Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 230756 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 356 AM EDT Wed Aug 23 2017 .SYNOPSIS... High pressure remains centered off the Mid Atlantic coast through tonight as a cold front begins to approach from the west. The front crosses the area late Wednesday afternoon through Wednesday night, with strong high pressure building north of the area from Thursday into the upcoming weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... No major changes necessary to the previous forecast. Still expecting a dry night aside from a stray shower late over northern areas. Previous discussion... Warm/humid tonight with little chance for any rain under a SW wind of 10 mph. Lows mainly in the mid to upper 70s. Clouds increase across the north ahead of the approaching cold front and lead shortwave. Have introduced a slight chance PoP for the Maryland Eastern Shore late tonight, but best chances for measurable precipitation remain north and west of the local area. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/... Models in good agreement with dropping the cold front into the local area Wednesday morning, then pushing the front across the area through Wednesday afternoon. Shearing vort lobe progged to ride along the front as winds increase aloft. The added forcing along the boundary along a narrow ribbon of high precipitable waters will result in scattered to numerous showers and thunderstorms Wednesday afternoon. Downslope flow from 1-3km will limit the coverage over the Piedmont, but hi-res and course resolution guidance indicates that the activity should become more organized central Virginia eastward as it interacts a moderately unstable air mass (mixed-layer CAPE values 500-1500 J/kg) and marginal shear (25-30 knots). Dry mid levels and an inverted V sounding indicate the main threat will be damaging winds and frequent lightning. SPC maintains a marginal risk for severe weather across the southeast half of the local area. Heavy rainfall is also possible as the cold front slows as it reaches southeast Virginia and northeast North Carolina Wednesday afternoon. Precipitable water values progged around 2 to 2.25 inches. Westerly flow in the mid levels indicates that the motion should prevent widespread heavy rainfall, but some areas could see periods of heavy rainfall. No headlines planned at this time. Flow becomes north to northeast behind the front, as dry air spreads into the area from the northwest. The front and upper wave push offshore Wednesday evening. Guidance indicates a wave of low pressure develops along the front over the Carolinas, keeping rain chances in northeast North Carolina and far southeast Virginia through Wednesday night. Highs Wednesday range from the mid 80`s northwest to around 90 southeast. Lows Wednesday night in the low to mid 60`s inland to the low 70`s near the coast. High pressure builds in from the northwest Thursday as the front stalls along the Southeast coast. Will keep low chance PoPs across northeast North Carolina Thursday nearest the front and deepest moisture. Otherwise, dry, cooler and less humid conditions expected. Highs Thursday forecast in the low to mid 80`s under a partly cloudy sky. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Cooler and drier for the late week period courtesy of building longwave upper level trough over the eastern United States. Meanwhile, broad 1024+ mb surface high pressure builds south over the interior northeast from Great Lakes Thursday and Friday, eventually setting up over New England and ridging down the east coast over the weekend into early next week. Forecast remains mostly dry, although a few showers possible along the coast in persistent onshore flow. Medium range guidance in relatively good agreement with developing a tropical system along and offshore of the southeast coast along the old frontal boundary early next week. Kept weekend dry, with low rain chances along the SE coast by Monday. Looking ahead, rain chances look to improve into the middle of next week, with moisture from the remnants of Harvey looming to the SW. For temperatures, high temperatures Fri-Mon will be at or just slightly below normal through the period, mainly in the upper 70s to low 80s. Early morning lows in the 50s inland to mid 60s along the coast. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... Early this morning, a cold front was moving into nrn/NW portions of the CWA. That front will slowly push SE acrs the region and off the coast today into Thu morning. Flight restrictions will be possible along and behind the front this aftn into Thu morning fm showers and tstms. The front should push SE of NE NC during Thu, with lingering showers possible over extrm SE VA/NE NC. Conditions are expected to improve Thu aftn thru Fri, as the front shifts farther SE and high pressure builds north of the region. Breezy NE winds expected near the coast Thu and Fri. && .MARINE... A cold front will approach the waters from the northwest and cross the area late this aftn through tonight. SW flow still avearges 15-20 kt over the Bay and coastal waters, have the SCA headlines through 7 am for the entire Bay and for the nrn coatl waters. Waves avg 2 to 3 feet in the bay and seas acrs the N are 4-5 ft. Winds shift to the N/NE 10 to 15 knots behind the front by late this morning N and by aftn farther S (and with convection this aftn winds will be locally much stronger but this will be handled w/ MWS/SMW`s as needed). Strong high pressure builds north of the region Thursday and into the weekend. Given the warm waters and some cold advection late tonight/Thu morning, expect a marginal SCA event over at least some of the Bay and probably the lower James Thu morning. Did not raise any SCA headlines as this will be mainly a 3rd period event (and still fairly marginal). Otherwise expect diminishing winds later Thu aftn through Fri as sfc high pressure builds a little farther south and the pressure gradient weakens. Waves in the lower Bay may briefly build to 3-4 ft Thu morning, then will subside to 1-2 ft with coastal seas 3-4 ft. Onshore (E-NE) flow for the weekend as high pressure builds NNW of the local area and then shifts east to New England. Winds remain elevated 10 to 15, occasional gusts to ~20 kt Sat, and then increase more significantly Sunday into next week as stalled front to the south lifts back N with low pressure developing along the boundary. Seas remain choppy Sat, and then will build to 5-7 ft or greater late Sun into next week. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until 7 AM EDT this morning for ANZ630>632-634-650-652. && $$ SYNOPSIS...TMG NEAR TERM...TMG SHORT TERM...LKB/SAM/TMG LONG TERM...MAM AVIATION...TMG MARINE...LKB

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