Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 011200 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 700 AM EST Thu Dec 1 2016 .SYNOPSIS... High pressure will build in from the southwest today into Saturday. The high moves overhead Sunday though a storm system developing over Gulf Coast states should begin to spread moisture our way Sunday into Monday. && .NEAR TERM /THROUGH TONIGHT/... As of 330 am EST Thursday... Models keeping northwest flow today in the low levels with variable solutions on extent of moisture and precip in the upslope area. Seems moisture will be limited enough to keep isolated threat in the Greenbrier Mountains. Temperatures favor a snow/rain shower mix, but again little qpf so not expecting accumulations. Winds should be brisk at times today across the mountains/foothills, with gusts as high as 25-30 mph, to possibly 35-40 mph early in the higher terrain. Temperatures will actually be near normal with highs from the 40s mountains, to 50s east. Tonight, the flow appears to weaken where winds tally off some, though center of high stays over the Gulf Coast states. With upper vort moving in the flow aloft across the mountains, some lift into the mountains may allow for a slight chance for more snow showers in the area west of Lewisburg, WV but again not much qpf if any. Lows will stay at or above normal with lows from the upper 20s to lower 30s mountains, to mid 30s east. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... As of 430 AM EST Thursday... A brief period of zonal flow will be in place at the beginning of this period as the previous upper low exits the northeast U.S. and a southern stream upper low deepens across Mexico and south Texas. This later system will be our next significant weather maker late in the weekend. For Friday...a very weak clipper system is evident in the WNW flow aloft, which could support development or continuation of light upslope snow showers. Support is minimal and the upper-level pattern is not overly favorable, but will continue with a low mentionable pop across western Greenbrier. Otherwise, mostly cloudy west to mostly sunny Piedmont. Temperatures will be seasonably cool as 850mb temps hover in the 0C south to -6C north range, trending upward slightly Saturday. This will equate to near to slightly below normal temperatures. Saturday, high pressure will linger but expect extensive high clouds to overspread the region as the southern stream system begins to move east into Texas and the flow aloft becomes more diffluent. The cloud cover and cool 850mb temps will keep surface temperatures seasonably cold. Sunday presents the biggest forecast challenge this period as the southern stream upper low strengthens and moves into the Mid- South and begins to take on a negative tilt. Strong isentropic lift will develop Saturday night and spread into the southwest part of the CWA as the southern stream system develops. With 850mb temps at or below 0C yet at 12Z Sunday and a likely in-situ wedge pattern, a period of snow or rain mixed with snow will be possible across the western mountains of NC and VA before warmer air arrives from the south. There are considerable differences between the GFS and the NAM with regard to how quickly the column will saturate, with the NAM much quicker to do so early Sunday. The BUFKIT sounding for Boone shows good potential for snow at 12Z Sun while the GFS shows a marked dry layer in place, not moistening up enough for precipitation until afternoon, at which point the entire forecast area is too warm for anything but liquid precipitation. Hopefully later model runs will get a better handle on this, but for now have continued with a mention of rain/snow western higher elevation areas Sunday morning, changing to all rain during the afternoon. Temperatures will remain just below normal Sunday, but warm above the critical freezing level by late morning/early afternoon even in the west, but will likely struggle to do so at the rate the models advertise given the wedge in place. QPF amounts Sunday will be light, mostly 1/2 inch or less as the main system remains well to our southwest at this point. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... As of 445 AM EST Thursday... The aforementioned Sunday event is just an antecedent short wave ejecting from the deep southern U.S. low. The main show for our region in assocation with this upper low will come later Monday into Tuesday as the system finally lifts across the Appalachians and Mid-Atlantic region. The strong negative tilt to the upper low as it moves across the area will lead to significant PVA/upward vertical motion and a good chance for a soaking rain, potentially another inch or so. Two concerns at this point are once again the potential for a brief period of mixed rain/snow at higher/colder elevations west of the Blue Ridge early Monday and the threat for thunderstorms into Tuesday. With respect to the winter weather threat, this looks to be less than what is possible on Monday as 850mb temps continue to warm, but a brief rain/snow mix in western/higher elevations cannot be ruled out around daybreak Monday. Later Monday into Tuesday 850mb temps surge back into the lower double- digits (e.g., +12C) with strong warm advection. However, significant SVR parameter and CAPE all suggest any notable threat for thunder will remain to the southeast of our CWA. Given this last event, however, I would say the threat for thunder Tuesday is non-zero at this point. Temperatures will be much milder through the period with highs warming into the 50s west and 60s east with lows only in the 30s and 40s after Monday. After this system passes, a significant surge of cold air, coldest of the season, looms to our west for late week. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... As of 650 AM EST Thursday... Northwest flow will keep stratocu banked up across the mountains for this period, resulting in mainly high end MVFR/low end VFR cigs at BLF/LWB. Appears ROA/BCB will be scattered most of the day though small period of bkn VFR cannot be ruled out. Winds will be west to west-northwest at 8-13kts with gusts to 20-25kts...higher in the mountains from mainly 14z-23z. High pressure will still be southwest of the region tonight though winds speed should weaken some. Extended aviation discussion... High pressure enters the area Saturday into early Sunday with VFR conditions. Will start to see moisture stream north from a storm system moving across the Gulf Coast states Sunday into Monday with increasing threat of mainly rain. Will likely see some sub-VFR cigs and possibly vsbys at most sites by Monday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...WP NEAR TERM...WP SHORT TERM...RAB LONG TERM...KK/RAB AVIATION...WP

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