000 FXUS61 KPHI 291945 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 345 PM EDT FRI AUG 29 2008 .SYNOPSIS... HIGH PRESSURE STILL ANCHORED OVER NORTHERN NEW ENGLAND WILL GRADUALLY MOVE EASTWARD TONIGHT, GIVING WAY TO ANOTHER AREA OF HIGH PRESSURE OVER THE GREAT LAKES REGION SATURDAY INTO SUNDAY. HOWEVER, A COLD FRONT IS EXPECTED TO MOVE THROUGH OUR AREA LATER SATURDAY, FOLLOWED BY THE AFOREMENTIONED SECOND AREA OF HIGH PRESSURE SETTLING IN FOR SUNDAY AND LINGERING THROUGH MOST OF NEXT WEEK. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... A SURFACE ANALYSIS THIS AFTERNOON PLACES HIGH PRESSURE ANCHORED OVER NORTHERN NEW ENGLAND. THIS PERSISTENT HIGH, ALTHOUGH WEAKER, HAS CONTINUED TO REMAIN AN ENTITY ALL THE WAY DOWN INTO DELAWARE. WEST OF THIS, A SURFACE TROUGH EXTENDED INTO SOUTHEASTERN PENNSYLVANIA FROM VIRGINIA. SURFACE OBSERVATIONS ALONG WITH RADAR IMAGERY SHOWS WHAT LOOKS TO BE A MESO-LOW NEAR KDCA THIS AFTERNOON. COULD THIS BE THE ACTUAL REMNANT CIRCULATION OF FAY? SOME ADDITIONAL SHOWER ACTIVITY HAS DEVELOPED WITH THIS. THE MODEL GUIDANCE SUGGESTS A SHORT WAVE TRACKS ACROSS THE AREA, AND THIS APPEARED TO HAVE TEAMED UP WITH THE AFOREMENTIONED SURFACE TROUGH AND PRODUCED AN ORGANIZED AREA OF RAIN CURRENTLY MOVING ACROSS PARTS OF EASTERN PENNSYLVANIA. THIS SURFACE TROUGH MAY LAG BEHIND THE SHORT WAVE THOUGH, ALLOWING THE AREA OF RAIN TO PERHAPS GRADUALLY WEAKEN WITH AN EASTWARD EXTENT. THE PRESENCE OF THE SURFACE HIGH WEDGING DOWN THE COAST HAS YET AGAIN ALLOWED A FAIR AMOUNT OF CLEARING ACROSS MONMOUTH, OCEAN, MERCER AND EVEN INTO BURLINGTON COUNTIES FOR AWHILE THIS AFTERNOON. SURFACE OBSERVATIONS ALSO SHOW SOME LOWER DEW POINTS IN THESE AREAS, WHICH EVEN MIXED OUT SOME FURTHER TO THE SOUTHWEST. THE 12Z LWX RAOB HAS A VEERING WIND PROFILE WITH HEIGHT IN THE LOWER LEVELS. MODEL DATA SHOWS THIS WITH SOME WAA AND THETA-E ADVECTION, HOWEVER THIS GRADUALLY DWINDLES DURING THE FIRST OF TONIGHT AS A WEAK SHORT WAVE EXITS THE REGION. THIS MAY BE JUST ENOUGH TO KEEP SHOWERS GOING, ESPECIALLY THIS EVENING. WE WILL MAKE A LAST MINUTE DECISION ON POPS GIVEN RADAR TRENDS, BUT WE WILL LIKELY HAVE TO CARRY AT LEAST LOW CHC POPS ACROSS A GOOD PART OF THE AREA THROUGH ABOUT MIDNIGHT. WE DID BUMP UP POPS TO LIKELY FOR PORTIONS OF EASTERN PENNSYLVANIA THROUGH THE REMAINDER OF THE AFTERNOON BASED ON RADAR TRENDS. A GOOD AMOUNT OF MOISTURE WITHIN THE ATMOSPHERE WILL CONTINUE THROUGH TONIGHT, WITH EVEN THE NORTHEASTERN AREAS ALSO SEEING AN INCREASE. THIS COUPLED WITH A LIGHT SOUTHEASTERLY FLOW IS EXPECTED TO MAINTAIN A WEALTH OF CLOUDS TONIGHT. FORECAST SOUNDINGS AS WELL AS MOS GUIDANCE SUGGEST A GOOD CHC OF STRATUS TO DEVELOP. AS A RESULT, WE WILL CONTINUE THE IDEA OF A CLOUDY/MOSTLY CLOUDY SKY. AS THE DEW POINTS COME UP SOME TONIGHT COUPLED WITH THE LIGHT WINDS, WE MAY SEE PATCHY FOG FORM PARTICULARLY IN AREAS THAT SAW SOME RAIN LAST NIGHT AND TODAY. AS FOR TEMPERATURES, MOS IS MOSTLY CLUSTERED FOR TONIGHT AND WAS GENERALLY FOLLOWED. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... SATURDAY MAY START OUT WITH LOW CLOUDS AND SOME FOG FOR MANY AS THE LOW-LEVEL MOISTURE POOLS. WE ARE EXPECTING SOME OF THIS TO MIX OUT DURING THE COURSE OF THE MORNING AS THE SUNSHINE DISSIPATES SOME OF IT. THE FORECAST SOUNDINGS DO SHOW A GOOD AMOUNT OF MOISTURE REMAINING WITH PRECIPITABLE WATER VALUES OF 1.50 TO 1.80 INCHES. THIS SHOULD ALLOW FOR A FAIR AMOUNT OF CUMULUS DEVELOPMENT AS A COLD FRONT MAKES ITS WAY INTO OUR AREA. THE OVERALL TIMING OF THE FRONT HAS NOT CHANGED MUCH, THEREFORE IT WILL BE MOVING THROUGH DURING THE AFTERNOON AND EVENING HOURS. FORECAST SOUNDINGS GENERATE ENOUGH CAPE TO MAINTAIN THE MENTION OF THUNDER, HOWEVER MIDLEVEL LAPSE RATES ARE NOT REAL IMPRESSIVE. A 250 MB JET IS FORECAST TO SLIDE JUST TO OUR NORTH, AND THE NORTHERN ZONES ESPECIALLY ARE CLOSER TO THE ENTRANCE REGION. THE UPPER FLOW DOES SHOW SOME DIFFLUENCE, HOWEVER THE OVERALL TAKE ON THIS FRONT CONTINUES TO BE THAT IT IS FAIRLY WEAK /LACKING A PRONOUNCED THERMAL GRADIENT/. THERE STILL IS ENOUGH EVIDENCE THAT SOME SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP, THEREFORE WE WILL MAINTAIN CHC POPS. SOME MODEL GUIDANCE STILL INSIST ON PERHAPS A CONVECTIVE LINE FORMING AHEAD OF THE FRONT, HOWEVER THE VERTICAL SHEAR LOOKS WEAK ENOUGH TO PRECLUDE AN ORGANIZED CONVECTIVE THREAT. THE COLD FRONT WILL SETTLE SOUTH AND EAST OF OUR CWA SATURDAY NIGHT WITH THE UPPER-LEVEL TROUGH AXIS ALSO PASSING OVERHEAD. THERE WAS SOME EVIDENCE THAT A WEAK WAVE DEVELOPS ALONG THE FRONT AND PERHAPS SLOW IT UP SOME, HOWEVER THIS LOOKS SCENARIO LOOKS RATHER SLIM AND RATHER WEAK EVEN IF IT DOES, WHICH SHOULD NOT HAVE A NOTED IMPACT ON THE FRONTAL PASSAGE. AS HIGH PRESSURE SLIDES INTO THE GREAT LAKES REGION SATURDAY NIGHT, MUCH DRIER AIR IS EXPECTED TO INFILTRATE OUR ENTIRE REGION. FORECAST SOUNDINGS SHOW THIS NICELY AS THE ATMOSPHERIC COLUMN DRIES FROM THE TOP DOWN. AS A RESULT, CLEARING IS EXPECTED FROM NORTHWEST TO SOUTHEAST. HIGH PRESSURE THEN BUILDS IN FROM THE NORTHWEST DURING SUNDAY AS A UPPER-LEVEL RIDGE BUILDS INTO THE GREAT LAKES. OUR WEATHER WILL STILL BE INFLUENCED TO SOME EXTENT AS A CLOSED LOW SITS JUST EAST OF NEW ENGLAND. WITH HEIGHTS GRADUALLY RISING ON SUNDAY THOUGH, WE ANTICIPATE A BUMP UP IN TEMPERATURES. AS FOR TEMPERATURES, WENT MAINLY WITH A COMPROMISE BETWEEN THE GFS AND ETA MOS AS THE GFS MOS LOOKS TO WARM FOR MANY LOCATIONS /ESPECIALLY ON SATURDAY/. WE UTILIZED MOSTLY THE 12Z MOSGUIDE DATA FOR DEW POINTS SUNDAY AS THE LOW-LEVEL MOISTURE MAY MIX OUT SOME DURING THE AFTERNOON. && .LONG TERM /MONDAY THROUGH FRIDAY/... THIS TIME FRAME IS STILL EXPECTED TO BE DOMINATED BY A SURFACE HIGH SLIDING ACROSS THE REGION IN RESPONSE TO AN AMPLIFYING UPPER-LEVEL RIDGE. IT APPEARS THE UNCERTAINTY THAT WAS MORE PRONOUNCED REGARDING AN UPPER-LEVEL LOW TO OUR EAST HAS DECREASED DUE TO ADDITIONAL MODEL GUIDANCE AGREEMENT. THE LATEST MODEL GUIDANCE HAS NOT CHANGED MUCH FROM 24 HOURS AGO, IN THAT THEY CONTINUE TO ADVERTISE A BUILDING/EXPANDING RIDGE ACROSS THE EASTERN UNITED STATES. THE ONLY NOTED CHANGE IS THAT THE ECMWF HAS BACKED OFF THE IDEA OF THE CLOSED LOW TO OUR EAST EVENTUALLY RETROGRADING. THIS IS IN RESPONSE TO THE UPPER RIDGE SLIDING FARTHER TO THE EAST, LIKE THE GFS HAD BEEN ADVERTISING, WHICH KEEPS THE CLOSED LOW FARTHER AWAY. THE 500 MB GFS ENSEMBLES ARE NEARLY ALL IN AGREEMENT WITH THE UPPER RIDGE DOMINATING OUR WEATHER THROUGH THE MAJORITY OF THIS TIME PERIOD. HPC NOTED THAT THE ECMWF ENSEMBLE MEAN IS ALSO IN GOOD AGREEMENT WITH THE OVERALL UPPER-LEVEL PATTERN. THE SREF 500 MB HEIGHT MEAN LOOKS RATHER SIMILAR WITH THE BUILDING RIDGE AND THE CLOSED LOW WELL TO OUR EAST. WE WILL BE ON THE WESTERN SIDE THOUGH OF THE CLOSED LOW ON LABOR DAY, HOWEVER RIDGING IS EXPECTED TO DOMINATE. HPC MAINLY LEANED TOWARD THE ECMWF FOR THEIR GUIDANCE, BUT DID BLEND IN A SMALL PERCENTAGE OF THE 12Z GFS MOS. BASED ON THE ABOVE, AN EXPANSIVE AREA OF HIGH PRESSURE WILL BE LOCATED OVER THE EASTERN GREAT LAKES AND SLIDING EASTWARD ON LABOR DAY. THIS WILL ALLOW OUR ENTIRE AREA TO BE UNDER A GENERAL NORTHERLY FLOW, AND THE SURFACE FLOW MAY TRY AND SHIFT TO THE NORTHEAST OR EAST, ESPECIALLY ALONG THE COAST AS THE GRADIENT LOOKS FAIRLY WEAK. THIS EXTENSIVE AREA OF HIGH PRESSURE AT THE SURFACE IS EXPECTED TO BE REINFORCED AS THE UPPER-LEVEL RIDGE AMPLIFIES THROUGH WEDNESDAY. GIVEN THE CONSENSUS OF THE BUILDING UPPER-LEVEL RIDGE, THIS IS EXPECTED TO TOSS AN INCREASINGLY WARMER AIR MASS INTO OUR REGION. THE ONLY POSSIBLE FLY IN THE OINTMENT IS PERHAPS A WEAK FRONTAL BOUNDARY THAT MAY SLIDE DOWN THE COAST AS A QUICK SHOT OF SOME COOLER AIR ALOFT MOVES SOUTHWARD ON THE EAST SIDE OF THE UPPER RIDGE. THIS FEATURE, IF EVEN EVENTUALLY PRESENT, LOOKS RATHER ILL-DEFINED. THIS FEATURE IS NOTED THOUGH IN THE THERMAL FIELDS AT ABOUT 850 MB WITH SOME WEAK CAA FOR A TIME MONDAY MORNING. EITHER WAY, THAT SHOULD BE RATHER SHORT LIVED AS RIDGING QUICKLY BUILDS EASTWARD. 850 MB TEMPERATURES ARE FORECAST TO NEAR +20C LATER MONDAY AND LAST THROUGH MOST OF THE WEEK. AS A RESULT, HIGH TEMPERATURES WERE BUMPED UP A BIT MORE. IF SOME MODELS ARE CORRECT, SOME AREAS MAY START SEPTEMBER WITH A HEAT WAVE /HIGHS 90 DEGREES OR HIGHER FOR 3 OR MORE CONSECUTIVE DAYS/. DURING THURSDAY AND FRIDAY, THE SURFACE HIGH MAY START BREAKING DOWN AS THE UPPER RIDGE COULD BEGIN TO BE KNOCKED DOWN AS SOME TROUGHING PUSHES INTO THE MIDWEST. SINCE HIGH PRESSURE IS ANTICIPATED TO BE THE MAIN WEATHER FEATURE THROUGH THE PERIOD, WE OPTED TO MAINTAIN A DRY FORECAST. OVERALL, WE DID NOT DEVIATE TO MUCH FROM HPC GUIDANCE, HOWEVER SOME BLENDING OF 12Z MOSGUIDE DATA WAS INTRODUCED IN SOME FIELDS MAINLY FOR COLLABORATIVE PURPOSES. THE SURFACE DEW POINTS MAY MIX OUT DURING THE AFTERNOON'S OF MONDAY AND TUESDAY, AND THE MOSGUIDE DATA BETTER REFLECTED THIS. THE OVERALL SURFACE FLOW LOOKS WEAK, THEREFORE A SEA BREEZE MAY OCCUR EACH AFTERNOON. THAT IS ALL FOR NOW. THANKS TO THE SURROUNDING OFFICES/HPC FOR THE COLLABORATION. HAVE A GOOD ONE! && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... CONDITIONS ARE VFR ACROSS THE TAF SITES WITH JUST SOME LIGHT PRECIPITATION FALLING AT THIS TIME NORTHWEST OF A KILG-KTTN LINE. OF CONCERN IS THE INCREASE IN THE LOW LEVEL MOISTURE THAT HAS BEEN FEEDING NORTH ALL DAY. DEW POINTS ARE IN THE MID AND UPPER 60S...UP ABOUT 10 DEGREES OVER THE PAST 24 HOURS. WHILE DEW POINTS NORTH OF KTTN ARE IN THE 50S I DO EXPECT TO SEE DP'S INCREASE THERE TOO. THIS WILL PRESENT A PROBLEM WITH AN ONSHORE MARINE FLOW AND LIGHTER WINDS AFTER DARK. UPSTREAM THE CIGS AND VSBY'S ARE FALLING INTO THE MVFR/IFR CATEGORY AND SEE THIS HAPPENING IN SOME OF OUR SITES LATE THIS EVENING FOR OUR DE/PA SITES AND THEN NJ TAF SITES AFTER MIDNIGHT... ESPECIALLY TOWARD MORNING. A COLD FRONT IS GOING TO PUSH THROUGH AND FINALLY CARRY THE REMNANT MOISTURE FROM FAY OFFSHORE AS A SUPER VFR HIGH PRESSURE SPREADS OVER THE REGION. SO AT LEAST 1/2 OF THE HOLIDAY WEEKEND WILL BE EXCELLENT VFR WEATHER. OUTLOOK... FAIR WEATHER EXPECTED SUN INTO A GOOD PART OF NEXT WEEK. && .MARINE... SEA STATE IS HALF SWELL AND HALF WIND WAVE. PERSISTENT ONSHORE FLOW IS STRONGEST SOUTH OF LITTLE EGG INLET AND PRODUCING 4 FT WAVES AT BUOY 44009 THAT ARE IN 5 AND 11 SECOND SETS. NEARSHORE...WAVES AT AVALON ARE 2.6 FT...1.9 FT AT OCEAN GROVE...2.2 FT AT BETHANY AND 2.6 FT AT OCEAN CITY MARYLAND. THESE OBSERVATIONS ARE CONSISTENT WITH THE WAVE WATCH MODEL. THE GRADIENT IS TIGHTER DOWN OVER THE SOUTHERN WATERS/DELAWARE BAY AS HIGH PRESSURE NORTHERN NEW JERSEY INTO NEW ENGLAND...INTERACTS WITH AN INVERTED TROUGH EXTENDING SOUTH FROM DELAWARE TO NORTH CAROLINA. THE TROUGH WILL MOVE EAST OVERNIGHT WITH A LOW FORMING ON IT OFFSHORE. IT BECOMES ABSORBED IN THE WESTERN ATLANTIC HIGH ON SATURDAY. A FRONT WILL APPROACH FROM THE WEST SATURDAY AFTERNOON AND OFF THE COAST BY EVENING. FOLLOWING THE FRONT WILL BE A STRETCH OF NICE WEATHER AS HIGH PRESSURE BUILDS OVER THE REGION SUNDAY INTO THE END OF NEXT WEEK. GREAT BACK TO SCHOOL WEATHER. IF YOU HAVE A CHANCE TO FISH OR GO BOATING THE UPCOMING WEEK WILL BE EXCELLENT. WATER TEMPERATURES ARE AT THEIR HIGHEST WITH AVERAGES OF 70 TO 75 DEGREES FROM NORTHERN NEW JERSEY TO DELAWARE. HAVE A NICE AND SAFE LABOR DAY WEEKEND AND REMEMBER TO WEAR YOUR PFD!!!!! && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GORSE/PRUITT NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...GORSE/HPC AVIATION...EBERWINE/PRUITT MARINE...EBERWINE/PRUITT