Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 201403 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 1003 AM EDT Fri Jul 20 2018 .SYNOPSIS... High pressure will sit along or just off the northern New England coast today into this evening. Low pressure will track northeast along the Mid Atlantic coast tonight and Saturday, bringing increasing chances for rain. An unsettled pattern is then expected to persist through at least the middle of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... As of 420 AM EDT Friday... Early this morning, sfc high pressure was cntrd just off the New England coast. The high will maintain dry wx acrs the area thru this aftn. Meanwhile, a potent upper low moves E from Wisconsin twd Michigan, but mostly remains un-phased with a weaker upper trough along the SE U.S. coast. This feature will enable an old sfc trough/boundary to develop into a more pronounced sfc low along the SC coast during today. The sky will start out partly to mostly sunny everywhere this morning, then the sky will become mostly cloudy this aftn into NE NC. Will maintain some 20-30% PoPs mainly confined to NE NC after 18Z, as sfc low pressure starting to lift NE along the SC coast, brings deeper moisture much to the north of that low. Highs will mainly range into the mid 80s, except lower 80s near the coast. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... As of 420 AM EDT Friday... An active period begins tonight, as models do agree on a sfc low pressure area lifting NNE along the coast tonight into Sat night. There area timing differences with the track of the low with the GFS the fastest, and the NAM the slowest. The ECMWF is in between those two and will favor it with the current fcst Pops. Thus, confidence is higher that deep moisture will overspread ESE zones later tonight into Sat morning, and reaches into the VA nrn neck and eastern shore through at least Sat aftn, with likely PoPs expected. Chance PoPs will be maintained farther inland (W of I95) where the consensus is for less in the way of deep moisture and lift. Still not particularly unstable, so mainly just showers with a slight chance for tstms tonight through Sat aftn. Highs on Sat have been trended down a few degrees given some easterly flow and low clouds for at least some of the day. For now, have highs into the mid 80s far S, to the upper 70s/lower 80s N (though it could end up even cooler if rain persists through the aftn). Have PoPs trending down in the late aftn into the evening for much of the area, as the sfc low lifts just off the VA ern shore and MD coasts twd New Jersey, with the next wave of activity more convective in nature arriving from the Mtns. PoPs will be 40-60% in some of the Piedmont Sat evening/chc PoPs elsewhere. More humid Sat night with lows mainly in the upper 60s to lower 70s. Consensus position of the upper trough Sun/Sun night is over the OH Valley swrd into ern TN and nrn GA, with deep moisture into the local area and diffluent zone aloft. Have 40-60% PoPs acrs the region during this time. Partly to mostly cloudy with highs on Sun in the upper 80s SE, to the lower 80s W/NW. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 330 PM EDT Thursday... Still expecting daily chances for showers and thunderstorms throughout the Mid-Atlantic during the extended period. An upper- level low will be located over Indiana/Ohio/Kentucky Sunday evening. This feature will slowly drift south/southwestward, and will be located along the Gulf Coast by midweek. With SE flow at the surface and southerly flow aloft, ample moisture will be in place on Monday (GFS forecast PW values are around 2.0"). Coupled with the upper low nearby, expect scattered to widespread showers and thunderstorms (with coverage peaking during the late afternoon hours) on Monday. Given this setup, went ahead and increased PoPs to ~60% for the bulk of the CWA. T-storms will still be possible on Tuesday and Wednesday, as we will still be under southerly flow aloft (with SE flow near the surface). Coverage will likely be highest over the western third of the CWA, but scattered (diurnally-driven) showers/t-storms will be possible throughout the area. Shower/t-storm chances continue through Thursday, with the 500mb through axis approaching the region from the west as a large upper low moves eastward across southern Canada. Went with PoPs around 60% over the far western CWA during the day on Tue/Wed, with 40-50% PoPs elsewhere. We continue to monitor the potential for some areas to receive several inches of rain next week. Not much in the way of temperature changes from Monday through Thursday. Highs will only be in the mid to upper 80s with the daily shower/t-storm chances. Expect overnight lows in the low-mid 70s. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... As of 200 AM EDT Friday... VFR conditions will prevail at all TAF sites today into early this evening, as sfc high pressure sits just off the nrn New England coast. Winds will be ESE 10-15 kt acrs SE VA/NE NC late this morning thru this aftn, with winds 10 kt or less elsewhere. VFR conditions should continue at RIC and SBY this evening, with increasing chc for showers over Srn/SE VA (PHF/ORF) and esply NE NC (ECG), as weak low pressure lifts up along the SC and NC coast. Increasing moisture/pcpn chcs then for late tonight thru Sat aftn at all TAF sites (with lower cigs and vsbys), as low pressure tracks nwrd along or just off the Mid Atlc coast. Best chcs for widespread showers and possible tstms will be mainly near the coast, but SCTD showers and an isolated tstm will be possible area-wide on Sat. An unsettled pattern looks to persist Sun-Tue with SCTD to numerous showers/tstms expected (highest coverage focusing in the aftn/evening). && .MARINE... As of 415 AM EDT Friday... High pressure off the New England coast will provide one more benign day over the area waters with east to southeast winds of 10 - 15 KT. But as the area of high pressure retreats the two low pressure systems will affect the area for the weekend. The first low is a coastal low that should form off the GA coast this afternoon and lift northward along the coast tonight and pass over eastern portions of Delmarva on Saturday. This low will enhance the easterly flow to near SCA levels, but expect with the longer fetch that the seas will be more than 5 FT on the ocean and 4 FT on the southern Bay. Now the timing on this low is still in question with the 00z GFS the fastest and the 00z NAM the slowest. So have split the timing difference with the ECMWF and have the low near the NC/VA border around 12z and out of the area by 00z with the flow turning from E ahead of the low to SW by Sat evening. Have raised SCA flags mainly due to the increase in the seas but winds appear to be near SCA levels as well. Did leave the northern two Bay zones and the river zones out at the moment as the winds appear to be marginal and with the uncertainty on the strength and timing of the low not as confident for this zones along with the hazard being a 3rd period advisory. The coastal low will lift away from the area on Saturday night with conditions beginning to settle down so will have the SCA go away from south to north during the overnight hours. The second low that is moving from the Great Lakes today into the Ohio Valley by Sunday will increase the flow again out of the south Sunday afternoon and into early next week. While the winds generally remain below SCA levels, the persistent southerly to southeasterly flow the will develop as the surface low settles into the Tennessee river valley and the strong Bermuda high that develops will help push seas up to SCA levels so additional headlines may be needed Sunday night into early next week. && .EQUIPMENT... KDOX radar is inoperable due to a failure of the motor. All parts will not arrive until Tuesday July 24. Return to service is unknown at this time. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory from 8 AM to 4 PM EDT Saturday for ANZ632- 634. Small Craft Advisory from 8 AM Saturday to 1 AM EDT Sunday for ANZ654-656-658. Small Craft Advisory from 8 AM Saturday to 4 AM EDT Sunday for ANZ650-652. && $$ SYNOPSIS...TMG NEAR TERM...TMG SHORT TERM...LKB/TMG LONG TERM...ERI AVIATION...TMG MARINE...ESS EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.