Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 130839 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 339 AM 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 330 AM EST Wednesday... 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 bare 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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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.
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&& .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 /09Z WEDNESDAY THROUGH SUNDAY/... As of 1230 AM EST Wednesday... Aviation conditions will improve through the TAF valid period as the Alberta Clipper lifts northeast of the area, surface winds back more to the west, and upslope clouds and snow showers come to an end by morning. Overnight, we will still see bands/fingers of snow showers with brief moderate snow bursts, accompanied by brief MVFR vsbys and MVFR-IFR ceilings, tracking from the Great Lakes southeast toward the Alleghanys and Blue Ridge. As the upper flow becomes more westerly, the trajectories will become far less favorable for this to continue. Snow showers should end by or before 12Z in the west. VFR conditions are expected throughout most if not all of the TAF valid period in the east. Gusty WNW-NW winds will continue for the next several hours with gusts of 25-30kts common west of the Blue Ridge and 20-25kts east of the Blue Ridge, decreasing slowly after 08Z. Winds will become more W-WSW after daybreak with speeds mostly in the 8-12kt range through the day. It should be noted that some gusts to 50kts will be possible across Watauga, Ashe, and Grayson counties at the higher elevations for the next few hours before that threat diminishes. VFR conditions expected from late Wednesday morning through the remainder of the TAF valid period. Medium to high confidence in ceilings, visibilities and winds during the TAF period. Extended Discussion... Weak high pressure builds in Wednesday evening followed by another weaker clipper system Thursday that passes by mostly to our north. Conditions then trend VFR for the weekend, with the next chance for sub-VFR being Sunday night into Monday with a system emanating out of the mid-Mississippi Valley. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Wind Chill Advisory until 9 AM EST this morning for VAZ007- 009>020-022>024. Wind Advisory until 7 AM EST this morning for VAZ015>017-022. NC...Wind Chill Advisory until 9 AM EST this morning for NCZ001-002- 018. Wind Advisory until 7 AM EST this morning for NCZ001-002-018. WV...Wind Chill Advisory until 9 AM EST this morning for WVZ042>044- 507-508. && $$ SYNOPSIS...PM NEAR TERM...PM SHORT TERM...DS LONG TERM...JH AVIATION...AL/KK/RAB is the U.S. government's official web portal to all federal, state and local government web resources and services.