Mesoscale vortices observed at the ends of a line segment of convective cells, usually cyclonic on the northern end of the system and anticyclonic on the southern end, for an environment of westerly vertical wind shear (in the Northern Hemisphere). The vortices are generally strongest between 2 and 4 km above ground level, but may extend from near the surface to about 8 km above ground level. They have been observed at scales between 10 and 200 km, and often have lifetimes of several hours. In extreme cases, the larger cyclonic vortices may become balanced with the Coriolis force and last for several days.