Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 200815 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 315 AM EST Fri Jan 20 2017 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As Of 220 AM EST Friday... Overall seeing a little slower onset of rain this morning per lack of echoes on radar and surface observations mainly showing mid deck clouds. For the rest of the early morning leaned toward the high-res models show slower timing but still looks like it will be wet morning commute for most of the region. Best lift passes across between 10z-15z, then shifts to the mid- Atlantic this afternoon. Warm front lingers south of us this afternoon so question is will any clearing take place? The downscaled NAM and Canadian as well as the HiRes-ARW showing some clearing across portions of southern VA into NC while the GFS hangs in the lower clouds longer. Think some breaks possible but overall staying mostly cloudy with patchy drizzle may occur as the rain pulls out early in the afternoon. Tricky temperature forecast given rainy morning followed by dry afternoon but lingering cloud cover. Will go a degree or two under guidance especially from the Greenbrier Valley south to the NC foothills and east, with readings in the 50s. Appears enough clearing and earlier exit of rain will allow temperatures to reach the lower 60s over southern WV into the Mountain Empire of Southwest VA. Tonight weak southerly flow with dissipating warm frontal boundary may set up a fog and low clouds scenario, especially in the foothills/piedmont. Guidance actually advertising dense fog in some locations, but cloud cover may limit this. Should be mainly dry with lows in the 40s.
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&& .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
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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.
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&& .LONG TERM /TUESDAY THROUGH THURSDAY/...
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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.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/... As of 1210 AM EST Thursday... Fast moving negatively tilted short wave will rotate through the region late tonight/early Friday, followed by an extended period of southwest flow preceding another short wave during the weekend and a deep low pressure area slated to move through the southeast U.S. early next week. This system will be in/out fairly quickly, but will leave low clouds, drizzle, fog in its wake given the persistence of southwest flow aloft remaining in place. It appears that the timing of this system is still even slower than thought at 00Z, with the main wave of rain coming through in the 13Z-17Z time frame as opposed to 08Z-14Z time frame earlier considered. HRRR/GFS used for timing. HRRR also shows redevelopment of convection during the afternoon, which was not indicated in previous runs. Have not included that scenario with this package, but if future runs continue to show this, it may need to be considered. For now, planning on evolution of rain to fog/drizzle/low clouds during the evening. Current VFR ceilings will quickly deteriorate to MVFR/IFR after the rain spreads into the region, then settle into an IFR/LIFR condition during the afternoon in fog, drizzle, low clouds. Visibility will drop into the MVFR category, occasionally IFR during the rainfall, then settle mainly into IFR-LIFR category during the afternoon/evening in fog and drizzle. Winds will be mostly east-southeast 3-5kts tonight, becoming southeast 4-8kts as the rain moves into the region. Some low end gusts are possible at KBLF with the southeast flow. Winds will become light and variable or calm east of the Blue Ridge after the rain moves out of the region, but become SSW-SW 4-8kts with again some low end gusts at KBLF during the afternoon Friday. Winds will trend back toward light and variable Friday evening, expect KBLF which should keep Medium confidence in ceilings and visibilities through the TAF valid period. Medium confidence in wind speed/direction through the TAF valid period. Extended Aviation Discussion... As noted above southwest flow aloft will persist ahead of a deep upper low that will develop across the southeast states over the weekend, then move off the southeast U.S. coast Monday. Low clouds, drizzle, and fog are likely to persist Friday night with additional waves of rain moving into the area late Saturday and persisting into Monday. At this point it appears that the only period of potential VFR cigs would be Saturday afternoon. Otherwise, much of the period will be characterized by MVFR or worse ceilings and visibilities. Winds will become strong and gusty from the northwest Monday night into Tuesday as the major weather system moves up the east coast. Ceilings and visibilities should finally improve east of the Blue Ridge after Tuesday, but likely persist with MVFR and upslope flow west of the Blue Ridge. && .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...WP SHORT TERM...DS LONG TERM...AMS AVIATION...RAB CLIMATE...AMS

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