Some minor tornadoes, however, may evolve only through the organizing stage, some others may skip the mature and shrinking stages and go directly into the decay stage. An extremely steep horizontal air pressure gradient between the tornado center and outer edge that is responsible for a tornado's violence, occurs during mature stage. The Coriolis effect is also present, but the system is so small that its influence is negligible. Thus, winds in a tornado may rotate in either clockwise or counter-clockwise, but the latter dominates by far in the Northern Hemisphere. Tornadoes take about 100 lives each year, even though over 100 may die in a single day.
Tornadic winds blow down trees, power poles, buildings, and other structures.
A sequence of tornadoes, non-supercell tornadoes, over distances of 100 km or more are relatively more frequent, but less destructive than a single supercell tornado . Tornadoes occur in many parts of the world, but no country experience more tornadoes than the US, which averages 700 to 1100 annually and experienced a record 1293 tornadoes during 1992. Although tornadoes have occurred in every states, most occur in tornado alley, a region that stretches from central Texas to Nebraska. Central Oklahoma has the highest annual incidence of tornadoes, whereas local tornado maxima occur in central Illinois and Indiana and in southern Mississippi. The maximum tornado frequency shifts northward in late Spring and southward in early Autumn following the sun.