Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 300856 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 356 AM EST Wed Nov 30 2016 .SYNOPSIS...
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A cold front slides east to the mountains this afternoon, and east of the piedmont this evening. High pressure will track from the lower Mississippi Valley Thursday to the Southern Appalachians Friday morning. Expect drier and cooler weather for the end of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 340 am EST Wednesday... Radar has been pretty active this morning, with elevated instability leading to thunderstorms moving across the New River Valley/Mountain Empire and Alleghany Highlands, as well as portions of the piedmont. The latest RAP showed this elevated instability lingering into mid morning. There will be a break in the showers across the southeast CWA with main axis of lift and moisture transport staying with the front and upper dynamics across the TN Valley into the Central Appalachians. Therefore will have higher pops in the mountains this morning then models shift the axis east into the piedmont by late afternoon. There is a decent amount of lift and wind energy to give most of not all the forecast area a good rain. Unstable air is limited by clouds and showers but with increase in the jet should be enough dynamical forcing to string some thunder in the forecast, especially in the foothills/piedmont. The Storm Prediction Center shows our eastern 2/3rds of the forecast area in a marginal risk, mainly concerned about winds mixing down with line of showers and isolated storms. Will mention this in the HWO, but more along/east of the Blue Ridge as think the west will be stable enough to keep stronger winds from mixing down past 4000 ft. Some of the higher terrain this morning could see some gusts to 45 mph, although not enough to have a wind advisory. Temperatures despite the clouds and showers will warm into the lower to mid 70s east to mid to upper 60s west. Tonight, the front moves east of the forecast area by midnight with showers ending. There will be clearing skies as we head into late tonight in the east while upslope keeps clouds in the mountains, with slight chance of showers over western Greenbrier County. Colder air will star to track in overnight west of the Blue Ridge with lows in the upper 30s to lower 40s, while the foothills/piedmont slide into the mid 40s to around 50. There will be a gradient behind the front tonight but 8h winds are around 30 kts or less, so winds should be under 30 mph in the gust dept, except possible gusts to 35 mpg across the Alleghany Highlands, higher ridges.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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As of 320 PM EST Tuesday... Upslope precipitation above 3000 feet will primarily be light snow while lower elevations transition from rain to flurries Thu morning. Pressure rises behind the front will also bring breezy and gusty conditions to the area subsiding Thursday evening. The northern and southern stream becomes separated starting Friday with zonal flow over the region. Looking aloft, the forecast area will be under the influence of the northern stream with 85h temperatures running -4C to -6C going into the weekend. Friday`s high temperatures will range in the 40s across the area with 30`s along ridgetops. Besides a few mountain fair weather cumulus clouds, Friday will remain dry.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 300 PM EST Tuesday... A closed low over north Mexico will generate a disturbance over Texas Saturday. Moisture from this disturbance will get caught in zonal flow and bring an increase in clouds over the region for the weekend. An area of dry high pressure will become anchored over the area keeping bulk of the moderate to heavy rain south across the Gulf states this weekend. On Monday, the closed low exits Mexico and enters the midwest. This system will bring warm Gulf moisture over a lingering dry surface high Monday. Precipitation falling into this dry high will create an insitu wedge. Depending on the timing and availability of cold air, precipitation could start out as a light snow across the mountains, changing to rain over time. Both the GFS and ECM agree on this solution, but differ on timing, precipitation amount and p-type. The GFS has precipitation entering Monday whereas the ECM is Tuesday. For now, we will carry low PoPs for the area and a rain/snow mix for p-type mainly across the mountains. && .AVIATION /09Z WEDNESDAY THROUGH SUNDAY/... As of 1145 PM EST Tuesday... Expecting MVFR to IFR clouds to fill in over southwest Virginia, northwest North Carolina and southeast West Virginia tonight. LIFR fog developed at locations that had rain Tuesday afternoon and stay cloud free longer. Winds will pick up overnight, especially at higher elevations as the low level increases from the southwest. Low confidence on the timing for when visibilities will improve as fog erodes. Area of upper diffluence that was providing lift for the showers and thunderstorms over Mississippi and Tennessee will move into the region late tonight. Guidance was in good agreement keeping much of the area dry until after 06Z/1AM. Some warm air advection also in the region tonight and Wednesday morning which will aide in lift. Next band of heavier showers and will cross the region from west to east Wednesday afternoon allowing for widespread sub-VFR cigs and vsbys until the front crosses Wednesday evening. Shallow convection may enhance the winds. High confidence on the passage of the front and associated moderate showers but lower confidence on the exact timing. Extended aviation discussion... Improving conditions expected after the upper low and final short wave move east of the area later Wednesday night. Conditions should become VFR east of the Blue Ridge into the weekend. Upslope clouds and potentially a weak clipper system could bring a low chance of rain or snow showers into the western sites Thursday and Friday along with lingering MVFR cigs before conditions improve there as well over the weekend. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/WP NEAR TERM...WP SHORT TERM...RCS LONG TERM...RCS AVIATION...AMS/JH

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