIGH PRESSURE WILL PREVAIL 
LATER SUNDAY THROUGH MONDAY WHILE ANOTHER COLD FRONT IS EXPECTED TO 
SWING THROUGH OUR AREA EARLY TUESDAY. HIGH PRESSURE SHOULD BUILD 
TOWARD OUR REGION FROM THE WEST WEDNESDAY.  

&&

.NEAR TERM /THROUGH TONIGHT/...
LOW CLOUDS HAD ABOUT COMPLETED THEIR COVERAGE OF OUR AREA...AND WARM 
ADVECTION HIGH CLOUDS WERE SWEEPING OVER THE AREA AS WELL EARLY THIS 
MORNING AS THE IMPENDING WEATHER-MAKER MAKES ITS INITIAL MOVE TOWARD 
OUR AREA. MANY SECTIONS ESPECIALLY OVER EASTERN AREAS WERE ACTUALLY 
ABOVE FREEZING BEFORE SUNRISE...AS WARMER AIR WAS ARRIVING ON 
DEVELOPING NORTHEASTERLY WINDS. ACCORDING TO MODEL FIELDS SUCH AS 
PRECIPITATION, OMEGA, AND MID LEVEL RELATIVE HUMIDITY, AS WELL AS 
RADAR TRENDS, PRECIPITATION LOOKS ON TARGET FOR LATE MORNING OR 
MIDDAY SOUTH AND LATER THIS AFTERNOON NORTH...SO A TREND OF 
INCREASING PRECIPITATION PROBABILITIES NORTHWARD MAKES SENSE DURING 
TODAY. HIGHER ELEVATIONS OF THE NORTHWESTERN ZONES...MAINLY CARBON 
AND MONROE...LOOK LIKE THEY WILL RETAIN COLD AIR NEAR THE SURFACE, 
AND PERHAPS AT THE SURFACE TOO. THE INHERITED FREEZING RAIN ADVISORY 
WAS RETAINED, BUT BACKED UP FOR A START TIME OF 17Z (FOR THIS 
AFTERNOON). THERE APPEARS TO BE ENOUGH OF A WARM NOSE ALOFT TO MELT 
MOST PRECIPITATION TO RAIN BEFORE IT REACHES THE GROUND, ESPECIALLY 
IF IT DEVELOPS LATER IN THE AFTERNOON AS PLANNED. HOWEVER, THERE 
ALWAYS SEEMS TO BE A LAYER THAT CAN CAUSE SOME ICE PELLET FORMATION, 
SO SLEET WAS ADDED IN FAR NORTH AS WELL, BUT THIS SHOULD BE MINIMAL; 
IF IT WASN'T WE WOULD CHANGE THE ADVISORY TO A WINTER WEATHER TYPE.

REGARDING HIGH TEMPERATURES AND TEMPERATURE TRENDS, NAM AND GFS MOS 
WERE SIMILAR FOR SOUTHERN AND CENTRAL SECTIONS, BUT IT APPEARS THE 
GFS MOS IS TOO WARM NORTH, ESPECIALLY WHEN MODEL SOUNDINGS ARE 
OBSERVED FOR COMPARISON TO THE LOW LEVELS.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
THE FREEZING RAIN ADVISORY WAS EXPANDED SOUTHWARD AND EASTWARD A BIT 
TO LEHIGH, NORTHAMPTON, WARREN, SUSSEX, AND MORRIS COUNTIES FOR 
TONIGHT. TEMPERATURES SHOULD BE JUST WARM ENOUGH TODAY AT THE 
VULNERABLE LOCATIONS TO KEEP FREEZING RAIN FROM OCCURRING, BUT 
SLIGHT COOLING TONIGHT ESPECIALLY WITH ANY HEAVIER PRECIPITATION 
MAY DROP TEMPERATURES TO THE FREEZING LEVEL, HENCE THE ADVISORY 
ISSUANCE. THE FREEZING RAIN ADVISORIES WERE EXTENDED JUST INTO 
SATURDAY MORNING WHEN TEMPERATURES ARE EXPECTED TO RISE ENOUGH TO 
PRECLUDE ANY FURTHER PROBLEMS. 

OTHERWISE, NAM QPF HAS BEEN CONSISTENT ON THE 00Z AND THE 06Z FOUS 
DATA, WITH AMOUNTS AT OR JUST OVER 1 INCH. CATEGORICAL PRECIPITATION 
CHANCES ARE FORECAST FOR TONIGHT, AND WITH THE SLOW MOVEMENT OF THE 
STORM...THE CHANCES SHOULD REMAIN FAIRLY HIGH INTO SATURDAY UNTIL 
DRY SLOTTING OCCURS AND DROPS PRECIPITATION CHANCES FOR OR DURING 
THE AFTERNOON. 

THE WARMER TEMPERATURES WILL BE ACROSS THE REGION SATURDAY AND 
SATURDAY NIGHT, WITH HIGHS SATURDAY IN THE UPPER 40S TO LOWER 50S 
EXPECTED. THESE READINGS, ALONG WITH THE RAINFALL (WHICH COULD TOTAL 
1.0 TO 1.5 INCHES) WILL MAKE A SIGNIFICANT DENT IN THE SNOW PACK. 
THE HYDROLOGY SECTION BELOW ADDRESSES ANY UPCOMING HYDROLOGIC 
ISSUES. 

ANY LINGERING PRECIPITATION SHOULD END EARLY SUNDAY MORNING ONCE
A COLD FRONT CROSSES THE AREA. THERE WILL STILL BE A SMALL CHANCE
FOR SHOWERS (RAIN AND/OR SNOW) MAINLY ACROSS THE NORTH.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AT THE START OF THE PERIOD, A RATHER LARGE UPPER LEVEL TROUGH WILL 
BE SITUATED OVER THE EASTERN HALF OF THE UNITED STATES. THIS FEATURE 
IS SEEN TO PROGRESS SLOWLY EASTWARD AND FINALLY MOVE OFF THE COAST 
MONDAY.

MEANWHILE, A SURFACE LOW OVER EASTERN CANADA WILL DRAG A COLD FRONT 
ACROSS THE REGION SUNDAY NIGHT INTO MONDAY, WITH A REINFORCING COLD 
FRONT DROPPING THROUGH SOMETIME LATE MONDAY INTO TUESDAY. THIS WILL 
BRING COLDER AIR BACK INTO THE AREA, AND AS A RESULT THERE REMAINS 
THE POSSIBILITY FOR SOME SNOW SHOWERS ACROSS THE AREA AND WE HAVE 
INCLUDED A SLIGHT CHANCE OR CHANCE FOR SNOW SHOWERS. IT LOOKS 
LIKE ANY LINGERING SNOW SHOWERS WILL END BY TUESDAY MORNING.

AS THE UPPER TROUGH FINALLY EXITS THE REGION, SURFACE HIGH PRESSURE 
WILL BUILD IN FROM THE WEST. THIS HIGH WILL REMAIN IN CONTROL OF OUR 
WEATHER FROM TUESDAY THROUGH THURSDAY.

&&

.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY AND SURROUNDING AREAS.

A MARINE DECK OF STRATA-CU HAS BEEN ADVECTING INLAND ALL EVENING. 
WHAT BEGAN AT THE COAST HAS NOW REACHED A MSV-KHGR-KEKN LINE. BASES 
ARE BETWEEN 2,2-3,000 FT. CONDITIONS WILL LOWER TO MVFR AT TIMES 
THIS MORNING BUT CONTINUE DOWN TO IFR CATEGORIES THIS AFTERNOON INTO 
SATURDAY MORNING.

THE COLD AIR MASS WE HAVE NOW WILL BE WARMING THROUGH THE LOWER 
LAYERS TODAY INTO SATURDAY THEN TURN COLD AGAIN. 

THE FOLLOWING IS THE FREEZING LEVEL INFORMATION FOR A FEW SITES.

STA 2512Z 25/18 26/00 26/06 26/12 26/18 27/00 27/06 27/12Z
LGA 02085 05940 04075 04190 07895 08895 11005 10205 10020
PHL 07625 09220 05490 07595 08895 10705 10710 10410 09115
IPT 000/ 01395 02395 01395 02095 07195 07670 05855 00185
DCA 08430 08660 06895 08990 10605 10510 10110 09315 05140 

THE FIRST THREE VALUES ARE THE FREEZING LEVEL ABOVE THE GROUND
LEVEL THE LAST TWO ARE THE RH AT THAT LEVEL. 

THERE MAY BE SOME LO LVL WINDSHEAR AT TIMES ESPECIALLY LATER THIS 
AFTERNOON AND EVENING. SFC WINDS WILL BE AROUND 050-070 DEGREES AT 
15 TO 20 KT AND FORECAST WINDS AT 1,500 FT AROUND 120 DEGREES AT 30 
KTS. WINDS AT 5,000 FT WILL BE 50 TO 55 KT THIS EVENING FROM THE 
SOUTHEAST.   

THE WORST OF THE FLYING CONDITIONS WILL BE FROM THE PERIOD 22Z TODAY 
THROUGH AROUND 16Z ON SATURDAY AS LOW PRESSURE MOVES TO THE 
NORTHEAST AND CLEARS THINGS OUT. THE WEATHER WILL THEN BE VFR INTO 
SUNDAY AFTERNOON. 

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

&&

.MARINE...
AT 3AM...NOAA BUOY REPORTS WINDS FROM THE NORTHEAST(060 DEGREES) AT 
12-14 KT WITH A 4 FT SEA EVERY 6 SECONDS. AMBROSE LIGHT WINDS 050 
DEGREES AT 15-17 FT AND 2 FT SEA EVERY 14 SECONDS. HUDSON CANYON 
BUOY WINDS 060 AT 14-14 KT WITH A 4 FT EVERY 6 SECONDS. 

WITH CONDITIONS QUICKLY LATER TODAY WILL BE ISSUING SMALL CRAFT FOR 
SOUTHERN WATERS AND DELAWARE BAY FIRST THEN CHANGING TO GALE 
WARNINGS THIS EVENING. NORTH OF LITTLE EGG INLET...SMALL CRAFT WILL 
CHANGE TO GALE WARNINGS AFTER MIDNIGHT. IT IS GOING TO BE VERY ROUGH 
IN THE DELAWARE BAY AS THE WINDS BLOW FROM THE SOUTHEAST UP THE BAY. 
VERY CHOPPY CONDITIONS IN THE CONFINES OF THE BAY AND ALSO ON THE 
OCEAN. WAVE FORECASTS FOR BUOY 44009 SUGGEST ABOUT 14 FEET EVERY 4 
TO 6 SECONDS AFTER MIDNIGHT. THE ROUGHEST CONDITIONS WILL BE FROM 
LATER THIS AFTERNOON THROUGH SATURDAY AFTERNOON. IMPROVEMENT LATE 
SATURDAY AS THE WIND GRADIENT SHIFTS TO THE NORTHEAST AND A LOW 
PRESSURE MOVES INTO THE WATERS NEAR LONG ISLAND. THIS WILL DEADEN 
THE WINDS AND SEAS FOR ABOUT A 36 HOUR PERIOD BEFORE A FRONT MOVES 
IN FROM THE WEST LATE SUNDAY WITH SHIFTING COOLER NORTHWEST WINDS 
AND SMALL CRAFT ADVISORIES WILL PROBABLY BE IN EFFECT.

FOR THE CANYONS...GALES ARE EXPECTED TONIGHT INTO SATURDAY AND AGAIN 
MONDAY INTO TUESDAY. CHECK THE WEATHER BEFORE HEADING TO THE 
OFFSHORE CANYONS.

&&

.HYDROLOGY...
CERTAINLY NOT OUT OF THE WOODS, BUT THE HSA IS BETTER OFF THAN 24 
HOURS AGO. BOTTOM LINE, THE CAPACITY TO HOLD WATER IN THE CREEKS AND 
STREAMS HAS INCREASED A BIT. THIS WAS POSSIBLE DUE TO THE COLD
TEMPERATURES WHICH WERE CAUSING LITTLE IF ANY MELTING AND
SUBSEQUENT RUNOFF. WITH LITTLE IF ANY WATER ENTERING INTO OUR
CHANNELS, WATER LEVELS HAVE BEEN ABLE TO DECREASE. EVEN IF JUST A
BIT, EVERY INCH IS IMPORTANT.

USING A BELL SHAPED CURVE, WE FEEL THAT 1.00 TO 1.25 INCHES OF RAIN 
IS MOST LIKELY TO OCCUR THROUGH SATURDAY NIGHT. A LITTLE LESS OR A 
LITTLE MORE IS POSSIBLE, BUT WE FEEL CHANCES OF THIS OCCURRING 
AREN'T AS GREAT. THE 00Z NAM FOUS WAS INDICATING SLIGHTLY OVER AN
INCH /1.07/ FOR PHILADELPHIA FOR THE EVENT TOTAL.

WITH TEMPERATURES TOPPING OUT AROUND 50 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, 1.00 TO 1.25 INCHES OF NEW RAINFALL, 
COMBINED WITH UP TO 1.10 INCHES OF LIQUID WATER FROM THE SNOW, WE'RE 
LOOKING AT POSSIBLY 2.35 INCHES. IF WE GET 1.50 INCHES OF RAIN, WE 
COULD BE LOOKING AT 2.6 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.

&&

.TIDES/COASTAL FLOODING...
THE INCREASING SOUTHEAST WINDS WHICH WILL REACH GALE FORCE AT TIMES 
WILL BRING WATER LEVELS UP ABOUT 1 FOOT ABOVE NORMAL ON THE OCEAN 
FRONT AND UP TO 2 FEET UP THE DELAWARE RIVER. HOWEVER, TIDAL 
FLOODING IS NOT EXPECTED SINCE WE ARE NOT IN THE STRONG 
GRAVITATIONAL CYCLE OF THE MOON.  HIGH TIDES IN THE UPPER DELAWARE 
BAY WILL BE BETWEEN 5 AND 6 OCLOCK THIS EVENING AND MORNING SATURDAY 
AND ALONG THE OCEAN FRONT BETWEEN 230 AND 330 PM AND AM SATURDAY.  

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...FREEZING RAIN ADVISORY FROM 6 PM THIS EVENING TO 9 AM EST 
     SATURDAY FOR PAZ061-062.
     FREEZING RAIN ADVISORY FROM NOON TODAY TO 9 AM EST SATURDAY 
     FOR PAZ054-055.
NJ...FREEZING RAIN ADVISORY FROM 6 PM THIS EVENING TO 9 AM EST 
     SATURDAY FOR NJZ001-007-008.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 1 AM EST 
     SATURDAY FOR ANZ450>452.
     GALE WARNING FROM 1 AM TO 4 PM EST SATURDAY FOR ANZ450>452.
     SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ430-
     431-453>455.
     GALE WARNING FROM 7 PM THIS EVENING TO 10 AM EST SATURDAY FOR 
     ANZ430-431-453>455.

&&

$$
 
SYNOPSIS... / O'HARA
NEAR TERM... / O'HARA
SHORT TERM...O'HARA /
LONG TERM...MEOLA
AVIATION...EBERWINE
MARINE...EBERWINE
TIDES...EBERWINE
HYDROLOGY...KRUZDLO