Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 281102 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 702 AM 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 Piedmont will continue to lift along the boundary into central Virginia through daybreak as weak shortwave energy lifts across the region. Areas of fog will also linger through early morning across central Virginia, before lifting/eroding by mid morning. The upper low drops southward today, centering over Indiana late today. 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 precipitable water values into the region. Scattered to numerous showers expected to develop early afternoon as the better forcing arrives, and persist through the day and into the overnight period. Have increased POPs across the area to high end likely and categorical. Theta-e advection and dewpoints in the mid to upper 60`s will result in marginal instability. Deep layer shear progged on the order of 30-35 knots, resulting in a chance of thunderstorms. Gusty winds are possible, but the main impact will be locally heavy rainfall in thunderstorms that develop. 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 /12Z WEDNESDAY THROUGH SUNDAY/... Improving conditions expected through mid morning as visibilities and ceilings improve. However, widespread MVFR conditions and overcast skies expected to persist through the morning hours. A weak boundary remains over the region today as an upper level disturbance drops into the region. Expect another round of widespread showers and embedded thunderstorms to develop late morning through the afternoon, spreading northeast through the day. Lower chances southeast Virginia/northeast North Carolina. MVFR conditions expected. Outlook: Unsettled weather conditions expected through the end of the work week as waves of low pressure lift along the cold front. Showers with late day thunderstorms will be possible each day. && .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...SAM SHORT TERM...SAM LONG TERM...MAS AVIATION...AJB/SAM MARINE...LKB TIDES/COASTAL FLOODING...

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