Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 271946 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 346 PM EDT WED AUG 27 2014 .SYNOPSIS... A WEAK COLD FRONT WILL SLIDE ACROSS THE REGION TONIGHT, HELPING TO KEEP HURRICANE CRISTOBAL WELL EAST OF THE MID ATLANTIC COAST INTO THURSDAY. HIGH PRESSURE BUILDS IN THURSDAY AND FRIDAY, THEN SHIFTS OFFSHORE INTO SATURDAY. A WARM FRONT SHOULD LIFT NORTH ACROSS THE REGION SATURDAY, THEN A FRONTAL BOUNDARY MAY STALL TO OUR NORTH SUNDAY AND MONDAY. THE NEXT COLD FRONT IS SCHEDULED TO ARRIVE WEDNESDAY. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... AN UPPER SHORTWAVE TROUGH OVER THE GREAT LAKES THIS AFTERNOON WILL MOVE EASTWARD INTO THE NORTHEAST STATES TONIGHT. THE COLD FRONT ASSOCIATED WITH THIS FEATURE IS STILL BACK TO OUR NORTH AND WEST OVER CENTRAL NY-WESTERN PA. FARTHER DOWNSTREAM, HURRICANE CRISTOBAL IS LOCATED WELL OFF THE EAST COAST, ABOUT 500 MILES SOUTHEAST OF FENWICK ISLAND, DE. THE BULK OF THE SYNOPTIC LIFT FROM THE TROUGH WILL STAY NORTH OF THE REGION. LIKEWISE, THE STRONGEST MID-LEVEL WINDS (40-50 KT AT H5) WILL ALSO STAY NORTH. THE EFFECTS OF THIS CAN BE SEEN THE ORIENTATION OF THE COLD FRONT, WITH THE SOUTHERN EDGE OF THE FRONT PROGRESSING EASTWARD MUCH SLOWER ACROSS PA. THE BEST LIFT ALONG THE FRONT ITSELF ISN`T EXPECTED TO ARRIVE INTO NORTHEAST PA/NORTHERN NJ UNTIL SEVERAL HOURS AFTER PEAK HEATING. KEPT POPS LOW WITH THE FROPA AND CONFINED ANY MENTION OF SHOWERS AND STORMS TO THE LEHIGH VALLEY, THE POCONOS AND NORTHWESTERN NJ. THE BEST WINDOW FOR CONVECTION ACROSS THE THESE FAR NORTHERN ZONES WILL BE BETWEEN ABOUT 6 AND 9 PM, WHICH IS JUST AHEAD OF THE FRONT. THIS ACTIVITY SHOULD WANE SHORTLY AFTER WITH THE LOSS OF DAYTIME INSTABILITY. THE FRONT GRADUALLY ADVANCES TO THE SOUTH AND EAST THROUGH NORTHEAST PA AND NORTHERN NEW JERSEY LATE THIS EVENING AND ACROSS THE REST OF THE FORECAST AREA OVERNIGHT. FROPA WILL BE MARKED BY A WIND SHIFT FROM THE SOUTHWEST TO THE NORTHWEST AND A PERIOD OF BKN CLOUD COVER. ADJUSTED MIN TEMPS UP A COUPLE OF DEGREES FROM MOS GUIDANCE WITH NORTHWEST WINDS BEHIND THE FRONT HELPING TO LIMIT THE AMOUNT OF RADIATIONAL COOLING. FORECAST MIN TEMPS RANGE FROM THE MID 50S IN THE POCONOS TO AROUND 70 IN THE URBAN I-95 CORRIDOR AND ALONG COAST. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... THE COLD FRONT IS EXPECTED TO MOVING SOUTH OF THE DELMARVA DURING THE MORNING ON THURSDAY. HIGH PRESSURE WILL BUILD IN FROM THE GREAT LAKES BEHIND THE FRONT. THE OFFICIAL NHC FORECAST CALLS FOR HURRICANE CRISTOBAL TO BE LOCATED ABOUT 500 MILES OFF THE MID-ATLANTIC COAST 12Z THURSDAY BEFORE ACCELERATING TO THE EAST-NORTHEAST, MOVING FARTHER OUT TO SEA DURING THE DAY. THE PRESSURE GRADIENT BETWEEN THE HIGH TO OUR NORTHWEST AND THE COLD FRONT TO OUR SOUTH/HURRICANE CRISTOBAL TO OUR EAST WILL PRODUCE A BREEZY NORTHWEST WIND 10-15 MPH ACROSS OUR AREA. THESE WINDS WILL USHER IN RELATIVELY COOL AND DRY AIR WITH THE SOURCE OF THIS POST-FRONTAL AIRMASS FROM CANADA. FORECAST MAX TEMPS IN THE LM80S FOR MOST OF THE REGION, EXCEPT MU70S IN THE MOUNTAINS. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... THE OVERALL SYNOPTIC SETUP IS COMPRISED OF AN UPPER-LEVEL TROUGH EXITING THE NORTHEAST THURSDAY NIGHT INTO FRIDAY, THEN A SHORT WAVE TROUGH TRACKING ACROSS THE NORTHERN PLAINS AND MIDWEST WILL BUILD A RIDGE ACROSS THE EAST FRIDAY AND INTO THE WEEKEND. THIS RIDGE MAY HOLD FOR AWHILE, HOWEVER ADDITIONAL SHORT WAVES WILL CARVE OUT ANOTHER UPPER-LEVEL TROUGH THAT EVENTUALLY SHIFTS EASTWARD ACROSS THE MIDWEST AND GREAT LAKES REGION. AN ASSOCIATED COLD FRONT SHOULD ARRIVE TOWARD THE END OF THIS TIME FRAME, ALTHOUGH AN INITIAL FRONT MAY STALL TO OUR NORTH BEFORE RETREATING NORTHWARD. WE USED A MODEL BLEND FOR THURSDAY NIGHT THROUGH SATURDAY, THEN WENT WITH THE 12Z WPC GUIDANCE. SOME ADJUSTMENTS WERE THEN MADE FOLLOWING ADDITIONAL COLLABORATION WITH OUR SURROUNDING OFFICES. FOR THURSDAY NIGHT AND FRIDAY...AN UPPER-LEVEL TROUGH WILL BE EXITING TO OUR EAST FOLLOWED BY SOME RIDGING. THIS WILL PUSH HIGH PRESSURE ACROSS THE NORTHEAST AND MID ATLANTIC REGIONS. THE CENTER OF THE SURFACE HIGH WILL PROBABLY BE LOCATED JUST TO OUR NORTH, THEREFORE A NORTHWEST TO NORTH SURFACE WIND SHOULD OCCUR. THIS WILL HELP ADVECT A DRIER AIRMASS INTO THE AREA ALONG WITH COOLER AIR THROUGH FRIDAY. HOWEVER, THE SURFACE HIGH SHOULD BE SHIFTING OFFSHORE FRIDAY NIGHT ALLOWING FOR A RETURN FLOW TO START BECOMING ESTABLISHED. A SYSTEM MOVING ACROSS THE NORTHERN PLAINS AND MIDWEST WILL ASSIST IN WAA DEVELOPING NORTHBOUND UP THE OHIO VALLEY. THIS SHOULD ALSO ORGANIZE A WARM FRONT TO OUR SOUTHWEST. FOR SATURDAY AND SUNDAY...THE BUILDING OF AN UPPER-LEVEL RIDGE IS FORECAST TO OCCUR DURING THIS TIME FRAME, HOWEVER SHORT WAVE ENERGY TRAVELING FROM THE MIDWEST TO THE GREAT LAKES REGION WILL TRY AND FLATTEN IT SOME. DUE TO THE RIDGE AND ALSO SURFACE HIGH PRESSURE SITUATED OFFSHORE, A SOUTHWESTERLY FLOW OF WARM/HOT AND INCREASINGLY MORE HUMID AIR WILL OVERSPREAD THE AREA. WHILE THERE MAY BE SOMEWHAT OF A MOISTURE SURGE AS A WARM FRONT LIFTS NORTH ACROSS THE AREA SATURDAY, THE OVERALL FORCING LOOKS WEAK WITH MUCH OF THE ENERGY FOCUSED CLOSER TO THE GREAT LAKES. THEREFORE, WE MAINTAINED A DRY FORECAST FOR SATURDAY. AN INITIAL DISTURBANCE MAY END UP WEAKENING AS IT TRAVERSES A FRONTAL BOUNDARY TO OUR NORTH AND WEST SUNDAY AS IT RUNS INTO THE NORTHWEST FLANK OF THE UPPER-LEVEL RIDGE. DESPITE THIS, THERE COULD BE SOME CONVECTION ON THE SOUTHEASTWARD FLANK OF THIS WEAKENING DISTURBANCE SUNDAY. IF A LEE SIDE TROUGH DEVELOPS, THIS COULD ALSO BE THE FOCUS FOR SOME CONVECTIVE DEVELOPMENT WITHIN THE LARGE WARM SECTOR. GIVEN THE HEAT AND HIGHER HUMIDITY IN PLACE, SOME THUNDERSTORMS COULD BE LOCALLY STRONG FROM OUR WESTERN ZONES AND ESPECIALLY WEST OF OUR CWA. THIS CARRIES LOWER CONFIDENCE THOUGH DUE TO SOME UNCERTAINTY ON CONVECTIVE INITIATION AND COVERAGE AND THE TIMING OF EMBEDDED FEATURES. FOR NOW, WE CARRIED CHC POPS OR LESS DURING SUNDAY. FOR MONDAY AND TUESDAY...AS AN UPPER-LEVEL TROUGH RELOADS ACROSS THE NORTHERN PLAINS AND MIDWEST MONDAY, A RIDGE IS STILL NEAR OUR AREA MAINTAINING A SOUTHWESTERLY FLOW. THERE APPEARS TO BE A STALLED BAROCLINIC ZONE THOUGH TO OUR NORTH, HOWEVER AS OF NOW THERE IS NO REAL STRONG SURFACE HIGH TO PUSH THIS SOUTHWARD, PLUS THE RIDGING FARTHER SOUTH MAY BE STRONG ENOUGH TO KEEP IT AT BAY. HOWEVER, THE MODEL GUIDANCE SUGGESTS THAT WITHIN A RATHER WARM AND MOIST AIRMASS A LEE SIDE TROUGH MAY BE PRESENT AND EVEN SHARPEN UP SOME. WITH ANY SUBTLE SHORT WAVES TRACKING AROUND THE NORTHWESTERN PERIPHERY OF THE LINGERING RIDGE, SOME CONVECTION COULD DEVELOP IN TANDEM WITH THE LEE SIDE TROUGH. AS A RESULT, WE WILL CARRY SLIGHT CHC TO LOWER CHC POPS ESPECIALLY INLAND. THERE ARE SOME TIMING DIFFERENCES IN THE MODEL GUIDANCE, THEREFORE WE FOLLOWED MORE CLOSELY TO THE 12Z WPC GUIDANCE. FOR WEDNESDAY...AN AMPLIFYING UPPER-LEVEL TROUGH FROM THE MIDWEST AND GREAT LAKES REGION SHOULD PUSH A COLD FRONT INTO OUR REGION. WHILE THERE ARE SOME TIMING DIFFERENCES IN THE MODEL GUIDANCE, WE DID STAY CLOSER TO WPC GUIDANCE. THIS BRINGS THE ACTUAL COLD FRONT INTO OUR AREA LATER IN THE DAY. AS HEIGHTS FALL, THE FRONT ARRIVES AND LARGE SCALE FORCING GENERALLY ARRIVES, SOME CONVECTION IS POSSIBLE. IF THIS OCCURS DURING PEAK HEATING WITH ENOUGH SHEAR, CONVECTION COULD BE MORE ORGANIZED. OVERALL, WE WENT RATHER CLOSE TO THE 12Z WPC GUIDANCE. && .AVIATION /20Z WEDNESDAY THROUGH MONDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THERE IS A VERY LOW CHANCE OF SHRA/TSRA LATE THIS AFTN AND THIS EVE (ABOUT 20 PERCENT FOR RDG/ABE AND 10 PERCENT FARTHER S/E) AS A COLD FRONT APPROACHES FROM THE NW. COVERAGE/FORECAST CONFIDENCE TOO LOW TO INCLUDE IN TAFS. OTHERWISE, VFR WILL PREVAIL THRU TNGT. LIGHT SW WINDS 5-10 KT THIS AFTN WILL BECOME NW TNGT BEHIND COLD FROPA. BASED ON OBSERVATIONS AND SHORT-TERM GUIDANCE, PUSHED BACK TIMING OF THE FRONT AND ASSOCIATED WIND SHIFT A FEW HRS WITH THE 18Z TAFS. FROPA MAY NOT OCCUR UNTIL CLOSER TO 06Z FOR PHL (THIS WILL LIKELY OCCUR 2-3 HRS EARLIER AT RDG/ABE AND 2-3 HRS LATER AT ACY/MIV). NW WINDS AROUND 10-15 KT EXPECTED ON THU. SLIGHTLY HIGHER GUSTS TO 20 KT POSSIBLE AS DAYTIME MIXING DEEPENS. OUTLOOK... THURSDAY NIGHT AND FRIDAY...VFR. LIGHT WINDS BECOMING NORTHEAST, AND THEN SOUTHERLY FRIDAY. SATURDAY AND SUNDAY...A CHANCE OF LOCAL FOG EACH EARLY MORNING, OTHERWISE MAINLY VFR. SOME INCREASE IN CLOUDS POSSIBLE SATURDAY AS A WARM FRONT LIFTS NORTHWARD. SOME SHOWERS AND THUNDERSTORMS ARE POSSIBLE SUNDAY, WITH A CHANCE FOR LOCALLY SUB-VFR CONDITIONS. SOUTH AND SOUTHEAST WINDS SATURDAY 5-10 KNOTS, BECOMING SOUTH-SOUTHWEST SUNDAY. MONDAY...VFR, WITH THE EXCEPTION OF POSSIBLE BRIEF TIMES OF MVFR ASSOCIATED WITH A SHOWER OR THUNDERSTORM. LOWER CONFIDENCE REGARDING PRECIPITATION COVERAGE. SOUTHWESTERLY WINDS GENERALLY NEAR 10 KNOTS. && .MARINE... THE SEAS HAVE TAKEN LONGER TO BUILD ACROSS THE DELAWARE AND NJ WATERS (BUOY 44009 HAS BEEN STEADY AROUND 3-4 FT FOR MOST OF THE DAY) THAN PREVIOUS GUIDANCE HAD INDICATED, BUT IT WILL ARRIVE LATER TODAY AND TONIGHT. LATEST BUOY OBS THIS AFTN ALONG THE EASTERN COAST SHOW LARGE SWELLS FROM HURRICANE CRISTOBAL HAVE REACHED SE VA AND NC. EXPECT 4-6 FT SEAS TO DEVELOP IN THE DE/SRN NJ WATERS OVER THE NEXT FEW HOURS AND EXPAND NORTHWARD THIS EVE. HAVE UPDATED WORDING IN THE SCA TO ACCOUNT FOR THIS. LOCALLY HIGHER SEAS UP TO 7 FT STILL POSSIBLE LATE TONIGHT INTO THU MORNING. SCA CONTINUES FOR THE ATLANTIC WATERS THRU THU. OUTLOOK... AS TROPICAL CYCLONE CRISTOBAL MOVES FARTHER AWAY FROM THE AREA, THE SWELLS ARE EXPECTED TO SUBSIDE. WHILE 5-FOOT SWELLS MAY PERSIST A LITTLE LONGER THURSDAY NIGHT, WE HELD OFF ON EXTENDING THE SMALL CRAFT ADVISORY ATTM DUE TO SOME UNCERTAINTY. HIGH PRESSURE BUILDS IN OVER THE WEEKEND BEFORE SHIFTING OFFSHORE AND ALLOWING FOR A RETURN FLOW INTO NEXT WEEK. THE FLOW MAY STRENGTHEN FOR A TIME SUNDAY INTO MONDAY, HOWEVER OVERALL THE CONDITIONS ARE ANTICIPATED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA. && .RIP CURRENTS... LONG-PERIOD SWELLS FROM HURRICANE CRISTOBAL HAS TAKEN A BIT LONGER TO REACH THE DE/NJ BEACHES SO FAR THIS AFTN, BUT ENHANCED RIP CURRENTS HAVE ALREADY BEEN REPORTED MIDDAY BY DE/NJ BEACH PATROLS AND OBSERVERS. THE THREAT OF RIP CURRENTS WILL ONLY INCREASE LATE THIS AFTERNOON AND TONIGHT AS SWELLS IN THE SURF ZONE CONTINUE TO BUILD. THE RISK OF DROWNING WILL BE MAGNIFIED IF OPTING TO SWIM AFTER LIFEGUARDS GO OFF DUTY. THE HIGH RIP CURRENT RISK WILL LIKELY CONTINUE INTO THURSDAY WITH CRISTOBAL SEVERAL HUNDRED MILES OFFSHORE. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...HIGH RIP CURRENT RISK UNTIL 11 PM EDT THIS EVENING FOR NJZ014- 024>026. DE...HIGH RIP CURRENT RISK UNTIL 11 PM EDT THIS EVENING FOR DEZ004. MD...NONE. MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 PM EDT THURSDAY FOR ANZ450>455. && $$ SYNOPSIS...GORSE NEAR TERM...KLEIN SHORT TERM...KLEIN LONG TERM...GORSE AVIATION...GORSE/KLEIN MARINE...GORSE/KLEIN RIP CURRENTS...KLEIN

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