Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 131809 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 109 PM EST Wed Dec 13 2017 .SYNOPSIS... Arctic air encompasses the region this morning. Strong northwest winds will persist early this morning before diminishing. Another clipper will cross the Great Lakes and Ohio Valley tonight and early Thursday with another round of elevated wind speeds, although temperatures will not be as cold. && .NEAR TERM /THROUGH TONIGHT/...
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As of 108 PM EST Wednesday...Early-afternoon update increased sky cover a bit sooner into southeast West Virginia and the New River Valley for the afternoon hours. A fast-moving Alberta Clipper and related upper disturbance centered over southern Wisconsin is extending a surface warm front east-southeast into the western Appalachians, contributing to faster increase in cloud cover. Think lower cloud cover shouldn`t impede warming much at all as it comes in mostly after sunset, so otherwise no other changes needed attm. This clipper system will become a focus for sensible wx into the tonight/Thursday period. More on that later... Previous discussion issued at 330 AM... Arctic airmass over the region is resulting in temperatures in the teens. Winds are gradually beginning to diminish, but still resulting in single and sub-single digit wind chills. Snow showers across the mountains yesterday and last night have left a dusting to as much as 2 inches of new accumulation. The wind has drifted quite a bit of this onto the roads, and with temperatures in the teens its making for some icy travel per road treatments not being very effective at these temperatures. If we can grin and bear it through lunch-time, then we should see a market improvement for the afternoon. Coldest of the airmass is already in place with 850 MB Temps of m15 deg C. That means its all uphill from here, with models indicating warming throughout the day and 850 mb readings near 0 deg C by the end of the day. Temperatures at the surface will still struggle to get much above freezing for high temperatures, but with full sunshine it will hopefully allow road treatments in the mountains to be a lot more effective at clearing some of the ice and snow from the highways. East of the Blue ridge where little or no snow occurred yesterday, the sun should allow temperatures to make a run for 40 degrees by mid afternoon. Another fast moving upper level disturbance (clipper front) can be seen on the water vapor imagery entering the upper Midwest this morning. This clipper is forecast to move across the Great Lakes and Ohio Valley, farther north than the last system. Greatest pressure rises with this feature are expected to pass north of our region, never the less, we will get a surge of wind tonight and early Thursday. Forecast 850mb winds of 50kts may require need for a wind advisory for parts of our region tonight, but will allow existing advisories to play out before issuing any new headlines. As for potential snow with tonight`s clipper, it looks to be a lot less compared to Tuesday`s event. Depth of the moisture profile on Tuesday was all the way up to 8000 ft. Tonight`s forecast depth is only to 4500 ft which suggests any accumulation will be confined to the highlands of WV with trace amounts as far south as the high country of NC. For now will go with 1-2 inches of new accumulation for NW Greenbrier and mainly flurries elsewhere. With the passage of the clipper, the 850 MB temperatures slip back to about m5 deg C. This suggests a relatively milder night with lows in the 20s to around 30 (compared to the teens from last night).
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&& .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/... As of 335 AM EST Wednesday... Thursday, the pressure gradient behind the departing shortwave trough will slacken, allowing for decreasing winds throughout the day. However, conditions early Thursday morning will still be on the very gusty side. Thursday into early Friday, the area will transition into a brief zonal pattern, with building high pressure across the region. This will yield dry and cooler conditions across the area. Late Friday afternoon into Friday night, the next Great Lakes upper level shortwave trough will progress west to east, north of the region. The tail end of the trough axis will cross the region with shallow moisture. Increasing northwest flow will once again increase across the region with isolated upslope snow showers across portions of southeast West Virginia continuing into and through Friday night. By Saturday, an upper level shortwave ridge will move into the region, helping to decrease the winds once again, and bring slightly milder conditions to the area. && .LONG TERM /SUNDAY THROUGH TUESDAY/... As of 258 PM EST Tuesday... High amplitude pattern seen during the past week will finally begin to flatten this weekend and gradually work into weak upper ridging across the southeast states early next week. This should basically act to cut off any added cold air intrusions with more of a Pacific nature airmass from Sunday through Tuesday. However a leftover wave across the Gulf states may push far enough north within increasing warm advection aloft to bring some light precipitation Sunday into Sunday night before drying returns Monday. However timing of this system remains iffy with some solutions much slower with rain lingering into Monday. This would support mainly a rain event with perhaps some mix at the onset if earlier arrival occurs Sunday morning. Otherwise running with mainly chance pops Sunday into Monday morning, then dry Monday afternoon/Tuesday under slightly higher heights and south of most northern stream energy at this point. Good moderation in temperatures to occur through the period as the cold pool aloft lifts out Saturday followed by decent west/southwest flow through Tuesday. This supports highs rebounding to near normal to start and then above normal into Day 7 including some 50s ahead of the next weak front && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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As of 104 PM EST Wednesday... VFR conditions through about 04z Thursday. Will see lowering VFR low- mid deck through this time period, with southwesterly gradient winds of 8-10 kts with occasional gusts to near 20 kts during the afternoon/evening hrs. Each of these effects due to the approach of another fast- moving Alberta Clipper system. After 04z, aviation conditions begin to deteriorate particularly for the western mountain terminals, due to northwesterly upslope snow showers, low ceilings and strong post-frontal northwest winds. Though VFR conditions should predominate Lynchburg, Danville and Roanoke through the TAF period, should see ceilings drop to MVFR at Bluefield and potentially at Lewisburg and Blacksburg. Lower confidence in overnight ceiling forecast for Lewisburg and Blacksburg. Will see most persistent snow showers with highest confidence mainly on the West Virginia side and in the southern Blue Ridge in NC, but there may be periods between 09-14z with potential snow showers/flurries as far east at Lewisburg, Blacksburg and Roanoke. Snow showers look to abate by noon Thursday, with ceilings also trending VFR. Northwesterly winds become gusty post-frontal overnight lasting into midday Thursday, though the core of strongest winds should be between around 07-13z offering potential for low- level wind shear and turbulence along the spine of the Blue Ridge. Medium to high confidence in ceilings, visibilities and winds through 04z. Medium confidence in ceilings, visbys and winds 04z through 18z. Extended Discussion... Looking at VFR conditions with abating wind speeds/gusts Thursday afternoon and evening. Other than an outside shot of MVFR/VFR ceilings and possible upslope snow showers at Bluefield Friday night, VFR conditions should prevail until Sunday night. A better shot exists for sub-VFR conditions from a system system forecast to emanate from the mid-Mississippi Valley Sunday night into Monday.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...AL/PM SHORT TERM...DS LONG TERM...JH AVIATION...AL/PM is the U.S. government's official web portal to all federal, state and local government web resources and services.