Area Forecast Discussion
Issued by NWS Wakefield, VA

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694 FXUS61 KAKQ 301122 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 722 AM 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/... Latest GOES water vapor imagery depicts the stubborn and anomalous upper low over central Kentucky. Plume of deep moisture has located along the coast, with blended total precipitable waters upwards of 150 to 200 percent. Showers, some heavy at times, persist over the Maryland Eastern Shore as an upper level disturbance lifts over the Delmarva. They heavy rain threat continues through the morning thanks to anomalous moisture and diffluent flow aloft. Elsewhere, showers associated with another spoke of energy lifting around the upper low has spread into the Piedmont. Stable low levels has resulted in fog and stratus between the areas of showers. The flood watch for the Maryland Eastern Shore has been extended up noon to account for potential of locally heavy showers. Another piece of energy expected to lift around the southern periphery of the upper low today as surface low pressure slowly lifts along the southeast coast. The stalled frontal boundary remains over the Piedmont. The boundary will provide enhanced low- level convergence this afternoon as the upper level disturbance lifts into the region. Mid level dry air also begins to punch into the region from the southwest. Drying mid levels and dewpoints in the upper 60`s progged to result in marginal instability this afternoon. Instability could be enhanced by breaks in the clouds. Deep layer shear will also be increased thanks to deep southerly flow upstream of the upper low. The result will be a line of showers and thunderstorms lifting across the region this afternoon into this evening. Hi-res guidance disagreeing on the exact evolution of the showers/thunderstorms, but based on the air mass and associated upper level forcing, expect the line to be fairly organized. SPC has the area in a marginal risk for severe weather. The main limitation being CAPE and clouds. Gusty winds and small hail are possible, but locally heavy rainfall remains the main threat. Best coverage will be north and west of Richmond. Highs generally in the upper 70`s to low 80`s. 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 /11Z FRIDAY THROUGH TUESDAY/... Onshore flow and an anomalously moist air mass has resulted in widespread IFR conditions across the region early this morning. Conditions have been bouncing between MVFR and IFR at KORF/KPHF/KECG...but expect overall IFR conditions to persist through 12-14Z. Ceilings improve to MVFR mid morning. Showers have diminished inland, but persist over the Maryland Eastern Shore. Heavy rain remains a threat at KSBY. Onshore surface winds are generally at or below 10 knots. Another round of showers and thunderstorms expected across the region this afternoon. Showers may be heavy at times. MVFR ceilings expected to persist through the afternoon from KRIC to KSBY while improving southeast. Winds become east to southeast at or below 10 knots. Outlook: Unsettled conditions persist through the overnight with another period of IFR conditions possible. Flight conditions finally begin to improve Saturday as the front pushes offshore. High pressure builds in from the southwest through early next week as low pressure remains over the Northeast. && .MARINE...
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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.
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&& .TIDES/COASTAL FLOODING...
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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.
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&& .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...Coastal Flood Advisory until 1 PM EDT this afternoon for MDZ024-025. Flash Flood Watch until noon EDT today for MDZ021>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 noon EDT today for VAZ098. Coastal Flood Advisory until 1 PM EDT this afternoon 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 1 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...AJB/SAM MARINE...LKB TIDES/COASTAL FLOODING...AKQ

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