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