Formation of Tornadoes. 



591 



752. Unsteady Action of Tornadoes. A tornado seldom 

 displays a uniformly destructive power and oftentimes 

 the point of the funnel fails to reach the ground and con- 

 siderable gaps are passed in the path where little dam,: 

 done. This unsteady action is often due to the slowing 

 up of the rotary motion in the cloud due to the great fric- 

 tion developed at the ground. After withdrawing to the 

 upper air the speed increases sufficiently to allow the fun- 

 nel to grow to the surface again and resume the destructive 

 work. 



When the funnel reaches the surface it does not always 

 describe a straight path along the ground, but tends to 

 cross and recross the main axis of movement. 



FIG. 276. Diagram showing the rotary movement of winds in a tornado 



753. Character of the Tornado Path. It is usually true 

 that the path of a destructive tornado is not symmetrical, 

 one si<lc being wider than the other, as represented in Fig. 

 275, where it will be seen that the northwest side is nar- 

 rower than the southeast side. Not only is the zone of de- 

 structive winds wider on the south side but that of the 

 sensible winds is also. On account of this character of 

 the tornado track it is clear that if one has an occasion to 

 escape from an ordinary tornado, the shortest path would 



