Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 161801 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 101 PM EST Thu Nov 16 2017 .SYNOPSIS... A weak cold front will push east of the region this afternoon allowing high pressure to gradually build in from the northwest this afternoon through Friday. Another stronger cold front will then bring more showers and windy conditions to the region this weekend. Cold high pressure will build in behind the front for early next week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 100 PM EST Thursday...Temperatures have warmed in many areas well into the 50s, with low/mid 60s being more common in the lee of the Blue Ridge, perhaps aided by compressional warming effects off the Blue Ridge given favorable northwest flow. Air mass has also dried considerably as well with good mixing. Early-afternoon update essentially accounts for warmer temperatures using warmer guidance, and lowered dewpoints blending the 12z GEM dewpoints into the going forecast to show a lower trend. Should see lowest RH`s in the low 20s to mid-30s percent areawide, lowest values in the foothills of the Blue Ridge. Highs were also accordingly adjusted upward a few degrees in most locales. Continues to be pretty breezy especially west of the mountains, but gusts have shown a lowering trend over the last couple hours with peak gust speeds being in the 20 to 28 mph range as opposed to the near 35 mph range experienced this morning. Previous discussion issued at 940 AM... 850 mb front now crossing the Blue Ridge responsible for a quick uptick in winds early this morning with better cool advection now pushing off the Blue Ridge. Latest short term guidance showing a lingering 35-40 kt northwest jet through the afternoon as the 5h trough to the north pivots across so likely to be close to advisory levels at times along the highest ridges. However morning raobs show a rather high level inversion that should keep the better speeds aloft despite an added boost in pressure rises later on. Otherwise expecting mainly sunny skies east of the Blue Ridge, and over most of the mountains excluding the far northwest where added upslope clouds likely to filter southeast before mixing out. Also given such a warm start and strong downslope offset of any weak cool advection out east, raised highs a category in spots with mostly 50s west to mid 60s east. Previous discussion as of 605 AM EST Thursday... Brought up winds and wind gusts per latest observations around the area and mesoanalysis showing best 8h winds arriving around 10am. Still not windy enough for advisory although some of the highest ridges of the Alleghanys in Bath County could reach 45-50 mph. Also lowered pops and increased clouds a little further east early on. Previous discussion from early morning... Radar mainly quiet this morning with just a few lingering showers in Halifax County Virginia, and some very light echoes over the New River Valley. However, surface obs showing some light rain, sprinkles over WV, far SW VA as upslope kicks in behind front. High- res models are showing showers thru mid morning in the far western slopes though not expecting more than scattered coverage. We get clipped by 8h thermal trough of zero to -3C in WV to the Alleghanys today so some flurries/snow showers will be around but no accumulation. Another wave this evening passing north may send a few flurries or rain showers toward Greenbrier/Bath for a couple hours but overall airmass seems too dry to have any precip. Winds will be gusty through the morning, but best surge of winds appears to occur toward dusk as 6 hr pressure rises increase to 6 mb, though 8h jet is about 30-40kts. Have increased gusts late afternoon to early evening but should stay below advisory levels in the higher ridges. Model soundings and pattern suggest clouds sticking around through the day in Greenbrier to Bath county with cu field spreading eastward but more scattered into the Blue Ridge north of Roanoke. Rest of the area should be mainly sunny. Highs today should be milder than Wednesday despite post-frontal. Winds will keep it feeling cooler in the mountains but aid in downslope warming lee of the Blue Ridge. Looking at upper 40s to lower 50s mountains, but colder in the higher terrain of the Alleghanys, with 60 to 65 in the foothills/piedmont and Roanoke. Tonight, winds stay up as mentioned above, but should start to see it ease off after midnight in the valleys/piedmont as the surface high shifts into the Central Appalachians by dawn Friday. Should see lows in the mid to upper 20s in the valleys and parts of the piedmont with upper 20s to lower 30s elsewhere= where winds stay up longer. Also upslope appears to keep some clouds around a little longer over the WV mountains toward the New River Valley north and west of I-81, so this may stall temps a little.
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&& .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... As of 200 AM EST Thursday... During the Friday into Friday night time period, an upper level ridge is expected to build over the area, all while a broad region of surface high pressure extends north to south across the U.S. east coast. By Saturday, both of these features will be shunted to the east in response to an approach upper level shortwave trough across the western Great Lakes region and an associated approaching surface cold front. The resultant weather pattern for our area during this time period will be for moderating temperatures, increasing cloud cover, and precipitation along our western extent by late in the day Saturday. Saturday night the cold front is expected to race eastward across the region. The front itself is forecast to present a narrow strip of moisture coincident to the passage. This feature is expected to bring measurable, albeit, light precipitation to the entire forecast area. A more prolonged period of light precipitation is expected across parts of southeast West Virginia, south into the Northern Mountains of North Carolina Sunday, then becoming less organized and sparse heading into and through Sunday night. Increasing, strong, northwest flow behind the front will be responsible for this prolonged period of additional light precipitation. Model guidance is suggesting northwest 850mb winds will peak in the 40 to 50 kt range on the backside of the departing front, with decent pressure rises and cold air advection. Confidence is still high enough for an wind outlook in the Hazardous Weather Outlook during the Saturday night and early Sunday time period. As the cold air enters the region, look for scattered snow showers to become more probable, especially across portions of southeast West Virginia, south into the higher elevations of neighboring southwest Virginia, and farther south into the Northern Mountains of North Carolina. Temperatures on Sunday will be tricky. While a true diurnal curve is not expected, neither is an all day temperature decrease thanks to the the northwest flow cold air advection. A mix of the two seems most likely, with better chance of some warming in the east thanks to strong subsidence, and a better chance of limited temperature movement in the west thanks to a greater abundance of cloud cover. On Sunday night, drier and colder air will continue to enter the region on strong northwest winds, although they will be trending a little weaker. Look for any lingering isolated snow showers in the far west to decrease in coverage and finally end during the night. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... As of 130 PM EST Wednesday... Winds should slowly diminish Monday as the upper trough lifts out and high pressure builds in from the southwest into Tuesday. Another weak mid level feature likely to pass across Tuesday night into Wednesday before the high weakens and the split flow begins to tap return flow moisture resulting in more clouds Day7 but dry at this point. However will stay below seasonal normals with only a slight boost in highs on Tuesday at this point. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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As of 100 PM EST Thursday... VFR conditions through the remainder of the afternoon. Main impact to aviation is the west-northwest wind gusts which approach 30 kts, though 20-26 kts will be more commonly observed. These gusts unlikely to subside until boundary layer decouples by around mid-evening. Aircraft can also expect areas of localized turbulence in/around the mountain ridges as satellite trends had been showing stable wave clouds earlier this morning. For tonight, continued VFR conditions should be prevalent at most TAFs, along with wind speeds abating to light and variable values. Winds at elevation should also begin to subside to around 15-20 kts by midnight, with less turbulent conditions more probable. Shallow moisture gets shunted down the western slopes of the Appalachians, leading to a period of MVFR stratus ceilings being at Bluefield after 03z. Confidence was lower on MVFR ceilings further east into Lewisburg and Blacksburg and only shown SCT020 here. Moisture depth is shallow and convective mixing should thin out the stratus layer by early morning. VFR high clouds should overspread the TAFs Friday with light and variable winds as surface ridge builds overhead. Extended Discussion... VFR conditions anticipated through Saturday. May see brief low-level wind shear during the Friday overnight period as southwest low- level flow increases to around 40 kts atop calm/decoupled winds. Breezy southwest winds for Saturday with gusts to around 20-25 kts west of the Blue Ridge. A potent cold front moving across the forecast area during the Saturday overnight period into early Sunday. Main impacts are from sub-VFR ceilings/visbys due to low clouds and rain (changing to higher elevation snow showers Sunday morning) and a wind shift to northwest leading to gusty surface and ridgetop winds. May have lingering MVFR stratus western Appalachians Sunday night but should be VFR everywhere else with wind gusts abating. Conditions then transition to VFR Monday into Tuesday.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK/WP NEAR TERM...AL/JH/WP SHORT TERM...DS LONG TERM...JH AVIATION...AL/WP

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