Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 272222 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 622 PM EDT THU AUG 27 2015 .SYNOPSIS...
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HIGH PRESSURE WILL SETTLE ACROSS OUR REGION TONIGHT AND FRIDAY, THEN MOVE OFFSHORE DURING THE WEEKEND. A WEAKENING COOL FRONT IS FORECAST TO ARRIVE LATE SUNDAY INTO MONDAY, THEN HIGH PRESSURE BUILDS IN FOR MONDAY INTO TUESDAY. A WEAK SYSTEM MAY SLIDE ACROSS OUR AREA TUESDAY, AS HIGH PRESSURE CONTINUES TO BUILD NEARBY INTO THURSDAY.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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THE GFS HAD A SCINTILLATING 500MB 12Z INITIALIZATION AND WAS BETTER THAN THE WRF/NAM. IT WAS ALSO SLIGHTLY BETTER THAN THE NAM AT 850MB. BOTH MODELS WERE VERY VERY GOOD AT 925MB. THIS SOUNDS LIKE A BROKEN RECORD, BUT THE INITIALIZED TIME DP/DT THE RIDGE IN THE CENTRAL/WESTERN CONUS CONTINUES TO TREND STRONGER THAN PREVIOUSLY FORECAST. WHILE SOME OF THE MESOSCALE MODELS ARE SHOWING STRATOCU LEVEL MOISTURE CONTINUING THROUGH THE NIGHT, THE SUBSIDENCE INVERSION STILL DOES NOT LOOK OVERBEARING AND THERE IS NO FORECAST OMEGA. WE WILL FOLLOW A SIMILAR PATH TO LAST NIGHT OF CLEARING MOST OF OUR CWA, BUT KEEPING CLOUDS LONGER FAR NORTHWEST. LAST NIGHT OUR PFM SITE MIN TEMP BIAS WAS 0.5F TOO COLD. EVEN WITH THE CENTER OF THE SURFACE HIGH STILL IN NORTHWEST PA BY MORNING, THE BOUNDARY LAYER WIND IS WEAK ENOUGH FOR DECOUPLING TO OCCUR AGAIN.A WE WILL GO AGAIN TOWARD THE LOW END OF STAT GUIDANCE. LIKE LAST NIGHT`S ERRORS, WE MAY BE A BIT TOO COOL NORTHWEST IF CLOUDS LINGER LONGER THAN PREDICTED AND/OR MORE MOVE IN TOWARD MORNING.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
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THE HIGH PRESSURE SYSTEM WILL EASE ACROSS OUR CWA. THE TRANSITION TO WARMER AND MORE HUMID WEATHER SLOWLY STARTS ON FRIDAY. STILL ANOTHER SPECTACULAR LATE AUGUST DAY. THE PREDICTED CONVECTIVE TEMPERATURES ARE NOT SUPPOSE TO BE REACHED TIL THE AFTERNOON AND WITH LESS OF AN ANTECEDENT MOISTURE POOL BETWEEN 925MB AND 850MB FORECASTING LESS CU THAN TODAY. THE 250MB JET WILL BE FARTHER TO THE SOUTHEAST, SO NO JET STREAM CIRRUS PROBLEMS. AIR MASS MODIFICATION BY LATE IN THE AFTERNOON SUGGESTS A 1-3F BUMP IN MAX TEMPS FROM TODAY. THIS IS MUCH CLOSER TO NAM MOS THAN THE COOLER GFS MOS WHERE THE STAT GUIDANCE PARTS WAYS ON FRIDAY. OVERALL LIGHT WIND PATTERN WITH THE SEA AND BAY BREEZE MAKING MORE OF AN INLAND ADVANCE THAN THE PAST TWO DAYS LATE IN THE AFTERNOON.
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&& .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
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THE SYNOPTIC SETUP IS COMPRISED OF A RIDGE EAST OF THE CAROLINAS WITH AN INITIAL ZONAL FLOW ACROSS THE NORTHEAST AND MID ATLANTIC REGIONS. A SHORT WAVE TROUGH IS FORECAST TO BE TRAVERSING THE MIDWEST AND GREAT LAKES REGIONS SATURDAY AND SUNDAY, HOWEVER THIS FEATURE MAY END UP WEAKENING AS IT GETS TO THE NORTHEAST WITH THE WESTERN ATLANTIC RIDGE BUILDING WEST AND NORTH SOME. THE LEFTOVERS OF THE SHORT WAVE TROUGH SLIDES ACROSS OUR AREA TUESDAY AND WEDNESDAY, THEN AN UPPER-LEVEL RIDGE EXPANDS ACROSS THE OHIO VALLEY AND GREAT LAKES REGION EASTWARD THROUGH THURSDAY. WE USED A MODEL BLEND FOR FRIDAY NIGHT INTO SUNDAY, THEN THE 12Z WPC GUIDANCE THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE FOLLOWING ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES. FOR FRIDAY NIGHT...A RIDGE CENTERED TO OUR SOUTHEAST WILL ALLOW SURFACE HIGH PRESSURE TO BE OVER OUR AREA. THIS WILL BE ASSISTED BY A SHORT WAVE TROUGH MOVING ACROSS THE MIDWEST AND UPPER GREAT LAKES, ALTHOUGH THERE IS SOME VARIATIONS WITHIN THE MODEL GUIDANCE ON THE AMPLITUDE OF THIS FEATURE. OVERALL, CONTINUED QUIET WEATHER FOR OUR AREA DURING THIS TIME IS ANTICIPATED. FOR SATURDAY AND SUNDAY...A SHORT WAVE TROUGH IS FORECAST TO BE SLIDING ACROSS THE GREAT LAKES REGION DURING THIS TIME, HOWEVER IT MAY END UP WEAKENING AS IT APPROACHES THE NORTHEAST. SOME MODEL GUIDANCE MAINTAINS THIS FEATURE AS IT APPROACHES SUNDAY NIGHT AND ESPECIALLY BEYOND, HOWEVER WITH THE WESTERN ATLANTIC RIDGE TENDING TO BUILD SOME AND EVEN EXPAND A BIT WESTWARD, THIS FEATURE SHOULD NOT HAVE MUCH IN THE WAY OF AN IMPACT ON OUR WEATHER ESPECIALLY SINCE IT LOOKS TO APPROACH SLOWLY. THE POSSIBLE FLY IN THE OINTMENT MAY BE LATE SUNDAY AS COME CONVECTION UPSTREAM WITHIN THE LINGERING UPPER-LEVEL WEAKNESS COULD SPILL INTO OUR NORTHWEST ZONES. A SOUTHERLY FLOW OF WARMER AIR IS EXPECTED TO OCCUR EACH DAY WITH AT LEAST SOME INCREASE IN THE DEW POINTS AS WELL. THE LATTER SHOULD BE MORE NOTICEABLE DURING SUNDAY AS THE SOUTHERN FLOW IS MORE ESTABLISHED THEN, ALTHOUGH THE MOISTURE RETURN DOES NOT APPEAR TO BE SUBSTANTIAL. FOR MONDAY AND TUESDAY...AS A TROUGH MIGRATES ACROSS THE PACIFIC NORTHWEST, DOWNSTREAM RIDGING IS EXPECTED TO OCCUR. THE MODEL GUIDANCE SHOWS A HIGHER AMPLITUDE RIDGE OCCURRING DURING THIS TIME FRAME WITH THE AXIS MAINLY TO OUR WEST. SOME MODEL GUIDANCE HAS BEEN SHOWING THE WEAKENING SHORT WAVE TROUGH MIGRATING OVERHEAD DURING THIS TIME. THERE STILL COULD BE SOME CONVECTION THAT DEVELOPS WITH DAYTIME HEATING WITHIN A MOISTENING AIR MASS, HOWEVER THERE DOES NOT APPEAR TO BE ANY PRONOUNCED LARGE SCALE FORCING MECHANISM. THEREFORE, WE WENT WITH A DRY FORECAST. OTHERWISE, VERY WARM TO HOT AND HUMID FOR MUCH OF THE AREA. THE FLOW LOOKS LIGHT ENOUGH TO ALLOW FOR AFTERNOON SEA BREEZE DEVELOPMENT. FOR WEDNESDAY AND THURSDAY...A SIMILAR SYNOPTIC SETUP DURING THIS TIME FRAME AS WELL WITH RIDGING GENERALLY HOLDING. THIS KEEPS HIGH PRESSURE AT THE SURFACE CLOSE BY, WITH A BLOCKING TYPE PATTERN IN PLACE. TROPICAL CYCLONE ERIKA MAY BE LURKING OFF THE SOUTHEASTERN U.S. COAST, HOWEVER THERE IS A LOT OF UNCERTAINTY. THERE ARE SOME HINTS IN THE GUIDANCE THAT A TROUGH SLIDES ACROSS THE NORTHEAST THURSDAY BEFORE THE RIDGE BUILDS AGAIN, HOWEVER IT LOOKS WEAK AND BYPASSES THE TROPICAL SYSTEM. SOME GUIDANCE BRINGS THE TROPICAL SYSTEM FARTHER NORTH, HOWEVER THAT WOULD BE INTO THE RIDGE OVERALL. THE TROUGH OUT WEST WILL ASSIST IN THE DOWNSTREAM RIDGE PLACEMENT AND STRENGTH, THEREFORE MORE UNCERTAINTY WITH THE FLOW ACROSS THE EAST. FOR THE LATEST FORECAST INFORMATION ON TROPICAL CYCLONE ERIKA, VISIT THE NATIONAL HURRICANE CENTERS WEB SITE. OTHER THAN A RATHER LOW CHC FOR DIURNALLY DRIVEN CONVECTION, NO REAL ORGANIZED TRIGGERS APPEAR TO BE PRESENT ATTM FOR RAIN CHCS WHICH THE AREA NEEDS. THE VERY WARM AND HUMID CONDITIONS SHOULD PERSIST FOR MUCH OF THE AREA, WITH PERHAPS SOME RELAXATION IF THE AFOREMENTIONED TROUGH IS ABLE TO KNOCK THE HEIGHTS/TEMPERATURES DOWN SOME FOR A TIME.
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&& .AVIATION /22Z THURSDAY THROUGH TUESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TONIGHT...SOME RESIDUAL VFR CLOUDINESS NORTHWEST THIS EVENING AND MAINLY CLEAR ELSEWHERE. WINDS WILL BECOME LIGHT AND VARIABLE, POSSIBLY CALM AT SMALLER AIRPORTS. THE MOST FAVORED WIND DIRECTION WOULD BE NORTHWEST TO NORTH. LATE AT NIGHT ADDITIONAL CLOUDS ARE POSSIBLE FAR NORTHWEST (BEYOND TAF SITES) AIRPORTS. THIS MIGHT PRODUCE SOME MVFR CIG AGAIN. CONFIDENCE NOT HIGH. ALSO WITH ANOTHER NIGHT IN THE SAME AIR MASS, THE MOST FOG PRONED SMALLER AIRPORTS MIGHT HAVE SOME GROUND FOG FORM TOWARD MORNING. FRIDAY...LESS OVERALL VFR CLOUDINESS. CUMULUS COVERAGE SHOULD BE FEW TO SCATTERED. FAVORED LIGHT NORTH WINDS IN THE MORNING SHOULD BECOME 5 TO 10 KNOTS AT THE END OF THE TAF FCST PERIOD. A SEA BREEZE FRONT IS EXPECTED TO MAKE A STRONGER INLAND INTRUSION FRIDAY AFTERNOON AND THE SOUTHEAST WIND SHIFT AT KACY REPRESENTS THAT FEATURE. OUTLOOK... FRIDAY NIGHT AND SATURDAY...VFR. LIGHT SOUTHWESTERLY WINDS AT NIGHT, INCREASING UP TO 10 KNOTS DURING THE DAY SATURDAY. SUNDAY...A CHANCE OF LOCAL FOG EARLY, OTHERWISE VFR. A FEW SHOWERS AND THUNDERSTORMS MAY DEVELOP IN THE AFTERNOON AND EVENING WELL TO OUR WEST AND NORTHWEST. MONDAY AND TUESDAY...A CHANCE OF LOCAL FOG EACH MORNING, OTHERWISE MAINLY VFR. THERE COULD BE A SHOWER OR THUNDERSTORM AROUND ESPECIALLY TUESDAY AFTERNOON.
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&& .MARINE...
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NO MARINE HAZARDS EXPECTED TONIGHT AND FRIDAY. THIS EVENING AND OVERNIGHT, THE GENERALLY NORTHERLY GRADIENT WIND AROUND THE SURFACE HIGH IS PREDICTED TO RETURN. ON FRIDAY, WITH THE SURFACE HIGH PASSING ACROSS THE MARINE WATERS, WIND SPEEDS WILL BECOME LIGHTER WITH MORE VARIABILITY IN DIRECTION AS THE MORNING AND EARLY AFTERNOON PROGRESS. THEN A LIGHT EAST TO SOUTHEAST CIRCULATION AROUND THE SURFACE HIGH SHOULD DEVELOP. THIS WILL LIKELY ALSO START WORKING ITS WAY INTO DELAWARE BAY LATE. OUTLOOK... FRIDAY NIGHT THROUGH TUESDAY, HIGH PRESSURE GENERALLY DOMINATES THE WEATHER WITH LIGHTER FLOW. A SOUTHERLY FLOW HOWEVER SHOULD INCREASE SOME AT TIMES, ESPECIALLY DURING THE AFTERNOON AND EVENING HOURS PARTICULARLY NEARSHORE WITH THE DEVELOPMENT OF SEA/BAY BREEZES. OVERALL, THE CONDITIONS ARE ANTICIPATED TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GORSE NEAR TERM...GIGI SHORT TERM...GIGI LONG TERM...GORSE AVIATION...GIGI/GORSE MARINE...GIGI/GORSE

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