No Rain in October Climatology

With the progs continuing to show a dry pattern through the end of the month there have been a number of comments and inquiries about how common it is to get zero or very little rain in October.
Here are some factoids in regards to the past 164 years of San Francisco October rainfall dating back to 1849.

- There have been 13 previous years (8% of the time) when there have been no measurable (i.e.,≥ 0.01") in October.
- There have been a total of 32 years (19%) with a tenth of an inch or less for the month.
- Ironically both the wettest (49.27" in 1861-62) and driest (7.42" in 1850-51) rainfall seasons (i.e., July 1 - June 30)  in SF history have occurred in years when there was no rain in October.
- The average rainfall for the season after an October with less than a tenth of an inch of rain is 21.04". 

- Normal (1981-2010) San Francisco rainfall in October in 1.12 inches and there are normally  4 days with measurable rainfall. 


Jan Null, CCM
Golden Gate Weather Services