Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 300110 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 910 PM EDT FRI APR 29 2016 .SYNOPSIS... A WEAK SYSTEM MOVES ACROSS OUR AREA THROUGH THIS EVENING, THEN HIGH PRESSURE BUILDS DOWN FROM THE NORTH SATURDAY. LOW PRESSURE IS FORECAST TO TRACK ACROSS OUR AREA SUNDAY INTO EARLY MONDAY BEFORE SHIFTING OFFSHORE DURING MONDAY. HIGH PRESSURE MAY EXTEND INTO OUR AREA TUESDAY INTO WEDNESDAY. AS LOW PRESSURE TRACKS NORTHWARD OFFSHORE THURSDAY INTO FRIDAY, A COUPLE OF COLD FRONTS ARE FORECAST TO APPROACH OR MOVE THROUGH OUR AREA. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... FOR TONIGHT...A SHORTWV TROF NOW LOCATED APPROX OVER LAKE ERIE WILL MOVE ESE ACROSS THE AREA WITH SOME WEAK LOW-LEVEL WARM ADVECTION AND UVV AHEAD OF IT. THIS WILL RESULT IN INCREASE SHOWERS AS CAN ALREADY BE SEEN ON THE REGIONAL RADAR LOOP. INDICATIONS ARE THAT THE MOST CONCENTRATED SHOWER ACTIVITY WILL BE ACROSS THE POCONOS, LEHIGH VLY AND NORTHERN NJ. PRECIP AMOUNTS SHOULD BE SOMEWHAT HIGHER THERE ALSO ALTHOUGH PROBABLY NO MORE THAN ONE-QUARTER INCH OR SO...WITH LESSER AMOUNTS FOR PHL AND SOUTH. THE SHOWERS SHOULD TAPER OFF SHORTLY AFTER MIDNIGHT. COOLING OVERNIGHT WILL BE LIMITED BY THE CLOUD COVER AND LOWS IN THE LOW TO MID 40S ARE EXPECTED. POPS ACRSS THE SRN 2/3S OF THE REGION RMAIN QUITE LOW. WILL INTRODUCE A 20% ACRS THESE AREAS AS THERE ARE A FEW SHWRS DEVELOPING. THE MAIN ACTIVITY IS ACRS THE N, ASSOCD WITH A S/WV. OTHERWISE, JUST SOME MINOR ADJUSTMENTS TO TEMPS. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... FOR SATURDAY...WEAK HIGH PRESSURE WILL BUILD IN FROM THE NORTH AND THERE WILL ALSO BE SOME RIDGING ALOFT BEHIND THE SHRTWV TROF. A DRIER AIRMASS WILL BE IN PLACE PROVIDING CONSIDERABLY MORE SUNSHINE THAN TODAY. THUS DAYTIME HEATING WILL ALLOW FOR MILDER AFTERNOON TEMPS ON SATURDAY WITH HIGHS IN THE LOW 60S...EXCEPT COOLER NEAR THE ATLANTIC COAST SINCE WINDS WILL STILL BE COMING OFFER THE OCEAN. SOME MID TO HIGH-LEVEL CLOUDS WILL BE SPREADING IN FROM THE SW IN THE AFTERNOON AHEAD OF THE NEXT SYSTEM. HOWEVER THE ASSOCD PRECIP SHOULD NOT REACH THE AREA UNTIL AFTER DARK. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... THE SYNOPTIC PATTERN IS FORECAST TO BE COMPRISED OF A RIDGE THAT QUICKLY SLIDES ACROSS THE EAST SATURDAY NIGHT. PLENTY OF ENERGY STRETCHES FROM THE GREAT LAKES BACK INTO THE FOUR CORNERS AREA, AND THE UPPER-LEVEL FLOW ACROSS THE EAST BACKS TO MORE SOUTHWESTERLY. AS THE NORTHERN PORTION OF A TROUGH AMPLIFIES ACROSS THE GREAT LAKES SUNDAY NIGHT INTO MONDAY THEN EASTWARD DURING MONDAY, LOW PRESSURE TRACKS FROM THE PLAINS TO THE UPPER OHIO VALLEY THEN ACROSS OUR REGION. THERE LOOKS TO BE PLENTY OF MOISTURE TRANSPORT AHEAD OF AND WITH THIS FEATURE, WHICH SHOULD RESULT IN A DECENT AMOUNT OF RAINFALL FROM LATE SATURDAY NIGHT INTO MONDAY. THE TROUGH THEN LIFTS OUT THEREAFTER, HOWEVER A MORE SIGNIFICANT TROUGH IS FORECAST TO AMPLIFY INTO THE EAST WEDNESDAY AND THURSDAY. WHILE SOME INDIVIDUAL MODEL RUNS SHOW THE POTENTIAL FOR THE UPPER-LEVEL TROUGH TO CLOSE OFF FRIDAY SOMEWHERE OVER THE EASTERN STATES, THERE IS A LACK OF CONSISTENCY/AGREEMENT. THIS WOULD RESULT IN COOLER AND MORE UNSETTLED WEATHER ACROSS THE EAST. WE USED A MODEL/CONTINUITY BLEND INTO MONDAY, THEN BLENDED IN THE 12Z WPC GUIDANCE THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE FOLLOWING ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES. FOR SATURDAY NIGHT AND SUNDAY...AS AN UPPER-LEVEL RIDGE AXIS QUICKLY SHIFTS TO OUR EAST SATURDAY NIGHT, SURFACE HIGH PRESSURE ALSO EASES OFFSHORE. ON ITS HEELS IS ENERGY EJECTING OUT OF THE PLAINS WITHIN A BACKING UPPER-LEVEL FLOW. THIS WILL RESULT IN INCREASING DOWNSTREAM WAA AND MOISTURE ADVECTION ALONG WITH ISENTROPIC LIFT. AS A RESULT, WE ARE ANTICIPATING RAIN OVERSPREADING THE ENTIRE REGION BY LATE SATURDAY NIGHT WITH IT CONTINUING FOR MUCH OF SUNDAY. THE MODEL GUIDANCE SHOWS THE PW VALUES SURGING INTO THE 1.0-1.5 INCH RANGE THROUGH SUNDAY. THIS COMBINED WITH AMPLE LIFT MAY ALLOW THE RAIN TO BE MODERATE/HEAVY AT TIMES. RAINFALL AMOUNTS BY LATE SUNDAY OF AROUND AN INCH ARE POSSIBLE FOR MUCH OF THE AREA, HOWEVER THIS SHOULD FALL OVER A LONG ENOUGH PERIOD OF TIME. THE FORECAST SOUNDINGS OVERALL INDICATE A PRONOUNCED VEERING PROFILE IN THE LOWER LEVELS AS A LOW-LEVEL JET MOVES THROUGH DURING A PORTION OF SUNDAY. THE LEADING EDGE OF THE WAA SURGE AND INCREASING 850 MB FLOW COULD ALLOW THE RAIN TO RAMP UP QUICKLY TOWARD 12Z SUNDAY. DESPITE THE SHOWERY WEATHER OF LATE, THE REGION COULD USE MORE RAIN. THERE IS ALSO AT LEAST SOME INSTABILITY FORECAST SUNDAY AFTERNOON AND EVENING MAINLY SOUTH OF PHILADELPHIA. THIS WILL BE DETERMINED BY HOW FAR NORTH THE INCOMING WARM FRONT GETS. GIVEN THE FORECAST ATTM, WE KEPT A MENTION OF SOME THUNDER ACROSS THE SOUTHERN ZONES SUNDAY AFTERNOON INTO THE EVENING. THE BEST ISENTROPIC LIFT MAY START TO SHIFT TO OUR NORTHEAST BY SUNDAY AFTERNOON AND EVENING, ALLOWING THE STEADY RAIN TO END AND BECOME MORE SHOWERY. THIS OCCURS AS SURFACE LOW PRESSURE ARRIVES RIGHT OVER OUR AREA BY DAYBREAK MONDAY. FOR MONDAY AND TUESDAY...AS AN UPPER-LEVEL TROUGH AMPLIFIES ACROSS THE NORTHEAST AND MID ATLANTIC REGIONS MONDAY, SURFACE LOW PRESSURE WILL BE SHIFTING OFFSHORE. WHILE MONDAY IS LOOKING DRIER WITH TIME AS THE SURFACE LOW DEPARTS, RESIDUAL MOISTURE AND LIFT WITH THE INCOMING TROUGH SHOULD PRODUCE SHOWERS ESPECIALLY THE FIRST HALF OF THE DAY. IT APPEARS THE WARM SECTOR IS IN OUR SOUTHERN AREAS MONDAY BEFORE THE SURFACE LOW SHIFTS OFFSHORE. WHILE SOME THUNDER CANNOT BE RULED OUT WITHIN THE WARM SECTOR, THE SURFACE LOW IS FORECAST TO EXIT TO THE EAST DURING THE FIRST PART OF MONDAY. GIVEN LESS CERTAINTY FOR SOME THUNDER MONDAY, WE OPTED TO NOT INCLUDE A MENTION. ANY LEFTOVER SHOWERS SHOULD END EARLY MONDAY NIGHT AS THE TROUGH AXIS SHIFTS OFFSHORE AND THE LOW-LEVEL FLOW TURNS MORE FROM THE NORTH AND NORTHWEST. A WEAK AREA OF HIGH PRESSURE MAY THEN EXTEND INTO OUR AREA FROM THE WEST TUESDAY. FOR WEDNESDAY THROUGH FRIDAY...AN UPPER-LEVEL TROUGH IS FORECAST TO AMPLIFY INTO THE EAST DURING THIS TIME FRAME. AS THIS STARTS TO OCCUR, A FRONTAL BOUNDARY TO OUR SOUTH AND EAST MAY HAVE A WAVE OF LOW PRESSURE RUNNING UP THE FRONT. THIS COULD AT LEAST BRUSH OUR EASTERN AND SOUTHERN ZONES WEDNESDAY, HOWEVER THERE IS LOW CONFIDENCE WITH THIS. AS THE MAIN TROUGH TO OUR WEST ARRIVES THURSDAY, A SURFACE COLD FRONT WILL ALSO ARRIVE AND MOVE THROUGH. THE WAA AHEAD OF THE FRONT SHOULD ALLOW FOR WARMER TEMPERATURES WEDNESDAY AND THURSDAY BEFORE SOME COOLING TAKES PLACE ON FRIDAY. THE COOLING ON FRIDAY MAY ALSO BE ACCOMPANIED BY A SECONDARY COLD FRONT APPROACHING. THE SETUP FOR THURSDAY INTO FRIDAY COULD BE MORE UNSETTLED AS ENERGY OFF THE COAST ALONG AN OLD FRONT MAY ALLOW FOR A STRENGTHENING SURFACE LOW. THIS FEATURE, DEPENDING ON ITS TRACK AND ALSO STRENGTH/POSITION OF THE UPPER-LEVEL TROUGH, COULD ENHANCE PRECIPITATION OVER OUR AREA THURSDAY INTO FRIDAY ALONG WITH AN INCOMING COLD FRONT FROM THE WEST. GIVEN THE UNCERTAINTY ON THE SYNOPTIC EVOLUTION AND ASSOCIATED DETAILS, WE KEPT POPS NO HIGH THAN CHC. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,KMIV, KACY AND SURROUNDING AREAS. LTST TAF FCST IS MORE OPTIMISTIC THAN PREV. STILL HOLDING ONTO MVFR THRU THE NIGHT. IFR CAN NOT BE RULED OUT, BUT CONFIDENCE IS LOW. NOT CURRENTLY FCSTING IFR ATTM, EXCEPT AT KMIV. VSBY SHOULD NOT BE TOO MUCH OF AN ISSUE ALTHOUGH COULD BE TEMPORARILY REDUCED IN SHOWERS THIS EVENING. CONDITIONS WILL IMPROVE TO VFR SAT MORNING AND CONTINUE THROUGH THE DAY. WINDS WILL REMAIN LIGHT OVERALL. OUTLOOK... SATURDAY NIGHT THROUGH MONDAY...THE CONDITIONS LOWER TO MVFR/IFR SATURDAY NIGHT AND SUNDAY WITH PERIODS OF RAIN, THEN IMPROVE LATER MONDAY WITH SOME SHOWERS STILL EXPECTED DURING MONDAY. A FEW THUNDERSTORMS ARE POSSIBLE SUNDAY AFTERNOON AND EVENING, MAINLY SOUTH OF KPHL. EAST OR SOUTHEAST WINDS 10 KNOTS OR LESS. TUESDAY AND WEDNESDAY...VFR OVERALL AS WEAK HIGH PRESSURE ARRIVES. && .MARINE... NORTHEAST WIND WITH A FAIRLY LONG FETCH IS BLOWING INTO THE NJ COASTAL WATERS. THIS RESULTS IN BUILDING SEAS WHICH HAVE REACHED 5 TO 6 FEET AT BUOYS 44009...91 AND 65. HIGHER SEAS ARE EXPECTED TO CONTINUE THROUGH TONIGHT HENCE A SCA FOR HAZ SEAS HAS BEEN EXTENDED UNTIL 600 AM SAT. THIS SCA MAY NEED TO BE EXTENDED FURTHER INTO THE DAY ON SAT. OUTLOOK... SATURDAY NIGHT THROUGH MONDAY...NORTHEAST WINDS MAY BRIEFLY GUST TO 25 KNOTS ACROSS MAINLY THE NORTHERN ATLANTIC COASTAL WATERS SUNDAY AHEAD OF LOW PRESSURE. WHILE SEAS SHOULD BE MOSTLY IN THE 2-4 FOOT RANGE, TIMES OF 5 FOOTERS ARE POSSIBLE ON THE ATLANTIC COASTAL WATERS. TUESDAY AND WEDNESDAY...THE WINDS SHOULD BE BELOW SMALL CRAFT ADVISORY CRITERIA, HOWEVER SEAS COULD BUILD TO 5 ABOUT FEET DURING WEDNESDAY ON THE ATLANTIC COASTAL WATERS. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 AM EDT SATURDAY FOR ANZ450>455. && $$ SYNOPSIS...GORSE NEAR TERM...AMC/NIERENBERG SHORT TERM...AMC LONG TERM...GORSE AVIATION...AMC/GORSE/NIERENBERG MARINE...AMC/GORSE

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