Area Forecast Discussion
Issued by NWS Wakefield, VA

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480 FXUS61 KAKQ 282003 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 403 PM EDT Wed Sep 28 2016 .SYNOPSIS...
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An upper level low slowly drops south from the Great Lakes tonight through Friday. Meanwhile, high pressure builds well north of the region and steers a moisture rich airmass into the region tonight Through Thursday night.
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&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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Current wv imagery depicts an anomalous upper low dropping s across the lower Great Lakes, with deep sw flow aloft over the Mid-Atlantic region ahead of the upper low. At the surface, 1034mb high pressure is situated over se QB, which is ridging s through the ne US. Weak surface low pressure is depicted beneath the upper low, with an attendant boundary extending across the central Appalachians and central/se VA. Effective shear values of 30-40kt are co-located with 1000-1500 J/kg of MLCAPE across central/s- central VA down into central NC. This will interact with increasing forcing aloft and trigger sct-numerous showers/tstms through the late afternoon and evening hours. Some tstms could be severe, mainly producing hail and damaging wind gusts, with an isolated tornado possible in vicinity of the surface boundary. The deep layer flow will become more southerly through the night, which will allow a higher pw airmass to advect into the region. The primary threat associated with showers/tstms should transition to heavy rainfall by later this evening. Initially the heavy rainfall threat should be across the nw piedmont counties, and then gradually shift toward central VA (generally around and n of RIC metro) and toward the Nrn Neck and Ern Shore overnight. Mild and humid tonight with lows in the mid 60s nw, to around 70 se.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
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The upper low continues to digs swd through the Ohio and Tennessee Valleys Thursday into Thursday night. Meanwhile, upper ridging builds n of the Great Lakes across se Canada. At the surface, high pressure builds to around 1036mb per 28/12z GEFS over the same region. This will result in a strengthening easterly LLJ over the nrn Mid-Atlantic, potentially reaching -3 to -4 st dev at 925mb Thursday aftn, before gradually slackening Thursday night. This will continue to push a high pw airmass into the region and will result in a continued heavy rainfall threat across the nrn half of the area into Thursday night. Rainfall amounts could reach 3-5" across the far nrn tier counties bordered by 2-4". Locally higher amounts are possible. Unsettled conditions continue into Friday as the upper low lingers w of the area, but overall moisture transport should diminish, with the heavy rain threat diminishing. The upper low begins to fill and lift n by Saturday resulting in gradually improving conditions. The sky remains mostly cloudy to overcast through the period. High temperatures range from the upper 70s to low 80s, with lows generally in the 60s.
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&& .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
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Anomalous upper low will make its way through the eastern Great Lakes Sat night/Sunday and into New England by Monday where it becomes more of an open wave/trough. This feature then moves off the Northeast coast early next week. Based on the latest model guidance...have slowed the timing of pcpn exiting the FA with chc pops (30-50%) lingering across eastern areas Sat night...diminishing to slight chc pops across eastern areas by Sun eve. Will maintain dry wx Monday, then a lot of uncertainty develops by Monday night into the middle of next week. There`s the potential for the remnants of the upper low/trough to linger offshore (providing moist onshore/easterly flow locally) and also uncertainty with regards to the eventual track of TS Matthew. Will carry low end pops for now Tue-Wed. Highs through the period mainly in the 70s. Lows in the 60s.
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&& .AVIATION /20Z WEDNESDAY THROUGH MONDAY/... A very challenging aviation forecast for the next 24 hours. An east- west stationary front will remain across Virginia through the period. This will serve as the focus for showers and thunderstorms through Thursday. Some of these storms will likely contain very heavy rain especially across MD and inland VA allowing for areas of IFR at times especailly tonight. Could not rule out a severe storm either across interior VA late this afternoon into this evening. Lower chances for MVFR across the VA Tidewater and NE NC as this region will remain further away from the front. Slowly improving conditions Thursday but still chances for showers and storms especailly across the interior. Outlook...Unsettled weather persists into Friday with continued chances for showers and thunderstorms due to the frontal boundary remaining nearby. Improved weather for the weekend. && .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...
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MD...Flash Flood Watch from midnight EDT tonight through late Thursday night for MDZ021>023. NC...None. VA...Flash Flood Watch from 9 PM EDT this evening through Thursday evening for VAZ048-060>062-064-066>069-509>516. Flash Flood Watch from midnight EDT tonight through late Thursday night for VAZ075>078-083-085-517>522. 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 PM EDT Friday for ANZ650-652. Small Craft Advisory from 7 AM Thursday to 1 AM EDT Friday for ANZ630-631.
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&& $$ SYNOPSIS...AJZ NEAR TERM...AJZ SHORT TERM...AJZ/SAM LONG TERM...JDM AVIATION...MRD MARINE...LKB TIDES/COASTAL FLOODING...AKQ

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