Abstract
Tornado formation by turbulent mixing of two horizontal air currents and a vertical downdraft, as in the Wokingham model, has been simulated in the laboratory. Without the presence of the downdraft, vertices with lifetimes up to 20 see have been produced only when the horizontal air currents have an angular separation of 65°. Maximum stability occurs when one current is inclined 6° above the horizontal. Results suggest that tornado formation probability is independent of downdraft and critically dependent on local wind directions and geometries at intermediate altitudes in severe local storms.
