Download gif here.
The animated gif below illustrates statocumulus undulatus, complete with horizontal vortices embedded. This cloud feature formed ahead of a rather unimpressive MCS that moved across the south DeKalb, IL region during the early morning hours of 16 August 2012. I was in the DeKalb wind farm region trying to time-lapse a shelf (which never really materialized) when I noticed unique horizontal vortices embedded within the stratus ahead of the line. The vortex features only lasted about 3-4 minutes before they kinked up and dissipated. I don't think I've ever seen such a formation documented before. Higher-res stills are available from my storm chase blog.