Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 072052 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 352 PM EST Wed Dec 7 2016 .SYNOPSIS... 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. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... 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. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/... 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. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... Long term period starts off Fri night/Sat with dry weather as sfc high pressure builds directly over the Mid Atlc. Main story in the extended will be cold temps, with lows in the low/mid 20s Fri night and Sat night. High temps Fri and Sat avg in the low 40s both days. Next chance of pcpn arrives Sun night/Mon with an approaching cold front, with the best chance of rain being during the day Mon based on the 12Z GFS/ECMWF (40% pops). High temps Mon in the mid/upr 50s. && .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... SCAs for the lower Bay and Currituck Sound have been allowed to expire as winds continue to diminish. Weak high pressure will nose into the area by this afternoon and evening allowing the winds to relax further across the region, but the seas over the coastal sections will be slow to diminish so will keep sca flags up for seas through 10 pm. A surge of cold canadian air will arrive in the area on Thursday and will reinvigorate a cold front that is dissipating over the Central Appalachians today. This front will then push through the waters by Thursday afternoon. While there could be some showers with this front, expect strong NW winds to develop again with strong sca conditions. This cold air will allow mixing of the winds aloft to the surface and could keep sca conditions in place into Friday night or Saturday. The models are struggling some with the wave heights generated by these winds as the WNAwave guidance quickly reduces the seas on Friday while the NWPS guidance keeps seas in the coast areas up 7 to 9 Ft. FOr now have gone in the 5 - 7 FT range for now with the sca conditions. Finally by Saturday afternoon...with high pressure centered over the area, will see the winds relax and benign conditions returning through Sunday. && .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...MAS AVIATION...AJZ MARINE...ESS/JDM

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