Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 211933 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 333 PM EDT SAT MAY 21 2016 .SYNOPSIS...
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Low pressure off the Virginia coast will lift northeast of our region through the day Sunday. However, a second offshore low is expected to develop by Monday, before lifting away from the region on Tuesday. A ridge will build over our region mid week. By Friday, the ridge is expected to shift east as another low begins to slide over the Great Plains.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Surface low pressure will continue to move northeastward and out to sea tonight. However, a upper low level pressure system to our northwest will continue to be a focal mechanism for some scattered light showers across the region tonight with a decrease overnight in coverage. The more concentrated showers along the shore will move offshore early this evening. With cloudy skies, temperatures will be slow to fall tonight falling into the upper 40`s and low 50`s. Fairly good model agreement with the forecast for tonight.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
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The upper level low pressure system that will be to our northwest will drop southward on Sunday. The 12z GFS/CMC/UKMET are a bit further west than the 12Z ECMWF with this feature. With this forecast package, we opted to go with a slightly more west track of the low. This could potentially keep the highest coverage of showers across Eastern Pennsylvania throughout the day. The areal coverage of showers looks to be of a diurnal nature as low level lapse rates steepen (instability mechanism) to increase the coverage by the afternoon. Rainfall amounts are going to be light but a continued low freezing level around 10,000 feet may result in a few showers containing pea size hail in the afternoon hours. Coverage of hail looks to low to place in forecast attm. The track of the low will also effect the high temperatures. A further east and cloudier ECMWF keeps highs down in the low and mid 60`s for most. On the other hand, A further west low track would allow for breaks of sunshine and a chance at 70 degrees for Delaware and New Jersey.
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&& .LONG TERM /SUNDAY THROUGH SATURDAY/...
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Monday through Tuesday...As the upper level short wave trough digs and intensifies over the Mid Atlantic, a surface low will subsequently develop off the coast of VA/NC. As a result, expect the work week to begin with much of the same weather pattern we`re seeing this weekend. Northeasterly flow will temper max temperatures a bit, staying slightly below normal. However, thanks to air mass modification, we should see a modest warming trend into Tuesday and highs may be near normals. The moisture advection, thanks to persistent onshore flow, and synoptic scale lift thanks to the upper level low will result in continued rain chances. How quickly we dry out will be dependent on how quickly the low lifts out of the region. On this point, there are some slight differences between the models with the GFS being a bit slower to clear everything out. Would expect the bulk of the precipitation to be done by mid day Tuesday as the flow turns more northwesterly, but a few showers could linger into Tuesday evening. Wednesday and Thursday...Upper level ridge shifts east, with the ridge axis over our region by Thursday morning, bringing a lull in rain chances and a very noticeable warming trend, with 80s expected across much of the region both days. Friday and Saturday...ridge shifts further east offshore through this time, leaving our region on the periphery of the ridge. As such, could see primarily afternoon and evening showers and thunderstorms as shortwave troughs embedded in the upper level SW flow slide over the region.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight: Mainly VFR through early evening, some MVFR possible from KPHL and southeast with the steadiest showers through early evening. Ceilings will gradually lower by late evening likely becoming IFR for the overnight hours. Some MVFR VSBY restrictions will also occur throughout the night as well. Winds will be easterly- northeasterly around 10 knots. Sunday: Ceilings will start off IFR/MVFR in the pre-dawn hours and gradually lift to VFR by the afternoon. Chance for some brief scattered showers to impact TAF site, to low of a chance for TAF inclusion attm. Northerly winds around 10 knots. Outlook... Monday and Tuesday...Occasional MVFR conditions possible with showers and fog especially Monday night. Wednesday and Thursday...VFR conditions likely. Small chance of MVFR conditions with showers and thunderstorms Thursday afternoon and evening.
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&& .MARINE...
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SCA starting at 4 pm this afternoon. Easterly winds have increased but are still only around 20 knots on the bay attm. A window still looks present for some easterly wind gusts near 25 knots by evening both on the ocean and in Delaware Bay. Seas will be slow to rise and should get above five feet tonight on the ocean. Sunday: Winds will be more northerly and lighter. However wave heights will still run from five to eight feet. SCA in effect. RIP CURRENTS...Moderate risk for rip currents today as well with the onshore flow and increasing easterly winds. A cool, raw day to be out at the beach. Rip current forecast will be updated this evening for Sunday. Outlook... Sunday night into Monday...Seas are expected through this period and could be at or above 5 feet as early as Monday morning (especially on the southern coastal waters). Monday night...SCA conditions are likely on the coastal waters, primarily for seas above 5 feet, though gusts near or above 20 kt are possible. Tuesday...seas should slowly subside, though SCA conditions may linger through much of the day. Tuesday night through Thursday...winds and seas should stay below SCA criteria.
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&& .TIDES/COASTAL FLOODING...
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With the full moon today (Saturday), and on shore flow developing later today and persisting through at least Sunday morning, tide levels should be higher than normal on the Atlantic oceanfront and the Delaware Bay. However, we expect water levels to fall short of minor flooding thresholds at this point. The highest water levels are expected with the high tide cycles on Sunday and Monday evening.
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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 6 PM EDT Monday for ANZ452>455. Small Craft Advisory until 6 AM EDT Monday for ANZ450-451. Small Craft Advisory until 10 PM EDT this evening for ANZ430- 431.
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&& $$ Synopsis...Johnson Near Term...Gaines Short Term...Gaines Long Term...Johnson Aviation...Gaines/Johnson Marine...Gaines/Johnson Tides/Coastal Flooding...Johnson

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