Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 020735 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 335 AM EDT TUE SEP 2 2014 .SYNOPSIS... A TROUGH OF LOW PRESSURE WILL WASH OUT OVER THE REGION THIS MORNING. THIS WILL BE FOLLOWED BY A COLD FRONTAL BOUNDARY WHICH WILL MOVE THROUGH THE REGION TONIGHT. BY WEDNESDAY THIS COLD FRONT WILL BE LOCATED SOUTH OF THE REGION AS HIGH PRESSURE BUILDS OVERHEAD. HIGH PRESSURE WILL GRADUALLY MOVE FROM WEST TO EAST ACROSS THE EASTERN UNITED STATES THROUGH THE LATER HALF OF THE WEEK. ON SATURDAY ANOTHER COLD FRONTAL BOUNDARY WILL MOVE THROUGH THE REGION. THIS FRONTAL BOUNDARY WILL STALL TO OUR SOUTHEAST FOR THE EARLY PART OF NEXT WEEK WITH HIGH PRESSURE OVER THE GREAT LAKES. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... WHILE THE CALENDAR SAYS SEPTEMBER, IT WILL CONTINUE TO FEEL LIKE THE HEART OF SUMMER AS THE HEAT AND HUMIDITY REMAINS ACROSS THE AREA. THERE COULD BE SOME SLIGHT RELIEF THROUGH THE DAY AS THE SURFACE DEW POINTS ARE FORECAST TO LOWER SOME. SYNOPTICALLY, HIGH PRESSURE CONTINUES TO BE CENTERED IN THE WESTERN ATLANTIC HELPING TO PUMP UP THE HEAT AND HUMIDITY WITHIN A SOUTHWESTERLY FLOW. THERE IS HOWEVER A NOTABLE UPPER-LEVEL TROUGH THAT WILL BE SWINGING ACROSS THE GREAT LAKES REGION AND THE UPPER OHIO VALLEY THROUGH THE DAY. THERE IS A SURFACE FRONT WITH THIS FEATURE, HOWEVER IT WILL REMAIN WELL TO OUR WEST DURING THE DAY. THERE SHOULD BE A PRE-FRONTAL TROUGH DEVELOPING GIVEN THE WARM TO HOT AIRMASS. THE EVENTUAL SURFACE FRONT MAY JUMP INTO THIS TROUGH AS WE WORK OUR WAY INTO THE SHORT TERM /TONIGHT/. THE FORECAST CHALLENGES FOR TODAY REVOLVES AROUND THE CONVECTIVE CHCS AND ALSO THE HEAT INDICES. A SUBTLE SHORT WAVE VERY EARLY THIS MORNING HELPED TO SUSTAIN SOME CONVECTION ACROSS THE UPPER DELMARVA INTO SOUTHWESTERN NEW JERSEY, HOWEVER THESE HAVE GENERALLY DISSIPATED. AS THE UPPER-LEVEL TROUGH PROGRESSES EASTWARD, THE MAIN SHORT WAVE IS FORECAST TO LIFT TO OUR NORTH LATE THIS AFTERNOON. THIS LEAVES BEHIND THE TAIL END OF IT SLIDING INTO OUR AREA. AS A RESULT, THE LARGE SCALE FORCING SHOULD SLIDE TO OUR NORTHWEST LATER THIS AFTERNOON. THERE WILL HOWEVER BE INSTABILITY IN PLACE ALTHOUGH THIS CAN BE AFFECTED BY THE LOWERING DEW POINTS /AT LEAST SBCAPE/. THERE IS SOME INCREASE IN THE MID LEVEL FLOW, HOWEVER THE CORE /50-60 KNOTS/ OF IT IS FORECAST TO REMAIN WELL TO OUR WEST WHICH IS WHERE THE SLIGHT RISK FOR SEVERE THUNDERSTORMS IS INDICATED. THAT STRONGER FLOW IS EXPECTED TO ALLOW FOR CONVECTIVE DEVELOPMENT WELL TO OUR WEST AND THIS IS WHAT WE WILL PROBABLY HAVE TO WAIT AND SEE WHAT SURVIVES AS IT TRACKS EASTWARD. IN ADDITION, SOME ISOLATED ACTIVITY COULD FIRE ALONG THE PRE-FRONTAL TROUGH. AS A RESULT, WE SLOWED DOWN THE POP INCREASE FROM WEST TO EAST. WHILE AN ISOLATED CELL COULD FORM THIS AFTERNOON FARTHER EAST FROM LOCAL CONVERGENCE, MUCH OF THE TIME WILL PROBABLY BE RAIN-FREE. REGARDING THE HEAT, THE 850 MB TEMPERATURES ARE FORECAST TO BE A FEW DEGREES WARMER THAN YESTERDAY. THE FORECAST SOUNDINGS INDICATE THE POTENTIAL FOR BETTER MIXING BEING PRESENT AS THE PRESSURE GRADIENT TIGHTENS SOME AND THE LOW-LEVEL LAPSE RATES STEEPEN. THEREFORE THIS SHOULD RESULT IN HIGH TEMPERATURES INTO THE LOWER TO EVEN MID 90S FOR MANY INLAND AREAS. THE MIXING HOWEVER SHOULD LOWER THE SURFACE DEW POINTS SOME IN THE AFTERNOON, KEEPING THE HEAT INDICES A BIT LOWER. AS A RESULT, WE ARE EXPECTING THE HEAT INDICES TO REMAIN UNDER ADVISORY CRITERIA INCLUDING THE PHILADELPHIA METRO AREA. HIGH TEMPERATURES WERE A BLEND OF THE NAM/GFS MOS, ALTHOUGH THE WARMER NAM MOS WAS FAVORED FOR SOME AREAS WHICH ALSO GOT US CLOSE TO CONTINUITY. THE HOURLY GRIDS WERE TWEAKED USING THE LAMP/LAV GUIDANCE, ESPECIALLY THIS MORNING TO HELP ASSIST WITH TEMPERATURE/DEW POINT TRENDS THUS FAR. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... THE AFOREMENTIONED UPPER-LEVEL TROUGH WILL GENERALLY GLANCE OUR AREA, WITH A FRONTAL BOUNDARY SWEEPING THROUGH. THE MAIN FORCING AND ASSOCIATED MID LEVEL JET MAX IS FORECAST TO BYPASS OUR AREA TO THE NORTHWEST. THERE STILL IS SOME INCREASE IN THE FLOW WITH THIS SYSTEM AS THE TAIL END OF THE SHORT WAVE MOVES THROUGH. THIS IN CONJUNCTION WITH ENOUGH INSTABILITY SHOULD SUPPORT SOME CONVECTION THIS EVENING BEFORE WEAKENING TAKES PLACE. THE AMOUNT OF SHEAR LOOKS LOW AND THEREFORE STORM ORGANIZATION SHOULD BE WEAK AND POTENTIALLY EVEN DISAPPEAR AS THE EVENING WEARS ON. THE FORECAST SOUNDINGS INDICATE SOME OPPORTUNITY FOR SOME STRONGER CORES ACROSS OUR WESTERN ZONES AND TOWARDS THE DELMARVA, HOWEVER GIVEN THE BEST FORCING AND SHEAR MISSING OUR AREA THE SEVERE WEATHER THREAT LOOKS RATHER LOW AS OF NOW. THEREFORE, NO ENHANCED WORDING WAS CARRIED ATTM. WE USED CHC POPS THIS EVENING THEN THESE LOWER FROM WEST TO EAST. ANY LINGERING CONVECTION SHOULD BE DONE AFTER MIDNIGHT AS THE FRONTAL BOUNDARY SHIFTS EASTWARD. THE MODEL GUIDANCE SHOWS A PLUME OF PW AROUND 2 INCHES SURGING AHEAD OF THE SURFACE FRONT, THEREFORE ANY CONVECTION WILL HAVE THE POTENTIAL TO PRODUCE BRIEF TORRENTIAL DOWNPOURS. ANY FLOOD THREAT SHOULD BE LIMITED HOWEVER. THERE IS NO SIGNIFICANT AIRMASS CHANGE BEHIND THE SURFACE FRONT DESPITE A WIND SHIFT TO THE NORTHWEST. AS THE CLOUDS THIN OUT SOME SURFACE COOLING WILL TAKE PLACE, HOWEVER THE DEW POINTS LOOK TO REMAIN ON THE MUGGY SIDE FOR MUCH OF THE NIGHT. SOME LOWERING SHOULD START TO TAKE PLACE THOUGH LATE MAINLY OVER OUR WESTERN ZONES. THE COMBINATION OF LIGHT WINDS AND LINGERING LOW-LEVEL MOISTURE, MAY ALLOW FOR SOME FOG TO DEVELOP PARTICULARLY WHERE DRY AIR ADVECTION IS DELAYED. WE ARE NOT EXPECTING A LOT OF FOG, AND GIVEN LOWER CONFIDENCE WE HELD OFF INCLUDING A MENTION ATTM. AS FOR LOW TEMPERATURES, AN EVEN BLEND OF THE GFS/NAM WAS MAINLY USED. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... WEDNESDAY THROUGH FRIDAY: DRY WITH FEW CLOUDS, FLOW TURNING GRADUALLY TO THE SOUTHWEST BY FRIDAY. THINK THE 00Z GFS IS TO QUICK SHOWING SOME RETURN FLOW POPS. MUGGY AND HOT AS WELL BUT TEMPS WILL BE UNDER HEAT ADVISORY CRITERIA. FAIR SHOT AT 90 THU/FRI FOR PHL. WENT AT OR A TOUCH ABOVE MET/MAV GUIDANCE ON TEMPERATURES BASED ON THE 925/850 MB TEMPERATURE PROFILES. FRIDAY NIGHT THROUGH SATURDAY NIGHT: A FRONTAL BOUNDARY MOVING SOUTH FROM THE GREAT LAKES WILL BE A TRIGGER FOR SOME SCATTERED SHOWERS AND THUNDERSTORMS. CLOUDS SHOULD INCREASE FROM NORTHWEST TO SOUTHEAST FRIDAY NIGHT AND SATURDAY. CONTINUED SOUTHWEST FLOW WILL BE IN PLACE AS WELL AHEAD OF THE FRONT. 925 MB TEMPS ARE LIKELY TO BE A TOUCH HIGHER THAN THU/FRI INDICATING SLIGHTLY WARMER SURFACE TEMPERATURES. TEMPERATURES COULD POSSIBLY MAKING A RUN AT THE LOW PERHAPS MID 90`S BASED ON HOW QUICKLY THE CLOUDS INCREASE. WENT WARMER THAN WPC/MEX GUIDANCE IN THESE PERIODS TO ACCOUNT FOR THE WAA AHEAD OF THE FRONT. IN TERMS OF ANY STRONG TO SEVERE STORMS. A MODEST AMOUNT OF INSTABILITY (CAPE AROUND 1500 J/KG) WILL BE PRESENT WITH MODERATELY STEEP LAPSE RATES. HOWEVER THE LACK OF SHEAR IN PLACE WILL LIKELY PREVENT ANY WIDESPREAD COVERAGE OF STRONG TO SEVERE STORMS. CONTINUED THUNDER IN GRIDS FOR SAT-SAT NIGHT WITH CHANCE POPS. SUNDAY THROUGH TUESDAY: NORTHEAST FLOW WILL DEVELOP EARLY NEXT WEEK WITH THE FRONT TO OUR SOUTH AND HIGH PRESSURE OVER THE GREAT LAKES. THE 00Z GFS IS THE MOST AGGRESSIVE CLEARING THE FRONT DURING THE DAY SUNDAY WITH ONLY LINGERING SHOWERS ACROSS THE SOUTH. THE 00Z ECMWF AND CMC SLOW THE FRONT ALLOWING FOR ADDITIONAL SHOWER CHANCES FOCUSED ACROSS THE SOUTH, PARTICULARLY ON SUNDAY BUT LINGER ISOLATED SHOWERS INTO MONDAY AND TUESDAY. THE ECMWF APPEARS TO BE FASTER THAN IT`S PREVIOUS RUN AND SOME MEMBERS WITHIN THE 18Z GFS ENSEMBLE SUITE ARGUE FOR A SLOWER FRONTAL PASSAGE. A MIDDLE GROUND WILL BE USED WITH CHANCE POPS DECREASING FROM NORTH TO SOUTH SUNDAY WITH SLIGHT CHANCE POPS ACROSS THE SOUTH MONDAY. CLOUDS AND SHOWERS MAY KEEP HIGHS DOWN ON SUNDAY AND LOWS HIGHER AT NIGHT. ON MONDAY AND TUESDAY AMPLE SUNSHINE MAY ALLOW MOST AREAS TO GET A TOUCH WARMER THAN WHAT MODELED TWO METER TEMPERATURES OR WPC GUIDANCE SUGGEST. RADIATIONAL COOLING MONDAY NIGHT IS LIKELY AS WELL ACROSS MOST OF THE REGION WITH THE FAVORED REGION JUST INLAND OFF THE NJ COAST AND NW PHL COULD HAVE A RELATIVITY CHILLY NIGHT. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...LOCAL MVFR TO PERHAPS IFR VISIBILITIES DUE TO FOG EARLY, OTHERWISE VFR. A FEW SHOWERS AND THUNDERSTORMS MAY DEVELOP THIS AFTERNOON MAINLY WEST OF KPHL AND THEREFORE A VCSH WAS CARRIED AT KRDG AND KABE, THEN THIS WAS SHIFTED EASTWARD TOWARD EVENING. A TEMPO GROUP MAY BE ADDED ESPECIALLY FOR KABE AND KRDG WITH THE 12Z TAF ISSUANCE. LIGHT AND MOSTLY VARIABLE WINDS TO START, BECOMING SOUTHWEST AND INCREASING TO 10-15 KNOTS. SOME LOCAL GUSTS UP TO 20 KNOTS SHOULD OCCUR THIS AFTERNOON AS ENOUGH MIXING DEVELOPS. TONIGHT...A FRONTAL BOUNDARY WILL MOVE THROUGH WITH SOME SHOWERS AND THUNDERSTORMS ARRIVING FROM THE WEST, WHICH MAY TEND TO DIMINISH WITH AN EASTWARD EXTENT. A WIND SHIFT TO THE NORTHWEST IS ANTICIPATED WITH ANY CONVECTION AND ALSO AS THE FRONT MOVES THROUGH. MVFR CEILINGS WITH VISIBILITIES AS LOW AS IFR WILL BE POSSIBLE WITH ANY SHOWER OR THUNDERSTORM, OTHERWISE VFR. THERE IS A CHANCE SOME LOCAL FOG DEVELOPS LATE AS CLOUDS THIN AND THE WINDS DROP OFF WITH THE LOW-LEVEL MOISTURE REMAINING. OUTLOOK... WEDNESDAY THROUGH FRIDAY NIGHT: VFR SATURDAY: MVFR TO IFR RESTRICTIONS POSSIBLE IN ANY AFTERNOON OR EVENING THUNDERSTORMS. && .MARINE... A SOUTHERLY FLOW WILL BE MAINTAINED TODAY WELL AHEAD OF A SURFACE FRONT. THERE WILL BE SOME INCREASE LATER THIS AFTERNOON AND EVENING AS THE PRESSURE GRADIENT TIGHTENS SOME, HOWEVER THESE ARE EXPECTED TO REMAIN BELOW ADVISORY CRITERIA. THE WINDS WILL SHIFT TO THE WEST AND NORTHWEST LATER TONIGHT BEHIND THE FRONTAL PASSAGE. SOME THUNDERSTORMS ARE POSSIBLE WITH THE FRONT MAINLY THIS EVENING, HOWEVER THESE COULD WEAKEN BEFORE REACHING OUR MARINE AREA. SEAS WILL BE IN THE 2 TO 4 FEET RANGE OVER THE COASTAL WATERS, AND 2 FEET OR LESS ON DELAWARE BAY. OUTLOOK... WEDNESDAY THROUGH FRIDAY NIGHT: SUB SCA SEAS AND WINDS EXPECTED ATTM. SATURDAY: SOME STRONG WIND GUSTS POSSIBLE FROM THUNDERSTORMS, OTHERWISE SUB SCA SEAS AND WINDS. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GAINES NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...GAINES AVIATION...GAINES/GORSE MARINE...GAINES/GORSE

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