Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 250351 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1151 PM EDT Sat Mar 24 2018 .SYNOPSIS... Low pressure over the Tennessee valley will advance east overnight crossing the central Appalachians tonight before sliding offshore the Carolinas Sunday morning. This system is producing significant amounts of heavy wet snow for parts of the Virginias and Carolinas. && .NEAR TERM /THROUGH SUNDAY/... As of 1145 PM EDT Saturday... Extended Winter storm warnings into the Piedmont of North include Henry, Surry, Stokes, Rockingham, and Caswell. Per coordination with NWS GSP will also add Wilkes and Yadkin for mainly freezing rain and sleet. Significant snow accumulations are ongoing across the New River Valley with upwards of 12 to 15 inches of wet snow. I don`t think I have ever seen as much snow hanging in the trees as with this system. Power outages will likely mount as the snow continues. There is a sharp gradient in the snow vs. no snow with areas north and east of Roanoke receiving very little snow while areas just to the west are buried. Strong warm air advection up through the Tennessee valley is resulting in a change over to sleet and freezing rain for areas west of I-77. 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. Strong low-level frontogenetic forcing is resulting in 1-2 inch an hour snowfall rates and focus where the heaviest precipitation within a narrow corridor which bisects the southwestern 1/2 of our CWA. The precipitation is expected to lighten in intensity and start to taper off from northwest to southeast after 2AM as the upper level system driving the low level forcing crosses the mountains and moves east. 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 /04Z SUNDAY THROUGH THURSDAY/... As of 733 PM EDT Saturday... Poor flying condition tonight into Sunday because of winter storm with widespread IFR to VLIFR in snow of varying intensities. 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. Accumulation on runways is expected with 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 into tonight. 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 Sunday morning. Most TAF sites will become VFR on Sunday, with potential MVFR SCT to BKN against the Blue Ridge. Northeast winds around 4-8 kts expected tonight into Sunday. Low confidence in visibilities, ceilings and winds. Extended Aviation Discussion... Models indicate some drying north of ROA/LYH during the day Sunday with VFR expected especially in the north. Easterly upslope low level flow may 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. Rain is likely on Thursday with sub-VFR conditions. && .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 VAZ007-009>018- 022-032-033-043. Winter Weather Advisory until noon EDT Sunday for VAZ019-023- 034-044-045. NC...Winter Storm Warning until noon EDT Sunday for NCZ001>006- 018>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/PM SHORT TERM...DS LONG TERM...DS AVIATION...JH/KK EQUIPMENT...PM is the U.S. government's official web portal to all federal, state and local government web resources and services.