Area Forecast Discussion
Issued by NWS Blacksburg, VA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KRNK 241945 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 345 PM EDT Sat Mar 24 2018 .SYNOPSIS... Low pressure will move east out of the Central Plains today and into the Tennessee Valley tonight before sliding offshore the Carolinas by Sunday morning. This system will bring a mix of winter weather to the region tonight through Sunday morning. A wedge of high pressure will remain over the Mid Atlantic region Monday and Tuesday. && .NEAR TERM /THROUGH SUNDAY/... As of 343 PM EDT Saturday... Much of the Blacksburg forecast area, with exception for far southwest VA through the High Country, remains on the cold side of a surface low located near southeast MO. Precipitation falling into the cold side of a strong warm frontal boundary has produced periods of moderate to locally heavy snow at times in the western mountains. Reported snow amounts have been as much as 5 inches have been reported to this point. Forecast models continue to show substantial 1-1.5" liquid- equivalent QPF axis extending across the New River Valley through the Blue Ridge foothills into the Piedmont of NC. Further to the north and east, liquid-equivalent QPF tapers off rather sharply. This sharp gradient in QPF is an expectation as strong low-level frontogenetic forcing moves in between 01-07z across roughly the southern third of the CWA, and will likely serve to focus where the heaviest precipitation will fall. Little significant change made to snow/sleet and ice accumulations, essentially accounting for snow/sleet that`s already fallen on the ground. The only notable change to headlines was to add Yadkin County into the Winter Weather Advisory issued earlier this afternoon, per collaboration with NWS Raleigh. There`s increased confidence on impacted travel conditions starting late this afternoon in the New River Valley to the Roanoke area with moderate to at times heavy snow between about 6 PM and 11 PM, and starting early to mid-evening into part of Southside and into the Piedmont of NC. In the latter areas, temperatures remain warm enough to support mostly rain or rain/snow mix. However heavier precipitation rates are expected to flip precip over to a period of moderate snow in Southside and the Piedmont of NC, which should be more than capable of sticking on pavement when factoring in precip intensity and time of night. Visibilities should be low in each area and accumulations on pavement will combine to make for very difficult travel. It`s not to say that travel won`t be difficult from Greenbrier County eastward into Campbell Counties this evening, but it`s becoming more clear that snow intensities will not be anything more than light to perhaps moderate at times. Other area that is concerning is the NC High Country, with the potential for notable freezing rain accumulations. The warm nose has already made it into Watauga and Ashe Counties, with instances of snow this morning having now changed to sleet. As the surface low progresses southeast tonight, further warming aloft will support freezing rain with surface temperatures likely remaining sub-freezing. WPC has raised ice amounts to values that would support potential ice storm conditions; official ice accretions are less, offering as much as a quarter- inch of ice accretion, since some of the freezing rain that does occur would likely go to melt the 3 to 5 inches of snow that`s fallen. This icing in addition to the snow which has fallen still justifies the winter storm warnings in these counties. Snow should lighten in intensity and start to taper off from north to south mainly after midnight across the northern third, then into the pre-dawn hours to the Virginia border. Precipitation should be tapering off in NC into the early Sunday morning hours. Into Sunday, as surface low exits off the Carolina coastline, building strong wedging comes in with enhanced east/northeast flow. While conditions will trend dry Sunday afternoon, temps unlikely to climb much further than the low 40s. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... As of 343 PM EDT Saturday... Sunday night, a ridge of high pressure is expected to build south along the lee of the Central Appalachians. Low level boundary winds will continue to veer, taking on a east to southeast orientation as the night progresses. This will have the effect of producing some weak upslope flow along the eastern faces of the crest of the Blue Ridge across the Northern Mountains of North Carolina, north into the Grayson Highlands region of southwest Virginia. Anticipate some light rain/drizzle from this scenario, along with pockets of freezing rain/freezing drizzle where temperatures will be cold enough. The low level moisture looks shallow and warm enough to preclude ice nucleation. Monday, an upper level ridge will build across the area, and low level winds will continue to veer, taking on a southeast to south orientation by sunset. Anticipate a dry day with decreasing cloud cover as the weak upslope component fades as the winds shift their direction. Monday night into Tuesday, the upper ridge holds fast across the region, but a warm front is expected to head northeast across the area. There may be a period of time from late Monday night into early Tuesday morning where there will be slight chance for some freezing rain as patchy precipitation falls into a sub-freezing surface air. The greatest potential during this time frame will be near the crest of the Blue Ridge from roughly Floyd, VA , southwest into the Northern Mountains of North Carolina. By the afternoon, all locations are expected to be warm enough for plain rain, but still with most areas only having a slight chance. By Tuesday night, the warm front will be north of the area and the precipitation will again end across the region. However, by daybreak Wednesday, some patchy light rain may arrive in the far western sections of the region with the approach of a cold front. Temperatures during this portion of the forecast will average about 10 to 15 degrees below normal. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 343 PM EDT Saturday... The upper level ridge that was over the region for the first part of the week will break down on Wednesday in advance of another synoptic pattern shift to a amplifying long wave trough pattern across central CONUS. The eastern extent of this trough will be active with weather systems heading northeast either into or very near our region. The first will be on Wednesday into Thursday and have its origins from the southern stream jet and bring a series of waves of rain to the area. On Friday, a secondary upper stream shortwave trough will add an increased level of instability during its passage so that some isolated thunderstorms will be possible across the Piedmont region during the afternoon. As the axis of this upper system crosses the area Saturday night, enough colder air may work its way into western sections for a change over to snow for some of the higher terrain. Temperatures during this portion of the forecast will start near normal, but increase through Friday to readings averaging about five degrees above normal. Saturday readings will cool a little bit to near normal. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... As of 221 PM EDT Saturday... Poor flying conditions have already developed west of the Blue Ridge with IFR to VLIFR conditions at times in snow of varying intensities. Expect the worst conditions through 23z to be at Bluefield and Blacksburg. Further deterioration is expected into the Piedmont in VA and NC, but not until this evening. Near-term guidance continues to point to a band of moderate to locally heavy snow between 00-04z from Bluefield to Blacksburg and potentially for a brief time at Danville, with light to moderate snow at Roanoke. Lighter snows are expected closer to Lewisburg and Lynchburg more removed from the heaviest precipitation axis. The best chance for accumulation on runways is after sunset and in low-visibility snow. There is also some level of concern for aviation icing in/around the southern Blue Ridge closer to the warm nose aloft. IFR to VLIFR conditions should be common at most TAF sites this evening. Improvement to MVFR/VFR expected from north to south after midnight from Lynchburg and Lewisburg, and into the pre-dawn hrs for all other TAFs except Danville. Significant improvement there not expected until early morning. Most TAF sites VFR on Sunday, with potential MVFR cigs against the Ridge through 18z. Winds trend light northeast this afternoon (except south at Danville), then increase to around 4-8 kts. Moderate confidence in visibilities. Moderate to high confidence in ceilings and winds. Extended Aviation Discussion... Precipitation decreases from north to south late Saturday night. Models indicate some drying north of ROA/LYH during the day Sunday with VFR to the north. Easterly upslope low level flow will likely result in lingering low level cloudiness south of ROA-LYH with sub-VFR conditions continuing for western VA/NC. Dry weather will return on Monday and Tuesday with high pressure to the north wedged along the mountains. But the wedge may hold in MVFR lower clouds espcly on Monday. The wedge with erode on Tuesday and Wednesday in advance of the next low pressure system and rainfall. && .EQUIPMENT... As of 800 PM EDT Friday... The Mount Jefferson NWR has been fixed... it should be back on the air! && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Winter Storm Warning until noon EDT Sunday for VAZ010>018-022- 032-033. Winter Weather Advisory until noon EDT Sunday for VAZ007-009- 019-023-034-043>045. NC...Winter Storm Warning until noon EDT Sunday for NCZ001-002-018. Winter Weather Advisory until noon EDT Sunday for NCZ003-019. Winter Weather Advisory until noon EDT Sunday for NCZ004>006- 020. WV...Winter Storm Warning until noon EDT Sunday for WVZ042>044. Winter Weather Advisory until noon EDT Sunday for WVZ507-508. && $$ SYNOPSIS...AL NEAR TERM...AL SHORT TERM...DS LONG TERM...DS AVIATION...JH/PM EQUIPMENT...PM is the U.S. government's official web portal to all federal, state and local government web resources and services.