Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 191445 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1045 AM EDT Sun Mar 19 2017 .SYNOPSIS... Low pressure will strengthen as it tracks to the southeast of Cape Cod during today, then high pressure builds in tonight and Monday. A weak cold front moves through the area Monday night and stalls to our south, then low pressure tracks along it to our south while a stronger cold front arrives Tuesday night. Strong high pressure builds in from the northwest Wednesday before shifting off the Mid Atlantic coast Thursday night. A warm front will move into our region later Friday into Saturday as low pressure tracks toward the Great Lakes region. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A mid level low is forecast to sink southward across eastern Virginia before passing off the coast this afternoon. Meanwhile, A surface low pressure OUT AHEAD OF THE UPPER LOW iS on its way farther out to sea. One last bit of lingering showers can be found across Coastal Cape May county NJ and Sussex county DE. These showers should diminish over the next few hours as drier air arrives behind the departing low. Clearing has begun across the north and will push southward this afternoon. A northeast wind around 10 to 15 MPH with gusts near 20 MPH is forecast to back to the north and northwest today. Maximum temperatures are expected to range from the middle and upper 30s in the Poconos to the upper 40s in much of northeastern Maryland and Delaware.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... Surface high pressure is forecast to build into our region from the west for tonight. We are expecting a mostly clear sky along with a diminishing northwest wind. Low temperatures are anticipated to favor the 20s in eastern Pennsylvania and New Jersey, and the lower 30s on the upper Delmarva. && .LONG TERM /MONDAY THROUGH SATURDAY/... Synoptic Setup and Summary...A closed low will continue to shift away from the East Coast Monday as some ridging builds in from the west. An upper- level trough then amplifies from central to eastern Canada Monday through Tuesday with this also extending across the Northeast through Wednesday. This will sent a couple of cold fronts through our area, with the second one being stronger. Some energy within the flow looks to develop a wave of low pressure on the initial front as it stalls west-east to our south Monday night and Tuesday. A round of precipitation looks to slide across our southern areas Tuesday night, with perhaps some enhancement as the secondary cold front catches up. A shift in the pattern may then allow stronger ridging in the East Friday as a trough amplifies across the Plains and Midwest. The pattern will offer some warming, but also some shots of colder air. A more pronounced warm-up should occur Saturday as the warm sector of low pressure advancing toward the Great Lakes should expand northeastward. We used a model/continuity blend for Monday through Tuesday night, then blended in the 00z WPC Guidance thereafter. Some adjustments were then made following additional collaboration with our neighboring offices. For Monday and Tuesday...A closed low will continue to move farther offshore Monday giving way to some ridging into the East Coast. This will allow some warming ahead of a weak cold front. This front is being pushed by a trough that is amplifying from central to eastern Canada, although much of the forcing looks to be focused farther to the north and west. A band of showers should be with the front to our west, although these may begin to weaken as they arrive into our area Monday night. The front becomes stalled in an east-west fashion Tuesday just to our south. As some energy tracks along a tightening thermal gradient along this front, an area of precipitation looks to develop eastward along with surface low pressure. This feature looks to track to our south Tuesday night and early Wednesday, however the overrunning on the north side of the thermal boundary may extend into portions of our southern zones for a time. A secondary cold front will be arriving from the northwest, with colder air in its wake. Cold high pressure will be building southeastward from the Great Lakes, however it may be delayed until after this surface wave along the front shifts offshore. Therefore, precipitation type is more uncertain at this time however we will continue to indicate some snow or rain/snow mix overnight Tuesday. PoPs were increased some a bit northward for a time Tuesday night. For Wednesday and Thursday...Low pressure is forecast to quickly shift offshore early Wednesday allowing for clearing. A developing trough into the Plains results in downstream ridging. This will drive strong surface high pressure from the Midwest and Great Lakes regions Wednesday to right over our area Thursday. This will result in a brisk northerly flow Wednesday then less wind on Thursday. The high will be shifting offshore Thursday night setting the stage for a return flow to occur in advance of the next system. A colder airmass will in place once again for both of these days. For Friday and Saturday....A potentially strong trough in the Plains to the Great Lakes will shift eastward. This will drive surface low pressure from the Central Plains Friday to near the central Great Lakes and upper Ohio Valley Saturday. There are some mixed signals with how quick the associated warm front lifts northward and if it clears our region. A lower amplitude system would offer the warm front getting hung up over our area as low pressure moves more east instead of north=northeast, and therefore cooler air along with more precipitation. Given the uncertainty with the details this far out, we went with an even blend of continuity and the 00z WPC Guidance. There should be some warm advection showers or a period of rain preceding the warm front and therefore some PoPs were maintained especially starting later Friday. If any precipitation moves in faster Friday before temperatures can warm, some snow or mixed precipitation is possible across portions of the northern zones. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Another hour of MVFR at KACY and KMIV before VFR conditions return for the afternoon. VFR conditions are anticipated from this afternoon into tonight. Scattered clouds are expected for this afternoon with a clear sky for tonight. A northerly wind is forecast to range mainly from 10 to 15 knots with gusts around 20 knots today. The wind is expected to be northwest at 5 to 10 knots for tonight. OUTLOOK... Monday..VFR. Northwest winds 10 knots or less. Monday night...A period of MVFR conditions possible with showers as a weak cold front moves trough. Tuesday and Wednesday...A low pressure system tracks to our south Tuesday night and early Wednesday and should produce a period of mostly rain mainly south of PHL with MVFR/IFR conditions. Otherwise, VFR. Northerly winds Wednesday may gust to 25 knots. Thursday...VFR with light winds as high pressure is over the area.
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&& .MARINE... We will continue the marginal Gale Warning until 2:00 PM this afternoon for our ocean waters and for Delaware Bay as low pressure moves slowly away from the coast. We will keep the Small Craft Advisory for the upper part of Delaware Bay in effect for the same time period. The wind is forecast to diminish gradually during the afternoon and nighttime hours with Small Craft Advisory conditions expected on our ocean waters during that period. Wave heights on our ocean waters should favor the 6 to 9 foot range today, and the 5 to 7 foot range for tonight. Waves on Delaware Bay are expected to be 2 to 5 feet today and 1 to 4 feet tonight. OUTLOOK... Monday and Tuesday...The conditions are expected to be dropping below Small Craft Advisory criteria Monday, and then remaining below for Tuesday. Wednesday...Northwest winds increase along with colder air arriving. This should result in wind gusts to around 25 knots, then these conditions diminish at night as high pressure starts to arrive from the west. Thursday...The conditions are anticipated to be below Small Craft Advisory criteria as high pressure is over the region. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Gale Warning until 2 PM EDT this afternoon for ANZ431-450>455. Small Craft Advisory until 2 PM EDT this afternoon for ANZ430. && $$ Synopsis...Gorse Near Term...Iovino/PO Short Term...Iovino Long Term...Gorse Aviation...Gorse/Iovino/PO Marine...Gorse/Iovino

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