Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 091858 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 158 PM EST Fri Dec 9 2016 .SYNOPSIS... Canadian high pressure builds into the Mid-Atlantic today, settling over the region tonight into Saturday. The high slides offshore Sunday. Low pressure will push north of the area on Monday, with the associated cold front crossing the region late Monday. Another strong cold front impacts the region during the middle of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The current surface analysis shows large sprawling 1048mb high pressure centered from nw Canada through the Canadian Prairies and extending through the central US, with the sern fringe reaching the Mid-Atlantic and Southeast. The associated air mass has spilled over the mountains, with temperatures in the mid 30s this morning and dewpoints in the teens across the forecast area. An extension of the Arctic high will break off over the Midwest today, and builds eastward into the Ohio Valley late today. Ongoing cold air advection ahead of the building high will result in a cold/brisk day today. 850Mb temperatures drop to around -10C (-2 standard deviations) by this afternoon. Low level thicknesses yield temperatures in the upper 30`s to around 40, so continue to undercut statistical guidance. Highs forecast in the upper 30`s to around 40 (-1 standard deviation) under a sunny sky. A brisk northwest wind of 10-15 mph inland and 15 to 20 mph near the coast is expected and will keep wind chill values in the low to mid 30s. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/... Cold, Canadian high pressure builds into the region tonight as the mid level trough axis pushes offshore. Winds decouple away from the coast, with temperatures dropping into the upper teens to around 20 inland to the mid 20`s near the coast. The high finally builds over the mountains, centering over eastern North Carolina Saturday. 850Mb temperatures and low level thicknesses moderate somewhat Saturday thanks to westerly flow, but limited mixing and 850mb temperatures still around -8 to -10C will still result in a cold day. Highs similar to Friday, generally in the upper 30`s to low 40`s under a sunny sky. High pressure remains over the region Saturday night. Meanwhile, a northern stream trough dives into the Great Lakes region, resulting in increasing high clouds late. There should still be several hours of rather ideal radiational cooling conditions with lows again dropping into the low to mid 20`s. The initial wave pushes north of the region Sunday with a secondary wave diving into the Ohio Valley. The surface high slides offshore. Increasing clouds and limited mixing will again result in below normal temperatures. Highs generally in the mid 40`s to low 50`s southeast. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Sfc high pressure slides offshore by Sun aftn and winds become more sly on Sun. The combination of a weak coastal trough developing off the Carolina Coast Sun night and a warm front lifting north through the area should bring rain up along the Mid Atlantic coastal areas Sun night. A cold front associated with low pressure tracking along the St Lawrence River Valley is then expected to cross the region Mon and exit the coast late Mon night. Winds generally sw ahead of the front...becoming nly Tue. The cooler air behind the cold front is much more modified and what would be typical breezy conditions along the coast are not anticipated at this time. Sfc high pressure returns Tue/Tue night...followed by what could be a developing coastal low off the Southeast into Mid Atlantic coasts on Wed. A brief warm-up should be anticipated as the aforementioned warm front lifts through the region Sun night into early Mon. Areas north of the warm front should remain wedged and keep cooler air in place prior to the initial onset of precip. This could result in a rain/snow mix quickly transitioning to all rain overnight. Precip should remain as rain through Monday. Temperatures generally at to slightly below normal throughout the period. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... Not much change to the previous TAF forecast...High pressure and fair weather will remain in control through the TAF period. Generally SKC conditions will prevail through the period. Winds will generally remain out of the northwest at around 10-15 knots this afternoon. Winds could occasionally gust as high as 20 knots this afternoon, especially near the coast. Mainly clear skies and VFR conditions are expected for tonight. Outlook: High pressure builds into the area through Saturday. High pressure slides offshore on Sunday. There will be a chance for rain Monday as a cold front approaches from the west. Following the passage of the cold front Monday night, dry weather returns for Tuesday. && .MARINE... Update...SCA flags added back in for the Upper James and all rivers extended to end at midnight tonight. A secondary surge is occurring and is expected to persist through this evening before diminishing. Previous discussion... High pressure continues to build into the waters this morning, but the center of the high is still over the Central Plains. This has left a significant pressure gradient in place with the region sitting between this high and a strong low over The Canada Maritimes. The Northwest flow is in place with winds of 15 to 20 kt and gust 25 to 30 kt over the Bay and coastal waters. With the strong cold advection that remains in place through Friday evening, the strong nw flow will continue into tonight. Once the flow aloft becomes more westerly aloft and the cold advection weakens along with a relaxation of the pressure gradient, expect the winds to gradually weaken overnight Friday into Saturday. With seas lagging behind the winds, expect the SCA on the Bay and Coastal waters to continue through Friday night. For the weekend, the surface high will settle over the region allowing for a quiet period with relatively light wind and seas. By Sunday night, the sfc high slides off the coast and the flow begins to turn southerly. The models show a 40 - 60 kt low level jet developing ahead of cold front Sunday night. But the question becomes will these winds mix to the surface. The effective warm front should be near the Mason-Dixon line, however, the models show the low level front may be a weak wedging type boundary with a coastal front that may keep the low levels stable and the 950 mb jet from mixing down. This low level boundary should dissipate on Monday as the mixing improves ahead of the front, which should then allow the winds to mix better and the potential exist for SCA conditions just ahead of the cold frontal passage Monday and lingering into Tuesday in the cold advection the follows the front. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until midnight EST tonight for ANZ635>638. Small Craft Advisory until 4 AM EST Saturday for ANZ630>632- 634-650-652-654-656-658. && $$ SYNOPSIS...AJZ/SAM NEAR TERM...AJZ/SAM SHORT TERM...AJZ/SAM LONG TERM...BMD AVIATION...AJB MARINE...BMD/ESS is the U.S. government's official web portal to all federal, state and local government web resources and services.