Spouts and tornadoes are phenomena that are especially dangerous. They are accompanied by very strong winds and cumulonimbus, shower, hail, and charge clouds. The vertical dimensions of a tornado are, as a rule, several fold larger than its horizontal dimensions, since intensive motion usually begins in the cloud layer and reach the Earth very quickly. Typical features of spouts and tornadoes are not only extremely high wind velocities, but also very great velocity gradients. For instance, a downdraft of tens of meters per second at the center of a powerful tornado, and an updraft of the same intensity at a distance of only several tens of meters from the center are often observed. In accordance with the existing theory, a plane-parallel flow even with smaller velocity gradients is hydrodynamically unstable.