Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 190154 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 954 PM EDT Fri Aug 18 2017 .SYNOPSIS... As low pressure tracks well to our north, a cold front moves through late tonight into early Saturday. High pressure then builds in late Saturday and remains in place into Monday before shifting offshore. The next cold front is scheduled to arrive during Wednesday, then Canadian high pressure builds in for Thursday and Friday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... The cold front was still back across central Pennsylvania and eastern West Virginia around 9:30 PM. The boundary is forecast to pass through our region after midnight. Until that time conditions will remain warm and muggy. The last of the rain showers were in southern New Jersey and central and southern Delaware. They will continue to make their way off the coast and farther out to sea overnight. The potential for severe weather and flooding continues to decrease. As a result, all watches have been discontinued. All that remains in effect are a couple Flood Advisories where the rain continues to fall. The wind will be generally less than 10 MPH overnight at varying directions which may begin to favor the northwest and west with the arrival of the cold front. Low temperatures are expected to be mostly in the upper 60s and lower 70s. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... Cold front should be offshore early Saturday morning, and once west to northwest winds increase a bit, the drier airmass spreads east, and any lingering fog will burn off. Skies clear out in the afternoon. Dewpoints drop about 10-15 degrees, generally into the mid 60s, but temps will be fairly warm, topping off in the upper 80s to near 90 across the urban corridor of I-95 from Trenton to Wilmington, and in the Delmarva. Upper trough approaches from the west, and this may bring isolated late day showers and thunderstorms to far western portions of the forecast area. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... Summary...Lowering of the dew points through Sunday although remaining warm to hot, then moistures increases again with some convection especially Wednesday with the next cold front. A noticeably cooler and drier airmass arrives for Thursday and Friday in the wake of the cold front. Synoptic Overview...An upper-level trough is forecast to exit the Northeast Saturday night and Sunday, then the flow aloft turns more zonal through early next week. Another trough is forecast to amplify across eastern Canada and the Great Lakes to the Northeast Tuesday into Thursday, which then remains in the Northeast on Friday. We used a blend of continuity/guidance for Saturday night through Sunday night, then blended in the 12z WPC Guidance. For Saturday night and Sunday...The axis of an upper-level trough is forecast to slide across the region Saturday night, then quickly move across and exit New England Sunday. A short wave embedded within this trough is forecast to move through Saturday night, although it may shear out to the east-northeast. While some drying is expected to move in, enough lingering moisture and instability combined with lift may allow for some convection to arrive from the west before weakening. We therefore carried some slight chance PoPs in Saturday evening across parts of the western zones. The flow aloft then turns more zonal on Sunday with surface high pressure building in. This should be accompanied by more pronounced drying, and with plenty of heating during the day Sunday the dew points are anticipated to lower to more comfortable levels. A northwesterly breeze on Sunday may be light enough to allow for a sea breeze to develop in the afternoon. For Monday and Tuesday...The zonal flow aloft continues at least into Tuesday. This drives high pressure eventually offshore as it weakens some later Monday. The next upper-level trough amplifies eastward from the Midwest and Upper Great Lakes Tuesday. This will start to back the flow more southwesterly, and there may be a lee- side trough present on Tuesday. As the moisture begins to increase once again combined with the possibility for some convergence and enough instability, some convective development is possible Tuesday afternoon. We will carry slight chance PoPs as a result for Tuesday. Any isolated convection especially inland should tend to diminish during the night. It will turn more humid during this timeframe. For Wednesday through Friday...The prospects for convection will depend on the timing of an incoming cold front Wednesday. This will be due to an upper-level trough arriving from the west, however a pre-frontal trough may serve as the primary focus for showers and thunderstorms. We will continue with chance PoPs with the idea for at least scattered convection possible Wednesday. As of now, the cold front should be offshore to start Thursday and Canadian high pressure builds southeastward, which arrives over our area on Friday. A noticeably cooler and drier airmass overspreads our region for Thursday and Friday. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Overnight...VFR and MVFR. Low level moisture remains in place and some local low clouds and/or fog should develop. The extent of the low clouds/fog is of lower confidence. Saturday...Any fog dissipates early, otherwise VFR. Northwest winds increase to 5-10 knots, then shift to the west or southwest in the afternoon. Isolated late day shower or thunderstorm possible near KRDG/KABE. OUTLOOK... Saturday night and Sunday...VFR overall. Southwest winds 5 knots or less becoming northwest Saturday night, then northwest winds near 10 knots Sunday. Monday and Tuesday...Mainly VFR. Southerly winds around 10 knots. Wednesday...Sub-VFR at times with some showers and thunderstorms possible as a cold front arrives. Southwest winds 5-10 knots, becoming west. && .MARINE... The SCA has been cancelled as wind speeds and wave heights diminish gradually. The last of the showers and thunderstorms will move out to sea overnight. Tranquil conditions develop and will remain in place through Saturday. Fog may develop late tonight and into Saturday morning, which could reduce VSBYs down to 1 NM. OUTLOOK... Saturday night through Wednesday...The conditions are anticipated to be below Small Craft Advisory criteria. RIP CURRENTS... The rip current risk for Saturday is currently outlooked as low. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Gorse Near Term...Iovino Short Term...MPS Long Term...Gorse Aviation...Gorse/MPS Marine...Gorse/MPS

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