WEATHER TYPES ON THE PACIFIC COAST. 87 



Bain is almost entirely absent when this type becomes 

 perfectly established, and only occurs in light showers in 

 Oregon and Washington Territory, when the high happens 

 to drop down well on the California coast, creating a condi- 

 tion similar to that of the " South Pacific Anti-Cyclonic 

 Type," already described. Another feature of the dry sea- 

 son is the development of considerable intensity of the high 

 in Oregon, the pressure being at the same time very low in 

 southern California, creating the northerly winds in the 

 Sacramento and San Joaquin valleys. 



The boundary between the wet and dry season would, I 

 believe, be as definite as the sun's march north or south if 

 not for these disturbing weather types, which bring into 

 effect conditions overriding the gradual change of tempera- 

 ture. It is well established that the temperature of the Pa- 

 cific Ocean differs very little anywhere on the coast, and the 

 monthly variation is so slight that it may be disregarded. 

 We can in a general discussion say that the temperature of 

 the ocean washing our shores is about constant. It is 

 wholly different over the land, and the difference increases 

 in proportion to the distance from the sea. In the winter, 

 the prevalent type is such as to drive the ocean winds over 

 a country where the temperature is cooler than themselves^ 

 and where the condensing conditions are strong enough to 

 well deplete them of moisture; hence rain results upon the 

 western slopes and little remains for the Rocky Mountain 

 country. During the summer, on the contrary, the winds 

 from the Pacific Ocean passing at once over the drying 

 country, do not precipitate their moisture at all till the 

 Rocky Mountain summits condense them. Thus the rainy 

 season is transferred from this coast to these higher regions. 

 The change of one season to another is best illustrated by 

 projecting the curve of surface temperature of the Pacific 

 Ocean, with the mean daily temperature of a place in prox- 

 imity to it, for instance, San Francisco. As soon as the air 

 temperature curve permanently crosses the former, the 



