WEATHER CONDITIONS ON THE PACIFIC COAST 



In connection with the absence of rain during 

 December, 1876, it may be noted that there was 

 no rain between November 16, 1876, and January 

 16, 1877. Or, in other words, there was a period 

 of sixty consecutive days without rain in mid- 

 winter. 



Some of the months of heaviest rain were Jan- 

 uary, 1862, when 618.8 millimeters (24.36 in.) of 

 rain fell, and eighteen days of the month were 

 rainy. In January, 1911, 350.3 millimeters (13.79 

 in.) fell, distributed over eighteen days. In Jan- 

 uary, 1909, 267.0 millimeters (10.51 in.) fell, but 

 there were twenty-six rainy days, making it in this 

 sense the rainiest month known at San Francisco. 



August, like July, is practically a rainless month. 

 The mean rainfall is 0.5 millimeter (0.02 in.). 

 There has never been an August when the total 

 rainfall exceeded 6.4 millimeters (0.25 in.). Only 

 fourteen of the sixty-two months under considera- 

 tion have had a rainfall exceeding 0.2 millimeter 

 (0.01 in.). The greatest 24-hour rainfall was 3.0 

 millimeters (0.12 in.) on August 26, 1858. 



In the past sixty-two years, 1850 to 1911, there 

 have been 4207 rainy days. The yearly distribu- 

 tion is: January, 11; February, 10; March, 11; 

 April, 6; May, 4; June, 1; July, 0; August, 0; Sep- 

 tember, 2; October, 4; November, 7; December, 11. 

 For the year, average number 67. 



Thunderstorms occur infrequently at San Fran- 

 cisco. In the past twenty years there have been 

 twenty-nine, distributed as follows: 



January 2 April 3 July 1 October 3 



February 3 May 1 August 2 November 3 



March 1 June 1 September 2 December 7 



The greatest number recorded in any one year 

 was eight, in 1906. During the past twenty years 

 there have been eight years without record of a 

 thunderstorm. The storms are mild in character, 

 the lightning flashes of moderate intensity, and the 

 thunder usually limited to a few peals. Damage 

 from lightning is rare, although flagpoles have been 

 shattered and trees struck. 



There have been fifty-six hailstorms in the past 

 twenty years. January and December are the 

 months of maximum frequency. There is no record 

 of any hailstorm occurring during June, July, Au- 

 gust, and September. 



During winter storms the tops of the hills in 

 the southwestern portion of the city are occasion- 

 ally whitened by snowflakes. These melt rapidly 

 and snow of appreciable depth is rare. However, 

 snow can be seen frequently during winter months 



29 



