Severe Damage Wind 158 to 206 mph. Devastating Damage Wind 207 to 260 mph. Incredible Damage Wind above 261 mph. Only lasting an average of a few minutes tornadoes can produce winds in excess of 300 miles per hour. This is in contrast to hurricane situations that usually mean sustained winds of lower velocity.
Tornadoes usually occur in the spring, when thunderstorms are prevalent.
The tornado forms at the edge of the updraft, beside the air that is moving downward from the storm. The swirling wind, or the vortex, that rises to the funnel cloud from the ground creates very low air pressure within the funnel. The air that rushes in to equalize this pressure can be as dangerous as the vortex itself, and it is this reduced pressure inside the tornado which causes structures to explode when there is not adequate ventilation to adjust rapidly to the pressure imbalance. This air movement means that objects do not have to be hit directly by a tornado to sustain damage. Several of the buildings that we inspected after the tornado in Rockingham County had walls forced outward by this pressure differential.