Area Forecast Discussion
Issued by NWS Blacksburg, VA

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609 FXUS61 KRNK 211935 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 335 PM EDT Sat Apr 21 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 SUNDAY/... As of 205 PM EDT Saturday... High pressure will be extended from the eastern Great Lakes into the mid-Atlantic tonight-Sunday, while upper low moves across the southern Plains toward the lower MS Valley. Upper flow from the west should allow high clouds to increase overnight into Sunday. With a canopy of higher clouds from time to time tonight, low temps will be milder with mostly lower to mid 40s, though some 30s in the valleys of Southeast WV not out of the question. Still no frost/freeze worries tonight. Sunday, upper low will be in Arkansas, while 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 /SUNDAY NIGHT 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 /20Z SATURDAY THROUGH THURSDAY/... As of 105 PM EDT Saturday... Going to stay VFR this period with increasing high clouds overnight into Sunday morning. Expect mainly a light southeast wind, but could be variable in direction at times, though speeds should stay under 7 knots. High confidence through the period. Extended Aviation Discussion... Clouds will thicken and lower by late Sunday into Sunday night in advance of an approaching low in the Lower Mississippi River Valley. However, cloud bases should remain VFR until deeper moisture arrives Monday. SCT MVFR showers are possible in southern Virginia and northern North Carolina Sunday night with rain becoming widespread across the Mid Atlantic region on Monday. MVFR/IFR ceilings and visibilities are expected Monday night and Tuesday due to widespread rain and an upslope southeast wind. SCT MVFR showers will continue into Wednesday. && .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...WP SHORT TERM...DS LONG TERM...DS AVIATION...AMS/RCS/WP HYDROLOGY...DS

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