Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 260218 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1018 PM EDT MON AUG 25 2014 .SYNOPSIS... HIGH PRESSURE WILL REMAIN OVERHEAD THROUGH TUESDAY. THE CENTER OF THE HIGH SHIFTS TO OUR SOUTH BY WEDNESDAY AS A COLD FRONT MOVES THROUGH THE REGION. HIGH PRESSURE RETURNS THURSDAY AND FRIDAY. A WARM FRONT IS EXPECTED TO LIFT NORTHWARD THROUGH THE MID ATLANTIC THIS WEEKEND ONCE THE HIGH MOVE OFF THE NEW ENGLAND COAST. A COLD FRONT MAY APPROACH FROM THE GREAT LAKES CLOSER TO LABOR DAY. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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THE FORECAST FOR TONIGHT IS WELL ON TRACK AS THE DAYTIME CU HAVE DISSIPATED AND ALL THAT REMAINS CLOUD-WISE ARE SOME PATCHY AND DECREASING CI MOVING AROUND THE UPPER RIDGE. SFC WINDS HAVE BECOME VERY LIGHT OR CALM UNDER THE RIDGE OF HIGH PRESSURE NOW OVER THE MID-ATLANTIC REGION. WITH SFC DEWPTS A COUPLE OF DEGREES HIGHER NOW THAN YDA EVENING...PATCHY GROUND FOG IS LIKELY AGAIN OVERNIGHT TONIGHT. PREVIOUS DISCUSSION BELOW... OUR WEATHER WILL BE DRIVEN BY AN UPPER-LEVEL RIDGE THAT WILL CONTINUE TO BUILD ACROSS THE MID ATLANTIC REGION THROUGH TONIGHT. AS THIS OCCURS, SURFACE HIGH PRESSURE WILL CONTINUE TO SET UP SHOP OVER OUR CWA. THIS IS PROVIDING LESS AND LESS WIND, HOWEVER THERE IS STILL AN ONSHORE COMPONENT TO THE LOW- LEVEL FLOW GIVEN THE SURFACE HIGH IS WEDGED DOWN INTO THE CAROLINAS. DUE TO THE DRIER AIR AND ADDITIONAL SUBSIDENCE, ANY FLAT CUMULUS IS EXPECTED TO DISSIPATE EARLY THIS EVENING. OTHER THAN A BIT OF HIGH LEVEL CLOUDS AT TIMES THROUGH TONIGHT, THE SKY SHOULD BE CLEAR TO MOSTLY CLEAR. THIS COMBINED WITH LIGHT TO CALM WINDS AND A COOLING BOUNDARY LAYER MAY SET UP CONDITIONS RIGHT FOR SOME PATCHY FOG AGAIN. THIS MAY END UP BEING A SHALLOW GROUND FOG AND MOSTLY OVER FIELDS AND OTHER OPEN AREAS, WHICH HAS LESS IMPACT. AS FOR LOW TEMPERATURES, WE USED A NAM/GFS MOS BLEND THEN MADE SOME TWEAKS FOR SOME OF THE TYPICALLY COOLER SPOTS. THE HOURLY GRIDS WERE ADJUSTED BASED ON THE LATEST OBSERVATIONS, THEN THE LAMP/LAV GUIDANCE WAS BLENDED IN TO ASSIST ESPECIALLY WITH TEMPERATURE AND DEW POINT TRENDS THROUGH THIS EVENING.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
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WHILE WE WILL REMAIN UNDERNEATH A STRONG UPPER-LEVEL RIDGE, IT IS FORECAST TO FLATTEN SOME THROUGH TUESDAY. THIS IS DUE TO A SHORT WAVE TROUGH SLIDING FROM NEAR THE UPPER GREAT LAKES REGION ON NORTHWARD. AS THIS OCCURS, THE FLOW ALOFT WILL TEND TO BECOME MORE ZONAL. AT THE SURFACE, HIGH PRESSURE OVER THE REGION TO START SHOULD BEGIN TO SHIFT EAST AND NORTHEASTWARD. THIS WILL RESULT IN A LIGHT FLOW REGIME, WITH THE SURFACE FLOW TENDING TO BE FROM THE SOUTHWEST. AMPLE HEATING OF THE SURFACE THOUGH COMBINED WITH THE WEAKER WINDS SHOULD RESULT IN SEA/BAY BREEZE DEVELOPMENT DURING THE AFTERNOON. THIS WILL MAINTAIN AN ONSHORE FLOW COMPONENT AT THE COAST AND ACROSS PORTIONS OF THE DELMARVA ESPECIALLY. GIVEN THE PRESENCE OF HIGH PRESSURE AT THE SURFACE AND ALOFT ALONG WITH THE AIR MASS MODIFYING SOME MORE, A GOOD AMOUNT OF SUNSHINE IS FORECAST. THERE COULD BE A BIT OF CUMULUS THEN ALSO A TOUCH OF HIGH LEVEL CLOUDS AT TIMES, BUT OTHERWISE PLENTY OF SUNSHINE IS ANTICIPATED. AS FOR HIGH TEMPERATURES, AN EVEN BLEND OF THE GFS/NAM MOS WAS USED BUT THEN SOME DOWNWARD ADJUSTMENTS WERE MADE ESPECIALLY ALONG THE COAST AND ACROSS PORTIONS OF THE DELMARVA GIVEN THE ONSHORE FLOW. WE MAY HAVE A QUICK JUMP IN TEMPERATURES DURING THE MORNING HOURS, WHICH MAY ALLOW FOR EVEN WARMER THAN CURRENTLY FORECAST AFTERNOON TEMPERATURES INLAND.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
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A LARGE UPPER RIDGE IS FORECAST TO REMAIN CENTERED OVER THE SOUTHERN APPALACHIANS TUESDAY NIGHT. THE NORTHEASTERN PERIPHERY OF THE RIDGE WILL START TO BREAK DOWN AS A COLD FRONT MOVES ATOP THE RIDGE INTO THE GREAT LAKES/UPSTATE NY TUESDAY NIGHT AND NEW ENGLAND/NORTHERN MID-ATLANTIC STATES WEDNESDAY AND WEDNESDAY NIGHT. HIGH PRESSURE REFLECTED AT THE SURFACE IS ALSO FORECAST TO RETREAT SOUTH OF OUR REGION DURING THIS TIME. KEPT POPS WITH FROPA WEDNESDAY AFTERNOON/ EVENING VERY LOW ACROSS THE MOUNTAINS SINCE A DIRECT FETCH OF GULF OF MEXICO OR ATLANTIC MOISTURE AROUND THE RIDGE TO OUR SOUTHEAST WILL BE ABSENT. REMOVED ANY MENTION OF PRECIP EAST OF THE DIVIDE AS DOWNSLOPING FLOW OFF THE HIGHER TERRAIN SHOULD HELP TO DRY OUT THE BOUNDARY LAYER. TRENDED WARMER FOR MAX TEMPS WEDNESDAY WITH THE SETUP ALLOWING FOR STRONG SOLAR HEATING TO OCCUR IN PRE- FRONTAL WARM SECTOR. MAX TEMPS IN THE UPPER 80S TO LOWER 90S WILL BE COMMON (COOLER ALONG THE COAST AND IN THE MOUNTAINS). IF PHL REACHES 90F, IT WOULD ONLY BE THE SECOND 90-DEGREE DAY THIS AUGUST (LAST AUGUST, THERE WERE ZERO 90-DEGREE DAYS DURING THE ENTIRE MONTH). THE COLD FRONT IS EXPECTED TO MOVE SOUTH OF THE AREA OVERNIGHT WEDNESDAY NIGHT BEFORE STALLING NEAR THE VA-NC BORDER THURSDAY. HIGH PRESSURE BUILDS BACK INTO THE AREA DURING THIS TIME. THE HIGH WILL SHIFT INTO NEW ENGLAND ON FRIDAY. SLIGHTLY COOLER AND DRIER CONDITIONS CAN BE EXPECTED DURING THIS TIME. THE CENTER OF HIGH EVENTUALLY SHIFTS OFF THE NEW ENGLAND COAST FRIDAY NIGHT AND THIS WEEKEND. RETURN FLOW AROUND THE OFFSHORE HIGH WILL DEVELOP DURING THIS TIME, ALLOWING THE OLD FRONTAL BOUNDARY TO OUR SOUTHWEST TO LIFT BACK NORTHWARD. THE TREND WILL BE FOR INCREASING TEMPERATURES AND HUMIDITY THROUGHOUT THE HOLIDAY WEEKEND, ALTHOUGH THERE IS UNCERTAINTY CONCERNING HOW QUICKLY THE FRONT MAKES IT INTO THE FORECAST AREA. SHOWERS AND STORMS RETURN TO THE FORECAST FOR THE HOLIDAY WEEKEND, PARTICULARLY ON SUNDAY AND MONDAY WHEN AN AREA OF LOPRES AND ATTENDANT COLD FRONT APPROACH FROM THE GREAT LAKES. THERE ARE STILL SIGNIFICANT MODEL SPREAD WITH THE STRENGTH OF THE UPPER RIDGE AND THE TIMING OF THE COLD FRONT.
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&& .AVIATION /02Z TUESDAY THROUGH SATURDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TONIGHT...VFR OVERALL. LOCALIZED FOG MAY OCCUR TOWARD MORNING, HOWEVER IT MAY BE SHALLOW GROUND FOG. OUR CONFIDENCE IS LOW THAT IT WOULD HAVE AN IMPACT ON ANY TERMINALS, THEREFORE IT WAS NOT INCLUDED AT THIS TIME. SOUTH-SOUTHEAST WINDS AROUND 5 KNOTS, BECOMING LIGHT AND VARIABLE OR CALM. TUESDAY...VFR. LIGHT AND VARIABLE WINDS TO START, BECOMING SOUTHWESTERLY AT 5-8 KNOTS. A SEA/BAY BREEZE IN THE AFTERNOON SHOULD AFFECT KACY, KMIV AND KILG WITH WINDS MORE FROM THE SOUTHEAST. OUTLOOK... TUESDAY NIGHT...VFR CONDITIONS AND LIGHT WINDS. WEDNESDAY AND WEDNESDAY NIGHT...PREDOMINATELY VFR. A STRAY SHRA OR TSRA CANNOT BE RULED OUT, MAINLY IN VC OF ABE/RDG DURING THE AFTN AND EARLY EVE. THURSDAY THROUGH FRIDAY NIGHT...VFR AND DRY EXPECTED. SATURDAY...MAINLY VFR BUT ISOLATED SHRA/TSRA POSSIBLE AS A WARM FRONT MOVES THRU.
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&& .MARINE...
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AS OF 900 PM...SEAS AT BUOY 44009 HAVE SUBSIDED TO BETWEEN 4.0 AND 4.5 FEET. THIS SLOW DOWNWARD TREND IS EXPECTED TO CONTINUE AND THE SCA FOR DELAWARE COASTAL WATERS WILL LIKELY EXPIRE AT MIDNIGHT AS CURRENTLY PROJECTED. PREVIOUS DISCUSSION BELOW... HIGH PRESSURE WILL REMAIN IN CONTROL OF OUR WEATHER THROUGH TUESDAY. THE CIRCULATION AROUND THIS HIGH THOUGH IS RESULTING IN AN ONSHORE FLOW, ALTHOUGH IT IS LIGHTER. THIS WILL ALSO BE ENHANCED SOME WITH SEA AND BAY BREEZE DEVELOPMENT THROUGH TUESDAY AFTERNOON. THE SEAS AT BUOY 44009 HAVE BEEN SUBSIDING SOME THIS AFTERNOON, BUT HAVE TRENDED NEARLY STEADY STATE AT 5 FEET. THIS MAY CONTINUE FOR AWHILE AS THE ONSHORE FLOW COMPONENT CONTINUES DESPITE THE WINDS LESSENING SOME. WHILE IT MAY BECOME MORE MARGINAL, WE WILL GO AHEAD AND EXTEND THE SMALL CRAFT ADVISORY THROUGH MIDNIGHT FOR NOW AS WE HAVE LOWER CONFIDENCE BEYOND THIS. WE WILL ALSO GO AHEAD AND CANCEL THE TWO NORTHERN ZONES FROM THE CURRENT ADVISORY, AS SEAS SHOULD BE JUST UP TO 4 FEET. IT APPEARS THE MAIN 5 FOOTERS ARE OFF THE DELAWARE COAST NOW. ELSEWHERE, THE CONDITIONS ARE EXPECTED TO BE BELOW ADVISORY CRITERIA THROUGH TUESDAY. OUTLOOK... TUESDAY...WINDS AND SEAS BELOW SCA CRITERIA WEDNESDAY THROUGH THURSDAY NIGHT...SWLY WINDS WILL STRENGTHEN AHEAD OF A COLD FRONT LATE WEDNESDAY. NW WINDS BEHIND THE FRONT MAY APPROACH SCA CRITERIA WEDNESDAY NIGHT AND THURSDAY, BUT THE MAIN THREAT WILL BE SEAS. LONG-PERIOD SWELLS ASSOCIATED WITH CRISTOBAL MAY START TO REACH THE NEAR-SHORE WATERS AS EARLY AS WEDNESDAY AND CONTINUE. SEAS COULD REACH SCA CRITERIA DURING THIS PERIOD. HOWEVER, TIMING AS WELL AS WAVE HEIGHTS ASSOCIATED WITH THESE SWELLS IS STILL VERY UNCERTAIN AT THIS TIME. FRIDAY THROUGH SATURDAY...WINDS WILL BE LIGHT. LATEST MODEL PROJECTIONS SHOW SEAS GRADUALLY SUBSIDING DURING THIS PERIOD AS CRISTOBAL MOVES FARTHER OUT TO SEA.
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&& .RIP CURRENTS...
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THE PRELIMINARY RIP FORECAST FOR TUESDAY IS MODERATE FOR BOTH NJ AND DE BEACHES. WINDS AND WAVES ARE SLOWLY DECREASING AS THE SURFACE HIGH PRES RIDGE SHIFTS SOUTHWARD. HWVR RIP-PRODUCING CONDS STILL MAY BE SOMEWHAT ENHANCED...IN CONTINUITY FROM MONDAYS HIGH LEVELS. THIS FCST WILL BE RE-EVALUATED EARLY TUESDAY MORNING. PREVIOUS DISCUSSION BELOW... THE THREAT OF DANGEROUS RIP CURRENTS WILL BE ENHANCED HEADING INTO WEDNESDAY AND THURSDAY AS CRISTOBAL TRACKS WELL EAST OF THE MID ATLANTIC COAST. LATEST PROJECTIONS SHOW THE POTENTIAL FOR A HIGH RIP CURRENT RISK, BUT THERE IS STILL UNCERTAINTY THIS FAR OUT SO STAY TUNED AS WE REFINE THE FORECAST.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ454-455.
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&& $$ SYNOPSIS...KLEIN NEAR TERM...AMC SHORT TERM...GORSE LONG TERM...KLEIN AVIATION...GORSE/KLEIN MARINE...GORSE/KLEIN RIP CURRENTS...GORSE/KLEIN/AMC

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