Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 020106 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 906 PM EDT SAT AUG 1 2015 .SYNOPSIS... A HIGH PRESSURE SYSTEM OVER THE LOWER OHIO VALLEY WILL SLOWLY MOVE SOUTHEAST THROUGH MONDAY. THE NEXT COLD FRONT FROM THE GREAT LAKES IS EXPECTED TO CROSS OUR REGION LATE MONDAY INTO EARLY TUESDAY, EVENTUALLY STALLING JUST SOUTH OF OUR AREA WEDNESDAY AND THURSDAY AS A WAVE OF LOW PRESSURE MOVES ALONG IT. THE FRONTAL BOUNDARY IS FORECAST TO REMAIN NEARLY STATIONARY TO THE SOUTH OF THE DELMARVA PENINSULA ON FRIDAY AND SATURDAY AS ADDITIONAL WAVES OF LOW PRESSURE MOVE ALONG IT. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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SOME RESIDUAL INSTABILITY AND THE WEAK TROUGH/FRONT CROSSING THE SE PART OF THE AREA HAVE TRIGGERED A FEW SCT SHOWERS. THERE WERE A FEW LTG IMPULSES OFF ACY EARLIER WITH A COUPLE OF THE CELLS. THE ACTIVITY WILL DIMINISH OVER THE NEXT FEW HOURS. WE HAVE JUST KEPT IN THE SMALL CHC/SLGT CHC POPS IN THE FCST FROM EARLIER. OTHER THAN THAT...FEW CHANGES WERE NEEDED TO THE FCST WITH SKIES MOSTLY CLR AROUND THE AREA THIS EVENING. TEMPERATURES WERE NOT CHANGED FOR THE LOWS EARLIER WHICH ARE A BLEND OF MAV/MET MOS.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... HIGH PRESSURE BUILDS TO OUR SOUTHWEST, WITH OUR AREA ON THE NORTHEAST SIDE OF THE HIGH. PW VALUES ARE FORECAST TO DROP BELOW ONE INCH, AND WITH NO SHORT WAVE/VORTICITY IMPULSES, SUNDAY IS EXPECTED TO BE A PRECIPITATION FREE DAY. TEMPERATURES SUNDAY ARE EXPECTED TO BE A DEGREE OR TWO LOWER THAN SATURDAY FOR MANY LOCATIONS, ALTHOUGH HIGHS ARE STILL FORECAST TO BE ABOVE NORMAL. HIGH TEMPERATURES ARE A BLEND OF MIXED 925MB ECMWF TEMPERATURES, MAV/MET MOS, AND MOSGUIDE. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... A HOT START AND RELATIVELY COOL AND WETTER LOOKING FINISH TO THE LONG TERM. THE DETAILS THOUGH AS TO WHAT OCCURS AFTER WE GET THERE REMAINS MUDDLED. BOTH THE WRF-NMM AND GFS HAD A VERY GOOD 500MB INITIALIZATION WITH THE GFS SLIGHTLY BETTER AT 850MB AND THE WRF- NMMB NOTICEABLY BETTER AT 925MB (GFS WARM BIAS). THE GFS DP/DT GENERALLY SHOWS A FLATTER TROF IN THE EAST AND BROADER RIDGE OUT WEST, WITH DECENT RUN TO RUN CONTINUITY. TO THAT END, THE 12Z OP GFS LOOKED MORE IN SYNC WITH THE GEFS MEAN THAN THE 06Z RUN DID. BUT THE MEDIUM RANGE MODELS REMAIN AT ODDS AS TO HOW ENERGY FROM THE PACIFIC TROF WILL TRANSLATE OVER THE WRN NOAM RIDGE INTO THE ERN NOAM TROF. THERE HAS BEEN LITTLE RUN TO RUN CONTINUITY OR CONSISTENCY BETWEEN MODELS. DEVELOPING CONVECTIVE SYSTEMS AND THEIR PREDECESSOR AND/OR EMERGING SHORT WAVES SEEM TO BE THE DRIVERS OF THIS. BUT AT THIS POINT ITS DIFFICULT TO DIFFERENTIATE BETWEEN FEEDBACK MCV(S) AND LEGITIMATE TRIGGERS. THUS THIS PART OF THE FORECAST IS LONG ON CONTINUITY AND SHORT ON BEING ABLE TO DIFFERENTIATE DRY WEATHER DAYS. THE GREATEST IMPACT TO OUR WEATHER SHOULD BE A HOT DAY ON MONDAY CLOSE TO URBAN CORRIDOR HEAT HEADLINE LEVELS, POSSIBLY STRONG STORMS IF THEY CAN ARRIVE IN TIME ON MONDAY EVENING AND HEAVY RAIN POTENTIAL IF ANY OF THE SUBSEQUENT WAVE OR WAVES OF LOW PRESSURE CAN BACK INTO OUR CWA. THE LONG TERM START RELATIVELY EASY WITH A QUIET SUNDAY NIGHT. BECAUSE DEW POINTS HEADING INTO SUNDAY NIGHT SHOULD BE RELATIVELY LOW AND WINDS LIGHT WITH FEW CLOUDS, WE HAVE MIN TEMPS IN OUTLYING, MORE RURAL LOCATIONS GETTING TO RELATIVELY COMFORTABLE LEVELS. ON MONDAY OUR CWA SHOULD SPEND MOST OF THE DAY IN A SUBSIDENCE REGION BETWEEN THE UPWARD MOTION FROM THE APPROACHING FRONT AND PRECIPITATION OFFSHORE ASSOCIATED WITH OUR OLD CFP FROM THURSDAY NIGHT. PREDICTED CONVECTIVE TEMPS GET REACHED LATE IN THE DAY, SO WE KEPT IN A LOW CHANCE "NORTHWEST" DURING THE AFTERNOON. THIS GFS RUN IS ON THE HOT SIDE (INITIALIZED HOT TOO) OF THE ENSEMBLE CLUSTER. OF LATE THE PREDICTED 2M TEMPS AS IS HAVE COME AS CLOSE AS ADDING ABOUT 10C TO 925MB TEMPS. THIS KEPT OUR MAX TEMPS CLOSE TO CONTINUITY. BECAUSE SOUTHWEST WINDS ARE EXPECTED TO INCREASE MONDAY AFTERNOON AND THE DEEPER MOISTURE ALOFT IS STILL WEST, DEW POINTS ARE PREDICTED TO DROP. THIS HAS AFTERNOON HEAT INDEX VALUES TOPPING IN THE 90S (MID 90S URBAN CORRIDOR) FOR NOW. IN TERMS OF THUNDERSTORM STRENGTH, THE CURRENT FORECAST SCENARIO LOOKS ABOUT SIX HOURS TOO LATE TO MAXIMIZE IN OUR FORECAST AREA. ON PAPER, THIS ONE HAS VIGOR AS THERE IS A PREDICTED EML, TT(S) ABOVE 50 (TEMPS AT 500MB ARE RELATIVELY LOW), DCAPES ABOVE 1000J AND BULK SHEAR VALUES NORTH OF 30 KNOTS ESPECIALLY IN THE NORTHWEST HALF OF OUR CWA. BUT BECAUSE OF ITS LATER ARRIVAL TIME AND ALSO BECAUSE ITS GOING INTO A LESSER SHEARED ENVIRONMENT, WE KEPT CHANCE POPS AND DECREASED THEM TOWARD THE COAST. SOME MODELS HAVE NO MEASURABLE SOUTHEAST OF I95 CORRIDOR. ITS BEEN THE SUMMER OF 1000+J (WRF-NMMB) VS 0J (GFS) MIXED LAYER CAPES AND TUESDAY IS NO EXCEPTION. THE GFS IS EXTREMELY DRY AND VERY CONFINED WITH ITS APPROACHING VIGOROUS SHORT WAVE. WHILE THE NAM/WRF HAS VERIFIED HOT, THE SYNOPTIC SET-UP (LOOKS TO PROBABLY BE A SECONDARY CFP) INDICATES THAT A PRECIPITATION CHANCE BE INCLUDED. WE KEPT LOW CHANCE IN THE FORECAST. THERE SHOULD BE A DROP IN DEW POINTS TUESDAY, BUT WITH THE DOUBLE FRONT STRUCTURE, TEMPERATURES SHOULD BE LOWER, BUT NOT AS MUCH OF A DROP OFF. MAX TEMPS AOA STAT GUIDANCE. THERE IS BETTER MODELING CONSENSUS ABOUT THE LACK OF PCPN FOR TUESDAY NIGHT AND WEDNESDAY. WE WANT TO SEE AT LEAST ONE MORE SOUNDING RUN BEFORE REMOVING ALL POPS. REGARDLESS OF POPS, TEMPERATURES AND DEW POINTS WILL BE LOWER. THEN FOR THURSDAY THROUGH SATURDAY, NO MODELS ARE KEYING ON ANY SPECIFIC 12 HOUR PERIOD AS THE WETTEST IN UNISON. THE ONLY CONSISTENCY IS THAT THEY ARE ALL DIFFERENT AND IF WE WENT BACK TO THE PREVIOUS SOUNDING RUN, THEY WERE ALL DIFFERENT AGAIN. UNTIL THIS WAVE TRAIN SETTLES, WE HAVE KEPT CHANCE POPS IN ALL THREE DAYS. IT WOULD SEEM THAT SOUTHERN PARTS OF OUR CWA HAVE HIGHER CHANCES AND HIGHER CHANCES OF HVYR PCPN THAN NORTH, BUT THAT IS ABOUT AS CONFIDENT A STATEMENT AS WE CAN MAKE RIGHT NOW. THIS FORECAST KEPT MUCH OF A CONTINUITY/WPC BLEND. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. A FEW ISOLATED SHOWERS ARE POSSIBLE THE REST OF THE EVENING, BUT CHANCES OF HITTING A TAF SITE ARE MINIMAL SO THEY ARE NOT INCLUDED IN THE TAFS. WINDS WILL BECOME LIGHT AND VARIABLE/CALM FOR MANY LOCATIONS OVERNIGHT, ALTHOUGH ANY DIRECTION WILL LIKELY BECOME MORE NORTHWESTERLY. THE NORTHWESTERLY WINDS AROUND 5-10 KNOTS WILL BECOME MORE WESTERLY AFTER SUNRISE SUNDAY, THEN SOUTHWESTERLY DURING THE DAY. OUTLOOK... SUNDAY NIGHT THROUGH MONDAY MORNING...VFR CONDITIONS ARE EXPECTED AT THE TERMINALS. SOME MVFR CONDITIONS AT RURAL AIRPORTS IN FOG EARLY MONDAY. MONDAY AFTERNOON...MAINLY VFR, BUT WITH SCATTERED SHOWERS AND TSTMS WITH MVFR CONDITIONS LATE. MONDAY NIGHT...PREDOMINATELY MVFR DUE TO CIG AND VSBY RESTRICTIONS AS WELL AS FROM SCATTERED SHOWERS AND TSTMS. TUESDAY...MAINLY VFR CONDITIONS. SOME ISOLATED TO PERHAPS SCATTERED SHWRS/THUNDERSTORMS ARE POSSIBLE. TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...PREDOMINANTLY VFR. THURSDAY...SOME MVFR CONDITIONS POSSIBLE DURING SHOWERS AND TSTMS.
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&& .MARINE... SUB-SMALL CRAFT ADVISORY CONDITIONS WILL CONTINUE THROUGH SUNDAY, ALTHOUGH WINDS WILL GUST AROUND 20 KNOTS AT TIMES THIS AFTERNOON INTO TONIGHT. OUTLOOK... SUNDAY NIGHT THROUGH MONDAY MORNING...SUB-ADVISORY CONDITIONS ARE EXPECTED. MONDAY AFTERNOON THROUGH TUESDAY...SOME WIND GUSTS COULD BE AROUND 25 KNOTS PLUS WITH SEAS INCREASING TO AROUND SMALL CRAFT ADVISORY CRITERIA FOR THE COASTAL WATERS LATE MONDAY INTO TUESDAY ASSOCIATED WITH THE SOUTHWEST FLOW PRECEDING A COLD FRONT PASSAGE. MODELS SOMETIMES INCREASE SEAS TOO QUICKLY, SO THIS MAY HOLD OFF TO MONDAY NIGHT. TUESDAY NIGHT THROUGH THURSDAY...SUB-SCA CONDITIONS EXPECTED. CONFIDENCE IS MODERATE DUE TO WAVES OF LOW PRESSURE MOVING SOUTH OF OUR FORECAST WATERS. STRONGER LOWS MIGHT BRING SMALL CRAFT ADVISORY CONDITIONS TO THE OCEAN WATERS. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GIGI/KLINE NEAR TERM...ROBERTSON/O`HARA SHORT TERM...ROBERTSON LONG TERM...GIGI AVIATION...GIGI/KLINE/ROBERTSON MARINE...GIGI/KLINE/ROBERTSON

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