Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 220546 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 146 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 TODAY/... As of 130 AM EDT Sunday... Surface high pressure was located across far southeast VA/northeast NC with a dry airmass still firmly entrenched across our region with the 00Z RNK sounding showing 0.35" PW values. A canopy of high clouds will continue to drift over our area, especially north of highway 460, keeping low temperatures slightly warmer compared to the past couple of days. However, with such a dry air mass in place and thinning cirrus in the southern portion of our forecast area, brought down low temps a few degrees closer to colder NAM MOS and HRRR guidance values. For Sunday, an upper low will be in Arkansas, while an inverted through extends northeast into KY, from a surface low over MS. Anticipate some lowering and thickening of cloud cover through the day, but no rain. With the clouds and southeast winds have temps at or below mos, with upper 50s to lower 60s NC mountains through the New River Valley into the Alleghanys/Greenbrier, with mid to upper 60s elsewhere. && .SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... As of 245 PM EDT Saturday... This portion of the forecast is looking more and more likely to be one with plenty of wind and plenty of rain. A slow moving upper level low pressure system will progress from the Lower Mississippi River Valley northeast into parts of the Tennessee and Lower Ohio River Valleys. The result for our region will be a developing southeast flow into the region that will be tapping the Atlantic Ocean for moisture, all while an in situ cold air damming wedge develops. The rain, clouds and strong inversion will help keep daytime temperatures on the cool side, and overnight lows near normal for most of the region. The southeast flow will be persistent during this period, and peak in speed at 850 mb around 45 to 50 kts across the mountains Monday night. The area defined by an area of between Bluefield, WV to Marion, VA to Richlands, VA will likely be very gusty as this orientation of a flow yields downsloping, mixing conditions there outside the influence of the wedge. Currently, forecast gusts in this area, and neighboring higher terrain, are in the range where a wind advisory would be warranted, but we are too early for any type of official product at this point. However, the concern will be mentioned in the Hazardous Weather Outlook. Another concern during this portion of the forecast will be the potential for localized flooding Monday through Tuesday night and then . Please see the HYDROLOGY section of this discussion for details. The precipitation will start to exit the region Tuesday night, but not by a significant amount. Rather than having the region with categorical POPs, we will start trending to more regions of likely and chance POPs as the upper low continue a northern trek into the Great Lakes region. This will help start veering winds more southerly, and we will start to lose the strong Atlantic moisture fetch. && .LONG TERM /WEDNESDAY 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 /06Z 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...WP NEAR TERM...JR/PH/WP SHORT TERM...DS LONG TERM...DS AVIATION...RCS HYDROLOGY...DS

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