Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 072124 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 424 PM EST Wed Dec 7 2016 .SYNOPSIS...
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Weak high pressure builds into the region tonight. Weak low pressure tracks along the Virginia North Carolina border Thursday morning through early afternoon, followed by a cold front later Thursday afternoon. Canadian high pressure builds into the area Friday through the weekend.
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&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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Current GOES WV imagery depicts a broad trough over much of the Conus aside from the Southeast. A deep stacked low is centered near James Bay, and strong wsw flow exists from the Desert Southwest through the Mid-Atlantic, with an embedded shortwave trough over the s-central Plains. At the surface, large sprawling 1056mb high pressure is centered over nw Canada and is ridging sewd into the nrn and central plains, with an extension spilling from the Ohio Valley into the Mid-Atlantic in the wake of low pressure departing offshore. This extension of high pressure will break off from the main high and become centered over the Mid-Atlantic tonight as a cold front becomes defined over the Lwr Great Lakes. Meanwhile, the s-central plains trough will rapidly track ewd toward the srn Appalachians. Locally the sky should be mostly clear this evening (after aftn sc/cu over the Ern Shore dissipates). Clouds then increase after midnight from w-e with most of the area becoming mostly cloudy to overcast by morning. Temperatures drop quickly through the 40s this evening, with overnight lows ranging from the low/mid 30s n, to the upper 30s/around 40 s.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
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The aforementioned srn stream system quickly tracks across the region in vicinity of the VA/NC border Thursday morning through early aftn. A shear axis and strong flow aloft will provide subtle forcing for ascent along with pw values of 0.5-0.9". Downslope flow and marginal moisture return will be limiting factors for pcpn. Forecast PoPs are 20-30% and highest over se VA/ne NC, with any QPF on the order of a few hundredths of an inch. A vigorous upper trough will dig over the Great Lakes Thursday and push the aforementioned cold front through the Ohio Valley and into the Mid-Atlantic region by late aftn. Mostly cloudy to overcast most of the day with clearing arriving in the Piedmont by mid-late aftn as the cold front pushes through. Cloud cover should hold highs in the upper 40s to low 50s. Much colder air surges into the region Thursday night as the large arctic high continues to build through the central Conus and nudges ewd into the Southeast. 850mb temperatures drop to -8 to -10C (-1 to -2 st dev) late Thursday night. Lows drop into the mid/upper 20s under a quickly clearing sky. A cold/brisk day is anticipated Friday as the Arctic high builds from the Central Plains toward the srn Appalachians. 850mb temps drop to around -10C (-2 st dev) Friday afternoon. Strong CAA will prevent temperatures from reaching their full potential Friday afternoon, even with a sunny sky. MOS guidance continues to show highs generally in the low/mid 40s, but these numbers seem on the high-side. Some Piedmont locales may struggle to get out of the 30s, with around 40/low 40s elsewhere. A brisk northwest wind of 10-15 mph inland and 15 to 20 mph near the coast is expected to keep wind chill values in the low to mid 30s. The high builds into the region Friday night into Saturday. By this point the airmass will have modified enough to lose its arctic characteristics. Still cold and well below normal nonetheless, with lows Friday night in the upper teens to low 20s inland, to the low/mid 20s for se coastal locations. Limited mixing Saturday will keep highs in the upper 30s to low 40s despite some warming at 850mb. Sunny with a light nw wind becoming sw.
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&& .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
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Sfc high pressure slides overhead Sat night and offshore by Sun morning. Winds become more southerly and breezy...especially as a weak coastal trough begins to develop along the Carolina and Mid Atlantic coasts Sun night. Meanwhile, another upper level trough digs across the Midwest and Ohio Valley Sun/Sun night...followed by a strong cold front pushing through the area Mon and a more progressive, westerly flow pattern aloft for Tue/Wed. A brief warm-up should be anticipated with the coastal trough Sun night into early Mon...along with increasing chances of precipitation Sun evening through Mon evening with the passage of a cold front. The Piedmont may remain wedged and keep cooler air in place prior to the initial onset of precip. This could result in precip starting as light snow showers Sun evening before quickly transitioning to all rain overnight. Precip should remain as rain through Monday, however if any precipitation lingers into Mon night, it could easily transition back to light snow showers as another round of cooler, modified arctic air and sfc high pressure return to the region Mon night through mid week. Temperatures generally at to slightly below normal throughout the period.
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&& .AVIATION /21Z WEDNESDAY THROUGH MONDAY/... Low pressure is situated off the coast this aftn, with high pressure building into the Ohio Valley. Widespread sc has developed over the Delmarva as of 18z, with few-sct cu elsewhere. Cigs over the Ern Shore are averaging 1.5-2.5kft. This general trend should continue through ~22z with clouds dissipating through 00z. A northerly wind of 5-10kt is expected through the aftn. A quick moving low pressure system will approach from the west tonight and track across the region Thursday morning through early aftn. Clouds are expected to increase late tonight, with a period of mvfr cigs possible Thursday morning through midday. A period of light rain is possible (20-30% chc). A cold front will push this system offshore and cross the region later Thursday aftn. High pressure builds into the area Thursday night through Saturday. High pressure slides offshore Sunday as another cold front approaches from the west. This cold front crosses the region Sunday night into Monday. && .MARINE...
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A weak cold front crosses the waters late this aftn into this evening...with cooler air filtering down over the waters the rest of tonight into Thu. Winds generally nw-n aob 15kt during this timeframe. Seas have been slow to subside through today, and have therefore extended SCA flags for ocean through 500 AM Thu morning when seas finally drop below 5ft. Meanwhile, an upper level trough sits just north of the region on Thu...slowly sagging swd Thu night and then sliding across the area on Fri. Winds become more wnw as the day progresses with speeds remaining aob 15kt. Wind speeds increase to 15-20kt Thu evening for Bay/Ocean/Sound/Mouth of James River as a strong 125-150kt jet sags south over the waters in advance of the upper trough. A much colder arctic airmass arrives after midnight Thu night as the sfc pressure gradient tightens and speeds increase to 20-30kt (aforementioned areas) and 15-20kt (Rivers); still w-nw direction. SCA flags will likely be issued beginning with this initial surge in winds. Gale force gusts may still be possible (especially as skies clear with the strong jet streak overhead), however confidence is low at this time. The cold air begins to equalize and the sfc pressure gradient starts to relax late Fri night into early Sat as sfc high pressure axis shifts ewd and closer to the waters. Winds remain within solid SCA speeds through Sat morning before diminishing below 15kt all waters by Sat aftn. Seas build to 5-7ft north (possibly up to 8ft near 20nm Fri evening)/5-6ft south by Fri morning and are expected remain steadfast through early Sat morning before subsiding below 5ft by Sat aftn. The high slides overhead Sat night (light/variable winds) and offshore by Sun morning. Winds become more sly on Sun with a possible surge in speeds to 10-15kt into Sun night as a weak coastal trough starts to develop off the Carolina and Mid Atlantic coasts. The trough axis is expected to stall just offshore on Mon with winds becoming more sw-w aob 15kt. Seas average 2-3ft Sat night through Sun Night and may build to 4ft near 20nm on Mon. Waves 1-2ft.
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&& .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until 5 AM EST Thursday for ANZ650-652- 654-656-658. && $$ SYNOPSIS...AJZ/SAM NEAR TERM...AJZ SHORT TERM...AJZ/SAM LONG TERM...BMD AVIATION...AJZ MARINE...BMD

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