WEATHER MAPS 



293 



The rate of progress of the storm is not the same as the velocity 

 of the wind. The velocity of the wind depends on the isobaric 

 gradients. A weak cyclone, that is, a cyclone in which differences 

 of pressure are not great, gives rise to weak winds even though 

 the center of the storm moves rapidly. A strong cyclone, that is, 

 one in which the differences of pressure are great (Fig. 243), gives 



IfU 



Mean tracks and average daily movement of storms in the United States. 



Fig. 250. The heavier lines show the tracks of anticyclones, and the lighter 

 lines the paths of cyclones. Off the South Atlantic coast, anticyclones 

 are likely to turn northward. (U. S. Weather Bureau.) 



rise to strong winds, even though the cyclone itself moves forward 

 slowly. 



The course of a cyclone may be shown on a single map, as in 

 Fig. 249. The row of arrows shows that the low of Maine has moved 

 from Colorado, while that of Oklahoma has advanced from Nevada. 

 The shading indicates precipitation. 



The mean tracks of cyclones and anticyclones for the United 

 States are shown in Fig. 250, the heavier lines showing the average 

 paths of anticyclones, and the lighter lines the tracks of cyclones. 



Some anticyclones enter the United States from the Pacific, 

 while others start north and northwest of Montana, or at any rate 



