UPDATE 8:30 AM, 2/19: Winter storm warning remains in effect; snow developing by afternoon/evening most locations in SW Virginia
UPDATE 8:30 AM: Cooling processes have worked very efficiently to get snowflakes to the surface right off the bat this morning. But these are only preliminary light bands of precipitation, and probably won’t amount to a lot, with surface temperatures still above freezing for most and a warm ground. Accumulations will require heavier snow later and colder surface temperatures, and that can only happen with the upper level low moving just south of us later today and this evening. It’s still back to the west in the Tennessee/Mississippi area. We’ll just have to watch it develop to see where the precipitation bands form. END UPDATE
UPDATE 6:40 AM: Radar and model trends suggest all of Southwest Virginia is on track for widespread precipitation today, changing to snow from higher elevations downward through the day as evaporational (precipitation falling through dry air aloft), dynamic (freezing level lowered by atmospheric lift changing atmospheric pressure) and advection (cold air moving in along the surface on northeast winds) cooling processes drop surface temperatures from the current 40s to near freezing. Winter storm warnings remain posted across Southwest Virginia, and have in fact been expanded south and east, for 3-6-inch amounts possible, as the upper-level low brings colder air aloft and heavier precipitation by evening. If there are heavier amounts than that, it would seem the counties immediately along the Virgnia-North Carolina border (Grayson, Carroll, Patrick, Henry, etc.) would be favored to have a shot with heavier bands developing by late afternoon and evening. Regions along and west of Interstate 77 are also targeted with higher potential of 8-plus, even slight chance of 12-plus amounts, according to the Hydrometeorological Prediction Center. But this is always difficult to nail precisely. END UPDATE
Some new forecast model data from Saturday night suggests the storm system may veer a little farther to the south. The result would be less moisture into much of Southwest Virginia, and lighter precipitation, including snowfall, in much of the region. The exception would be near the Virginia-North Carolina border. This may not be a final result, as the main upper-level energy that would trigger precipitation remains back in the central U.S. late Saturday evening. That will move just south of us late Sunday, and that’s when there will likely be the best chance of snow — beginning as rain, sleet or mix. We’ll need to monitor trends on the models and radar during the day on Sunday, but the higher end amounts above 6 inches seem unlikely at this point. Let’s take a fresh look at things in the morning to see how they have progressed.