Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 290525 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 125 AM EDT Wed Mar 29 2017 .SYNOPSIS... A cold front will slide east across the region early this evening before exiting offshore overnight. High pressure then works in from the north later tonight into Thursday behind the front. Another storm system moves in from the southwest with showers and storms by the end of the week. && .NEAR TERM /THROUGH TODAY/... As of 945 PM EDT Tuesday... Analysis of the latest HRRR and RAP13 guidance, and trends on regional radars, prompted an extension of isolated showers across parts of western Greenbrier County and Summers County West Virginia by a couple of hours overnight. Still expect a quick conclusion of the precipitation after midnight or 100 AM EDT. Adjusted cloud cover accordingly to account for this increased duration of isolated showers. Also, adjusted hourly temperatures and dew points through the next few hours to account for the latest observations, and expected trends into the early morning hours of Wednesday. No changes were made to the expected low temperatures of the night. No other notable changes were made at this time. As of 755 PM EDT Tuesday... Cold front was just east of the Blue Ridge this evening. Radar showed spotty light showers over the mountains. Have trimmed back probability of precipitation to account for current radar trends. Brief period of upslope clouds/spotty showers mainly northwest sections through early tonight. Upper heights begin to build in the wake of the front overnight with surface high pressure slowly starting to nose in from the north by morning. Thus expecting some clearing espcly Blue Ridge east overnight with more filling in of low clouds mountains later tonight. Expect this along with only weak cool advection to keep lows mostly in the 45-50 range west to low/mid 50s east with some patchy dense fog around espcly valleys and out east where heavier rain has occurred. High to the north will slowly evolve into more of a wedge formation east of the mountains later Wednesday as it builds well to the north. Expect weak sinking motion along with dry air aloft and weak northwest flow to initially allow more sun to develop during the morning before trajectories become a bit more northeast during the afternoon. This may set up a weak convergence zone just east of the mountains where clouds may fill in with heating during the afternoon so boosting clouds a bit. Cant totally rule out a sprinkle or light shower as well but too iffy to include much mention at this point. Otherwise temps dependent upon the amount of insolation before clouds reform so stayed on the low end of Mos which gives 60s mountains to lower 70s southeast. && .SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/... As of 300 PM EDT Tuesday... Surface high pressure over southeastern Canada will wedge south down the east coast Wednesday night. This wedge is relatively shallow, roughly 2kft feet thick, and will remain mainly along and east of the Blue Ridge into Friday morning. This wedge may bleed just west of the Blue Ridge, into the New River Valley and Alleghany Highlands Wednesday night but will likely erode during the day Thursday. Stratus clouds will accompany this wedge and as the flow becomes southeasterly Thursday morning, light rain/drizzle/fog is possible across eastern slopes of the North Carolina High Country and Grayson Highlands. Southeasterly flow is expected along the south-central Virginia Blue Ridge going into the afternoon and evening to spread light precipitation northward. A once strong low pressure system coming out of the Rockies early this week will track slowly eastward over the Midwest. A weak short wave ejected out ahead of this low will increase rainfall rates across the mountains Thursday evening. This wave will likely erode any wedge environment over the mountains. Rain moving east of the Blue Ridge and over the foothills Thursday night may enhance the wedge some. However, rain will be relative warm to keep enhancements minor. The upper level low will open as it tracks over the Ohio-Tenn Valleys Thursday night. A stronger ejected short wave is expected to track from the southern Appalachians and along the Blue Ridge Friday morning. This wave also appears to track along the western wedge boundary. High rainfall rates and mixing will erode what is left of the wedge through the day Friday. The upper level trough swings over the region Friday afternoon and evening pushing heaviest precipitation east. Some scattered mountain showers are expected with the passing of the trough/cool pool with all rain ending by midnight. Overnight lows Wednesday night will fall into the mid to upper 40s. With a wedge in play and light rain forecasted, temperatures Thursday will only warm into the lower 50s. Areas outside of the wedge, such as Bluefield and Richlands, could see temperatures in the lower to mid 60s. Winds remain southeasterly and the atmosphere saturated. Temperatures may fall some during the evening then rise through the early morning hours as the wedge erodes. With the removal of the wedge Friday and despite copious amounts of rain falling, temperatures should manage to recover into the low to mid 60s by the end of the day. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 300 PM EDT Tuesday... Surface high pressure builds over the region Saturday, however drier air does not enter the area until Saturday night. Lingering theta-E ridge will likely result in a good amount of fair weather cumulus clouds over the area, becoming clear in the evening. Conditions remain dry into Monday morning, then we wait on the next system tracking across Texas to the Tennessee Valley Tuesday. Precipitation pattern may be similar to Thursday-Friday`s event with light rain over a weak wedge followed by short waves from an upper level low/trough to our west. Temperatures Saturday will be near normal with above normal temperatures Sunday. Temperatures cool down Monday with rain falling into a wedge. Tuesday will be wet with slightly above normal temperatures as wedge erodes. && .AVIATION /05Z WEDNESDAY THROUGH SUNDAY/...
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As of 125 AM EDT Wednesday... Post frontal upslope winds have generated low clouds across the mountains early this morning with IFR to MVFR cigs reported at 05Z (1 AM EDT) at KBLF and KLWB. Satellite imagery indicates this blanket of low clouds continues to expand across the mountains and expect to see IFR to MVFR cigs reach KBCB, but confidence lower these cigs reach KROA. Meanwhile east of the Blue Ridge, skies are clear but patchy fog is possible in the valleys with light winds and ground moisture from showers/storms that passed over this region on Tuesday afternoon. VFR clouds from northern VA may slip south into KDAN/KLH before dawn. High pressure slowly builds in from the north on Wednesday with a low level wedge of cooler air developing east of the mountains. Should see some drying under the increasing subsidence from the mid morning to the early afternoon...but also some uncertainty with the degree of residual cloud cover given heating and flow turning light north . Confidence low that KBLF and KLWB will see clearing. The threat for IFR and MVFR ceilings and visibility increase late in the TAF period tonight with widespread stratus along with light rain and drizzle, especially along the Blue Ridge. Extended Aviation Discussion... High pressure moves offshore Wednesday night into Thursday with the Mid Atlantic region remaining in the wedge. The next storm system moves in the Mississippi Valley Thursday night into Friday. The highest probability of rain will be on Friday along with sub-VFR cigs/vsbys with the showers. Once the low passes, northwest flow sub-VFR ceilings will remain into Saturday across the mountains with gusty northwest winds possible.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...AMS/DS/JH SHORT TERM...RCS LONG TERM...RCS AVIATION...AMS/PH

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