Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 251840 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 240 PM EDT MON AUG 25 2014 .SYNOPSIS... HIGH PRESSURE WILL REMAIN IN CONTROL OF OUR WEATHER THROUGH TUESDAY. A COLD FRONT SHOULD SLIDE SOUTHEASTWARD INTO THE MID ATLANTIC REGION DURING MID WEEK. IN THE WAKE OF THE COLD FRONT, HIGH PRESSURE BUILDS IN DURING THURSDAY AND FRIDAY. A WARM FRONT MAY LIFT NORTHWARD NEAR OUR AREA SATURDAY, THEN A COLD FRONT APPROACHES SUNDAY. && .NEAR TERM /THROUGH TONIGHT/...
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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 /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 AIRMASS 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 SUNDAY/...
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CONSIDERABLY DIFFERENT MODEL SOLUTIONS FROM BOTH THE GFS AND ECMWF THAN THE MODEL RUNS 24 HOURS AGO. WEDNESDAY AND THURSDAY...THE BIGGEST CHANGE IN THE LATEST LONG RANGE MODEL RUNS IS WITH THE TIMING OF THE COLD FRONT. WHILE THERE HAD BEEN A TREND UP THROUGH YESTERDAY`S 00Z MODEL RUNS OF DELAYING THE ARRIVAL OF THE COLD FRONT (OR NOT EVEN BRINGING IT THIS FAR SOUTH AT ALL), THE 12Z RUNS, AND NOW THE LATEST 00Z RUNS HAVE SPED UP THE ARRIVAL OF THE FRONT. SHOWING THE FRONT ARRIVING IN OUR REGION ON WEDNESDAY OR WEDNESDAY NIGHT. INTERESTINGLY, TO START THIS PERIOD, MID AND UPPER LEVEL FLOW IS NEARLY ZONAL (SUGGESTING THAT THE FRONT MAY NOT DIG AS FAR SOUTH). HOWEVER, BOTH THE GFS AND ECMWF SHOW AN UPPER LEVEL SHORT WAVE TROUGH QUICKLY DIGGING SOUTHEAST OUT OF NORTH CENTRAL CANADA, CROSSING THE NORTHEASTERN U.S. BY WEDNESDAY NIGHT. THERE WILL BE SOME CHANCE OF THUNDERSTORMS ALONG THE FRONT, THOUGH WITH DRIER SOUTHWESTERLY FLOW IN THE PERIODS LEADING UP TO THIS, THERE IS SOME QUESTION OF MOISTURE AVAILABILITY, AND THUS HOW WIDESPREAD PRECIPITATION WILL BE. THE LIMITED LOW LEVEL MOISTURE ALSO HAS AN IMPACT ON INSTABILITY, AS DOES THE EXPECTED NIGHT TIME ARRIVAL OF THE FRONT. THUS...AT THIS TIME SEVERE STORMS SEEM UNLIKELY, BUT IF THE FRONT ARRIVES DURING DAY LIGHT HOURS, NOT COMPLETELY OUT OF THE QUESTION. ON A SIDE NOTE FOR THIS PERIOD, CRISTOBAL IS STILL EXPECTED TO BE WELL OUT TO SEA, AND BY THIS POINT RACING FURTHER AWAY FROM THE REGION. THUS, THE ONLY IMPACTS WE ARE EXPECTING FROM CRISTOBAL ARE LONG PERIOD SWELLS AND AN ENHANCED RIP CURRENT RISK, THOUGH THE TIMING OF BOTH IS UNCERTAIN. FRIDAY...THE CONTINENTAL POLAR AIR MASS SETTLES IN OVER THE REGION, ALBEIT BRIEFLY, BY FRIDAY, LEADING TO A COOL AND DRY DAY. FRIDAY NIGHT THROUGH SUNDAY...AS THE HIGH SHIFTS NORTHEAST OFF THE COAST, LOW LEVEL SOUTHERLY FLOW RETURNS BRINGING A WARMING TREND, AND MORE MOISTURE. THIS COULD SET THE STAGE FOR THE BEST CHANCE OF THUNDERSTORMS OVER THE NEXT WEEK EITHER SATURDAY OR SUNDAY AS A SECOND COLD FRONT COULD APPROACH THE REGION.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. REST OF THIS AFTERNOON...VFR. NORTHEAST TO EAST WINDS AT 5-10 KNOTS, BECOMING SOUTHEAST. 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 EXPECTED. WEDNESDAY THROUGH THURSDAY...MOSTLY VFR CONDITIONS EXPECTED. A SMALL RISK OF THUNDERSTORMS AS A COLD FRONT COULD PUSH THROUGH WEDNESDAY OR THURSDAY. FRIDAY...VFR CONDITIONS LIKELY.
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&& .MARINE...
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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 SUBSIDED 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 NIGHT...WINDS AND SEAS ARE EXPECTED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA. WEDNESDAY THROUGH FRIDAY...WINDS WILL STAY BELOW SCA CRITERIA. WE COULD BEGIN TO SEE LONG PERIOD SWELLS ASSOCIATED WITH TROPICAL CYCLONE CRISTOBAL, WHICH WILL STAY WELL OUT TO SEA, AS EARLY AS WEDNESDAY. HOWEVER, TIMING AS WELL AS WAVE HEIGHTS ASSOCIATED WITH THESE SWELLS IS STILL VERY UNCERTAIN AT THIS TIME.
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&& .RIP CURRENTS...
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THE RISK OF DANGEROUS RIP CURRENTS REMAINS AT HIGH THROUGH THIS EVENING, DUE TO THE COMBINATION OF TODAY`S NEW MOON AND LINGERING CHOPPINESS TO THE WAVES WITHIN THE SURF ZONE. WE THEN TURN TO MORE OF A LONG PERIOD SWELL SETUP LATER THIS WEEK ASSOCIATED WITH TROPICAL STORM CRISTOBAL TRACKING WELL EAST OF THE MID ATLANTIC COAST. THIS SHOULD KEEP THE RISK OF DANGEROUS RIP CURRENTS ELEVATED.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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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 UNTIL MIDNIGHT EDT TONIGHT FOR ANZ454-455.
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&& $$ SYNOPSIS...GORSE/JOHNSON NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...JOHNSON AVIATION...GORSE/JOHNSON MARINE...GORSE/JOHNSON RIP CURRENTS...GORSE

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