Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 250600 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 200 AM EDT Tue Apr 25 2017 .SYNOPSIS... Wet and unsettled weather will continue tonight into Tuesday, as a slow moving area of Low pressure center moves from the southern Appalachians to along the South Carolina coast by Tuesday morning and northeast along the coast Tuesday afternoon. High pressure builds into the region late Tuesday night and Wednesday. && .NEAR TERM /THROUGH TODAY/... As of 1153 PM EDT Monday...Refreshed the PoPs/Wx grids to account for current radar and observational trends, and adjusted QPF amounts slightly, increasing them in the Southside and NC Piedmont by up to an additional tenth of an inch, while reducing them west of the Blue Ridge. Pronounced stream of moisture/rainfall currently on radar across much of the eastern Carolinas then trailing back westward into the Piedmont Triad/Triangle areas in North Carolina and into our southern and eastern counties. Rainfall in our area has been comparatively lighter to that taking place in the Carolinas, with recent 3-hourly amounts of around 0.25-0.35" in the Southside/northern NC Piedmont areas. Feel that this area still has the best chance at seeing brief periods of at times heavier rains as the band begins to pivot north-northwest. More light to moderate rainfall to extend from the Piedmont to the Blue Ridge foothills. Along and west of the Blue Ridge, only very light rain is expected being more further removed from the deeper moisture shield. No other changes made with this update. Previous near-term discussion issued at 405 PM follows... Flood watch has been expanded east of the Blue Ridge Mountains into Tuesday morning. An easterly upslope flow will enhance the rain tonight especially east of the Blue ridge mountains. The rain will be heavy at times into tonight. This area has the greatest chance for the redevelopment of heavy showers and could aggravation and/or maintenance of existing flooding. Upper divergence to the northeast of the mid level low will help generate efficient rain. Current, WSR- 88d images showed an area of convection across central North carolina lifting northward into our region. Additional rainfall of 1 to 2 inches is possible mostly in the east, on top of what has already fallen or saturated ground. Rainfall totals will be lighter in the western mountains. Vertically-stacked cyclone will slowly move east tonight into Tuesday. Moisture plume on the eastern periphery of the cyclone, associated with PWAT values of up to 1.3 inches will continue to be drawn back westward, supporting a continued period of rain particularly for the central Virginia Piedmont and into the Southside of Virginia. Weak forcing elsewhere across the CWA supports periods of light showers into Tuesday morning. As the low center pulls away, rain chances will decrease from west to east on Tuesday. CAD wedge will continue tonight holding temperatures generally from around 40 degrees in the mountains to the lower 50s in the Piedmont. A slow erosion of the wedge will allow temperatures to rebound into the lower 50s in the mountains to near 60 degrees in the Piedmont. && .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... As of 406 pm EDT Monday... Closed low continues to slowly fill and lift northeastward up the Mid Atlantic coast Tues night into Wednesday, as modest upper ridge builds over the central Appalachians through Wednesday. This evolution may tend to be a bit slower than model forecasts and thus some uncertainty about how long to leave some scattered showers across the northeast portion of the forecast area Tues evening. Held on to some low chance to slight chance pops through midnight for now but for the early evening time frame may have to increase this if the low indeed proves stubborn to rotate on out. More confident that at some point over night any showers, as well as clouds, will begin to break up and move east of the area. Clearing skies across all but the far northeast and light winds, combined with saturated ground, will lead to fog development in many areas overnight into Wednesday morning. Possibility of some dense areas but for now included generic patchy and areas of fog until we get a better handle on clearing potential. Wednesday under the ridge it is much drier and we finally warm up significantly under mainly clear skies. Guidance giving some lower 80s from Roanoke Valley into the Piedmont but thinking is that a percentage of the solar energy will go into evaporation of the saturated ground so high temps likely to be a few degrees cooler than this. Went with mid to upper 70s most locations...except for highest ridges in the upper 60s. Upper trough and weakening surface cold front approach late in the day Thursday and there appears to be enough lower level moisture with increasing southerly low-level winds, which will add some weak upslope along ridges, and plenty of moisture still in the ground, to warrant at least a slight chance for showers and thunderstorms as far east as the Blue Ridge, even though it is fairly dry aloft. With scattered convection closer to front possibly sneaking in to far west by late in day will include this area with chance pops, lingering into the evening and overnight as this weak boundary tries to move through Appalachians, but dissipates at the same time. Thursday should be slightly warmer ahead of front under warm advection and in part due to the ground not being quite as saturated as the previous day, so went pretty close to guidance in the low to mid 80s in many locations. Friday may end up being a dry day with airmass behind the dissipating boundary somewhat drier and still very warm, and no obvious signs of any lingering convergent zones, but there is some limited instability and some of the guidance suggests a shower or two is possible over the higher terrain. Kept a slight chance pop then from the Blue Ridge west, but we may eventually be able to lower this. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 355 pm EDT Monday... Upper ridge will attempt to hold on through the weekend for continued well above normal temperatures. With low level moisture combined with these warm temperatures, this will result in just enough instability for the possibility of isolated to scattered mainly mountain diurnal convection. Models hinting at potential for some warm frontal showers just to our west on Saturday so will need to keep a an eye on that as we get closer. Otherwise, digging trough to the west approaches and models in general agreement that associated cold front approaches late on Monday and should be quite a big stronger than the one late this week. If the front moves through during max heating Monday afternoon will need to watch potential for severe weather as well, and this will be a fairly fast moving system. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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As of 200 AM EDT Tuesday... Poor Flying conditions will persist again today as slow moving upper level cutoff low slowly meanders across the eastern Carolinas. This Low is forecast to drift northeast and away from the area Wednesday. Until then, expect predominantly low IFR ceilings and areas of rain and drizzle. The tight pressure gradient around the area of low pressure will also result in a strong northeasterly low level jet, which will favor an extended period of low level wind shear, these winds persisting until the low moves off the Mid-Atlantic Coast later today and tonight. Extended Aviation Discussion... Better flying wx is expected for the second half of the week, though another front may bring scattered MVFR showers/storms toward late Thursday in the mountains. Drier and much warmer weather will return for Friday and Saturday.
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&& .HYDROLOGY... As of 415 PM EDT Monday.... Storm Totals Accumulations for the 72 hours from 8AM Friday through 8Am Monday were in the 2 to 6 inch range roughly south of a line from Bluefield West Virginia to Lynchburg VA. Runoff from this rainfall had resulted in small stream flooding with numerous roads and low water crossings closed due to flooding. Many trees fell due to the saturated ground and several minor rock and mud slides were reported. All of this runoff has now flowed into sections of the New, Roanoke, Yadkin, and Dan River Basins. Multiple River Flood Warnings were in effect. Additional rainfall tonight will be heaviest in the eastern upslope areas of the Virginia Foothills and piedmont. The river forecasts will be updated as additional information comes in from the River Forecast centers. A Flood Watch remains in effect west of the Blue Ridge until 8PM. The Flood Watch along and east of the Blue Ridge was now in effect through 8AM Tuesday. && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...Flood Watch until 8 AM EDT this morning for VAZ022>024-032>035- 043>046-058-059. NC...Flood Watch until 8 AM EDT this morning for NCZ003>006-019-020. WV...None.
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&& $$ SYNOPSIS...KK NEAR TERM...AL/KK SHORT TERM...SK LONG TERM...SK AVIATION...PM HYDROLOGY...AMS

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