IV-33 



rivers draining to the coast. There 1s a tendency for precipita- 

 tion along the northern Atlantic coast to be heaviest during the 

 cooler months and for much of 1t to fall as snow; the Pacific 

 coast, except for Alaska, has a similar precipitation pattern 

 with much less snowfall. The southern Atlantic, Gulf, and 

 Alaskan coasts receive their heaviest precipitation in the summer 

 and fall, as do Puerto Rico and the Virgin Islands. 



Local air, water, and ground temperatures, which govern the form 

 1n which precipitation occurs, are primarily a matter of solar 

 radiation, which becomes more Intense in latitudes nearer the 

 equator. Local temperatures are, however, greatly moderated by 

 local precipitation, cloud cover, nearby ocean conditions, and 

 prevailing winds. Two examples serve to illustrate this point: 



(1) Key West, Fla., on an island in the warm waters 

 of the Gulf of Mexico, has an average temperature 



of 77°F.; Brownsville, Tex., 1n about the same 

 latitude but on the mainland, has an average tempera- 

 ture of 74°F. At Key West annual temperatures, 

 moderated by the marine environment, range over only 

 49 degrees, whereas the range at Brownsville is 85 

 degrees. 



(2) Astoria, Oreg., at the mouth of the Columbia 

 River, and Portland, Me., are both in the same 

 latitude in zones of prevailing westerly winds. At 



