Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 261937 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 337 PM EDT Mon Sep 26 2016 .SYNOPSIS...
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A cold front will move across the area tonight, and then stall off the Mid-Atlantic coast on Tuesday. An upper low will meander over the eastern United States for the rest of the week, lifting to the northeast and departing sometime this weekend. Meanwhile, several waves of low pressure will develop along that stalled boundary and move up the East Coast.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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High pressure, over New England, has shifted to the east. A cold front across the Ohio Valley this afternoon will push eastward and start to move into our area late tonight. For the most part, we will only deal with increasing cloudiness from west to east through tonight. Rain, associated with the front, will start to enter the region late tonight, mainly after midnight, and spread eastward. There may be enough lift present for some isolated thunderstorms and heavy rain, mainly across our southern areas. With plenty of cloud cover present, temperatures will not drop off too much overnight, remaining in the upper 50s to mid 60s through much of the area.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
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The cold front continues its eastward movement but it looks like it gets hung up as it moves through the I-95 corridor and starts to slow down considerably. This will keep the precipitation hanging around longer and areas to the south and east of I-95 may see rain through much of the day. Although, precipitation should remain lighter as the best forcing moves away from the region. Areas to the west of I-95 will start to clear out by mid to late morning with the sun peeking through and starting to help dry out the area. Areas that break out on Tuesday will be warmer than those that remain stuck under relatively thick cloud cover. Highs into the low to mid 70s across eastern Pennsylvania and central to northern New Jersey with southern New Jersey and much of Delaware remaining in the upper 60s to near 70. If the front moves further east faster, then temperatures may rise a couple degrees above forecast due to less cloudiness.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
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An extended period of unsettled weather is on tap for the rest of the week, and possibly into the upcoming weekend. Nearly vertically stacked closed low, along with several strong shortwaves, will dive into the Great Lakes and Ohio Valley Tuesday night. Meanwhile, frontal boundary remains stalled along the Mid- Atlantic. With these shortwaves rotating around the low and interacting with the stalled front, several waves of low pressure will develop over the Southeast U.S., and will lift to the north along the East Coast. Where the uncertainty lies is where each low will actually track, and where the axis of rainfall will develop. First swath of rain looks to come up the coast sometime Wednesday afternoon, with the bulk of the rain falling Wednesday night and Thursday. Latest GFS has a swath of rain across central NJ and into E PA, whereas the ECMWF has that swath over southern PA, MD, and VA. These details have yet to be worked out, but with onshore flow ahead of the low, abundant low level moisture will stream into the region, allowing for at least some periods of moderate to locally heavy rain. Another wave of low pressure looks to come up the coast on Friday, but there is less certainty with that track. The closed upper low, meanwhile, does not look to even begin to depart until sometime Saturday night into Sunday morning, and even then, models are not in good agreement as to the timing and placement of it. Therefore, will carry chance PoPs into the weekend. Regardless of where the rain does end up falling, given the onshore flow that will be in place, can at the very least expect cloudy and cool weather through the week with temps running a few degrees below the seasonal averages, with highs ranging from the low to mid 60s across northern zones to the low to mid 70s across southern zones. Latest WPC QPF forecast suggests about 2-5 inches of rain across the region, but that is over the entire period ending on Monday. Given how dry the area has been, this should not result in widespread flooding, and this rain is much needed.
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&& .AVIATION /20Z MONDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of the afternoon...VFR conditions will continue through this afternoon. Ceilings will remain above 3000 ft across the terminals with wind gusts up near 20 knots. Winds will start to subside toward evening. Tonight...VFR conditions at the start of the period with deteriorating conditions as a cold front approaches from the west. MVFR ceilings and visibilities, along with rain, will start to push in with the frontal boundary tonight. Showers are expected to impact KRDG/KABE around 03-04Z, KPHL/KILG/KTTN/KPNE around 04-05Z, and KMIV/KACY around 06-07Z. Periods of IFR conditions are possible. There is a chance for isolated thunder with the front but confidence is too low to include in the TAFS at this time. Tuesday...Behind the front, conditions will start to clear quickly. Ceilings will start to clear out from west to east and winds will become more westerly, especially for areas along I-95 and to the west. Areas to the east of I-95 will continue to have MVFR/IFR conditions through much of the day as the front slows down and takes longer to clear those areas. OUTLOOK... Tuesday night through Saturday...Sub-VFR conditions likely in showers and fog. Best chances for more widespread rain appear to be on Thursday and Friday. Forecast confidence: low.
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&& .MARINE...
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A Small Craft Advisory is in effect for all waters from tonight through Tuesday morning. Southerly winds around 10 to 15 knots will increase as the gradient tightens ahead of an approaching cold front. In addition, seas will start to build and will near 5 feet by late tonight. The cold front will slow down as it nears the coastline and is expected to move offshore Tuesday morning. Winds just ahead of the front will be out of the south to southwest and will quickly turn to the west-northwest behind the front. highest gusts are expected to occur during the morning just ahead of and behind the front, with a quick drop off as the front moves slowly to the east. Seas will remain elevated through the mid morning, and will then subside, falling below 5 feet by late morning. OUTLOOK... Tuesday night through Wednesday...Winds and seas below SCA threshold. Wednesday night through Saturday...E winds 15-20 KT with 25-30 KT gusts possible across northern ocean waters. A period of gale force gusts is possible Wednesday night. Seas may build to 6-8 FT. A SCA will likely be needed for the ocean waters for at least Wednesday and Thursday. Low confidence in forecast thereafter, but SCA may continue to be needed into the start of the weekend. RIP CURRENTS... Even though waveheights will likely be a bit lower today compared to yesterday, increased southerly winds by this afternoon will still likely contribute to a moderate risk for the formation of dangerous rip currents today. This moderate risk may continue into the first part of Tuesday before diminishing toward afternoon as winds and seas subside behind a cold front. RIP CURRENTS... Even though waveheights will likely be a bit lower today compared to yesterday, increased southerly winds by this afternoon will still likely contribute to a moderate risk for the formation of dangerous rip currents today. This moderate risk may continue into the first part of Tuesday before diminishing toward afternoon as winds and seas subside behind a cold front.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 11 AM EDT Tuesday for ANZ430-431- 450>455.
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&& $$ Synopsis...MPS Near Term...Meola Short Term...Meola Long Term...MPS Aviation...Meola/MPS Marine...Meola/MPS

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