Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 281913 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 313 PM EDT SUN SEP 28 2014 .SYNOPSIS... HIGH PRESSURE WILL BE IN PLACE NEAR WEST VIRGINA THROUGH MONDAY AND MOVE OFFSHORE BY TUESDAY WITH A LOW PRESSURE OFF THE MID-ATLANTIC COASTLINE. ON TUESDAY A COLD FRONTAL BOUNDARY WILL MOVE SOUTHEAST FROM THE GREAT LAKES AND BE LOCATED OFF THE MID-ATLANTIC COASTLINE BY WEDNESDAY WITH CONTINUED LOW PRESSURE WELL OFFSHORE. ANOTHER STRONGER COLD FRONTAL BOUNDARY WITH AN ASSOCIATED LOW PRESSURE SYSTEM ACROSS THE GREAT LAKES WILL MOVE FROM WEST TO EAST ACROSS MOST OF THE CENTRAL AND EASTERN UNITED STATES FRIDAY AND SATURDAY. HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT BY SUNDAY. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... HIGH PRESSURE CENTERED WELL OFF THE MID-ATLANTIC COAST WILL MAINTAIN A SOUTHERLY FLOW OVER THE REGION THROUGH THE OVERNIGHT HOURS. DEWPOINT TEMPERATURES WILL BE JUST A LITTLE HIGHER BECAUSE OF THIS FLOW, SO PATCHY FOG COULD POP UP IN A FEW MORE PLACES COMPARED TO PREVIOUS NIGHTS, BUT DENSE FOG IS NOT EXPECTED. LOW TEMPERATURES WILL RANGE FROM THE LOW 50S IN THE NORTH TO THE LOW 60S SOUTH, WHICH IS WELL ABOVE AVERAGE FOR LATE SEPTEMBER. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... HIGH CLOUDS WILL BE MORE NOTICEABLE ON MONDAY AS MOISTURE FROM A SYSTEM OVER THE SOUTHEAST U.S. STREAMS NORTH. THE GFS INDICATES SOME SHOWER ACTIVITY OVER THE SOUTHERN PORTIONS OF OUR CWA DURING THE AFTERNOON HOURS, BUT THE ECMWF IS LESS AGGRESSIVE SO NO PRECIPITATION WAS INCLUDED IN THE GRIDS ATTM. THE INCREASED CLOUDINESS SHOULD KEEP TEMPERATURES A FEW DEGREES COOLER THAN SUNDAY. HIGHS ARE EXPECTED TO RANGE FROM THE LOW 70S NORTH TO THE MID TO UPPER 70S SOUTH. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... MONDAY NIGHT THROUGH WEDNESDAY NIGHT: MODELS HAVE COME INTO A GREATER AGREEMENT OF ANY COASTAL LOW PRESSURE STAYING WELL OFFSHORE. HOWEVER, THIS WILL KEEP WINDS FROM THE NORTHEAST AND EAST OVER THIS PERIOD AND KEEP TEMPERATURES DOWN AS WELL. STAYED RELATIVITY CLOSE TO MAV/MET GUIDANCE ON TEMPERATURES IN THIS PERIOD WITH LITTLE MODEL SPREAD PRESENT. THE ECMWF ENSEMBLE SPREAD AND MANY GFS ENSEMBLE MEMBERS ACTUALLY IMPLY THE LOW PRESSURE SYSTEM WILL STAY EVEN FURTHER OFFSHORE THAN FEATURED IN THE OPERATIONAL RUNS. INCREASED CONFIDENCE ANY COASTAL LOW WILL STAY OFFSHORE, PERHAPS A NORTHWARD EXTENSION OF A INVERTED TROUGH INTO OUR REGION BUT LEFT FORECAST DRY MONDAY NIGHT ATTM. DID INCLUDE SOME PATCHY FOG AROUND SUNRISE TUESDAY. MAIN FEATURE IN THIS PERIOD WILL BE A WEAK FRONTAL BOUNDARY LIKELY TO PASS THROUGH TUESDAY NIGHT INTO WEDNESDAY. BEHIND THE FRONT THERE LOOKS TO BE A NICE SPIKE IN VORTICITY ASSOCIATED WITH A UPPER LEVEL LOW. HOWEVER THE SURFACE BOUNDARY WILL BE DECAYING AND MOISTURE WILL BE LIMITED. BUFKIT SOUNDINGS ONLY INDICATE PW VALUES UNDER 1 INCH AND VERY DRY MID LEVELS WITH RH ONLY AROUND 50%. SO EVEN WITH GOOD MID-LEVEL SUPPORT IT`S GOING TO BE HARD TO GENERATE ANYTHING MORE THAN SOME SCATTERED SHOWERS WITH LIGHT QPF, CHANCE POPS AS WELL. WITH STEEPING LAPSE RATES AND SOME VERY LIMITED CAPE (UNDER A FEW HUNDRED J/KG) WEDNESDAY AFTERNOON, A FEW ADDITIONAL SPOTTY LIGHT SHOWERS ARE POSSIBLE WITH THE DEVELOPMENT OF SCATTERED CUMULUS. AREAS NW OF PHL WOULD BE FAVORED FOR THIS WITH HIGHER TERRAIN. THURSDAY THROUGH SATURDAY: BOTH THE GFS AND ECMWF SHOW A COASTAL LOW WELL OFFSHORE THAT STALLS OR MOVES SLOW EAST TO START. THIS WILL KEEP THE REGION IN A EASTERLY FLOW THAT TURNS MORE SOUTHEAST BY FRIDAY AHEAD OF THE NEXT FRONTAL BOUNDARY. THIS FRONTAL BOUNDARY IS LIKELY TO MOVE THROUGH SOMETIME IN THE FRIDAY NIGHT AND SATURDAY TIME PERIOD. THIS FRONT WILL HAVE QUITE A BIT MORE MOISTURE TRANSPORTED NORTH FROM THE GULF OF MEXICO COMPARED TO THE FRONT IN THE TUESDAY NIGHT TIMEFRAME. PW VALUES LOOK TO BE HIGHER AROUND 1.5 INCHES, SO SOME HEAVY SHOWERS CAN NOT BE RULED OUT. INSTABILITY LOOKS ALMOST NON-EXISTENT, PERHAPS 100 J/KG AS SHOWN ON THE 00Z ECMWF. NO ADDITION OF THUNDER TO THE GRIDS FRIDAY NIGHT AND SATURDAY. A FACTOR WHICH WOULD LIMIT PRECIPITATION IS THAT THE AREA OF MAXIMUM MID-LEVEL ENERGY AND DYNAMICS WILL BE PASSING WELL TO OUR NORTHEAST. GIVEN THE POTENTIAL FOR LIMITED MID AND UPPER LEVEL SUPPORT, LEFT POPS IN THE CHANCE RANGE. SATURDAY NIGHT AND SUNDAY: NORTHWEST FLOW WITH DRIER AIR AND HIGH PRESSURE BUILDING IN FOR SATURDAY NIGHT AND SUNDAY. STUCK CLOSE TO WPC GUIDANCE ON TEMPERATURES EXCEPT FOR SUNDAY GIVEN THE MODELED 925 MB TEMPERATURES WHICH SUGGEST HIGH TEMPERATURES MAY BE SEVERAL DEGREES COOLER. FOR SUNDAY MORNING 12Z GFS LOW TEMPERATURES COUPLED WITH LIGHT WINDS INDICATE THE POTENTIAL FOR PATCHY FROST. HOWEVER THINK THIS IS TO COOL ATTM. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. .TONIGHT AND MONDAY...VFR CONDITIONS EXPECTED. SOME PATCHY FOG IS POSSIBLE LATE SUNDAY NIGHT / EARLY MONDAY MORNING, BUT WITH NO MAJOR IMPACT ON AVIATION EXPECTED. SOME HIGH CLOUDS...ALL WITH CIGS AOA 10000 FEET, ALONG WITH LIGHT SOUTHWESTERLY WINDS 10 KT OR LESS. OUTLOOK... MONDAY NIGHT AND TUESDAY: SOME LOW MVFR CLOUDS AND PATCHY FOG AROUND SUNRISE TUESDAY OTHERWISE VFR. TUESDAY NIGHT AND WEDNESDAY: SOME MVFR CEILINGS POSSIBLE TUESDAY AND WEDNESDAY WITH SOME SCATTERED SHOWERS, OTHERWISE VFR. E/NE WINDS AROUND 10 KNOTS. WEDNESDAY NIGHT THROUGH FRIDAY: VFR. NE WINDS 5 TO 10 KNOTS BECOMING SOUTHEAST. && .MARINE... PLEASANT CONDITIONS EXPECTED ON THE WATERS AND MONDAY AS HIGH PRESSURE CONTINUES TO MOVE EAST. SRLY OR SERLY WINDS TONIGHT...BECOMING SWRLY ON MONDAY...ALL GENERALLY 10 KNOTS OR LESS. WAVES 2 TO 3 FT ON THE OCEAN AND 1 TO 2 FT ACROSS DEL BAY. OUTLOOK... MONDAY NIGHT AND TUESDAY: WINDS AND SEAS INCREASE WITH DEVELOPING EASTERLY FLOW BUT REMAIN BELOW SCA CRITERIA. TUESDAY NIGHT THROUGH FRIDAY: WITH LOW PRESSURE OFF THE COAST A AVERAGE EASTERLY FLOW IN LIKELY TO REMAIN IN PLACE. THIS WILL KEEP SEAS ABOVE FIVE FEET WITH A BRIEF LULL POSSIBLE FRIDAY AFTERNOON, WINDS WILL LIKELY ALSO REMAIN ABOVE SCA CRITERIA THROUGH MOST OF THE PERIOD. && .TIDES/COASTAL FLOODING... A 1 FOOT OR GREATER ONSHORE FLOW POSITIVE DEPARTURE SURGE IS POSSIBLE FOR MID AND LATE WEEK. RIGHT NOW THE BEST CHANCE FOR MINOR COASTAL FLOODING WOULD BE WITH THE WEDNESDAY AFTERNOON TIDAL CYCLE BUT DEPARTURES LOOK ABOUT 1/2 FOOT SHORT NOW ON WEDNESDAY. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GAINES NEAR TERM...MIKETTA SHORT TERM...MIKETTA LONG TERM...GAINES AVIATION...GAINES/MIKETTA MARINE...GAINES/MIKETTA TIDES/COASTAL FLOODING...DRAG/GAINES

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