Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 281807 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 207 PM EDT Wed Sep 28 2016 .SYNOPSIS... Low pressure tracks north across the North Carolina and Virginia piedmont this afternoon and tonight. An upper level low slowly drops south from the Great Lakes region resulting in unsettled weather conditions into the weekend. && .NEAR TERM /THROUGH TONIGHT/... Latest GOES water vapor imagery centers a deep/anomalous upper low over the western Great Lakes region with a plume of high water vapor lifting into the Mid-Atlantic region. At the surface, a weak quasi-stationary boundary has located over the forecast area. Scattered showers over the Nrn Neck/Lwr MD Ern Shore will continue to lift ne along the boundary late this morning. The upper low drops swd today, centering over IN late today. The associated surface low drops over the Ohio Valley. Diffluent flow over the local area and increasing winds aloft will provide strong forcing for ascent along the stalled frontal boundary. Deep layer southwesterly flow will advect anomalous pw values into the region. Scattered to numerous showers expected to develop by mid- afternoon as the better forcing arrives, and persists through the day and into the overnight period. Continued with high end likely and categorical PoPs from mid-aftn through the overnight period. Theta-e advection and dewpoints in the upper 60s will result in increasing instability. Instability will be dependent on how much (partial) clearing occurs as current vis imagery depicts some breaks in the cloud cover. Given this, there is the potential for an axis of 1200-1800 J/kg of 0-1km MLCAPE centered over the VA piedmont by this aftn. Deep layer shear is progged on the order of 30-40 knots. Meanwhile, there will be some low-level turning in vicinity of the lingering sfc boundary. In summary, this will result in a slight risk for severe tstms this aftn/early evening from the I-95 corridor westward into the piedmont, with the main threats being strong wind gusts and iso tornadoes. Highs range from the mid 70`s northwest to low 80`s southeast. The upper low slowly drifts southward tonight as another area of surface low pressure approaches from the northwest. Height falls over the region progged to develop a wave of low pressure along the frontal boundary tonight, with an area of strong isentropic lift across the Piedmont to the Maryland Eastern Shore. The result will be ongoing categorical POP`s and the potential for moderate to locally heavy rainfall. Lows forecast in the mid to upper 60`s under a cloudy sky. Rainfall totals through the near term expected to range from 1-2 inches across the Piedmont and central Virginia to one quarter to one half inch northeast North Carolina. && .SHORT TERM /THURSDAY THROUGH FRIDAY/... Anomalous upper-level low centers over Kentucky Thursday, with deep layer southerly flow over the Mid-Atlantic. At the surface, an associated area of low pressure and attendant cold front drop into north central North Carolina. High pressure located over the Northeast will help keep low pressure south of the region, with onshore flow north of North Carolina. Deepest moisture and theta-e/instability axis begin to pivot northward, but showers with embedded thunder persist. Best coverage and heaviest precipitation forecast Richmond northward through the day, tapering off to solid chance POPs far southern Virginia and northeast North Carolina late Thursday. Highs Thursday range from the mid 70`s northwest to low 80`s southeast. The upper low moves very little Thursday night as a frontal boundary pivots northward from North Carolina, locating over the forecast area. By that time, the deepest moisture progged to be north of the region, but precipitable waters around 1.5 inches and strong upper level dynamics will keep solid chance to likely POPs in the forecast. Lows in the mid to upper 60`s. Forecast has trended wetter and cloudier Friday than 12 hours ago as the stubborn upper low remains centered in the vicinity of eastern Kentucky. Deep layer southerly flow prevails, but the deepest moisture continues to pivot north and east of the region. Strongest onshore moisture flux progged north of the region, keeping the heaviest rain away from the local area. However, the combination of continued upper vertical motion and the presence of the frontal boundary will keep solid chance to likely POPs across the region through the day Friday. Sky remains mostly cloudy to cloudy. Highs forecast in the mid 70`s northwest to low 80`s southeast. Per SREF and GEFS mean guidance, storm total rainfall amounts expected to range from 3-4 inches north and west of Richmond to around one half inch in northeast North Carolina. Rainfall amounts generally 1-3 inches elsewhere. No flood watch products issued on this shift as the anomalous flow remains north of the region. However, localized minor flooding from several periods of showers (some heavy at times) is possible. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Long term period starts off Fri night/Sat with an upper-level cutoff low and associated sfc low centered over the OH Valley. Better rain chances will stay north of the area, but included at least a 20-30% chance of showers especially over ne areas where the highest moisture will be located. Mainly dry conditions thereafter into Sun and Mon as the cutoff low weakens and slides ne into Canada. As for temps, highs will generally be in the mid/upper 70s with lows ranging from the mid/upper 50s over the Piedmont to the mid/upper 60s near the coast. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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A very challenging aviation forecast for the next 24 hours. An east- west stationary front will remain across Virginia through the period. This will serve as the focus for showers and thunderstorms through Thursday. Some of these storms will likely contain very heavy rain especially across MD and inland VA allowing for areas of IFR at times especailly tonight. Could not rule out a severe storm either across interior VA late this afternoon into this evening. Lower chances for MVFR across the VA Tidewater and NE NC as this region will remain further away from the front. Slowly improving conditions Thursday but still chances for showers and storms especailly across the interior. Outlook...Unsettled weather persists into Friday with continued chances for showers and thunderstorms due to the frontal boundary remaining nearby. Improved weather for the weekend.
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&& .MARINE... Latest analysis shows a broad area of surface low pressure over the region, with another area of low off the coast. Strong/anomalous surface high pressure is situated over eastern Canada. The pattern over the next few days will feature this strong high building over eastern Canada, ridging into New England and the northern mid-Atlc region. This will make for a persistent and rather strong E/NE flow over northern portions of the marine area. Have added Bay zones N of New Pt Comfort to the SCA as well as the coastal waters from Cape Charles to Parramore Island (beginning late tonight or Thu morning). Seas are expected to build to 6-8 ft over northern waters, while remaining around 4 ft across the south). It is possible that marginal SCA conditions could make it to NC border for 5 ft seas by Thu aftn and that lower Bay could also get to marginal SCA levels (but confidence is rather low at this occurring and given that it would be 3rd period did not go that far with the headlines). Seas will slowly subside Fri-Sat (though the headlines will likely need to be extended through at least Fri night eventually). A lighter SSE flow expected Sat leading to sub-SCA conditions with 1-2 ft waves over the Bay and 2-4 ft seas over coastal waters. && .TIDES/COASTAL FLOODING... The synoptic pattern with strong High pressure centered over eastern Canada with a slow moving boundary/sfc low pressure inland over the Carolinas/Mid-Atlantic will bring persistent ENE flow to the area Thu-Fri. Strongest winds expected for the northern areas, with minor tidal/coastal flooding becoming a concern for Ocean City/Chincoteague/Wachapreague by Thu evening and Fri morning high tide cycles. Also some potential for flooding into the Bay (both lower and mid-upper Bay) by Fri-Sat as seas remain elevated and water is expected to struggle to exit the bay for several days. No coastal flood watches have been issued as chance for moderate- severe flooding is low, but we may eventually need to issue Coastal Flood Advisories. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory from 7 AM Thursday to 6 AM EDT Friday for ANZ654. Small Craft Advisory from 7 PM this evening to 6 AM EDT Friday for ANZ650-652. Small Craft Advisory from 7 AM Thursday to 1 AM EDT Friday for ANZ630-631. && $$ SYNOPSIS...SAM NEAR TERM...AJZ/SAM SHORT TERM...SAM LONG TERM...MAS AVIATION...MRD MARINE...LKB TIDES/COASTAL FLOODING...

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