Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 180209 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 909 PM EST Fri Feb 17 2017 .SYNOPSIS... High pressure both at the surface and aloft remains in control through tonight. Increasing clouds and limited chances for rain then approach from the southwest later Saturday into Saturday night. Dry and unseasonably mild temperatures are expected late in the weekend into early next week, possibly approaching daily record highs. && .NEAR TERM /THROUGH SATURDAY/...
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As of 906 PM EST Friday... The forecast is pretty much on track with clear skies this evening. Temperatures are a little slower to fall with some lingering mixing of the winds. Still should see differences between elevations overnight with valleys/rural areas dropping into the mid 30s while ridges/urban areas like Roanoke fall to the lower 40s. Should see some cloud cover arrive from the southwest late. Previous discussion from Friday afternoon... An outstanding Friday afternoon across the central Appalachians and Piedmont region today, with mild temperatures in the 50s to 60s under subsidence both at the surface and aloft, along with a moderate southerly breeze. Dewpoints are still on the low side, leading to afternoon relative humidities in the 20 to 30 percent range. To the southwest, we`re watching an upper level low and a low- level Gulf of Mexico moisture return that will primarily influence the latter half of the forecast period - Saturday and more so Saturday night. For Tonight: Mid-level ridge will continue to build over the forecast area, with clear skies and lightening southerly winds the rule. Conditions should be near ideal for strong radiational cooling when you add those factors in with what is a dry air mass, even in the midst of steadily warming 850 mb temperatures (near +10C by morning). While the 12z MET MOS appears to be too cold, I`ve blended in the milder MAV MOS guidance into a consensus blend to better show the likely spatial variation (i.e. milder temps along the ridges and locally cooler temps in the lower river valleys). That gives lows in the upper 30s in the lower elevations/valleys to the mid 40s along the ridges. For Saturday: We start the day off clear, but will see increasing/thickening cloud cover as we progress through the morning and early afternoon. This is moisture is advected northward along the eastern periphery of the aforementioned deamplifying upper low. Today`s models have begun to trend back on rainfall amounts, and the NAM is the wetter compared to the 12z GFS and ECMWF output through Saturday afternoon. I`ve kept only slight to low Chance-level PoPs in the grids through the afternoon, as BUFKIT soundings reveal substantial dry plume of air at low-levels that would need to saturate up. Feel that the best chance for showers would be late in the day and mainly confined to the Mountain Empire region and perhaps the Grayson Highlands/NC mountains. Despite more cloud cover than today, particularly the latter half of the day, with milder 850 mb temperatures I`ve shown highs a couple degrees warmer than today...60s to lower 70s. These are at or near record highs, and as the potential for additional records are possible this weekend, see the Climate section for these records at our long term climate sites. Lighter southwesterly winds expected on Saturday than today.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 308 PM EST Friday... Saturday night, the axis of a shortwave trough is expected to shift eastward through the region. Precipitation is still expected in the form of rain showers across the western extent of the area in association with steeper lapse rates near the axis. Lower in the atmosphere, the associated 850mb and surface front will already be east of the area, and general flow will be northwest. This will yield subsidence across eastern parts of the area, and greatly limit the extent to which precipitation arrives across the Piedmont. This same northwest flow will help to maintain lingering isolated showers across western parts of the area into Sunday, with decreasing coverage during the day. Sunday night into Monday night, surface high pressure will build into the area from the west, and then shift to closer to the coast by late Monday night. Higher in the atmosphere, an upper level ridge will be building into the area, with its axis over the region by late Monday night. This pattern is expected to yield dry conditions across the region, with a general trend toward milder temperatures. The GFS offers a solution that bring a little bit moisture into the area on the return southerly flow by late Monday night, with light rain or drizzle near the crest of the Blue Ridge. Currently only entertaining increased cloud cover during this time period without mention of any precipitation potential. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 308 PM EST Friday... During this portion of the forecast, the upper ridge over the region will shift east in response to a shortwave trough heading eastward through the Great Lakes region. Southerly flow in advance of this trough, and in the wake of the ridge, will tap Gulf of Mexico moisture, and advect it northward into our region by Tuesday night. Look for increasing chances of showers during this time period with a cold frontal passage late Tuesday night into early Wednesday. Showers will linger during the day Wednesday. Wednesday night into Thursday, solutions between the GFS and ECWMF are consistent with a quick return to a southerly wind flow pattern across the region. What differs is the degree to which moisture impacts the area with some light rain across the area Wednesday night into Thursday. Thursday night into Friday, the guidance is in fairly decent agreement of amplifying or closing off an upper trough/low across the Upper Mississippi River Valley. Very strong southerly low level flow is progged to develop in advance of this system`s associated cold front that will be near the Mississippi River by Friday afternoon. This flow will tap the Gulf of Mexico, once again sending moisture into our region in the form of scattered rain showers and cloud cover. While there are indications from the GFS that surface based instability may be sufficient for some thunderstorm activity on Friday, will leave it out of the forecast at this time given it is alone on this solution for our area, and it is the Day 7 time period. Temperatures during this portion of the forecast will cool slightly on Tuesday, but still average some ten degrees above normal. Temperatures will start to rebound again Wednesday through Friday and be in the neighborhood of fifteen to twenty degrees above normal. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... As of 631 PM EST Friday... VFR conditions will prevail tonight into Saturday. After 12z Saturday, there will be a general lowering/thickening of predominantly mid clouds. Gusty Southwest winds around 4-10 kts with gusts to 20 kts will diminish this evening to 5-8 kts. With a low-level jet of 35 kts approaches the west tonight into Saturday morning, There is the potential for instances of low- level wind shear. KLWB is the airport with the best opportunity between 09z and 13z. Winds will be from the south at 4-9kt Saturday. Extended Aviation Discussion... Next potential for sub-VFR conditions is late Saturday into Sunday as a disturbance moves into the area from the Deep South. Warmer temperatures will accompany this system, so any precipitation should be in the form of rain showers. Lower ceilings associated with these showers may linger into Sunday before clearing and return to VFR Sunday night through Tuesday. MVFR rain showers are possible Tuesday night into Wednesday. && .CLIMATE... As of 302 PM EST Friday... Record High Temperatures and Year of Occurrence Feb 18 Blacksburg, VA..65 in 2011 Bluefield, WV...64 in 1997 Danville, VA....77 in 1976 Lynchburg, VA...75 in 2011 Roanoke, VA.....72 in 2011 Feb 19 Blacksburg, VA..65 in 1994 Bluefield, WV...66 in 1994 Danville, VA....73 in 1981 Lynchburg, VA...76 in 1939 Roanoke, VA.....77 in 1939 Feb 20 Blacksburg, VA..68 in 1984 Bluefield, WV...67 in 1986 Danville, VA....74 in 1971 Lynchburg, VA...76 in 1930 Roanoke, VA.....75 in 1939 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AL NEAR TERM...AL/WP SHORT TERM...DS LONG TERM...DS AVIATION...AL/KK CLIMATE...AL

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