Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 300612 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 212 AM EDT Fri Sep 30 2016 .SYNOPSIS... An upper level low lingers over the Ohio Valley tonight through Friday. Meanwhile, high pressure builds well north of the region and steers a moisture rich airmass into the region tonight into Friday. Slowly improving conditions are expected into the weekend as the upper low lifts back to the north. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... The trapped upper low continues to spin over the Ohio valley tonight with the showers now becoming more banded. The 18z nam hinted that the rain would take on this banded structure with an area over the far northeastern portion of the cwa and in the far western portions along the piedmont and stretching in central and northwestern VA. This is what has developed as the drier air aloft begins to wrap around the southern side of the low and pushed into the Mid Atlantic states. So have adjusted pops to lowering down to chance of showers overnight, expect in the bands where have kept low likely values. The area over the central piedmont is a little more uncertain however, but satellite imagery does show convection beginning to fire over SC and this is expected to lift northward overnight into the central piedmont, which is the reason for the higher pops. Therefore, have dropped the flash flood watch for all but the Lower MD Eastern Shore, where some flooding continues. Otherwise, made just a few minor tweaks to the overnight lows based on current readings. prev discussion Current GOES water vapor imagery depicts the center of an anomalous upper low nearly stationary near the IN/KY border. Upstream of the upper low, a plume of anomalous moisture extends from the coasts of NC/se VA to the Delmarva and into Ern PA/NJ. Blended TPW imagery shows pw values of 1.5-2.0", which is around 150- 200% of normal. At the surface, low pressure is centered over wrn NC with a trough off the NC coast. 1038mb high pressure is centered over se QB and is ridging sw through New England and into the nrn Mid-Atlantic. Visible imagery depicts cloud cover over most of the area. Showers and embedded tstms are expanding in coverage from se VA/ne NC nw through central VA in vicinity of a southeasterly LLJ. Farther to the ne, an area of rain continues to gradually push wwd over the Lower Ern Shore associated with a strong easterly LLJ centered along the nrn Mid-Atlantic Coast. This general pattern should continue through the evening producing some pockets of moderate to heavy rain. The latest data does depict that the LLJ structures begin to weaken overnight, and hence rain rates and areal coverage should diminish. The most sensitive areas with respect to heavy rainfall will be from central VA in vicinity of the RIC metro to the Nrn Neck, and over the Lower MD Ern Shore. These areas received 4-6" of rain last night, with localized amounts up to 8". The flash flood watch will remain in effect from the piedmont through the Lower MD Ern Shore. Otherwise, mostly cloudy to overcast tonight and breezy along the coast. Lows range from the mid 60s nw to around 70 se. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... Unsettled conditions continue into Friday as the upper low lingers w of the area, but overall moisture transport should diminish and be shunted n, with the heavy rain threat diminishing. Secondary shortwave energy does rotate around the upper low resulting in 60-70% PoPs across the piedmont. Pcpn potential will be lower toward the coast and generally 20-40%. Highs range from the low/mid 70s nw, to the low 80s se under a mostly cloudy to overcast sky. The upper low begins to fill and lift n by Saturday resulting in gradually improving conditions. The sky remains mostly cloudy along with slight chc/chc PoPs. High temperatures Saturday range from the mid/upper 70s nw to low 80s se, after morning lows generally in the 60s to around 70. && .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 /06Z FRIDAY THROUGH TUESDAY/...
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Onshore flow and an anomalously moist air mass has resulted in widespread IFR conditions across the region early this morning. Combination of stratus (ceilings as low as 300 feet) and fog (visibilities as low as 1 mile) observed. TAF sites expected to be plagued by IFR conditions through at least 12Z, before improving to MVFR mid to late 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, but a few gusts to 20 knots expected along the coast. 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.
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&& .MARINE... Sfc low pressure over wrn NC and SC with strong/anomalous sfc high pressure (1035 mb+) centered over eastern Canada. The pattern thru tonight will feature the strong high remaining over eastern Canada, ridging into New England and the northern mid-Atlc region. A persistent/strong E/NE flow will prevail over northern portions of the marine area into early Fri morning, so a Gale Warning will remain in effect until 4 am Fri. Elsewhere, SCA`s will remain ovr the srn Ches Bay or Rivers into this evening or early tonight, and until 7 am Fri for the nrn Ches Bay zns. SCA`s will then be in effect for the coastal waters due to seas fm Fri thru Sat. Winds diminish from S to N tonight and for all areas on Fri, as the surface low lifts N and pressure gradient weakens. Coastal seas will diminish but still remain elevated at 4-6 ft into Fri night and possibly Sat due to residual swell. SSE flow expected Fri ngt and Sat leading to sub-SCA conditions elsewhere with 1-2 ft waves over the Bay. Calmer marine conditions expected Sat ngt thru Mon. && .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 continue to bring persistent ENE flow to the area this evening/Fri. Departures avg 1.0 to 2.0 feet for the most part. Have updated CFW to upgrade a couple of Coastal Flood Advisories to Coastl Flood Warnings for this evening into early Fri morning. Have issued Coastal Flood Warnings for the Lower Maryland and VA Eastern Shore areas on the ocean side (Ocean city inlet down to Chincoteague and Wachapreaque). Also, the VA nrn neck areas for Lewisetta. Have kept Coastal Flood Advisories for the other areas adjacent to the Ches Bay and the James/York/Rappahannock Rivers. Will likely need to extend these advisories into Fri night and possibly Sat as offshore seas remain elevated and water is expected to struggle to exit the bay for several days. && .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...Flash Flood Watch until 6 AM EDT early this morning for MDZ021>025. Coastal Flood Advisory until 8 AM EDT this morning for MDZ021>023. NC...None. VA...Coastal Flood Advisory until 4 AM EDT early this morning for VAZ076-078-084>086-089-090-093. Coastal Flood Advisory until 1 PM EDT this afternoon for VAZ095>097-523>525. Coastal Flood Warning until 5 AM EDT early this morning for VAZ075-077. MARINE...Small Craft Advisory until 6 PM EDT Saturday for ANZ652-654. Small Craft Advisory until midnight EDT tonight for ANZ656-658. Gale Warning until 4 AM EDT early this morning for ANZ650. Small Craft Advisory until 7 AM EDT this morning for ANZ630- 634.
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&& $$ SYNOPSIS...AJZ/SAM NEAR TERM...ESS SHORT TERM...AJZ/SAM LONG TERM...LSA AVIATION...AJB/SAM MARINE...TMG/JEF TIDES/COASTAL FLOODING...

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