Weather Conditions on the Pacific Coast 

 Thus at San Francisco relative humidity through- 

 out the year is high; but during the summer months, 

 owing to low temperatures, the absolute weight of 

 water vapor per unit of volume and the vapor 

 tension are much less than at coast stations of the 

 Atlantic. Notwithstanding high relative humidity 

 in summer, the vapor tension and absolute humidity 

 are low at San Francisco. 



Rainfall. — Rainfall records have been main- 

 tained in San Francisco for a period of sixty-five 

 years. The greatest 24-hour rainfall occurred on 



Figure 4 

 Eainfall chart for California. 



January 28, 1881, when 118.6 millimeters (4.67 in.) 

 fell. The next greatest 24-hour rainfall was on 

 September 24, 1904, when 909 millimeters (3.58 in.) 

 fell. The longest rainless period was in 1903, when 

 no rain fell from April 16 until October 9, 175 

 days. In 1911 there was no rain from June 6 to 

 October 1, 116 days. 



