Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 231748 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 148 PM EDT Fri Mar 23 2018 .SYNOPSIS... High pressure extending south across the region will linger to the north of the area into Saturday. Low pressure will track east into the Tennessee Valley Saturday before redeveloping off the Carolinas by Sunday. This system looks to result in widespread wintry weather during the weekend before a wedge of high pressure brings drier weather later Sunday into Monday. && .NEAR TERM /THROUGH TONIGHT/... As of 1020 AM EDT Friday... Have bumped up highs a few degrees based on current obs along with gridded LAMP guidance. No other changes at this time. Quiet weather to continue today under weak high pressure that along with persistent northwest flow will keep very dry air in place. Still likely to see some mountain wave clouds at times given pieces of energy rotating along the back of the upper trough, otherwise mostly sunny. Given some slight warming at 85h this afternoon along with eastern downsloping, appears highs to bounce back well into the 50s east and into the 40s west despite a gusty northwest wind. Ridging weakens overnight with weak wedging developing from the north late under strong high pressure north of the Great Lakes. Cross sections continue to show very dry air in place ahead of the upstream developing wave and subsequent warm front that will help spill overrunning east toward the far western sections late. Latest GFS again the fastest to bring light precip into the I-77 corridor while most others show mainly increasing clouds through 12z. Since already running with low pops across the southwest only opted to slow down precip chances with mainly light snow pushing into the southwest third late with light accumulations toward daybreak. Lows mainly 20s to around 30 with coldest lows north and east where clouds will be less early on. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 420 AM EDT Friday... There is moderate chance of another impactful winter storm to affect a large part of the western half of the RNK CWA Saturday into the early morning hours of Sunday. Light to moderate snowfall amounts are also expected across eastern areas during the weekend. Significant accumulations of snow are likely along/west of the Blue Ridge. Models continue to key on a strong short wave embedded within the back side/base of a persistent northeastern U.S. trough. This short wave will track quickly from the Northern Plains southeast into the central/southern Appalachians today through Saturday. This is a part of the same system that brought heavy rainfall to southern California yesterday. Strong dynamics will combined with PWATS of 0.7 to 1.0 to bring general qpf to the region of 0.25 to 0.75 inch. With 850mb temperatures largely at or below 0C, most of this precipitation will fall in the form of snow. Model soundings show most if not all of the atmospheric column, except perhaps in some warmer areas right near or at the surface, below 0C throughout the duration of the event. With an average 10/1 ratio for the rain to snow ratio, this potentially could bring 2-8 inches of snow to much of the CWA. The main thing that changed from yesterday`s forecast for this event is not so much the amounts, but more the exact track of the storm system and where the heaviest snow will likely fall. Given the tight, compact nature of this Alberta Clipper type system, significant variations in snow amounts will occur over a short distance. Yesterday the model consensus track was from central WV through west central VA then toward north central/northeast NC. Latest models, including even now the 06Z NAM, have shifted the track about 100 miles further southwest, now through the New River Valley and more northwest NC then north central NC. As a result, the heaviest snow has shifted from yesterday`s thinking closer to the I64 corridor and the Greenbrier Valley into the southern Shenandoah Valley more now to the New River Valley and the mountains of southwest VA and northwest NC. Again, there will be a sharp gradient in snow amounts from potentially 8+ inches in the core of the heaviest snowfall, to less than 1 inch across the eastern and northeastern parts of the CWA. Following a conference all with WPC and neighboring offices, have decided to leave the Winter Storm Watch in place for the original set of counties and added, because of the new projected track of the storm system, Grayson, Ashe, and Watauga counties. Confidence is still not high enough to upgrade to a third period warning or issue any advisories, although most likely both will be coming with the afternoon forecast package. Time of year, time of day, and relatively warm ground temperatures will have a significant impact on how much snow accumulates, when, and where. Across the Piedmont of VA/NC, much of this may translate to a "white rain". Once the storm system moves out of the area Sunday, a high amplitude yet progressive ridge will progress from the central U.S. into the eastern U.S. reaching the forecast area by Wednesday. In advance of this ridge, northwest flow aloft bringing cold air from Canada and the northeast will remain in place with much below normal temperatures and mostly dry conditions. Temperatures will run around 15-20 degrees below normal through Monday with highs in the 30s mountains to 40s Piedmont and lows in the 20s mountains to the 30s Piedmont. && .LONG TERM /TUESDAY THROUGH THURSDAY/... As of 520 AM EDT Friday... A high amplitude upper ridge will reach the CWA midweek and take until Friday to shift to the east. Once it does shift to the east, a conveyor build of southwest flow and deep moisture will slowly shift from the Tennessee Valley into our region, promising to bring several days of wet weather but with mild well above freezing temperatures (hence, no winter weather!). In general the GFS appears to be on the fast end of bringing this moisture into the CWA toward Thursday/Friday. Until the upper ridge reaches the area, conditions should be mostly dry, at least Mon-Wed with just increasing mid/high clouds and a slow moderate trend in temperatures. However, a classic wedge setup is also expected to develop underneath the upper ridge, likely abating the warmup much more quickly than most would like. Will plan on highs in the 40s and 50s during the first part of the week warming to the 50s west and lower to mid 60s east by the end of the week. Too early to say whether or not rainfall will become an issue later in the week as timing is not certain at this point. Hydro issues, if any, should be just beyond this forecast period. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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As of 140 PM EDT Friday... High pressure should maintain overall VFR conditions through much of the valid TAF period. The wind will gust out of the northwest this afternoon with gusts up to 25kts likely then wind speeds will lighten overnight. High and mid clouds will increase from southwest to northeast overnight with ceilings lowering to MVFR south and west of KBLF by daybreak Saturday. Models were a few hours slower with the arrival of the precipitation on Saturday so have delayed any start of snow or MVFR ceilings at KROA, KDAN, KLYH and KLWB. Medium to high confidence that MVFR conditions will develop shortly after the 18Z/2PM end of the TAF forecast period. Extended Aviation Discussion... Conditions will deteriorate from west to east Saturday afternoon as snow and/or mixed winter precip advances east. Should see most locations in southwest Virginia, northwest North Carolina and southeast West Virginia drop to MVFR before 00Z/8PM. Some freezing rain is possible in the mountains of North Carolina, and bands of heavy snow are expected in the NRV, potentially at KBCB and KBLF Saturday afternoon and evening based on BUFKIT forecast soundings from the GFS and NAM. Precipitation decreases from north to south late Saturday night. Models indicate a bit faster drying as well by Sunday when spots across the north could return to VFR Sunday afternoon with lingering sub-VFR to the south for much of the day. Dry weather will return on Monday and Tuesday with high pressure to the north wedged along the mountains. But the wedge may hold in MVFR lower clouds espcly on Monday. The wedge with erode on Tuesday and Wednesday in advance of the next low pressure system and rainfall.
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As of 140 PM EDT Friday... The Mount Jefferson NWR remains off the air. Technicians are enroute to the site with a new part for the radio.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...Winter Storm Watch from Saturday morning through Sunday morning for VAZ010>020-022-023. NC...Winter Storm Watch from Saturday morning through Sunday morning for NCZ001-002-018. WV...Winter Storm Watch from Saturday morning through Sunday morning for WVZ042>044-507-508. && $$ SYNOPSIS...JH NEAR TERM...AMS/JH SHORT TERM...RAB LONG TERM...AL/RAB AVIATION...AMS/JH EQUIPMENT...AMS is the U.S. government's official web portal to all federal, state and local government web resources and services.