A train of cyclonic shear vorticies formed along the periphery of an intense polar vortex which was centered just north of the Great Lakes on 30 September 1997. These mesoscale circulation features formed as lobes of positive vorticity (00 UTC | 12 UTC) were generated by cyclonic speed shear just north of the jet axis (00 UTC | 12 UTC). Each individual wave can be seen to evolve into a closed circulation as it rounds the base of the large-scale trough of low pressure over the eastern U.S..
