Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 190545 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1245 AM EST Sun Nov 19 2017 .SYNOPSIS... A strong cold front will sweep southeast through the region tonight preceded and accompanied by gusty winds and scattered to numerous showers. Much colder air on blustery winds will arrive behind the front on Sunday, 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. && .NEAR TERM /THROUGH TODAY/... As of 832 PM EST Saturday... Regional WSR-88d showed showers entering the western mountains. Adjusted POPs for the onset of showers (earlier timing) and movement east tonight. Made some minor adjustments in temperatures for tonight into Sunday morning. Latest surface meso obs starting to show winds gusts above 30 mph in elevations above 2800 feet. Wind advisories looks good, will freshen up NPW to remove evening wording. Post frontal upslope snow showers with light accumulation seem reasonable. Will watch evolution with front for additional potential ISC grids adjustments. As of 648 PM EST Saturday... Wind advisories remain in effect until noon EST Sunday across the higher terrain. Made some minor adjustments in temperatures utilizing the surface obs, trends and blended towards GLAMP. Shaped pops towards HRRR and Hiresw-ARW-East tonight into Sunday morning. More changes later... As of 330 PM EST Saturday... Strong cold front moving through the OH and TV Valley will sweep east through the Blacksburg forecast area tonight, preceded and accompanied by scattered to numerous showers. Instability is very limited with this feature, such that thunder, if any, will remain isolated and likely confined to the extreme western or southwestern portion of the forecast area where some mid level buoyancy will be maximized. Strong prefrontal winds approaching 45 knots just above the developing inversion layer, and strong post-frontal winds behind the front of the same magnitude with 6-hour pressure rises around 10 millibars support ongoing Wind Advisories though Noon on Sunday for the mountains and the VA foothills. Some localized gusts to around 50 knots possible across elevations at or above 5K feet, but see no need at the present time to hoist High Wind Warning for this area considering limited areal coverage. Fast moving system should keep precipitation amounts tonight to under one half inch, with most areas receiving a quarter inch or less. Strong cold advection and increased upsloping should help transition rain to snow showers later tonight across the western flanks of the Appalachians - with a continuation through Sunday - perhaps into the early part of the short-term period as a second short wave trof races northeast through SE WV Sunday afternoon into early evening. Some spotty snowfall amounts in the 1-2" range are possible across the highest terrain, such as at Mount Rogers, VA and across Western Greenbrier County, WV; however, most other upsloping areas from the mountains of NW NC north through SW VA into SE WV should receive only an inch or less. With the strongest cold air advection to arrive on Sunday, expect to see temperatures flatline near freezing or even slowly fall during the day, especially across the higher terrain where clouds will hold fast. East of the Blue Ridge into the Piedmont, downslope clearing and a bit later arrival of the coldest air should allow temperatures to recover into the lower or mid 50s. && .SHORT TERM /TONIGHT THROUGH TUESDAY/... As of 215 AM EST Saturday... While snow showers are likely to be ongoing in the mountains of southeastern WV, a secondary shortwave trough/500 mb vort max progged to ripple through the northwest cyclonic flow likely to lead to a brief enhancement of snow showers in southeast WV at least. Shortwave is expected to move across the northern half of the forecast area through midnight, with a reinforcing shot of colder air awaiting behind it. Froude number is initially unblocked which supports possible flurries as far east as the Alleghany Highlands in VA early Sunday evening, but are expected to become more neutral to blocked by overnight. The moisture layer also begins thinning out and PoPs taper from south to north toward dry by the pre-dawn hours. Any accumulations of less than an inch would be confined to western Greenbrier southwest into parts of Mercer County before midnight, with just a few flakes into the Alleghany Highlands. Passage of the shortwave and pressure rises may initially maintain gusty ridgetop winds into Sunday evening; though as inversion height shrinks the mixed layer around midnight, a decrease in wind speeds and gusts along the ridges can be expected. A rather cold night with many areas likely to fall below freezing, with the coldest values in the low 20s in southeast WV and the Mountain Empire region. A broad area of high pressure then begins to settle into the region Monday into Tuesday. Shot of colder air is brief, and low-level temperatures begin to moderate as we tap into a modest west to southwesterly component. It will be pretty chilly early on Monday with apparent temperatures west of the Blue Ridge in the teens through the morning commute, so bring along an extra layer as the holiday workweek begins. Monday and Tuesday overall appear uneventful otherwise with high pressure and ridging aloft in control. May see a few high clouds intrude into Tuesday, but overall lots of sunshine this period. Forecast calls for dry conditions Monday with highs low 40s to lower 50s, lows mid 20s to near freezing Monday night, and highs back well into the 50s come Tuesday. && .LONG TERM /TUESDAY NIGHT 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. The GFS and ECMWF indicate show a trough in the southern branch of the jet across the Mississippi Valley/Deep South, and a more potent northern stream trough over the Great Lakes/Upper Midwest Tuesday night. Both also show a weak Gulf coast low developing on an old frontal zone around the Wednesday timeframe. Question that will likely govern what unfolds is if phasing can occur between the two streams. This isn`t indicated at all in the GFS, which would serve to keep us at least partly cloudy but dry. The ECMWF on the other hand was indicating a little more phasing in its 00z run, which would do two things: (1) bring an area of showers further north into the Blue Ridge and Piedmont Tuesday night/overnight and (2) tap into colder temperature profiles behind the departing system for the Thanksgiving holiday Thursday. Less phasing was noted in the 12z ECMWF, so while still some level of uncertainty to be accounted for, sided a little closer to the more temperate GFS idea for the Tuesday through Thursday timeframe. This keeps temperatures slightly below normal, with only a limited chance for PoPs east of the Blue Ridge on Tuesday night. Even if the more pessimistic ECMWF solution plays out, it still wouldn`t likely lead to any significant/impactful weather. 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 /06Z SUNDAY THROUGH THURSDAY/... As of 1235 AM EST Sunday... Local radar showed a pre-frontal band of showers from eastern West Virginia into western North Carolina. Winds ahead of these showers were from the southwest with gusts up to 20 knots. Winds shift to the west behind the showers with gusts to 30 knots. Ceilings were generally VFR with this precipitation with a few spots of MVFR ceilings with the heavier rain. An intense cold front extended from Lake Erie to northwest Georgia early this morning. The front was moving rapidly east and will turn the winds to the northwest with gusts of 30 to 45 knots through the rest of the morning. Clouds will clear out east of the Blue Ridge this afternoon, but MVFR ceilings are expected in the mountains for much of the day. Strong upslope winds will also result in MVFR rain or snow showers on the western slopes of the Appalachians, including at KLWB and KBLF. Any snow accumulation at these airports will be light. High confidence on the winds and ceilings and visibilities during the taf period, but medium confidence on the timing. Extended Discussion... Higher pressure and a weakening pressure gradient should allow for northwest winds to slowly abate by late tonight, along with decreasing clouds across the western flanks of the Appalachians. Widespread VFR conditions are expected thereafter from Sunday night into Friday. && .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 NEAR TERM...KK/WERT SHORT TERM...AL LONG TERM...AL AVIATION...AMS/KK is the U.S. government's official web portal to all federal, state and local government web resources and services.