Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 211424 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1024 AM EDT Wed Mar 21 2018 .SYNOPSIS... A complex area of low pressure across the region will consolidate offshore this morning before deepening and heading north along the Mid-Atlantic coast this afternoon. The system will finally pull moisture out of the region later tonight into Thursday as it continues to strengthen while passing off New England by Thursday morning. High pressure briefly returns to the region on Friday followed by another potential winter weather system over the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 1021 AM EDT Wednesday...Steadiest snow presently extends from Monroe and Greenbrier Counties, then arcing east/southeast across central VA, Southside into the Piedmont of NC. Further south and west of these areas, precipitation intensity has turned lighter, on the southern end of a west-east deformation/trough axis that extends from closed 925-850 mb low located off the coast of VA. Primary steady snow area should gradually pivot north/northeast with time into the late morning/early afternoon hours, with precipitation intensity trending lighter into the afternoon in the Piedmont/Southside areas. It may still be snowing (or mixing with rain/"white rain") the steadiest snow should be mostly confined into the Alleghany Highlands/Greenbrier County area. Will make no changes to headlines attm, with decisions forthcoming on the Winter Weather Advisory in NC at noon. Will review 12z guidance before making that decision but conditions should not be getting substantively worse in those areas. Kept snow accumulations the same as well, with any additional snow accumulations through afternoon ranging from an additional inch in the Piedmont and High Country of NC, 1-2" in the VA Blue Ridge/New River Valley with 2-5" in the Greenbrier/Alleghany Highlands areas. By late afternoon/evening, would expect additional snow in the more favored upslope areas with northwesterly flow commencing. This should see western sections (including Mtn Empire, NC High Country counties as well as Summers, Mercer and western Greenbrier) see an uptick in precip (snow) while precipitation winding down elsewhere. Did make some downward adjustments to hourly temperatures, most noticeably in the foothills and VA/NC Piedmont. Would expect limited insolation which will keep temperatures from climbing more rapidly, with perhaps some boost from downslope with progged northwest/west-northwest low-level wind regime. This results in a slightly slower changeover to rain/snow or rain, but by that point steadier precip should have since ended. Previous discussion follows... Latest radar trends show that precip across the region has become more spotty/banded in nature with a long band lingering along the Blue Ridge while some spots have switched back to rain where precip has become lighter. This likely due to some weak subsidence in the wake of the meso low that brought the initial batch of heavier snow/sleet before midnight. Otherwise not a lot of change to going headlines with the upper low now west of the mountains progged to cross the region this morning allowing the surface low off the Va capes to deepen while heading slowly north by this afternoon. Expect once this happens and the flow becomes more northwest, will see snow increase across the western ridges per enhanced upslope with some filling in elsewhere of at least light snow as the transition takes place and the conveyor belt of deeper moisture swings back south for a bit. This supports continued heavy snow espcly north/northeast sections to along the Blue Ridge. Elsewhere questions about coverage southern sections before things get too warm this morning and along the I-77 corridor where currently see some rain and where the HRRR leaves a void this morning. Otherwise will continue with high pops early this morning, then tapering central/west after midday as downsloping increases and lift in the deformation zone quickly shrinks away to the north. This should lead to only a few bands of snow/rain remaining by mid to late afternoon except for continued upslope snow showers in spots. Kept highs below mos although a late day surge could occur southern sections where snow will be less. System wraps up well to the northeast overnight allowing the pressure gradient to ramp up on strong cold advection around the deepening coastal system. This likely to bring advisory level winds to the Blue Ridge given a decent jet aloft and packing of isotherms along the mountains. Therefore will continue to wrap into the current warning for now. However upslope snowfall looks to wane after midnight as things dry from aloft and the flow turns a bit more northerly. This supports trimming back on pops and added amounts overnight out west with clouds lingering until late elsewhere. Lows quite cold with most in the 20s making for wind chills in the teens or perhaps single digits by morning. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 245 AM EST Wednesday... Better subsidence arrives Thursday as we slide in between the exiting low to the northeast and the next upstream system organizing to the northwest. However appears overall clearing may be slow on Thursday given some trapped low level moisture and containing strong upslope flow in the west. Therefore kept highs on cool side of guidance pending the degree of insolation that develops espcly east where could jump into the 50s with upper 30s to 40s elsewhere. Models also show a 85h 40 knot jet persisting across the mountains into Thursday as expect wind advisory speeds may linger at least during the morning given the degree of subsidence. Also below guidance for highs on Thursday where little to no sunshine expected. Will gradually see some warm advection kick in on Friday just in advance of the next upstream system that may bring back high clouds during the day and lowering cloud bases from northwest to southeast Friday night. Some spotty light rain or snow could also work in far western sections late but likely wont include for now. Highs again mostly 40s to low 50s. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 140 PM EST Tuesday... Low pressure tracks from Missouri on Saturday night, across the Tennessee Valley and Carolinas to the western Atlantic by Sunday night. Some differences in the guidance how far south this low will move, which in turn will impact where the winter weather will be on the northern side of the baroclinic zone. Timing has been consistent, keeping the best probability of precipitation from Saturday afternoon into Sunday morning. Surface high pressure wedges down the east slopes of the Appalachians Monday and Tuesday. Precipitation over the Tennessee and Ohio Valley may spill east into the mountains but the probability remains low. Temperatures will remain below normal through the period, especially daytime highs. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... As of 700 AM EDT Wednesday... Poor flying conditions to continue this morning with widespread sub-VFR in snow and rain including mountain obscurations. These low conditions look to gradually improve espcly along and east of the Blue Ridge this afternoon as winds shift to the west and northwest which should bring steady precip to an end with more showery nature though snow showers will persist into the afternoon along/west of the mountains, with rain/snow shower mix in the east through early afternoon. Cigs/vsbys anticipated to at least go MVFR this afternoon outside of the WV mountains. Northwest winds are expected to become gusty in the afternoon with a few gusts over 25-30 kts possible. Tonight into Thursday, the upslope snow showers will continue to gradually decrease in coverage with northwest winds remaining strong through the day Thursday with gusts to 30-35 kts likely espcly mountains. Extended Aviation Discussion... Mainly VFR conditions are expected by Thursday night through Friday night under weak high pressure. Saturday into Sunday, a return to sub-VFR conditions is expected as our next potential winter weather system crosses the area. && .EQUIPMENT... As of 1021 AM EDT Wednesday... The Mount Jefferson NWR remains off the air. The radio unit needed to repair the system is expected to arrive tomorrow (Thursday). The earliest this system will again be operational will be tomorrow. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Winter Storm Warning until 8 AM EDT Thursday for VAZ007- 009>020-022>024-035. Winter Weather Advisory until 6 PM EDT this evening for VAZ032- 033-043-044-058-059. Winter Storm Warning until 6 PM EDT this evening for VAZ034- 045>047. NC...Winter Storm Warning until 8 AM EDT Thursday for NCZ001-002- 018. Winter Weather Advisory until noon EDT today for NCZ003>006- 019-020. WV...Winter Storm Warning until 8 AM EDT Thursday for WVZ042>044- 507-508. && $$ SYNOPSIS...JH NEAR TERM...AL/JH SHORT TERM...AMS/JH LONG TERM...AMS AVIATION...DS/JH/WP EQUIPMENT...AL/AMS is the U.S. government's official web portal to all federal, state and local government web resources and services.