Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 231930 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 330 PM EDT THU JUN 23 2016 .SYNOPSIS...
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A front will remain nearly stationary near Delmarva through Friday, as waves of low pressure move along it. The front will move southward Friday night, as high pressure over New England builds into the region for this weekend. As the high moves offshore Monday, a slow moving cold front will approach from the northwest Tuesday, and move through the region Wednesday.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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High pressure will begin to build in from the north later tonight. Before this happens, scattered showers and perhaps a tstm will affect the area with the waning instability of the day this evening. After the showers diminish, skies will become partly cloudy. Patchy fog will develop with visibilities possibly dropping into the 3-4 sm range in some areas. It will be seasonably cool overnight with lows in the low to mid 60s across the metro areas and the Delmarva and 50s across the Srn Poconos and nrn NJ. Winds will be mostly light from the N or NE.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
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The high will continue to build in Friday. A E to NE surface winds may bring some low level moisture off the ocean, so there may be extra cloudiness across the area during the morning. The op models and mos indicate some low chc pops for showers across the region. It appears that the better chc will be across the Delmarva, away from the onshore flow. I have therefore mentioned some chc pops for those areas during the late morning and afternoon.
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&& .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
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A mid-level ridge will build over the middle Atlantic this weekend, giving way to cyclonic flow aloft early next week, as the trough is reestablished over the northeast conus. After a pleasant weekend, there will be a renewed chance of showers and thunderstorms in the Monday thru Wednesday time frame. Temperatures are expected to be at or slightly above normal through the period, with uncomfortable humidity levels anticipated by Tuesday. Friday night thru Sunday...Dry. Clouds Saturday morning, particularly over Delmarva, will move offshore for a mostly sunny day. The column will dry out rapidly, given confluence aloft, as the mid-level flow goes anticyclonic with the region within the right front quadrant of the upper jet. In fact, it will be a struggle to reach convective temperatures on Saturday and Sunday, so cumulus should be limited. With the dry air mass in place and clear skies, went below guidance on low temperatures Sunday morning, especially at the typically good radiators. The surface flow will generally be out of the east this weekend, which may advect some slightly higher dew points well inland by Sunday morning, with the setup favorable for patchy ground fog. On Monday, the surface high moves southeast, as a lee trough is established in advance of a cold front over the Great Lakes. This will favor a southerly flow, with time sections indicating a rapid increase in low level moisture during the day. The flow aloft also becomes diffluent, with weak shortwaves traversing the mid Atlantic, as the southern edge of the westerlies approach the region. This will favor a chance of diurnally driven showers and thunderstorms, particularly northwest of I-95 in the evening, closer to the lee trough and instability axis. There will be a renewed chance of showers and thunderstorms on Tuesday, as a cold front moves into the region. There is general model agreement that this front will become stationary across our region on Tuesday as the mid-level trough approaches, and the tropospheric flow veers, becoming increasingly parallel to the front. As the right rear quadrant of the upper level jet approaches, Bulk Shear will increase. However, there is uncertainty on the placement of the front, and thus the instability axis. In fact, the more favorable shear and instability may be dislocated. Thus, there is still a lot of uncertainty with regard to how organized and robust the convection will be. The front is forecast to move offshore by Wednesday, as the mid- level trough axis crosses the region, turning the large scale flow westerly. There is disagreement in the 12Z/23 model suite with regard to the timing of the front exiting the coast. For now, we have maintained a slight chance of thundershowers on Wednesday, in continuity with the previous forecast. Fair weather is expected to return for Thursday.
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&& .AVIATION /19Z THURSDAY THROUGH TUESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. Scattered showers and perhaps a tstm are developing across Berks county and the Lehigh valley as of the mid afternoon and these should sweep e-se through the early evening. These could affect some of the delaware Valley terminals shortly, but the confid in this is low and the areas coverage should be low as well. We have opted to VCSH a few of them with the 18z issuance. Amds expected. Winds will be shifting more wrly then nwrly through the early evening. Tonight...showers diminish and winds become light. Patchy fog expected and this is included in the tafs. Fri...An erly or nerly flow may bring some lower clouds across the area during the morning. Probably will remain VFR, but somewhat uncertain. Outlook... Friday night...There is the potential for MVFR in low clouds and SHRA at ACY and MIV, otherwise, VFR at the remainder of the TAF sites. Saturday and Sunday...Predominantly VFR. Patchy ground fog may lead to sub-VFR conditions late Saturday night and early Sunday morning, mainly at ABE, MIV, and RDG. Monday and Monday night...Predominately VFR. MVFR possible in isolated SHRA/TSRA northwest of ACY and MIV, mainly Monday evening. Tuesday...More widespread SHRA/TSRA across the TAF sites may lead to MVFR at times. Otherwise, predominantly VFR.
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&& .MARINE...
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Except for some scattered showers and perhaps a tstm on the waters this evening, the weather on the waters will be rather uneventful thru Friday. Winds tonight should remain mostly around 10 knots or less and seas (ocean) mostly 2 to 3 ft tonight. Friday will become NE to E and increase to more like 10 to 15 knots and seas will increase a bit to 3 to 4 ft. Outlook... A persistent onshore flow will be established in the Friday night thru Sunday period. This will peak Friday night into Saturday, particularly the southern NJ and DE coastal waters. The guidance has trended upwards over the past 24 hours in terms of winds, but is still sub-SCA. Nevertheless, northeast winds may briefly reach SCA criteria late Saturday morning into Saturday afternoon, as 3-hourly pressure rises maximize, particularly over the southern NJ and DE coastal waters. Confidence is not high enough for a SCA at this point in the forecast, but this potential will need to be reevaluated. Otherwise, with the persistent onshore flow, seas will build to the 3-4FT range. Looking ahead to the Sunday night thru Tuesday period, winds are anticipated to remain below SCA criteria attm. RIP CURRENTS: Based on the expected wind, wave and swell conditions we are anticipating a moderate risk for the development of dangerous rip currents for Saturday along the New Jersey shore and at the Delaware Beaches.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Franck Near Term...O`Hara Short Term...O`Hara Long Term...Franck Aviation...Franck/O`Hara Marine...Franck/O`Hara

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