Weatber predictions. m 



spirally around the center of lowest depression 

 with an upward trend, the motions being in a 

 direction reversed to that of the hands of a 

 clock. In the centers of high pressure the 

 current is downward instead of upward and 

 the direction of the wind around it is opposite 

 to that around the low-pressure area. The 

 fundamental factor in predicting the weather 

 is the direction of movement of these areas of 

 low pressure. In almost all cases the direc- 

 tion of movement is from the west to the east, 

 but not always in a straight line. These 

 movements, however, are classified so that 

 after the direction has become established one 

 can predict with considerable accuracy as to 

 whether it will move in a curved or a straight 

 line. By movement we do not refer to the di- 

 rection of the wind at any particular point, 

 but the onward movement of the whole 

 cyclonic system, which is usually from twenty- 

 five to thirty miles an hour, but in some cases 

 the speed is much greater. 



Not only does the upward movement of the 

 whole system vary, but the velocity of the 

 wind around any given cyclonic center varies. 

 There are about eleven classes of cyclones that 

 appear in the United States, each class having 

 its own path of movement and origin. A 

 large number of these appear to originate 

 north of the Dakotas, and move directly east 

 to the Gulf of St. Lawrence. Three other 



