Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 250127 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 927 PM EDT MON AUG 24 2015 .SYNOPSIS... A COLD FRONT OVER CENTRAL PENNSYLVANIA WILL MOVE INTO OUR AREA LATE TONIGHT AND OFF THE COAST ON TUESDAY. A HIGH PRESSURE SYSTEM FROM THE NORTHERN PLAINS IS EXPECTED TO REACH THE FORECAST AREA ON FRIDAY AND MOVE OFFSHORE ON SATURDAY. THE HIGH PRESSURE SYSTEM IS THEN PREDICTED TO REMAIN NEARLY STATIONARY OFF THE EASTERN SEABOARD ON SUNDAY AND MONDAY. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... AS OF 9 PM EDT...THE COLD FRONT WAS JUST ENTERING WESTERN SECTIONS OF THE REGION. THUNDERSTORMS, ALTHOUGH LIMITED IN COVERAGE, HAVE BEEN STRONGER THAN PREVIOUSLY ANTICIPATED, ESPECIALLY IN THE DELMARVA REGION. IT LOOKS LIKE THE INSTABILITY JUST AHEAD OF THE FRONT WAS POORLY MODELED, WITH THE 00Z KIAD SOUNDING SHOWING AROUND 1500 J/KG OF MOST UNSTABLE CAPE. STILL, WITH LIMITED COVERAGE, AND A SLIGHTLY FASTER ARRIVAL OF THE FRONT, IT LOOKS LIKE MOST AREAS WILL REMAIN DRY. SO DECREASED POPS FOR MOST LOCATIONS EXCEPT DELMARVA. WITH REGARDS TO TEMPERATURES AND WINDS, ANOTHER MILD NIGHT IS IN STORE OVERALL AS MOST OF THE REGION WILL CONTINUE WITH A SOUTH TO SOUTHWEST WIND IN ADVANCE OF THE FRONT, BEFORE SHIFTING TO A WESTERLY DIRECTION DURING THE OVERNIGHT TO EARLY MORNING HOURS TUESDAY. OUR NORTHWEST ZONES WILL BEGIN TO FEEL THE COOLER/DRIER AIR ADVANCING INTO THE REGION AS MINIMUM TEMPS SHOULD BOTTOM OUT IN THE LOWER 60S. ELSEWHERE, LOW TEMPERATURES MAINLY IN THE UPPER/MID 60S ARE ANTICIPATED. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... THE PREVIOUSLY MENTIONED COLD FRONT WILL BE SLOWING AS IT TRIES TO EXIT THE COAST DURING THE DAYTIME TUESDAY. WITH THIS BOUNDARY LINGERING ACROSS OUR FAR EASTERN AREAS TO JUST OFFSHORE, SOME SCATTERED SHOWERS MAY HANG AROUND THROUGH THE MORNING HOURS, ESPECIALLY FOR LOCATIONS NEAR THE COAST. THEREAFTER, ANY REMAINING SHOWER ACTIVITY SHOULD BE PASSING OFFSHORE. OTHERWISE, FOR THE REMAINDER OF THE FORECAST AREA, A BROAD AREA OF HIGH PRESSURE TO OUR WEST, STRETCHING ACROSS THE PLAINS TO MIDWEST, WILL BEGIN TO BUILD EAST TOWARD OUR REGION. THIS WILL ALLOW FOR CLEARING SKIES THROUGH THE DAY, ACCOMPANIED BY WESTERLY WINDS BRINGING IN A DRIER AIRMASS. MODELED DEWPOINTS ARE SHOWN TO BE DROPPING INTO THE 50S FOR MUCH OF THE REGION BY THE AFTERNOON. FOR TEMPERATURES, WE PRIMARILY TOOK A MET/MAV GUIDANCE BLEND, AND WE ANTICIPATE HIGHS TO BE MAINLY IN THE 80S ACROSS THE REGION. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... THE 500MB INITIALIZATION HAS CONTINUED A RECENT TREND IN WHICH THE GFS LOOKS BETTER IN WRN NOAM WHILE THE WRF/NAM AND GFS LOOK EQUALLY AS GOOD FARTHER EAST ACROSS THE CENTRAL AND ERN CONUS AS WELL AS SOUTHERN CANADA. AT 850MB AND 925MB THE WRF/NAM INITIALIZATION WAS CLOSER THAN THE GFS. DP/DTING THE GFS INITIALIZATION, THE LEANING IS TOWARD A HIGHER AMPLITUDE PATTERN. DP/DTING THE GFS OVER THE UPCOMING WEEKEND, THERE IS NO RUN TO RUN CONTINUITY WITH THE SHORT WAVES AND PCPN. OVERALL A QUIET PERIOD AS AN ANOMALOUSLY DEEP TROF OVER THE EASTERN CONUS AT THE START OF THE LONG TERM LIFTS INTO NORTHEASTERN CANADA AND GETS REPLACED BY A MORE RIDGE DOMINATED PATTERN OVER THE CONUS. COOLER THAN NORMAL WEATHER (ESPECIALLY MIN TEMPS) AT THE START OF THE LONG TERM WILL SLOWLY BE TEMPERED AND BECOME WARMER THAN NORMAL BY THE END OF OUR DETERMINISTIC FORECASTS. BY MID TUESDAY EVENING ALL OF THE MODELS HAVE THE FRONT SUFFICIENTLY OFFSHORE TO KEEP THE DRY FORECAST GOING. DRIER AIR WILL BE FILTERING IN BEHIND THE FRONT AND WITH THE PREDICTED GRADIENT WEAK ENOUGH FOR DECOUPLING SHOULD BE A RELATIVELY COOL NIGHT IN SUBURBAN AND RURAL AREAS. STAT GUIDANCE HAS A REASONABLE TAKE ON THIS AND WE WENT PRETTY MUCH IN LINE. ON WEDNESDAY, THE DOMESTIC MODELS ARE KEYING ON OPPOSITE ENDS OF OUR CWA WITH LOW PCPN CHANCES, WITH THE GFS IN SUSSEX COUNTY DE AND THE NAM MUCH CLOSER TO SUSSEX COUNTY NEW JERSEY. DONT KNOW IF THE DP/DT TREND WITH THE GFS HAS BEEN CARRIED TOO FAR, BUT MOST OTHER 12Z MODELS ARE MORE PROGRESSIVE WITH THE TROF THAN THE GFS. ALSO THE GEFS MEAN IS FASTER. THIS REMOVES SUSSEX COUNTY DE FROM THE EQUATION. AT THE GEOGRAPHICAL OTHER END OF THE SPECTRUM, THE NAM BRINGS SHOWERS INTO THE NWRN PART OF OUR CWA. WHILE OTHER MODELS DO NOT IN SPITE OF DECENT PVA. THE LATTER PROBABLY BECAUSE PREDICTED MSTR IS LAGGING, BUT ALWAYS LIKED THE LOOK OF PVA VS MSTR AS A BETTER PREDICTOR AT THIS FORECAST TIME RANGE. WE ARE GOING TO KEEP IN THE LOW CHANCE POPS. PATTERN HAS A VERY AUTUMNAL LOOK TO IT FOR OUR NWRN CWA. BOTH MODELS PREDICTED THERMAL FIELDS SUPPORT HIGHER GFS MOS FOR MAX TEMPS. SIMILAR SCENARIO FOR WEDNESDAY NIGHT WHERE THE GRADIENT LOOKS LOOSE ENOUGH FOR DECOUPLING AND ANOTHER PLEASANT NIGHT, ESPECIALLY OUTLYING AREAS. WE DO NOT BELIEVE THE DAYTIME CU SHOULD BE TRAPPED UNDER THE INVERSION, BUT THAT IS ONE SCENARIO THAT MIGHT MAKE OUR MIN TEMPS TOO LOW. THE LAST OF THE SHORT WAVES BEFORE THE TROF FLATTENS IS PREDICTED TO COME THROUGH ON THURSDAY. HERE WE GET TOO FAR OUT IN TIME TO HAVE CONFIDENCE IN THE SHORT WAVE PLACEMENT. WE ARE DEFERRING TO CONSENSUS AND MODEL QPF. WHILE WE WILL SHOW A DIURNAL INCREASE IN SKY COVER, WE WILL GO POPLESS. PREDICTED THERMAL FIELDS SUGGEST A 2-3F BUMP DOWN IN MAX TEMPS WHICH WE FOLLOWED. THE THERMAL TROF AND THE END OF THE COOLER NIGHTS WILL OCCUR ON THURSDAY NIGHT. THE AIR MASS MODIFICATION WILL START ON FRIDAY. BECAUSE OF THE RELATIVELY CHILLY START, HIGHS ARE NEARLY THE SAME AS THURSDAY. OVER THE WEEKEND A NON GFS MODELING CONSENSUS HAS A CENTRAL CONUS WEAK TROF SHEARING OUT AND A COLD FRONT FROM EASTERN CANADA DISSIPATING BEFORE REACHING OUR CWA. AS THE PREVIOUS SHIFT MENTIONED, WHILE THERE IS A CHANCE (VS NO CHANCE ON FRIDAY)FOR PCPN NEITHER 12Z MODEL CONSENSUS SCENARIO SUPPORTS A HIGH ENOUGH CONFIDENCE TO INCLUDE A CHANCE. WE ARE MUCH MORE CONFIDENT THAT THE UPWARD TREND IN TEMPERATURES WILL CONTINUE OVER THE WEEKEND AND INTO MONDAY. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. FOR THE 00Z TAFS...EXPECT MOSTLY VFR CONDITIONS, UNLESS A TAF SITE IS DIRECTLY IMPACTED BY A SHRA OR THUNDERSTORM, IN WHICH CASE MVFR OR EVEN BRIEF IFR CONDITIONS ARE POSSIBLE. AT THIS POINT THOUGH, COVERAGE IS QUITE LIMITED, SO IT IS QUITE UNCERTAIN AS TO IF ANY TAF SITE WILL BE AFFECTED. SEVERAL MODELS CONTINUE TO SHOW A POTENTIAL FOR LOW CLOUDS AND BR BETWEEN 06 AND 15Z FOR MANY TAF SITES. HOWEVER, IT LOOKS LIKE THE COLD FRONT, AND THUS DRIER AIR, WILL BE SLIGHTLY FASTER THAN PREVIOUSLY EXPECTED. PLUS, THE TREND OVER THE LAST SEVERAL NIGHTS HAS BEEN FOR THE CONDITIONS TO BE DRIER THAN EXPECTED. SO HAVE LEFT THIS OUT OF THE TAFS FOR NOW. OTHERWISE, EXPECT VFR CONDITIONS THROUGH THE DAY TOMORROW. OUTLOOK... TUESDAY NIGHT THROUGH SATURDAY...PREDOMINATELY VFR CONDITIONS. EVERY LATE NIGHT/EARLY MORNING SOME LOW CLOUDS AND FOG ARE POSSIBLE AT MORE RURAL AIRPORTS, ESPECIALLY IF LOCATED IN VALLEYS OR NEAR CREEKS OR RIVERS. && .MARINE... WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS THROUGH TONIGHT AND TUESDAY. A GENERAL SOUTHERLY FLOW WILL CONTINUE THROUGH MOST OF TONIGHT IN ADVANCE OF A COLD FRONT, FOLLOWED BY A WIND SHIFT TO THE SOUTHWEST/WEST FOR THE WATERS ONCE THE FRONT NEARS AND SLOWLY PASSES BY TO THE EAST LATER ON TUESDAY. THERE COULD BE SOME WIND GUSTS AT TIMES TO AROUND 20 KNOTS. IN ADDITION, SEAS FOR THE COASTAL WATERS WILL AVERAGE IN THE 3 TO 4 FOOT RANGE. ISOLATED THUNDERSTORMS ARE POSSIBLE LATE TONIGHT AND INTO TUESDAY AS THE COLD FRONT NEARS AND PASSES OFFSHORE. GUSTY WINDS WILL BE POSSIBLE WITH THESE STORMS. OUTLOOK... TUESDAY NIGHT THROUGH SATURDAY...NO MARINE HEADLINES ARE ANTICIPATED AS A BUILDING HIGH PRESSURE SYSTEM REACHES AND THEN REMAINS NEAR OUR COASTAL WATERS. && .RIP CURRENTS... THERE IS A MODERATE RISK FOR THE FORMATION OF DANGEROUS RIP CURRENTS ALONG THE NEW JERSEY SHORE ON TUESDAY. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...DRAG/GIGI NEAR TERM...JOHNSON/KLINE SHORT TERM...KLINE LONG TERM...GIGI AVIATION...DRAG/GIGI/JOHNSON MARINE...DRAG/GIGI/KLINE RIP CURRENTS...JOHNSON

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