Area Forecast Discussion
Issued by NWS Blacksburg, VA

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483 FXUS61 KRNK 191440 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 940 AM EST Sun Nov 19 2017 .SYNOPSIS... Much colder air on blustery winds will arrive today, with clearing skies across the Piedmont, but with abundant clouds over the mountains along with some upsloping snow showers across the western flanks of the Appalachains. High pressure builds in from the southwest late tonight into Monday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 938 AM EDT Sunday...Only noticeable change made to the going forecast was to force more -RA/-SN as opposed to pure -RA in the grids for today. Radar showing narrow bands of light returns in the strong northwesterly cold advection, which have been leading to intervals of rain or snow showers per METARs in the mountains of western Summers, Mercer and Greenbrier Counties, the Mountain Empire to about Wytheville, and into Ashe, Alleghany and Watauga Counties. As surface temperatures are near or just above freezing, this is probably a wet/low-SLR type snow and limited accumulations reflected in the forecast appear to be holding up. Expect intervals of snow showers to predominate these areas, perhaps extending as far east as Giles and Craig Counties. It`s a little milder but drier in the Piedmont. From a messaging perspective, will continue to carry the Wind Advisory through to its expiration at noon since it is still breezy, though the strongest winds capable of causing damage have already passed. Recent gusts at Boone in the low- 40s MPH are pretty much the strongest gust observations through the last couple hrs this morning. Doppler profiler winds this morning indicate a gradual downward trend. Also do note some wave clouds around the mountains seen in visible imagery, so certainly should be bumpy for aircraft flying aroud the mountains. Do expect another uptick in winds/gusts with the passage of the secondary shortwave trough now over IL/IA later tonight but appears to be to just sub- Advisory levels. More to come later... Previous near-term discussion issued at 220 AM follows... 500MB trof deepening over the eastern United States this morning. GOES16 water vapor loops showed a well defined short wave crossing into Virginia early this morning. A second vorticity maximum will track across the area late this afternoon into early this evening. Colder air aloft will provide some instability today and strong upslope northwest wind behind the cold front will result in a prolonged period of showers along the west slopes of the Appalachians. No change needed to wind advisory at this time. Expecting strong cold air advection this morning and 6hr pressure rises of 14 to 18 mb. By this evening pressure rises slacken but the second short wave will bring another brief increase of the low level jet which will extended the gusty conditions. Will be leaning toward NAM Nest and MET guidance for lows tonight. Temperatures will be in the 50s ahead of the front this morning then drop behind the cold front today. High temperatures for most locations in southwest Virginia, southeast West Virginia and northwest North Carolina will be in the morning. Much of the HiRes guidance has the pre-frontal showers into central Virginia and North Carolina by 09Z/4AM, leaving only showers in the mountains for the rest of the day. Models diminish upslope flow and low level moisture after 03Z/10PM this evening. Snow showers will taper off to flurries by midnight but cloud cover will take until around sunrise to dissipate.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... As of 218 AM EST Sunday... Upper pattern stays transitory this period, with a shortwave ridge Monday over the west side of the mountains, then next trough digs into the upper Great Lakes with broad troughing southward into the lower Mississippi Valley, early Tuesday. At the surface high pressure moves from overhead Monday to off the NC coast Monday night. Will see some increasing moisture in southwest flow but models overall keep us dry, with main surge of deeper moisture passing over the southeast Tuesday. Cannot rule out a few showers as we head into Tuesday night across the east, and with the next front over the west, but looks marginal. Models are showing a split flow regime midweek with northern stream trough over the Northeast-Mid-Atlantic with west southwest flow aloft over our forecast area, with a digging shortwave moving into the mid and lower MS Valley Wednesday-Wednesday night. At the moment models are keeping the deeper moisture and showers well south going during this time across the Gulf Coast states, but may bear watching if the the shortwave stays further north, which could push some rain toward our southern forecast area Thanksgiving. Overall, temperatures will be close to normal for lows and at or below normal for highs. May see some uptick in winds from the northwest as northern wave pushes across Wednesday per latest ECM. && .LONG TERM /THURSDAY THROUGH SATURDAY/... As of 300 PM EST Friday... GFS ensemble indicates a 500 mb pattern resembling a cold season positive Pacific-North American (PNA) teleconnection regime centered around the Thanksgiving holiday period. This often translates to mean troughiness at 500 mb into the central and eastern US, as repeated shortwave troughs round the top of a large ridge across the Pacific Coast and dig/reinforce cyclonic flow aloft. Overall an unsettled holiday period but nothing that would significantly hamper travel plans attm. Kept highs for the Thanksgiving holiday only in the 40s with partly cloudy skies and dry conditions. Looks to be a warming/moderating trend to temperatures Friday into the holiday weekend and will likely trend temperatures to near/above late-November normals. Weather pattern then turns more unsettled after the holiday weekend with a larger degree of guidance solution spread. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... As of 545 AM EST Sunday... A cold front extended from central New York through southern Georgia and had crossed through KLYH and KDAN as of 10Z. Winds were from the west to northwest with gusts of 15 to 25 knots. Cloud cover was clearing rapidly east of the Blue Ridge with MVFR clouds along the western slopes. Strong upslope winds will result in prolonged MVFR rain or snow showers on the western slopes of the Appalachians, including at KLWB and KBLF today. Any snow accumulation at these airports will be light. Winds gusts will be as high as 40 knots, especially at higher elevations this morning, then will gradually diminish this afternoon and evening. After midnight the pressure gradient will slacken and wind gusts will drop off then less than 20 knots at most locations. As the winds diminish upslope precipitation will end. Several models show low level moisture and resulting cloud cover eroding across southeast West Virginia and southwest Virginia late tonight. High confidence on the winds, ceilings and visibilities today, but medium confidence on the timing of how quickly ceilings over the mountains will improve to VFR tonight and when wind gusts will diminish. Extended Discussion... Mainly VFR conditions are expected Monday into Friday. Exceptions would be some lower cigs with a front/trough Tue night-Wed in the mountains, and again Thanksgiving. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Wind Advisory until noon EST today for VAZ007-009>020-022>024- 032>035. NC...Wind Advisory until noon EST today for NCZ001-002-018. WV...Wind Advisory until noon EST today for WVZ044-507-508. && $$ SYNOPSIS...WERT/WP NEAR TERM...AL/AMS SHORT TERM...WP LONG TERM...AL AVIATION...AMS/KK

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