Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 230353 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1053 PM EST Wed Feb 22 2017 .SYNOPSIS... Weak high pressure off the mid-Atlantic coast will stay situated here through Thursday morning. A frontal boundary across the Great Lakes into the southern Plains shifts slowly southeast to the Ohio Valley by Friday. The main cold front across the midwest will pass through our area Saturday. && .NEAR TERM /THROUGH THURSDAY/...
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As of 1030 PM EST Wednesday... Dense Fog Advisory until 10AM Thursday. Rain has ended, but still leaves the forecast area in a moist stance with the relative humidity near 100%. Combine this with clearing skies aloft and conditions are ripe for dense fog per radiational cooling paving the way for a super saturated boundary layer. Lowest elevations appear to be most suseptive to fog formation with near calm winds. Light winds at ridge top level will provide a bit more mix and less of a problem for elevations above 3000 feet. For the remainder of the overnight the main forecast focus will be on the fog. Forecast soundings maintain shallow layer of moisture near surface with clearing aloft. With weak wind flow, the stable air will keep this moisture trapped near the surface until daytime mixing can scour it out Thursday. Thursday, frontal boundary situated from the Eastern Great Lakes, southwest to the Southern Plains, in the morning, will slowly advance south to a PIT-IND-TOP line by late in the day. Models break the in-situ wedge as sfc flow turns more southwest. Will see more sunshine in the piedmont in the afternoon, with sunshine at times in the west followed by more clouds ahead of a shortwave that passes across KY into Ohio in the afternoon. This shortwave combined with some low level convergence across the mountains may lead to some showers and even thunderstorms in the afternoon, mainly from the Alleghanys southwest to southern WV, with limited coverage southeast to the foothills. As wedge erodes, expect temperatures to soar to the lower to mid 70s east of the mountains, with mid to upper 60s across the west. Some record high temps may be approached and/or broken. See climate section below. Even record warm low temperatures will be possible for Thursday 2/23.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... As of 250 PM EST Wednesday... Thursday night through Friday night, the area will be under a region of deep south to southwest flow, with its origins from the eastern Gulf of Mexico. A warm front will lift north of the area Thursday night. While some patchy light rain will be possible early in the evening for the area of the region west of the Blue Ridge, coverage will decrease through the night as the front continues heading north of the area. Lingering upslope light rain will remain possible near the crest of the Blue Ridge, especially in areas southwest of Floyd, VA into the Northern Mountains of North Carolina. On Friday, most of the area will be precipitation-free, save a few locations near the crest of the Blue Ridge thanks to local upslope conditions. Friday night into early Saturday, a cold front will approach the region from the west, and cross the area during the day Saturday. Look for increasing chance of rain showers with the approach and passage of this feature. There will also be a slight chance of thunderstorms with the passage. By Saturday night, the front will be to our east, and northwest winds will be on the increase. The northwest winds will yield some gusts approaching 40 to 45 mph at the highest elevations. Also, colder air will start working its way into the area. Lingering upslope rain showers across parts of southeast West Virginia, south into the Northern Mountains of North Carolina are expected to transition to snow showers by Sunday morning. Temperatures Thursday night through Saturday are expected to average about twenty degrees above normal. Saturday night, behind the cold front, temperatures will fall to readings near normal. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 300 PM EST Wednesday... Gusty winds will continue into early Sunday behind Saturday`s cold frontal passage. These winds will weaken quickly during the day and back southwest as the next upper level trough deepens across the Central Plains. This same upper trough will move east and be over the Ohio Valley by mid-day Monday. A warm front in advance of this system will head north through our region, bringing a return of patchy light precipitation to the area during the day Monday. There may be an issue of a brief period of a wintry mix across the northwest section of the area early Monday as a potential warm nose develops over a sub-freezing boundary layer and surface. For now, will keep things simple by reflecting a rain versus snow forecast based solely on whether the forecast surface temperatures is above or below freezing. Monday night the system`s associated cold front is expected to cross the area. Look for the precipitation to become more showery Monday night into early Tuesday. Model guidance for the remainder of Tuesday into Tuesday evening is not clear. The GFS is progressive with the cold front making significant headway east of the region. The ECMWF is not progressive, stalling the feature over the area, all while suggesting another wave will move northeast along this boundary, keeping a generous coverage of rain across the area Tuesday afternoon into Tuesday night. Our forecast will reflect a blend of these solutions. While rain will be forecast Tuesday afternoon and evening, it will not be to the degree offered by the ECMWF. For late Tuesday night into Wednesday, model agreement improves with solutions bringing yet another upper low/trough from the Central Plains states into the Ohio Valley. Warm frontal rain is expected late Tuesday night into early Wednesday, with a generous coverage of showers and some isolated thunderstorms across the area Wednesday afternoon coincident to the cold frontal passage. Temperatures Sunday and Monday will be normal for this time of year. Reading moderate through mid-week with temperatures some ten to fifteen degrees above normal expected. && .AVIATION /04Z THURSDAY THROUGH MONDAY/...
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As of 1030 PM EST Wednesday... Dense fog advisory along and just east of the Blue Ridge through 10am Thursday. In spite of clearing aloft, a very moist boundary layer with RH values of 100% has allowed for the formation of dense fog with widespread visibilities under 1/2SM Lack of wind will allow this fog to persist through mid-morning Thursday before daytime heating begins to mix the boundary layer and allow for improvement. Until then expect Widespread LIFR. This is a situation where the valleys and lowland areas will contain more stratus and fog as compared to the ridges. Ridge tops will likely remain above the stratus layer. The fog/stratus looks to burn off Thursday morning with a return to VFR conditions by the afternoon. However, a weak frontal boundary will brush the region as an area of low pressure moves through the Great Lakes region tomorrow. This may bring a shower to locations west of the Blue Ridge so will include VCSH after 18Z all sites except KDAN and KLYH. Winds will be light through the period. Extended Aviation Discussion... Thursday night-Friday, we will be well into the warm sector with VFR conditions and much above normal temperatures. Surface wind gusts of 20 to 30 kts possible across the higher terrain. Band of showers and isolated thunderstorms with MVFR conditions arrive late Friday night into early Saturday along and ahead of a strong cold front. Drier weather and increasing northwest winds follow behind the front on Saturday afternoon through Sunday. Approach of another front Monday will provide increasing clouds and possibly showers and MVFR cigs to BLF/LWB late in the day.
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&& .CLIMATE... As of 245 PM EST Wednesday... Warm temperatures set to occur again Thursday with increase in westerly flow in the low levels. Question will be cloud cover. At the moment with some sunshine look for highs and lows to approach or break records for Feb 23rd. Thursday 02/23/2017 Site Record High/Year Record Warm Low/Year Bluefield 74 1975 51 1975 Danville 73 1980 50 1981 Lynchburg 74 1943 52 1925 Roanoke 76 1943 54 1925 Blacksburg 69 1980 46 1990 && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...Dense Fog Advisory until 10 AM EST Thursday for VAZ007-009>020- 022>024-032>035-043>047-058-059. NC...Dense Fog Advisory until 10 AM EST Thursday for NCZ001>006- 018>020. WV...Dense Fog Advisory until 10 AM EST Thursday for WVZ042>044-507.
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&& $$ SYNOPSIS...AMS/WP NEAR TERM...PM/WP SHORT TERM...DS LONG TERM...DS AVIATION...MBS/WP CLIMATE...WP

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