Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 031533 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1133 AM EDT THU SEP 3 2015 .SYNOPSIS... A BACKDOOR COLD FRONT WILL SLIDE SOUTHWESTWARD ACROSS THE AREA LATER TONIGHT AND EARLY FRIDAY MORNING. HIGH PRESSURE WILL THEN BUILD INTO OUR REGION FROM THE NORTH SATURDAY AND SUNDAY BEFORE SHIFTING OFFSHORE EARLY NEXT WEEK. A WEAKENING COLD FRONT IS THEN FORECAST TO GRADUALLY ARRIVE LATER WEDNESDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A PRESSURE TROUGH WAS LOCATED NEAR CAPE CODE, EXTENDING SOUTHEASTWARD TO JUST OFF THE NJ AND DELMARVA COAST. A LEE SURFACE TROUGH IS FORECAST TO DEVELOP INLAND THIS AFTERNOON NEAR I-95 WHERE NORTHERLY WINDS TO THE WEST OF THE TROUGH AXIS CONVERGE WITH ONSHORE FLOW ASSOCIATED WITH THE INLAND MOVING SEA-BREEZE. SKIES WILL REMAIN SUNNY THRU THE REMAINDER OF THE MORNING BEFORE CU FIELD DEVELOPS DURING THE PEAK HEATING HOURS THIS AFTERNOON. IT SHOULD REMAIN DRY THRU AT LEAST EARLY AFTERNOON. MADE SOME MINOR TWEAKS TO THE POP/WX GRIDS FOR TODAY BY CONFINING ISOLATED SHOWERS AND STORMS TO FAR SOUTHERN AND FAR NORTHERN ZONES. ACROSS THE LOWER DELMARVA, ENHANCED LOW-LEVEL CONVERGENCE ALONG THE TROUGH AXIS IS FORECAST IN ADDITION TO LOCALLY HIGHER INSTABILITY, WHICH MAY YIELD AN ISOLATED STORM OR TWO DURING THE MID AFTERNOON. ISOLATED SHOWERS AND STORMS WERE ALSO HIGHLIGHTED IN NORTHEAST PA AND NORTHWEST NJ. THE FOCUS FOR CONVECTION UP THERE WILL BE TERRAIN CIRCULATIONS AS WELL AS A BACKDOOR COLD FRONT THAT WILL BE DROPPING SOUTHWARD FROM UPSTATE NY. THIS ACTIVITY IS FAVORED LATE IN THE DAY DUE TO A DELAYED ARRIVAL OF THIS FRONT. THE LATE SEASON HEAT WILL CONTINUE ANOTHER DAY WITH HIGHS IN THE LOWER 90S ACROSS MOST OF THE AREA (EXCEPT COOLER NEAR THE COAST AND IN THE HIGHER ELEVATIONS OF NORTHEAST PA/NORTHWEST NJ). THE HEAT INDEX MAY TOP OFF IN THE 94-96F RANGE FOR THE HOT SPOTS WITHIN THE URBAN I-95 CORRIDOR. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... THE SLIGHT CHANCE OF A SHOWER OR THUNDERSTORM WILL CONTINUE INTO EARLY TONIGHT WITH SOME LINGERING INSTABILITY AND WITH THE SURFACE TROUGH. A COLD FRONT APPROACHING FROM THE NORTH IS ANTICIPATED TO DROP THROUGH OUR REGION LATE TONIGHT. THE FRONT IS NOT EXPECTED TO ENHANCE OUR CHANCE FOR PRECIPITATION AS CONDITIONS ARE FORECAST TO STABILIZE GRADUALLY DURING THE NIGHT. MINIMUM TEMPERATURES SHOULD BE MAINLY IN THE UPPER 60S AND LOWER 70S. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... THE SYNOPTIC SETUP IS COMPRISED OF A RIDGE SLIDING EASTWARD OVER OUR AREA FRIDAY AND SATURDAY. THIS RIDGE IS THEN FORECAST TO FLATTEN OUT EARLY NEXT WEEK AS A SHORT WAVE TROUGH SLIDES ACROSS THE NORTHERN TIER OF STATES. OVERALL, THIS PATTERN SHOULD FAVOR WARMTH AND DRYNESS ALTHOUGH A BRIEF BREAK OCCURS SATURDAY INTO SUNDAY IN THE WAKE OF A BACKDOOR COLD FRONT. THE REGION NEEDS RAIN, HOWEVER IT LOOKS LIKE THE CHCS ARE RATHER LOW GIVEN NO ORGANIZED SYSTEMS MOVING THROUGH. WE USED A MODEL/CONTINUITY BLEND FOR FRIDAY INTO SUNDAY, WITH A 00Z WPC GUIDANCE/CONTINUITY BLEND THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE AFTER ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES. FOR FRIDAY...A BACKDOOR COLD FRONT IS FORECAST TO BE SHIFTING WEST AND SOUTH OF OUR AREA. ANY CONVECTION SHOULD THEREFORE BE SHIFTING SOUTHWESTWARD WITH TIME AS SURFACE HIGH PRESSURE STARTS TO BUILD ACROSS NEW ENGLAND. THIS WILL RESULT IN THE LOW-LEVEL FLOW BEING FROM THE EAST OR NORTHEAST, AND WITH MORE OF AN OCEAN INFLUENCE SOME COOLING OF THE AIR MASS IS ANTICIPATED. THE DRIER AIR MAY WIN OUT AND THEREFORE DESPITE THE ONSHORE FLOW WE SHOULD HAVE SOME DECREASE IN THE CLOUDS ESPECIALLY ACROSS THE NORTHERN AREAS. HOWEVER IF THE TRANSITION IS DELAYED OR IS NOT CLEAN LIKE SOME GUIDANCE SUGGESTS, THEN A PERIOD OF LOW CLOUDS MAY BE POSSIBLE BEFORE THE DRIER AIR PRESSES FARTHER SOUTH. IF THIS WERE TO OCCUR, THE SOUTHERN AND WESTERN PORTIONS OF THE AREA SHOULD HAVE THE HIGHEST CHC. SINCE THE PROSPECTS OF SHOWERS AND THUNDERSTORMS IS ON THE LOWER SIDE, WE KEPT THE POPS AT OR BELOW LOW CHC, WITH THE BETTER CHC LOOKING LIKE THE WESTERN ZONES TO PORTIONS OF THE DELMARVA. THERE DOES APPEAR TO BE A WINDOW WHERE BREEZY CONDITIONS DEVELOP ESPECIALLY CLOSER TO THE COAST. THE IDEA OF MORE CLOUDINESS/LOW CLOUD DEVELOPMENT WAS INCORPORATED INTO THE SKY GRIDS IN THE AFTERNOON AND AT NIGHT, MAINLY FOR THE SOUTHERN PORTIONS OF THE CWA. FOR SATURDAY AND SUNDAY...AS THE UPPER-LEVEL RIDGE CRESTS ACROSS THE AREA, SURFACE HIGH PRESSURE SHOULD EASE EASTWARD. THIS WILL ALLOW THE ONSHORE FLOW TO WEAKEN AND EVENTUALLY TURN SOUTHERLY. THERE COULD BE SOME RESIDUAL CLOUDINESS MAINLY ACROSS THE FAR SOUTHERN ZONES TO START SATURDAY DEPENDING ON THE DRY AIR PUSH, OTHERWISE NO SIGNIFICANT WEATHER IS ANTICIPATED ATTM. WE START TO LOSE THE COOLER ONSHORE INFLUENCE, AND THEREFORE THE DAYTIME TEMPERATURES ARE ANTICIPATED TO REBOUND SUNDAY AFTERNOON FOR MUCH OF THE AREA. FOR MONDAY THROUGH WEDNESDAY...A SHORT WAVE TROUGH MOVING NEAR THE U.S.-CANADIAN BORDER SHOULD FLATTEN THE RIDGE. THIS WILL ALSO FORCE HIGH PRESSURE MORE OFFSHORE, AND A WEAK COLD FRONT SHOULD BE GRADUALLY SLIDING EASTWARD ACROSS THE GREAT LAKES. THE BULK OF THE ENERGY LOOKS TO TRACK WELL TO OUR NORTH TUESDAY, THEREFORE THE CHCS FOR CONVECTION SHOULD MOSTLY REMAIN TO OUR WEST. SOME GUIDANCE SUGGESTS THE INITIAL SHORT WAVE TROUGH LIFTING WELL INTO CANADA AS A SECONDARY SHORT WAVE TROUGH CROSSES THE MIDWEST WEDNESDAY. IT IS A WEAK COLD FRONT WITH THIS FEATURE THAT MAY END UP MOVING THROUGH OUR AREA LATER WEDNESDAY. THERE IS MORE UNCERTAINTY WITH THE TIMING OF THESE FEATURES THIS FAR OUT. GIVEN THE LINGERING RIDGE TO THE SOUTH, A SLOWER EASTWARD PROGRESSION OF THE SURFACE FRONT MAY RESULT. AS THE FLOW IS MORE SOUTHERLY, A RATHER WARM AIR MASS LOOKS TO BE IN PLACE WITH SOME INCREASE IN THE DEW POINTS. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR THRU THE AFTN AND INTO THE EVE. SOME VISIBILITY RESTRICTIONS ARE AGAIN POSSIBLE LATE TONIGHT WITH FOG. ISOLATED SHOWERS AND THUNDERSTORMS MAY DEVELOP IN VICINITY OF ABE AND RDG TERMINALS AFTER 18Z TODAY BEFORE THE ACTIVITY DECAYS THIS EVENING WITH THE LOSS OF DAYTIME HEATING. HOWEVER, THE CHANCE OF ANY OF OUR TAF SITES BEING AFFECTED IS LOW AND WE WILL NOT MENTION THE POTENTIAL IN THE TAF PRODUCTS. THE WIND IS FORECAST TO FAVOR THE NORTH AND NORTHWEST FOR TODAY AT LESS THAN 10 KNOTS. HOWEVER, A SURFACE TROUGH IS EXPECTED TO MOVE INLAND FROM THE OCEAN AND IT SHOULD AFFECT KACY THIS AFTERNOON BRINGING THE WIND AROUND TO EAST AND SOUTHEAST THERE. A LIGHT AND VARIABLE WIND THIS EVENING SHOULD BECOME NORTHEAST LATE TONIGHT AS A COLD FRONT DROPS THROUGH OUR REGION FROM THE NORTH. WIND SPEEDS ARE FORECAST TO REMAIN LESS THAN 10 KNOTS. OUTLOOK... FRIDAY...VFR OVERALL. SOME SHOWERS OR THUNDERSTORMS ARE POSSIBLE, ESPECIALLY FROM NEAR THE KPHL AREA ON WEST AND SOUTH. THERE IS A CHANCE FOR A PERIOD OF LOW CLOUD /MVFR/ DEVELOPMENT IN THE AFTERNOON AND EVENING ESPECIALLY FROM ABOUT KRDG TO KPHL TO KACY ON SOUTHWARD, HOWEVER THIS IS OF LOWER CONFIDENCE AT THIS TIME. EAST- NORTHEAST WINDS INCREASE TO 10-15 KNOTS, WITH SOME GUSTINESS IN THE AFTERNOON AND EVENING MAINLY CLOSER TO THE COAST. SATURDAY THROUGH MONDAY...MOSTLY VFR. EAST-NORTHEAST WINDS MAINLY 10- 15 KNOTS SATURDAY, DIMINISHING AND BECOMING SOUTHEASTERLY SUNDAY BEFORE TURNING SOUTH-SOUTHWEST ON MONDAY. && .MARINE... A SURFACE TROUGH IS FORECAST TO BE OVER OUR COASTAL WATERS THIS MORNING BEFORE IT DRIFTS INLAND THIS AFTERNOON. A COLD FRONT IS EXPECTED TO ARRIVE FROM THE NORTH LATE TONIGHT. THE WIND IS ANTICIPATED TO BE VARIABLE THIS MORNING BEFORE SETTLING INTO THE SOUTHEAST FOR THIS AFTERNOON AND EARLY TONIGHT. THE WIND IS EXPECTED TO BECOME EAST TO NORTHEAST LATE TONIGHT. SPEEDS SHOULD REMAIN AT 10 KNOTS OR LESS. WAVE HEIGHTS ON OUR OCEAN WATERS ARE FORECAST TO BE 1 TO 2 FEET FOR THIS AFTERNOON AND TONIGHT WITH WAVES ON DELAWARE BAY BEING 2 FT OR LESS. OUTLOOK... FRIDAY AND SATURDAY...AS A BACKDOOR FRONT MOVES THROUGH, THE WINDS WILL TURN FROM THE EAST AND NORTHEAST AND INCREASE. IT APPEARS THAT GUSTS TO AROUND 25 KNOTS OCCUR FROM NORTH TO SOUTH ON THE COASTAL WATERS LATER FRIDAY AFTERNOON THROUGH SATURDAY MORNING BEFORE A DECREASE BEGINS. AS A RESULT, A SMALL CRAFT ADVISORY LOOKS TO BE NEEDED. THE ONSHORE FLOW WILL ALSO BUILD THE SEAS TO AROUND 5 FEET STARTING LATE FRIDAY ON THE COASTAL ATLANTIC WATERS. SUNDAY AND MONDAY...THE WINDS ARE ANTICIPATED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA AS THEY SHIFT FROM EAST-NORTHEAST TO SOUTHEAST AND SOUTH. THE SEAS ARE CURRENTLY ANTICIPATED TO BELOW ADVISORY CRITERIA, HOWEVER THIS WILL DEPEND ON HOW HIGH THEY GET ON THE ATLANTIC COASTAL WATERS FRIDAY AND SATURDAY. && .RIP CURRENTS... THE THREAT FOR DANGEROUS RIP CURRENTS WILL BE ENHANCED FRIDAY AND THE UPCOMING LABOR DAY WEEKEND. NORTHEASTERLY WINDS SURGE BEHIND A BACKDOOR COLD FRONT OF 10 TO 15 KT WILL ARRIVE FRIDAY MORNING AND INCREASE TO 15-20 KT FRIDAY AFTERNOON THRU SATURDAY. WAVES WILL BUILD IN RESPONSE TO THIS WIND SURGE, FORECASTED TO INCREASE TO 4-7 FT BY LATE IN THE DAY FRIDAY. THE WINDS AND WAVES ALONG THE COAST SHOULD GRADUALLY SUBSIDE LATE SATURDAY INTO SUNDAY. SUBJECT TO CHANGE SEVERAL DAYS OUT, BUT IN-HOUSE GUIDANCE IS SUGGESTING A MODERATE RIP CURRENT RISK FRIDAY AND MODERATE TO POSSIBLY NEAR HIGH FOR SATURDAY. THE RISK SHOULD SUBSIDE A BIT BY SUNDAY BUT IT MAY STILL BE MODERATE. IT IS PARTICULARLY IMPORTANT FOR SAFETY AWARENESS TO SHARE THIS INFORMATION TO BEACHGOERS AND LIFEGUARDS WITH THE BEACH CROWD ANTICIPATED TO BE LARGER THAN NORMAL GIVEN IT`S LABOR DAY WEEKEND AND THERE IS PLENTY OF SUNSHINE IN THE FORECAST. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GORSE NEAR TERM...KLEIN SHORT TERM...IOVINO LONG TERM...GORSE AVIATION...GORSE/IOVINO/KLEIN MARINE...GORSE/IOVINO/KLEIN RIP CURRENTS...KLEIN

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