Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 301812 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 212 PM EDT Fri Sep 30 2016 .SYNOPSIS... An upper level low lingers over the Ohio Valley today. Meanwhile, high pressure builds well north of the region and steers a moisture rich airmass into the region through today. Slowly improving conditions are expected into the weekend as the upper low lifts back to the north. && .NEAR TERM /THROUGH TONIGHT/... The Delmarva is presently getting a much need break from heavy rain, which has totaled up to 6-12" across DE/Lwr MD Ern Shore over the past 48 hours. This water will result in rising main stem rivers through the afternoon and potentially into tonight. Follow the latest flood warnings for more details. Current GOES WV imagery continues to depict a stubborn anomalous upper low over central KY. A plume of deep moisture extends from off the SC/GA coast nwd into central NC/s-central VA, and nw across the central Appalachians. Another plume to the east has pushed offshore brining the need break in rain to the Delmarva. Showers and embedded tstms are developing across central NC and streaming nwd into the Piedmont. This activity is being triggered by the combination of the aforementioned moist plume/mid-level theta-e ridge, a push of mid-level dry air on the wrn flank of the moisture stream, a spoke of shortwave energy rotating around the upper low. The interaction of the push of dry air into the moist airmass will create some convective instability aloft. Strong mid-level flow (55-65kt at 500mb) will result in strong deep layer shear. This combination could trigger some strong to marginally severe tstms this afternoon and evening, which is reflected in the marginal outlook from SPC. The main threats are hail and locally strong wind gusts. The main limiting factor will be the lack of SB/BL CAPE with an in situ wedge airmass in place. The best coverage will be west of Richmond initially through early afternoon, before shifting ewd later this afternoon and evening. Locally heavy rainfall will produce an isolated flood threat for the more sensitive areas. Otherwise, mostly cloudy to overcast. Strong high pressure to the n will maintain the in situ wedge airmass over the piedmont with highs around 70/low 70s, gradually ranging/rising to the low 80s se where some breaks in cloud cover are expected. Area of showers lifts northeastward this evening toward the northeast zones as the front begins to lift. Deepest moisture flux and convergence pushes offshore, which will limit overall rainfall amounts. However, additional localized flooding is possible in the areas sensitive from the previous days rain. Drying inland this evening through the overnight with some breaks in the clouds possible over the southern Piedmont. Mild again with lows in the mid to upper 60s. && .SHORT TERM /SATURDAY/... Dry air continues to entrain into the system Saturday as the upper low fills and lifts northward. The result will be gradually improving conditions. Addition energy lifts over the region in southwest flow aloft, so can`t rule out isolated to scattered showers east of interstate 95. Sky conditions also improve with a partly cloudy sky inland, but remaining moistly cloudy near the coast. Highs Saturday range from the upper 70`s to low 80`s, but less humid as dewpoints drop into the upper 50`s to low 60`s inland. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Anomalous upper low over the Ohio Valley during the short term will make its way slowly north and northeast early next week...allowing for high pressure to build into the Mid Atlantic States. A chance for showers remains Sunday over the Chesapeake Bay and portions of Hampton Roads and east and end all areas by Monday morning. A strong surface high will remain over southeast Canada which will increase its influence across the Eastern Seaboard early next week with its associated easterly flow. A chance for showers returns to the forecast Tuesday and Wednesday. Tropical Cyclone Matthew may have an influence late in the week...especially in the marine area. Uncertainty remains in terms of the timing and track. Refer to guidance from the National Hurricane Center and extended forecasts from the Weather Prediction Center for details. High temperatures from 75 to 80 Sunday and Monday lower to around 70 in the northern Piedmont to the upper 70s northeast North Carolina by Thursday. Lows will range through the 60s. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... The combination of low pressure over the Ohio Valley and a stationary front from North Carolina to off the Virginia coast was producing a moist onshore flow over the Mid Atlantic States. Satellite showed clearing over the coastal waters and portions of the Bay and mostly cloudy sky over the TAF sites. Occasionally where the sky clears over southeast portions...the clouds fill back in with a broken MVFR layer. IFR cigs were over SBY and may continue through nearly all of the TAF period. Thunderstorm activity was beginning to develop over far southern Virginia and south into eastern North Carolina and was spreading northward. With the unstable airmass in place...put VCTS for portions of the afternoon at all the TAF sites except SBY. IFR (and possibly LIFR) redevelops late this evening and overnight at RIC and SBY. It may need to be added to PHF but is unlikely at ORF and ECG. Conditions improve during the mid to late morning Saturday. && .MARINE... Update...SCA for mouth of Ches Bay extended through 400 PM this aftn. Waves will average 3-4ft during this time before subsiding. Previous Discussion... Strong/anomalous sfc high pressure (1035 mb+) still centered over eastern Canada with a weak trough of low pressure along the VA coast. The stronger pressure gradient is shifting N and winds have diminished significantly except across the northern coastal zones where 20-25 KT winds persist for a few more hrs. SCA`s for the mouth of the Bay have been extended through 1 pm (for 4 ft waves) Elsewhere, SCA`s will remain in effect through today/tonight for southern coastal waters (and into Sat farther N as seas are slow to subside with residual 9-10 sec period swell). Calmer marine conditions expected Sat ngt thru Mon. && .TIDES/COASTAL FLOODING... Update... Allowed coastal flood advisory for Virginia Beach to expire at noon. Tide levels for this area as well as Eastern Currituck will be within 0.3ft of minor flooding thresholds through high tide this evening and nuisance flooding may be possible in the persistent onshore flow. Also extended flood advisory for Maryland Beaches through Saturday morning as water levels near Ocean City remain just above 4ft during high tide. Previous discussion... 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 continue to bring persistent ENE flow to the area this evening/Fri. As of 11Z, Departures avg 1.5 to 2.0 feet for the most part. Have updated CFW to expand the Coastal Flood Warning to include all of the VA Northern Neck zones through the upcoming high tide cycle that occurs late this morning into the aftn and the MD eastern shore counties along the Bay (both for moderate flooding expected). Elsewhere, have continued coastal flood Advisories (and expanded to include VA Beach) to include both the upcoming morning/early aftn High tide cycle and the following late evening/early Sat am cycle. Looking at latest currents data in the lower Bay suggests outgoing tides are slowly strengthening but water will remain piled up in the Bay for at least 2 more cycles. In addition, high rip risk for all beaches as seas are remaining elevated at 5-7 ft with 9-10 second dominant periods. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...Coastal Flood Advisory until 11 AM EDT Saturday for MDZ024-025. Coastal Flood Warning until 9 PM EDT this evening for MDZ021>023. NC...None. VA...Coastal Flood Advisory until 4 AM EDT Saturday for VAZ089-090- 093. Coastal Flood Advisory until 2 AM EDT Saturday for VAZ084>086- 095>097-523>525. Coastal Flood Advisory until 11 AM EDT Saturday for VAZ099-100. Coastal Flood Warning until 5 PM EDT this afternoon for VAZ075>078. MARINE...Small Craft Advisory until 10 PM EDT Saturday for ANZ650-652- 654. Small Craft Advisory until midnight EDT tonight for ANZ656-658. Small Craft Advisory until 4 PM EDT this afternoon for ANZ634. && $$ SYNOPSIS...AJZ/SAM NEAR TERM...AJZ/SAM SHORT TERM...AJZ/SAM LONG TERM...LSA AVIATION...LSA MARINE...BMD/LKB TIDES/COASTAL FLOODING...

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