Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 141021 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 521 AM EST Sun Jan 14 2018 .SYNOPSIS... Cold high pressure will extend south across the region today and tonight before weakening Monday into Monday night. A second surge of Arctic air comes in behind a cold front that passes through the area later Tuesday into Tuesday night. Arctic high pressure follows the front with very cold air for the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... As of 255 AM EST Sunday... Low clouds/flurries continue across the far northwest early this morning but should finally see moisture fade after daybreak as northwest flow weakens and drier air spills in from the north. However may still need to carry some flurry mention through 12z before soundings show the column quickly drying by mid morning. Otherwise winds also slowly diminishing so only keeping the wind chill advisory in northwest Greenbrier and not expanding as mostly higher elevation criteria attm. Upper trough will pivot across the region as well this morning allowing more of west/southwest flow aloft to take shape later today as surface high pressure shifts off to the north. This should allow winds to become light today but with only a small rebound in the cold temps given faint warming aloft. Could also see some added high clouds swing in from the west later, but overall mainly sunny and continued cold with highs 20s mountains to low/mid 30s east. Cold surface high will continue to extend south across the area overnight as another shortwave axis approaches around the mean upper trough to the north late. This feature combined with weak warm advection aloft likely to bring some increase in mid/high clouds overnight as depicted via latest model relative humidity sections. However arrival time and opaqueness the key to how low temps go overnight given such dry air in place and light winds. Mos guidance showing a decent spread in spots in response to clouds with the Mav on the warm side and the Euro/Met quite cold espcly valleys. For now will trend overall colder east per less clouds late with lows 8-15, while keeping the mountains/foothills mostly mid teens, except single digits valleys. && .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
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As of 450 AM EST Sunday... A deepening upper trough will once again dominate the eastern U.S. through this period, similar to what we saw the week after Christmas and into the first week of January. However, it is not expected to linger as long as a series of vigorous upper short waves moving through the Pacific into the western U.S. will help to break down the cold eastern U.S. trough/polar vortex more quickly. As the cold air from the weekend begins to moderate ever so slightly Monday a strong clipper system is evident across the western Great Lakes. That system will dive rapidly southeast into the Mid-Atlantic region by Tuesday night and Wednesday. Moisture is of course quite limited with the dominate Arctic air mass over the region and the trough is positive tilted. However, strong CAA and reasonable dynamics will be enough to squeeze out some snow in association with a strong upper-level jet aligned with the eastern side of the trough. This will occur Tuesday night into Wednesday morning. Snow amounts of 1-3 inches appear to be possible, mainly west of the Blue Ridge, but accumulating snow east of the Blue Ridge of an inch or so will be possible with this event as it goes beyond just being upslope driven. The trough will swing through and east of the area by Wednesday afternoon taking any synoptic driven snow with it. Upslope snows may continue for a bit longer across the Alleghanys, but that also should be relatively limited given less than favorable upslope conditions. Upslope could bring another inch of snow to areas such as western Greenbrier county. Another issue to address during this period will be negative wind chills once again as another surge of pure Arctic air moves through the area. With 850mb temps a bit shy of last week`s event, bottom out around -10 to -15F in the west to 0 to -5 in the east. Wind Chill Advisory and perhaps even a Winter Weather Advisory will be needed with later forecasts. Actual surface temperatures will be well below normal through the entire period with max temperatures remaining below freezing west of the Blue Ridge most of the period and lows in the single digits and teens west to teens and around 20 east. I do feel that we will stop short of the below zero readings this time, unless we get a snow pack in the west, then locations such as Burkes Garden and Lewisburg will likely see readings just below zero by Thu morning.
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&& .LONG TERM /THURSDAY THROUGH SATURDAY/...
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As of 1100 AM EST Saturday... Wind chills may be an issue again Thursday morning as this could well be the coldest morning otherwise. However, winds will be diminishing, which could offset the wind chill issue. Heading into Thursday and Thursday night, an already tight pressure gradient may trend even tighter, than thus yield even gustier winds across the area. A lot will depend upon how much offshore development there is a of a coastal low on the tail end of the departing upper trough. Guidance still varies on this potential as well. Late Thursday night into Friday, and continuing in Saturday, look for the synoptic pattern to trend zonal across the area with a broad upper ridge building across the Gulf Coast states. Anticipate a warming trend heading into the weekend, with little if any precipitation. The only very small chance currently offered would be on Saturday just along the eastward side of the crest of Appalachians. Guidance suggests that slightly higher moisture content air may get lifted upslope in a narrow region, especially the area of the North Carolina Foothills. Temperatures may be cold enough at the onset for an hour or two of very light freezing rain before temperatures rise above freezing for the remainder of the day. Temperatures during this portion of the forecast will start about 10 to 20 degrees below normal Wednesday night into Thursday morning. From Thursday afternoon into the weekend, anticipate a warming trend that will bring readings to values around five degrees above normal by Saturday.
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&& .AVIATION /10Z SUNDAY THROUGH THURSDAY/... As of 1159 PM EST Saturday... Lingering MVFR clouds and flurries in upslope NW flow west of the Blue Ridge will continue to gradually decrease overnight. Expect VFR conditions Sunday as cold and dry high pressure moves out of the Ohio valley and into New england, bringing the Appalachians and central mid Atlantic region fair weather and good flight conditions through Sunday. Winds will also gradually diminish. Extended Discussion... VFR expected across the region Sunday night and Monday under high pressure. MVFR snow showers are possible Tuesday and Wednesday from a clipper system. This will lead to another surge of Arctic air. Drier weather is anticipated for Thursday and Friday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...Wind Chill Advisory until 10 AM EST this morning for WVZ508. && $$ SYNOPSIS...JH NEAR TERM...JH SHORT TERM...RAB LONG TERM...DS/RAB AVIATION...PM

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