Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 270438 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1238 AM EDT SAT JUN 27 2015 .SYNOPSIS... HIGH PRESSURE WILL MOVE ACROSS TO THE NORTH OF OUR AREA AND OFF THE NEW ENGLAND COAST SATURDAY. LOW PRESSURE WILL TRACK ALONG A FRONTAL BOUNDARY SATURDAY, LIFTING TO THE OUR NORTH AND EAST SUNDAY. WEAK HIGH PRESSURE WILL ARRIVE FOR MONDAY. A COLD FRONT WILL CROSS THE AREA TUESDAY INTO WEDNESDAY. A SECOND COLD FRONT WILL SLOWLY MOVE THROUGH THE REGION LATER THIS WEEK. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... THE RAINFALL RATES ALONG THE LOWER SCHUYLKILL RIVER VALLEY WERE DECREASING GRADUALLY AROUND 1230 AM. THE SHOWERS WERE CONTINUING TO REDEVELOP ALONG REMNANT BOUNDARIES. BASICALLY, THE PRECIPITATION HAS BEEN REGENERATING ITSELF BUT IT SHOULD DISSIPATE SLOWLY OVER THE NEXT FEW HOURS. RADAR BASED RAINFALL AMOUNTS OF 4 INCHES OR MORE WERE INDICATED, ESPECIALLY IN MONTGOMERY COUNTY FROM AROUND COLLEGEVILLE TO CONSHOHOCKEN. WE HAVE RECEIVED REPORTS OF ROAD CLOSURES. DUE TO THE LATE HOUR, WE ANTICIPATE GETTING ADDITIONAL REPORTS FROM THOSE AREAS COVERED BY FLASH FLOOD WARNINGS IN THE MORNING. ADDITIONAL LIGHT TO MODERATE SHOWERS WERE INDICATED ALONG ANOTHER REMNANT BOUNDARY ACROSS THE POCONOS AND NORTHERN NEW JERSEY. RAINFALL AMOUNTS THERE HAVE BEEN GENERALLY LESS THAN A HALF INCH. WHILE THE SHOWER ACTIVITY IS ANTICIPATED TO LESSEN, A LARGE AREA OF RAIN ASSOCIATED WITH THE WARM ADVECTION IN ADVANCE OF LOW PRESSURE IN THE OHIO RIVER VALLEY SHOULD REACH OUR FORECAST AREA LATE TONIGHT. WE ARE EXPECTING THE RAIN TO AFFECT MAINLY EASTERN PENNSYLVANIA AT THAT TIME BEFORE SPREADING FARTHER EAST. AN EAST TO SOUTHEAST WIND IS FORECAST OVERNIGHT AND TEMPERATURES ARE EXPECTED TO DROP ONLY A FEW DEGREES FROM THEIR MIDNIGHT READINGS. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 AM SUNDAY/... WE HAVE ISSUED A FLOOD WATCH FOR MOST OF OUR WESTERN ZONES AND INCLUDING SOME OF THE PHILLY METRO AREA FROM SATURDAY AFTERNOON THROUGH EARLY SUNDAY MORNING...WHEN WE EXPECT THE HEAVIEST OF THE RAIN TO FALL. DID NOT THINK A FLASH FLOOD WAS PRUDENT GIVEN OUR GUIDANCE REMAINS ON THE HIGHER SIDE, EVEN WITH THE RECENT CONVECTIVE RAINS. THAT BEING SAID WE DO NOT EXPECT ANY MAIN STEM RIVER FLOODING TO BE AN ISSUE, THIS WATCH IS MOSTLY FOR THE SMALLER STREAMS AND CREEKS, LOW-LYING AREAS AND THE URBAN CORRIDOR WHERE OUR HEADWATER GUIDANCE REMAINS RATHER LOW...SMALL BASIN STREAMS/CREEKS THAT USUALLY RESPOND QUICKLY TO HEAVIER RAIN....AGAIN NOT FLASH FLOODING. THERE ARE SOME THINGS THAT WE QUESTIONED WITH THE POTENTIAL FOR FLOODING ON SATURDAY. FOR STARTERS, JET STREAK POSITIONING DOES NOT SEEM IDEAL FOR ENHANCED LIFT PLACING US IN THE RIGHT EXIT REGION. ITS VERY POSSIBLE THAT THE SURFACE WARM FRONT WILL ONLY BE ABLE TO PROGRESS AS FAR NORTH AS NORTHERN DELMARVA BEFORE STALLING AGAIN WITH RAIN FALLING TOWARDS THE NORTH AS THE LOW-LEVEL FRONT MOVES THROUGH...NOT A TRUE WARM SECTOR SETUP. GUIDANCE SHOWS STRONGER THETA-E SURGE ACROSS THE SOUTHERN ZONES... WITHIN WARM SECTOR, BUT COULD SEE MORE DRYING AS THE WINDS VEER SOUTHWEST LATER IN THE DAY. THERE IS SOME WEAK INSTABILITY LATE IN THE DAY, ALL ELEVATED, BUT EVEN THE SHOWALTER INDICES ARE NOT THAT EXCITING. WHAT WE ARE FOCUSING ON MAINLY IS THE LONG EASTERLY FETCH OFF THE ATLANTIC THAT WILL USE THE OUR WESTERN ZONE UPSLOPE COMPONENT TO HELP LOCALLY ENHANCE RAINFALL. PWATS ARE EXPECTED TO CLIMB UP TOWARDS THE 2 INCH MARK WITH A SECONDARY LOW PRESSURE FORMING RIGHT AROUND THE CITY LATE TONIGHT...TRIPLE POINT ENHANCEMENT. LASTLY, A 45-50 KNOTS 850MB JET PUMPING INTO THE AREA WITH A VERY STRONG ISENTROPIC LIFT WILL FURTHER HELP THE HEAVY RAIN POTENTIAL. OUTSIDE OF OUR FLOOD WATCH, A WIDESPREAD 1 TO 2 INCHES OF RAIN IS EXPECTED BUT GIVEN THE LONG DURATION OF THE EVENT, NOT EXPECTING MUCH IN THE WAY OF FLOODING ISSUES. THERE IS ALSO THE CHANCE FOR AFTERNOON/LATE EVENING CONVECTION ACROSS OUR DELMARVA ZONES...IN THE WARM SECTOR, AS MUCAPE CLIMBS UPWARDS OF 750J/KG AND WITH A DECENT AMOUNT OF SHEAR IN PLACE. GOOD LOW-LEVEL VEERING PROFILES MAY ALLOW FOR A FEW SPINNING STORMS SHOULD ANY FORM DURING THIS TIME FRAME. && .LONG TERM /SUNDAY THROUGH SATURDAY/... SUNDAY...THINGS START TO WIND DOWN ON SUNDAY AS THE LOW LIFTS TO THE NORTHEAST. SHOWERS WILL GRADUALLY TAPER OFF WITH HIGHEST CHANCES REMAINING ACROSS THE NORTHERN AREAS WHERE SOME WRAPAROUND MOISTURE LINGERS. CLOUDY SKIES WILL CONTINUE AND AREAS ALONG THE COAST SHOULD SEE SOME SUN BY THE AFTERNOON. MONDAY...A WEAK AREA OF HIGH PRESSURE WILL CROSS THE REGION, KEEPING US DRY WITH MOSTLY SUNNY SKIES. WINDS WILL START TO BECOME MORE SOUTHWESTERLY AND THIS WILL BE THE START OF DECENT WARM AIR ADVECTION INTO OUR AREA. TUESDAY THROUGH FRIDAY...WARM AIR ADVECTION WILL CONTINUE ACROSS THE REGION AND WE SHOULD BE ABLE TO SEE TEMPERATURES REACH INTO THE MID 80S BY THE AFTERNOON. AS WE GO THROUGH THE DAY, WE WILL SEE AN INCREASE IN CLOUDINESS AS A COLD FRONT STARTS TO PUSH TOWARD THE AREA FROM THE GREAT LAKES REGION. THE COLD FRONT DOESN`T LOOK LIKE IT WILL REACH THE AREA UNTIL LATE TUESDAY CLEARING THE COAST EARLY WEDNESDAY MORNING. A SECOND COLD FRONT WILL MOVE TOWARDS OUR AREA REACHING OUR WESTERN ZONES LATE WEDNESDAY. THE FRONT WILL SLOWLY SAG THROUGH THE REGION THE MODELS DIFFER AT THE SPEED AND LOCATION OF THIS FRONT WITH IT POSSIBLY STALLING IN OR NEAR OUR FORECAST AREA. WHILE SHOWERS AND THUNDERSTORMS LOOK POSSIBLE THROUGH MUCH OF THE PERIOD, IT DOES NOT LOOK LIKE IT WILL BE A TOTAL WASHOUT. TEMPERATURES THROUGH THIS PERIOD LOOK TO REMAIN NEAR NORMAL. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY, AND SURROUNDING AREAS. 00Z TAFS BRING IFR/WINDY CONDITIONS DURING THE DAY ON SATURDAY. OVERNIGHT...LOWERING VFR CIG. SOME MVFR VSBYS DUE TO FOG POSSIBLE TOWARD MORNING AT MORE RURAL AIRPORTS AND TERMINALS. SLIGHTLY STRONGER EAST WIND. SCATTERED SHOWERS WILL CONTINUE BUT MAY NOT AFFECT OUR TAF SITES. SATURDAY MORNING...CIGS LOWERING FURTHER. CONFIDENCE ABOUT THEM REMAINING VFR IS DECREASING. RAIN SHOULD ARRIVE AT NORTHWEST TERMINALS AND OTHER WESTERN AIRPORTS IN PA. MVFR CONDITIONS ONCE RAIN ARRIVES. EAST WINDS AVERAGING AROUND 10 KNOTS WITH GUSTINESS STARTING FROM KPHL METRO AIRPORTS EAST AND SOUTHEAST. SATURDAY AFTERNOON...ALL TERMINALS PREDICTED TO DROP TO IFR IN RAIN AND FOG. RAIN SHOULD BE HEAVY, ESPECIALLY NORTHWEST TERMINALS. EAST TO SOUTHEAST WINDS SUSTAINED SPEEDS INCREASING TO CLOSE TO 15 KNOTS WITH GUSTS AVERAGING CLOSE TO 25 KNOTS. OUTLOOK... SATURDAY NIGHT...IFR CONDITIONS CONTINUING. GUSTY EAST WINDS SHIFTING TO THE WEST. SUNDAY...SHOWERS CONTINUE THROUGH SUNDAY, TAPERING OFF BY THE LATE AFTERNOON. WEST SOUTHWEST WINDS AROUND 10 TO 15 KNOTS WITH GUSTS AROUND 20 KNOTS. MONDAY...VFR CONDITIONS EXPECTED. WESTERLY WINDS AROUND 5 TO 10 KNOTS. TUESDAY...MAINLY VFR CONDITIONS EXPECTED. SUB-VFR CONDITIONS POSSIBLE IN ANY SHOWERS OR THUNDERSTORMS THAT MAY DEVELOP. SOUTHERLY WINDS AROUND 10 KNOTS. WEDNESDAY...MAINLY VFR CONDITIONS EXPECTED. SUB-VFR CONDITIONS POSSIBLE IN SHOWERS OR THUNDERSTORMS WITH CLEARING TOWARD LATE AFTERNOON/EVENING. WESTERLY WINDS AROUND 5 TO 10 KNOTS. && .MARINE... WE HAVE ISSUED A SCA FOR ALL OUR COASTAL WATERS STARTING FIRST ACROSS THE SOUTH AND THEN NORTH AS A WARM FRONT LIFTS THROUGH THE REGION. SEAS WILL ALSO INCREASE BEHIND THE FRONT UPWARDS OF 5-7 FEET AS STRONGER EASTERLY FLOW OCCURS JUST AHEAD OF THE WARM FRONT...WINDS VEER TOWARDS THE SOUTH LATE SATURDAY. GUSTS UPWARDS OF 30 KNOTS ARE EXPECTED THOUGH A VERY BRIEF PERIOD OF GALE FORCE GUSTS MAY OCCUR, MOSTLY ACROSS OUR NORTHERN WATERS WHERE THE TIGHTEST PRESSURE GRADIENT EXISTS. OUTLOOK... SUNDAY...THE SMALL CRAFT ADVISORY REMAINS UP THROUGH SUNDAY WITH LINGERING ADVISORY CONDITIONS IN A WEST- SOUTHWEST FLOW, WITH SEAS REMAINING ELEVATED BUT GRADUALLY SUBSIDING THROUGH THE EVENING. MONDAY...WINDS AND SEAS ARE ANTICIPATED TO SUBSIDE BELOW ADVISORY CRITERIA. TUESDAY...AN INCREASE IN A SOUTHERLY FLOW MAY BUILD THE SEAS ON THE OCEAN TO ADVISORY CRITERIA. WEDNESDAY...SUBSIDING SEAS WITH SUB-ADVISORY CONDITIONS EXPECTED ACROSS THE AREA WATERS. && .HYDROLOGY... WE`VE ISSUED A FLOOD WATCH FOR 8 COUNTIES ACROSS THE HSA...6 COUNTIES IN SOUTHEAST PA, CECIL COUNTY IN MD, AND NEW CASTLE COUNTY IN NORTHERN DE. LIGHT RAIN WILL MOVE INTO THE REGION SATURDAY MORNING. INTENSITIES WILL INCREASE IN THE AFTERNOON AS A CONVECTIVE CONTRIBUTION IS ADDED INTO THE MIX. THIS IS A STRONG SYSTEM TO BEGIN WITH EVEN WITHOUT THE SAID CONVECTIVE CONTRIBUTION. PER THE NAEFS, THE STRENGTH OF THE PARENT SURFACE LOW (SUB 1000 MB) ONLY OCCURS ONCE EVERY 5 TO 10 YEARS FOR THIS TIME OF YEAR (3 STANDARD DEVIATIONS). TWO TO TWO AND A QUARTER INCHES OF RAINFALL ARE EXPECTED. THE RAINFALL COMES TO AN END LATE SATURDAY NIGHT. SMALL CREEKS AND STREAMS WILL BE MOST VULNERABLE DURING THIS EVENT ALONG WITH POOR DRAINAGE AND URBAN AREAS. MAINSTEM RIVERS SUCH AS THE SCHUYLKILL AND DELAWARE ARE NOT EXPECTED TO FLOOD. && .TIDES/COASTAL FLOODING... A FEW SPOTS ALONG THE DELAWARE BAY AND DELAWARE RIVER MIGHT EXPERIENCE MINOR TIDAL FLOODING SATURDAY EVENING AND NIGHT. A SOUTHEAST FLOW WILL DEVELOP TONIGHT AND INCREASE OVERNIGHT INTO SATURDAY. THE ONSHORE FLOW WILL PERSIST INTO SATURDAY NIGHT. WINDS LOOK TO BE IN THE 10-20 MPH RANGE WITH HIGHER GUSTS. THE STRONGEST WINDS SHOULD OCCUR SATURDAY EVENING AND COINCIDE WITH RUNOFF AND THE HIGH TIDES. && .RIP CURRENTS... THE INITIAL FORECAST FOR RIP CURRENT FOR SATURDAY IS MODERATE. BUT OUR IN HOUSE PROCEDURE NEARLY GAVE US A HIGH RISK WITH THE SHORT PERIOD BEING THE LIMITING FACTOR. NOT EXACTLY A GREAT BEACH DAY WITH STRONG ONSHORE WINDS AND RAIN ON THE WAY. WE WILL REACCESS OVERNIGHT. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...FLOOD WATCH FROM NOON EDT TODAY THROUGH LATE TONIGHT FOR PAZ060-061-070-071-101>104. NJ...NONE. DE...FLOOD WATCH FROM NOON EDT TODAY THROUGH LATE TONIGHT FOR DEZ001. MD...FLOOD WATCH FROM NOON EDT TODAY THROUGH LATE TONIGHT FOR MDZ008. MARINE...SMALL CRAFT ADVISORY FROM 7 AM THIS MORNING TO 6 PM EDT SUNDAY FOR ANZ452>455. SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 6 PM EDT SUNDAY FOR ANZ450-451. SMALL CRAFT ADVISORY FROM 7 AM THIS MORNING TO 11 PM EDT THIS EVENING FOR ANZ430-431. && $$ SYNOPSIS...MEOLA NEAR TERM...IOVINO SHORT TERM...HEAVENER LONG TERM...MEOLA AVIATION...GIGI/MEOLA MARINE...GORSE/HEAVENER/MEOLA HYDROLOGY...KRUZDLO TIDES/COASTAL FLOODING...KRUZDLO RIP CURRENTS...GIGI

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