Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 180225 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 925 PM EST Fri Nov 17 2017 .SYNOPSIS... Dry high pressure across the region tonight into Saturday will give way to an approaching cold front that is forecast to sweep through the region Saturday night. Much colder air on gusty northwest winds will follow in its wake into early next week. High pressure quickly regains control over our weather pattern next week with little in the way of additional precipitation expected. && .NEAR TERM /THROUGH SATURDAY/...
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As of 925 PM EST Friday... With temperatures dropping quickly this evening, decided to lower low temperatures especially in the valleys overnight. However, warm advection will hold temperatures up along the ridges overnight into Saturday morning. Have a good night ! As of 624 PM EST Friday... Made some minor adjustments in temperatures for this evening into tonight. Adjusted cloud cover for tonight into Saturday. Overall, forecast is in good shape for tonight. As of 245 PM EST Friday... Sprawling area of high pressure in place across the eastern Ohio Valley, Appalachians and Piedmont region this afternoon. This is leading to good sunshine, at times filtered by high cloudiness spilling into the region from the west. Well to our west, a southwesterly warm sector regime is in place across the TN Valley ahead of an organizing surface low near northwest Kansas. Overall, a rather uneventful first part of the evening as high pressure begins to slide off to our east allowing for more of a southerly return to commence. Periodic high clouds can be expected to continue into the first part of the overnight, with temperatures falling rather quickly through midnight. Later tonight, high clouds become a bit greater in areal coverage with stronger warm advection taking place, buoyed by what the 12z 3-km NAM depicts as a southwesterly 35 to 40 kt 850 mb jet. Expect to see a rather wide spatial variability in lows this evening, as lower-elevation/deeper mountain valleys remain decoupled enough to allow for radiational cooling and lows in the 30s. Across the ridges though, effects of southerly warm advection, higher wind flow and some radiational effects should keep temperatures here from falling much farther than the upper 30s to mid 40s. Then Saturday begins the period of more active weather, especially the latter half of the day. Clouds will continue to slowly lower and thicken into a multilayered deck, earliest and lowest with western extent. However some higher resolution guidance indicates some lower stratus working its way northward into our southern Blue Ridge foothills and upper NC Piedmont in response to strong moisture return. Of more notable interest is the increase in southwesterly winds at elevations above about 3000 feet. Southwesterly jet should continue to increase from the overnight into the day Saturday. By mid to late afternoon, the 3-km NAM and the GFS indicate 850 mb winds of 50 to 55 kts depending on the model. An inversion forecast by the models may keep some of this from fully mixing, and it`s climatologically tougher to verify Advisory criteria wind gusts on a southwesterly component. Still, the best chance of highest southwesterly gusts of up to 40 to 45 mph will be along the Mountain Empire, Grayson Highlands, Mercer County in WV and perhaps into the higher peaks in Ashe/Watauga Counties in the afternoon. Those with outdoor recreation interests should be aware that conditions will be rather breezy above above 3000 ft tomorrow. Southerly winds in lower elevations should top out around 15 mph with afternoon gusts to 25- 30 mph. Currently only the 12z NAM-12km shows any measure of precipitation out ahead of the front, but there are enough arguments against introducing anything higher than slight chance PoPs including dry sub-cloud air and light precip rates in conjunction with the breezy conditions probably making it less likely it`ll actually measure. So, overall an increasingly breezy day with dewpoints on the rise. Temperatures ranging from the mid 50s to middle 60s, maybe a spot upper 60 value closer to the NC Piedmont.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... As of 250 PM EST Friday... Strong cold front and associated lead shortwave energy still on track to cross the region Saturday night before quickly exiting by early Sunday. Models continue to show a swath of showers along and just behind the boundary overnight which should clear most of the region prior to daybreak Sunday. Although instability remains limited, latest progs suggest a bit stronger lift just west of the region which may allow ongoing shallow convection with thunder to spill into the far west Saturday evening. Thus included a brief thunder mention along the West Va border, with showers initially a bit slower to enter the west early on followed by categorical to likely pops into the early morning hours of Sunday. Rainfall totals mainly around one half inch west to a quarter inch or less east. Again main concern with a surge in wind speeds with the frontal passage, and then lingering winds within the cold advection into Sunday as subsequent upper energy crosses from the northwest. Latest GFS quite impressive with post frontal subsidence per pressure rises and drying behind the boundary espcly western sections around midnight and east to the Blue Ridge shortly thereafter. This likely enough for advisory levels winds from the foothills west with possible warning criteria southern Blue Ridge into the NC ridges. However given third period and after coordination with surrounding offices, will hold off on any headlines for wind at this point, including watches given the forecast brief nature for higher speeds mainly along the ridgetops. Other aspect is with possible snow accumulations over the higher western elevations given the sharp drop in temperatures as the strong cold advection arrives into Sunday morning. Appears just enough residual moisture remaining long enough per forecast raobs for upslope snow showers to be a bit more widespread espcly northwest including western Greenbrier down to BLF. This could result in an inch or so of snow at higher elevations despite warm ground conditions. These snow showers/flurries likely to linger through much of Sunday given the passage of the coldest air aloft under the upper trough. Therefore kept some higher pops going northwest Sunday morning before slowly tapering back to mainly flurries by late in the day. Otherwise will be a windy/breezy day under strong northwest winds and chilly temperatures that wont get out of the 30s far west and 40s to around 50 elsewhere. Should see clouds/winds diminish during Sunday night in the wake of the upper system and in advance of high pressure sliding in from the southwest. With cold air in place under less gradient and clearing skies will likely see a very cold overnight with 20s across the board. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 300 PM EST Friday... Upper trough lifts out early Monday allowing high pressure to build in for early next week under shortwave ridging. This will allow winds to finally diminish Monday afternoon as the gradient weakens before heights rise Tuesday resulting in warming temperatures to more seasonal levels under more sun/light winds. A more upper level split flow regime looks to develop for the rest of the week following a weak cold front that will dip through from the northwest Tuesday night as the pattern unfolds. Frontal passage looks mainly dry with perhaps more clouds/isolated showers espcly south/west into early Wednesday before high pressure builds in Wednesday afternoon through Friday. This should result in overall quiet weather with slightly below normal temperatures through Day7. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... As of 637 PM EST Friday... VFR conditions will continue through 19z Saturday, then MVFR conditions with convection will enter the forecast area. Lower clouds will spread east Saturday afternoon into Saturday night. Biggest impact to aviation operations will be winds and wind shear in the western mountains after 09z Saturday morning. Winds through midnight should remain light variable tending southeast. NAM- 3km low- level winds depict a southwesterly low- level/ridgetop jet of 35 kts after 09z propagating along the ridges, further strengthening to near 50 kts late in the TAF period. This will contribute to pockets of low- level wind shear. Areas of mechanical turbulence appear possible in and around the mountains beginning overnight tonight and into Saturday. Into Saturday afternoon, southwest surface winds should increase to 6-12 kts with surface gusts 18-25 kts. Medium confidences in ceilings,visibilities and winds during taf period. Extended Discussion... A powerful cold front moves across the TAFs Saturday night into Sunday. This will lead to several impacts to aviation, including a period of rain changing to mountain snow showers (possible -SHSN at Bluefield) and a frontal wind shift to northwest with wind gusts further increasing areawide. Best chance at sub-VFR conditions is Saturday night into Sunday. For Sunday, may see a continuation of sub-VFR stratus in the western Appalachians, with breezy/gusty northwesterly wind conditions areawide also continuing. May see mountain snow showers coming to an end later Sunday afternoon. Northwesterly winds finally abate by late Sunday evening. Conditions then transition to VFR Monday through Thursday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AL/JH NEAR TERM...AL/KK SHORT TERM...JH LONG TERM...JH AVIATION...AL/KK

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