Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 310126 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 926 PM EDT SUN AUG 30 2015 .SYNOPSIS... A WEAKENING COLD FRONT WILL ARRIVE TONIGHT, OTHERWISE HIGH PRESSURE WILL REMAIN CENTERED MAINLY NEAR THE MID ATLANTIC REGION THROUGH MUCH OF THIS WEEK. A WEAK COLD FRONT SHOULD SLIDE SOUTH THROUGH OUR REGION THURSDAY NIGHT OR FRIDAY. THEREAFTER, HIGH PRESSURE WILL RESIDE ALONG THE EASTERN NEW ENGLAND COAST THROUGH SUNDAY, PROBABLY PROVIDING A LITTLE RELIEF FROM THE HEAT THIS COMING WEEKEND. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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A SHORT WAVE TROUGH WILL ARRIVE INTO THE NORTHEAST TONIGHT AND AS IT DOES IT SHOULD TEND TO WEAKEN. A WEAK COLD FRONT AT THE SURFACE IS TIED TO THIS FEATURE, AND WITH SOME INCREASE IN MOISTURE AN ISOLATED SHOWER OR STORM COULD CONTINUE INTO THE OVERNIGHT. THE OVERALL LIFT, SHEAR AND INSTABILITY LOOKS WEAK ENOUGH TO KEEP ANY CONVECTIVE CORES FROM GETTING TO ROBUST. THE INITIATION EARLY ON APPEARED TO BE DRIVEN BY TERRAIN IN NORTHEASTERN PENNSYLVANIA, AND VISIBLE SATELLITE IMAGERY THIS AFTERNOON SHOWS THE MAIN CUMULUS DEVELOPMENT MAINLY OVER THE HIGHER TERRAIN. THE FLOW BELOW ABOUT 10000 FEET IS 15 KNOTS OR LESS. WE THEREFORE KEPT LOW POPS POPS GOING INTO THE OVERNIGHT, NORTH AND WEST OF PHILADELPHIA. CLOUDS WILL ALTERNATE BETWEEN PARTLY AND MOSTLY CLOUDY OVERNIGHT. IT WILL BE A WARMER NIGHT ACROSS MUCH OF THE AREA AS THE DEW POINTS TEND TO HANG NEAR THE MUGGY LEVEL. A MOS BLEND WAS USED FOR THE LOW TEMPERATURES. HOWEVER WITH CLOUD COVER THE TEMPERATURES WERE SLOW TO FALL IN SPOTS AND LOWS HAVE ADJUSTED UPWARD A FEW DEGREES IN SPOTS WITH THE 9:30 PM UPDATE.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... AN UPPER-LEVEL TROUGH IS FORECAST TO AMPLIFY SOME ACROSS NEW ENGLAND ON MONDAY. THE SOUTHWESTERN EXTENT OF THIS FEATURE REACHES INTO THE MID ATLANTIC REGION. THIS PROVIDES SOME CYCLONIC FLOW ALOFT, WHILE AT THE SURFACE WEAK HIGH PRESSURE GENERALLY REMAINS NEARBY. A WEAK SURFACE FRONT OR TROUGH LOOKS TO BE DRAPED ACROSS OUR AREA, AND WHILE A SHOWER OR THUNDERSTORM CANNOT BE RULED OUT THIS IS OF LOW CONFIDENCE. THE MODEL GUIDANCE OVERALL DOES NOT HAVE A STRONG SIGNAL FOR CONVECTIVE DEVELOPMENT, AND SINCE THE CHC LOOKS RATHER LOW WE OPTED TO LEAVE OUT ANY MENTION ATTM. IT IS POSSIBLE A FEW ISOLATED CELLS ARE AROUND TO START THE DAY AS SOME FORECAST SOUNDINGS DO SHOW SOME INCREASE IN MID LEVEL INSTABILITY AROUND DAYBREAK. OTHERWISE, A DECENT AMOUNT OF MID TO HIGH LEVEL CLOUDS SHOULD BE AROUND WHICH WILL COMBINE WITH SOME CUMULUS DEVELOPMENT. A RATHER WARM TO HOT AFTERNOON IS EXPECTED GIVEN THE SOUTHWESTERLY FLOW AND ANY NOTABLE COOLING ALOFT IS MOSTLY ACROSS NEW ENGLAND. AS A RESULT, WE LEANED CLOSER TO THE WARMER GFS MOS FOR MOST PLACES REGARDING HIGH TEMPERATURES. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... 500 MB: IN GENERAL, A FAIRLY STRONG SUMMER RIDGE OF HIGH PRESSURE WILL PREVAIL ALONG THE EAST COAST THROUGH NEXT SUNDAY WITH ONLY A MINOR WEAKENING OF THIS RIDGE OVER OUR AREA LATE WEDNESDAY INTO FRIDAY, AS A STRONG SHORT WAVE DIVES SEWD TOWARD THE MARITIMES (55N/55W). THAT PERMITS A LITTLE MORE NORTHERLY COMPONENT ALOFT LATE THIS COMING WORKWEEK AND SO AN ASSOCIATED SURFACE BOUNDARY SLIPS SOUTHWARD. ITS COOLING EFFECTIVENESS FELT PRIMARILY ON THE COASTAL PLAIN. TEMPERATURES: AUGUST THROUGH THE 29TH WAS AVERAGING NEAR OR ABOVE NORMAL. KMPO AND KGED WERE THE ONLY TWO OF THE 8 CLIMATE SITES BELOW NORMAL. KTTN KACY AND KPHL WERE AVERAGING ~1 TO ~2F ABOVE NORMAL AND WILL WARM THESE LAST TWO DAYS OF THE MONTH. CALENDAR DAY DEPARTURES TUESDAY THROUGH THURSDAY WILL BE 6 TO 12 DEGREES ABOVE NORMAL WITH THE LARGEST POSITIVE DEPARTURES N AND NW OF KPHL OVER E PA AND THE NORTHWEST HALF OF NJ. THEREAFTER, FRIDAY THROUGH SUNDAY SHOULD STILL AVERAGE 5 DEGREES OR MORE ABOVE NORMAL, POSSIBLY STILL 10 DEGREES ABOVE, ESPECIALLY NW OF I-95. HOW MUCH COOLING OCCURS FRIDAY AND BEYOND IS DEPENDENT ON THE STRENGTH OF ONSHORE FLOW. IT APPEARS THE GREATEST IMPACT OF COOLING ONSHORE FLOW WILL BE THE SOUTHERN NJ AND DE COASTS. SST`S ARE WELL ABOVE AVERAGE SO THE COOLING EFFECTIVENESS IS LESS. FORECAST BASIS: UNLESS OTHERWISE NOTED, 12Z/30 GFS MOS WAS THE PRIMARY GUIDANCE MONDAY NIGHT-TUESDAY NIGHT, 12Z/30 MEX MOS WEDNESDAY THROUGH THURSDAY, THEN THE 1521Z/30 WPC GRIDDED ELEMENTS OF MAX/MIN TEMP, 12 HOUR POP, 6 HOUR DEWPOINT- SKY-WIND FROM THURSDAY NIGHT ONWARD. THE EXCEPTION HERE...WAS MEX AND WPC MIN TEMPS WERE BLENDED 50 50 FRI NIGHT AND SAT NIGHT. HAZARDS... A HEAT WAVE WILL BE IN PROGRESS THROUGH THURSDAY FOR THE I-95 CORRIDOR EASTWARD TO NEAR THE COASTS, ITS DURATION SHOULD BE AT LEAST 4 DAYS WHETHER OR NOT IT BEGINS THIS AFTERNOON OR MONDAY. THE QUESTION, DOES IT BREAK ANYTIME FRIDAY-SUNDAY OR JUST GO ON AND ON THROUGH EARLY NEXT WEEK IN THE INTERIOR NEAR AND NW OF I-95. IT IS POSSIBLE THE I-95 CORRIDOR COULD SEE AN EXTENDED HEAT WAVE BEYOND 6 DAYS (TODAY-SUNDAY THROUGH THURSDAY LOOK SOLID FOR 90-95F AND FRIDAY LOOKS LIKE A BETTER THAN EVEN CHANCE OF 90 PLUS). MAX HEAT INDEX VALUES IN THIS HEAT WAVE SO FAR ARE FORECAST TO BE IN THE MID TO UPPER 90S. THERE IS A SLIM CHANCE WE WILL NEED A HEAT ADVISORY FOR THE URBAN CORRIDOR EITHER OF ANY THREE AFTERNOONS BETWEEN THIS COMING WEDNESDAY AND FRIDAY. THUNDERSTORM DRENCHING RAINS? NEAR THE COOL FRONT FRIDAY BUT OVERALL AS PER WPC, THE DRY SPELL IS GOING TO LAST QUITE AWHILE, POSSIBLY THROUGH THE START OF LABOR DAY WEEK. THE DAILIES... MONDAY NIGHT-THURSDAY...FAIR AND HOT AFTERNOONS WITH PATCHY FOG POSSIBLE LATE AT NIGHT OVER THE COUNTRYSIDE, MAINLY NW NJ AND E PA. LIGHT WINDS TEND TO BE W-NW DURING EACH AFTERNOON. SMALL CHC OF CONVECTION E PA AND NNJ WED AFTN AND THU AFTN PER INSTABILITY INDICATORS INCLUDING KI. THU NIGHT-FRIDAY...A SWD MOVING COLD FRONT MAY SPAWN HEAVY SOUTHWARD MOVING CONVECTION BUT ONLY IN A PWAT OF 1.6 INCHES. SLOW MOVERS- GULLY WASHERS WHERE THEY OCCUR BUT LITTLE PREDICTABILITY ATTM EXCEPT MOST OF THE ACTIVITY SHOULD REMAIN JUST INLAND. POTENTIALLY STILL 90F VCNTY KPHL SWWD AND WESTWARD ON FRIDAY. DEWPOINTS HIGHER, AROUND 70F AND 1400J ML CAPE. 0-6KM BULK SHEAR IS POOR FOR ANY SVR. STRATUS FOG POTENTIAL AT NIGHT AND IN THE MORNING, ESPECIALLY I-80 NORTHWARD. NEXT WEEKEND...FAIR AND VERY WARM. SLIGHT CHANCE FOR AFTN/EVENING CONVECTION POCONOS TO THE LEHIGH VALLEY AND KRDG PER ECMWF KI AND A TENDENCY FOR UPSLOPE FLOW-LIFT. OVERALL CONFIDENCE THESE NEXT 6 DAYS: ABOVE AVERAGE. && .AVIATION /01Z MONDAY THROUGH FRIDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDITIONS OVERNIGHT THROUGH MONDAY. SOUTHWEST WINDS SHOULD REMAIN AROUND 5 KNOTS OVERNIGHT. ANY SHOWERS LOOK TO REMAIN AWAY FROM THE TAF SITES ATTM. THE MAIN CONCERN OVERNIGHT WILL BE FOR SOME VERY PATCHY FOG TOWARD SUNRISE, IT LOOKS TOO PATCHY FOR TAF INCLUSION ATTM. PERIODS OF CLOUDS AROUND 20,000 FEET WILL CONTINUE TO MOVE NORTHWARD THROUGH THE REGION THROUGHOUT THE TAF PERIOD AND MAY BE COMPLEMENTED WITH SOME CUMULUS AROUND 5,000 FEET. WIND GUSTS MONDAY AFTERNOON MAY APPROACH 20 KNOTS IN SOME SPOTS AS WELL, MODERATE CONFIDENCE WITH THE GUSTS. OUTLOOK... MONDAY NIGHT THROUGH WEDNESDAY...VFR CONDITIONS EXPECTED THOUGH LOCALIZED MVFR/IFR CONDITIONS WITH FOG/ST POSSIBLE EACH MORNING, MAINLY NEAR KABE- KRDG. LIGHT WIND, TENDS BE NW EACH AFTERNOON. THURSDAY...MOSTLY VFR CONDITIONS. ISOLATED THUNDERSTORMS POSSIBLE LATE. IFR CIGS/VSBY POSSIBLE N OF I-80 LATE THU NIGHT. FRIDAY...MOSTLY VFR WITH BRIEF IFR CONDS POSSIBLE IN TSTMS. MVFR OR IFR CIGS DEVELOPING IN NELY FLOW NEAR AND N OF I-80 WITH POSSIBLE IFR VSBY IN FOG AT NIGHT. OVERALL LONG TERM AVIATION FCST CONFIDENCE: ABOVE AVERAGE.
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&& .MARINE... THE CONDITIONS ARE ANTICIPATED TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA THROUGH MONDAY. HIGH PRESSURE GENERALLY REMAINS NEAR THE MID ATLANTIC WHICH WILL KEEP A SOUTHWESTERLY FLOW ACROSS OUR AREA. AN INCREASE INTO THIS EVENING IS EXPECTED DUE TO MIXING AND A SEA BREEZE CIRCULATION, AND GUSTS TO 20 KNOTS ARE POSSIBLE. THE SEAS OVERALL ARE ANTICIPATED TO BE IN THE 1 TO 3 FOOT RANGE ACROSS OUR WATERS. OUTLOOK... MONDAY NIGHT THROUGH THURSDAY...WINDS AND SEAS SHOULD STAY WELL BELOW SMALL CRAFT ADVISORY CRITERIA. WATER TEMPERATURES ARE ABOVE NORMAL. FRIDAY...ATLC SEAS MAY INCREASE AS AN EASTERLY FLOW DEVELOPS BUT ATTM, BELOW SCA CRITERIA. && .RIP CURRENTS...
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A LONG PERIOD EAST TO SOUTHEAST SWELL WILL DECREASE TO 9-10 SECONDS ON MONDAY. THIS COMBINED WITH SOUTHERLY WINDS AROUND 15 MPH MAY RESULT IN ANOTHER DAY OF MODERATE RIP CURRENTS, PARTICULARLY FOR NEW JERSEY. IN THE MEANTIME, SWIM SAFELY WITHIN THE WATCHFUL SAFETY VIEW OF OUR BEACH PATROLS.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...DRAG/GORSE NEAR TERM...GAINES/GORSE SHORT TERM...GORSE LONG TERM...DRAG AVIATION...GAINES/DRAG MARINE...DRAG/GORSE RIP CURRENTS...DRAG/GAINES

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