WEATHER CONDITIONS ON THE PACIFIC COAST 

 mean temperature of 288 A. (59.2 F.). The cool- 

 est hour, 6 A.M., has a mean temperature of 273 

 A. (50.9 F.). 



The highest temperature ever recorded in San 

 Francisco is 311 A. (101 F.). This occurred 

 September 8, 1904, during a prolonged period of 

 warm weather. For four consecutive days maxi- 

 mum temperatures exceeded 305 A. (90 F.). This 

 was the warmest spell of which there is record 

 in San Francisco. 



The lowest temperature recorded since 1871 is 

 271 A. (29 F.), which occurred January 15, 1888. 

 In the last twenty years the temperature has not 

 fallen below 273 A. (32 F.). 



The absolute range of temperature from 1871 

 to 1911 is 40 A. (72 F.). 



Sunshine. The amount of sunshine received at 

 San Francisco is not as large as might be expected, 

 but nevertheless compares favorably with that of 

 other cities in the United States. The average num- 

 ber of hours in a year, based upon hourly records 

 from 1894 to 1910, is 2807, or 63 per cent of the 

 possible. The average number of hours of sunshine 

 for different months is: 



Per Cent Per Cent 



Hours of Hours of 



Possible Possible 



January 147 50 July 308 68 



February 163 63 August 258 61 



March 213 67 September i 252 68 



April 256 66 October _ 236 68 



May 294 67 November 175 58 



June 34'5 75 December 160 54 



It is interesting to compare the number of hours 

 of sunshine at Mount Tamalpais for a year with 

 the number at San Francisco, fourteen miles away. 

 In 1910 the total number of hours of sunshine at 

 Mount Tamalpais was 3258, or 70 per cent of the 

 possible; at San Francisco, 3019 hours, or 66 per 

 cent of the possible. The difference, amounting 

 to 239 hours, equivalent to the total sunshine of 

 an average month, shows how much sunshine is 

 lost at San Francisco through the summer after- 

 noon fog. In some years there is a difference of 

 as much as 500 hours in the annual amounts of 

 sunshine at the two stations. In some seasons the 

 lower station receives more sunshine than the 

 upper, the clouds forming and remaining on the 

 mountain crest. The fogs can be seen to great 

 advantage from the station at Mount Tamalpais. 

 The fogs are caused by the mixing of air streams 

 of different temperatures and different vapor con- 

 tent. Some are caused by cooling due to elevation 



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