Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 121749 AAB AFDRNK Area Forecast Discussion...UPDATED National Weather Service Blacksburg VA 149 PM EDT Thu Oct 12 2017 .SYNOPSIS... High pressure to the north will wedge southward along the eastern slopes of the Blue Ridge this afternoon. This wedge will give way on Saturday in advance of another cold front, which in turn will cross the region on Monday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 100 PM EDT Thursday... No major changes are planned for the afternoon forecast update. Have made some minor tweaks to the hourly temperature, dew point, wind, and sky cover grids to reflect the latest observations and expected trends through the afternoon. These trends include low level cloud cover/drizzle/light rain continuing to progress into the region from the northeast, and limited additional increase in temperatures where this cloud cover has already arrived. As of 1030 AM EDT Thursday... Strong high pressure over eastern Canada should wedge southward along the eastern slopes of the Blue Ridge this afternoon. However, the timing of this cold air damming pattern to begin is still questionable given such a warm air mass over the region and the tendency for the wedge to develop slower during the daytime hours. Cloud cover still remains prevalent over most of the region, so high temperatures were dropped a couple degrees. Low clouds and northeast winds have already reached the Piedmont at this time. In addition, mesoscale models show light rain with patchy drizzle gradually developing by the afternoon. The wedge should strengthen overnight with loss of heating and a stronger push of cool advection within a maritime air mass from the northeast. Southeast flow just off the surface will also increase to allow for better lift over the cool pool while enhancing upslope flow along the eastern slopes. This pattern supports a good swath of drizzle and fog overnight with the favored upslope areas along the southern Blue Ridge. Lows should be mainly in the lower 50s to the lower 60s.
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&& .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... As of 300 AM EDT Wednesday... The large area of high pressure moving through New England will remain wedged down east off the Appalachians into the weekend. This will keep most of the region in clouds and some light rain/drizzle, but better conditions will prevail along the far western flank of the wedge where more in the way of sun is expected. As the parent high slips further offshore on Saturday the wedge will start to break down but there looks to be enough low level moisture lingering to keep clouds around through Saturday night. By Sunday a cold front will be approaching from the west before slowly moving across the region Sunday night. This will bring a chance for late day showers far west with a better chance for more widepspread precipitation in Sunday night. Temperatures in the wedge on Friday will cool a good deal but since it has been so warm lately this cooling will only bring us down to normal levels for the middle of October. As the wedge loses its grip temperatures will rebound over the weekend with readings ahead of the front on Sunday into the lower and middle 80s east of the Blue Ridge, middle 70s/near 80 west. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... As of 200 PM EDT Wednesday... Models starting to come into better consensus with the timing and location of a synoptic scale trough crossing the eastern United States Sunday and Monday with the ECMWF on the slower side of the solutions. Strong cold front crosses the Mid Atlantic region early Monday and both GFS and ECMWF showing good upper diffluence ahead of the front on Sunday night. Most favorable location for thunderstorms ahead of the front on Monday will be in the piedmont of Virginia and North Carolina based on the timing of the front. Rest of precipitation will be post frontal. ECMWF consistent in showing 850MB temperatures behind the front dropping into the +4 to +8 range. Precipitable water values drop well below one half inch. Air mass begins to moderate Wednesday. Expect low level winds up to 30 knots with pressure rises on 2 to 5MB/3hr behind the front with decent cold air advection so will be increasing the winds on Monday afternoon and Monday night. As high pressure moves in Tuesday winds will diminish. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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As of 130 PM EDT Thursday... Low level cloud cover with some patchy drizzle and light rain will continue to progress into the area this afternoon from northeast to southwest. While ceilings of the leading edge of this cloud cover is in the MVFR/low VFR range, conditions will gradually deteriorate to IFR as we progress into the evening hours, especially, but not limited to, areas east of the crest of the Blue Ridge. Within the mountains many of the ridge tops will be obscured as we head into the evening hours, and remain that way into Friday. Light rain and drizzle will become more widespread, especially in areas near the crest of the Blue Ridge, as we progress through the overnight. Patchy fog will also accompany this light precipitation. On Friday, lee side ridge will continue through at least the morning hours, with limited improvements of flight categories through the conclusion of the current TAF forecast cycle, 18Z/2PM Friday. About the only area that may see conditions better than IFR/MVFR will be an area west of a KBLF-KMKJ line that will be along, or just outside the influence of the cold air damming scenario. Extended Aviation Discussion... Friday afternoon and night limited change expected as compared to conditions on Friday. Saturday, the lee side wedge will give way to increasing southwest flow ahead of our next synoptic scale upper trough and associated cold front. This will allow for more areas to experience VFR conditions, a trend that will continue into Sunday. Sunday night into Monday, a substantial cold front is expected to cross the area with scattered showers and some storms. Sub- VFR conditions are expected to accompany the stronger showers/storms. Also, in the wake of the cold front, lingering moisture in the west will likely manifest as some upslope sub- VFR ceilings Sunday night into Monday morning. High pressure will continue to build into the area on Tuesday. Other than some early morning patchy mountain and river valley fog, VFR conditions are expected.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/PW NEAR TERM...DS/JH/PW SHORT TERM...MBS LONG TERM...AMS AVIATION...DS

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