Area Forecast Discussion
Issued by NWS Blacksburg, VA

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352 FXUS61 KRNK 241752 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1252 PM 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/...
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As of 1245 AM EST Friday... Sunny skies and light winds will continue to prevail this afternoon. Have increased the forecast high temperature by a few degrees at a few locations, but the change is not a drastic deviation from the earlier numbers. Hourly temperature, dew point, and wind grids were tweaked to better reflect the current observations and expected trends through the afternoon hours. As of 1000 AM EST Friday... Other than some dissipating patchy fog near Belews Lake, sunny skies prevailed across the region, and are expected to remain sunny throughout the day. Have tweaked hourly temperatures, dew points, and winds to better match the current observations, and expected trends heading into the early afternoon. 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.
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&& .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 /18Z FRIDAY THROUGH WEDNESDAY/...
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As of 1230 PM EST Friday... High pressure will continue to provide for VFR conditions through the conclusion of the valid TAF period, 18Z/1PM Saturday. Low level winds will be on the increase tonight in advance of an approaching cold front. While surface winds will remain relatively light, an increasing low level jet will yield 30 to 35 kt winds around 850mb towards daybreak Saturday. Look for the development of low level wind shear around this this time over parts of the area. Currently, none is specifically forecast within any of the TAFs. However, the area between KBCB and KBLF will have the best opportunity to experience LLWS. Extended Discussion... On Saturday afternoon 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 sections the area along with some periods of MVFR ceilings also along western slopes. Otherwise VFR conditions Saturday afternoon 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...DS/SK SHORT TERM...RCS LONG TERM...AMS AVIATION...DS/RAB/SK

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