Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 031415 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 915 AM EST WED FEB 3 2016 .SYNOPSIS... STRONG LOW PRESSURE WILL TRACK NORTHEASTWARD TODAY THROUGH THE GREAT LAKES AND INTO EASTERN CANADA AS ITS ASSOCIATED WARM FRONT LIFTS NORTH THROUGH OUR AREA. A COLD FRONT WILL THEN CROSS OUR REGION LATE TONIGHT AND LINGER ALONG THE COAST THROUGH THURSDAY. LOW PRESSURE WILL DEVELOP ON THE FRONT OFF THE MID ATLANTIC COAST THURSDAY NIGHT AND DEPART FRIDAY. HIGH PRESSURE WILL GRADUALLY BUILD INTO OUR AREA FROM THE SOUTHWEST LATE FRIDAY AND SATURDAY. A COLD FRONT FROM THE NORTHWEST IS FORECAST TO CROSS THE AREA SUNDAY, FOLLOWED BY ANOTHER LOW PRESSURE SYSTEM AFFECTING THE REGION EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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KEPT THIS SIMPLE SINCE WE`VE BEEN TALKING ABOUT IT FOR SEVERAL DAYS. ITS ONLY A MATTER OF TIMING FOR MODERATE TO HEAVY RAINFALL AS A CORRIDOR OF MUCH ABOVE NORMAL MOISTURE FOR FEBRUARY, PRECEDES A SLOW MOVING COLD FRONT INTO EASTERN PENNSYLVANIA LATE TODAY. AHEAD OF IT, A GUSTY SOUTHERLY FLOW OF 25 TO 35 MPH WILL DEVELOP OVER THE DELMARVA UP TO I-95 THIS AFTERNOON, WHIPPING NEAR RECORD WARMTH INTO THE REGION. MEANWHILE THE RIPE SNOWPACK IN EASTERN PA AND CENTRAL-NNJ WILL BE RAINED ON AND AS DEWPOINTS APPROACH 50...DENSE FOG SHOULD FORM THIS AFTERNOON SINCE WINDS THERE WILL BE LIGHTER OUT OF THE SOUTH. THE REGION EAST OF I-95 MAY NOT SEE ANY RAIN UNTIL MIDDAY OR THIS AFTERNOON. THUNDER POSSIBLE LATE TODAY DELMARVA. THE HYDRO SECTION HAS MUCH MORE ON REASONING AND THE RELATIVELY HIGH PROBABILITY OF MINOR TO MODERATE SMALL STREAM FLOODING. FOR THE MID-MORNING UPDATE, SLOWED THE PRECIP DOWN A BIT, AS IT IS STILL MAINLY CONFINED TO CNTRL PA, BUT THE OVERALL FCST RATIONAL HAS NOT CHANGED.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... RAIN WILL STILL BE FALLING IN OUR REGION THIS EVENING AND PROBABLY HEAVY AT TIMES NEAR AND EAST OF I-95 EARLY IN THE NIGHT. HOW THIS GOES TONIGHT STILL HAS UNCERTAINTY...THE UKMET STILL ROBUST. RAIN DIMINISHES SUBSEQUENT TO THE WIND SHIFT TO WEST AND NORTHWEST. DENSE FOG MAY DEVELOP IN THE FRONTAL ZONE. RIGHT NOW I HAVE AREAS OF FOG MAINLY OVER THE REMAINING SNOW PACK OF EASTERN PA AND NORTHERN NJ BUT WE MAY NEED TO EXPAND THAT TO THE COASTS AND DELMARVA IN LATER FORECASTS. AGAIN...THE UKMET AND ECMWF ARE BLENDED IN WITH THE THINKING FOR TONIGHT. && .LONG TERM /THURSDAY THROUGH TUESDAY/... WHILE THE BULK OF HEAVIER RAIN WILL HAVE ENDED BY THURSDAY MORNING ACROSS THE FORECAST AREA WITH THE COLD FRONT HAVING PUSHED OFFSHORE, THE POTENTIAL FOR SOME LINGERING LIGHTER RAIN DOES EXIST FOR EASTERN PARTS OF THE CWA AS THE COLD FRONT LINGERS NEARBY TO THE EAST. AS NOTED BY THE PREVIOUS SHIFT, THE SOUTHWESTERLY MID LEVEL FLOW WILL SLOW THE PROGRESS OF THE FRONT AND THE ASSOCIATED CLEARING BEHIND IT. BUT AS THE DAY WEARS ON, THE FRONTAL BOUNDARY WILL DRIFT A LITTLE FARTHER OUT TO SEA WITH ANY LINGERING LIGHT RAIN MOSTLY ENDING INTO MIDDAY/EARLY AFTERNOON. TEMPERATURE-WISE, THURSDAY IS STILL EXPECTED TO BE A RELATIVELY MILD DAY WITH THE MID LEVEL TROUGH AXIS STILL OFF TO OUR WEST DURING THE DAYTIME, AS HIGH TEMPERATURES REACH MOSTLY THE UPPER 40S AND LOWER 50S ACROSS OUR AREA. A COLDER AIRMASS BEGINS TO RETURN ACROSS THE AREA INTO THURSDAY NIGHT, AND TO COMPLICATE MATTERS, THE UKMET AND SREF ARE INDICATING THE POTENTIAL FOR SOME ACCUMULATING SNOW LATE THURSDAY NIGHT ACROSS EASTERN PORTIONS OF NJ AND PERHAPS INTO SOUTHERN DE AS AN AREA OF LOW PRESSURE DEVELOPS ALONG THE STILL LINGERING OFFSHORE COLD FRONT BOUNDARY. POPS HAVE BEEN INCREASED INTO THE 40 TO 50 PERCENT RANGE TO REFLECT THIS POTENTIAL. THE LOW PRESSURE AND THE LINGERING FRONT ARE THEN FORECAST TO DEPART OUT TO SEA INTO FRIDAY MORNING. THE RETURN OF COLDER, MORE SEASONAL FEBRUARY-LIKE TEMPERATURES WILL NOT BE FAR BEHIND AS THE MID LEVEL TROUGH AXIS PASSES TO OUR EAST FRIDAY MORNING. MAINLY QUIET CONDITIONS AND AMPLE SUNSHINE ARE ANTICIPATED FOR THE BULK OF FRIDAY AS HIGH PRESSURE TO THE SOUTHWEST GRADUALLY BUILDS OVER THE MID ATLANTIC REGION. WITH NORTHWEST WINDS AROUND 10 TO 15MPH, DAYTIME HIGHS ON FRIDAY SHOULD MAX OUT MOSTLY IN THE LOWER 40S, WITH SOME MID/UPPER 30S FOR OUR NORTHERN ZONES. SIMILAR CONDITIONS ARE ANTICIPATED SATURDAY FOR THE REGION, BUT WITH MILDER DAYTIME TEMPERATURES AND SOME CLOUDS ADVANCING IN FROM THE WEST AS THE AREA OF HIGH PRESSURE ADVANCES EAST AND OFFSHORE. BY SUNDAY, A COLD FRONT MAY APPROACH OUR REGION FROM THE NORTHWEST, BUT WITH LIMITED MOISTURE ASSOCIATED WITH THIS BOUNDARY, WE HAVE KEPT A DRY FORECAST FOR SUNDAY, WITH DAYTIME HIGHS REACHING MAINLY IN THE 40S, EXCEPT FOR SOME MID/UPPER 30S INTO THE SOUTHERN POCONOS. OF NOTE, THE GFS AND ECMWF CONTINUE TO DEVELOP AN AREA OF LOW PRESSURE OFF THE SOUTHEASTERN SEABOARD SUNDAY, TAKING IT OUT TO SEA SUNDAY NIGHT, WITH LITTLE OR NO IMPACT FOR OUR REGION. THROUGH THE REMAINDER OF THE LONG TERM PERIOD, THERE IS MORE MODEL SPREAD WITH REGARDS TO A POSSIBLE LOW PRESSURE SYSTEM PASSING ACROSS THE GREAT LAKES MONDAY AND ANOTHER AREA OF LOW PRESSURE POSSIBLY DEVELOPING OFF THE EAST COAST TUESDAY. WHILE THE TIMING OF PRECIPITATION ACROSS OUR REGION REMAINS A LOW CONFIDENCE FORECAST AT THIS TIME, THE OVERALL PATTERN AND A BROAD LONGWAVE TROUGH OVER THE GREAT LAKES TO NORTHEAST AND MID ATLANTIC SUGGESTS A COLDER TREND INTO EARLY NEXT WEEK, AND WE GENERALLY FOLLOWED SUPERBLEND AND/OR WPC GUIDANCE WITH REGARDS TO TEMPS AND POPS AT THIS EXTENDED TIME RANGE. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...IFR CONDS HAVE NOW MOVED INTO KABE AND KRDG. THE REST OF THE AREA REMAINS VFR. THE OVERALL TREND IS DOWNWARD. HOWEVER, THE ONSET OF STEADIER PRECIP IS A BIT SLOWER, SO ITS PSBL THAT ARPTS FURTHER E MAY BE A BIT SLOWER GOING DOWN AND STAYING DOWN, THOUGH THERE STILL COULD BE SOME UP AND DOWN OVER THE NEXT FEW HOURS. ITS PSBL THE CURRENT TAF IS A BIT TOO PESSIMISTIC, ESPECIALLY IN THE ERLY AFTN, BUT NEED TO SEE HOW FAST THE PRECIP MOVES IN. ONCE THE PRECIP MOVES IN, IT WILL BE HVY AT TIMES THRU LATE AFTN AND EVE, SO IFR AND EVEN LIFR CAN BE EXPECTED. TONIGHT....IFR CONDS IN RAIN FOG SLOWLY IMPROVES FROM WEST TO EAST, ESPECIALLY AFTER 06Z/4. SOUTH-SOUTHWEST WIND DIMINISHES EARLY AND THEN SHIFTS TO NORTHWEST. OUTLOOK... THURSDAY...CONDITIONS IMPROVING BACK TO VFR FOR MUCH OF THE REGION, EXCEPT SOME LINGERING LOWER MVFR IN LIGHT RAIN POSSIBLE FOR THE SOUTHEAST SITES, INCLUDING KACY/KMIV. FRIDAY THROUGH SUNDAY...MAINLY VFR CONDITIONS.
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&& .MARINE... SCA CONTINUES AS POSTED...REMAINING IN EFFECT UNTIL MIDNIGHT ON DELAWARE BAY. A SMALL CRAFT ADVISORY WILL REMAIN IN EFFECT FOR OUR OCEAN WATERS FOR THE ENTIRE NIGHT. SEAS INCREASE ON THE ATLC WATERS TO BETWEEN 7 AND 9 FEET LATE TODAY AND TONIGHT. A FEW SOUTHERLY GUSTS TO 35 KT ARE POSSIBLE THIS AFTERNOON BUT THIS MAY BE BE HANDLED WITH AN SMW. SMALL CHC OF A TSTM DE WATERS LATE TODAY. OUTLOOK... THURSDAY...A SMALL CRAFT ADVISORY WILL CONTINUE THROUGH THE DAYTIME THURSDAY FOR THE ATLANTIC COASTAL WATERS DUE TO WAVE HEIGHTS STILL RUNNING IN THE 5 FOOT RANGE. FRIDAY...BREEZY NORTHWEST WINDS ARE EXPECTED, AND GUSTS TO AROUND 25 KNOTS MAY OCCUR LEADING TO MARGINAL SCA CONDITIONS. SATURDAY AND SUNDAY...WINDS AND SEAS LOOK TO REMAIN BELOW ADVISORY CRITERIA FOR THE MOST PART, BUT THERE IS SOME POTENTIAL FOR OFFSHORE LOW PRESSURE TO PASS EAST OF OUR WATERS ON SUNDAY, WHICH COULD ENHANCE SEAS AND WIND GUSTS. && .HYDROLOGY... **THE RISK FOR EXTENSIVE MINOR TO MODERATE FLOODING APPEARS TO BE INCREASING** WE`VE UPDATED THE FFA AT 550 AM WITH ANOTHER GO AT COUNTY INFORMATION. THE UPSTREAM TROUGH AND ASSOCIATED RIDGE AHEAD OF IT ARE LIKELY TO SLOW THE FRONTAL PASSAGE ACROSS OUR AREA PERMITTING A LONGER DURATION IN 4 TO 5 SD ABOVE NORMAL PWAT OF 1.4" OR GREATER. THIS PLUS DIFFLUENT 1000-500 THICKNESS AND WEAK LOW PRESSURE ALONG THE FRONT CROSSING THE DELMARVA IN THE WARMEST SECTOR OF THE FRONT ACROSS OUR AREA SHOULD ENHANCE LOW LVL CONVERGENCE AND ASSOCIATED RFALL. MODELS ARE SLOWING AND THE DEPARTURE OF THE RAIN TONIGHT. ADDITIONALLY...PROBABILITIES OF 1 INCH OF RAIN BY BOTH THE SREF AND GEFS ARE EXPANDING AND MERGING TO COVER VIRTUALLY ALL OF THE FORECAST AREA. THE UKMET FOR 3 CONSECUTIVE CYCLES HAS FORECAST 1+ INCHES ALONG THE I95 CORRIDOR. SO THERE WILL STILL BE CORRIDOR OF .75 INCH BY 12Z THURSDAY WHICH WILL BE LESSEN POTENTIAL FLOODING IMPACT WHILE OTHER AREAS WILL SEE 1.5 INCHES. THIS COMBINED WITH THE MELTING OF THE 1-2" SWE IN THE SNOWPACK NEAR I-78 SHOULD RESULT IN CONSIDERABLE POOR DRAINAGE FLOODING LATE TODAY AND TONIGHT WITH NUMEROUS CREEKS AND STREAMS RESPONDING TO BANKFULL OR EXCEEDING FLOOD STAGE TONIGHT AND THURSDAY WITH SOME OF THE FLOODING LINGERING INTO FRIDAY. THOSE LIVING NEAR SMALL STREAMS THAT TEND TO EASILY FLOOD SHOULD BE PREPARED FOR ANOTHER FLOOD EPISODE. ADDITIONALLY FROZEN GROUND AND RUNOFF MAY FORCE BASEMENT FLOODING IN AREAS OF POOR DRAINAGE, ESPECIALLY IN THE VULNERABLE COUNTIES NEAR THE I-78 CORRIDOR. IMPACTS...THE THREAT OF MINOR TO MODERATE RIVER FLOODING APPEARS TO HAVE INCREASED FOR THE PASSAIC AND RARITAN BASINS IN NJ AND AM THINKING THIS ALSO INCLUDES SCHUYLKILL BASIN IN PA. ADJACENT BASINS (TO THOSE MENTIONED ABOVE) IN NJ AND ACROSS SOUTHEAST PA, SHOULD ALSO PLAN FOR SOME FLOODING AND KEEP UP WITH THE LATEST FORECASTS IN CASE. FORECAST...WHEN THURSDAY ROLLS AROUND, IT APPEARS MUCH IF NOT ALL THE SNOW THAT IS ON THE GROUND ACROSS THE HSA WILL HAVE MELTED. THE SNOW HAS REALLY RIPENED THE LAST 24 HOURS AND IS READY TO GO. THIS SNOWMELT COMBINED WITH 0.75 TO 1.5 INCHES OF RAIN EXPECTED LATER TODAY AND TONIGHT IS GOING TO RESULT IN FLOODING FOR SOME OF THESE RIVER BASINS. WE WILL PROVIDE A LISTING AROUND 5 AM. THE THREAT OF FLOODING WILL BE TWO-FOLD. FIRST THIS AFTERNOON AND EARLY TONIGHT, AND THEN LATER TONIGHT THROUGH THURSDAY. THE FIRST THREAT WILL INCLUDE LOW-LYING, POOR DRAINAGE, STREET, AND SMALL CREEK FLOODING. THIS WILL HAVE AN IMPACT ON THIS EVENINGS COMMUTE FROM THE I95 CORRIDOR WESTWARD THROUGH EASTERN PA AND EASTERN MD. THE THREAT STEMS FROM RAPIDLY MELTING SNOW, PERIODS OF HEAVY RAIN, FROZEN GROUND, AND POSSIBLY CLOGGED OR RESTRICTED STORM DRAINS. THE SECOND THREAT STEMS FROM THE RUNOFF FLOWING FROM THE TRIBUTARIES INTO THE LARGER RIVERS. IT`S AT THIS TIME, TONIGHT THROUGH THURSDAY, WHERE WE SHOULD SEE AS MANY AS A DOZEN RIVER FORECAST POINTS EXCEED FLOOD STAGE WITH SEVERAL HAVING A GOOD CHANCE GOING TO MODERATE. SNOW WATER EQUIVALENT, OR SWE, IS HIGHEST RIGHT ALONG THE I78 CORRIDOR AND LOCATIONS JUST TO THE NORTH AND SOUTH. GENERALLY, SWE VALUES ARE RUNNING BETWEEN 1 AND 2.0 INCHES HERE. COMBINE THIS WITH THE EXPECTED RAINFALL, THIS AREA COULD HAVE TO DEAL WITH OVER 3.00 INCHES OF POTENTIAL RUNOFF. HEADLINES...THE FLOOD WATCH CONTINUES AS UPDATED YESTERDAY. THE WATCH IS FROM MIDDAY TODAY THROUGH THURSDAY AFTERNOON COVERING BOTH OF THE POTENTIAL FLOOD THREATS MENTIONED ABOVE. PREPARE FOR AREAS OF LOWLAND AND SMALL STREAM FLOODING INCLUDING DETOURS BECAUSE OF CLOSED ROADS NEAR SOME OF THE FLOODED STREAMS AND RIVERS AND POOR DRAINAGE AREAS. OUR FORECAST AREA BREAKDOWN...UPPER EASTERN SHORE OF MARYLAND (KENT, QUEEN ANNE`S, TALBOT AND CAROLINE)...SOME NUISANCE FLOODING IS LIKELY THIS AFTERNOON AND EARLY TONIGHT. THE FLOOD WATCH INCLUDES CECIL COUNTY WHERE BOTH THE HEAVIER RAIN IS EXPECTED AND REMAINING SWE IS HIGHEST. DELAWARE...NUISANCE FLOODING IS LIKELY LATE TODAY AND TONIGHT, ESPECIALLY IN NEW CASTLE COUNTY WHERE BOTH THE RAIN IS EXPECTED AND REMAINING SWE IS HIGHEST. SMALL CREEKS AND STREAMS WILL LIKELY APPROACH OR EXCEED BANKFULL, ESPECIALLY ACROSS NORTHERN NEW CASTLE. NEW JERSEY...NUISANCE FLOODING WILL LIKELY OCCUR THIS AFTERNOON INTO TONIGHT ACROSS THE WATCH AREA. A NUMBER OF SMALL CREEKS AND STREAMS WILL APPROACH OR EXCEED BANKFULL IN CENTRAL AND NORTHERN NEW JERSEY. IN ADDITION, THERE IS A THREAT OF RIVER FLOODING TONIGHT INTO THURSDAY. THIS THREAT LIES FROM NEAR TRENTON NORTHEASTWARD WHICH INCLUDES PORTIONS OF THE PASSAIC AND RARITAN BASINS. NO FLOODING IS EXPECTED ALONG THE DELAWARE. PENNSYLVANIA...NUISANCE FLOODING WILL OCCUR, MAINLY THIS AFTERNOON AND EVENING ACROSS THE WATCH AREA. SMALLER CREEKS AND STREAMS SUCH AS THE NESHAMINY, PERKIOMEN, BRANDYWINE, AND CHESTER WILL LIKELY EXCEED FLOOD STAGE. IN ADDITION, THERE IS A THREAT OF RIVER FLOODING TONIGHT INTO THURSDAY. THIS THREAT LIES ACROSS THE SCHUYLKILL BASIN. NO FLOODING IS EXPECTED ALONG THE DELAWARE. && .TIDES/COASTAL FLOODING... TIDAL FLOODING IS POSSIBLE AT THE TIMES OF HIGH TIDE MONDAY AND TUESDAY OF NEXT WEEK ALONG THE ATLANTIC COASTS OF NEW JERSEY AND DELAWARE, DEPENDING ON THE TIMING OF NORTHWARD DEVELOPMENT OF A POTENTIALLY STRONG COASTAL STORM. && .CLIMATE... LISTED BELOW ARE THE RECORD HIGH TEMPERATURES AND RECORD RAINFALL FOR TODAY. WE CONTINUE TO FORECAST TEMPS WITHIN 3F OF RECORD THIS AFTERNOON AT ALL SITES EXCEPT KRDG AND KABE. ALSO...IT APPEARS THERE IS A SOMEWHAT BETTER CHANCE OF A RECORD BREAKING DAILY RAINFALL AT ONE OF THE 8 CLIMATE SITES...BEST CHC BEING KILG OR KABE. THIS BECAUSE THE FRONTAL BOUNDARY AND FAVORABLE UPPER AIR PATTERN AND ASSOCIATED CAUSATIVE SHORT WAVE ARE SLOWING DOWN....PERMITTING A LONGER DURATION IN THE PWAT AXIS OF GREATER THAN 1.4 INCHES (4-5 SD ABOVE NORMAL FOR THIS TIME OF YEAR). RECORD MAX RECORD RAIN PERIOD OF RECORD ---------- ----------- ---------------- ACY...66-2006 1.61-1880 1874 PHL...62-2006 1.64-1939 1872 ILG...64-1991 1.40-1939 1894 ABE...63-1991 1.37-1982 1922 TTN...62-2006 1.57-1939 1865 GED...68-2006 1.47-1973 1948 RDG...63-1991 1.40-1939 1869 MPO...52-1973 2.19-1983 1901 && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR PAZ060-061-070-071- 101>106. NJ...FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR NJZ009-010-012-013- 015>019. DE...FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR DEZ001. MD...FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR MDZ008. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST THURSDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR ANZ430-431.
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&& $$ SYNOPSIS...DRAG/KLINE NEAR TERM...DRAG/NIERENBERG SHORT TERM...DRAG LONG TERM...KLINE AVIATION...DRAG/KLINE/NIERENBERG MARINE...DRAG/KLINE HYDROLOGY... TIDES/COASTAL FLOODING... CLIMATE...

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