Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 040805 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 405 AM EDT SAT JUL 4 2015 .SYNOPSIS... LOW PRESSURE OVER SOUTHEAST VIRGINIA WILL MOVE OUT TO SEA SOUTHEAST OF CAPE COD BY THIS EVENING. WEAK HIGH PRESSURE FOLLOWS LATE TONIGHT AND SUNDAY, THEN SHIFTS OFFSHORE MONDAY. A WARM FRONT MOVES SLOWLY NORTHEAST THROUGH THE MID ATLANTIC STATES TUESDAY WITH A COLD FRONT TO FOLLOW LATE WEDNESDAY OR THURSDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... THE EVENING WATER VAPOR SATELLITE IMAGERY SHOWS A POSITIVELY- TILTED UPPER TROUGH OVER THE MIDWEST. MOISTURE IS STREAMING AHEAD OF THE TROUGH FROM THE WESTERN GULF OF MEXICO NORTHEASTWARD TOWARD THE CENTRAL APPALACHIANS AND MID-ATLANTIC COAST. AT THE SURFACE, A STATIONARY FRONTAL BOUNDARY WAS POSITIONED TO OUR SOUTH NEAR THE VA-NC BORDER. REGIONAL RADAR MOSAIC THIS EVENING SHOWED A BAND OF LIGHT SHOWERS TO OUR SOUTH AND WEST OVER WESTERN PA/VA/CENTRAL MD THAT WAS ASSOCIATED WITH DPVA FROM A LEADING MID-LEVEL SHORTWAVE TROUGH AND ISENTROPIC LIFT. POPS THRU TONIGHT CLOSELY FOLLOW THE LATEST HRRR, RAP AND NCEP WRF-NMM, WHICH SEEM TO HAVE HAD A GOOD HANDLE ON THE PROGRESSION OF THESE SHOWERS THUS FAR. PRECIP IS GENERALLY EXPECTED TO ADVANCE NORTHEASTWARD INTO THE EASTERN SHORE OF MD THIS EVE, DELAWARE CLOSE TO MIDNIGHT AND EASTERN PA/NJ LATE TONIGHT INTO THE EARLY MORNING. THE BEST LIFT WITH THE FRONT AND THE UPPER TROUGH WILL REMAIN UPSTREAM OF THE AREA TONIGHT. THE CWA WILL BE LOCATED ON THE COOL/STABLE SIDE OF THE BOUNDARY. THERE IS SOME RESIDUAL DRY AIR IN THE MID AND LOW-LEVELS. THEREFORE, DO NOT EXPECT THE PRECIP TO BE STEADY OR HEAVY TONIGHT IN THIS SETUP. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... STILL LOTS OF UNCERTAINTY IN THIS PERIOD. THERE IS CONSIDERABLE DISAGREEMENT BETWEEN MODELS AND RUN-TO-RUN ON INDIVIDUAL MODEL RUNS. FOR THE MOST PART, THE MAIN DETERMINISTIC MODELS HAD A SLIGHTLY DRIER TREND WITH THE 12Z/18Z RUNS. HOWEVER, THIS HAS BEEN THE CASE THE LAST FEW DAYS, WITH THE 00Z RUNS TENDING TO BE WETTER SOLUTIONS. AT THIS POINT, THINK THE HIGHEST CHANCES WILL STILL COME BEFORE 21Z. THINK THAT IT WILL MOSTLY BE A STEADY RAIN GIVEN A RATHER STABLE ATMOSPHERE IN PLACE. AS FAR AS RAIN AMOUNTS, HAVE FAVORED LIGHTER AMOUNTS GIVEN THE UNCERTAINTY OF HOW MUCH MOISTURE ADVECTION WE WILL HAVE. THE THREAT OF THUNDERSTORMS, HEAVY RAINFALL AND FLOODING LOOKS TO BE DWINDLING GIVEN THESE RECENT TRENDS. MOST MODEL SOLUTIONS CONTINUE TO SHOW THE PRECIP LIFTING OUT QUICKLY FROM MID TO LATE AFTERNOON. THIS TIMING MAY ALLOW FOR SOME OUTDOOR 4TH OF JULY FESTIVITIES TO TAKE PLACE LATE IN THE DAY. THE GROUND MAY BE DAMP THOUGH IN PARTS OF THE AREA THAT RECEIVE THE STEADIER/HEAVIER RAINFALL (MOST LIKELY DELMARVA AND SOUTHERN NJ). WITH ALL THE CLOUD COVER IN PLACE, IT LOOKS TO BE A RATHER COOL DAY (HIGHS IN THE 60S IN THE MOUNTAINS AND 70S ELSEWHERE). && .LONG TERM /SUNDAY THROUGH FRIDAY/... 500MB: A TROUGH CENTERED NEAR THE TENNESSEE VALLEY SUNDAY WILL WEAKEN NORTHEASTWARD ACROSS THE MID ATLANTIC STATES TUESDAY. A WEAK WEST SOUTHWEST FLOW PREVAILS THEREAFTER WITH WEAK EMBEDDED DISTURBANCES. TEMPERATURES: CALENDAR DAY TEMPERATURES NEAR OR SLIGHTLY BELOW NORMAL ON SUNDAY WARM TO ALMOST 5 DEGREES ABOVE NORMAL TUESDAY AND WEDNESDAY AND POSSIBLY REMAIN ABOVE NORMAL THURSDAY AND FRIDAY. FORECAST BASIS: UNLESS OTHERWISE NOTED, THIS 330 AM SATURDAY JULY 4TH FORECAST WAS GENERALLY A 50 50 BLEND OF THE 00Z/4 GFS/NAM MOS GUIDANCE SUNDAY-MONDAY, 00Z/4 MEX MOS MONDAY NIGHT AND TUESDAY, THEN THE 0521Z/4 WPC GRIDDED ELEMENTS OF MAX/MIN TEMP, 12 HOUR POP, 6 HOUR DEWPOINT- SKY-WIND FROM TUESDAY NIGHT THROUGH NEXT FRIDAY WITH THE EXCEPTION OF MAX TEMPS TUESDAY AND WEDNESDAY WHEN THE 00Z/4 MEX BLENDED WITH EVEN WARMER 00Z/4 ECMWF 2M TEMPS PREVAILED. THE DAILIES... SUNDAY...AFTER ANY EARLY MORNING PATCHY FOG DISSIPATES...SCT-BKN AOA 5000 FT. WEST WIND GUST 15 MPH. CONFIDENCE: ABOVE AVERAGE. MONDAY....INCREASING CLOUDS. ST/FOG POSSIBLE LATE MONDAY NIGHT? SOUTH WIND GUST 15 MPH MONDAY AFTERNOON. CONFIDENCE: ABOVE AVERAGE. TUESDAY...AREAS OF SHOWERS AND EMBEDDED TSTMS WITH PWAT OF 1.75 TO TO 2 INCHES, MLCAPE 1200J, AND WEAK STEERING WHICH COULD MEAN SEVERAL INTENSE TSTMS WITH EXCESSIVE SHORT DURATION RAINFALL (POOR DRAINAGE FLOODING FOR STARTERS). SOUTHERLY WIND GUST 20 MPH. NEAR 90F PHILLY AREA. CONFIDENCE: ABOVE AVERAGE. WEDNESDAY...LIKELY A HOT DAY. TSTMS LATE IN THE DAY AHEAD OF THE APPROACHING AND EVENTUALLY SLOWING COLD FRONT. 1000J MLCAPE. COULD BE STRONG TSTMS E PA. HEAT INDEX RIGHT NOW MODELED 99 PHL AND NEAR 100 DELMARVA. WILL BE REEVALUATED NEXT SEVERAL DAYS. NO HEAT INDEX ACTION ATTM IN THE MORNING HWO. CONFIDENCE: ABOVE AVERAGE. THURSDAY...UNCERTAINTY ON TIMING BUT TSTMS ARE IN THE FCST WITH ANOTHER SHORT WAVE PASSAGE. ALSO UNCERTAINTY ON TEMPS, DEPENDENT ON TIMING CONVECTIVE RELATED SKYCOVER. CONFIDENCE: AVERAGE OR BELOW AVERAGE. FRIDAY...PROBABLY DRYING OUT AFTER THURSDAYS PROBABLE SHORT WAVE PASSAGE. CONFIDENCE: AVERAGE OR BELOW AVERAGE. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDITIONS EXPECTED THROUGH THE OVERNIGHT WITH CEILINGS AOA 5,000 FEET. SOME LIGHT RAIN SHOWERS MAY BEGIN TO MOVE INTO THE REGION BY 05Z WITH CHANCES INCREASING FROM SOUTH TO NORTH OVERNIGHT. THE STEADIEST AND HEAVIEST SHOWERS LOOK TO BE FROM 13-18Z SATURDAY, WHICH WILL CORRESPOND TO THE HIGHEST CHANCE FOR MVFR CEILINGS/VSBYS FROM PHL/PNE TO THE SOUTHEAST. RDG AND ABE COULD ESCAPE THE PROSPECTS FOR ANY MVFR RESTRICTIONS. ACY HAS HIGHEST LIKELIHOOD TO SEE MVFR CONDITIONS WITH THE SLOWEST RISE IN CEILINGS LATE IN THE DAY. CEILINGS WILL LIKELY LIFT TO VFR AND BECOME BROKEN BY 19Z OUTSIDE OF ACY WHERE AN ONSHORE FLOW WILL TEND TO KEEP THEM LOWER. WINDS WILL BE AT OR UNDER 10 KNOTS FROM THE SOUTH LATE THIS EVENING THEN SHIFTING TO EASTERLY FOR MOST OF SATURDAY. A WIND SHIFT TO A MORE WESTERLY DIRECTION IS LIKELY TO START BY SATURDAY EVENING. OUTLOOK... SUNDAY...VFR SCT-BKN AOA 5000 FT. WEST WIND MAX GUST 15 KT DURING THE AFTERNOON. PATCHY MVFR FOG POSSIBLE TO START THE DAY AND AGAIN LATE SUNDAY NIGHT. HIGH CONFIDENCE. MONDAY...VFR SCT-BKN AOA 5000 FT DURING THE DAY WITH A CHANCE OF IFR ST/FOG LATE MONDAY NIGHT AHEAD OF A WARM FRONT. SOUTHERLY WIND MAX GUST 15 KT DURING THE AFTERNOON. HIGH CONFIDENCE. TUESDAY...VFR SCT-BKN AOA 5000 FT WITH SCT TSTMS AND ASSTD BRIEF IFR CONDS IN HEAVY RAIN, ESPECIALLY E PA DURING THE AFTN-EVENING. HIGH CONFIDENCE. WED...VFR SCT-BKN WITH A PRETTY GOOD CHANCE OF AFTN OR NIGHTTIME TSTMS. IFR CONDS POSSIBLE IN TSTMS. CONFIDENCE: AVERAGE OR ABOVE AVERAGE. && .MARINE... WINDS AND SEAS SHOULD STAY BELOW SCA CRITERIA TONIGHT INTO TOMORROW MORNING. BY TOMORROW AFTERNOON, WINDS AND SEAS COULD BUILD TO NEAR 25 KT/5 FT, PRIMARILY ON THE NORTHERN ATLANTIC WATERS. HOWEVER, THERE IS CONSIDERABLE UNCERTAINTY AND HAVE CAPPED WINDS/SEAS JUST BELOW SCA THRESHOLD. OUTLOOK... SUN NIGHT THRU WED...NO MARINE FLAGS ARE ANTICIPATED AS OF THIS WRITING. && .TIDES/COASTAL FLOODING... TONIGHT AND SUNDAY EVENING. WHILE SOME TIDAL SITES MAY APPROACH MINOR TIDAL FLOODING LEVELS, CURRENT DATA INDICATES THEY WILL REMAIN BELOW CRITERIA. && .RIP CURRENTS... THERE IS A MODERATE RISK OF RIP CURRENTS ON SATURDAY ALONG THE NEW JERSEY SHORE GIVEN THE CONTINUED ONSHORE FLOW AND MODERATE PERIOD SWELLS. THE RISK IS LOW FOR DELAWARE. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...DRAG 404 NEAR TERM...AMC WILL UPDATE 412 SHORT TERM...AMC WILL UPDATE 412 LONG TERM...DRAG 404 AVIATION...AMC/DRAG 404 MARINE...AMC/DRAG 404 TIDES/COASTAL FLOODING...404 RIP CURRENTS...404

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