Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 261950 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 350 PM EDT TUE AUG 26 2014 .SYNOPSIS... HIGH PRESSURE WILL REMAIN OVER THE AREA THROUGH WEDNESDAY MORNING. A COLD FRONT WILL MOVE FROM NORTHWEST TO SOUTHEAST ACROSS THE REGION LATE WEDNESDAY AFTERNOON AND WEDNESDAY NIGHT. HIGH PRESSURE RETURNS THURSDAY AND FRIDAY. A WARM FRONT LIFTS THROUGH THE REGION SATURDAY FOLLOWED BY A COLD FRONT APPROACHING FROM THE NORTHWEST SUNDAY INTO MONDAY. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... A STRONG UPPER-LEVEL RIDGE WILL FLATTEN SOME THROUGH TONIGHT AS A SHORT WAVE TROUGH SLIDES ACROSS THE UPPER GREAT LAKES REGION. THIS SHORT WAVE WILL DRIVE A COLD FRONT EASTWARD ASSOCIATED WITH A SURFACE LOW THAT IS FORECAST TO TRACK WELL TO OUR NORTH ACROSS CANADA. MEANWHILE, SURFACE HIGH PRESSURE FROM THE CENTRAL APPALACHIANS NORTHEASTWARD WILL NARROW AND WEAKEN AS THE RIDGE FLATTENS. THE HIGH WILL TEND TO SHIFT NORTHEASTWARD, ALLOWING A RETURN FLOW TO BECOME BETTER ESTABLISHED ACROSS MUCH OF OUR AREA. SINCE HIGH PRESSURE ALOFT AND AT THE SURFACE ARE THE DOMINATING WEATHER FEATURES, THE DAYTIME SHALLOW CUMULUS WILL DISSIPATE THROUGH EARLY THIS EVENING. WHILE THERE COULD BE SOME HIGH CLOUDS AROUND THROUGH THE COURSE OF THE NIGHT AT TIMES, IT APPEARS THAT ANOTHER NIGHT OF A CLEAR OR MOSTLY CLEAR SKY SHOULD OCCUR. THIS WILL ASSIST IN DECENT COOLING OF THE BOUNDARY LAYER ONCE AGAIN, ALTHOUGH THE AIRMASS IS MODIFIED BUT THE DEW POINTS WILL BE UP A BIT. THIS COMBINATION SHOULD RESULT IN SOME PATCHY GROUND FOG ONCE AGAIN LATE, ESPECIALLY IN FIELDS AND OTHER OPEN AREAS. LOW TEMPERATURES WERE AN EVEN BLEND OF THE NAM/GFS MOS, ALTHOUGH SOME UPWARD TWEAKS WERE MADE FOR THE HIGHLY URBANIZED AREAS SUCH AS CENTER CITY PHILADELPHIA. THE HOURLY GRIDS WERE ADJUSTED WITH THE LATEST OBSERVATIONS, THEN THE LAMP/LAV GUIDANCE WAS BLENDED IN TO HELP ASSIST WITH TRENDS THROUGH THIS EVENING. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... THE UPPER-LEVEL RIDGE IS FORCED SOUTHWESTWARD SOME AS THE AFOREMENTIONED SHORT WAVE TROUGH AMPLIFIES AS IT SLIDES ACROSS SOUTHEASTERN CANADA AND THE EASTERN GREAT LAKES. AT THE SURFACE, A WEAK COLD FRONT WILL BE ARRIVING DURING THE AFTERNOON. THE MODEL GUIDANCE SHOWS A FAIRLY NARROW CORRIDOR OF HIGHER THETA-E AIR SURGING AHEAD OF THE COLD FRONT. THIS IS ALSO DEPICTED NICELY WITHIN THE MODEL GUIDANCE AS A PW PLUME OF 1.50 TO 1.80 INCHES. DESPITE THIS CORRIDOR OF INCREASED MOISTURE, THERE DOES NOT APPEAR TO BE A LOT OF FORCING WITH THE FRONT. THE FLOW ALOFT IS WEST-NORTHWEST, AND WHILE SOME CONVERGENCE SHOULD OCCUR AT THE SURFACE IT IS GENERALLY WEAK. THERE SHOULD BE SOME CONVECTIVE DEVELOPMENT UPSTREAM WITHIN THE RIBBON OF HIGHER MOISTURE CONTENT AND CLOSER TO SOME MORE NOTED HEIGHT FALLS, HOWEVER ACROSS OUR AREA THIS IS NOT MUCH OF A FACTOR. THEREFORE, WE SLOWED DOWN THE POP INCREASE SOME DURING THE AFTERNOON BUT DID MAINTAIN SOME SLIGHT CHC TO LOW CHC POPS NORTH AND WEST OF INTERSTATE 95 BY LATE IN THE DAY. THE FORECAST SOUNDINGS SOUTH AND EAST OF HERE SHOW MORE OF A CAP OCCURRING THROUGH THE DAY. IF STORMS ARE ABLE TO ARRIVE ACROSS OUR NORTHWEST ZONES EARLY ENOUGH, PERHAPS SOME PULSE TYPE UPDRAFTS COULD RESULT GIVEN THE LIGHT ENOUGH WIND FIELD. OTHERWISE, A HOT AND SOMEWHAT HUMID DAY IS ANTICIPATED AS 850 MB TEMPERATURES TOP OUT NEAR +18C. THIS COMBINED WITH SOME WESTERLY FLOW ALOFT SHOULD ALLOW TEMPERATURES TO REACH OR JUST EXCEED 90 DEGREES FOR SEVERAL INLAND LOCALES. SOME OF THE GUIDANCE CAME IN A LITTLE COOLER, HOWEVER GIVEN THE AIRMASS JUST ABOVE THE SURFACE WE STAYED RATHER CLOSE TO CONTINUITY FOR MUCH OF THE AREA. HURRICANE CRISTOBAL IS FORECAST TO TRACK WELL EAST OF THE MID ATLANTIC COAST LATER WEDNESDAY, HOWEVER BUILDING SWELLS WILL ARRIVE FROM SOUTH TO NORTH. FOR MORE INFORMATION, SEE THE RIP CURRENT SECTION BELOW. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... THE COLD FRONT IS EXPECTED TO ADVANCE SOUTHEASTWARD THROUGH THE FORECAST AREA DURING THE EVENING, ALTHOUGH MODELS HAVE TRENDED SLIGHTLY SLOWER WITH THE PROGRESSION OF THE FRONT AND THE FROPA MAY BE DELAYED UNTIL OVERNIGHT FOR THE DELMARVA. AN ISOLATED SHOWER OR TSTM POSSIBLE NEAR THE FRONT EARLY IN THE EVENING ACROSS THE HIGHER TERRAIN BEFORE CONVECTION WANES AFTER SUNSET WITH THE LOSS OF DAYTIME HEATING. THE PREDOMINANT IMPACT THE FROPA MAY HAVE IS A FEW HOURS OF MOSTLY CLOUDY SKIES AS WELL AS A WIND SHIFT OUT OF THE NW AND ARRIVAL OF COOLER/DRIER AIR IN ITS WAKE. THE OFFICIAL NHC FORECAST FOR HURRICANE CRISTOBAL IS FOR THE CENTER TO STAY ABOUT 450 MILES OR SO EAST THE DELMARVA COAST WEDNESDAY NIGHT, WHICH IS WELL OFFSHORE TO BRING ANY DIRECT IMPACT FROM THE TROPICAL CYCLONE TO THE AREA. HIGH PRESSURE BUILDS IN FROM THE GREAT LAKES THURSDAY. POST- FRONTAL CAA REGIME WILL CONTINUE. FORECAST H8 TEMPS ARE 4-8 C LOWER ON THURSDAY THAN ON WEDNESDAY, TRANSLATING TO MAX TEMPS THURSDAY IN THE LOWER 80S (EXCEPT 70S IN THE MOUNTAINS). THESE TEMPERATURES COMBINED WITH DEWPOINTS ONLY IN THE 50S WILL LEAD TO A PLEASANT LATE SUMMER DAY. THE PRESSURE GRADIENT BETWEEN THE HIGH AND CRISTOBAL WILL PRODUCE A NW WIND 10-15 MPH. A QUIET WX PATTERN WILL CONTINUE THROUGH THE REMAINDER OF THE WORK WEEK WITH HIGH PRESSURE OVERHEAD. TEMPS WILL BE RIGHT AT, IF NOT A COUPLE OF DEGREES BELOW NORMAL THURSDAY NIGHT AND FRIDAY. THE CENTER OF HIGH PRESSURE IS FORECAST TO SHIFT OFF THE NEW ENGLAND COAST FRIDAY NIGHT INTO SATURDAY. WINDS AT THE SURFACE WILL BEGIN TO VEER OUT OF THE SOUTHEAST AND EVENTUALLY SOUTH DURING THIS TIME. WAA PATTERN WILL DEVELOP AS THE OLD FRONTAL BOUNDARY THAT MOVES THROUGH WEDNESDAY AND STALLS TO OUR SOUTH THURSDAY/FRIDAY WILL LIFT BACK NORTHWARD AS WARM FRONT DURING THE BEGINNING OF THE HOLIDAY WEEKEND. THE RESULT WILL BE AN UPTICK IN TEMPS, HUMIDITY AND CLOUD COVER. COULD SEE ISOLATED MORNING SHOWERS AND AFTERNOON SHOWERS/STORMS ON SATURDAY WITH THE FROPA. ISENTROPIC LIFT IS RATHER SHALLOW/WEAK. NOT EXPECTING A WASHOUT FOR SATURDAY. THE WARM FRONT WILL LIFT NORTHWARD INTO NEW ENGLAND ON SUNDAY. FARTHER SOUTH, THE HEAT AND HUMIDITY WILL CONTINUE TO INCREASE AS OUR AREA BECOMES SITUATED DEEPER INTO THE WARM SECTOR. SIDED CLOSELY WITH WPC GUIDANCE, WHICH INDICATES HIGHS AROUND 90F ON SUNDAY. MEANWHILE A NORTHERN STREAM SHORTWAVE TROUGH IS PROGGED TO MOVE EASTWARD THROUGH THE GREAT LAKES/MIDWEST AND NORTHEAST STATES DURING THE SUNDAY-MONDAY PERIOD. THERE IS STILL UNCERTAINTY IN THE TRACK AND TIMING OF THIS SYSTEM, WHICH IS COMMON THIS FAR OUT. THINK THE 12Z OPERATIONAL GFS IS TOO FAST WITH THE TROUGH AND WITH BREAKING DOWN THE DOWNSTREAM UPPER RIDGE. ACCORDINGLY, KEPT THE HIGHEST POPS SUNDAY ACROSS THE HIGHER TERRAIN IN THE NORTHWEST PORTION OF THE CWA, BUT LOW OVERALL AS THE BEST LIFT SHOULD STILL RESIDE NORTHWEST OF THE AREA. CHANCES FOR SHOWERS AND STORMS INCREASE LABOR DAY AS A COLD FRONT TRIES TO MOVE INTO THE AREA. DRIER WEATHER FOR TUESDAY BEHIND THE FRONT. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. REST OF THIS AFTERNOON...VFR. MAINLY SOUTHEASTERLY WINDS LESS THAN 10 KNOTS. TONIGHT...VFR OVERALL. SOME LOCALIZED FOG IS POSSIBLE TOWARD MORNING, MAINLY AT KMIV AND KRDG. SOUTHERLY WINDS AROUND 5 KNOTS, BECOMING LIGHT AND VARIABLE OR CALM. WEDNESDAY....MAINLY VFR. A LATE DAY SHOWER OR THUNDERSTORM IS POSSIBLE MAINLY NEAR KTTN, KABE AND KRDG. SOUTHWEST WINDS INCREASING TO 5-10 KNOTS, HOWEVER TURNING SOUTHEASTERLY MAINLY AT KACY. OUTLOOK... WEDNESDAY EVENING...AN ISO SHRA OR TSRA THROUGH ABOUT SUNSET TO THE N/W OF THE PHILLY TERMINALS. UNLESS THERE ONE OF THESE STORMS MOVES DIRECTLY OVER A TERMINAL, VFR CONDITIONS EXPECTED. THURSDAY THROUGH FRIDAY NIGHT...VFR AND DRY WITH HIPRES OVERHEAD. SATURDAY THROUGH SUNDAY...SHRA AND TSRA CHANCES INCREASE AS THE WEEKEND PROGRESSES. ATTM, BETTER PRECIP CHANCE BOTH DAYS WOULD APPEAR TO BE CLOSER TO THE PA MTS OUT TOWARD RDG/ABE. && .MARINE... HIGH PRESSURE WILL SHIFT TO THE NORTHEAST AND WEAKEN THROUGH TONIGHT, THEN A WEAK COLD FRONT ARRIVES LATER WEDNESDAY. THIS WILL RESULT IN A WEAK ONSHORE FLOW AIDED BY SEA/BAY BREEZE INTO THIS EVENING, THEN THE FLOW SHOULD TURN MORE SOUTHWESTERLY. HOWEVER HURRICANE CRISTOBAL IS FORECAST TO TRACK WELL EAST OF THE MID ATLANTIC COAST LATER WEDNESDAY AND THIS SHOULD HELP KEEP AN EAST OR NORTHEAST FLOW ACROSS OUR SOUTHERN OCEAN WATERS. THE CONDITIONS ARE EXPECTED TO BE BELOW SMALL CRAFT ADVISORY THROUGH TONIGHT, THEN INCREASING SWELLS ARRIVE DURING WEDNESDAY. AS THESE ARRIVE AND BUILD, A SMALL CRAFT ADVISORY GOES INTO EFFECT STARTING AT 14Z ACROSS THE SOUTHERN OCEAN ZONES THEN WORKING NORTHWARD. WE ARE EXPECTING SUB-ADVISORY CONDITIONS ON DELAWARE BAY THROUGH WEDNESDAY. OUTLOOK... WEDNESDAY NIGHT AND THURSDAY...THE OUTER EFFECTS OF HURRICANE CRISTOBAL WILL REACH OUR MARINE ZONES WEDNESDAY NIGHT. SCA ISSUED FOR THE ATLANTIC ZONES FOR WEDNESDAY NIGHT AS SEAS ARE FORECAST TO BUILD TO 5-7 FT. WINDS SHOULD FOR THE MOST PART REMAIN UNDER 25 KT, SO SCA FOR HAZARDOUS SEAS WAS ISSUED. HOWEVER, A BRIEF NW WIND SURGE THAT APPROACHES THE SCA THRESHOLD IS POSSIBLE BEHIND THE COLD FRONT EARLY THURSDAY MORNING. LONG PERIOD SWELLS NEAR 15 SECONDS ARE ALSO EXPECTED. SEAS SHOULD GRADUALLY SUBSIDE THURSDAY BUT THE SCA WILL LIKELY NEED TO BE EXTENDED INTO THIS PERIOD. THURSDAY NIGHT THROUGH SUNDAY...SEAS CONTINUE TO SUBSIDE AS CRISTOBAL MOVES FARTHER AWAY FROM THE EAST COAST. NO MARINE HEADLINES EXPECTED THROUGH THE WEEKEND. && .RIP CURRENTS... THE RISK OF DANGEROUS RIP CURRENTS REMAINS MODERATE THROUGH THIS EVENING, DUE TO THE WAVE PERIOD AROUND 8 SECONDS AND SOME LINGERING ROUGHNESS TO THE SURF. FOR WEDNESDAY, HURRICANE CRISTOBAL IS FORECAST TO TRACK WELL EAST OF THE MID ATLANTIC COAST. HOWEVER, BUILDING SWELLS WILL RADIATE OUTWARD FROM THE HURRICANE AND AFFECT OUR COASTAL AREAS. AS OF NOW, WAVES IN THE SURF ZONE LOOK TO BUILD TO 4 TO 6 FEET, POSSIBLY TO 7 FEET WEDNESDAY NIGHT. WHILE WIND IS NOT EXPECTED TO BE AN ISSUE, RATHER LONG PERIOD SWELLS WILL CREATE ROUGH CONDITIONS WITH A STRONGER CURRENT. AS A RESULT, A HIGH RISK OF DANGEROUS RIP CURRENTS WILL BE ISSUED FOR WEDNESDAY. WHILE THE RIP CURRENT RISK MAY NOT BE QUITE AS HIGH ON THURSDAY AS WEDNESDAY, IT WILL BE ENHANCED NONETHELESS AS CRISTOBAL MOVES EVEN FARTHER OUT TO SEA. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...HIGH RIP CURRENT RISK FROM WEDNESDAY MORNING THROUGH WEDNESDAY EVENING FOR NJZ014-024>026. DE...HIGH RIP CURRENT RISK FROM WEDNESDAY MORNING THROUGH WEDNESDAY EVENING FOR DEZ004. MD...NONE. MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 10 AM WEDNESDAY TO 6 AM EDT THURSDAY FOR ANZ452>455. SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 2 PM WEDNESDAY TO 6 AM EDT THURSDAY FOR ANZ450-451. && $$ SYNOPSIS...KLEIN NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...KLEIN AVIATION...GORSE/KLEIN MARINE...GORSE/KLEIN RIP CURRENTS...GORSE/KLEIN

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