Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 240500 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 100 AM EDT Thu May 24 2018 .SYNOPSIS... High pressure noses down from the Ohio Valley and Mid Atlantic late tonight into Thursday, then moves off the coast by Friday. Warmer air returns on the backside of the high Saturday along with increasing humidity and the threat for more rain. && .NEAR TERM /THROUGH TODAY/... As of 724 PM EDT Wednesday...An already limited convective threat spatially continues to gradually wane early this evening. Some scattered storms with brief downpours and gusty outflow still remain possible through 800 PM in Wilkes and Yadkin Counties, where moderate instability still exists in proximity to synoptic cold front. A number of higher-resolution solutions also point to re- development of scattered showers or storms from Charlotte County southwest through eastern Pittsylvania and Caswell Counties over the next hour or two. This potentially may stem from an outflow boundary now racing northwestward from earlier severe storms in the Norfolk area. Thunderstorm threat indicated the most aggressively by the 18z 3-km NAM, which had handled the earlier storms in central Rockingham County the best, with some hints of developing in recent runs of the HRRR. Presently pretty unimpressive thus far in these eastern counties, but will continue to watch carefully. So all told, I made some small tweaks to PoPs through 02z to carry scattered mention of thunder from Charlotte to Caswell Counties, while tapering PoPs down to all dry elsewhere. Threat of thunder should end after 02z as boundary layer stabilizes and northerly flow advects deep- layer dry air from large high over the Ohio Valley. All areas dry before midnight. Aforementioned high pressure ridges into the region after midnight, allowing for northerly winds to slacken. In spite of dry advection/falling dewpoints, with how wet the ground is, we should have favorable hydrolapse profiles for patchy fog, best chance in the western mountains toward sunrise but also potentially in the Piedmont. Visibility guidance off the NAM and HRRR don`t suggest the potential but I`m not convinced it`s recognizing how damp the soils are. No changes to low temps attm. With drier air, should be a more comfortable night than experienced recently. Previous near-term discussion issued at 135 PM follows... A weak trough moved over the mountains this morning and has stalled stalled over the foothills this afternoon. Behind this trough are slightly drier conditions with modest CAPE values around 1000 J/KG. Under afternoon heading and with an approach cold front, a few showers and thunderstorms are possible along and west of the Blue Ridge this afternoon. Ahead of this surface trough, PWATS are around 1.50 inches and CAPE values 1500-2500 J/KG. As the cold front crosses the mountains this afternoon, scattered showers and thunderstorms are expected across the piedmont and along the VA/NC border south. A few of these showers could become strong to severe and produce heavy downpours late this afternoon into the evening hours. Since the ground remains wet, there is a concern for flooding today. However, steering currents are faster than the past couple of days and heavy rain from stronger storms should remain brief. The main threat into this evening will be damaging straight-line winds and hail. SPC has a marginal risk roughly from a line east from Buckingham VA south to Reidsville, NC. Drier air shifts toward the mountains of WV/VA north of Bluefield to Roanoke this evening then slowly edges southward overnight, but still some slowness in frontal boundary may keep the southeast in the soupy airmass one more night. Most of the convection will wane by midnight. Fog will form in the deeper valleys by dawn Thursday. Tonight`s lows will be a touch cooler over the mountains, but still 10 degrees above normal, from the lower 50s in the Greenbrier Valley, to mid to upper 50s rest of the mountains, surging up to around 60 Roanoke to Lynchburg north, and in the lower to mid 60s southeast to the NC foothills. Highs for Thursday will be closer to normal with 70s west of the Blue Ridge to lower 80s east. && .SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/... As of 230 PM EDT Wednesday... Weak residual front well to the south will dissipate by Friday as high pressure remains in place under shortwave ridging aloft. However a gradual return to weak southerly flow aloft should bring moisture back around the surface high espcly southwestern sections by the end of the week. Per latest model trends looks like any showers Thursday night will be quite isolated and closer to the NC mountains before expanding a bit, mainly west of the Blue Ridge Friday, as the flow around the primary high offshore deepens a bit. Expect most showers to fade with loss of heating given lack of support Friday night with increasing coverage across the area from west to east Saturday with the combination of heating/moisture and deeper southwest flow. Thus will have likely pops far west Saturday with chances elsewhere similar to the latest SREF model ensemble. Should again see things diminish Saturday night with loss of heating, but perhaps lingering longer into the night with more moisture around so kept in chance pops for now. High temps mostly upper 70s to mid 80s, except perhaps a little warmer east Saturday under warming aloft despite possible offset by late day clouds/showers. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 130 PM EDT Wednesday... Rather wet pattern looks to return through the period as tropical moisture heads back north ahead of low pressure across parts of the Gulf states and added weak upper troffiness dropping in with a surface front to the north. Pending future evolution of the tropical low to the south, appears will see deepening south/southeast flow take shape by early next week with an influx of both Gulf and Atlantic moisture around the rather large mid level circulation heading out of the Gulf. This should set the stage for at least more diurnally driven convection late in the weekend espcly mountains, and across the region through midweek. However decent surface high pressure building in from the north next week and potential for more organized convection to the south may tend to at least slow down northward expanse of deeper moisture which could mean less coverage at times. Thus plan to have higher chance to likely pops during heating and overall lower chances at night unless the core of the tropical juice ends up farther north/northeast. This could also mean some heavy rain producers at times given such high forecast Pwats of better than 1.5 inches. Otherwise will be turning more humid under varying degrees of clouds with highs mostly 70s mountains to low 80s east and lows mostly in the muggy 60s. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... As of 1259 AM EDT Thursday... TAFs will be VFR, thru the period, though potential for at least MVFR mist/fog at Blacksburg, ans Lewisburg between 09-12z. Visibility forecast is of low confidence given falling dewpoints, but the potential for IFR or lower fog isn`t out of the question. High confidence in ceilings/winds through the TAF period, moderate to low confidence on visbys in fog. High confidence in VFR visbys Thursday. .Extended Aviation Discussion... VFR Friday. Tropical like moisture streams back north as a warm front moves through Saturday with a return to showers/storms and potential sub-VFR conditions and heavy rain thru the holiday weekend. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RCS/WP NEAR TERM...AL/RCS SHORT TERM...JH LONG TERM...JH AVIATION...AL/RCS/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.