Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 230124 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 924 PM EDT Sat Jul 22 2017 .SYNOPSIS... A frontal boundary extended from the southern Great Lakes to our region this afternoon. Low pressure will ride eastward along the front and it should pass through our area tonight. Another low is expected to follow on Monday. The second low is forecast to pull the boundary southward and away from our region allowing high pressure to build down from the northwest for the middle part of the new week. A cold front from the northwest is anticipated to arrive on Thursday night. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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It was an active late afternoon and early evening across much of the area, mainly from Central NJ and Berks County on south to the Delmarva where several areas of thunderstorms moved on through. Activity initially developed in Central NJ along the sea breeze while activity elsewhere developed from what was left of any MCSs (Mesoscale Convective Systems) that moved east from Central Pennsylvania and Central Maryland as well as Northern Virginia. This activity has either moved offshore or weakened altogether. Radar mainly shows light showers with embedded moderate to heavier showers as of 9 PM across Central NJ and Bucks County heading east. We cannot rule out any thunder here given how unstable things are, but lightning detection has shown a downward trend in activity across our area. The heavier activity near Ocean City, Maryland and Chincoteague, Virginia was heading offshore and should not bother southern Delaware with just some light showers there. The grids were revamped overnight based on the latest radar trends initially for the first 3 hours. Afterwards, we leaned towards the NAM 3 km, which seems to best have a handle of QPF based on the look of satellite. All eyes now turn to the convective complex that has impacted southwest PA and West Virginia this evening. Most of the models, including the global models at higher resolutions, and some of the higher resolution short term models like the HRRR and RAP, take energy from this complex and move it across Central PA toward Central and North Jersey overnight. Given the 500 mb flow is west-northwest and the 1000-500 mb thickness contours are also west to east (basically zonal), I am not sold on this activity heading further north. MCSs like to track parallel to the 1000-500 mb thickness contours and thus I think the NAM 3 km is more likely which would take it towards DC/central Maryland and then toward the Delmarva and far South Jersey (Cape May/Atlantic/Cumberland and maybe far southern Ocean Counties) overnight. As a result, we updated the grids to reflect this thinking. The heavy rain threat is greatest south of a line from Wilmington to Atlantic City but may get as far north as Philadelphia overnight if convection sneaks up that far. So we kept in enhanced wording for heavy rains and gusty winds given the complex now as we see things. Further north, it looks to stable overnight for much thunder and north of Trenton and Freehold/Asbury Park we yanked it. Temperatures overnight will be mild as cloud cover increases across the region. Fog may start to develop in some areas towards late tonight/early morning, especially where heavy rain has fallen. Lows will drop down into the low to mid 70s across the region, with some mid to upper 60s across parts of the southern Poconos and northwest New Jersey.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... Another slightly muggy day on tap for the region but temperatures will not be quite as high as they have been recently. Sky conditions will be pretty cloudy which should help to keep the temps a bit lower. With a boundary across the region it may be the tale of two cities (or parts of the forecast area). Areas to the north of the boundary should remain slightly cooler than those areas to the south of the boundary. For now, anticipate that the boundary will remain just south of or along the Mason-Dixon line. Areas to the north will remain in the 80s, while areas to the south look likely to reach into the lower 90s. Low pressure is slated to travel along the boundary and another round of showers and thunderstorms is expected, mainly during the afternoon and evening hours. Once again the abundance of moisture across the region will bring the threat for heavy rain and we will need to monitor it closely, especially for those areas that see heavy rain today. SPC continues the slight/marginal risks across our forecast area for Sunday with damaging winds being the greatest threat. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... Unsettled conditions are forecast to continue from Sunday night into Monday night. The frontal boundary is expected to remain in our region on Sunday night with another low expected to pass through our area on Monday. We are anticipating the likelihood of showers and thunderstorms associated with another convective complex on Sunday night. Precipitable water values should be in excess of 2 inches across the central and southern parts of our forecast area. As a result, we will mention the potential for heavy rain at that time. The chance of showers and thunderstorms will continue into Monday and Monday night with the passage of the low. The low is expected to begin pulling the front to our southeast and south on Monday night. The axis of a mid level short wave trough approaching from the northwest is anticipated to pass overhead on Tuesday afternoon and it will be followed by a shot of dry weather for the mid week period. A cold front is expected to approach from the northwest on Thursday and it should pass through our region from Thursday night into early Friday. We will mention a chance of showers and thunderstorms with the front. Dry weather is forecast to return for next weekend. Temperatures are expected to be seasonable during the new week with no excessive heat events in sight. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...Scattered showers will continue to impact mainly KABE and to a lesser extent KRDG through 06Z, with the possibility of an isolated TSRA. The other terminals have seen showers and thunderstorms pass through and should remain quiet through 02Z Sunday. Additional showers/storms may follow in the wake of convection but confidence is lower as to timing and coverage. The greatest threat overnight for SHRA/TSRA will be at ACY late and possibly MIV and ILG with a lesser risk at PHL if activity makes it that far northward. TAFs were adjusted to the latest thinking. MVFR/IFR ceilings and visibilities are likely to occur in the wake of the convection and persist into the morning hours. Best chances will be at those locations that see heavy rain. There is potential for strong to severe storms today with gusty to damaging downburst winds and torrential rainfall. Patchy fog may form tonight especially in areas where any heavier rain fell early. Visibility could drop to MVFR or lower for a few periods. Sunday...Fog/low clouds early should clear into the afternoon but skies are expected to remain pretty overcast. VFR conditions are expected to return late morning/early afternoon but confidence is low that we see significant clearing through the day. Another round of showers and thunderstorms is expected, mainly during the afternoon/evening hours. Winds...light southerly winds today will become more west to southwest overnight and then will become more north to northeast on Sunday morning. Winds speeds are expected to remain around 10 knots or less. OUTLOOK... Sunday night...MVFR and IFR conditions in showers and thunderstorms. The rain may become heavy. Monday...A chance of showers and thunderstorms with conditions improving to VFR outside of any areas of rain. Monday night...Conditions lowering to MVFR and possibly IFR. A chance of showers and thunderstorms. Tuesday...MVFR and IFR conditions in the morning improving to VFR. Tuesday night through Thursday...Mainly VFR.
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&& .MARINE... Sub-small craft advisory conditions are expected to continue on the area waters. Winds will generally be south to southwest through this evening around 10 knots. Winds will become more west tonight and then northerly into Sunday. Seas are 2 to 3 feet on the ocean today and will gradually rise to 3 to 4 feet on Sunday. While seas are expected to remain below 5 feet, they may near 5 feet on the outer waters late tonight into Sunday. Showers and thunderstorms will impact the area waters through tonight, with locally higher seas and gusty winds. OUTLOOK... Sunday night through Thursday...No marine headlines are anticipated. RIP CURRENTS... A moderate risk for risk currents is expected to continue through this evening. The underlying 10-12 second period continues to show up on guidance and is impacting the rip current risk. Additionally, with the new moon is occurring on Sunday, and a moderate risk looks likely for New Jersey with a low risk for Delaware for Sunday. && .TIDES/COASTAL FLOODING... There is Coastal Flood Advisory in effect for this evening`s high tide along the New Jersey and Delaware coasts and along Delaware Bay. The surge at this morning`s high tide was about +0.4 to +0.6 feet. There will be an onshore component to the wind today and it should bring the surge up around +0.6 to +0.7 feet by evening. The astronomical tides with the upcoming new moon are quite high, as was the case with the new moon in both May and June. As a result, the somewhat unimpressive surge values will likely result in some minor flooding. If heavy rain occurs coincident with the high tide, the potential for flooding will increase. Conditions may be similar for Sunday evening`s high tide. An onshore flow is anticipated for Sunday, especially in areas from Atlantic City up to Sandy Hook. && .EQUIPMENT... Dew point readings at KDOV continue to measure too high compared to surrounding locations and should be treated as unrepresentative of the area. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...Coastal Flood Advisory until midnight EDT tonight for NJZ012>014-020>027. DE...Coastal Flood Advisory until midnight EDT tonight for DEZ002>004. MD...None. MARINE...None. && $$ Synopsis...Iovino Near Term...Meola/Stachelski Short Term...Meola Long Term...Iovino Aviation...Iovino/Meola/Stachelski Marine...Iovino/Meola Tides/Coastal Flooding...Iovino Equipment...PHI is the U.S. government's official web portal to all federal, state and local government web resources and services.