Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 170806 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 306 AM EST Fri Nov 17 2017 .SYNOPSIS...
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Dry high pressure across the region will give way to an approaching cold front that is forecast to sweep through the region Saturday night. Notably colder air and gusty winds will follow in its wake into early next week. High pressure quickly regains control over our weather pattern by the middle of the week with little in the way of additional precipitation expected.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 145 AM EST Friday... Today the center of surface high pressure will slowly shift east to the coast of the Carolinas. This will progressively place our region within a increasing southwest flow. Despite the center of the high shifting east, there still will be plenty of dry air in the lower portions of the atmosphere the southwest flow will not yet have tapped any significant moisture source. Regarding temperatures, the presence of the cooler high will yield slightly cooler readings in the east today as compared to readings on Thursday. However, the increasing southwest flow should allow for some warm air advection across the west, with slightly higher readings there as compared to 24 hours prior. Highs today will range from the mid to upper 50s across most of the region. The higher elevations across the mountains will be cooler, in the lower 50s. Tonight, the center of the high will shift east of the coast while a shortwave trough progresses into the Great Lakes and Lower Ohio River Valley region. Its associated cold front is expected to be positioned across Missouri and Oklahoma by daybreak Saturday. Isentropic lift in advance of the system is expected to be maximized across the Upper Ohio Valley. For our region, we are expected to remain precipitation-free through tonight, however, look for increasing mid to high level cloud cover, especially along and west of the crest of the Blue Ridge, such that most of the entire area will be cloudy by daybreak Saturday. Only parts of Southside Virginia and neighboring sections of north central North Carolina will have more clear sky than clouds. Temperatures will trend milder thanks to the cloud cover and warm air advection. Lows tonight will range from the low to mid 30s across most the region. The exception will be the roughly the Bluefield, WV to Tazewell and Marion, VA region where upper 30s to lower 40s will be more common.
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&& .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
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As of 237 AM EST Friday... Cold front Saturday morning will stretch from Illinois to northern Texas. Will see increasing clouds as warm advection starts to pool moisture northeast ahead of the upper trough. Leaned toward a blend of the GFS/ECM as they are reasonable in timing of the system moving across into Saturday night. Saturday starts off dry in the morning but look for showers arriving toward the WV mountains by midday and reaching the Blue Ridge by dusk. Appears best lift/wind energy with this system stays over the Ohio Valley as the strong low moves from IL/MO to the eastern Great Lakes. Despite lack of instability with no thunder mentioned in the forecast, a narrow line of convective showers will shift from WV to the piedmont during the night. Most will see rain but should see most coverage west of the Blue Ridge. 8h jet of 55-60kts could send some strong winds to the surface in the line of showers, so something to watch. Rainfall totals with this front will average a quarter to one half inch, with locally higher amounts possible in the mountains. Behind the front two issues to deal with and first will be winds. As the line of showers pushes east there is a strong subsidence signal at 5h that supports a small window of stronger winds post fropa. Limiting factor to the strongest winds will be cloud cover as models keep the lower levels saturated. Running our local wind guidance tool, suggests some wind headlines are likely, especially for the Blue Ridge of NC into southwest VA, but at the moment since its not until 4th period of the forecast and mainly looking like advisory level winds, will keep mention in the HWO and not have any headlines. Gusts over 55 mph not out of the question at the highest ridges like Mt Rogers. Strongest pressure rises start to come into the mountains by 12z Sunday, but the core of strong 8h jet has already shifted northeast into PA. Still some 35-45kt winds at 8h suggest potential for advisory into Sunday as airmass dries out east of the mountains of WV to NW NC. Other issue will be rain to snow as strong cold advection kicks in Sat night in the mountains. Soundings showing deeper moisture shifting out as the cold air arrive so at the moment looks like a coating of snow will accumulate on the higher ridges of Greenbrier to NW NC early Sunday morning, and the winds will also blow the snow around. Snow tapers to flurries and dries up from south to north Sunday afternoon. A lull in the strongest winds occurs during late morning to mid afternoon Sunday before a secondary surge of pressure rises and another core of stronger 8h winds arrives Sunday evening. Could potentially see another wind advisory for the Blue Ridge late Sunday afternoon into Sunday night. Will also mention this in the HWO. As for temps, Saturday will be mild ahead of the front with breezy southwest winds, sending temps into the lower to mid 60s, except a few mid to upper 50s in the mountains. Sat night will be a tale of two temperature regimes as the piedmont stays elevated with showers and winds keep it mixed as the cold air arrives more toward dawn Sunday, so at the moment thinking mid to upper 40s until dawn, then may see a dip toward the lower 40s. Further west, temps by dawn should drop into the 30s. A chilly Sunday in the west with highs from the mid 30s to lower 40s, with downslope and more sun allowing temps to reach the lower to mid 50s in the foothills/piedmont despite cold air advection. Monday-Monday night will see high pressure move from the southern Appalachians, to off the NC coast. Should be mainly clear with temps staying below normal. After a cold start Monday morning in the 20s, temps will slowly warm into the 40s in the mountains as the high pressure stays overhead, with lower 50s southeast. Monday night temps should be little milder and near normal with mid 20s to lower 30s. Some return flow on the backside of the high could keep some of the higher ridges warmer than the valleys.
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&& .LONG TERM /TUESDAY THROUGH THURSDAY/...
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As of 130 PM EST Thursday... Rather quiet period with flat upper flow early on giving way to passing troffiness aloft by midweek and an overall split flow regime into Thanksgiving. This should keep things mainly dry but cool through the period with perhaps more clouds with the impulse/front Tuesday night per latest model consensus. Temps to stay below normal, mainly 40s/low 50s for highs, except for a little bump ahead of the front on Tuesday when most should reach the milder 50s.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/... As of 1130 PM EST Thursday... Wind speeds will continue to lighten and will become variable to calm as surface high pressure moves from the Ohio Valley into the Mid Atlantic region through 12Z/7AM. Satellite pictures showed MVFR clouds over southeast West Virginia. As the upslope flow diminishes, the clouds will erode. High confidence ceilings will be VFR after 11Z/6AM. Conditions will be VFR throughout the day Friday. Once daytime mixing begins winds will generally be from the south to southeast. Mid and upper level clouds spread into the area from the west on Friday night. Ceilings will remain VFR through Saturday morning. A low level jet develops from the southwest late Friday night but models show any resulting low level wind shear will be after the 06Z end of the TAF forecast period. Extended Discussion... VFR conditions anticipated through Saturday. May see low-level wind shear Friday night as southwest low-level flow increases to around 40 kts. Breezy southwest winds for Saturday with gusts to around 20-25 kts. Even stronger gusts are possible at higher elevations. A potent cold front moving across the forecast area Saturday night 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 very 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. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...DS NEAR TERM...DS SHORT TERM...WP LONG TERM...JH AVIATION...AL/AMS

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