Area Forecast Discussion
Issued by NWS Blacksburg, VA

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833 FXUS61 KRNK 210100 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 900 PM EDT Tue Mar 20 2018 .SYNOPSIS... Low pressure will cross the region overnight, and deepen off the coast of New England as a Nor`easter by Thursday morning. High pressure briefly returns to the region on Friday. Over the weekend, anther potential winter weather system will cross our region. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/... As of 850 PM EDT Tuesday... Latest radar, upper air analysis and high-res models are favoring a corridor of higher QPF from far Southwest VA into the foothills of VA overnight. Bumped up snow amounts such that portions of southside VA have been added to an advisory, but looking at the best accumulations of up to 2 inches from northern Halifax, to northern Henry, with less than an inch along the NC/VA border. Some potential for 4-5 inches in northern Buckingham to western sections of Bedford along the Blue Ridge, but not enough to warrant a warning. Previous early evening discussion... Forecast updated to reflect some sleet mixing in with rain in the southwest, but also lowering temps further north compared to previous forecast. Warnings/advisories on track, but will re- evaluate latest high-res models and mesoanalysis to see if changes are needed to total snowfall amounts and/or headlines. Previous discussion from mid afternoon... Not a whole lot has changed regarding the synoptic transition of the events that are expected tonight into Wednesday. What has changed is the degree to which warmer air will allow for rainfall for a slightly longer period of time than originally anticipated. Also, low level profiles are hinting at the potential of sleet at the onset of the change from from liquid to frozen. Both of these factors will place a greater limit on the amount of forecast snow expected at the lower elevations. The opposite is true at the higher elevations, especially those along and north of Route 460. Northern sections of the New River Valley of southwest Virginia, north into the Alleghany Highlands, and the higher ridges of southeast West Virginia will have a slightly higher forecast of snow thanks to those elevations remaining colder, and a bit more qpf than earlier offered to generate snowfall. So, while we will keep our advisories and warnings in place, the range between valley and ridge top has increased. Some mountain valley locations may only see around an inch of snow, but its neighboring ridge tops have values more in the 4 to 8 inch range. The highest snowfall totals, 8 to 11 inches, are forecast across western sections of Greenbrier County. The warning likely will be divided into a northern section where amounts will be higher, to a southern section where amounts will be borderline for achieving measured warning criteria, but the travel concerns with the potential for blowing snow on the backside of the system would justify a continuation of the warning for impact. The eastern bordering Winter Weather Advisory is of a similar status whereby the rain/sleet scenario will keep snowfall numbers a little lower. However, along the elevations of western Amherst County, snowfall amounts have increased enough to justify an average forecast across the county that just clips the lower end of warning criteria. This county will be upgraded from an Advisory to a Warning, and placed in the aforementioned northern warning group. Winds will be gusty on across the higher terrain of mainly the Mountain Empire region and southern New River Valley of southwest Virginia, south into the Northern Mountains of North Carolina. Here gusts of 35 to 45 mph will be common at the higher peaks starting late tonight through the day Wednesday. Blowing snow is expected at these locations by Wednesday morning. Low temperatures tonight will range form the upper 20s to around freezing across the mountains to the low to mid 30s across the Piedmont. On Wednesday, high temperatures will range from the low to mid 30s across the mountains to the upper 30s to lower 40s across the Piedmont. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 330 PM EST Tuesday... Wednesday evening the closed upper low is just off the Virginia coast. Deformation area around upper low crosses through Virginia through Wednesday evening. Surface and low level winds come around to the northwest which will kick in upslope on the west side of the central Appalachians and suppress amounts in the foothills. Little additional accumulation expected in the piedmont but more snow adding to totals in the western mountains. Expect much of the upslope snow showers to end by Thursday morning. Clearing will take longer but there will be some breaks in the cloud cover by Thursday afternoon. Models show a 40 to 50 knot low level jet from the northwest along the Blue Ridge Wednesday night and Thursday morning. Another low re- enforces the upper trof over the eastern United States on Friday and Friday night. Have stayed below guidance for lows on Wednesday night in areas that will have new snow. Also below guidance for highs on Thursday where little to no sunshine expected. && .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 /01Z WEDNESDAY THROUGH SUNDAY/... As of 730 PM EDT Tuesday... Not a quiet night for aviation as storm system will bring rain then sleet/snow to the area with low cigs/vsbys. This system will stick around into Wednesday and overall looking at sub-MVFR conditions through at least midday Wednesday before 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. Cigs/vsbys anticipated to at least go MVFR Wed afternoon outside of the WV mountains. Northwest winds are expected to become gusty in the afternoon with a few gusts over 30kts not out of the question. Extended Aviation Discussion... Wednesday night into the daytime Thursday, the upslope snow showers will continue to gradually decrease in coverage with decreasing wind speeds. Mainly VFR conditions are expected by Thursday night through Friday night. Saturday into Sunday, a return to sub-VFR conditions is expected as our next potential winter weather system crosses the area. && .EQUIPMENT... As of 335 PM EDT Monday... The Mount Jefferson NWR remains off the air. The radio unit needed to repair the system is expected to arrive on Wednesday. The earliest this system will again be operational will be Wednesday afternoon. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Winter Storm Warning from midnight tonight to 8 AM EDT Thursday for VAZ007-009>020-022>024-035. Winter Weather Advisory from midnight tonight to 8 AM EDT Thursday for VAZ032>034-043>047-058-059. NC...Winter Storm Warning from midnight tonight to 8 AM EDT Thursday for NCZ001-002-018. WV...Winter Storm Warning from midnight tonight to 8 AM EDT Thursday for WVZ042>044-507-508. && $$ SYNOPSIS...DS/WP NEAR TERM...DS/WP SHORT TERM...AMS LONG TERM...AMS AVIATION...DS/WP EQUIPMENT...AMS is the U.S. government's official web portal to all federal, state and local government web resources and services.