Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 010115 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 915 PM EDT TUE SEP 30 2014 .SYNOPSIS... A WEAKENING COLD FRONT WILL SLOWLY SAG THROUGH THE REGION TONIGHT ALLOWING HIGH PRESSURE TO WORK IN FROM THE NORTH LATER ON WEDNESDAY. THE HIGH WILL SLIDE TO OUR EAST BY FRIDAY BEFORE A MORE POTENT COLD FRONT SWEEPS THROUGH FRIDAY NIGHT INTO SATURDAY MORNING. ANOTHER BREAK BETWEEN COLD FRONTS IS EXPECTED THROUGH MONDAY. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... A LINE OF SHOWERS AND THUNDERSTORMS CONTINUES TO PROGRESS OUT OF SOUTH CENTRAL PENNSYLVANIA INTO SOUTHEASTERN PENNSYLVANIA THIS EVENING AND IS EVER SO SLOWLY MOVING TOWARDS OUR AREA. THIS ACTIVITY IS ASSOCIATED WITH A FRONTAL BOUNDARY MOVING ACROSS THIS AREA AND IS BEING ENHANCED BY A STRONG DIFFLUENT AREA ALOFT AND VORTICITY IMPULSE AHEAD OF AN APPROACHING MID-UPPER LOW MOVING INTO WESTERN PENNSYLVANIA. MEANWHILE, A WEAKENING BACKDOOR COLD FRONT WILL CONTINUE TO SLOWLY SETTLE SOUTHWARD ACROSS THE AREA THROUGH THE OVERNIGHT WHICH WILL KEEP A CONTINUED EASTERLY TO NORTHEAST FLOW ACROSS THE AREA AND PROVIDE AMPLE MOISTURE. SHORT TERM MODEL GUIDANCE INDICATES THE LINE OF SHOWERS AND THUNDERSTORMS MOSTLY WEAKENING BEFORE IT GETS TO OUR AREA, HOWEVER, SINCE IT IS APPROACHING THE AREA, HAVE DECIDED TO INCREASE THE POPS ACROSS OUR WESTERN ZONES AND EXTEND THE CHANCE OF THUNDERSTORMS A FEW HOURS. ELSEWHERE ISOLATED TO SCATTERED SHOWERS MAY STILL DEVELOP ANYWHERE AS THE COLD POOL ALOFT SLIDES ACROSS THE AREA. GUIDANCE WAS ALSO INDICATING THE POTENTIAL FOR PATCHY FOG, AND WE KEPT THIS IN THE FORECAST WITH THE EAST-NORTHEAST FLOW AND AMPLE MOISTURE. FOR OVERNIGHT TEMPERATURES, WE MOSTLY TOOK A BLEND OF MET/MAV GUIDANCE AND EXPECT LOWS MOSTLY IN THE 50S, EXCEPT SOME LOWER 60S ALONG THE COAST AND IN MORE URBAN AREAS. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... THROUGH THE DAYTIME WEDNESDAY, THE PREVIOUSLY MENTIONED UPPER LOW WILL BE SWINGING BY TO OUR NORTHEAST, AND BY LATE IN THE DAY, SURFACE HIGH PRESSURE TO OUR NORTH WILL BEGIN TO SLOWLY BUILD TOWARD OUR REGION. THERE WILL STILL BE THE POSSIBILITY FOR ISOLATED TO SCATTERED SHOWERS, ESPECIALLY THROUGH MORNING TO ABOUT MIDDAY, AND WE SLOWLY TRAIL POPS OFF THROUGH THE AFTERNOON. SKIES WILL BE MAINLY CLOUDY THROUGH MIDDAY BEFORE SOME SLOW THINNING OCCURS LATE-DAY. MAXIMUM TEMPERATURES WERE A BLEND OF MET/MAV GUIDANCE WITH CONTINUITY, AND WE EXPECT HIGHS MOSTLY IN THE LOW TO MID 70S. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... OPERATIONAL MODELS ARE IN PRETTY GOOD AGREEMENT WITH THE LARGE SCALE FEATURES THROUGH THE WEEKEND. THE FIRST SUCH FEATURE BEING THE DEPARTING UPPER LEVEL CUT-OFF LOW THAT SHOULD BE TO OUR IMMEDIATE EAST. THEN WE HAVE THE POTENTIAL PHASING OF A STRONG NORTHERN AND SOUTHERN STREAM SYSTEM TO OUR WEST THAT CARVES OUT A VERY LARGE AND DEEP CLOSED LOW/TROUGH ACROSS THE UPPER MID-WEST BY LATE FRIDAY NIGHT. THURSDAY...RATHER DRY DAY EXCEPT FOR SOME LINGERING SHOWERS EARLY ON ACROSS OUR EASTERN PORTIONS. THERE COULD STILL BE SOME MID-LEVEL INSTABILITY TO WORK WITH AS THE MID-LEVEL COLD POOL SCRAPES BY BUT NOT EXPECTING MUCH QPF WITH. MID AND UPPER LEVEL RIDGING BECOME MORE PROMINENT ON THURSDAY WHICH SHOULD GIVE WAY TO LATE DAY SUNSHINE. TEMPERATURES WILL BE IN THE LOW-70S; AT OR SLIGHTLY BELOW NORMAL. FRIDAY...MODEL GUIDANCE MAY BE BREAKING DOWN THE RIDGING OVERHEAD A BIT TOO FAST, ESPECIALLY GIVEN THE DOWNSTREAM UPPER LEVEL LOW IS STILL LINGERING BY AND THE APPROACH OF A DEEPENING TROUGH UPSTREAM, THE RIDGE SHOULD BUILD SLIGHTLY BEFORE BREAKING. ONSHORE FLOW AHEAD OF THE NEXT TROUGH AND ATTENDANT SURFACE FRONT MAY ALLOW FOR SCATTERED SHOWERS TO BREAK OUT ALONG THE HIGHER ELEVATION LOCATIONS ACROSS OUR WESTERN ZONES BY LATER FRIDAY AFTERNOON. DO NOT SEE MUCH IN THE WAY OF CONVECTION WITH THIS ACTIVITY GIVEN THE STABLE LOWER ATMOSPHERE. WE SEE A INCREASE IN SHOWER COVERAGE AND POSSIBLY INTENSITY BY LATE FRIDAY NIGHT AS A STRONGER COLD FRONT INCHES CLOSER. DAYTIME TEMPERATURES SHOULD REMAIN MUCH THE SAME, LOW-70S WITH INCREASING COLD COVER. SATURDAY...TRANSITION DAY WITH A STRONG FRONT EXPECTED TO SWEEP THROUGH DURING THE MORNING HOURS. DEEP SOUTHWEST FLOW AHEAD OF THE FRONT WILL ALLOW PWATS TO CLIMB TO WELL ABOVE NORMAL MAKING FOR HEAVIER RAINFALL. ANTECEDENT CONDITIONS ARE STILL PRETTY DRY ACROSS THE REGION SO NOT EXPECTING ANYTHING OUT OF THE ORDINARY TO OCCUR WITH THE POSSIBLE HEAVIER RAIN. LOTS OF CLOUD COVER AND COLD AIR ADVECTION OCCURRING DROPPING TEMPERATURES BACK INTO THE MID TO UPPER-60S. SUNDAY - TUESDAY...CLOSED MID-LEVEL LOW ESTABLISHES ITSELF OVER NORTHERN ONTARIO DURING THE SATURDAY THROUGH TUESDAY TIMEFRAME. PREFERRED THE CMC AND UKMET EVOLUTION OF THE MID-LEVEL HEIGHT FIELD OVER THE GFS AND ECMWF...BOTH OF WHICH HAVE A MORE NEGATIVELY TILTED TROUGH AND PLACEMENT OF THE CLOSED LOW FURTHER SOUTH AND EAST. THERE IS STILL QUITE A BIT UNCERTAINTY AS SHOWN BY BOTH THE GEFS AND ECENS SPREAD IN MID-LEVEL HEIGHT FIELDS FROM THE MEAN AND THIS THINKING IS SUPPORTED BY THE LATEST MODEL VERIFICATIONS WHICH INDICATE A LESS AMPLIFIED SOLUTION. EXPECT WINDS TO DECREASE SATURDAY NIGHT AS A RIDGE OF HIGH PRES NOSES INTO THE REGION. IF THE BOUNDARY LAYER DECOUPLES ENOUGH W/ LIGHT WINDS...COULD SEE LOW TEMPS IN THE 35-40 RANGE IN THE NORTHWEST INTERIOR OF OUR CWA. SUNDAY IS SHAPING UP TO BE THE COOLEST DAY OF THE PERIOD...WITH 850 HPA TEMPS SUPPORTING HIGHS SEVERAL DEGREES BELOW NORMAL...MID 50S IN THE POCONOS TO MID 60S IN SOUTH JERSEY. A WEAK COLD FRONT IS PROGGED TO MOVE THROUGH THE REGION EARLY ON TUESDAY...PRESENTING THE BEST CHANCE OF PRECIPITATION DURING THIS TIMEFRAME. TEMPERATURES WILL RETURN TO SEASONABLE LEVELS ON MONDAY AND CONTINUE THROUGH TUESDAY && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. LATE EVENING THROUGH OVERNIGHT...VFR CONDITIONS TO START OUT, BEFORE MVFR/IFR CONDITIONS DEVELOP OVERNIGHT. ISOLATED/SCATTERED SHOWERS MAY IMPACT SEVERAL OF THE TAF SITES LATER THIS EVENING INTO THE OVERNIGHT HOURS, WITH THE HEAVIEST SHOWERS MOST LIKELY AT ABE/RDG. THERE REMAINS SOME THUNDERSTORM ACTIVITY TO OUR WEST, BUT WE EXPECT MUCH OF THIS TO WEAKEN BEFORE REACHING THE AREA; WILL AMEND IF THE STORMS GET WITHIN A COUPLE OF HOURS FROM A TAF SITE, WHICH SOULD MOST LIKELY BE RDG AND AFTER LOCAL MIDNIGHT. WEDNESDAY...POSSIBLE MVFR/IFR CONDITIONS WILL LIKELY LAST THROUGH THE MORNING, BEFORE BECOMING VFR AROUND MIDDAY TO EARLY AFTERNOON FOR THE TAF SITES. AN ISOLATED TO SCATTERED SHOWER REMAINS POSSIBLE THROUGH THE MORNING. NORTHEASTERLY WINDS ARE EXPECTED, MOSTLY IN THE 8 TO 10 KNOT RANGE. OUTLOOK... THURSDAY...MVFR EARLY BECOMING VFR. EASTERLY WINDS EXPECTED. POSSIBLE LINGERING SHOWER EARLY AT MIV/ACY, OTHERWISE DRY. FRIDAY...MOSTLY VFR. RAIN, HEAVY AT TIMES LATE, OVERSPREADS THE AREA FROM THE WEST. REDUCED VSBYS AND CIGS IN HEAVY SHOWERS. WINDS BACK SOUTH-SOUTHWEST. SATURDAY...MVFR/IFR EARLY IN HEAVY RAIN, TRENDING VFR. WINDS CONTINUE TO BACK TO THE WEST-NORTHWEST. && .MARINE... AN EAST-NORTHEAST FLOW WILL BECOME MORE NORTHEASTERLY ACROSS OUR AREA WATERS THROUGH THIS EVENING AND TONIGHT. SPEEDS ARE EXPECTED TO INCREASE THROUGH THE OVERNIGHT, AND FROM EARLY MORNING WEDNESDAY THROUGH THE DAYTIME, SOME GUSTS BETWEEN 20 TO 25 KNOTS ARE POSSIBLE. IN ADDITION, SEAS WILL ALSO BE BUILDING IN THE INCREASING NORTHEAST FLOW. SEAS ARE EXPECTED TO BUILD TO AROUND 4 FEET BY AROUND DAYBREAK WEDNESDAY, AND FORECAST LEVELS SHOULD REACH 5 FEET FROM ABOUT GREAT EGG INLET NORTHWARD DURING THE DAYTIME WEDNESDAY. WE THEREFORE DECIDED TO RAISE A SMALL CRAFT ADVISORY FOR OUR NORTHERN ATLANTIC COASTAL WATERS, FROM GREAT EGG INLET NORTHWARD TO SANDY HOOK, BEGINNING AT 15Z WEDNESDAY. FOR DELAWARE BAY, WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS THROUGH TONIGHT AND WEDNESDAY. OUTLOOK... THURSDAY - FRIDAY...SCA CONDITIONS WILL LIKELY PERSIST ON OUR WATERS THROUGH EARLY FRIDAY AS WE CONTINUE WITH THE EASTERLY ONSHORE FLOW. SEAS WILL CONTINUE TO RUN AROUND 5 FEET. WINDS BEGIN TO BACK TOWARDS THE SOUTH-SOUTHEAST BY FRIDAY AHEAD OF THE NEXT COLD FRONT. SATURDAY...STRONG COLD FRONT MOVES THROUGH. WINDS BACK TOWARDS THE WEST-NORTHWEST LATER IN THE DAY AND WITH STRONGER COLD AIR ADVECTION OCCURRING, WE COULD SEE A RETURN TO SCA CONDITIONS. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY FROM 11 AM WEDNESDAY TO 6 AM EDT THURSDAY FOR ANZ450>452. && $$ SYNOPSIS...HEAVENER NEAR TERM...KLINE/ROBERTSON SHORT TERM...KLINE LONG TERM...FRANCK/HEAVENER AVIATION...HEAVENER/KLINE/ROBERTSON MARINE...HEAVENER/KLINE

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