Cold Waves. 583 



HIGH areas, following them in their course across the 

 country. 



742. Forecasting Warm and Cold Weather. Since 

 strongly developed storms tend to draw the air into them- 

 selves across long distances, it is clear that when they pass 

 to the south during the cold months of the year cold waves 

 are likely to follow their passage. On the other hand, if 

 the low area has passed to the north it can only bring air 

 from the south northward, importing but little cold with 

 it. To <be able to forecast the path of a storm then is also 

 to be able to forecast the temperature changes which are 

 likely to follow. 



73. Long Warm and Dry Periods. It frequently hap- 

 pens that a series of storms follow along a single track, one 

 after another for several weeks together, and Fig. 270 rep- 



Fiu. 270. Chart showing conditions which determine dry weather in the 

 eastern United States. 



resents one of these sets of conditions. During the month 

 of October, 1895, all but four of the fifteen low areas re- 



