Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 160233 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 933 PM EST MON DEC 15 2014 .SYNOPSIS...
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HIGH PRESSURE ALONG THE EAST COAST WILL MOVE OFFSHORE OVERNIGHT. LOW PRESSURE IN THE GREAT LAKES TUESDAY WILL PUSH A WARM FRONT NORTH INTO THE MID ATLANTIC STATES, WITH SECONDARY LOW PRESSURE DEVELOPING NEAR LONG ISLAND TUESDAY NIGHT. THE COLD FRONT PASSES OFFSHORE WEDNESDAY MORNING AS THE LOWS COMBINE AND HEAD FOR THE CANADIAN MARITIMES THURSDAY. HIGH PRESSURE IN THE GREAT LAKES ASSERTS CONTROL HERE ON FRIDAY. LOW PRESSURE IN GEORGIA SATURDAY MORNING IS FORECAST TO INTENSIFY AS IT MOVES NORTHEASTWARD OFF THE MID ATLANTIC COAST SUNDAY.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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HIGH PRESSURE AT THE SURFACE IS ELONGATED FROM NEW ENGLAND TO THE EASTERN CAROLINAS THIS EVENING. THIS FEATURE WILL EASE OFFSHORE OVERNIGHT AS AN UPPER-LEVEL RIDGE ALSO SHIFTS TO OUR EAST. THE STRONG SUBSIDENCE INVERSION THAT HAS PERSISTED WHILE STILL PRESENT HAS NOW WEAKENED SOME. THIS IS EVIDENT BY COMPARING THE 00Z STERLING, VA RAOB TO THE 12Z AND EVEN YESTERDAY`S 00Z. THE LOW-LEVEL FLOW CONTINUES TO SHIFT MORE FROM THE SOUTH-SOUTHWEST AHEAD OF THE NEXT SYSTEM, AND THIS ALONG WITH SOME DRYING ERODED THE EARLIER LOW CLOUDS. SOME LOW CLOUDS THOUGH ARE STILL HOLDING ON NEAR THE POCONOS ON WESTWARD. IT APPEARS THAT MUCH OF THE AREA WILL HAVE LITTLE IN THE WAY OF CLOUDS FOR AWHILE OTHER THAN SOME HIGH CLOUDINESS, HOWEVER SOME FORECAST SOUNDINGS SHOW A LAYER BENEATH THE INVERSION MOISTENING AGAIN OVERNIGHT. THIS COULD BE ENHANCED SOME BY WAA AHEAD OF A WARM FRONT. THEREFORE, WE STILL MAINTAIN SOME INCREASE IN CLOUDS THROUGH THE OVERNIGHT HOWEVER OUR CONFIDENCE HAS DECREASED REGARDING THE EXTENT OF LOW CLOUD REDEVELOPMENT. IF THE LOW CLOUDS DO REDEVELOP ACROSS THE AREA OVERNIGHT, THEN COMBINED WITH A LIGHT DEVELOPING SOUTHEASTERLY SURFACE FLOW MAY RESULT IN PATCHY DRIZZLE. THE NORTHWEST ZONES PROBABLY HAVE THE BETTER CHC OF THIS GIVEN SOME LIGHT UPSLOPE COMPONENT. SOME FOG /FREEZING FOG/ IS ONGOING ACROSS THE HIGHER TERRAIN OF THE POCONOS, AND THEREFORE PATCHY FOG IS CARRIED ACROSS PORTIONS OF THE NORTHWEST ZONES. GIVEN LOWER CONFIDENCE REGARDING THE LOW CLOUD REDEVELOPMENT, DRIZZLE WAS NOT INCLUDED. A PATCHY FOG MENTION WAS EXPANDED THOUGH SOME ACROSS PORTIONS OF EASTERN PENNSYLVANIA, NORTHWESTERN NEW JERSEY AND INTERIOR SOUTHERN NEW JERSEY. THE HOURLY GRIDS WERE ADJUSTED BASED ON THE LATEST OBSERVATIONS, WHICH INCLUDED SHOWING COLDER TEMPERATURES IN SEVERAL PLACES SO FAR GIVEN THE LACK OF CLOUDS AND LIGHT WINDS. THE LOW TEMPERATURES NEEDED TO BE LOWERED SOME FOR SEVERAL LOCALES.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... TUESDAY IS EXPECTED TO START OUT DRY AND CLOUDY, BUT PRECIPITATION IS EXPECTED BY THE END OF THE DAY. A WARM FRONT IS EXPECTED TO LIFT ACROSS THE AREA DURING THE DAY AS AN AREA OF LOW PRESSURE LIFTS INTO THE GREAT LAKES REGION. LOW LEVEL LIFT WILL INCREASE AS THE WARM FRONT LIFTS ACROSS THE AREA AND A COLD FRONT APPROACHES FROM THE WEST. AS AN INITIAL SHORT WAVE/VORTICITY IMPULSE LIFTS ACROSS THE AREA DURING THE AFTERNOON, SHOWERS WILL SPREAD ACROSS THE AREA FROM SOUTHWEST TO NORTHEAST. PW VALUES DO APPROACH AN INCH, SO IT WOULD NOT BE SURPRISING TO SEE A FEW BRIEF HEAVIER DOWNPOURS, MAINLY FOR THE DELMARVA AND SOUTHERN NEW JERSEY. HIGHS WERE A BLEND OF MAV/MET MOS AND MOSGUIDE. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... 500 MB: A NEGATIVE TILT SHORT WAVE IN WESTERN PA TO START TUESDAY EVENING LIFTS EAST NORTHEAST AND BEGINS THE PROCESS OF PULLING A CLOSED LOW EASTWARD FROM THE GREAT LAKES REGION INTO THE MARITIMES BY THURSDAY. THEN SEVERAL SHORT WAVES NOW APPROACHING CALIFORNIA WILL HAVE REACHED THE SOUTHERN PLAINS FRIDAY MORNING. THEY WILL MOVE EAST AND OFF THE MID ATLANTIC COAST SUNDAY. THE QUESTION: AMPLITUDE... EITHER WEAKENING AS PER THE 00Z AND 12Z/15 GEFS OR WELL DEFINED AND SIGNIFICANT AS PER THE 00Z AND 12/15 ECMWF ENS. TEMPERATURES: DECEMBER THROUGH THE 14TH HAS AVERAGED NEAR NORMAL NORTHWEST FRINGE OF OUR FORECAST AREA (KRDG/KMPO) AND A BIT ABOVE NORMAL ELSEWHERE. WEDNESDAY WILL BE ABOUT 10 DEGREES ABOVE NORMAL AND THE REST OF THE LONG TERM FORECAST PERIOD THROUGH NEXT MONDAY WITHIN 4 DEGREES OF NORMAL. THERE IS POSSIBLY SOME SUBTLY COOLER AIR COMING INTO OUR AREA THURSDAY AND FRIDAY AND AGAIN NEXT SUNDAY NIGHT...MODELED BY THE ECMWF AND NOT BY THE GFS. FORECAST BASIS: IN A NUTSHELL AND UNLESS OTHERWISE NOTED WITHIN THE DAILIES. THIS FORECAST IS A 50 50 BLEND OF THE 12Z/15 MAV/MET FOR TUESDAY NIGHT-WEDNESDAY NIGHT. THE 12Z/15 MEX MOS WAS NOT USED THURSDAY... INSTEAD RELYING HEAVILY ON OUR PHI OFFICE PREVIOUS 330 AM FCST. THEREAFTER THE 1523Z/15 WPC D4-8 ELEMENTS OF DEWPOINTS/ WIND/SKY/POP/MAX-MIN TEMPS. SREF AND GEFS PROBS FOR QPF AND 12Z/15 ECMWF 2METER TEMPERATURES WERE CHECKED. THE DAILIES... CONFIDENCE: OVERALL ABOVE AVERAGE THROUGH FRIDAY THEN AVERAGE OR BELOW FOR THE WEEKEND. TUESDAY NIGHT...LEFTOVER POPS ASSTD WITH CFP AND THE EVENING NEGATIVE TILT SHORT WAVE PASSAGE (500 MB VORT MAX AND ASSOCIATED 120M 12 HR HFC VCNTY KAVP AT 06Z/17). PROBABLY DRY AFTER MIDNIGHT WITH PARTIAL CLEARING POSSIBLE. SHOWERS MAY HAVE ENDED PHILADELPHIA AREA SOUTHWESTWARD THROUGH TO CHESAPEAKE BAY AND ALL OF DELAWARE BY THE START OF THIS FORECAST TUESDAY EVENING. IT IS POSSIBLE THE VORT MAX WILL HAVE A CLUSTER OF SHOWERS PASSING THROUGH THE POCONOS JUST BEFORE MIDNIGHT. (NO SNOW EXPECTED THERE... FAR TOO WARM BELOW 6000 FEET). WE HAVE ADDED PATCHY FOG TO NORTHERN NEW JERSEY LATE AT NIGHT AND MAY NEED TO EXPAND THE COVERAGE PATCHY FOG IN FUTURE FORECASTS FOR TUESDAY NIGHT. WEDNESDAY...MAINLY DRY WITH VARIABLE CLOUDS...A BIT OF SUN AT TIMES. A SECOND SHORT WAVE PASSAGE WEDNESDAY NIGHT (100M 12 HR HFC THROUGH E PA) ASSOCIATED WITH THE EASTWARD PASSAGE OF THE CLOSED LOW ACROSS NEW YORK STATE MAY GENERATE MIDDAY SHOWERS AHEAD OF IT IN THE POCONOS (BOUNDARY LAYER STILL ON THE WARM SIDE FOR ANY SNOW) AND THEN SOME SNOW SHOWERS...ALSO OVER THE POCONOS AT NIGHT...A WEAK WINDEX EVENT. NW WIND GUST 20-25 MPH. -1C AT 850MB AROUND 18Z. THURSDAY...PARTLY SUNNY. EXCEPT POCONOS AND EXTREME NORTHWEST NJ WHERE IT SHOULD BE MOSTLY CLOUDY WITH A POSSIBILITY OF NW FLOW FLURRIES. NW WIND GUST 25-30 MPH WITH SOMEWHAT MORE UNSTABLE LAPSE RATES (850MB SLIGHTLY COLDER, AROUND -4C, FOLLOWING THE LATE WEDNESDAY NIGHT SHORT WAVE- TROUGH PASSAGE) AND SLIGHTLY STRONGER GRADIENT FLOW ASSOCIATED WITH A SOMEWHAT INVIGORATED MARITIMES LOW. 12Z/15 GFS MOS TEMPS LOOKED ABOUT 5 TO 8 DEGREES TOO WARM FOR A VARIABLY CLOUDY DAY. RAISED THE 330 AM FCST TEMPS BY 2 DEGREES BUT NO MORE THAN THAT DUE TO THE SIGNIFICANTLY COOLER 00Z/15 ECMWF 2M TEMPS. FRIDAY...PARTLY TO MOSTLY SUNNY. NW WIND GUST 20 MPH. 850MB -5C. NEXT WEEKEND...ALL DIRECTLY ASSOCIATED WITH THE INTENSITY OF THE SHORT WAVE AND SFC LOW TRACK. MARGINAL LOW LEVEL THERMAL PROFILE AOB 800MB FROM I95 SEWD (RAIN I95 SEWD AND SNOW NW OF I95 IF PCPN REACHES THAT FAR NORTH). COULD BE A NOREASTER? THE 12Z ECMWF ENSEMBLES ARE MUCH STRONGER WITH THIS SYSTEM THAN THE GEFS...FORMING A CLOSED LOW OVER PA BY SUNDAY MORNING...IN OTHER WORDS STRONGER THAN EVEN THE 12Z ECMWF OP RUN. PART OF THIS STRONGER ECMWF ENSEMBLE APPEARS TO BE RELATED TO THE 12Z/15 ECMWF CONTROL WHICH APPEARS TO BE TOO INTENSE AT ALL LEVELS. NEVERTHELESS, NEED TO MONITOR MODEL TRENDS FOR THIS POTENTIAL WINTER EVENT. WE SAW THE 12Z/15 GGEM OP RUN HAS EDGED NORTH. FOR NOW WE USED THE WPC GRIDDED GUIDANCE. MONDAY...WPC GRIDDED GUIDANCE STRAIGHT UP. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. OVERNIGHT...VFR FOR AWHILE, HOWEVER MVFR CEILINGS REMAIN WEST OF KABE AND KRDG. SOME REDEVELOPMENT OF THE MVFR CEILINGS ARE ANTICIPATED, HOWEVER OUR CONFIDENCE HAS DECREASED. SOME FURTHER DELAY OF THIS WAS INDICATED IN THE LATEST AMENDMENTS. SOME FOG SHOULD DEVELOP ESPECIALLY AROUND KABE AND KRDG AND PERHAPS KMIV. WINDS MAINLY LIGHT AND VARIABLE. TUESDAY...VFR/MVFR CEILINGS /MVFR MAY IMPROVE TO VFR FOR A TIME/, HOWEVER LOWER CLOUDS SHOULD BECOME MORE DOMINANT IN THE AFTERNOON AS A WARM FRONT LIFTS THROUGH. SHOWERS ARE EXPECTED TO ARRIVE FROM SOUTHWEST TO NORTHEAST IN THE AFTERNOON, AND THERE IS THE POTENTIAL FOR IFR CEILINGS TO DEVELOP BY LATE IN THE DAY. THE VISIBILITIES WILL BE REDUCED TO MVFR DURING HEAVIER SHOWERS. LIGHT AND VARIABLE WINDS, BECOMING SOUTHEASTERLY 5-8 KNOTS. OUTLOOK... TUESDAY NIGHT...MVFR CONDS IN SHOWERS ENDING EARLY, THEN PATCHY IFR CONDITIONS IN STRATUS/FOG IS EXPECTED. WIND LIGHT BECOMING WEST LATE. CAUSE: CLEARING ALOFT WITH LIGHT WIND IN THE SATURATED BOUNDARY LAYER. CONFIDENCE; ABOVE AVERAGE WEDNESDAY...VFR BKN CIGS AOA 3000 FT. NW WIND GUST 20-25 KT. CONFIDENCE ABOVE AVERAGE. THURSDAY...VFR SCT-BKN AOA 3500 FT. NW WIND GST 25-30 KT. CONFIDENCE ABOVE AVERAGE. FRIDAY...VFR SCT-BKN AOA 3000 FT. NW WIND G 20 KT. CONFIDENCE ABOVE AVERAGE. SATURDAY... VFR CIGS AOA 10000 FT POSSIBLY LOWERING TO MVFR OR IFR CONDITIONS AT NIGHT IN PCPN. LIGHT WIND BECOMING INCREASING NE. CONFIDENCE: AVERAGE.
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&& .MARINE... SUB-SMALL CRAFT ADVISORY CONDITIONS TONIGHT AS HIGH PRESSURE BUILDS EAST OF THE WATERS TONIGHT. SUB-SMALL CRAFT ADVISORY CONDITIONS CONTINUE INTO TUESDAY, ALTHOUGH WINDS AND SEAS INCREASE ALONG WITH SHOWERS AS A WARM FRONT LIFTS ACROSS THE AREA. OUTLOOK... TUESDAY NIGHT...SUB-ADVISORY CONDITIONS ARE EXPECTED. CONFIDENCE ABOVE AVERAGE. WEDNESDAY AND THURSDAY...WHILE SEAS ARE EXPECTED TO REMAIN GENERALLY BELOW SCA LEVELS, NORTHWEST WIND GUSTS SHOULD REACH THE SCA THRESHOLD OF 25 KNOTS AT TIMES DURING WEDNESDAY AFTERNOON THROUGH THURSDAY... POSSIBLY 30 KT. SCA EXPECTED. CONFIDENCE: ABOVE AVERAGE. FRIDAY...MOSTLY SUB-ADVISORY CONDITIONS ARE EXPECTED. SOME NORTHWEST WIND GUSTS COULD STILL BE IN THE 20 PLUS KNOT RANGE, THOUGH. CONFIDENCE: ABOVE AVERAGE. SATURDAY...SCA LIKELY AT NIGHT...POSSIBLY A GALE BUT FOR NOW SCA IS FAVORED FOR A START. CONFIDENCE: AVERAGE. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...DRAG NEAR TERM...GORSE SHORT TERM...ROBERTSON LONG TERM...DRAG AVIATION...DRAG/GORSE MARINE...DRAG/ROBERTSON

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