Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 110150 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 950 PM EDT Thu Aug 10 2017 .SYNOPSIS... High pressure will move offshore through tonight. A frontal boundary will lift northward into the region Friday and remain nearby through Saturday. A cold front will cross the region late Saturday into Sunday. The front stalls just south of the region on Sunday and will slowly push offshore through Tuesday. High pressure then builds in for Wednesday and Thursday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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Winds have again become very light to calm this evening with a relaxed pressure gradient over the area. Temps are also similar to last evening, however some mid-level warm-advection cloudiness is on the increase which should end up keeping overnight mins several degrees warmer than last night. Radar shows some showers over west PA but latest models are not showing any QPF reaching east PA overnight, so decided to push back the slight chc pops to 10Z Fri and later. Previous discussion: The mid and upper level trough gets closerto the region overnight. It will be making very slow progress so will stay well west of the region through the near and short term (and much of the weekend). However, with the addition of return flow already, plus an approaching surface low, could see showers begin to move into the region late tonight. Instability will be almost non-existent, so do not expect any thunderstorms overnight, but could see isolated showers, primarily west of the fall line. Given increasing cloud cover, expect temperatures to stay up a bit more overnight than what we have seen the last few nights. Lows tonight are expected to range from the upper 50s to upper 60s across the region. Also due to the increasing clouds, the risk for fog development is lower than what we have seen the last few nights, so for now will not include it in the grids. However, if the mid level clouds are slower to propagate across the area than forecast, then patchy fog is possible especially on the Coastal Plains.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... The trough (both at the surface and through the mid and upper levels) continues very slow progress east. As such, expect continued chances for showers, possibly expanding across the region by tomorrow afternoon. Instability, even through the day time hours, remains quite limited. Still there may be enough elevated instability for a few thunderstorms. We continue the trend of near or slightly below normal temperatures as increased cloud cover should help to keep temperatures a few degrees below what we are seeing today. Highs are forecast to range from the lower 70s in the Poconos to mid 80s in Delmarva and the urban corridor. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Friday night through Tuesday...Unsettled weather starts to the period as the frontal boundary located to our south, lifts into our area. A mid-level shortwave will rotate through the region Friday night, which will help to generate some showers and thunderstorms Friday night into early Saturday. The boundary doesn`t appear to lift all the way through the region and just settles across our area on Saturday. It will finally get the push out of the way by the cold front that arrives Saturday night. With a surface trough in the area on Saturday, along with the lingering boundary, additional showers and thunderstorms may develop through the day. The cold front crosses the area late Saturday into Sunday and looks to make it to the coast by Sunday morning. However, the boundary stalls and will linger near our coast through early next week. This will keep the chance for some showers/thunderstorms through much of the period, although chances will be increased closer to the coast and less the further inland you go. The models have started to trend a bit drier on Monday but this will be very dependent on the location of the stalled boundary. Started to drop POPs just a little bit but want to see more run to run consistency before wiping out any chance of precipitation in the region. Tuesday through Thursday...the front picks up some speed and drops further to the south of the region. Conditions will start to dry out as the high starts to build in from the west. High pressure will build across the region for Wednesday and Thursday with mostly dry weather expected across our area. Near normal temperatures are expected through this period. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR conditions are expected through the TAF period. Showers may begin to move into E Central PA (including KABE and KRDG) late tonight, though the chance is too low to mention at this time, and even if showers move in, conditions are likely to stay VFR with hardly any visibility restrictions and ceilings near or above 4000 ft AGL. The chance expands across all terminals after 18Z, and some thunderstorms are possible during the day time hours as well. However, the chance remains too low to mention in the TAFs at this time. Winds should generally keep a southeasterly or southerly direction. However, through the overnight hours when wind speeds will be light (5 kt or less), local valley effects could result in variable direction. After 12Z though, winds are once again expected to settle out of the southeast with speeds less than 10 kt. Outlook... Friday night through Saturday...MVFR conditions, possibly IFR at times, as showers and thunderstorms move through the region. Saturday night through Tuesday...Mainly VFR conditions. Showers and thunderstorms are possible, which may cause brief periods of MVFR/IFR to occur.
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&& .MARINE... Winds and seas are expected to remain below small craft advisory conditions tonight and Thursday. Outlook... Friday night through Tuesday...Sub-Small Craft Advisory conditions are expected to continue through the entire period. Rip Currents... There is an underlying long period (11 second) swell observed at nearby buoy locations, but wave heights remain low (2 feet or less). Thus, the forecast is for a low risk for the formation of dangerous rip currents to continue tomorrow. We will continue to monitor the long period swell, however. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Meola Near Term...AMC/Johnson Short Term...Johnson Long Term...Meola Aviation...Johnson/Meola Marine...Johnson/Meola is the U.S. government's official web portal to all federal, state and local government web resources and services.