Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 220427 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1227 AM EDT SUN MAY 22 2016 .SYNOPSIS...
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Low pressure well off the Delaware coast will track farther out to sea 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 AM THIS MORNING/...
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Surface low pressure located well off the Delaware coast will continue to move northeastward overnight. Meanwhile, an upper- level trough remains to our west. A more pronounced short wave sliding across Pennsylvania appears to be responsible in producing more widespread lift and therefore an uptick in the rain occurred earlier. This activity is now gradually weakening and shifting north and east. The pops were adjusted upward longer to better capture ongoing radar trends. A downward trend in the pops was then maintained toward daybreak as the overall lift should weaken. The hourly temperature and dew point grids were adjusted based on the latest obs, then the lamp/lav guidance was blended in. The gusty winds mainly along portions of the coast are expected to gradually diminish as the pressure gradient slowly weakens.
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&& .SHORT TERM /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 NIGHT 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 /04Z SUNDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Overnight: Conditions vary from VFR across the north at ABE and RDG, to IFR at ILG/MIV/PHL, and MVFR at ACY/PNE/TTN. We expect IFR conditions to develop for all sites through the overnight, except for ABE/RDG where we expect MVFR conditions to develop. Some rain will continue. Generally northeast to north winds 5-10 knots, with some gusts 15-20 knots possible from PHL south and eastward. Sunday: Ceilings will start off IFR/MVFR in the morning, and begin lifting from north to south, and may eventually lift to VFR by the afternoon. Scattered showers could continue occur through the day. North to northeast winds will start the day, becoming northwest for ILG/PHL and points westward. Winds are expected to become southeast for TTN and points south and east. 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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The Small Craft Advisory for Delaware Bay has been cancelled as the winds continue to gradually diminish. The Small Craft Advisory will continue for the Atlantic coastal waters with no change with building seas expected and gusts 25-30 knots, especially across the southern half of the waters. 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 is expected for Sunday. Northeast winds will be lighter than Saturday, but a higher swell height will likely lead to moderate risk for the formation of dangerous rip currents. 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 Saturday and an onshore flow 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.
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&& $$ Synopsis...Johnson Near Term...Gorse Short Term...Gaines Long Term...Johnson Aviation...Gaines/Johnson/Robertson Marine...Gaines/Gorse/Johnson/Robertson Tides/Coastal Flooding...

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