Area Forecast Discussion
Issued by NWS Blacksburg, VA

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764 FXUS61 KRNK 200601 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 201 AM EDT Sun May 20 2018 .SYNOPSIS... A frontal boundary across the region will slowly lift north as a warm front today. Several waves of low pressure will ride north along the front acting to enhance showers and thunderstorms. Warm and humid conditions will continue this weekend. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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As of 1215 AM EDT Saturday... ...FLASH FLOOD WATCH HAS EXPIRED... The Flash Flood Watch for portions of North Carolina and Virginia has expired. Isolated pockets of heavy rain will continue for the next hour or two. The threat for widespread flash flooding has ended tonight. Please continue to monitor for river flood warnings and localized flooding problems and heed remaining road closures.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH MONDAY NIGHT/... As of 315 AM EDT Saturday... Though important mesoscale details remain rather elusive in the period, which limits forecaster confidence on specific details to no better than moderate, large-scale regime favors a continuation of the wet weather pattern we`ve been stuck in of late. It`s unclear we`ll see the high rain rates as over the last couple days. Given the state of the soil moisture conditions, rivers, and south-to- north rain training on the eastern end of another subtropical low coming out of the eastern Gulf suggest that a renewed flood threat may again be a focal point in this period, at least in a localized sense. Overall synoptic regime will remain generally little changed, as a continued influx of subtropical moisture looks to resume again as another upper low moves up from the eastern Gulf. Meanwhile early in the short-term period (Sunday night into Monday), the westerlies which have been largely to our north will begin to buckle somewhat more to the south into the mountains of eastern WV into the northern/central Blue Ridge, with ill-defined/subtle mid-level vort maxes in this mid-level westerly regime serving as foci for additional showers and thunderstorms. Sunday night and early Monday, there`s some indication in the 12z guidance of a weakened convective complex as the stronger westerlies build south. Storms may again fire on remnant outflow from this overnight activity on Monday afternoon. Shear isn`t particularly strong suggesting disorganized pulse multicells are most probable if convection develops, but there is enough progged modest to moderate instability amid filtered sun to partly cloudy skies to offer a window of isolated to scattered strong storms north of Route 460. SPC does show a Marginal Risk/5% severe probability for this general area Monday. Any threat likely wanes with the diurnal cycle. Monday night through Tuesday night look to feature continued chances for showers and embedded thunder, with SREF showing PWATs of 1.25-1.5" advecting north/north-northeast against the Blue Ridge. Convective parameters are lower for Tuesday given abundant cloud cover, PoPs are toward the lower Likely range. From Sunday night through Tuesday, shown areal-average rain amounts between a half to an inch of rain, with localized potential for more in more persistent downpours that may unfold. Given partly to mostly cloudy skies governing much of the period, kept temperatures on the lower end of the guidance envelope on the highs, and milder side of guidance for the lows. Generally highs mid 70s to mid 80s and lows in the 60s, with a continued somewhat humid feel (dewpoints in the 60s). && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 315 AM EDT Saturday... Global models point to Wednesday and Thursday as days with a relative minimum in rain chances, as a high pressure area over New England wedges down the Appalachians. This will likely shunt the subtropical plume of moisture further to the south and allow for a couple of somewhat drier days. Temperatures begin to trend somewhat more seasonal for the midweek period. An early look at Friday and the Memorial Day weekend looks unsettled with a potential return the chances for rain showers and thunderstorms back into our area. This is indicated by most global models as a cold front slowly sags south from the Great Lakes/mid- Mississippi Valley, with another potential surge of moisture of subtropical origin returns from the south. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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As of 200 AM EDT Sunday... MVFR/IFR SCT to BKN clouds will continue east of the mountains this morning. West of the mountains outside of the showers and thunderstorms ceilings were VFR. isolated showers and thunderstorms will move east across the region early this morning. Plenty of low level moisture and light winds will result in areas of fog this morning. As weak high pressure builds over the Mid Atlantic region today, moisture will decrease. Southwest Virginia, northwest North Carolina and southeast West Virginia will become VFR by late morning, with medium confidence in this timing. Diurnally driven isolated MVFR showers and thunderstorms will develop this afternoon into tonight. Medium confidence in ceilings, visibilities and winds during the taf period. .Extended Aviation Discussion... Another weak cold front will bring increasing coverage of showers and thunderstorms again on Monday. Scattered MVFR showers and thunderstorms are possible Monday night into Tuesday with another round likely Wednesday. Conditions are expected to improve later in the week.
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&& .HYDROLOGY... Update as of 1000 AM EDT Saturday... A flood warning has been issued for the Roanoke River at Brookneal, and the flood warning for the Dan River at South Boston has been upgraded to moderate flood stage. Previous discussion... A Flash Flood Watch is in effect portions of forecast area until Midnight for the potential for heavy rains. The Flood Warning continues for the following rivers in North Carolina and Virginia... Dan River near Danville Dan River at Paces affecting Halifax County Dan River at South Boston affecting Halifax County The Flood Warning continues for the following rivers in Virginia.. Roanoke (Staunton) River at Randolph affecting Charlotte and Halifax Counties Several days of heavy rainfall with amounts ranging from 2 to as much as 6 inches across parts of the Roanoke and Dan River basins will cause flooding along the river in parts of Rockingham, Pittsylvania, the City of Danville and downstream in Halifax County. Flash Flooding is a main concern until Midnight, as well as flooding on small creeks, streams, and smaller rivers as a result of bands of tropical rain showers and thunderstorms that are expected across the area. Added heavy rain will likely cause more flooding especially along and east of the Blue Ridge this afternoon into this evening as bands tend to train across the region. These bands will be very efficient rainfall producers with rates of 2 inches or more per hour possible. This could result in another 1 to 3 inches of rain in spots. Given such wet antecedent conditions, it wont take much additional rain to cause at least minor flooding. && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...None. NC...None. WV...None.
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&& $$ SYNOPSIS...JR NEAR TERM...JR SHORT TERM...AL LONG TERM...AL AVIATION...AMS/KK HYDROLOGY...JH/KK

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