Area Forecast Discussion
Issued by NWS Wakefield, VA

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606 FXUS61 KAKQ 251125 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 725 AM EDT Tue Apr 25 2017 .SYNOPSIS... Low pressure tracks across the North Carolina coastal plain today...then continues northeast along the Mid Atlantic coast tonight and Wednesday. High pressure builds into the area Thursday. A cold front stalls north of the region on Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Latest GOES water vapor imagery depicts compact/deep upper low over South Carolina. Associated surface low is centered over southeast North Carolina with a coastal boundary extending northeastward into northeast North Carolina. Latest radar depicts a band of heavy rainfall associated with theta-e advection and marginal instability just south of the local area, spreading into central North Carolina. As the best moisture flux and theta-e advection spreads northward ahead of the advancing surface low, expect widespread showers to spread into southeast Virginia between 4 and 6 am. Increasing low level winds will also result in a ramp up of east winds, with gusts of 30 to 40 mph (45 mph along the coast) early this morning. Latest hi-res guidance indicates the heaviest precipitation south of the region will begin to wane (decreasing rainfall rates) as the air mass is slightly drier and more stable over the forecast area. However, warm air advection and favorable dynamics will still result in moderate to locally heavy rainfall as the band lifts northward over the region through the morning hours. Categorical POPs have been maintained this morning. Band of deepest moisture and strongest moisture flux pushes north of the forecast area late morning/early afternoon as the surface low lifts into the southeast portion of the local area. Energy wrapping around the upper low and cold air advection aloft will keep scattered to numerous showers in the forecast through the afternoon across much of the region. Theta-e advection and temperatures warming into the 70`s across the far southeast local area will maintain at least some marginal instability. Given the steepening lapse rates and marginal instability, have kept mention of thunder across the southeast. Main threat would be locally heavy rainfall. Additional rainfall amounts expected to range from around one half inch over the Piedmont to around 1 inch along the coast. Minor/nuisance flooding is possible given the rainfall of late, but based on latest 3 hour flash flood guidance and anticipated rainfall, no headlines needed. Easterly winds subside this morning first across the south, and then northward through early afternoon. Wind advisories remain in place along the immediate coast. Surface winds become north to northeast inland this afternoon, diminishing to 5-15 mph. Cloudy conditions will prevail (again!) for the day with a large temperature gradient from the Piedmont to the coast. Highs generally in the upper 50`s/low 60`s inland to the low to mid 70`s across southeast Virginia and northeast North Carolina. && .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/... Upper/surface low pressure lifts along the Mid-Atlantic coast this evening, and then north of the local waters late tonight. Wrap around moisture keeps chance to likely POPs across the northeast local area through late tonight. Given the recent rainfall and saturated soils, have included patchy fog across much of the region. However, cloud cover and light winds will limit the overall coverage. Lows tonight generally in the mid to upper 50`s. Low pressure lifts along the Northeast coast Wednesday as an upper level ridge builds over the region. Thermal soundings indicate mid level moisture trapped beneath a strong subsidence inversion aloft, which will help keep clouds around through the day. However, given the late April sun, anticipate several breaks in the clouds inland. Soundings also indicate very little mixing, but given height rises and warming low level temps/thicknesses, forecast highs are generally in the mid to upper 70`s. Cooler along the coast. Mild Wednesday night under a partly clear to mostly clear sky. Lows forecast in the upper 50`s to low 60`s. Ridge axis slides offshore ahead of an approaching cold front Thursday. Increasing return flow and 850mb temps around +14 to +16C (around +1 standard deviation) result in warm (and dry) conditions with highs generally in the 80`s. Cooler along the coast. Plenty of sunshine expected. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Long term period will feature above normal temps with mainly dry wx. For Thu night/Fri, deep SWly flow continues across the eastern seaboard as an upper-level ridge then builds in through the weekend allowing for warm temps and dry wx as most of the energy aloft will stay N and W of the local area. At most a 20% chance of a late day shra/tstm Fri and Sat. High temps Fri through Sun in the 80s, pushing near 90 Sat and Sun. Low temps in the mid/upr 60s. && .AVIATION /11Z TUESDAY THROUGH SATURDAY/...
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Widespread IFR conditions observed over the region this morning as low pressure lifts over eastern North Carolina. Ongoing showers over the region this morning lifts north of the region by late morning/early afternoon as the upper level low lifts along the Southeast coast. IFR visibilities are expected under the heaviest showers. Areal coverage of the precipitation decreases across the region mid to late morning, but still expect light rain/drizzle and IFR conditions to persist. Additional scattered to numerous showers expected across the region this afternoon as the upper low lifts over the region. A thunderstorm is possible across the southeast. Easterly winds gust to 25 to 35 knots this morning, diminishing at or below 10-15 knots this afternoon as the surface low lifts over the region. Outlook: Precipitation lifts northeast of the region overnight, but IFR conditions expected to persist through late tonight. Conditions begin to slowly improve late tonight into Wednesday as the system moves farther north. Dry weather is in store for Thursday and Friday as high pressure builds over the southeast states.
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&& .MARINE... Current analysis indicating sfc low pressure centered just S/SW of Cape Hatteras, with E/NE flow ongoing across the local marine area. Thus far, winds have been at SCA levels but have remained below Gale criteria. Pressure falls have not been that significant and therefore will be relying on mixing the stronger winds aloft to the surface. High res models depict a short period with Gale force gusts possible for the lower Bay and southern coastal waters through mid morning, with higher winds lingering across the northern coastal waters into early aftn. Overall, this event looks marginal but will maintain continuity and keep the Gale Warning in effect through 10 am S to 1 pm N. SCA headlines remain in effect for the upper James/York/Rappahannock Rivers where gusts up to 30 kt are expected. Seas up to 8-12 ft, with a high surf advisory remaining in effect for 8-9 ft waves in the surf zone. No cold air surge in the wake of this system later today and tonight, so aside from high seas lingering for the coastal waters/mouth of Bay, expect rapidly improving conditions later today and tonight. Seas should fall off to below 5 ft later Wed/Wed night. Winds begin to shift to the S Thu/Fri w/ sub-SCA conditions to prevail. && .TIDES/COASTAL FLOODING... Current tidal departures are averaging around 1.5 to 1.75 feet in the lower Bay and southern coastal waters due to ongoing onshore flow, while departures farther N are genly 1 ft or less. Have raised coastal flood advisories for zones adjacent to the lower Bay/James/York River, as well as the VA eastern shore. This will be for the upcoming high tide later this morning. More uncertainty exists farther N in the Bay up the coast and have continued with another round of statements for these areas for now. Surprisingly, despite continued onshore flow, currents data from Cape Henry Channel shows that water has been exiting the Bay at the same rate that it has been coming in/ i.e. piling of water into the Bay has been fairly minimal so far. ESTOFS and CBOFS data suggest this will change later today through tonight with the potential for water to become trapped in the Bay and for eventual minor flooding for the mid/upper Bay by tonight. May need to raise a coastal flood advisory later today for some of these locations, but did not do this yet because of how the winds associated with this system have genly underperformed so far. && .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...High Surf Advisory until 6 PM EDT this evening for MDZ025. Wind Advisory until 1 PM EDT this afternoon for MDZ025. NC...High Surf Advisory until 1 PM EDT this afternoon for NCZ102. VA...Coastal Flood Advisory until 2 PM EDT this afternoon for VAZ089-093-523>525. Coastal Flood Advisory until 11 AM EDT this morning for VAZ095>097-099-100. High Surf Advisory until 1 PM EDT this afternoon for VAZ098. High Surf Advisory until 6 PM EDT this evening for VAZ099-100. Wind Advisory until 1 PM EDT this afternoon for VAZ099-100. MARINE...Gale Warning until 1 PM EDT this afternoon for ANZ630>632-634- 654-656-658. Gale Warning until 4 PM EDT this afternoon for ANZ650-652. Small Craft Advisory until 4 PM EDT this afternoon for ANZ635>637. Gale Warning until 10 AM EDT this morning for ANZ633-638.
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&& $$ SYNOPSIS...MPR/SAM NEAR TERM...SAM SHORT TERM...SAM LONG TERM...MAS AVIATION...SAM/JEF MARINE...LKB/MAS TIDES/COASTAL FLOODING...

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