Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 220706 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 306 AM EDT Sun Apr 22 2018 .SYNOPSIS... High pressure will stay anchored from the Great Lakes to the Middle Atlantic through Sunday night, while low pressure shifts from the southern Plains and Texas to the lower Mississippi Valley. This low will then track to the North Carolina and Virginia coast by Wednesday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 300 AM EDT Sunday... For today, an upper low will be in Arkansas, while an inverted trough extends northeast into Kentucky, from a surface low over Mississippi. Meanwhile, over the Mid Atlantic, two surface high pressure systems will join forces to keep rain out of the area for one more day. We will see an increasing in high clouds as moisture from the upper low rides over the merged surface ridge. Despite thickening high clouds, temperatures across the mountains will be slightly warmer than normal with highs in the mid to upper 60s, with the exception of higher ridges being in the upper 50s. The foothills and piedmont counties will experience slightly cooler than normal temperatures today. With a cool light southeast breeze, highs in the east will range in the upper 60s to lower 70s. Clouds will continue to lower tonight as the upper low moves over eastern Tennessee and closer to the area. Saturation of the environment will take some time as the dry high over the Mid Atlantic holds off rain from entering the area until later Monday morning. Some light rain from southeast upslope flow may fall by sunrise, but the bulk of the heavier rain is not scheduled until later in the day. With moisture continuing to pump into the region overnight, temperatures will remain mild with lows ranging in the 40s.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY/...
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As of 150 AM EDT Sunday... Upper low becomes vertically stacked and drifts from the Tennessee Valley into the Ohio Valley during this time frame. At the surface a triple-point low forms Tuesday then moves northeast to the Virginia coast Tuesday night and Wednesday. Upper pattern is somewhat blocky with a ridge preventing much eastward movement of the upper low. But timing of precipitation similar to last several runs with steady rain filling in from southwest to northeast across southwest Virginia, southeast West Virginia and northern North Carolina on Monday. This a favorable scenario for a classic upslope heavy rain event along the Blue Ridge and foothills to the east. With deep and very strong isentropic lift and upslope bringing precipitable water values around 1.5 inches into the region, anticipate 0.5 to 1.0 inches of rain every 6 hours from 18Z/2PM Monday through 18Z/2PM Tuesday. Will stay on the cool side of guidance for maximum temperatures on both Monday and Tuesday due to very limited solar insolation and a strong in-situ wedge. Once the surface low reaches the Virginia coast, surface winds will become west then northwest eroding the wedge. At this time, models have this occuring on Tuesday night. Not particularly meaningful cold air advection behind this system but there may be enough of a downslope component to the wind along with the deeper moisture pulling out of the area, that there may be some breaks in the clouds east of the Blue Ridge on Wednesday. Breaks or not, will still have Wednesday warmer than Tuesday.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... As of 320 PM EDT Saturday... The upper low over the Great Lakes will get caught up in the northern stream jet, open as a wave, and eject eastward with the prevailing flow. Its associated cold front/trough axis will cross our region, and help bring winds around the the northwest Wednesday into Wednesday night. This will result in our winds shifting northwest, and allowing for upslope rain showers across the west, and decreasing coverage of precipitation east of the Blue Ridge. Our weather pattern will remain quite progressive through the remainder of the forecast period. Two additional northern stream shortwave troughs are expected to zip through the region. Each will bring a return of showers to the area, with the greatest concentration across the mountains. The first will be Wednesday night into Thursday. The second will occur either Friday or Saturday, as model agreement isn`t as strong on this second one. Our forecast will reflect the quicker of the two solutions with enough colder air arriving in its wake for the potential for some snow showers along the highest peaks and ridges of southeast West Virginia, south into the Northern Mountains of North Carolina. Temperatures during this portion of the forecast will trend colder with readings by Saturday some five degrees below normal. && .AVIATION /07Z SUNDAY THROUGH THURSDAY/... As of 130 AM EDT Sunday... VFR conditions should be the rule through the forecast period as high pressure is firmly in control. Expect increasing high clouds into tomorrow ahead of a low pressure system moving in from the west. Over the course of the day, increasing moisture will lead to a thicker cloud deck and some lowering. Winds will mainly be light and variable or even calm through the morning hours. During the day, winds should predominantly be from the south-southeast, however speeds should remain under 8 knots. There exists some possibility for light rain in the southwest section of the forecast area late in the TAF period, but should remain far enough away to impact any of the TAF locations. High confidence for VFR conditions through the bulk of the TAF period, with uncertainty growing near the end for small potential to introduce MVFR conditions in the NW NC mountains. Extended Aviation Discussion... Clouds will thicken and lower by sunrise Monday in advance of an approaching low moving across Tennessee. However, cloud bases should remain VFR until deeper moisture arrives later Monday. SCT MVFR ceilings are possible in southern Virginia and northern North Carolina overnight Sunday with rain becoming widespread across the Mid Atlantic region by Monday afternoon. MVFR/IFR ceilings and visibilities are expected Monday night and Tuesday due to widespread rain and an upslope southeast wind. The lower pressure system is expected to track north into the Ohio Valley Wednesday. Low clouds and showers are possible across the mountains. A cold front is forecasted to move across the region Thursday, bringing rain to the entire forecast area. && .HYDROLOGY... As of 310 PM EDT Saturday... Monday through Tuesday night, rainfall amounts over one inch are forecast for the vast majority of the area, with locations along and near the NC/VA border nearing two inches. Along and upstream of the crest of the Blue Ridge, the strong southeast flow will yield strong upslope enhancement with rainfall totals here possibly in the two to three inch range with some isolated spots nearing four inches. Flooding will be concern in the near term, especially along the crest of the Blue Ridge within our forecast area, and across parts of Southside Virginia and neighboring sections of the Foothills and Piedmont of North Carolina. In the slightly longer term, Tuesday into Wednesday, the GEFS based SERFC Ensemble River Forecasts is offering a more likely than not chance of some minor flooding along the Dan River as runoff from this event travels downstream. While this statement does not constitute an official forecast, it is a heads-up for an above average potential for flooding within this river basin. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RCS NEAR TERM...RCS SHORT TERM...AMS LONG TERM...DS AVIATION...RCS HYDROLOGY...DS

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