Helicity, Vorticity, and Supercells

How do streamwise horizontal vorticity and helicity relate to thunderstorm rotation and possible tornadoes? Well, a significant streamwise component of vorticity aligned with the inflow leads to higher helicity value. When flow with high helicity encounters a convective updraft, the vorticity tilts up toward vertical, as this animation illustrates. Thus high helicity leads to updraft rotation within a supercell. Rotating supercells are sometimes associated with the occurrence of tornadoes.