Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 112341 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 741 PM EDT Wed Oct 11 2017 .SYNOPSIS... A cold front will approach then cross the area overnight. Thursday into Friday, a nose of high pressure will work its way south along the lee of the Appalachians. This wedge will give way on Saturday in advance of another cold front, which in turn will cross the region on Monday. && .NEAR TERM /THROUGH THURSDAY/...
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As of 741 PM EDT Wednesday...Surface low analyzed near Pittsburgh extends a surface cold front southwestward through central WV. Warm and conditionally unstable air mass lies ahead of it across the forecast area, though a fair amount of southwest/west- southwest surface wind exists limiting convergence/convective coverage. May see some increase along the frontal boundary as it moves into eastern WV in the next hour or two, though past few runs of the HRRR have become less and less enthused on those prospects. Generally reduced PoPs areawide but kept any mention of isolated to scattered PoPs across WV and in our southern Shenandoah and central VA Piedmont counties through late evening. Air mass remains unstable enough for a couple thunderstorms though that will be waning with sunset. In fact the surface front largely clears the forecast area prior to midnight. Also made some adjustments to cloud cover. Late-afternoon visible/infrared imagery depicted an expansive blanket of post- frontal stratus, its eastern extent currently across central KY and eastern OH. Recent RAP and 18z NAM BUFKIT RH profiles show shallow saturated layer atop a strong subsidence inversion at Beckley setting in after around 2 AM. So I did opt to increase sky cover significantly from eastern WV into the western part of the New River Valley and the Mtn Empire in VA. At least some stratus associated with developing post-frontal wedge in eastern VA may potentially intrude as early as the pre-dawn hours in Buckingham, Appomattox and Charlotte Counties. So much of the area should be beginning to turn at least partly cloudy. Previous near-term discussion issued at 230 PM follows... A frontal boundary lifted slowly north during the course of the day, and is currently positioned across the eastern panhandle of West Virginia, eastward into the Delmarva Peninsula. A cold front was approaching our region from the west, located currently from roughly central Ohio, south into eastern Kentucky and Tennessee. Across the forecast area, very warm temperatures with high dew points for this time of the year cover the area. Instability was noted across the entire area, with the greatest over Southside Virginia and neighboring north central North Carolina. Over the past few hours, showers have been developing over this area, with the greatest concentration currently over central Pittsylvania County, VA. Heading into the evening, the activity will continue across the southeast portion of the area, but is expected to also increase across the northwest with the approaching, and subsequent arrival, of the cold front. Isolated thunderstorms cannot be ruled out, especially over the southeastern parts of the area. The bulk of the precipitation will end by midnight, with lingering showers across the far northeast section of the area through sunrise Thursday. There will be a slight chance in airmass, as somewhat lower dew points arrive behind the cold front. However, conditions still will remain above normal for this time of year. Low temperatures will range from the mid to upper 50s across the mountains to the lower to upper 60s across the Piedmont. During the day Thursday, the cold front will continue progressing out of the area, all the while a nose of high pressure works its way south along the lee of the Appalachians. Anticipate a northeasterly flow to advect low level moisture into the region prompting plenty of cloud cover and light rain/drizzle/fog expanding in coverage across primarily eastern sections of the forecast area. By sunset, the light rain/drizzle is expected to have expanded southwest into the Foothills of North Carolina. The far western sections of the area will remain outside this building wedge of high pressure and experience little or no precipitation. High temperatures will range in the 70s, with the coolest readings across the northern and northeastern sections of the area.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... As of 210 PM EDT Wednesday... Strong wedge in place Thursday night and Friday with abundant moisture from the surface through about 5000 feet AGL. Mid and upper levels will be dry. No question about overcast sky over the mountains and through the foothills and piedmont. Western edge of clouds will be just west of Lewisburg to Bluefield to Boone. Not as obvious is the occurrence and amount of any light rain. Isentropic lift and upslope better over eastern slopes of the central Appalachians on Thursday night than on Friday night when the lift shifts into the southern Appalachians. Will have the highest probability of rain overnight Thursday night. Wedge and low moisture erode on Saturday. Winds become more southwest on Saturday night. Clouds will keep temperatures nearly steady on Friday but anticipate enough peaks of sun on Saturday to result in warmer temperatures. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 200 PM EDT Wednesday... Models starting to come into better consensus with the timing and location of a synoptic scale trough crossing the eastern United States Sunday and Monday with the ECMWF on the slower side of the solutions. Strong cold front crosses the Mid Atlantic region early Monday and both GFS and ECMWF showing good upper diffluence ahead of the front on Sunday night. Most favorable location for thunderstorms ahead of the front on Monday will be in the piedmont of Virginia and North Carolina based on the timing of the front. Rest of precipitation will be post frontal. ECMWF consistent in showing 850MB temperatures behind the front dropping into the +4 to +8 range. Precipitable water values drop well below one half inch. Air mass begins to moderate Wednesday. Expect low level winds up to 30 knots with pressure rises on 2 to 5MB/3hr behind the front with decent cold air advection so will be increasing the winds on Monday afternoon and Monday night. As high pressure moves in Tuesday winds will diminish. && .AVIATION /23Z WEDNESDAY THROUGH MONDAY/...
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As of 741 PM EDT Wednesday... VFR initially as we await the approach and eventual passage of a surface cold front which as of this writing was located across central WV. May see isolated to widely scattered showers or even a thunderstorm as this feature sweeps across the airspace through 03z. Potential for MVFR visibilities in showers which affect any specific TAF; treated as prevailing VCSH mainly for western terminals with TEMPO MVFR showers. Expect a deterioration in flight categories for the after- midnight and overnight hours behind the cold front. Conditions begin to deteriorate earliest at Lewisburg and Bluefield with post-frontal IFR to LIFR stratus; patchy areas of fog with MVFR to IFR visibility possible pretty much anywhere but most likely where rainfall occurred today. While stratus in the west begins to erode Thursday morning to a VFR deck, we then start to develop wedge conditions for Thursday with high likelihood of MVFR to LIFR ceilings along with areas of drizzle or light rain for sites within and east of the Blue Ridge and Alleghany Highlands. Some guidance brings these conditions into Lynchburg as early as mid- morning; general trend is for a westward deterioration in flight categories through the day. Winds begin west/southwest 4-6 kts then become northwest with FROPA through midnight; winds steadily continue to veer overnight to a northeasterly direction 4-8 kts on Thursday. Extended Aviation Discussion... Sub-VFR conditions will continue across central and eastern parts of the area Thursday afternoon through Friday night. Saturday, the lee side wedge will give way to increasing southwest flow ahead of our next synoptic scale upper trough and associated cold front. This will allow for more areas to experience VFR conditions, a trend that will continue into Sunday. Sunday night into Monday, a substantial cold front is expected to cross the area with scattered showers and some storms. Sub- VFR conditions are expected to accompany the stronger showers/storms. Also, in the wake of the cold front, lingering moisture in the west will likely manifest as some upslope sub- VFR ceilings Sunday night into Monday morning.
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&& .CLIMATE... Record high temperatures for Wednesday October 11th... Roanoke......89...1919 Lynchburg....89...1919 Danville.....90...1954 Blacksburg...80...2010 Bluefield....80...2010 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...DS NEAR TERM...AL/DS SHORT TERM...AMS LONG TERM...AMS AVIATION...AL/DS CLIMATE...JH

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