825 
FXUS61 KPHI 152010
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
410 PM EDT FRI APR 15 2011

.SYNOPSIS...
HIGH PRESSURE TO OUR NORTH WILL PUSH FARTHER AWAY FROM THE REGION 
TONIGHT AS A LOW PRESSURE SYSTEM NEARS THE GREAT LAKES. THE LOW 
PRESSURE WILL TRACK NORTHWARD INTO CANADA DURING SATURDAY AND SEND A 
STRONG COLD FRONT THROUGH OUR AREA LATE SATURDAY NIGHT. HIGH 
PRESSURE WILL THEN BUILD INTO THE MID ATLANTIC FOR SUNDAY AND 
MONDAY, FOLLOWED BY ANOTHER FRONTAL BOUNDARY APPROACHING BY TUESDAY 
INTO WEDNESDAY. 

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
HIGH PRESSURE OVER EASTERN CANADA ALLOWED FOR FAIR DAYTIME WEATHER 
AS IT NOSED DOWN ALONG THE EAST COAST. THIS HIGH WILL GRADUALLY BE 
SLIDING AWAY FROM THE AREA TONIGHT AS A LOW PRESSURE SYSTEM 
CONTINUES TO STRENGTHEN OVER THE CENTRAL PLAINS AND HEAD TOWARD THE 
GREAT LAKES DURING THE OVERNIGHT. THE MODELS ALSO INDICATE THAT A 
MID LEVEL RIDGE WILL BE PASSING OVER THE AREA DURING THE OVERNIGHT. 
IN GENERAL, CLOUD COVER PROGRESSIVELY INCREASES THROUGH THE FORECAST 
AREA DURING THE OVERNIGHT IN RESPONSE TO THESE SYNOPTIC SCALE 
FEATURES. MODELS ARE IN FAIRLY GOOD AGREEMENT THAT TONIGHT SHOULD BE 
PRIMARILY DRY THROUGH THE FORECAST AREA, BUT THE INITIAL BATCH OF 
PRECIPITATION SHOULD REACH OUR WESTERN ZONES NEAR DAYBREAK. THE GFS 
AND NAM DEPICT EASTERLY SURFACE WINDS PROGRESSIVELY INCREASING 
THROUGH THE EARLY MORNING HOURS. FOR LOW TEMPERATURES, A BLEND OF 
THE MOS GUIDANCE WAS USED.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
AS THE LOW PRESSURE SYSTEM TRACKS THROUGH THE GREAT LAKES REGION 
DURING SATURDAY, ITS ASSOCIATED COLD FRONT WILL BE APPROACHING OUR 
AREA AND IS EXPECTED TO SWING THROUGH LATE SATURDAY NIGHT. THE 
MODELS BRING THE HEAVIEST RAIN THROUGH OUR CWA FROM SATURDAY 
AFTERNOON THROUGH SATURDAY NIGHT. FOR FURTHER INFORMATION ON QPF 
AMOUNTS AND THE POSSIBILITY FOR ANY FLOODING, PLEASE REFER TO THE 
HYDROLOGY SECTION. A CHANCE FOR THUNDERSTORMS WAS RETAINED IN THE 
FORECAST FOR THE SATURDAY AFTERNOON TO EVENING TIMEFRAME FOR THE 
DELMARVA, AS WELL AS SOUTHERN TO CENTRAL PARTS OF NEW JERSEY. THERE 
IS LITTLE IN THE WAY OF SURFACE BASED CAPE OR LIFTED INDEX, BUT 
GIVEN THE LOOK OF FORECAST SOUNDINGS, ELEVATED CONVECTION IS 
POSSIBLE. SPC STILL KEEPS OUR EXTREME SOUTHERN DELMARVA ZONES IN A 
SLIGHT RISK, WITH GENERAL THUNDERSTORMS INDICATED AS FAR NORTH AS 
CENTRAL NEW JERSEY. BUFKIT SOUNDINGS AND MODEL WIND DATA DEPICT WIND 
GUSTS REACHING AROUND 40 KNOTS FOR THE FORECAST AREA FROM SATURDAY 
AFTERNOON THROUGH SATURDAY NIGHT, AND A WIND ADVISORY HAS BEEN 
ISSUED WITH THE AFTERNOON FORECAST PACKAGE. 

THE COLD FRONT QUICKLY EXITS THE AREA SUNDAY MORNING, AND AN AREA OF 
HIGH PRESSURE OVER THE SOUTHEASTERN STATES GRADUALLY BUILDS TOWARD 
THE MID ATLANTIC REGION DURING SUNDAY. THIS SYSTEM WILL KEEP 
CONDITIONS MAINLY QUIET FOR THE FORECAST AREA THROUGH MONDAY. A 
BLEND OF GFS AND NAM MOS GUIDANCE WAS USED FOR TEMPERATURES THROUGH 
THE SHORT TERM PERIOD. 

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
THE FORECAST IS A BLEND OF THE 00Z ECMWF/GFS AND THE LATEST 
GEFS/EUROPEAN ENSEMBLES. WE DID MAKE THE END OF THE PERIOD A LITTLE 
DRIER BASED ON THE 12Z ECMWF. 

THE LONG TERM STILL LOOKS LARGELY UNSETTLED. A BAROCLINIC ZONE STILL 
IS FORECAST TO ESTABLISH ITSELF NEAR OUR REGION EARLY IN THE PERIOD, 
AND THE MID-LEVEL FLOW IS STILL FORECAST TO BE ZONAL. 

WE ALSO STILL SEE A RELATIVELY WEAK IMPULSE AFFECTING US AROUND 
TUESDAY; THE BAROCLINIC ZONE REMAINING IN PLACE IN ITS WAKE, AND 
SAID ZONE BECOMING A SURFACE WARM FRONT ASSOCIATED WITH SURFACE LOW 
PRESSURE THAT DEVELOPS IN RESPONSE TO A FAIRLY SHARP APPROACHING 
MID-LEVEL IMPULSE. THE LOW PRESSURE SYSTEM IS FORECAST TO MOVE FROM 
THE PLAINS ON TUESDAY TO NORTH OF OUR AREA AROUND THURSDAY; LIFT THE 
WARM FRONT THROUGH THE AREA AROUND MID-WEEK, AND PULL THE COLD FRONT 
THROUGH OUR AREA AROUND THURSDAY. WE SHOULD FIRST SEE SOME WARM 
SECTOR AIR ALOFT AND THEN BE IN THE WARM SECTOR, SO CONVECTION 
REMAINS A POSSIBILITY DURING THE MID-WEEK PERIOD.

WE ARE NOW ALLOWING FOR THE POSSIBILITY OF COOL HIGH PRESSURE 
BUILDING INTO THE AREA FOR THE END OF THE WORK WEEK BECAUSE OF 
INDICATIONS FROM THE 12Z ECMWF. HOWEVER, DRYING MIGHT BE TRANSIENT, 
SINCE THE MID-LEVEL FLOW STILL LOOKS ZONAL AT THE END OF THE LONG 
TERM. 

TEMPERATURES ARE FORECAST TO START ABOVE NORMAL, AND THEN DROP TO 
NEAR NORMAL TOWARD THE END OF THE PERIOD. 

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY AND SURROUNDING AREAS.

A DOWNHILL FORECAST WAS ISSUED FOR OUR TERMINALS THROUGH THE TAF 
PERIOD, ALTHOUGH OUTSIDE OF KACY, WIDESPREAD MVFR CONDITIONS ARE NOT 
FORECAST TO DEVELOP UNTIL EARLY SATURDAY MORNING ELSEWHERE.

THE ONSHORE FLOW DEVELOPED A SC DECK IN NJ WITH CIGS BETWEEN 3K
AND 4K. FORECAST SOUNDINGS ARE NOT SHOWING AN INCREASE IN LOW LEVEL 
MOISTURE THE REST OF THE AFTERNOON AND EVENING. WE ORIGINALLY 
THOUGHT THIS LAYER OF CLOUDS WOULD DISSIPATE AS IT EXPANDS A BIT 
DURING THE AFTERNOON. AS SUCH IT HAS NOT AND IS PRETTY MUCH REMAINED 
IN PLACE OVER CENTRAL NEW JERSEY. THE GENERAL MOTION THOUGH SHOULD 
TAKE THIS LAYER TOWARD THE NORTH THE REST OF THE AFTERNOON INTO 
EARLY EVENING. THIS SHOULD BE THE SOURCE POINT OF EXPANSION OF THE 
LOW CLOUDS AS THE NIGHT PROGRESSES. WINDS THROUGH THE AFTERNOON WILL 
HAVE SOME GUSTINESS FROM THE EAST, BUT NOT ON THE EXPECTED SCALE OF 
SATURDAY.

TONIGHT THE CONTINUED ONSHORE FLOW, THE STRATOCU SOURCE IN NORTHERN 
NEW JERSEY AS WELL AS THE APPROACH OF THE FRONTAL SYSTEM FROM THE 
MIDWEST WILL BRING CLOUDS INTO THE TERMINAL AREA FROM THREE 
DIRECTIONS. WE ARE FORECASTING A WIDESPREAD MVFR DECK OF STRATOCU TO 
FORM OR LOWER. RAIN SHOULD THEN DEVELOP, INITIALLY ON THE LIGHT SIDE 
WITH THE ONSHORE FLOW PRIOR TO NOON MOST TERMINALS WHICH SHOULD 
SOLIDIFY MVFR CONDITIONS. WINDS WILL ALSO START INCREASING FROM THE 
EAST AND SOUTHEAST WITH GUSTS EXCEEDING 30 KNOTS EXPECTED BY 18Z. IN 
THE KPHL 30HR TAF, WE INCREASED THE WINDS FURTHER AND LOWERED CIGS 
AND VSBYS CLOSER TO IFR CONDITIONS.

.OUTLOOK...
A PERIOD OF IFR CONDITIONS IS PROBABLE AS THE HEAVIER RAIN FROM
THE MIDWEST SYSTEM SWEEPS ACROSS THE TERMINALS LATE SATURDAY
AFTERNOON INTO SATURDAY EVENING. THERE IS ALSO A LOW CHANCE OF
THUNDERSTORMS. HIGH PRESSURE MOVES BACK IN ON SUNDAY WITH DRIER
AIR AND A RETURN TO VFR CONDITIONS. GUSTY WEST WINDS WILL OCCUR ON
SUNDAY, BUT NOT ON THE SCALE OF LATER SATURDAY. LATER MONDAY INTO
WEDNESDAY, A FRONTAL BOUNDARY IS FORECAST TO STALL NEAR OR CLOSE
TO THE TERMINAL AREA. THIS SHOULD BRING SOME MVFR CONDITIONS AT
TIMES IN ANY PRECIPITATION.

&&

.MARINE...
WE HOISTED GALE WARNINGS FOR ALL OF OUR MARINE AREAS STARTING AROUND 
16Z SATURDAY. PRIOR TO THE GALES SMALL CRAFT ADVISORY CONDITIONS ARE 
UNDERWAY AND WE KEPT THAT HEADLINE. THE SOUTHEAST WINDS, GALE FORCE 
GUSTS REACHING INTO THE LOWER 40S, SHOULD PEAK SATURDAY EVENING AND 
THEN SLOWLY DECREASE LATER SATURDAY NIGHT. SMALL CRAFT ADVISORY 
WINDS SHOULD THEN CONTINUE IN THE WESTERLY FLOW ALL AREAS INTO 
SUNDAY BEFORE FALLING BELOW CRITERIA SUNDAY NIGHT. SMALL CRAFT 
ADVISORY CONDITIONS DUE TO SEAS MIGHT PERSIST INTO SUNDAY NIGHT ON 
THE OCEAN WATERS.  

A FRONTAL BOUNDARY IS THEN FORECAST TO SETTLE OVER OR NEAR OUR AREA 
WATERS LATER MONDAY INTO WEDNESDAY. RIGHT NOW IT LOOKS AS THOUGH 
WINDS SHOULD REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA, ALTHOUGH 
SOUTHERLY SWELLS OF SMALL CRAFT ADVISORY CRITERIA GENERATED SOUTH OF 
THIS BOUNDARY MIGHT EFFECT OUR OCEAN WATERS TUESDAY INTO WEDNESDAY.

&&

.HYDROLOGY...
A FLOOD WATCH WILL NOT BE ISSUED THIS AFTERNOON.

WHILE WE FEEL A FEW ADVISORIES MIGHT NEED TO BE ISSUED TOMORROW 
EVENING FOR LOW-LYING OR POOR DRAINAGE FLOODING, THE NUISANCE TYPE, 
WE DON'T FEEL THE EXPECTED RAINS WILL GENERATE FLOODING THAT WILL BE 
A SIGNIFICANT THREAT TO LIFE OR PROPERTY.

WE THINK 0.75 TO 1.75 INCHES OF RAINFALL ACROSS THE HSA IS A SOLID 
GENERAL ESTIMATE FOR TOMORROW AND TOMORROW NIGHT. CAN'T RULE OUT 
SOME SPOTTY 2.00 INCH AMOUNTS. WE CONTINUE TO PUT THE HEAVIEST RAINS 
OVER THE SOUTHERN POCONOS, THE LEHIGH VALLEY AND NORTHWEST NJ WHERE 
HEADWATER GUIDANCE HAPPENS TO BE THE HIGHEST. WE HAVE THE LEAST 
AMOUNT OF RAIN PAINTED OVER SOUTHERN NJ. THAT ALL SAID, A FEW 
SMALLER CREEKS AND STREAMS ACROSS THE HSA COULD SEE 3/4 BANKFULL TO 
BANKFULL. 

A GOOD CHUNK OF REAL ESTATE WOULD NEED TO SEE RAINFALL IN EXCESS OF 
2.00 INCHES DURING THIS EXPECTED 12 HOUR EVENT FOR THERE TO BE ANY 
SERIES CONCERNS. WE'RE JUST NOT SEEING THAT NOW.

WE ARE NOT EXPECTING ANY OF OUR BIGGER BODIES OF WATER, WHERE GAGES 
AND FORECAST POINTS RESIDE, TO FLOOD EITHER, ALTHOUGH 3/4 BANKFULL 
COULD PUT A COUPLE AROUND CAUTION STAGE.

KEEP UP WITH THE LATEST. SUBSEQUENT QPF FORECAST COULD CHANGE THE 
NEXT 12 TO 24 HOURS CAUSING SOME WATCHES AND/OR WARNINGS TO BE 
ISSUED. DON'T BE TAKEN BY SURPRISE.

&&

.TIDES/COASTAL FLOODING...
A COASTAL FLOOD WATCH WAS ISSUED FOR THE EVENING/NIGHTTIME HIGH 
TIDE CYCLE ON SATURDAY NIGHT FOR THE ATLANTIC COAST, OUR PART OF 
RARITAN BAY, DELAWARE BAY AND TIDAL SECTIONS OF THE DELAWARE RIVER. 
THIS SYSTEM HAS SIMILARITIES IN STRENGTH AND STRUCTURE TO THE 
DECEMBER 1, 2010 EVENT IN WHICH THE HIGH TIDE DEPARTURES AVERAGED 
AROUND 2 FEET, SLIGHTLY HIGHER IN THE DELAWARE RIVER. THE HIGH 
ASTRONOMICAL TIDES ASSOCIATED WITH THE UPCOMING FULL MOON AND THE 
POORLY TIMED COINCIDENTAL HIGHER OF THE TWO DAILY ASTRONOMICAL TIDES 
HAVE INCREASED THE RISK. THE EASTERLY FLOW VEERING TO THE SOUTHEAST 
WOULD PLACE THE GREATEST RISK FOR MODERATE TIDAL FLOODING IN 
DELAWARE BAY AND TIDAL SECTIONS OF THE DELAWARE RIVER. IF THE WINDS 
VEER TO THE SOUTHEAST SOONER, THE LEAST CHANCE WOULD BE TOWARD NYC 
IN RARITAN BAY AND NORTH COASTAL NEW JERSEY. OUR LOCAL STUDY 
PROCEDURE IS FORECASTING TIDAL DEPARTURES CLOSE TO 2.0 FEET ABOVE 
NORMAL WHICH FOR MOST PLACES IS BORDERLINE BETWEEN MINOR AND 
MODERATE TIDAL FLOODING THRESHOLDS. THE EXCEPTION IS UPPER DELAWARE 
BAY WHERE WE WOULD CLEARLY BE IN THE MODERATE TIDAL FLOODING 
CATEGORY AND LIKELY ALSO THE DELAWARE RIVER. ADJUSTING THE 
MRPSSE GUIDANCE UPWARD BASED ON CURRENT ERRORS WOULD GIVE DEPARTURES 
SLIGHTLY BELOW OUR LOCAL STUDY. ON THE OTHER HAND SOME OF THE DBOFS 
AND CBOFS GUIDANCE IS MORE BULLISH WITH TIDAL FLOODING. BASED ON 
WHAT OCCURRED IN EARLY DECEMBER AND MID MARCH ALSO, AT THIS JUNCTURE 
IT LOOKS TOO ROBUST. 

THE HIGH TIDE CYCLE IN CHESAPEAKE BAY LAGS THE OCEAN BY 12 HOURS AND 
THUS THE SATURDAY EVENING HIGH TIDE CYCLE IS THE ASTRONOMICALLY 
LOWER OF THE TWO HIGH TIDE CYCLES. ONLY MINOR TIDAL FLOODING 
OCCURRED ON DECEMBER 1ST AND IT NORMALLY TAKES HISTORICALLY EVEN 
STRONGER SYSTEMS TO GET MODERATE TIDAL FLOODING ON OUR SIDE OF 
CHESAPEAKE BAY. THUS CONFIDENCE IS TOO LOW ABOUT MODERATE TIDAL 
FLOODING OCCURRING TO ISSUE A COASTAL FLOOD WATCH THERE.

THIS WILL BE A ONE TIDE CYCLE EVENT AS WINDS WILL SHIFT TO THE WEST 
BY THE TIME OF THE NEXT HIGH TIDE CYCLE. THE WINDS WILL COME CLOSE 
TO SHIFTING IN THE DELAWARE RIVER AS THE SATURDAY NIGHT HIGH TIDE 
CYCLE IS OCCURRING WHICH CERTAINLY WOULD HELP. 

AS FOR THIS TONIGHT'S HIGH TIDE CYCLE, BASED ON 
GUIDANCE/OBSERVATIONS WE SHOULD COME ABOUT HALF A FOOT SHORT OF 
MINOR TIDAL FLOODING LEVELS.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...WIND ADVISORY FROM NOON SATURDAY TO MIDNIGHT EDT SATURDAY 
     NIGHT FOR PAZ054-055-060>062-067>071.
     COASTAL FLOOD WATCH FROM SATURDAY EVENING THROUGH LATE 
     SATURDAY NIGHT FOR PAZ070-071.
NJ...WIND ADVISORY FROM NOON SATURDAY TO MIDNIGHT EDT SATURDAY 
     NIGHT FOR NJZ001-007>010-012>027.
     COASTAL FLOOD WATCH SATURDAY EVENING FOR NJZ012>014-020>027.
     COASTAL FLOOD WATCH FROM SATURDAY EVENING THROUGH LATE 
     SATURDAY NIGHT FOR NJZ016>019.
DE...WIND ADVISORY FROM NOON SATURDAY TO MIDNIGHT EDT SATURDAY 
     NIGHT FOR DEZ001>004.
     COASTAL FLOOD WATCH SATURDAY EVENING FOR DEZ002>004.
     COASTAL FLOOD WATCH FROM SATURDAY EVENING THROUGH LATE 
     SATURDAY NIGHT FOR DEZ001.
MD...WIND ADVISORY FROM NOON SATURDAY TO MIDNIGHT EDT SATURDAY 
     NIGHT FOR MDZ008-012-015-019-020.
MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT SATURDAY FOR ANZ430-431-
     450>455.
     GALE WARNING FROM NOON SATURDAY TO 6 AM EDT SUNDAY FOR 
     ANZ450>455.
     GALE WARNING FROM NOON SATURDAY TO 2 AM EDT SUNDAY FOR ANZ430-
     431.

&&

$$
SYNOPSIS...KLINE
NEAR TERM...KLINE
SHORT TERM...KLINE
LONG TERM...DELISI
AVIATION...GIGI
MARINE...GIGI
HYDROLOGY...KRUZDLO
TIDES/COASTAL FLOODING...GIGI