CLIMATIC REGIONS OF THE UNITED STATES 303 

 IV. CLIMATIC REGIONS OF THE UNITED STATES 



323. Climatic Areas. The area of the United States pre- 

 sents nearly every variety of climate to be found in the 

 temperate zone. The United States may be divided roughly 

 into nine fairly well-defined climatic areas. But within each of 

 those areas there is considerable variation due to local causes. 

 Altitude largely affects temperature and wind. Nature of the 

 earth's surface largely determines wind velocity and direction 



FIG. 227 Climatic regions of the United States. 



and often rainfall. The proximity of cities, forests, and bodies 

 of water largely determines the purity of the air, the presence 

 of dust and smoke, the prevalence of fogs and of local winds 

 (Fig. 227). 



324. First Region. The first region comprises southern 

 Wisconsin, much of Iowa and Illinois, Indiana, Ohio, the 

 Lower Peninsula of Michigan, Pennsylvania, New York, and 

 New England. This region has an average temperature for 

 July of 70 to 75 and for January of 20 to 30. It has a 



