Area Forecast Discussion
Issued by NWS Blacksburg, VA

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016 FXUS61 KRNK 180448 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1148 PM EST Sun Dec 17 2017 .SYNOPSIS... A weak disturbance will cross the region overnight into Monday with high pressure returning to the region by Tuesday. Another disturbance will skirt mainly the southern half of the region Tuesday night into Wednesday. The next strong cold front to impact our region will cross the area on Saturday. && .NEAR TERM /THROUGH MONDAY/...
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As of 1135 PM EST Sunday... Should stay fairly cloudy overnight with lower level moisture trapped below subsidence inversion. Models overall keep it dry through the night, but model soundings suggest potential for drizzle or very light at times west of I-77 in WV. Temperatures will fall just a few degrees with lows mainly in the lower to mid 30s. Patchy fog also not out of the question in the river valleys. Previous early evening discussion... Forecast updated to increase pops over the north/east per radar/observations. High-res models continue to favor the west through the night for best chance of rain/showers, but overall should see a weakening trend in coverage. Otherwise, forecast on track. Previous discussion from early afternoon... Patchy light rain, and probably a few pockets of sleet, were progressing across the region in advance of a disturbance in the central part of the country. The moisture was doing its best to reach the surface through a decent dry layer aloft. Enough of a dew point depression exists that as the column moistens, some saturation at or below a wet bulb of 32 degrees or colder is expected for a few parts of the area. The resultant temperature profile may yield some brief sleet within the mix of the patchy light rain. Precipitation east of the crest of the Blue Ridge will even more limited than that across the mountains. As we head through the overnight hours, the same weather is forecast during the evening, with perhaps a little snow in the mix over higher elevations of southeast West Virginia. By midnight, and lasting into Monday, moisture will be on the decrease, becoming very shallow, just a little bit above the boundary layer. Any remaining light precipitation will be very light rain or drizzle across mainly parts of southeast West Virginia. Despite falling temperatures, lack of saturation with the dendritic growth zone will be lacking. Any light precipitation that falls with surface conditions at or below freezing will be in the form of light freezing rain or freezing drizzle. This scenario looks probable for perhaps only an hour or two around daybreak Monday across the highest elevations of western Greenbrier County, West Virginia. Elsewhere, where the light precipitation is forecast, temperatures are forecast to remain above freezing. Skies are forecast to remain cloudy across the entire region overnight. By Monday, enough drier air is expected work its way into the area to allow for clearing skies east of the crest of the Blue Ridge where a weak downslope component will help add to the cloud dissipation. Locations across the mountains will remain mostly cloudy to cloudy on Monday. Low temperatures tonight are forecast in the low to mid 30s across the mountains with mid 30s across the Piedmont. High temperatures Monday of the upper 40s to the lower 50s are forecast across the mountains with upper 50s to around 60 across the Piedmont.
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 110 PM EST Sunday... Not much of a break on Tuesday between the low level moisture eroding over the mountains in the morning and the mid and high clouds spreading in from the southwest in the afternoon ahead of the next system. With all that cloud cover will be trending toward cooler guidance in the mountains for maximum temperatures Tuesday. Clouds and precipitation in North Carolina and southern Virginia will also limit warm up on Wednesday. Will stay close to cooler guidance for highs. Best upper diffluence is on Tuesday night and Wednesday morning in the right rear quadrant of a 140 knot upper jet. Will be trimming northern extent of precipitation chances and lean toward the GFS placement of the best probability of precipitation for Tuesday night and Wednesday. Partial thicknesses off the ECMWF and GFS were showing the potential for mixed winter weather on the northern edge of any remaining precipitation late Wednesday night and Thursday morning. But BUFKIT shows precipitation has ended by the time lower levels get that cold. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 110 PM EST Sunday... Upper low that entered the Pacific Northwest on Wednesday will drop southeast into New Mexico by Thursday night before tracking through the Great Lakes on Saturday morning. After that long range models have significant differences. WPC favoring the Ecmwf and ECMWF ensemble which digs the long wave trof over the central United States and brings the polar northern stream upper low into the northern Mississippi Valley and western Great Lakes on Sunday and Monday. Surface high pressure crosses Virginia on Thursday, then southwest winds will increase ahead of the the next cold front. The surface cold front will pass through the Mid Atlantic states on Saturday but then become parallel to the upper flow on Sunday. Truly colder air and potential for winter precipitation will not be reaching the region before Sunday. && .AVIATION /06Z MONDAY THROUGH FRIDAY/...
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As of 1140 PM EST Sunday... Sub-VFR in the mountains will persist through the period, with BLF/LWB at times dropping below 1000ft through 10z. Westerly flow is going to keep MVFR cigs at BLF at least until Monday evening while LWB may jump above MVFR by the end of the period. The other taf sites will also have MVFR at times early before scattering out after dawn. Extended Discussion... Through Friday, the bulk of the region will maintain VFR conditions as a split-flow pattern establishes itself across CONUS, with our little part of the world remaining in between systems. The exception to this rule may be on Wednesday when a southern stream system may be far enough north to provide sensible weather to at least the southern half of the region. Our next cold front may arrive Friday night into Saturday. The latest model guidance offers increasing, gusty winds both ahead and in the wake of the front, along with sub-VFR conditions.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...DS NEAR TERM...DS/WP SHORT TERM...AMS LONG TERM...AMS AVIATION...DS/WP

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