Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 180459 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1259 AM EDT Sun Jun 18 2017 .SYNOPSIS...
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A warm front will remain in the vicinity of northern New Jersey tonight, then lift northward on Sunday. Return flow around a strong Bermuda high will result in warm and humid conditions through Monday. A cold front is expected to move through the area Monday night and stall just to our south midweek. A secondary cold front passes through Wednesday night. The boundary may return back northward as a warm front late in the week. Another cold front could approach from the west early next weekend.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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1230 am update: Only remaining showers are occurring generally north of a Jim Thorpe to Morristown line. Updated PoPs to diminish them through the night as they continue to weaken. Removed thunder from the forecast tonight as well, and updated patchy fog in the grids based on latest expected temperature/dew point spreads. There has been a recent uptick in lower visibilities northwest of the Fall Line and in northern/central New Jersey, so may need to include a little bit more emphasis on fog in subsequent updates. Previous discussion... 930 PM ESTF: Updated PoPs for showers and thunderstorms that continue to redevelop in the I-95 urban corridor. These are slowly propagating northwest, and that trend should continue through the overnight, as moisture axis and more unstable air shifts west into the Lehigh Valley and southern Poconos. This activity should then gradually diminish after midnight. Scattered showers and a few tstms will continue across much of the area into the evening. A warm front lifting across the area will cause these showers and there will also be some lingering fog across the coastal areas. Breaks have develop across Delmarva and SE NJ, but overcast conditions continue over the southern Poconos, lehigh Valley and much of nrn NJ attm. Overnight, showers will diminish but more low clouds and some fog will once again be across the region. Lows overnight will remain mild with readings in the upper 60s north and low/mid 70s south/east. It will remain humid overnight.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/... Winds will become more SWrly on Sunday and some drier air will be over the area. We expect some sunshine by late morning and into the afternoon. Then skies will become cloudy again as some daytime showers/sct tstms develop. It will be a warm and humid day with highs reaching the mid/upper 80s in many areas. We will hold pops in the chc range for now, with the highest chcs N/W. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Sunday night through Monday night...An active weather pattern looks to be in store with an upper trough amplifying over the Great Lakes/ Midwest region. The trough may become negatively tilted by the time it progresses through the region Monday night. Deep southerly flow between the downstream Bermuda ridge and upstream cold front will continue to the feed of warm, moist air up the eastern seaboard. Monday afternoon and night contain the highest PoPs (60-80 percent) in the period. Convection is expected to initiate during peak heating Monday afternoon over the higher terrain along a pre-frontal (either just to our west or in our far western zones in E PA). The orientation of the deep-layer shear vectors relative the boundary favors convection growing upscale into multi-cellular line segments or possibly even a more organized line. Models indicate a stronger wind field and deep lift arriving just ahead of the cold front Monday evening, which could enhance the intensity and coverage of storms and sustain convection past sunset. Damaging winds and excessive rainfall/flash flooding will be the primary threats Monday afternoon and evening. The D3 Severe Thunderstorm Outlook from SPC depicts areas west of I-95 in an enhanced risk for while east of I- 95 is in a slight risk. The D3 Excessive Rainfall Outlook from WPC places the entire CWA in a marginal risk. Tuesday through Thursday...Drier air moves into the area in wake of the cold fropa. Isolated showers cannot be ruled out on Tuesday or Wednesday with a series of weak shortwave troughs passing through (especially later on Wednesday when a secondary cold front arrives). However, think most areas should stay dry. There is more uncertainty for Thursday as models disagree on how much lift and shower activity will arrive when a warm front returns northward toward the region. Accordingly, PoPs were capped at 30 percent. Temperatures will be near normal with afternoon highs in the low to mid 80s and nighttime lows in the 60s. Friday and Saturday...The heat and humidity starts to build (but not to excessive levels) after a warm front lifts north of the region. Diurnal showers and storms may develop each day, but the better chances for precip of the two days looks to be Saturday with a cold front possibly approaching from the west. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. For the 06Z TAFs...Spotty/occasional MVFR to IFR conditions are occurring at KABE, KTTN, and KILG with more prevalent IFR at KACY. Conditions will likely deteriorate somewhat at all terminals through the rest of the overnight, but latest guidance has come in a little more optimistic in general. Nevertheless, expect more widespread MVFR/IFR in the 06Z to 13Z time frame. VFR conditions should develop across the region by 15Z with isolated/scattered storms possible this afternoon, especially north/west of KPHL. Coverage is expected to be low, and confidence in timing is too limited for TAF mention anywhere at this point. Winds will pick up from the S or SSW to speeds of 10-15 kts with gusts to 20+ kts this afternoon. OUTLOOK... Sunday night...Highest probability for showers and storms will be during the evening and inland toward RDG/ABE. Brief/localized restrictions to MVFR or IFR possible if the convection directly impacts a terminal. IFR also possible overnight in fog/low clouds, but this may be confined to coastal sites (ACY). Monday...A period of VFR in the morning and early afternoon before showers and storms arrive from the west. Storms are likely to bring at least temporary restrictions to the terminals but despite the high confidence, there is still uncertainty in timing of storms. SWly winds could gust to 25 kt during peak heating. Monday night...Showers and storms continue. Temporary LIFR visibility possible in heavy rain. Tuesday through Thursday...Generally VFR. Low chances for showers each day.
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&& .MARINE... Marine dense fog advisory issued for the northern NJ waters into mid-morning Sunday where areas of dense fog will reduce visibility to 1 NM or less at times. Winds and seas pick up tonight and therefore the SCA issued earlier for the ocean will continue. Seas will slowly increase to around 5 ft. Scattered showers tonight and Sunday afternoon. Slight chc for a tstm. Sunday night and Monday...The SCA was extended into Monday for our coastal zones with S-SW winds gusting to 25 kt and seas 5-6 ft. Monday night and Tuesday...Winds will weaken but seas will likely remain around 5 ft. Thus, a SCA will likely be needed. Tuesday night through Thursday...Winds and seas expected to remain below SCA criteria. RIP CURRENTS... Rip current risk for Sunday is HIGH. We continue to expect a period w/frequent oscillations between a 6-8 second easterly swell and a 15-17 second swell, with the latter containing the majority of the wave energy. Winds and seas will be more elevated compared to Saturday, with low tide occuring during the mid-morning and late evening. The primary wave period is forecast to be 5 to 7 seconds from the south during the period from Sunday though Wednesday. However, the underlying 14 to 18 second southeasterly swell is expected to linger into the mid week period. As a result, the risk for the development of dangerous rip currents is anticipated to be at least moderate through the period along the coasts of Delaware and New Jersey. && .HYDROLOGY... Locally heavier rainfall amounts from the showers that moved through this morning exceeded an inch in a few spots in E PA and NJ. With the same moisture-rich airmass remaining in place through the weekend and into Monday/Monday night, heavy downpours with any showers and storms that develop will could produce locally heavy rainfall. The flooding threat looks to be very localized and predominately limited to poor-drainage areas through Sunday night. The potential for heavy rainfall increases heading into Monday afternoon with the greatest concern falling roughly within a 12-h period from about 18Z Monday - 06Z Tuesday. Models generally indicate widespread rainfall with 24-hr QPF ending 12Z Tuesday between 0.75-1.50 inches while some of the higher-res models like the NAM that go that far out show locally higher amounts of 2-3 inches. However, confidence in QPF amounts is low since convective-allowing models have better skill with convective setups like this but they do not yet run this far out to cover this event. A Flash Flood Watch may be needed as we get closer to the event depending on the antecedent conditions as areas that receive locally heavy rainfall this weekend will have a heightened risk for flooding. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...High Rip Current Risk through this evening for NJZ014-024>026. DE...High Rip Current Risk through this evening for DEZ004. MD...None. MARINE...Small Craft Advisory until 6 PM EDT Monday for ANZ450>455. Dense Fog Advisory until 10 AM EDT this morning for ANZ450. Dense Fog Advisory until 8 AM EDT this morning for ANZ451.
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&& $$ Synopsis...Klein Near Term...CMS/O`Hara Short Term...O`Hara Long Term...Klein Aviation...CMS/Klein/O`Hara Marine...Klein/O`Hara Hydrology...Klein

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