Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 201746 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1246 PM EST Fri Jan 20 2017 .SYNOPSIS... A warm front will bring a period of rain early today before dissipating this afternoon and evening. A small period of dry weather occurs tonight then a frontal boundary situated across the Gulf Coast states starts to increase the moisture and rainfall again by Saturday night into Sunday. The low with this system will move to Virginia by Monday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1245 PM EST Friday... In the wake of the early/mid-morning warm frontal rainband that made its way across our forecast area, we`ve seen ceilings turn overcast and generally drop in what appears to be something of an in-situ wedge reinforced by light rain and light east flow. The likely development of a shallow inversion also contributing to what`s turned out to be a rather gray Friday. While southwest winds in the Virginia Mountain Empire into southeast West Virginia have allowed for some mixing and comparatively milder temperatures, temperatures elsewhere have run several degrees colder (in the 40s). I`ve tried to lower both hourly temps and highs downward by several degrees as the prospect for substantial warming continues to dwindle as guidance points to shallow inversion lasting well into the evening keeping the overcast around. Areas of mist/light ground fog long with patchy drizzle may also be possible and I`ve kept this going in the Wx grids per trend in araa METARs. Temps were lowered into the lower 50s for many areas, with the best chance at upper 50s readings being in the Mountain Empire into southeast West Virginia.
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&& .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 215 AM EST Friday... A wet and very mild period is expected during this portion of the forecast. A broad upper trough will be positioned from the Four- Corners region north to the Dakotas. Southwest flow in advance of this trough will bring Gulf of Mexico moisture and leading weak disturbances into and through the region. Anticipate rain showers to overspread the area from southwest to northeast starting slowly at first on Saturday, but growing in coverage and intensity Saturday night and continuing into Sunday. By Sunday evening, the main upper low is expected to have progressed eastward from the Four-Corners region to the lower Mississippi Valley region. The leading shortwave trough is expected to have lifted closer to the Mason-Dixon line, allowing for a decline in coverage Sunday evening. This break will be short lived as the upper low continues its progress eastward into either the Deep South or the Tennessee Valley. Either location will allow for the deformation on zone on the north side of the low to become situated over the area, and then slowly pivot as the low makes a swing northeast closer to the VA/NC/SC coast by Monday evening. By Monday night, the low is expected to be near, or north of the Delmarva Peninsula with flow across our region increasing from the northwest. Expect winds to become gusty Monday night with colder air moving into the region. Precipitation will continue in the west thanks to upslope flow and residual low level moisture. Enough cold air may reach the higher terrain of southeast West Virginia by daybreak Tuesday for some isolated snow showers in western Greenbrier County. Precipitation during event will be plentiful. Total amounts may be near two inches near the NC/VA border east of the crest of the Blue Ridge. Lesser amounts are expected the farther northwest one is from this location with an average of three-quarters of an inch across southeast West Virginia. If these amounts are realized, the potential will increase for minor flooding, especially across the southeast portion of the region. Increased surface based instability is also expected during this event, especially Sunday afternoon. The far westerns parts of the area, as well as, the far southern and southeastern sections may experience some isolated thunder. Temperatures will continue to be very mild during this part of the forecast. Temperatures will start the period off around twenty degrees above normal on Saturday and decline to readings still some five to ten degrees above normal on Monday. && .LONG TERM /TUESDAY THROUGH THURSDAY/... As of 200 PM EDT Thursday Once the surface low is off the coast on Tuesday, precipitation will be confined to favored western upslope areas. Winds will also increase Tuesday. There may be enough of a low level jet along with cold air advection and pressure rises for wind gusts in the 40 to 50 mph range. By Wednesday and Thursday a long wave positively tilted upper trof will extend from the Great Lakes across the central United States. Prevailing deep southwest flow over the Mid Atlantic region during this time frame results in differences among the models in how fast any front will progress east. For now WPC has surface front crossing the region Wednesday and Wednesday night. Behind this system is a much colder air mass. More upslope snow showers in the mountains are possible. At this time the models are showing snow showers for Thursday night. && .AVIATION /17Z FRIDAY THROUGH TUESDAY/...
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As of 1245 PM EST Friday... Flight categories through early evening should remain anywhere from MVFR to IFR (at times LIFR) due to low stratus along with MVFR/IFR mist/light ground fog. By early evening, shallow saturated subsidence inversion develops and stays in place through Saturday morning. This lends itself to relatively high confidence in prolonged degraded flight conditions through the overnight in prevailing IFR to VLIFR conditions for most of the TAFs (except mainly MVFR at BLF) from stratus and fog/mist. Confidence in lowest visibility in fog is low, but may dip as low as one-half mile into the overnight. Winds generally light and variable except at BLF where southwest winds 4-8 kts should prevail. Subsidence inversion begins to erode into Saturday which should allow for a slow improvement in flight categories through 18z Saturday, but would expect at least MVFR to IFR into Saturday. Rain begins to approach from the south very late in the TAF period associated with next frontal system, but unlikely to affect any of the TAFs through 18z Saturday. Extended Aviation Discussion... A slow-evolving but potent frontal system affecting a good part of the southeast CONUS will lead to a potentially long period of sub-VFR conditions this weekend due to low clouds/stratus and rain. Rain may at times be steady to heavy and may include a rumble or two of thunder, particularly Saturday night into Sunday. Precipitation begins to trend more showery/intermittent on Monday before trending VFR/MVFR for Tuesday.
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&& .CLIMATE... As of 305 PM EST Thursday... Record warm Mins for January 21 Blacksburg....42 in 1954 Bluefield.....47 in 1999 Danville......56 in 1954 Lynchburg.....51 in 1927 Roanoke.......51 in 1959 Record highs for January 21 Blacksburg....59 in 1954 Bluefield.....60 in 1999 Danville......68 in 1959 Lynchburg.....72 in 1932 Roanoke.......74 in 1932 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...WP NEAR TERM...AL/WP SHORT TERM...DS LONG TERM...AMS AVIATION...AL CLIMATE...AMS

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