Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 170048 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 748 PM EST TUE DEC 16 2014 .SYNOPSIS... LOW PRESSURE IN THE GREAT LAKES WILL PUSH A WARM FRONT NORTH INTO THE MID ATLANTIC STATES THIS EVENING, WITH SECONDARY LOW PRESSURE FORMING NEAR LONG ISLAND BY MIDNIGHT. THE COLD FRONT PASSES OFFSHORE WEDNESDAY MORNING AS THE LOWS COMBINE AND ARRIVE OVER THE CANADIAN MARITIMES THURSDAY. HIGH PRESSURE IN THE GREAT LAKES ASSERTS CONTROL HERE LATER ON FRIDAY. LOW PRESSURE IN GEORGIA SATURDAY IS FORECAST TO INTENSIFY AS IT MOVES NORTHEASTWARD OFF THE MID ATLANTIC COAST SUNDAY. WEAK HIGH PRESSURE FOLLOWS MONDAY BEFORE A STRONG LOW PRESSURE SYSTEM DEVELOPS OVER THE MISSISSIPPI VALLEY NEXT TUESDAY. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... THE WATER VAPOR IMAGERY THIS EVENING SHOWS A CLOSED LOW LIFTING NORTHEASTWARD FROM THE UPPER OHIO VALLEY. THIS FEATURE WILL CONTINUE TO TRACK NORTHEASTWARD THROUGH TONIGHT WHILE TAKING ON A NEGATIVE TILT. THE LARGE SCALE LIFT HAS BEEN FOCUSED IN A NARROWING RIBBON OF SHOWERS NOW PRESSING OFFSHORE. THERE ARE SOME OTHER SHOWERS FARTHER WEST BUT THESE ARE TENDING TO BE SCATTERED OR IN SMALL CLUSTERS. ANOTHER AREA OF SHOWERS IN CENTRAL PENNSYLVANIA IS WITH THE CLOSED LOW, HOWEVER THESE MAY TEND TO WEAKEN SOME AS THEY LIFT EAST- NORTHEASTWARD AS FORCING WEAKENS A LITTLE. AS A RESULT, THE POPS WERE ADJUSTED BASED ON RADAR TRENDS. OTHERWISE, LOW PRESSURE WILL TRACK TO OUR NORTHWEST AND A SECONDARY LOW IS FORECAST TO DEVELOP OFFSHORE OVERNIGHT. THE ASSOCIATED COLD FRONT WILL EVENTUALLY ARRIVE LATE. UNTIL THE COLD FRONT ARRIVES, A DECENT AMOUNT OF LOW-LEVEL MOISTURE IS FORECAST TO REMAIN IN PLACE AND DESPITE THE WINDS SHIFTING EVENTUALLY TO THE SOUTHWEST AND WEST, IT MAY TAKE QUITE A BIT OF TIME FOR THE CLOUDS TO THIN. WE SHOULD ALSO HAVE SOME FOG AROUND, ALTHOUGH WE HAVE LESS CONFIDENCE REGARDING DENSE FOG DEVELOPMENT. THE HOURLY GRIDS WERE ADJUSTED BASED ON THE LATEST OBSERVATIONS, AND THE LAMP/LAV GUIDANCE WAS BLENDED IN THROUGH THIS EVENING. OVERALL, NO MAJOR CHANGES WERE MADE OTHER THAN TO THE POPS. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... LOW PRESSURE WILL CONTINUE TO LIFT TO OUR NORTHEAST AND STRENGTHEN AS IT MOVES INTO THE GULF OF MAINE DURING THE DAY. THIS WILL LEAD TO A STRONG NORTHWEST FLOW ACROSS THE AREA DURING THE DAY, WITH GUSTS OF AT LEAST 20-25 MPH, WITH SOME GUSTS AROUND 30 MPH POSSIBLE. SKIES WILL LIKELY REMAIN PARTLY TO MOSTLY CLOUDY MOST OF THE DAY ACROSS MUCH OF THE AREA. IT IS ALSO POSSIBLE THAT THERE MAY BE ENOUGH MOISTURE AND LOW-LEVEL LIFT THAT A FEW ISOLATED SHOWERS MAY AFFECT OUR FAR NORTHERN COUNTIES. IF ANY SHOWERS DID OCCUR, RIGHT NOW THEY ARE EXPECTED TO BE MOSTLY RAIN, EXCEPT ACROSS THE POCONOS WHERE THERE COULD BE SOME SNOW SHOWERS LATER IN THE DAY. HIGHS WERE A BLEND OF MAV/MET MOS AND MOSGUIDE WHICH WERE IN PRETTY GOOD AGREEMENT. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... 500 MB (JETSTREAM): LOW PRESSURE OVER EASTERN NYS WILL MOVE TO THE MARITIMES THURSDAY. A TROUGH OF SEVERAL SHORT WAVES CURRENTLY APPROACHING CALIFORNIA REACHES THE SOUTHERN PLAINS FRIDAY MORNING AND SLIDES OFF THE MID ATLANTIC COAST SUNDAY. A HIGH AMPLITUDE TROUGH SHOULD BE ORGANIZING OVER THE MISSISSIPPI VALLEY NEXT TUESDAY. TEMPERATURES: CALENDAR DAY AVERAGES ABOUT 5 DEGREES ABOVE NORMAL THURSDAY, THEN 2 TO 5 DEGREES ABOVE NORMAL EACH DAY FROM FRIDAY THROUGH NEXT TUESDAY. THE OPERATIONAL ECMWF APPEARS TO HAVE BEEN BIASED TOO COOL IN PREVIOUS FORECASTS AND AM DISCARDING MUCH OF THE COLD BIAS...LEANING MORE HEAVILY ON THE 12Z/16 GFS. FORECAST BASIS: IN A NUTSHELL AND UNLESS OTHERWISE NOTED WITHIN THE DAILIES. THIS FORECAST IS A 50 50 BLEND OF THE 12Z/16 MAV/MET FOR WEDNESDAY NIGHT-THURSDAY NIGHT. USED THE WARMER OF THE NCEP TEMPERATURE GUIDANCE, ESPECIALLY AT NIGHT. THURSDAYS TEMPS MIGHT BE 2-3 DEGREES WARMER THAN CURRENTLY FCST. THE 12Z/16 MEX MOS WAS APPLIED FRIDAY AND FRIDAY NIGHT (BLENDED LOWER WITH THE PRIOR PHI FCST BUT IT APPEARS PRIOR ECMWF 2M TEMPERATURES HAVE BEEN FORECAST TOO LOW FOR THURSDAY- FRIDAY. 1522Z/16 WPC D4-8 ELEMENTS OF DEWPOINTS/WIND/SKY/POP/ MAX-MIN TEMPS WERE USED. HAVE BLENDED THE WPC DAYTIME MAX`S WARMER USING THE 12Z/16 GFS ON ALL DAYS THURSDAY - SUNDAY. SREF AND GEFS PROBS FOR QPF AND 12Z/16 ECMWF 2METER TEMPERATURES WERE CHECKED FOR THIS FORECAST BUT NOT DIRECTLY APPLIED. THE GEFS POPS APPEAR TOO CONSERVATIVE FOR SATURDAY NIGHT- SUNDAY MORNING WHEN COMPARED TO THE AMPLITUDE OF THE SHORT WAVE TROUGH CROSSING THE MID ATLANTIC COAST SUNDAY MORNING. THE DAILIES... WEDNESDAY NIGHT...LOW PRESSURE ALOFT DEPARTING EASTWARD FROM NYS HAS A LEFTOVER FINAL SHORT WAVE DEPICTED AT 500MB OF ABOUT A 90M 12 HR HFC CROSSING E PA WHICH SHOULD SET OFF SOME SNOW SHOWERS OR FLURRIES UP NORTH OF I80. OTHERWISE...PARTLY CLOUDY. W-NW WIND GUST 20-25 KT AT TIMES. THURSDAY - FRIDAY...DRYING TREND CONTINUES WITH ZONAL-ISH FLOW ALOFT FORMING BY FRIDAY AND NOT MUCH MOISTURE TO WORK WITH. GREAT LAKES SNOW SHOWERS MAY LEAK DOWN INTO THE POCONOS BOTH DAYS WHERE CONSIDERABLE CLOUDINESS EXISTS. OTHERWISE PARTLY CLOUDY TO CLEAR AND COOLER WITH 18Z 850 TEMPS ABOUT 4C COLDER (NEAR -6C) THAN THOSE VALUES OF 18Z WED (NEAR -2C). NW WINDS GUST 20-25 MPH THURSDAY AND NEAR 20 MPH FRIDAY. SATURDAY - SUNDAY...ONE LAST DAY, OR AT LEAST HALF DAY, OF TRANQUILITY ON SATURDAY BEFORE EAST COAST LOW PRESSURE NEARS FROM THE SOUTH- SOUTHWEST. DEPENDING ON THE QUICKNESS AND POSITION OF THE NORTHERN STREAM ENERGY, HELPING TO DEVELOP GULF COAST SURFACE INFLECTION, DICTATES HOW FAST PRECIPITATION OVERSPREADS FROM THE SOUTH LATER ON SATURDAY. IT IS STILL TOO EARLY TO GO INTO TOO MUCH DEPTH WITH THIS SYSTEM GIVEN THE AMOUNT OF SPREAD THAT WE ARE STILL SEEING. ONE THING THAT IS INDICATED TO WPC AND MYSELF IS ABOVE AVERAGE CONFIDENCE FOR PRECIPITATION TO SPREAD INTO OUR AREA SATURDAY NIGHT. THERMAL PROFILES LOOK MARGINAL FOR MUCH IF ANY SNOW SE OF I95... MAYBE A MIX IN THE 195 CORRIDOR AND COLD ENOUGH FOR SNOW NW OF I95. THE VORT MAX LOOKS PRETTY STRONG...EVEN WITH THE GEFS 50 METER SPREAD IN 500MB HEIGHTS OVER NJ 12Z SUNDAY. MONDAY...VARIABLE SOLUTIONS FROM MOSTLY SUNNY AND NICE TO LOTS OF LEFTOVER CLOUDS AS A WEAK RIDGE OF HIGH PRESSURE FROM DIXIE EDGES NORTHEAST OVER AREA. AM CONCERNED THERE WILL BE ALOT MORE LOW CLOUDINESS BELOW A POSSIBLE INVERSION, THAN CURRENTLY ADVERTISED. TUESDAY...CLOUDINESS BECOMING DOMINANT AND CHANCE OF SHOWERS AS THE MISSISSIPPI VALLEY TROUGH DEVELOPS EASTWARD. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TONIGHT...MVFR/IFR WITH AREAS OF LIFR CEILINGS CONTINUE, HOWEVER SOME IMPROVEMENT IS EXPECTED LATE AS THE FLOW TURNS TO THE SOUTHWEST AND WEST. OUR CONFIDENCE IS ON THE LOW SIDE REGARDING THE TIMING OF THE IMPROVEMENT. SOME SHOWERS ESPECIALLY NEAR AND EAST OF THE KPHL AREA, WILL BE AROUND BEFORE TAPERING OFF LATE. THE VISIBILITIES WILL BE REDUCED DUE TO THE SHOWERS AND ALSO SOME FOG. SOUTHEASTERLY WINDS AROUND 5 KNOTS, BECOMING LIGHT/VARIABLE OR SOUTHWEST THEN WEST-NORTHWEST LATE. WEDNESDAY...ANY MVFR OR LOWER CONDITIONS EARLY ARE EXPECTED TO IMPROVE TO VFR. WEST-NORTHWEST WINDS INCREASING TO 10-15 KNOTS WITH GUSTS TO 20-25 KNOTS. OUTLOOK... WEDNESDAY NIGHT...VFR SCT CLOUDS AOA 4000 FT EXCEPT POSSIBLE MVFR CONDS OVER THE POCONOS IN SCATTERED SNOW SHOWERS. NW WIND GUST 20-25 KT AT TIMES. CONFIDENCE: ABOVE AVERAGE. THURSDAY AND FRIDAY...VFR SCT-BKN AOA 3500 FT EXCEPT POSSIBLE MVFR CONDS IN SNOW SHOWERS OVER THE POCONOS. NORTHWEST WINDS SUSTAINED 10-15KT WITH GUSTS NEAR 25KT. CONFIDENCE: ABOVE AVERAGE. SATURDAY...VFR CIRRUS AND LIGHT WIND TO START THEN CIGS NEAR 3000 FT POSSIBLE LATE DAY OR NIGHT AS THE WIND TURNS NE AND PCPN DEVELOPS AT NIGHT. CONFIDENCE: ONLY AVERAGE BECAUSE OF THE UNCERTAIN TIMING OF LOWERING CIGS AND ALSO PTYPE UNCERTAINTY. SUNDAY...MVFR OR BRIEF IFR CONDS IN MORNING SNOW/RAIN THEN IMPROVING CONDITIONS DURING MIDDAY. NORTH OR NORTHEAST WIND BECOMING NORTHWEST. CONFIDENCE: ABOVE AVERAGE ON PCPN BUT BELOW AVERAGE ON PRECIPITATION TYPE AND TIMING THE IMPROVING CONDITIONS.
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&& .MARINE... SUB-SMALL CRAFT ADVISORY CONDITIONS EXPECTED ACROSS THE WATERS TONIGHT AS A WARM FRONT BEGINS TO LIFT ACROSS THE AREA. SOUTHEAST WINDS EARLY WILL BECOME VARIABLE AS AN AREA OF LOW PRESSURE DEVELOPS ALONG THE FRONT OVERNIGHT, BEFORE BECOMING WEST TO NORTHWEST BY DAYBREAK WEDNESDAY AS THE LOW MOVES TO OUR NORTHEAST. A SMALL CRAFT ADVISORY IS NOW IN EFFECT STARTING WEDNESDAY MORNING AS WINDS ARE EXPECTED TO INCREASE TO 25-30 KNOTS AS THE LOW STRENGTHENS AS IT MOVES INTO THE GULF OF MAINE. OUTLOOK... WEDNESDAY NIGHT 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 WEDNESDAY NIGHT THROUGH THURSDAY OR THURSDAY EVENING...POSSIBLY 30 KT. SCA IS POSTED EXCEPT FOR DE BAY WHERE UNCERTAINTY EXISTS ON MAX GUSTS. I RAISED WW3 ATLANTIC SEAS BY 1 FOOT 00Z THU-18Z THU. CONFIDENCE: ABOVE AVERAGE FOR THE SCA SCENARIO. 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...MODEL TRENDS SINCE YESTERDAY ARE LOWER ON THE EXPECTED WINDS. EITHER NO HAZARD OR POSSIBLE SCA. CONFIDENCE: AVERAGE. SUNDAY...SCA MAY DEVELOP IN THE WAKE OF THE DEPARTING COASTAL LOW. CONFIDENCE: AVERAGE. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY FROM 7 AM WEDNESDAY TO 5 PM EST THURSDAY FOR ANZ450>455. SMALL CRAFT ADVISORY FROM 7 AM TO 6 PM EST WEDNESDAY FOR ANZ430-431. && $$ SYNOPSIS...DRAG NEAR TERM...GORSE SHORT TERM...ROBERTSON LONG TERM...DRAG AVIATION...DRAG/GORSE MARINE...DRAG/ROBERTSON

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