Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 171210 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 710 AM EST Fri Nov 17 2017 .SYNOPSIS... High pressure builds back into the area through tonight. The front slides offshore Saturday with a cold front approaching the region from the west late. The cold front moves across the area Saturday night into Sunday morning. && .NEAR TERM /THROUGH TONIGHT/... Latest weather analysis features 1025+mb over the Ohio Valley and Great Lakes. Aloft, upper trough is in the process of ejecting E-NE offshore of New England this morning, with broad upper level ridging pushing across the eastern half of the CONUS. To the west, a potent upper shortwave is noted coming ashore along the WA/OR coastline. This feature will eventually carve out a deep shortwave trough that will traverse the intermountain west to the central Plains Fri/Sat...reaching the coast Sat night and Sunday. More on this system in the short term discussion below. Mostly sunny today, as cool/dry 1025+mb surface high pressure builds overhead from the central Appalachians/Ohio Valley this afternoon through tonight. Not quite as mild as yesterday, with highs in the mid to upper 50s over much of the area. Surface high slides offshore tonight and Saturday. Apart from some increasing thin cirrus, sky should remain mostly clear/clear overnight with early morning lows Sat morning in the mid 30s inland to the low/mid 40s coast. && .SHORT TERM /SATURDAY THROUGH SUNDAY/... Milder on Saturday in stronger return flow. Compressional warming out ahead of next (stronger) cold front will drive maxima well into the 60s...to around 70 across SE VA/NE NC, with low to mid 60s across northern zones. Quick dewpoint surge with warm front lifting across the area Sat aftn/night. Low level S-SW flow quickly increasing PW values into the 1"-1.25" range after 00z/Sun. Convective parameters remain weak, owing to the timing and the progressive system. And therefore will keep thunder mention out of the forecast. That said, a brief window for pops coincident with narrow axis of low-level convergence/forcing ahead of the frontal passage Sat evening (west) into late Saturday night/early Sunday morning (east of I-95). Will carry likely PoPs (55-70%) most areas Sat night, mainly west of RIC metro before midnight, then RIC Metro/south central VA by 06z/Sun, reaching the coast before sunrise Sun morning. Lows Saturday night in the 40s to low 50s. Some concern for gusty winds with and in the immediate wake of the frontal passage. Gusts to 30-40 mph (higher possible MD counties and northern neck) possible Sat night and Sunday morning. Cold front pushes offshore on Sunday. After some lingering clouds east (morning shower possible over coastal areas), subsidence behind the front should result in a mostly sunny sky with winds diminishing as gradient slackens. Still, breezy and cooler with highs in the 50s...to near 60 SE coast. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... High pressure is expected to build into the region Monday before moving offshore during the day on Tuesday. Cold air aloft and a northwest flow will lead to a chilly day on Monday with highs struggling to climb out of the upper 40s. Lows on Monday night will dip down into the lower 30s away from the coast and upper 30s to near 40 at the coast. Temperatures warm on Tuesday due to southerly flow on the backside of the high. Highs on Tuesday will range from the upper 50s to the lower 60s. A dry cold front is expected to drop into the region late Tuesday night. High pressure builds back into the region Wednesday through Thursday which will allow for continued cool but dry conditions. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... High pressure building over the region through the 12z TAF period and through tonight, will bring dry wx/VFR conditions across area terminals through Saturday evening. Clouds slowly increase late Saturday, then thicken/lower ahead of the next cold front to approach the region Saturday night. That front crosses the local area early Sunday morning, a brief period of sub-VFR cigs and rain showers are possible with the frontal passage late Saturday night into Sunday morning, clearing Sunday morning as cold high pressure builds back into the region, bringing a return to VFR conditions. A gusty NW wind is expected immediately behind the front on Sunday morning/aftn. High pressure gradually slides off the Southeast coast Monday and Tuesday. && .MARINE...
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Update...SCA for rest of rivers and Currituck Sound allowed to expire. Winds are trending downward this morning and will continue in this direction through the rest of today. Previous discussion...Cold front located south of the area early this morning. One last surge in NW winds occurring now with speeds generally 15-25kt and gusts around 30kt over coastal waters btwn 10-20NM. Seas 4-6ft. Waves 3-4ft. Winds taper off shortly after sunrise due to loss of typical morning diurnal effects. Seas subside to 3-5ft north and 3-4ft south by this aftn; waves subside to 2-3ft. Gale warning north of Parramore Island has been converted in SCA. Ongoing headlines are on track to expire at designated times. In addition, cancelled SCA for York and Rappahannock rivers. High pressure builds into the region from the west today and tonight with benign conditions expected. Winds tonight will be light and variable aob 10kt. Seas/waves 2-3ft. High pressure slides off the Carolina coasts Sat as a strong cold front approaches the region. The pressure gradient btwn these features will tighten up through the day, and breezy SW winds 15-25kt should be common by the aftn. Seas build to 4-5ft north of Parramore Island (waves 3-4ft) by aftn. While solid SCA conditions are anticipated for Sat through Sun night (SW winds 15-25kt Sat/Sat night; NW 15-25kt Sun/Sun night), the arrival of the cold front has now slowed (based on 17/0000Z model data) and may not cross the waters until Sun morning. This change is important in determining the possibility of gale force gusts over the coastal waters. If the front slows down by 3-6 hours, then the arrival of colder air would delay the onset of possible gale conditions (especially since gales are more difficult to achieve in a SW winds/warm air advection set-up). Confidence not high enough to issue a gale watch, however this is certainly a time period to watch closely for adverse conditions. Seas to build to 5-7ft on average Sat night into Sun morning before subsiding. Waves build to 4-5ft Sat night...then subside to 3-4ft Sun/Sun night. A secondary surge of colder air arrives Sun night into Mon morning and will likely extend solid SCA/possible gales during this time. High pressure builds across the Southeast States Sun night through Mon night with benign conditions anticipated during this time. The high slides off the Southeast Coast on Tue with sub-SCA conditions persisting.
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&& .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until noon EST today for ANZ630>632-634- 654-656-658. Small Craft Advisory until 4 PM EST this afternoon for ANZ650- 652.
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&& $$ SYNOPSIS...MAM NEAR TERM...MAM SHORT TERM...JDM/MAM LONG TERM...AJB AVIATION...AJZ/JDM/MAM MARINE...BMD

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