Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 280932 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 532 AM EDT THU MAY 28 2015 .SYNOPSIS... A COLD FRONT WILL MOVE ACROSS THE AREA TODAY. HIGH PRESSURE REESTABLISHES ITSELF OFF THE EAST COAST FRIDAY INTO SATURDAY. A COLD FRONT IS FORECAST TO MOVE ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY. HIGH PRESSURE WILL RETURN TO THE NORTHEAST EARLY NEXT WEEK WHILE THE FRONTAL BOUNDARY STALLS TO OUR SOUTH. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... COLD FRONT WILL BEGIN CROSSING OUR REGION TODAY. INTERESTINGLY, MOST MODELS AGREE THAT THE FRONT WILL BE MOVING THROUGH OUR WESTERN SECTIONS BY 18Z OR SHORTLY THEREAFTER DESPITE LARGE DIFFERENCES IN THE TIMING OF THE FRONT FOR OUR EASTERN COASTAL PLAINS (MORE ON THAT IN THE SHORT TERM SECTION). COULD BE A FEW SHOWERS THIS MORNING AS THE RIGHT REAR QUADRANT OF THE UPPER LEVEL JET PROPAGATES CLOSER TO THE REGION. HOWEVER, THE MAIN FOCUS FOR ANY STORMS, AND THUS HIGHEST POPS, LOOK TO BE AFTER 18Z IN THE VICINITY OF THE FRONT. ONE CHANGE FROM THE PREVIOUS FORECAST IS THAT IT NOW LOOKS LIKE THE HIGHEST CHANCES FOR STORMS WILL BE IN THE NORTHERN HALF OF THE REGION WHICH WILL BE CLOSER TO THE MID AND UPPER LEVEL TROUGH AXIS. MEANWHILE IN THE SOUTHERN HALF OF OUR CWA, AN UPPER LEVEL RIDGE LOOKS TO BUILD IN BY LATE THIS AFTERNOON, AND WHILE ANY ASSOCIATED SUBSIDENCE MAY NOT BE ENOUGH TO COMPLETELY SUPPRESS CONVECTIVE INITIATION IN THIS AREA, IT SHOULD BE A FACTOR IN LIMITING STORM COVERAGE. AS FOR HAZARDS, THERE IS THE POTENTIAL FOR GUSTY WINDS, PRIMARILY ACROSS NW NJ AS 0-6KM SHEAR VALUES COULD BE NEAR 40 KT (PRIMARILY SPEED SHEAR) WITH MODEST (LESS THAN 500 J/KG CAPE) INSTABILITY. WILL MENTION POTENTIAL FOR STRONG STORMS IN THIS AREA IN THE HWO. SHEAR VALUES, AND THUS STRONG STORM THREAT, DROPS OFF QUICKLY AS YOU GO FURTHER SOUTH THANKS AGAIN TO THE HIGH BUILDING IN. WITH THIS HIGH, ANY STORM MOTIONS ACROSS THE SOUTHERN HALF OF THE REGION SHOULD BE QUITE SLOW (15 KT OR LESS), BUT OTHER CONTRIBUTING FACTORS FOR A HEAVY RAIN THREAT ARE LIMITED, SO WILL HOLD OFF ON MENTIONING ANY HEAVY RAIN IN THE HWO. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... AS MENTIONED EARLIER, THERE ARE SOME BIG DIFFERENCES AMONG MODELS FOR THE TIMING OF THE FRONT FROM DELAWARE VALLEY AND POINTS FURTHER EAST. SOME MODELS, MOST NOTABLY THE NAM, BRING THE FRONT IN QUICKLY TO THE WESTERN ZONES, BUT THEN DON/T SHOW THE FRONT MOVING THROUGH THE EASTERN COASTAL PLAINS UNTIL NEAR OR AFTER 06Z. THIS DOESN/T SEEM REALISTIC EVEN WITH THE HIGH BUILDING IN. THE LOW ASSOCIATED WITH THIS COLD FRONT SHOULD BE QUICKLY PROPAGATING EAST THROUGH THIS TIME, SO SEE LITTLE REASON THAT THE FRONT WILL STALL. THUS FORECAST FAVORS A FASTER SOLUTION, HAVING THE FRONT MOVE OFF SHORE AROUND 06Z. REGARDLESS OF THE FRONTAL TIMING, LOSS OF DAYTIME HEATING AND THE RIDGE BUILDING IN SHOULD LEAD TO CHANCES FOR STORMS DECREASING THROUGH THE EVENING HOURS, AND WOULD EXPECT MOST, IF NOT ALL OF THE AREA TO BE DRY BY MIDNIGHT. THE ONE AREA WHERE THE TIMING DIFFERENCES COULD HAVE CONSIDERABLE IMPACT WILL BE WITH LOW TEMPERATURES OVERNIGHT. FOR NOW HAVE GONE WITH A BLEND OF THE FASTER SOLUTIONS (CMC, GFS, AND ECMWF), BUT WITH DRIER AIR MOVING IN BEHIND THE FRONT, THERE IS THE POTENTIAL FOR CONSIDERABLE RADIATIONAL COOLING IF THE FRONT PUSHES THROUGH FASTER THAN PREVIOUSLY EXPECTED. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... HIGH PRESSURE IS FORECAST TO REESTABLISH ITSELF ACROSS THE ATLANTIC ON FRIDAY, WITH OUR AREA ON THE WESTERN EDGE, WHILE THE RIDGE ALOFT BUILDS TO OUR EAST AS WELL. THIS SHOULD HELP KEEP THE WEATHER MOSTLY DRY INTO FRIDAY. HOWEVER, WITH RETURN FLOW ACROSS THE AREA, INSTABILITY IS FORECAST TO DEVELOP ACROSS THE THE AREA, ESPECIALLY FOR WESTERN AREAS. THIS DAYTIME INSTABILITY COULD LEAD TO A FEW ISOLATED SHOWERS/THUNDERSTORMS WITH ANY VORTICITY IMPULSE THAT MOVES ACROSS THE WESTERN EDGE OF THE RIDGE. THE SURFACE HIGH AND RIDGING ALOFT PUSH EASTWARD SLIGHTLY SATURDAY, WITH SOUTHWEST FLOW AT THE SURFACE ALOFT DEVELOPING. THIS WILL ALLOW FOR A COUPLE OF SHORT WAVE/VORTICITY IMPULSES TO MOVE ACROSS THE AREA LATE SATURDAY WHILE DAYTIME INSTABILITY DEVELOPS AS WELL. AN INCREASE IN SHOWER/THUNDERSTORM ACTIVITY IS POSSIBLE, ESPECIALLY FOR THE WESTERN PORTIONS OF THE AREA. A COLD FRONT IS THEN FORECAST TO MOVE ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY. THE LATEST GFS AND ECMWF HAVE PRETTY GOOD AGREEMENT WITH THE TIMING OF THE PRECIPITATION. BOTH AGREE THAT SUNDAY LOOKS TO BE THE PERIOD WITH HIGHEST PROBABILITY FOR PRECIPITATION AS THE FRONT MOVES ACROSS AND SOUTH OF THE AREA. PW VALUES INCREASE TO NEAR 2 INCHES, SO THERE COULD BE A PERIOD OF HEAVY RAINFALL WITH ANY SHOWERS THAT DEVELOP DURING THE TIME PERIOD. THERE REMAINS INSTABILITY FORECAST AHEAD OF THE FRONT, SO WE WILL KEEP THUNDERSTORMS IN THE FORECAST, BUT ONCE THE FRONT PASSES, THUNDERSTORM POTENTIAL DECREASES. HIGH PRESSURE RETURNS TO THE NORTHEAST EARLY NEXT WEEK AS THE FRONTAL BOUNDARY PUSHES SOUTH AND LIKELY STALLS JUST SOUTH OF OUR AREA. WITH THE HIGH TO OUR NORTHEAST, THIS WILL KEEP EASTERLY FLOW ACROSS THE AREA. SOUTHWEST-WESTERLY FLOW ALOFT WILL REMAIN ACROSS THE AREA AS WELL. SEVERAL SHORT WAVE/VORTICITY IMPULSES WILL LIKELY MOVE ACROSS THE AREA EARLY NEXT WEEK, WHICH COULD HELP CREATE PRECIPITATION ACROSS THE AREA. WITH THE EASTERLY FLOW ACROSS THE AREA, THE ATMOSPHERE SHOULD BE STABLE, SO WE HAVE REMOVED THUNDERSTORMS FROM THE FORECAST MONDAY AND TUESDAY DUE TO LACK OF INSTABILITY. && .AVIATION /10Z THURSDAY THROUGH MONDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. PATCHY FG/BR WILL LIKELY CONTINUE AT KRDG AND KABE THROUGH 12Z. FOR THE DELAWARE VALLEY AND COASTAL SITES (KPHL, KPNE, KTTN, KMIV, KACY AND KILG), EXPECT BRIEF INTERMITTENT IMPACTS (PRIMARILY MVFR EXCEPT AT KTTN) THROUGH THIS TIME AS WELL. AFTER SUNRISE, WINDS SHOULD SETTLE IN OUT OF THE SW. THERE MAY BE ISOLATED SHRA BETWEEN 12 AND 15Z, BUT COVERAGE WILL BE TOO LIMITED TO MENTION IN THE TAFS. A COLD FRONT IS EXPECTED TO APPROACH THE REGION AROUND 18Z. JUST AHEAD OF THE FRONT, COULD SEE ISOLATED TO SCATTERED THUNDERSTORMS, THOUGH HIGHER CHANCES LOOK TO STAY NORTH OF THE TAF SITES, WILL BE KEEPING A CLOSE EYE ON THIS THROUGH THE DAY THOUGH. AS FOR THE EXACT TIMING OF THE FRONT, AND THUS A SHIFT TO NORTHWESTERLY WINDS, RELATIVELY HIGH CONFIDENCE OF IT ARRIVING AT KRDG AND KABE BY 21Z. CONSIDERABLY LESS CONFIDENCE FOR THE OTHER TAF SITES. HAVE CHOSEN TO GO WITH A FASTER SOLUTION THAN WHAT THE NAM OR GFS LAMP ARE SHOWING GIVEN A RELATIVELY PROGRESSIVE OVERALL PATTERN, WITH AN ARRIVAL IN THE DELAWARE VALLEY BETWEEN 00 AND 03Z, AND AT THE COASTAL SITES BY 06Z. OUTLOOK... FRIDAY...GENERALLY VFR. ISOLATED SHOWERS/THUNDERSTORMS POSSIBLE FOR WESTERN TAFS. FRIDAY NIGHT...VFR EARLY, THEN LOWERING CIGS/VSBYS WITH STRATUS/FOG POSSIBLE OVERNIGHT. SATURDAY...LOWER CONDITIONS POSSIBLE EARLY, THEN BECOMING VFR DURING THE DAY. SCATTERED SHOWERS AND THUNDERSTORMS POSSIBLE WHICH MAY LOCALLY REDUCE CIGS/VSBYS. GUSTY SOUTH-SOUTHWEST WINDS AROUND 20 KNOTS. SATURDAY NIGHT-MONDAY...AN EXTENDED PERIOD OF MVFR/IFR CONDITIONS POSSIBLE. A CHANCE OF RAIN EACH DAY. BEST POTENTIAL FOR THUNDERSTORMS IS SUNDAY. && .MARINE... SEAS HAVE DIMINISHED. THUS, HAVE CANCELLED THE SCA A BIT EARLY. THIS AFTERNOON, A FEW GUSTS NEAR OR JUST ABOVE 20 KT ARE POSSIBLE ON THE ATLANTIC COASTAL WATERS, BUT SHOULD REMAIN BELOW SCA CRITERIA. HOWEVER, GUSTY WINDS ARE POSSIBLE IN THE VICINITY OF ANY THUNDERSTORMS THIS AFTERNOON AND EVENING. A WIND SHIFT WITH A COLD FRONT IS EXPECTED THIS EVENING INTO THE OVERNIGHT HOURS. OUTLOOK... FRIDAY-FRIDAY NIGHT...SUB-SMALL CRAFT ADVISORY CONDITIONS CURRENTLY EXPECTED, ALTHOUGH WINDS MAY GUST AROUND 20 KNOTS AT TIMES. SATURDAY-MONDAY...SEAS MAY RETURN TO 5 FEET OR GREATER LATE ON SATURDAY AHEAD AHEAD OF AN APPROACHING COLD FRONT. SEAS MAY REMAIN ELEVATED INTO MONDAY, AND WINDS MAY INCREASE TO 25 KNOTS. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...ROBERTSON NEAR TERM...JOHNSON SHORT TERM...JOHNSON LONG TERM...ROBERTSON AVIATION...JOHNSON/ROBERTSON MARINE...JOHNSON/ROBERTSON

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