Idealized evolution of vortex lines inferred from a sample of VORTEX supercells surveyed by Markowski et al. (2008), superimposed on a photograph of a supercell thunderstorm (courtesy of Jim Marquis; view is from the south). The numerals 1-4 can indicate either a single vortex line seen at four different times in a sequence, or four different vortex lines at a single time but in different stages of evolution. An environmental vortex line also is shown to illustrate, schematically, the relationship between the midlevel and low-level mesocyclone. None of the vortex lines have been derived from an actual three-dimensional wind synthesis of the storm appearing in the photograph; the vortex lines simply have been drawn atop a photo of a supercell thunderstorm (one that could easily represent a number of generic supercell thunderstorms) by compositing vortex lines computed from actual three-dimensional wind syntheses in the sample of VORTEX supercells.