300 



PHYSIOGRAPHY 



the northward, and the rain which was predicted for that city 

 falls farther north. 



2. Storms often change their rate of advance, and so arrive 

 earlier or later than predicted. The high of Oregon (Fig. 245) did 

 not advance for a day (Fig. 246), and so failed to bring the expected 

 changes to the area east of it. 



Fig. 255. This map shows the storm of the preceding day greatly 

 changed in character. (U. S. Weather Bureau.) 



3. A third cause of the failure of predictions is found in the fact 

 that storms sometimes appear and disappear without warning. 

 Fig. 246 shows a low of which there had been no indication on 

 the 25th, over Oklahoma. Fig. 248 shows that this low has dis- 

 appeared. 



4. A storm sometimes changes its character, becoming weaker 

 or stronger, etc. Figs. 254 and 255 afford an illustration. Nothing 

 in the map of the 20th would warrant the prediction of the condi- 

 tions of weather shown on the map of the 21st. 



