Area Forecast Discussion
Issued by NWS Wakefield, VA

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109 FXUS61 KAKQ 301936 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 336 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 /UNTIL 6 AM SATURDAY MORNING/... 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 /6 AM SATURDAY MORNING THROUGH 6 PM 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 FRIDAY/... 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 /20Z 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...
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Seeing a gradual downward trend in seas and waves in the mouth of Ches Bay. Will allow SCA for the Bay to expire at 400 PM as planned and keep remaining SCA flags unchanged with regard to previously determined end times. Main change has been increasing wind speeds over the waters from Fenwick Island to Chincoteague where sustained winds range from 10-20kt with gusts to around 25kt possible. These speeds are anticipated to diminish through this evening. Strong/anomalous sfc high pressure remains over sern Canada through tonight before weakening Sat aftn. Meanwhile, stacked low pressure over the Midwest will continue to drift north and slightly east during this same timeframe. This will translate into winds becoming more se through tonight and then more sly on Sat. Speeds will generally be aob 15kt during this time. Waves on Ches Bay will average 1-3ft tonight into Sat...while seas generally average 4-5ft until SCA expiration times when seas will then average 3-4ft during the same timeframe. Onshore 9-10 sec period swell should also be anticipated tonight through Sat aftn. Calmer marine conditions expected Sat night through Mon. Wind directions will be variable sw-w through Sun evening and then shift to a more nly direction Mon into early Tue. Winds are then expected to increase in response to a tightening pressure gradient caused by Hurricane Matthew (located off the Atlantic coast of FL) and another Canadian high pressure centered over se Canada/nrn New England Tue aftn into Wed night. Still a lot of uncertainty regarding Matthew`s storm track at this time, but the general trend will be for increasing onshore winds and continually building seas for the second half of next week.
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&& .TIDES/COASTAL FLOODING...
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Strong/anomalous sfc high pressure remains over sern Canada through tonight before weakening Sat aftn as stacked low pressure over the Midwest drifts north and slightly east during this same timeframe. This will translate into onshore/se winds through tonight and then more southerly (and decreasing) on Sat. As the winds shift and decrease, tidal anomalies will decrease incrementally by a few tenths of a foot with each passing high tide cycle. Several areas of concern are as follows: 1. Coastal flood warnings are in effect for the Nrn Neck through 500 PM this evening and also for the MD Lower Eastern Shore on Ches Bay through 900 PM tonight. These areas will be re-evaluated shortly. At this time, it does appear that the Nrn Neck will be transitioned to a coastal advisory for the next high tide overnight...while the MD Lower Eastern Shore (primarily near Bishops Head and vicinity) will continue in a warning for at least the next high tide cycle overnight as well. 2. Wrn Ches Bay areas from Hampton Roads to the Middle Peninsula will remain in a coastal flood advisory through tonight. With winds becoming more southerly by Sat morning, advisories in the far srn Bay may be allowed to expire with a continuation of advisories for the lower to middle Bay areas into Sat aftn. 3. Coastal flood advisory for Maryland Beaches and Ches Bay side of VA Eastern Shore will continue through Sat morning`s high tide cycle. 4. Coastal flood statement will be in effect for Virginia Beach and Eastern Currituck this evening as tide levels end up within 0.3ft of minor flooding thresholds. Nuisance flooding may be possible in the persistent onshore flow. * Surf zone forecast has ended for the season.
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&& .AKQ WATCHES/WARNINGS/ADVISORIES...
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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. Flash Flood Watch until midnight EDT tonight for VAZ064-075- 076-081>083-511>522. Coastal Flood Warning until 5 PM EDT this afternoon for VAZ075>078. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ656-658. Small Craft Advisory until 10 PM EDT Saturday for ANZ650-652- 654. Small Craft Advisory until 4 PM EDT this afternoon for ANZ634.
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&& $$ SYNOPSIS...AJZ/SAM NEAR TERM...AJZ/SAM SHORT TERM...AJZ/SAM LONG TERM...LSA AVIATION...LSA MARINE...BMD TIDES/COASTAL FLOODING...BMD

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