Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 200736 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 336 AM EDT MON OCT 20 2014 .SYNOPSIS... A HIGH PRESSURE SYSTEM NEAR NORFOLK WILL MOVE OFFSHORE TODAY. A LOW PRESSURE SYSTEM WITH AN ASSOCIATED COLD FRONT OVER LAKE SUPERIOR WILL DIVE SOUTHEAST REACHING OUR REGION DURING THE DAY ON TUESDAY. ANOTHER LOW PRESSURE SYSTEM WILL FORM OFF THE MID ATLANTIC COAST LINE ON TUESDAY AND THEN DRIFT SLOWLY NORTHEAST, REACHING CAPE COD ON THURSDAY AND NOVA SCOTIA ON FRIDAY. HIGH PRESSURE WILL THEN BRIEFLY MOVE IN FROM THE WEST LATE FRIDAY. A COLD FRONT SHOULD PASS THROUGH THE NORTHEAST AROUND SATURDAY NIGHT, WITH ANOTHER HIGH PRESSURE SYSTEM REACHING THE GREAT LAKES ON SUNDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... THE FROST ADVISORY AND FREEZE WARNING REMAINS IN EFFECT FOR EARLY THIS MORNING, AS MANY AREAS ARE WELL DOWN INTO THE 30S. THE HIGH LEVEL CLOUDS THOUGH MAY HAVE SLOWED THE TEMPERATURE DROP A LITTLE FOR SOME SPOTS. HIGH PRESSURE WILL BE SHIFTING OFFSHORE TODAY ALLOWING A SOUTHWESTERLY FLOW AT THE SURFACE TO DEVELOP. THIS FLOW WILL BE MUCH LESS COMPARED TO THE GUSTINESS THAT WAS OBSERVED YESTERDAY. A ROBUST SHORT WAVE DIVING SOUTHEASTWARD FROM THE MIDWEST WILL HELP CARVE OUT ANOTHER UPPER-LEVEL TROUGH ACROSS THE GREAT LAKES AND OHIO VALLEY DURING THE COURSE OF TODAY. DOWNSTREAM FROM THIS, SOME WEAK WAA IS FORECAST TO OCCUR ACROSS THE MID ATLANTIC. THIS COMBINED WITH THE PRESENCE OF AN UPPER-LEVEL JET WILL SPREAD AREAS OF MID AND HIGH LEVEL CLOUDINESS ACROSS THE REGION. THE MAIN LIFT ASSOCIATED WITH THE AMPLIFYING UPPER-LEVEL TROUGH IS FORECAST TO REMAIN TO OUR WEST, THEREFORE WE MAINTAINED A DRY FORECAST TODAY. WE DID CARRY SOME ADDITIONAL CLOUDINESS THOUGH FOR MANY AREAS. AS FOR HIGH TEMPERATURES, WE USED A MODEL/MOS BLEND WHICH RESULTS IN MILDER TEMPERATURES COMPARED TO YESTERDAY. THIS LINES UP WITH THE WEAK WAA THAT IS ALSO FORECAST THROUGH THE DAY ALONG WITH A SOUTHWESTERLY SURFACE FLOW. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... AN UPPER-LEVEL TROUGH WILL CONTINUE TO AMPLIFY ACROSS THE GREAT LAKES AND NORTHEAST. AS THIS OCCURS, LOW PRESSURE ORGANIZING AT THE SURFACE IS FORECAST TO BE IN THE GENERAL VICINITY OF THE EASTERN GREAT LAKES LATER TONIGHT. THERE IS SOME WAA BEING MAINTAINED AHEAD OF THIS SYSTEM, BUT OVERALL THE BEST FOCUS FOR THIS IS FORECAST TO BE TO OUR SOUTH AND EAST. IN ADDITION, A DECENT SHOT OF LOW-LEVEL THETA-E ADVECTION IS FORECAST TO ARRIVE THROUGH THE NIGHT. AS THE ATMOSPHERE MOISTENS AND THE LARGE SCALE ASCENT BEGINS TO OVERSPREAD THE REGION LATE, SOME SHOWERS COULD DEVELOP. THIS LOOKS TO BE ACROSS OUR WESTERN ZONES WHICH IS WHERE WE HAVE THE HIGHEST /CHC/ POPS LATE. THERE MAY ALSO BE ANOTHER AREA OF FOCUS, WHICH IS OFFSHORE WHERE THE LEADING EDGE OF THE STRONGER THETA-E ADVECTION INTERACTS WITH SOME INSTABILITY PARTIALLY DUE TO THE GULF STREAM. OVERALL, THE CLOUDS ARE FORECAST TO LOWER SOME THROUGH THE NIGHT FROM WEST TO EAST AND THE POPS WERE GRADUALLY INCREASED AS WELL. AS FOR LOW TEMPERATURES, WITH THE THICKENING CLOUDS AND A WEAK SOUTHWESTERLY FLOW IN PLACE IT WILL BE A MILDER NIGHT. OVERALL, WE USED A MOS BLEND WITH SOME MINOR ADJUSTMENTS. && .LONG TERM /TUESDAY THROUGH SUNDAY/... TUESDAY THROUGH THURSDAY NIGHT: A COASTAL LOW PRESSURE SYSTEM WILL DEVELOP OFFSHORE AND BE SLOW TO MOVE NORTHEAST THROUGHOUT THIS PERIOD. THE END RESULT WILL BE GRAY GLOOMY COOLER DAYS FEATURING RAIN SHOWERS AND SOME BRISK NORTHWESTERLY WINDS WEDNESDAY AND THURSDAY AFTERNOONS. THE FORMATION OF THIS LOW PRESSURE WILL START WITH TWO PIECES, A STRONG UPPER LEVEL LOW AND COLD FRONT DIVING FROM THE GREAT LAKES INTO THE MID-ATLANTIC AND A LOW PRESSURE FORMING OFF THE CAROLINA`S. THE UPPER LOW AND COLD FRONTAL BOUNDARY WILL LEAD TO CONTINUED SCATTERED SHOWERS ON TUESDAY TO THE REGION WITH A MOISTURE PLUME FROM THE CAROLINA LOW WELL OFFSHORE. BY TUESDAY NIGHT WE BEGIN TO SEE MORE INTERACTION BETWEEN THE FEATURES, PHASING. A PHASED LOW FORMS OFF THE SOUTHERN NEW ENGLAND COASTLINE BY WEDNESDAY WITH THE MAJORITY OF ATLANTIC MOISTURE BROUGHT INTO SOUTHERN NEW ENGLAND. TO COMPARE OUR REGION WOULD BE FAVORED FOR JUST SOME WRAP AROUND SHOWERS. OVERALL THE OPERATIONAL MODELS HAVE COME INTO BETTER CONSENSUS TODAY THAT THE ABOVE OUTCOME WILL OCCUR. THIS IS REFLECTED IN BOTH THE 00Z ECMWF ENSEMBLE MEAN COMPARED TO THE OPERATIONAL RUN AND THE 06Z GEFS. WITH THAT BEING SAID, CONFIDENCE CONTINUES TO INCREASE THAT THIS PERIOD WILL BE DOMINATED BY SOME SCATTERED SHOWERS LASTING THROUGH THURSDAY. AREAS FURTHER NORTHEAST CLOSER TO THE LOW STAND THE BEST CHANCE TO SEE THE MOST IN TERMS OF SHOWER ACTIVITY. TIMING DIFFERENCES ON THE SHOWERS ARE STILL PRESENT LEAVING SOME UNCERTAINTY WITH POPS, KEPT AT HIGH CHANCE TO LOW END LIKELY. TOTAL RAINFALL WILL BE UNDER ONE INCH FOR THIS EVENT. THE 12Z ECMWF AND NAM FROM TODAY DO INDICATE THE POTENTIAL FOR SOME HEAVIER SHOWERS ACROSS THE NORTH TUESDAY NIGHT INTO WEDNESDAY AS THE MID-LEVEL ENERGY BEGINS TO TRANSFER TO THE COAST, THIS WILL NEED TO BE WATCHED AS NEW DATA COMES IN. WITH PLENTY OF CLOUDS, LOW TEMPERATURES WILL STAY UP AT NIGHT CLOSE TO 50 FOR MOST OF US WHILE HIGHS STRUGGLE TOWARD 60, COOLER NW. NOT MUCH SPREAD IN THE MODELS AND THERE ENSEMBLES/ STATISTICAL GUIDANCE ON TEMPERATURES, WENT ON THE WARMER END EACH NIGHT AND THE COOLER END DURING EACH DAY. IN TERMS OF TIDES IT LOOKS AS THOUGH THE WIND DIRECTION WILL NOT CREATE DEPARTURES HIGH ENOUGH FOR MINOR COASTAL FLOODING OR CREATE LOW ENOUGH DEPARTURES FOR BLOWOUT TIDES ATTM. FRIDAY: LOW PRESSURE SYSTEM FINALLY DEPARTS WITH HIGH PRESSURE BUILDING BACK IN. THIS ALLOWS FOR CLEARING FROM SOUTH TO NORTH AND THE FIRST DRY DAY IN A WHILE. TEMPERATURES ARE FORECASTED TO BE CLOSER TO MEX GUIDANCE AND THE 12Z ECMWF MODELED TWO METER TEMPERATURES. CONTINUED NORTHWEST WINDS WITH THE BEST CHANCE OF MIXING TO LEAD TO SOME AFTERNOON WIND GUSTS AROUND 20 MPH. FRIDAY NIGHT THROUGH SUNDAY: DURING D+6 AND D+7, THE NEGATIVE NAO/POSITIVE PNA PATTERN OF THE PAST TWO WEEKS IS PROJECTED TO REVERSE. THIS TREND IS UNDERWAY, AND IS EVIDENT IN LESS HIGH- LATITUDE BLOCKING. THE MAIN MID-LEVEL FEATURES IN THIS TIMEFRAME ARE A CLOSED LOW LIFTING INTO THE CANADIAN MARITIMES ON SATURDAY, FOLLOWED BY A SHORT-WAVE MOVING THROUGH A MORE ZONAL FLOW ON SUNDAY. THERE IS MODEL DISAGREEMENT WITH THESE FEATURES, AS THE GFS EJECTS THE CLOSED LOW SLOWER THAN THE ECMWF, RESULTING IN A DELAYED RETURN TO A MORE ZONAL FLOW. THIS FURTHER RESULTS IN THE GFS MOVING THE SHORTWAVE FURTHER NORTHEAST, WHILE THE ECMWF TAKES IT MUCH FURTHER TO THE SOUTH OVER NEW ENGLAND. SOME OF THE GFS ENSEMBLE MEMBERS ALSO SUPPORT THE ECMWF SOLUTION. GIVEN THE GFS INITIALIZED MORE ROBUST WITH THE LEAD SHORT-WAVE /LOCATED OVER NORTHERN SASKATCHEWAN AS OF THIS WRITING/ THAT RESULTS IN THE CUT- OFF LOW, AND PREVIOUS GFS RUNS WERE MORE IN LINE WITH THE ECMWF, FEEL THE GFS SOLUTION IS UNREALISTIC. THE ECMWF SOLUTION IS ALSO MORE REPRESENTATIVE OF THE PROJECTED LACK OF HIGH-LATITUDE BLOCKING. OR SATURDAY, SHORT-WAVE RIDGING ALOFT WILL ALLOW HIGH PRESSURE TO BUILD IN FROM THE WEST, WITH TEMPS AT 850 HPA SUPPORTING HIGH TEMPERATURES AT SEASONABLE LEVELS. A COLD FRONT IS PROJECTED TO MOVE THROUGH THE REGION SOMETIME IN THE LATE SATURDAY INTO EARLY SUNDAY TIMEFRAME. AT THIS TIME, THE ECMWF INDICATES THE BEST DYNAMICS SITUATED TO THE NORTH AND LIMITED MOISTURE, BUT IT IS TOO FAR OUT TO SPECULATE ON PRECIP CHANCES. IF THE TIMING OF THE FRONT HOLDS, PROJECTED 850 HPA TEMPS WOULD SUPPORT BELOW NORMAL HIGHS ON SUNDAY. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...VFR, WITH A CEILING AT TIMES MAINLY AT OR ABOVE 15000 FEET. LIGHT AND VARIABLE WINDS, BECOMING SOUTHWESTERLY AND INCREASING TO AROUND 10 KNOTS. TONIGHT...VFR, WITH A CEILING LOWERING TO BETWEEN 5000-8000 FEET. SOME SHOWERS MAY APPROACH KABE AND KRDG TOWARD DAYBREAK. SOUTH-SOUTHWEST WINDS DIMINISHING TO 5 KNOTS, AND EVEN BECOMING LIGHT AND VARIABLE AT SOME TERMINALS. OUTLOOK... TUESDAY...SOME RESTRICTIONS TO MVFR WITH SCATTERED SHOWERS. TUESDAY NIGHT THROUGH THURSDAY... SOME MVFR RESTRICTIONS WITH SCATTERED SHOWERS. NORTH TO NORTHWEST WINDS WEDNESDAY AFTERNOON THROUGH THURSDAY FROM 10-15 KNOTS WITH HIGHER GUSTS. THURSDAY NIGHT AND FRIDAY: VFR, NORTHWEST WIND GUSTS FRIDAY AFTERNOON FROM 15-20 KNOTS. && .MARINE... TODAY AND TONIGHT...THE CONDITIONS ARE EXPECTED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA. HIGH PRESSURE SHIFTS TO THE EAST ALLOWING A SOUTH-SOUTHWEST FLOW TO DEVELOP. THIS WILL BE ON THE LIGHTER SIDE FOR MUCH OF TODAY, HOWEVER IS IS FORECAST TO INCREASE SOME LATER TODAY AND TONIGHT FOR A TIME. THE OVERALL BOUNDARY LAYER FLOW SHOULD BE LIGHT ENOUGH THOUGH TO KEEP THE WINDS BELOW 25 KNOTS. THE SEAS ARE ANTICIPATED TO BE AT OR BELOW 4 FEET. OUTLOOK... TUESDAY THROUGH WEDNESDAY: SEAS AND WINDS BELOW SCA CRITERIA BUT INCREASING WEDNESDAY WITH THE DEVELOPMENT OF A LOW PRESSURE TO OUR NORTHEAST. WEDNESDAY NIGHT THROUGH FRIDAY: OVERALL THINKING IS THAT WAVEWATCH IS UNDERDONE BY ABOUT A FOOT ON THE SEAS. SEAS WILL LIKELY BE AT OR OVER FIVE FEET THROUGH MOST OF THIS PERIOD WITH SOME DECREASE IN THE SEAS FRIDAY. NORTHWEST WIND GUSTS OVER 25 KNOTS ARE ALSO POSSIBLE EACH AFTERNOON. SCA POSSIBLE FOR MOST OF THIS TIMEFRAME. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...FREEZE WARNING UNTIL 8 AM EDT THIS MORNING FOR PAZ054-055-061- 062. FROST ADVISORY UNTIL 8 AM EDT THIS MORNING FOR PAZ060-101>106. NJ...FREEZE WARNING UNTIL 8 AM EDT THIS MORNING FOR NJZ001-007>010. FREEZE WARNING UNTIL 8 AM EDT THIS MORNING FOR NJZ020>022-027. FROST ADVISORY UNTIL 8 AM EDT THIS MORNING FOR NJZ012-013- 015>019-023. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GIGI NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...FRANCK/GAINES AVIATION...GAINES/GORSE MARINE...GAINES/GORSE

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