Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 212009 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 409 PM EDT Wed Jun 21 2017 .SYNOPSIS... A frontal boundary dissipates over the local area today as an upper level disturbance passes just north of the region. Bermuda High begins to shift back towards the Eastern Seaboard this afternoon through Thursday. The high becomes centered off the Southeast Coast Friday and Saturday as low pressure moves through eastern Canada. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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Latest analysis reveals diffuse cold front stretched from eastern New England to the Mason-Dixon line and back west into the middle Missouri Valley. Offshore, Bermuda high continues to slowly build toward the coast from this afternoon through tonight. Aloft, mid-level trough axis continues to edge east this morning, and will push offshore late this afternoon. Disturbances just ahead of this feature which allowed for sct/numerous showers across the E-SE portions of the area have largely pushed offshore by late morning. Drier air aloft will push in from the west (and also in subsidence behind the trough), quickly diminishing rain chances for the afternoon. Given light flow and plenty of low-level moisture, have retained a slight to low end chance pop across the coast through this evening. Dried things out tonight for the most part, with the exception being over the Northern Neck and Eastern Shore, where CAMs continue to depict some light shower activity in association with another very subtle shortwave pushing across. Kept 20-30% POP in for Iso to Sct showers over the NE corner of the CWA. Otherwise, partly to mostly clear with some patchy fog late, mainly away from the coast. Lows in the 60s to low 70s at the coast.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
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TS Cindy makes landfall near the TX/LA Gulf Coast late tonight into Thursday. An interesting weather pattern sets up as strong high pressure over the Desert SW creates an omega block with the Bermuda High in the east...effectively "trapping" TS Cindy in the middle. Thursday will be a dry day across the local area, courtesy of sfc ridge in place over the Mid-Atlantic coast. Incrementally warmer/more humid Thu with highs in the u80s to low 90s over inland sections...mid to upper 80s along the coast. However, a constant stream of subtropical moisture from the Gulf and Atlantic should arrive late Thursday night as showers and steadily march across the region into Friday night. Early morning lows mainly in the lower to middle 70s. Remnants of Cindy will be lifting NE across the west-central Gulf Coast toward the Mid-south by early Friday morning, with a couple of mid-level shortwaves out ahead of the storm pushing in our direction through the day on Friday. Meanwhile, a deepening midlevel trough will push a developing cold front toward the area Friday night into Saturday. Models agree that PW values trend above 2" for Friday. The also agree that the axis of heaviest rainfall will occur in two areas; first along a sharpening deformation axis, and the second with the core of the remnants. However, typical timing differences persist with these features, which prevent pops from going beyond high end chance to low end likely range at this time range. Overall, we`re keying in on a couple of time frames regarding the potential for heavy rainfall on Friday. First during the early to mid-morning hours, with quick slug of moisture as theta-e ridge builds east across the area. Then, after a bit of a lull, models indicate a period of some short-lived clearing by midday Friday. Should this clearing occur, resultant instability would likely quickly lead to additional convective development for the afternoon and evening on Friday, given favorable deep layer shear (35-45kt 0-6km) and nose of LLJ . SPC has placed the local area in a marginal risk area with this conditional instability in mind, with damaging winds the primary on hazard, along with the potential for some locally heavy rainfall. Given potential for high rain rates in the tropical airmass, rain could accumulate quickly. While certainly too early in the process for any headlines right now, will have to continue to monitor this potential over the next day or so. Will note heavy rain potential in HWO. Good model agreement with the eventual track of the remnants of Cindy. 12z suite of the GFS and ECMWF have trended a bit faster and farther N with the core remnants of Cindy. Expect a narrow axis of heavy rainfall Overall, Saturday appears the more stable/cloudy day, with periods of rain, occurring heavily at times Saturday morning into the afternoon. Have therefore continued POP upward into high end chance range for Saturday, ending from SW to NE saturday afternoon. Partly to mostly cloudy, warm and humid Saturday with highs mainly in the 80s, to near 90 SE zones.
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&& .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
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Cold front stalls along the Southeast coast Saturday night into Sunday as an upper level trough deepens over the Great Lakes region into the Ohio Valley. Deepest moisture pushes south of the local area Saturday night, but have kept low end chance POPs across the far southeast forecast area. Frontal boundary expected to remain in the vicinity of northeast North Carolina Sunday due to southwest flow aloft. Isolated to scattered diurnally driven showers and thunderstorms are possible across the southeast Sunday afternoon, nearest the boundary and better instability, but expect much of the forecast area to remain dry Sunday. Highs generally in the mid 80`s. Thereafter, medium range guidance drops a stronger cold front Monday/Monday night as additional energy dives down the back side of the upper trough. Guidance indicates the moisture and instability will be limited ahead of the front, but given the dynamics, have kept chance POPs Monday afternoon. Cooler Monday, with highs ranging from the low to mid 80`s. Trough axis swings across the region Tuesday as the front pushes offshore. Drying conditions expected Tuesday, but have kept slight chance to low end chance POPs across the far southeast given model uncertainty with respect to the front. Highs generally around 80 Tuesday as 850mb temperatures level off at 10-12C (-1 standard deviation). Inland locations (and along the immediate coast) could only warm into the upper 70`s. Dewpoints mix into the 50`s, resulting in pleasant afternoon conditions. Dry conditions forecast Wednesday as the trough pushes offshore and heights build over the Ohio Valley. Surface high pressure settles over the Mid-Atlantic. Highs Wednesday generally in the low 80`s.
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&& .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... VFR conditions across area terminals this afternoon. Some Sct CU noted mainly W-NW of a FVX to RIC to SBY line, which should persist this afternoon. Isolated showers will be possible along and mainly north of the SBY terminal late this afternoon through early evening. However, given low areal coverage and only minimal instability, mention has been held out for now and will continue to monitor. Mainly clearing sky tonight, with patchy fog late tonight. Winds will be too strong near the coast for fog formation. However, some sct low stratus will be possible after 09z tonight. Any lingering fog will dissipate by roughly 22/13-14Z Thursday with dry weather and VFR conditions anticipated. Outlook: Subtropical moisture moves into the region later Thursday through the upcoming weekend, with the remnants of Cindy pushing NE along and ahead of a developing cold front. Showers and thunderstorms with periods of moderate to heavy rainfall will be common Friday through Saturday. MVFR conditions are likely with short-lived IFR during this time in these areas of periodic moderate/heavy rainfall. Predominate VFR conditions return by Sunday, as surface high pressure builds across the region. && .MARINE...
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Latest surface analysis centers high pressure off the Southeast coast with a frontal boundary expected from the Ohio Valley into the northern Mid-Atlantic region. A southwest wind of 10-15 knots is observed over the waters this afternoon with waves of 1-2 feet and seas 2-3 feet. The frontal boundary remains north of the waters through tonight, before lifting northeast Thursday. A southwest wind of 10-15 knots prevails. Seas 2-4 feet and waves 1-2 feet. Bermuda high pressure remains in place Thursday night and Friday as a cold front tracks into the Great Lakes region. The pressure gradient strengthens over the local waters late Thursday night through Friday night with marginal SCA conditions possible. Southwest winds increase to 15-20 knots, primarily for the Bay and coastal waters. Seas build to 3-4 feet (upwards of 5 feet north north of of Parramore Island out 20 nm). Waves 2-3 feet. The front reaches the local area Friday night, pushing across the water Saturday before stalling along the Southeast coast Saturday night. A stronger cold front pushes across the waters Monday night with high pressure building over the waters through the middle of next week.
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&& .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...None. && $$ SYNOPSIS...MAM NEAR TERM...BMD/MAM SHORT TERM...ALB/BMD LONG TERM...ESS AVIATION...MAM MARINE...AJZ

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