Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 241147 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 647 AM EST Fri Nov 24 2017 .SYNOPSIS... A ridge of dry high pressure will shift east over the mid- Atlantic coast through tonight, with a return of light southwest flow and increasing breezes along the ridges tonight. A cold front will sweep across the Appalachians later on Saturday, bringing only a few light showers mainly to western slopes, as well as gusty winds along ridges behind it and cooler temperatures for Sunday. High pressure will build back in again for the early part of next week. && .NEAR TERM /THROUGH SATURDAY/... As of 300 AM EST Friday... High pressure continues to dominate today but will shift east to along the mid-Atlantic coast by evening with a return of light south to southwest flow and thus milder temperatures in store today compared to yesterday. Went close to warmest guidance given sunny skies and return to light southwest flow. This results in near to just above average highs for the date. Tonight, southwest flow at 850mb shifts to westerly and increases resulting in gusty winds along ridges and certainly milder, and while valleys will likely decouple initially and will see temps dropping quickly in the evening, some mountain valleys will remain steady or might even increase overnight as the winds pick up. Toward dawn Saturday a few mid to high clouds may also move in to the far west ahead of the approaching trough and surface front, and this may also help temps to steady out or even rise slightly in the far west after midnight. Went generally a little cooler than most guidance but this is tricky to nail down along the ridges with the mixing increasing throughout the night. More confident in going below guidance in the Piedmont where no mixing or clouds are expected. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... As of 314 AM EST Friday... A cold front will move quickly from the upper Mississippi Valley early Saturday morning to the Appalachian Mountains by late afternoon. This front will clear the piedmont during the early evening hours. Prefrontal showers will make a run at the mountains through the day, but may not make much progress past the western ridges of SE WV/SW VA. These showers will be moving into a relatively dry air mass and winds will quickly become westerly. Low level winds do back to the southwest as the front crosses the area, but given lack of moisture return, measurable rainfall should be confided to western slopes. With some support, a few sprinkles are possible for mountain counties bordering the Blue Ridge. Downsloping winds will severely limit precipitation chances east of the Blue Ridge. Given the lack of showers, temperatures will run 4F-8F warmer than normal Saturday with highs ranging from the 50s west to lower 60s east. The upper level trough will pivot over the Ohio Valley to the Mid Atlantic coast during the evening. The strongest vorticity maximum will stay north along the Mason-Dixon line. With some lingering low level moisture, a few upslope rain/snow showers are possible across western Greenbrier in the evening, then cold drier air surges in Sunday morning. Behind the front are some moderate pressure rises and a 40 kt low level jet. This coupled with a tight pressure gradient over the mountains will bring breezy and gusty conditions to the area Saturday night into Sunday morning. Winds 15-25 mph with gusts up to 35 mph are possible across the mountains, especially higher ridges along the Blue Ridge. Temperatures will not be as cold as they could be Saturday night, as mixing should keep temperatures in the 30s for majority of the area, mid to upper 20s across higher ridges. High pressure centered over the Tennessee Valley will edge into the region Sunday afternoon, allowing the winds to subside. The ridge center will eventually move overhead Sunday night. As the winds subside in the afternoon, so will the cold air advection. With plenty of sunshine, temperatures will approach normal values (mid 40s to mid 50s) Sunday afternoon. Under high pressure Sunday night, temperatures will drop into the 20s. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 110 PM EDT Thursday... Split flow pattern remains through Day 7, Thursday. Upper long wave trough will dig into the western United States Monday and Tuesday with a strong short wave separating from the southern end of the trough over the southeast United States on Wednesday. As typical, GFS is faster with this feature. Prefer the timing of the ECMWF which brings the short wave across the Mid Atlantic region on Thursday. Expecting dry weather and seasonal temperatures MOnday through Wednesday, then a chance of precipitation and cooler temperatures Thursday. At the surface a northern stream cold front will cross the area on Wednesday, then low pressure associated with the southern stream short wave tracks into the Tennessee Valley on Thursday. Will be slowing down better probability of precipitation until Thursday. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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As of 645 AM EST Friday... A progressive semi-zonal flow will remain in place across the U.S. with a series of dry northwest flow short waves. The northern stream will continue to dominate the Mid-Atlantic region with a dry west-northwest to northwest flow aloft. A series of mainly dry upper troughs and associated cold front will continue to pass through the area every few days with little or no moisture return in advance of these systems. Thus, a dry/VFR forecast will remain in place through this TAF valid period. very light south to southwest winds during the day will increase overnight mainly along the ridges, and shift more to the west. Of the TAF sites this will be most notable at BLF as others are likely to remain light and variable all night. High confidence in ceilings and visibilities through the TAF valid period. Medium confidence in wind direction, high confidence in wind speed through the TAF valid period. Extended Discussion... On Saturday a cold front will cross the area. It will be moisture starved for the most part, with at best some isolated showers across the western part of the area along with some periods of MVFR ceilings also along western slopes which is most likely at BLF and to a lesser extent LWB. Otherwise VFR conditions Saturday and Saturday night but with west to northwest winds behind the front of 10-20 kts with gusts to 30 along highest ridges. High pressure regains control of our weather pattern Sunday into Monday with VFR for the entire region. The next potential chance for sub-VFR conditions is not until late next week at the earliest.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...SK NEAR TERM...SK SHORT TERM...RCS LONG TERM...AMS AVIATION...RAB/SK

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